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PHOTOCATALYTIC FILM FOR SOIL FUMIGATION
[0001] The present invention relates to the field of soil fumigation, i.e. the treatment of soils or
5 plant substrates (composts, peats, rockwool, etc.), in particular substrates intended for
agriculture, for controlling nematodes, pathogenic fungi, weeds, harmful insects or bacteria.
[0002] The fumigation technique is today widely used for the disinfection of soils or plant
substrates, in particular those intended for intensive agriculture and in particular those intended
for tree cultivation, for horticulture and for market gardening.
10 [0003] This fumigation technique uses at least one fumigant, generally a volatile pesticidal
compound, which is introduced into the soil or the substrate to be treated, according to various
techniques known to those skilled in the art, for example using colters, or nozzles for injection
into the soil, or else by drip. This fumigation technique also comprises the use of at least one
fumigant in the form of a gas or fog, above the soil or plant substrate to be treated.
15 [0004] The fumigant diffuses into the soil or more generally into the substrate to be
disinfected, but also rises back up to the surface and can be dissipated into the atmosphere.
Large amounts of fumigant can thus be lost, leading to a loss of efficiency of the product used.
In addition, the fumigant thus dissipated into the atmosphere can be a nuisance or even toxic
for farmers and the entourage in the immediate proximity of the crops and fields treated.
20 [0005] In order to overcome this drawback, it is common practice to cover the soil treated by
fumigation with a polymer film which is impermeable to the vapors of the fumigant, as
described, for example, in EP-A1-0 766 913. This gas-impermeable, plastic sheet prevents
said fumigant from dispersing in the air above the soil or the substrate to be treated. In this
way, there is a space between the soil or substrate and the polymer film, in which the fumigant
25 vapors are concentrated, thus reinforcing the efficiency of said fumigant. Various types of films,
such as polyethylene films, or films of SIF (semi-inipermeable film), VIF (virtually impermeable
film) or TIF (totally impermeable film) type, are today used during soil or substrate treatments
by fumigation.
[0006] The films for disinfecting agricultural soils can be classified into two categories
30 according to the duration of use:
a) Category 1: "simple" protection: These films are kept in place during the required duration
of disinfection of the substrate to be treated, and are then removed before the substrate is
used for growing. This category comprises two subcategories, depending on whether or not
the films are assembled together by adhesive bonding:
35 i) films put in place without adhesive bonding, film on film,
ii) films of which the surface condition allows assembly of the strips by adhesive bonding in
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situ;
b) Category 2: protection and mulching: The films of this category first of all provide protection
during the disinfection, and are then kept in place as mulching films.
[0007] The polymer films are advantageously placed on the soil or substrate before or after
5 the treatment by fumigation, and left in place for the time necessary to allow effective control of
nematodes, phytopathogenic fungi, weeds, harmful insects, and other bacteria. After this
treatment period, the duration of which greatly depends on the soils or substrates to be treated,
on the climatic conditions, on the type of crop envisioned, and the like, the polymer films can
be, where appropriate, removed or simply perforated, in order to allow the planting of crops.
10 [0008] The use of polymer films in fields has other advantages, such as increased soil
temperature, in particular at the beginning of spring, fewer problems associated with the
appearance of weeds, moisture content retention, a reduction in the number of certain insect
pests, higher yields and a more efficient use of soil nutrients.
[0009] Most mulch films are generally black for weed killing, white for cooling, or clear for
15 short-duration disinfections or for warming the soil. The temperature of the soil under a plastic
mulch depends on the thermal properties (reflection, adsorption or transmittance) of the
particular constituent material of the film, with respect to the entering solar radiation.
[0010] For example, black mulches retain moisture content and heat while at the same time
preserving infestation by weeds. Black, the predominant color used in vegetable production, is
20 an opaque absorber and a radiator. Black mulch absorbs most ultraviolet (UV), visible and
infrared (IR) wavelengths of incident solar radiation and re-emits part of the absorbed energy in
the form of thermal or infrared radiation. A large part of the solar energy absorbed by black
plastic mulch is lost into the atmosphere by radiation and by forced convection.
[0011] On the other hand, transparent polymer films sparingly absorb solar radiation, but
25 transmit from 85% to 95% of said radiation, with a relative transmittance which depends on the
thickness and the degree of opacity of the film. The surface under these polymer mulches is
generally covered with drops of condensed water. This water is transparent to the entering
short-wave radiation, but is opaque to the leaving infrared thermal radiation, heat lost into the
atmosphere from an uncovered soil due to infrared radiation, but which is retained by the
30 transparent polymer mulch.
[0012] White films, for their part, can lead to a slight decrease in soil temperature compared
to an uncovered soil, since they reflect, into the plant cover, most of the incident solar radiation.
These mulches can be used to establish a crop when the soil temperatures are high, for
instance in very sunny regions and where any reduction in soil temperature is beneficial.
35 [0013] There is therefore today a large amount of polymer films used in agriculture. The use
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of such films could be coupled with the use of fumigant, as previously indicated. However,
when the polymer film is withdrawn or perforated, the fumigant still present in the form of
vapors between the soil and said film escapes into the atmosphere and can thus be harmful to
the environment, without mentioning the operators who are also widely exposed to said vapors
5 of said fumigant.
. [0014] In order to avoid exposure of the operators to the toxic and/or malodorous vapors of
fumigants, the wearing of filtering masks or of specific respiratory apparatuses has been
envisioned. Their use is, however, inconvenient and it is often noted that operators do not use
these devices, which are nevertheless often necessary.
10 [0015] In addition, fumigants are in most cases toxic products, the inhalation of which by
operators and the dissipation of which into the atmosphere should be avoided. Such is the
case, for example, of methyl bromide which is today used less and less frequently because of
its toxicity. Moreover, methyl bromide is now prohibited by the Montreal protocol, since this
fumigant is considered to be a substance capable of destroying the stratospheric ozone layer.
15 [0016] Patent application JP 9-263502 proposes another solution for avoiding the dispersion
of methyl bromide into the atmosphere. This solution consists in using a multilayer
photocatalytic film, an upper layer permeable to solar radiation, and a lower layer permeable to
the fumigant used. Particles of titanium dioxide, acting as a photocatalyst, are deposited
according to a "spray/coating" process on the lower layer, and then covered by lamination and
20 sealing of the upper layer.
[0017] However, the photocatalytic films presented in said patent application dating from
1996 are not entirely satisfactory, and have not, thus far, been marketed. The preparation
thereof on an industrial scale appears to be difficult to implement, and these films especially
would not exhibit the mechanical properties required by the standards relating to films for the
25 disinfection of agricultural soils (AFNOR NFT54-195), in particular with regard to the
specifications relating to delamination, tensile strength, tearing, slow perforation and bonding
ability of the film.
[0018] In addition, spray-deposited titanium dioxide (Ti02) particles have the drawback of
being able to be washed away by the condensation water running on or under the films.
30 Moreover, thje spray-coating technique imposes relatively low manufacturing rates^ thus
leading to a high final manufacturing cost for this type of structure.
[0019] More specifically, the examples of catalytic films described in patent application
JP 9-263502 are films composed of a first layer of poly(vinylidene chloride) or of nylon and of a
second layer of poly(ethylene) or of poly(vinyl chloride). A layer of ultrafine particles of titanium
35 dioxide is deposited between these two layers. The whole assembly is thermosealed on at
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least part of the surface of the film. Not only does this film therefore appear to be very difficult
to prepare, but it also requires a difficult thermosealing operation in the presence of the
photocatalyst particles.
[0020] Another example presented in patent application JP 9-263502 shows a bilayer film in
5 which the lower layer consist of poly(tetrafluoroethylene) comprising ultrafine particles of
titanium dioxide (up to a quantitative ratio of, 1:9). The nature of the other constituent polymer
film of the bilayer is not indicated.
[0021] The compatibility of the titanium particles with the poly(tetrafluoroethylene) does not
appear to be optimal (the film does not therefore appear to be very solid for the uses
10 envisioned) since it is indicated, in another example of this same patent application, that it is
preferable to use a flocculant ("bulking agent"), such as talc, aluminum hydroxide, calcium
carbonate or porous silica, to obtain a better distribution of the photocatalyst particles within the
polymer matrix.
[0022] Finally, the films described in patent application JP 9-263502 do not work with colored
15 films since they do not take into account the colorants of which they are composed and which
have the ability to adsorb the ultraviolet radiation required for the catalytic activity of the
titanium dioxide particles.
[0023] All these examples show that the manufacturing of photocatalytic films is not easy and
still remains today difficult to industrialize. There is, consequently, a need for photocatalytic
20 films which can be used in the fumigation field and which are therefore impermeable to
fumigant vapors, and which have a photocatalytic activity allowing efficient photocatalysis of
fumigants. Such films should be easily industrializable and should exhibit a mechanical
strength suitable for the uses envisioned, in order to be able to be easily handled and spread
out over the soils or substrates to be treated by fumigation.
25 [0024] Thus, and according to a first aspect, a subject of the present invention is a
photocatalytic film comprising at least one polymer layer (1), said layer comprising at least one
photocatalyst, and being both permeable to the vapors of at least one fumigating compound
and permeable to ultraviolet radiation capable of activating the photocatalyst.
[0025] The photocatalyst of the film according to the invention is a catalyst capable of
30 degrading said at le.ast one fumigant by photocatalysis, as described later in the present
description.
[0026] The film according to the present invention must be permeable to ultraviolet radiation
in order to allow the activation of the photocatalyst and the degradation of said at least one
fumigant. The film according to the present invention may also optionally be permeable to
35 visible radiation, i.e. be transparent, or more or less opaque. As will be seen later, the film of
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the present invention may also be partially or totally opaque to visible radiation, or even be
colored, the choice of the transparency, of the opacity and of the color of the film depending on
the use envisioned for the film of the present invention. In each of these variants, it should be
understood that the film of the present invention is always permeable to ultraviolet radiation.
5 [0027] The term "ultraviolet radiation" is intended to mean radiation having a wavelength
generally between approximately 280 nm and approximately 400 nm. The term "visible
radiation" is intended to mean radiation having a wavelength generally between approximately
400 nm and approximately 800 nm.
[0028] The term "permeable to ultraviolet radiation" and the term "permeable to visible
10 radiation" are intended to mean a polymer layer allowing at least a transmittance of
approximately 5%, preferably approximately at least 10%, more preferably approximately at
least 20%, of the ultraviolet radiation and of the visible radiation, respectively. The
transmittance is the ratio of the flux of photons transmitted relative to the flux of incident
photons, the flux being measured by UV or visible spectrophotometry in the wavelength range
15 under consideration.
[0029] The term "permeable to the vapors of at least one fumigating compound" is intended
to mean the permeability defined according to the NF T 54-195 standard, with a permeability
value of at least (i.e. greater than or equal to) 0.2 g/m^ • hour. Conversely, the impermeability
to fumigant vapors corresponds to a permeability strictly less than 0.2 g/m^ • hour.
20 [0030] The polymer layer (1) is advantageously a polymer film comprising at least one
polymer A preferably chosen from polyolefins and polyesters. Biobased and/or biodegradable
polyolefins and polyesters are quite particulariy prefen'ed.
[0031] For the purpose of the present invention, the term "polyolefin" is intended to mean a
random or block polymer or copolymer resulting from the polymerization, or respectively from
25 the copolymerization, of monomers which are olefins, preferably chosen from ethylene,
propylene, 1-butene, and the like, and also mixtures thereof
[0032] By way of examples of polyolefins, mention may be made of
- propylene-based polymers, such as propylene homopolymers, copolymers of propylene with
ethylene and/or an olefin comprising from 4 to 10 carbon atoms (for example, butene, pentene,
30 hexene, and the like), heterophasic polypropylenes or mixtures thereof it being possible for
these polymers to be obtained by any process known to those skilled in the art, e.g. in
suspension or in the gas phase with catalysts of Ziegler-Natta or metallocene type;
- polyethylenes chosen from ethylene homopolymers or copolymers comprising at least
50 mol% of ethylene and one ormore comonomers.
35 [0033] According to one preferred embodiment, the polymer layer (1) consists of a polymer A
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which is polyethylene obtained by polymerization, preferably homopolymerization, of ethylene.
As a variant, when the polymer A is a copolymer, the comonomer is preferably an a-olefin. The
preferred a-olefins have from 2 to 30 carbon atoms.
[0034] By way of a-olefin, mention may be made of propylene, 1-butene, 1-pentene,
5 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, 1-decene,
1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 1-docosene,
1-tetracosene, 1-hexacosene, 1-octacosene and 1-triacontene.
[0035] By way of other comonomers of the copolymers A, mention may also be made of:
• dienes, such as, for example, 1,4-hexadiene, ethylidene-norbornene, or butadiene,
10 • unsaturated carboxylic acid esters, such as, for example, alkyl acrylates or alkyl
methacrylates grouped together under the term "alkyl (meth)acrylates", it being possible for the
alkyl chains of these (meth)acrylates to contain up to 30 carbon atoms, with, as examples of
alkyl chains: methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, terf-butyl, pentyl, hexyl, heptyl,
octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,
15 heptadecyl, octadecyl, nonadecyi, eicosyl, heneicosyl, docosyl, tricosyl, tetracosyl, pentacosyl,
hexacosyl, heptacosyl, octacosyl, nonacosyl, and triacontyl, methyl, ethyl and butyl
(meth)acrylates being preferred,
• unsaturated carboxylic acids and salts thereof, for example acrylic acid or methacrylic acid
and the salts of these same acids,
20 • vinyl esters of carboxylic acids, among which mention may be made of vinyl acetate, vinyl
versatate, vinyl propionate, vinyl butyrate and vfnyl maleate, vinyl acetate being quite
particularly preferred.
[0036] The synthesis of these polymers and copolymers can be carried out by any process
known per se, and for example by high-pressure free-radical polymerization or
25 copolymerization (autoclave or tubular process) or according to two main methods in the case
of linear copolymers: the solution method and the fluidized bed method (in the gas phase). In
the latter case, the catalyst used may be of Ziegler-Natta or metallocene type, or else of
Phillips type. It is of course possible to use mixtures of two or more of the polyolefins and/or
copolyolefins described above.
30 [0037] Among the polyesters that can be used as polymer A, preference is given to biobased
or biodegradable polyesters, and more preferably those chosen from:
• polylactides: for example, polymers and copolymers of lactic acid (PLA) or else polymers
and copolymers of glycolic acid (PGA);
• homopolymeric or copolymeric poly(tiydroxyalkanoates) (or PHA): for example,
35 poly(hydroxybutyrates) (PHB), copolymers of hydroxybutyrate-valerate (PHBV), for example
•
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poly(3-hydroxybutyrate)-poly(3-hydroxyvalerate)s, copolymers of hydroxybutyrate-hexanoate
(PHBHx), and hydroxybutyrate-hexanoate copolymers (PHBO);
• poly(alkylene succinates) (PAS), for instance poly(ethylene succinate) or PES, and
poly(butylene succinate) or PBS;
5 • other polymers, such as poly(butylene succinate-adipate) or PBSA, poly(butylene adipateterephthalate)
or PBAT, poly(caprolactone) or PCL, or poly(trimethylene terephthalate) or PIT;
• thermoplastic starch (TPS) or starch-based mixtures.
[0038] It is of course possible to use mixtures of two or more of the polyesters and
copolyesters described above.
10 [0039] The term "biobased" or "renewable" applies to a natural source, the stock of which
can be reconstituted over a short period on the human scale, the source having to be renewed
as quickly as it is consumed. In the context of the present invention, the biobased materials
correspond to organic materials in which the carbon atoms come from non-fossil sources (cf.
ASTM 6866: Biobased Materials - organic materials in which the carbon comes from
15 contemporary (non-fossil) biological sources).
[0040] The term "biodegradable" applies to a material which can be degraded by
microorganisms. The result of this degradation is mainly the formation of water, of carbon
dioxide and/or of methane, and also possibly of by-products (residues, new biomass) which
are not toxic to the environment.
20 [0041] For the needs of the present invention, use is advantageously made of polyolefins
chosen from polypropylene, polyethylene, copolymers of ethylene and of an a-olefin,
ethylene/alkyi (meth)acrylate copolymers, and ethylene/carboxylic acid vinyl ester copolymers.
[0042] The polymer layer (1), of which polyethylene is particularly preferably the main
constituent, and advantageously the only constituent (polymer A), also comprises at least one
25 • photocatalyst capable of degrading by photocatalysis said at least one fumigant intended for
treating the soil or plant substrate. The expression "capable of degrading by photocatalysis
said at least one fumigant" means that the photocatalytic film, under the action of ultraviolet
radiation, degrades at least a part of the fumigant(s) intended for treating the soil or the plant
substrate covered with said photocatalytic film. The degree of degradation depends, of course,
30 on the amount of ultraviolet radiation, and is evaluated by comparison with a film of the same
nature but which is not photocatalytic, i.e. does not comprise photocatalyst particles. Such
measurements are presented in the examples given later in the description of the invention.
[0043] The photocatalytic effect corresponds to the photocatalytic effect well known to those
skilled in the art and uses "electron-hole" pairs photogenerated when the film is subjected to
35 radiation having a wavelength of less than 400 nm. These "electron-hole" pairs react with the
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oxygen and the moisture in ambient air and the hydroxyl groups or organic products adsorbed
at the surface of the photocatalyst particles present in the film, to give radicals, in particular
highly oxidizing superoxide and hydroxyl radicals. The photocatalysis therefore makes it
possible to decompose organic molecules at the surface of the photocatalyst particles, through
5 the formation of free radicals which will initiate breaking of the covalent bonds of said organic
molecules.
[0044] In order to confer the photocatalytic effect on the films of the present Invention, the
photocatalyst particles included in said film have an average particle size of between 0.5 nm
and 200 nm, preferably between 0.5 nm and 180 nm, more preferably between 0.5 nm and
10 100 nm, advantageously between 1 nm and 50 nm, particularly between 10 nm and 40 nm and
more particularly between 15 nm and 30 nm.
[0045] The average particle size (median diameter of the photocatalyst particles) is
measured by transmission electron microscopy (TEM) using a Philips CM200 apparatus
(200 kV, LaB6 filament, point-by-point resolution of 0.27 nm). Direct observation of the images
15 on a screen is possible through the use of a high-resolution CCD camera (11 Mpixels - Gatan
Orius 832 model). The median diameters of at least 500 photocatalyst particles are statistically
measured and their particle size distribution by number is established. The average particle
size is defined as the average value of all the particles measured.
[0046] Since the photocatalyst particles are ultrafine particles (of nanometric size), their use
20 may be difficult and may present risks of toxicity to users. For these reasons, inter alia, the
nanometric photocatalyst particles may be commercially available in the form of granulated
material, of aggregates or of agglomerates, the size of which can vary in wide proportions, for
example between a few hundred nanometers to a few micrometers, or even a few tens of
micrometers, for example between approximately 200 nm and 1 pm. This granulation material
25 or these aggregates or agglomerates of photocatalytic nanometric particles have the same
photocatalytic properties as the nanometric particles of which they are composed. For this
reason, this granulated material and these aggregates and agglomerates of nanometric
particles should not be confused with the particles of higher median diameter (greater than
200 nm) and which are generally used as pigment and/or agents for protecting against
30 ultraviolet radiation, as will be seen later in the present description.
[0047] Said at least one photocatalyst present in the photocatalytic film of the present
invention can be chosen from the photocatalysts known to those skilled in the art, and which
have an average particle size as defined above (0.5 nm to 200 nm), the most commonly used
isetng oxides, sulfides or carbides of metals having semi-conductive properties:
35 [0048] Advantageously, and by way of nonlimiting examples, the photocatalyst present in the
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film according to the present invention is chosen from titanium dioxide, silicon dioxide, zinc
oxide, tungsten trioxide, silicon carbide, iron II oxide or iron III oxide, cerium dioxide, zirconium
dioxide, tin dioxide, zinc sulfide, cadmium sulfide, silicon carbide, and the like, and also
mixtures of two or more of them in any proportions.
5 [0049] Preferably, the photocatalyst is photocatalytic nanometric titanium dioxide, owing to its
performance levels and its cost. Titanium dioxide exists in three crystalline forms, which are
brookite, anatase and rutile, but only the anatase and rutile structures have photocatalytic
properties and are of use in the film of the present invention. The anatase structure is more
effective than the rutile structure; however, anatase/rutile mixtures (preferably approximately
10 70/30 to approximately 80/20 by weight respectively) exhibit better results in terms of
photocatalysis than one or other of the structures alone.
[0050] According to one particularly preferred embodiment of the films of the present
invention, the photocatalyst is the nanometric titanium dioxide sold by the company Evonik
under the name Aeroxide® Ti02 P 25. Aeroxide® Ti02 P 25 is a white powder composed of the
15 two crystalline forms of Ti02, the anatase form which makes up more than 70% (by weight)
and the rutile form, the crystals of which measure on average 21 nm in terms of average
diameter and which have a specific surface area of 35 m^/g to 65 m^/g. It is also possible to
use, as previously indicated, granulated material, aggregates or agglomerates of nanometric
Ti02 particles, and in particular photocatalytic Ti02 particles in the form of granulated material,
20 and especially that sold by Evonik under the name Aeroperl® P25/20, the granulated material
of which has an average size of 0.25 pm and is made up of primary photocatalytic Ti02
particles having a median diameter of approximately 20 nm.
[0051] As previously indicated, only Ti02, in its rutile and anatase crystalline forms, exhibits
photocatalytic activity. Since the anatase form is much more active than the rutile form, it is
25 virtually the only one used for this application. Ti02 in amorphous form does not have
photocatalytic activity. Ti02 is partially crystalline in anatase or rutile crystalline form or in the
form of a mixture of anatase and rutile with a degree of crystallization preferably of at least
25%, preferably of at least 30%, for example between approximately 30% and 80% by weight
relative to the total weight of Ti02. The degree of crystallization and the nature of the crystalline
30 .phase are measured by X-ray diffraction (XRD), according to the techniques known to those
skilled in the art. The degree of crystallization represents the amount by weight of crystalline
Ti02 relative to the total amount by weight of Ti02 in the film. For the TiOa particles present in
the film, preference is quite particulariy given to those of which the nature of the crystalline
- -phase is predominantly the anatase crystalline form. The term "predominantly" means that the
35 anatase content of the Ti02 particles is greater than 50% by weight, preferably greater than
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60% by weight relative to the total weight of Ti02 particles. Preferably, the Ti02 particles used
in the films of the present invention have an anatase content greater than or equal to 70%,
more preferably greater than or equal to 80%.
[0052] It is of course possible to use one or more of the photocatalysts, described above, in
5 doped form, doped with any type of dope known to those skilled in the art, for instance
nitrogen, chromium, manganese, iron, platinum, and the like. It is also possible to combine
these doped or non-doped photocatalysts with other semiconductors which absorb in the
visible radiation range, for example cadmium sulfide (CdS), bismuth sulfide (BizSa), or tungsten
trioxide (WO3), and the like.
10 [0053] The amount of photocatalyst included in the polymer layer (1) can vary in large
proportions, in particular according to the desired effect, the thickness and the nature of the
film. As a general rule, the amount of photocatalyst is between 0.1% and 30% by weight of
photocatalyst relative to the total weight of the polymer layer (1), preferably from 0.1% to 20%
by weight, more preferably from 0.1% to 10% by weight of photocatalyst relative to the total
15 weight of the polymer layer (1).
[0054] The incorporation of photocatalyst into the polymer matrix (1) can be carried out
according to any means known to those skilled in the art for incorporating inorganic fillers into a
polymer matrix. It is, however, preferred to carry out said incorporation using a master-batch,
this being a technique which allows the distribution of the photocatalyst in the polymer matrix to
20 be as homogeneous as possible. The photocatalyst concentration in the polymer matrix for this
master-batch can range from 10% by weight to 50% by weight of photocatalyst relative to thetotal
weight of the polymer matrix comprising said photocatalyst. A polymer/photocatalyst
master-batch in which the photocatalyst is optimally dispersed on the nanometric scale in the
polymer matrix is then obtained. _
25 [0055] Thus, according to another aspect, the present invention relates to the process for
preparing a photocatalytic film, according to any method known to those skilled in the art for
preparing films from master-batches, said process comprising at least the following steps:
a) preparing granules of a master-batch from a first matrix of at least one polymer A as
previously defined and from nanometric particles, optionally in the form of granulated material,
30 aggregates or agglomerates, of at least one photocatalyst, the median diameter of which is as
previously defined, said particles being present in an amount of between 10% by weight and
50% by weight relative to the total weight of the master-batch, by mixing said first matrix and
said particles, then extrusion, for example, with a twin-screw extruder or a Buss coblender; and
b) preparing a photocatalytic film from the granules of the master-batch obtained in-step a) by
35 incorporating an amount of between approximately 5% and approximately 50%, preferably
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between approximately 5% and approximately 30% by weight, relative to the final polymer
prepared, of said granules obtained in step a) into a second polymer matrix (of nature identical
to or different than, preferably identical to, the first polymer matrix) which is molten or in the
form of granules and then melted.
5 [0056] The process described above allows the incorporation of an inorganic filler, in the form
of granules, directly with the granules of polymer of the film to be manufactured, without
modifying the extrusion line normally used (i.e. during the preparation of a film without the
addition of photocatalyst particles), while at the same time providing a uniform distribution of
said inorganic filler in this polymer matrix.
10 [0057] The thickness of the polymer layer (1) can vary in large proportions. However, the
polymer layer (1) must be sufficiently thick to confer acceptable mechanical strength on the film
according to the invention, and its thickness must not be too great, so as not to stiffen said film,
so that it remains easy to handle.
[0058] In addition, the thickness of the polymer layer (1) depends on its concentration of
15 photocatalytic filler which is intimately linked thereto. Indeed, by adjusting at least one of these
two parameters (thickness and/or amount of photocatalyst), it is possible to control the
degradation kinetics of the fumigant according to the climatic and edaphic conditions, such as
the amount of sunshine, the moisture content, and the like.
[0059] Thus, by way of example, the thickness of the polymer layer (1) can be
20 advantageously between approximately 5 pm and approximately 100 pm, preferably between
5 pm and 75 pm, preferably between 5 pm and 60 pm and more preferably between 5 pm and
50 pm.
[0060] According to one preferred embodiment, the thickness of the polymer layer (1) of the
photocatalytic films is between 5 pm and 50 pm and the photocatalyst content is between
25 0.05% and 10%, preferably between 0.1% and 6% and more preferably between 1% and 3%
by weight relative to the total weight of the polymer layer (1).
[0061] Yet another advantage of the photocatalytic film is that the polymer layer (1)
preferably comprises a uniform and homogeneous distribution of photocatalyst particles over
the entire thickness of the polymer. Thus, the photocatalytic effect is greatly improved
30 compared with the photocatalytic films known from the prior art, and in particular that disclosed
in patent JP 9-263502, in which only a fine layer of photocatalyst is deposited on the polymer
film.
[0062] Without being bound by theory, the photocatalytic film of the invention acts, on the
contrary, as an actual fumigant photocatalysis reactor, which consequently makes it possible^o-
35 achieve the desired effect of virtually total photodegradation of said fumigant, thus avoiding
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• -12-
potentially toxic and/or nauseating gas emissions when the polymer films are removed or
pierced.
[0063] According to one variant, the photocatalytic film of the present invention is a multilayer
photocatalytic film comprising:
5 a) at least one polymer layer (1) as previously defined, and
b) at least one layer of a second polymer film (2) impermeable to the vapors of said at least
one fumigant and permeable to ultraviolet radiation.
[0064] More particularly, the polymer layer (2) is a polymer film comprising at least one
polymer impermeable (i.e. having a permeability of less than 0.2 g/g/m^ • hour) to fumigant(s)
10 and permeable to ultraviolet radiation and optionally to visible radiation.
[0065] According to one particularly advantageous embodiment, the polymer layer (2) is
chosen from nitrogenous and/or oxygen-containing polar resins, for example from polyamides,
copolyamides, saponified copolymers of vinyl acetate and of ethylene (EVOH), polyesters and
copolyesters, for example polyglycolic acid (PGA), thermoplastic starches and mixtures of two
15 or more of them in any proportions.
[0066] For the purpose of the present invention, the term "polyamide" is intended to mean a
polymer or copolymer comprising the products of condensation:
• of one or more amino acids, such as aminocaproic, 7-aminoheptanoic, 11-aminoundecanoic
and/or 12-aminododecanoic acids;
20 • of one or more lactams, such as caprolactam, enantholactam and/or lauryllactam;
• of one or more diamines, optionally in salt form, such as hexamethylenediamine,
dodecamethylenediamine, metaxylylenediamine, bis-para-aminocyclohexylmethane and/or
trimethylhexamethylenediamine, with one or more diacids, for example chosen from isophthalic
acid, terephthalic acid, adipic acid, azelaic acid, suberic acid, sebacic acid and
25 dodecanedicarboxylic acid;
• or of mixtures of these monomers resulting in copolyamides.
[0067] It is possible to use mixtures of polyamide and/or copolyamides.
[0068] According to one preferred embodiment, the polymer used for the layer (2) of the film
according to the invention is polyamide-6 or polyamide-6,6. According to another preferred
30 embodiment, the polymer used for the layer (2) of the film according to the invention is a
saponified copolymer of vinyl acetate and of ethylene (EVOH).
[0069] As for the polymer layer (1), the thickness of the polymer layer (2) can vary in large
proportions. The polymer layer (2) must, however, be sufficiently thick to be impermeable to
the vapors of the fumigant(s)i and its thickness must not be too great so as not to needlessly
35 stiffen the multilayer film, which must remain easy to handle.
wo 2013/030513 PCT/FR2012/051960
[0070] By way of example, the thickness of the polymer layer (2) could be advantageously
between 2 pm and 25 pm, preferably between 2 pm and 15 pm and more preferably between
2 pm and 10 pm. The present invention also comprises the photocatalytic films in which the
polymer layer (2) is composed of several layers, for example PA6/EVOH/PA6 or PA6/PE/PA6.
5 [0071] The films according to the present invention also exhibit a mechanical strength which
is entirely appropriate for manipulation on the land, said mechanical strength materializing
through much easier handling. In particular, the films do not pierce and do not tear, even when
the film placed on the soil is trodden on by the feet of users, handlers, farmers and the like.
[0072] By comparison with a film not comprising a polymer layer (2) which is a layer acting
10 as a barrier to gases, for example when the film is a polyethylene film alone, the bilayer film
comprising a polymer layer (1) and a polymer layer (2), such as they have been described,
makes it possible to reduce the initial effective amount of fumigant, while at the same time
having the same biological efficacy.
[0073] In one preferred embodiment, the present invention relates to a film consisting of at
15 least one photocatalytic polyolefin layer (1) and at least one polyamide and/or EVOH layer (2)
which is placed on a soil or an agricultural substrate into which or onto which at least one
fumigant is injected.
[0074] In general, and in most cases, the polymers of the layer (1) and of the layer (2) are not
compatible, i.e. the two films have only a moderate-to-low affinity toward one another, so that
20 they can be assembled in the form of a bilayer film.
[0075] It is in fact known that certain polymers of different natures are only slightly compatible
with one another, and it is often difficult to make them interlinked. This is in particular the case
with films comprising a layer based on polyolefin(s) and a layer based on polyamide(s) or on
EVOH. _
25 [0076] Two possible methods can be used to overcome this drawback and to improve the
adhesion between the layer (1) and the layer (2):
- a) use of a compatibilizing agent, known to those skilled in the art, in the layer (1)
and/or the layer (2), preferably in the layer (1), and/or
- b) use of a "compatibility" or "coupling" layer (C), which can be understood to be a
30 coextrusion tie, between the layers (1) and (2).
[0077] For example, when the film according to the invention is a bilayer in which the layer
(1) is a "simple" polyolefin copolymer film (without compatibilizing agent) and the layer (2) is
polyamide, the adhesion between the two layers is approximately equal to zero. On the other
hand, when the bilayer consists of a polyolefin copolymer film (1) comprising a compatibilizing
35 agent and a polyamide layer (2), the adhesion between the layer (1) and the layer (2), without
wo 2013/030513 PCT/FR2012/051960
• -14-
using a tie between these layers, is greatly increased and generally reaches values ranging
from approximately 4 to approximately 10 N/15 mm.
[0078] The adhesion tests between the various constituent layers of the films according to
the present invention are carried out by peeling measurement at 180°C, with a linear speed of
5 20 mm/min on a film width of 15 mm.
[0079] In the rest of the present invention, it is considered that the .various constituent layers
of a film according to the present invention are "compatible" as long as the peeling test
measurement described at)ove gives a value of adhesion between two layers of at least
1 N/15 mm, preferably of at least 2 N/15 mm, more preferably of at least 3 N/15 mm and
10 advantageously of at least 4 N/15 mm.
[0080] As regards method a), in the case where the polymer (1) is a polyolefin, the
compatibilizing agents or the coextrusion ties are advantageously chosen from the polyolefins
below comprising an additional monomer X:
- propylene-based polymers, chosen from homopolymeric propylenes, copolymers of
15 propylene with ethylene or a monomer comprising from 4 to 10 carbon atoms (for example
butene, pentene, hexene, and the like), heterophasic polypropylenes or mixtures thereof, it
being possible for the synthesis of these polymers to be carried out by any process known to
those skilled in the art (for example in suspension, or in the gas phase with catalysts of Ziegler-
Natta or metallocene type);
20 - polyethylenes chosen from ethylene homopolymers or copolymers comprising at least
50 mol% of ethylene and one or more other comonomers; when the comonomer of the
copolymer is an a-olefin, a-olefins having from 2 to 30 carbon atoms are preferred, it being
understood that as second monomer, mention may be made of those chosen from:
• dienes, for example 1,4-hexadiene, ethylidene norbornene, butadiene;
25 • unsaturated carboxylic acid esters, such as, for example, alkyl acrylates or alkyl
methacrylates, grouped together under the term alkyl (meth)acrylates, it being possible for the
alkyl chains of these (meth)acrylates to have up to 30 carbon atoms, and among these alkyl
chains, mention may be made of methyl, ethyl, propyl, n-butyl, sec-butyl, isobutyl, te/t-butyl,
pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,
30 pentadecyl, hexadecyl, heptadecyl, octadecyl, nqnadecyl, eicosyl, hencosyl, docosyl, tricosyl,
tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl and nonacosyl chains, the preferred
unsaturated carboxylic acid esters being methyl, ethyl and butyl (meth)acrylates;
• vinyl esters of carboxylic acids, among which mention may be made of vinyl acetate,
vinyl versatate, vinyl propionate, vinyl butyrate or vinyl maleate, preferably vinyl acetate.
35 [0081] The polyolefins listed above result from copolymerizafion with at least one
•
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— 15 —
unsaturated additional functional monomer X chosen from unsaturated carboxylic acid
anhydrides, unsaturated dicarboxylic acid anhydrides, unsaturated carboxylic acids and
unsaturated epoxides.
[0082] More specifically, as monomer X, mention may be made of:
5 • unsaturated epoxides, for example aliphatic glycidyl esters and ethers, such as allyl glycidyl
ether, vinyl glycidyl ether, glycidyl maleate and/or itaconate, glycidyl acrylate and/or
methacrylate, but also alicyclic glycidyl esters and/or ethers, such as 2-cyclohexene-1-glycidyl
ether, cyclohexene-4,5-diglycidyl carboxylate, cyclohexene-4-glycidyl carboxylate,
5-norbornene-2-methyl-2-glycidyl carboxylate and/or endo-c/s-bicyclo(2,2,1)-5-heptene-
10 2,3-diglycidyl dicarboxylate, glycidyl methacrylate being quite particularly preferred;
• carboxylic acid and/or dicarboxylic acid anhydrides, e.g. chosen from maleic, itaconic,
citraconic, allyl succinic, cyclohex-4-ene-1,2-dicarboxylic, 4-methylenecyclohex-4-ene-
1,2-dicarboxylic, bicyclo[2,2,1]hept-5-ene-2,3-dicarboxylic and methylbicyclo[2,2,1]hept-5-ene-
2,2-dicarboxylic anhydrides, maleic anhydride being quite particularly preferred.
15 [0083] In the latter case, the copolymers resulting from copolymerization with at least one
comonomer X can advantageously be obtained by copolymerization of the monomers (first
comonomer, optional second comonomer, and optionally the functional monomer). This
polymerization can be carried out by means of a high-pressure free-radical process or a
solution process, in an autoclave or tubular reactor, these processes and reactors being well
20 known to those skilled in the art.
[0084] According to another embodiment, when the functional monomer X is not
copolymerized in the polymer chain, for example polyolefin chain, it can be grafted onto said
polymer chain, for example polyolefin chain. The grafting is also an operation known to those
skilled in the art. The case where several different functional monomers are copolymerized
25 and/or grafted onto the polymer chain, for example polyolefin chain, would not depart from the
context of the present invention.
[0085] It is of course possible to use blends of two or more polymers comprising one or more
units resulting from the copolymerization and/or grafting of one or more comonomer(s) X
described above, for instance blends of (co)polyolefins with polyolefins comprising at least one
30 unit originating from a comonomer X. Such compatibilizing polymers are known and described,
for example, in patents FR 2 291 225 and EP 0 342 066.
[0086] In the case where the polymer(s) of the polymer layer (1) is a biorenewable and/or
biodegradable copolyester, the coextmsion tie(s) or compatibilizing agent(s) can, for example,
t e such as those described in patent WO 2008/149019. --
35 [0087] The method b) previously indicated for improving the adhesion between the layer (1)
1
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and the layer (2) uses a compatibility or coupling layer (C) inserted between two noncompatible
layers.
[0088] This layer (C) can also be understood to be a coextrusion tie when the first two layers
(1) and (2) are prepared by extrusion.
5 [0089] This layer (C) which enables compatibility between the layers (1) and (2) can
advantageously be a polymer layer. The polymers which provide compatibility between
polyolefins and polyamides are well known to those skilled in the art and can, for example, be
chosen from copolymers of olefin(s) and of monomers X as defined above, for example
polyolefins grafted with (meth)acrylic acids or esters, and in particular chosen from:
10 - polyethylene, polypropylene, ethylene/a-olefin copolymers, for example ethylene/propylene
copolymers, ethylene/butene copolymers, all these products being grafted with unsaturated
carboxylic acid anhydrides such as, for example, maleic anhydride or glycidyl methacrylate,
- ethylene/alkyi (meth)acrylate/maleic anhydride copolymers, the maleic anhydride being
grafted or copolymerized,
15 - ethylene/vinyl acetate/maleic anhydride copolymers, the maleic anhydride being grafted or
copolymerized,
- ethylene/alkyi (meth)acrylate/glycidyl methacrylate copolymers, the glycidyl methacrylate
being grafted or copolymerized,
- ethylene/vinyl acetate/glycidyl methacrylate copolymers, the glycidyl methacrylate being
20 grafted or copolymerized,
- copolymers of ethylene/(meth)acrylic acid, optionally salts thereof,
- polyethylene, propylene or ethylene/propylene copolymers, these polymers being grafted with
a product which has a site that is reactive with amines, for instance maleic anhydride, epoxy,
and the Jike, these grafted copolymers being subsequently condensed with polyamides or
25 polyamide oligomers having a single amine end, for example with monoamino oligomers of
caprolactam, as described, for example, in patents US 5 070 145 and EP 0 564 338,
- blends of one or more of these polymers and/or copolymers.
[0090] As indicated above, such compatibilizing polymers are known and described, for
example, in patents FR 2 291 225 and EP 0 342 066.
30 [0091] The layer (C) can optionally comprise at least one photocatalyst, of nature and in an
amount identical to those described above for the polymer layer (1). The amount of said at
least one photocatalyst included in the layer (C) may, however, be lower than that present in
the polymer layer (1). The incorporation of said at least one photocatalyst into the polymer
layer (G) can be carried out according to any method known to those skilled in the art, and in
35 particular according to the method described above for the incorporation of said at least one
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photocatalyst into the polymer layer (1).
[0092] All these constituent films of the multilayer film according to the present invention can
be manufactured according to any technique known to those skilled in the art, and for example
according to the usual techniques of extrusion, of coextrusion of sheaths, extrusion and co-
5 extrusion of cast films, and the like, using one or more extruders.
[0093] As a variant, the compatibilizing polymer(s) described above can be incorporated into
the layer (1) or into the layer (2) or else into both the layers (1) and (2) previously defined.
[0094] In the above cases, the amount of compatibilizing polymer is the amount sufficient for
it to be possible for the polymers of the layers (1) and (2) to be assembled into a film having
10 the barrier properties and the mechanical properties mentioned above. This amount depends
on the reactive groups contained in the polyolefin and in the compatibilizing polymer itself.
Those skilled in the art can easily determine this amount. By way of example, this amount may
be from 5 to 20 parts of compatibilizing polymer, per 100 parts by weight of polymer of layer (1)
and of polymer of layer (2).
15 [0095] Preferably, the mixture of polymer of layer (1) and/or of polymer of layer (2) with the
compatibilizing polymer is in the form of a polymer matrix of the nodules of polymer (used to
prepare the layer (1) and/or the layer (2)) or of a blend of said polymers. These polymer blends
are manufactured according to the usual techniques of melt blending (twin-screw. Buss, single
screw), and other methods well known to those skilled in the art.
20 [0096] By virtue of the compatibilizing polymer, in the form of an intermediate layer (C) or
incorporated into the layer (1) and/or the layer (2), it is thus possible to obtain adhesions
greater than approximately 3 N/15 mm. By way of example, the thickness of the compatibilizing
polymer layer (C) can be advantageously between 2 |jm and 15 ^lm.
[0097] The various polymers and/or copolymers constituting the multilayer films according to
25 the invention can also contain one or more additives known to those skilled in the art, chosen
from antioxidants, UV-protecting agents, processing agents, agents for preventing extrusion
defects, antifogging agents, antiblocking agents, antistatic agents, nucleating agents and
colorants. These agents can be added to one or more of the constituent layers of the films of
the present invention, according to techniques and in weight proportions well known to those
30 skilled in the art.
[0098] In particular, the photocatalytic films of the present invention can comprise one or
more organic and/or inorganic agents for protection against ultraviolet radiation. This is
because the films of the invention are intended to be exposed to solar radiation for long periods
• -and-are thus liable to be degraded under the effect of ultraviolet (UV) radiation.^ they are not
35 protected, this degradation results in a plastic film which becomes opaque and friable.
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# -18-
According to one preferred embodiment, the photocatalytic films of the present invention
comprise, in addition to the photocatalyst nanoparticles, at least one agent for protecting
against degradation due to UV radiation, the most well known and commonly used of which is
Ti02 in its nonphotocatalytic form, preferably transparent to visible radiation (400 nm to
5 800 nm), but which must act as a barrier to UV radiation (280 nm to 400 nm), i.e.
nonphotocatalytic Ti02.
[0099] As agent for protecting against UV radiation, it is consequently possible to use
nonphotocatalytic particles, for instance Ti02 of micronic size (pigment), or nanometric
(photocatalytic) Ti02, or any other photocatalyst, the photocatalytic effect of which is inhibited,
10 for example, by coating said particles. Such particles of which the photocatalytic effect has
been inhibited but which have protective properties against UV radiation are, for example, Ti02
coated with a film of Si02 or AI2O3 or Zr02 or other metal oxides. This treatment makes it
possible to go from a photocatalytic activity of 6.01 mol/gh for an uncoated submicronic Ti02 to
0.11 mol/gh for a submicronic Ti02 coated with a film of metal oxide, which is similar to coated
15 rutile used as a pigment (0.07 mol/gh) and much lower than pigment anatase (0.87 mol/gh)
(see "Handbook of Fillers", ChemTec, 3rd Edition, (2010), page 148).
[0100] The use of Ti02 as pigment is known to give plastic mulch films the opacity and the
white color. The pigment Ti02 will have a maximum opacity with respect to the desired color if
the diameter of the particles of which it is composed is equal to half the wavelength of said
20 desired color. For example, for a blue-green light to which the eye is the most sensitive, the
average wavelength is 460 nm, and therefore a particle diameter of 230 nm will give the
maximum opacity with respect to visible radiation.
[0101] For this application, use is advantageously made of rutile Ti02 which has the highest
refractive index and which is 2.75. Use will, for example, be made of the rutile titanium dioxide
25 Ti-Pure®R-105 from DuPont or of the rutile-based Sachtleben® R 620 K from Sachtleben
having an average crystal size of 210 nm. These white plastic films have no photocatalytic
activity and can remain on a field for more than a year without degradation due to UV radiation.
[0102] Another advantage of the photocatalytic films of the present invention lies in the fact
that they comprise at least one photocatalytic agent, optionally in combination with at least one
30 agent for protecting against radiation, depending on whether it is desired for the film not to be
degraded by UV radiation or to be weakly degraded or slowly degraded by said UV radiation. It
is therefore possible to prepare photocatalytic films which comprise both a photocatalyst, for
example Aeroxide® Ti02 P25 from Evonik, and a protective white pigment, such as
Ti-Pure*^ R^'^O&.fFom DuPont or Sachtleben® R 620 K from Sachtleben. Aeroxide®-Tf©?R25 is
35 not used as a white pigment for coloring the plastic films because the size of its particles is too
wo 2013/030513 PCT/FR2012/051960
small to refract the visible light spectrum and therefore to give a homogeneous and opaque
white color.
[0103] The respective amounts of photocatalyst and of agent for protecting against UV
radiation will be adjusted by those skilled in the art according to the photocatalytic effect
5 desired and the duration of protection of the film desired, in particular according to the duration
of the fumigation treatment envisioned, to the atmospheric and edaphic conditions and to the
duration and the amount of sunshine observed on the soils and agricultural substrates to be
treated.
[0104] According to one variant of the invention, the photocatalytic films can also comprise
10 one or more "reinforcing" polymer layers (3), placed above and/or below the polymer layer (1)
or the polymer layers (1) and (2) or else inserted between the layers (1) and (2).
[0105] These reinforcing layers make it possible to further reinforce the structure of the
photocatalytic film. Of course, a reinforcing layer placed below the other layer(s) will have to be
permeable to the vapors of the fumigant, whereas the reinforcing layer placed above the other
15 layer(s) will have to be permeable to UV radiation, and advantageously impermeable to the
vapors of the fumigant.
[0106] The nature of these reinforcing layers may be of any type known to those skilled in the
art, and these layers can in particular comprise one or more of the polymers defined for the
polymer layers (1) and (2) previously defined. It should be understood that the adhesion of the
20 reinforcing layer(s) (3) can be improved by incorporating at least one compatibilizing agent into
the layer(s) (3), or else said layers can be coextruded with a compatibility polymer, as
previously described.
[0107] According to yet another variant, the invention relates to films for fumigation as have
just been described and which also comprise_£(ne or more colored layers. As previously
25 mentioned, the plastic films or sheets commonly used on soils or cultivation substrates may
need to be colored, depending on whether it is desired to benefit from the air or soil
temperature, to retain a certain degree of moisture, or the like.
[0108] The films of the present invention can thus comprise a colored additional layer (4),
which is white, black, or any other color defined according to the needs and the climatic and
30 edaphic conditions. This colored additional layer, which may be barely permeable or even
impermeable to UV radiation, forms the lower part of the film according to the invention, i.e. the
colored layer must be on the side of the soil or of the substrate.
[0109] In addition, and in order for it to be possible for the fumigant to reach the active layer,
which-is the polymer iayer (1) comprising the photocatalyst, the colored layer must be
35 permeable to said fumigant. Thus, the colored layer is a polymer layer advantageously
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# -20-
consisting of the same polymer(s) as that(those) used for the polymer layer (1), said colored
(or pigmented) layer also comprising at least one colorant (or pigment) of which the color and
the amount depend on the desired final color of the multilayer film according to the present
invention.
5 [0110] The colored layer (4) can optionally comprise at least one photocatalyst, of nature and
in an amount which are identical to those described above for the polymer layer (1). When the
colored layer (4) comprises at least one photocatalyst as indicated above, this colored layer (4)
can thus act on the fumigant vapors, just like the polymer layer (1) and it can therefore be
envisioned to eliminate photocatalytic film according to the invention. The incorporation of said
10 at least one photocatalyst into the colored layer (4) can be carried out according to any method
known to those skilled in the art, and in particular according to the method described above for
the incorporation of said at least one photocatalyst into the polymer layer (1).
[0111] Moreover, in the case where the colored layer and the adjacent layer are not
compatible with one another, it is possible to improve the adhesion between these two layers
15 by using a compatibilizing agent or a compatibility layer, according to one of the two solutions
a) and/or b) previously described.
[0112] The colored films are either commercially available or are easily obtained according to
processes known to those skilled in the art, for example by introducing pigment(s) into the
polymer matrix. The multilayer film according to the invention can thus have a total thickness
20 of, for example, between 10 pm and 300 [jm and preferably between 20 |jm and 150 |jm.
[0113] The multilayer film according to the invention can be put down on the soil either before
carrying out the injection of fumigant(s), or immediately after this injection. It is recommended,
if the film is put down before injection, not to damage the film with the injectors, and to provide
for a leaktight system, for example by superposition and adhesive bonding of the strips of films,
25 and/or by burying the edges of films in the earth, and/or any other techniques known to those
skilled in the art.
[0114] The photocatalytic films according to the invention exhibit, in addition to good
mechanical strength and gas-barrier effect properties, the ability to photocatalyze the fumigants
which are imprisoned between the soil or substrate and said film. This photocatalysis allows
30 decomposition, by virtue of ultraviolet radiation, for example the sun, lamps used in
greenhouses and the like, of the often toxic and/or malodorous organic compounds which are
used for the fumigation of said soils and substrates.
[0115] By virtue of the photocatalytic films of the present invention, it is possible to use
fumigants of any type which are known to those-skilled in the art, chosen from nematlcides,
35 herbicides, fungicides, insecticides and bactericides, for example those listed in the Pesticide
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• -21-
Manual, Tenth edition, ed. Clive Tombin). In the present invention, the term "fumigant" is
intended to mean any type of phytosanitary compound which complies at the same time with at
least the following two essential conditions: (i) not having, at the doses at which it is active, any
phytotoxicity on the crops put in place after the treatment and (ii) having the essential and rare
5 property of not being completely absorbed in the soils or substrates for cultivation and of
rapidly diffusing, in gas form, within the thickness of the soil to be treated, since
phytopathogenic organisms are often up to 50 centimeters at least below the surface of said
soil or of said substrate. Furthermore, for obvious productivity reasons, and also in order to limit
the risk of further infestation, the treatment time during which the fumigant acts must be as
10 short as possible.
[0116] By way of nonlimiting examples of fumigants, mention may be made of methyl
bromide, methyl iodide, methyl isothiocyanate (MITC), 1,3-dichloropropene, chloropicrin,
sulfuryl fluoride (SO2F2), phosphine, tetrathiocarbonate or other MITC-generating compounds,
for instance Metam-sodium and Dazomet, and also certain sulfur-containing compounds, such
15 as alkyl sulfides, dialkyi disulfides, dialkyi polysulfides, thiosulfinates and the like, and also
mixtures of two or more of them in any proportions.
[0117] All these fumigating compounds are known and widely described in the literature.
International application WO 2002/074083 describes in particular fumigants based on sulfurcontaining
compounds, and in particular the compounds corresponding to general formula (I)
20
R-S(0)n-S,-R' (I)
in which R is chosen from alkyl and alkenyl radicals containing from 1 to 4 carbon atoms, n is
_ equal to 0, 1 or 2, x takes the values ranging from 0 to 4, limits included, and R' is chosen from
25 alkyl and alkenyl radicals containing from 1 to 4 carbon atoms or, only when n = x = 0, R' can
represent a hydrogen atom or an alkali metal atom.
[0118] The fumigants mentioned above, alone or as mixtures, and in particular those of
formula (I) above, are quite particularly suitable for the fumigation of soils or substrates, in joint
use with the photocatalytic films previously described, because they meet three essential
30 conditions for being able to be used practically in soil or substrate disinfection: they exhibit
overall pesticidal properties (nematicidal, fungicidal, herbicidal, insecticidal, bactericidal); they
are capable of diffusing rapidly within the thickness of the soil to be treated; and they result in a
concentration of gas sufficient to kill the phytopathogenic organisms present.
[0119] Among the fumigants known today,-those corresponding to forrmila (I) above are
35 preferred for the needs of the present invention. Indeed, as substitutes for methyl bromide, the
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— 22 —
compounds of formula (I) are all the more advantageous since some are already present in
nature, originating from the natural degradation of cruciferous plants and alliums. In particular,
thiosulfinates, included in general formula (I), are products that are naturally given off when
alliums are milled and, in this respect, can be used in organic agriculture.
5 [0120] Furthermore, the compounds of formula (I) do not contain halogen atoms that
. generate halogenated radicals responsible for the catalytic destruction of stratospheric ozone,
the compounds of formula (I) present no danger to the ozone layer. As nonlimiting examples of
R and R' radicals, mention may be made of methyl, propyl, allyl and 1-propenyl radicals.
[0121] Among the compounds of formula (I), preference is given to those for which n = 0, i.e.
10 the compounds corresponding to formula (I'): R-S-Sx-R' (I')
in which R and R', which may be identical or different, preferably identical, each represent,
independently of one another, an alkyl or alkenyl, preferably alkyl, radical containing from 1 to
4 carbon atoms, and x represents 1, 2, 3 or 4.
[0122] Other preferred compounds are disulfides (n = 0, x = 1) and more particulariy dimethyl
15 disulfide (DMDS).
[0123] The fumigants described above, and in particular the compounds of formula (I)
described above, can be used in the pure state or in various forms, for example in aqueous,
organic or aqueous-organic emulsions or microemulsions, in the form of an emulsifiable
concentrate, in the form of products which are microencapsulated, nanoencapsulated or
20 supported by a solid, in aqueous, organic or aqueous-organic solutions, or else as a mixture
with one or more products having activity for the treatment of soils or substrates.
[0124] All the formulations defined above can be prepared according to methods well known
to those skilled in the art. Thus, for example, the aqueous emulsions and the microemulsions
can be obtained by adding one or more surfactants to the fumigating compound, and then by
25 adding to the mixture obtained a certain amount of water so as to obtain a stable emulsion or a
microemulsion.
[0125] More particulariy suitable for the preparation of the aqueous emulsions or the
microemulsions are surfactants with a predominantly hydrophilic nature, i.e. those having an
HLB (Hydrophilic Lipophilic Balance) greater than or equal to 8, which may be of anionic,
30 cationic, nonionic or amphoteric nature.
[0126] As nonlimiting examples of anionic surfactants, mention may be made of the alkali
metal, alkaline-earth metal, ammonium or triethanolamine salts of alkyl-, aryl- or
alkylarylsulfonic acids, of fatty acids of basic pH, of sulfosuccinic acid or of alkyl, dialkyi,
- alkylaryl or polyoxyethylene-alkylaryl esters of sulfosuccinic acid. Mention may also be
35 made of the alkali metal or alkaline-earth metal salts of esters of sulfuric, phosphoric.
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• -23-
phosphonic or sulfoacetic acid and of saturated or unsaturated fatty alcohols, and also the
alkoxylated derivatives thereof. Other further surfactants are represented by the alkali metal or
alkaline-earth metal salts of alkylarylsulfuric, alkylarylphosphoric or alkylarylsulfoacetic acids,
and also the alkoxylated derivatives thereof.
5 [0127] The cationic surfactants that can be used are, for example, those of the family of
quaternary alkylammoniums, of sulfoniums ,or of fatty amines at acid pH, and also the
alkoxylated derivatives thereof. As nonlimiting examples of nonionic surfactants, mention may
be made of alkoxylated alkyl phenols, alkoxylated alcohols, alkoxylated fatty acids, fatty esters
of glycerol or fatty derivatives of sugar.
10 [0128] The amphoteric surfactants that can be used are, for example, alkylbetaines or
alkyltaurines. The surfactants that are preferred for the preparation of the aqueous emulsions
and of the microemulsions are compounds based on alkyl benzenesulfonate and on
alkoxylated alkyl phenol.
[0129] For the formulations of fumigant(s) in solution form, the organic solvents that can be
15 used are hydrocarbons, alcohols, ethers, ketones, esters, halogenated solvents, mineral oils,
natural oils and derivatives thereof, and also aprotic polar solvents such as dimethylformamide,
dimethyl sulfoxide or N-methylpyrrolidone. Biodegradable solvents, and more particularly
methyl esters of rapeseed oils, are particularly suitable.
[0130] According to one variant of the present invention, two or more fumigants can be used,
20 jointly, as a mixture, alternately or sequentially. In particular, use may be made of two or more
fumigants having complementary or synergistic activities, chosen from 1,3-dichloropropene,
sulfuryl fluoride (SO2F2), phosphine, methyl iodide, chloropicrin (CI3C-NO2), Metam-sodium
(CHs-NHCSzNa), sodium tetrathiocarbonate (Na2CS4), MITC (CH3-NCS), Dazomet (MITC
generator), and the compounds of formula (I), in particular dialkyi disulfides, for example
25 DMDS.
[0131] In the context of the present invention, i.e. in combination with the photocatalytic films,
the fumigants and the compositions containing them can be applied according to any one of
the conventional methods for introducing pesticides into the soil, for instance injection using
colters, which enables deep introduction of the product, spraying onto the soil, drip via a
30 conventional irrigation system, or "sprinkler" type sprinkling. After introducing the fumigating
product(s) into the soil or the cultivation substrate, it is possible to perform spraying, for
example using a rotary spade in the case of injection into the soil.
[0132] The doses of fumigant(s) generally applied in order to obtain the desired effect are
generally between 150g/ha and 1000 kg/ha, preferably between4 kg/ha and 750 kg/ha, and
35 depend on the nature of the fumigant(s) used, on the degree of soil infestation, on the nature of
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the pests and of the phytopathogenic organisms, on the type of crop and of soil or substrate,
and on the methods of application.
[0133] At the doses indicated above, the desired general pesticidal (at the same time
nematicidal, fungicidal, herbicidal, insecticidal and bactericidal) effect is observed and no
5 phytotoxic effect, or only a negligible one, is observed. Combining the treatment using a
compound of formula (I) with a (simultaneous or nonsimultaneous) treatment with one or more
other pesticidal, insecticidal and/or fungicidal substances and/or with a fertilizer would not be a
departure from the context of the present invention.
[0134] The present invention also relates to the use of the photocatalytic films, as have just
10 been described, in processes for fumigating soils or substrates intended for crops, in particular
for market garden and horticultural crops, such as, for example and in a honlimiting manner,
strawberries, lettuces, tomatoes, melons, cucumbers, aubergines, carrots, potatoes,
ornamental flowers, and the like.
[0135] The films of the present invention can also be used on soils, substrates or more
15 simply items which are not necessarily intended for crops, but which suffer fungal infestations
and/or infestations by insects, nematodes, and other insects, larvae, nits, which are harmful.
The possible uses are, for example, in the fields of the storage of wood, hay, straw, cereals,
and more generally any food or non-food product capable of being degraded by fungi, insects,
larvae, nematodes and the like.
20 [0136] A subject of the invention is also a fumigation treatment kit comprising at least one
photocatalytic film as previously described, and at least one fumigant, preferably at least one
sulfur-containing volatile organic compound, preferably of formula (I) or of formula (I'), said
fumigant more preferably being dimethyl disulfide.
[0137] Another subject of the present invenfion is a process for fumigating a soil, a
25 cultivatable substrate or an item, comprising at least the following steps:
a) application in said soil, substrate or item, and/or at the surface of said soil, substrate or item,
of at least one fumigant, as has just been defined;
b) total or partial coverage of said soil, substrate or item with a photocatalytic film, as previously
defined, before or after step a);
30 c) exposure of said photocatalytic film to ultraviolet radiation, for a period of time which can
range from a few days to several weeks; and
d) optional total or partial removal or simple perforation of said photocatalytic film.
[0138] In the process described above, the possibility of injecting at least one fumigant
- between the film and the substrate is thus envisioned. - - . . - . , „ ,-.
35 [0139] In step d) of the above process, the film according to the invention can be removed.
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when it is considered that the fumigant(s) has (have) performed its (their) role. By virtue of the
photocatalyst, the fumigant(s) is (are) at least partially or even totally degraded and the
removal of the film causes only little or even no harm to either the handler or to the
environment.
5 [0140] As a variant, the film may be only partially removed, or may even remain in place. In
the latter case, the film can ,be perforated in one or more predefined places, where the crops,
such as the transplants for example, will be planted.
[0141] The injection of the fumigant(s) into the soil can be carried out according to any
technique known to those skilled in the art, and for example as previously described.
10 [0142] The photocatalytic film can be deposited on the soil, substrate or item before or after
this fumigation step, for example by simply unrolling the film on said soil, substrate or item. It is
advisable to ensure satisfactory leaktightness, for example by burying the edges of the film, in
order to avoid any leaking of the fumigant into the atmosphere, the fumigant having to t»e
retained, during the required fumigation time, between the soil, substrate or item and the
15 photocatalytic film.
[0143] The photocatalytic effect is provided by exposure to ultraviolet radiation, for example
direct sunlight or else by means of ultraviolet radiation lamps, used for example for crops in
greenhouses.
[0144] The effect of the ultraviolet radiation is the photocatalytic action of the particles of
20 photocatalyst(s) which degrades the vapors of the fumigant(s) which are given off from the soil
or substrate treated. After photocatalytic destruction of the vapors of the fumigant(s), the plastic
films can be totally or partially removed from the soils or substrates so as to allow planting of
the crops in the soils thus treated by fumigation.
[0145] Another advantage of the fumigation process of the invention using the photocatalytic
25 films as have just been defined lies in the fact that the products of photocatalytic degradation of
the fumigants can be useful for the growth of the crops.
[0146] This is because some fumigants can be decomposed, under the effect of the
ultraviolet radiation and of the photocatalyst, into mineral products that are useful for the growth
of crops. This is in particular the case with the fumigating compounds containing sulfur, and
30 more particularly with the fumigants of formula (I) defined above, and quite particularly dialkyi
disulfides, such as DMDS for example, which are decomposed by photocatalysis into various
sulfur oxidation products, until sulfates are formed.
[0147] Sulfates are well-known crop fertilizers. Thus, the fumigation process according to the
invention, using at least one fumigant comprising at least one sulfur atom, for example at least
35 one fumigant of formula (I), for example DMDS, and a photocatalytic film as previously defined,
wo 2013/030513 PCT/rR2012/051960
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makes it possible not only to effectively treat the phytopathogens present in crop soils and
substrates but also to provide fertilizer which is useful for the growth of said crops.
[0148] The figures appended to the present description illustrate some exemplary
embodiments of the invention, without, however, limiting the scope of said invention.
5 [0149] Figure 1 represents diagrammatically a film for fumigation according to the invention,
comprising a polymer layer (1) loaded with photocatalyst. This polymer layer (1) is placed
above a substrate (S) and is irradiated by solar radiation. This polymer layer (1) is permeable
to solar UV radiation which activates the photocatalyst. The fumigant vapors are represented
by the dashed arrows. These vapors can cross the polymer layer (1), which is permeable to
10 said fumigant vapors, and come into contact with the photocatalytic particles. The fumigant is
thus photocatalyzed before being able to completely cross the polymer layer (1).
[0150] Figure 2 represents a variant of a photocatalytic film according to the invention,
comprising:
- a polymer layer (1) loaded with photocatalyst particles, which is permeable to the fumigant
15 vapors and permeable to UV radiation, and
- a polymer layer (2) which is impermeable to the fumigant vapors and permeable to UV
radiation.
[0151] Figure 3 represents another variant of a photocatalytic film according to the invention,
comprising a polymer layer (1) and a polymer layer (2) as indicated in figure 2, and also a
20 reinforcing polymer layer (3), this polymer layer (3) being itself permeable to UV radiation.
[0152] Figure 4 represents yet another variant of a film according to the invention, comprising
a polymer layer (1) and a polymer layer (2) as indicated in figure 2, and also a compatibility
layer (C) as defined above.
[0153] Figure 5 also represents a,variant of a photocatalytic film according to the invention,
25 • comprising a polymer layer (1), a polymer layer (2), a polymer layer (3), as indicated in figure 3,
and also a colored polymer layer (4), this polymer layer (4) being itself permeable to the
fumigant vapors. The fumigant vapors cross the polymer layer (4) and reach the active polymer
layer (1) where the fumigant vapors come into contact with the photocatalyst particles
subjected to the UV radiation which has passed through the polymer layers (2) and (3).
30 [0154] The examples below illustrate the invention without, however, limiting the scope
thereof defined by the appended claims.
Example 1: Preparation of a polyethylene film loaded with photocatalytic Ti02
a) Preparation of the master-batch -
35 [0155] A microextruder, DSM Research model micro 15 twin-screw, is used. The chamber
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has a capacity of 15 ml with six heating zones (maximum temperature: 350°C) and a rotational
screw speed which can range from 1 to 250 revolutions per minute. Cooling can be carried out
under air or with a water circuit.
[0156] The polyethylene used is an LDPE (linear low-density polyethylene) with a melt flow
5 index (MFI) of 1 g/10min (190°C/2.6 kg) in the form of granules, which is sold by Aldrich
(reference: 428078). The titanium dioxide in powder form is Aeroxide® TiOa P 25 from Evonik.
[0157] A master-batch is prepared, in the microextruder, at a temperature of 235°C, for an
average melt temperature of approximately 224°C, with the speed of the two co-rotating
screws set at 200 revolutions per minute. The blending time after stabilization of the "couple" is
10 5 minutes.
[0158] 14 g of a 70/30 LDPE-TiOz master-batch are thus prepared by mixing 9.8 g of LDPE
and 4.2 g of Ti02. A rod 3 mm in diameter is obtained at the extruder outlet. This master-batch
is subsequently denoted MB1.
b) Preparation of the PE/TiO, film
15 [0159] The operating conditions are identical to those of the preparation of the master-batch,
namely: working temperature 235°C, average melt temperature: approximately 224°C, speed
of the two co-rotating screws set at 200 revolutions per minute, blending time after stabilization
of the "couple": 5 minutes.
[0160] 10 g of a PE polymer film containing 10% by weight of titanium dioxide are thus
20 prepared from a mixture of 6.67 g of LDPE and 3.33 g of the master-batch prepared in step a).
At the outlet of the microextruder, the mixture is in the form of a rod.
[0161] To obtain a film of which the average thickness is 500 pm, from the previously
manufactured rod, a press is used, with a working temperature of 150°C, a pressing time of
30 seconds, and a pressing pressure of 10'^ Pa. To_obtain a film of which the average
25 thickness is 50 pm, from the previously manufactured rod, the rod is drawn out according to
the conventional techniques known to those skilled in the art, for example according to the cast
film extrusion technique.
[0162] Films are prepared on a 3-layer laboratory line from Dr Collin, equipped with 3
extruders and a spiral mandrel die (50 mm in diameter). The symmetrical coextruded structure
30 is the following:
- 15 pm PE layer (LDPE 2200TC00 from Sabic), containing 15% of a PE-based coupling
agent (Orevac® OE825), the extrusion temperature is set at 220°C;
- 15 pm PA6 layer (Durethan® C38F), the extrusion temperature is set at 230°C;
- 15 pm PE layer (LDPE 2200TC00 from Sabic), this layer contains 15% of master-batch MB 1
35 and 15% of a PE-based coupling agent (Orevac OE825), the LDPE-based master-batch
wo 2013/030513 PCT/FR2012/051960
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MB1 (d ~ 918, Ml = 1) containing 30% of nanometric titanium dioxide (Aeroperl® P25/20 from
Evonik) was prepared beforehand by twin-screw compounding according to the rules known
to those skilled in the art; the extrusion temperature is 220°C.
[0163] The temperature of the die is set at 230°C, the die gap is adjusted to 1.2 mm, the
5 degree of swelling to 2.5 and the line speed at 5 m/min. The film obtained has a width of
200 mm. The adhesion measured at the PE/PA6 interface is ION/15 mm. The test is carried
out using a T-peeling test at 200 mm/min.
Example 2:
10 [0164] The effectiveness of the various types of films is tested with DMDS in a 0.351 leaktight
Pyrex reaction vessel which is transparent to UV radiation, with a relative humidity of 90% and
at a temperature of 45°C, so as to reproduce the actual conditions in the field. The film is
blocked between the walls and the upper window of the reaction vessel, the active layer being
oriented toward the bottom of the reaction vessel. The film is irradiated from above through the
15 Pyrex window.
[0165] The solar illumination is provided by virtue of a 150 watt Newport solar simulator,
equipped with a xenon lamp, without ozone, the light intensity of which is adjusted to 1 sun.
The distance between the Pyrex window of the reaction vessel and the lamp can be adjusted
in order to control the Irradiation power. An Oriel 91150 calibration solar cell makes it possible
20 to determine the amount of light in "sun" units for the solar simulator. With this simulator, all the
tests are carried out with one (1) "sun", equivalent to 1000 W.m"^ (100 mW.cm'^) at 25°C. The
area irradiated is 28 cm^.
[0166] The concentration of DMDS and of carbon dioxide (CO2) was automatically monitored
every 10 minutes by gas chromatography (Varian®4900 chromatograph), the chromatograph
25 being equipped with a TCD detector and with 2 chromatographic columns (CP-SII5CB for the
DMDS and Porapak® for the CO2).
[0167] Water-free and C02-free synthetic air is introduced into the reaction vessel. The
DMDS and the water are introduced into the reaction vessel with a microsyringe through a
septum. All the tests are carried out in parallel, on the one hand with irradiation and, on the
30 Other hand, without irradiation (in the dark). The test without irradiation corresponds to the
control test.
Test 1: Test on polyethylene film
[0168] The film tested is a monolayer film of polyethylene (PE) 50 |jm thick and loaded with
1.3% by weight of TIQz, under a relative humidity ofJ36%, at a temperature of 45''C and a
35 DMDS concentration of 10114 ppmv. A linear decrease in the DMDS concentration of 30% is
measured after 6 days of irradiation.
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Test 2: Test on transparent VIF-Ti02 films
[0169] For this test, a three-layer film (according to figure 3) having a total thickness of 45 \im
consisting of the following is used:
i) a PE film having a thickness of 15 pm, permeable to gases and to UV radiation, loaded with
5 3.3% by weight of Ti02, this film being in contact with the bottom of the measuring cell;
ii) a layer impermeable to gases and permeable to UV radiation; and
iii) a reinforcing layer permeable to UV radiation.
[0170] After introduction of DMDS under the film and irradiation with UV radiation, a linear
decrease in the concentration of DMDS is noted. After 50 hours of irradiation, the concentration
10 of DMDS decreased by close to 25%.
Test 3: Tests on transparent VIF-TiOz fifms
[0171] The film used in test 2 is used in a further test. The temperature of the test is set at
45°C, the relative humidity is 90%, and the initial concentration of DMDS is 25500 ppmv. The
test is carried out this time with an irradiation equivalent to 1.9 suns. A more rapid decrease in
IS the residual concentration of DMDS under the film is noted with 1.9 suns compared with 1 sun.
This result clearly shows the photocatalytic effect of the films.
[0172] Moreover, the concentration of carbon dioxide (CO2) is monitored. After 60 hours of
irradiation, the concentration of CO2 measured under the film makes it possible to deduce a
mineralization of 10% of the DMDS. This demonstrates once more the photocatalytic
20 properties of the film tested.
Test 4: Tests on transparent VIF-Ti02 films
[0173] Tests are carried out with a VIF-Ti02 film having a total thickness of 80 pm, containing
3.3% of TiOa in the active layer of PE which is 50 |jm thick. The conditions are: 1.9 suns, 90%
relative humidity, temperature: 45°C, concentration of DMDS: 25500 ppmv. .
25 [0174] The concentration of carbon dioxide is measured, which makes it possible to deduce
a degree of mineralization of 21% after 60 hours of in-adiation. These results show that, with a
film having the same Ti02 load of 3.3%, but with a greater thickness (15 pm compared with
50 pm in this test), the degree of mineralization increases significantly.
[0175] These tests show that the photocatalytic activity is variable according to the thickness
30 of the film; the thicker the film, the greater the photocatalytic activity at a constant level of
photocatalyst load.
Test 5: Tests on transparent VIF-TiOa films
[0176] Tests are again carried out as described in test 4 above; this time using a VIF-Ti02
film having a total thickness of 80 \sm, loaded with t=3% by weight of Ti02 for an active layer of
35 PE having a thickness of 50 |jm. The relative humidity is 90%, the temperature is 45''C and the
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concentration of DMDS is 25500 ppmv.
[0177] The degree of mineralization, deduced after measuring the CO2 fomied after 60 hours
of irradiation, is 11%. These tests show that the photocatalytic activity is directly linked to the
concentration of photocatalyst present in the active layer of the film.
5 Test 6: Tests on transparent VIF-TiOa films
[0178] VIF/Ti02 film (film prepared with an Orevac®-Ti02 master-batch), relative humidity:
90%, temperature: 45°C, amount of Ti02: 4.5%, film having a total thickness of 45 pm,
including 15 pm for the active PE layer, concentration of DMDS: 32 mg.lV
[0179] The photocatalysis of the DMDS is rapid and the formation of CO2 is already observed
10 after 20 hours of irradiation. The CO2 concentration increases up to 3000 ppmv after 60 hours
and corresponds to 12% mineralization of the DMDS.
[0180] This film prepared with the Orevac®-Ti02 master-batch enables a rapid decrease in
the concentration of DMDS.
[0181] All these results clearly demonstrate the capacity of the Ti02-doped films to
15 photocatalytically oxidize DMDS under solar irradiation.
Test 7: Test on colored (black or white) VIF-TIO2 films
[0182] The film tested here is a 4-layer film: layer 1: LDPE of 15 pm; layer 2: polyamide-6,6
of 15 pm; layer 3: LDPE of 15 pm; and layer 4; LDPE with white pigment (micrometric
pigmentary Ti02) of 5 pm. Only the PE layer, which is above the colored layer (layer 1),
20 contains the photocatalytic Ti02.
[0183] A white-colored film, having a total thickness of 45 pm, the active layer of which is an
LDPE layer of 15 pm, loaded with 3.3% Ti02, under a relative humidity of 90%, at a
temperature of 45°C, and a concentration of DMDS of 31 mg.r\ is tested.
[0184] The concentration of DMDS decreases by 1030 ppmv, while the formation of CO2 is
25 approximately 485 ppmv in 15 hours, which corresponds to a degree of mineralization of 16%.
[0185] This test demonstrates that it is possible to use photocatalytic films according to the
invention which are colored, without impairing the photocatalytic efficiency of said films.
Example 3 (comparative):
30 Preparation of a polyethylene film loaded with anti-UV TiQ2
[0186] The polyethylene used is an LDPE (linear low-density polyethylene) with a melt flow
index (MFI) of 1 g/10 min (190°C/2.6 kg) in the form of granules, sold by Aldrich (reference:
428078).
[0187] The anti-UV TiOz is the Light Stabilizer® 210 from DuPont. The-Ti02 crystals are
35 coated with a layer of AI2O3 and the average particle diameter is 135 nm.
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[0188] 14 g of 97/3 LDPE-Ti02 master-batch are prepared by mixing 13.58 g of LDPE and
0.42 g of Light Stabilizer 210 Ti02 in a microextruder, at a temperature of 235°C, for an
average melt temperature of approximately 224"'C, with the speed of the two co-rotating
screws set at 200 revolutions/minute. The blending time after stabilization of the "couple" is 5
5 minutes. A rod 3 mm in diameter is obtained at the extruder outlet.
[0189] This master-batch (3.33 g) is melt-blended with 6.67 g of LDPE, according to the
protocol described in step b) of example 1, and the mixture is subsequently extruded in rod
form. To obtain a monolayer film having an average thickness of 50 pm, the rod is drawn out
according to the conventional techniques known to those skilled in the art, for example
10 according to the cast film extrusion technique.
Test of the polyethylene film loaded with anti-UV T1O2
[0190] This transparent polyethylene (PE) monolayer film 50 pm thick, loaded with 3% by
weight of anti-UV Ti02, is tested, according to the protocol described in example 2, under a
relative humidity of 92% and at a temperature of 45°C and a concentration of DMDS of
15 11052 ppmv. No decrease in the concentration of DMDS is measured after 6 days of
irradiation, compared with the control test.
Example 4 (comparative):
Preparation of a polyethylene film loaded with pigmentary T1O2
20 [0191] For this film, the procedure of example 3 is reiterated, with the anti-UV TiOj being
replaced with Ti02, sold by DuPont under the name Ti-Pure® R-105, which is SiOa-coated,
rutile-form, pigmentary Ti02, the average particle size of which is 310 nm.
[0192] 14 g of 97/3 LDPE-Ti02 master-batch are prepared by mixing 13.58 g of LDPE and
0.42 g of Ti-Pure® R-105 Ti02 in a microextruder, at a temperature of 235''C, for an average
25 melt temperature of approximately 224°C, with the speed of the two co-rotating screws set at
200 revolutions/minute. The blending time after stabilization of the "couple" is 5 minutes. A rod
3 mm in diameter is obtained at the extruder outlet.
[0193] This master-batch (3.33 g) is melt-blended with 6.67 g of LDPE, according to the
protocol described in step b) of example 1, and the mixture is then extruded in rod form. To
30 obtain a monolayer film having an average thickness of 50 pm, the rod is drawn out according
to the conventional techniques known to those skilled in the art, for example according to the
cast film extrusion technique.
Test of the non-photocatalytic white polyethylene film
- [0194] This white polyethylene (PE) monolayer film having a thickness of 50 pm and loaded
35 with 3% by weight of pigmentary Ti02 is tested, according to the protocol of example 2, under a
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• -32-
relative humidity of 89% and at a temperature of 45"'C and a concentration of DMDS of
10645 ppmv. No decrease in the concentration of DMDS is measured after 6 days of
irradiation, compared with the control test.

}iVS- if WO 2013/030513 0^"^* ^^ PPCCTT//FFRR22001122//(0 51960
Claims
5 1. A photocatalytic film comprising at least one polymer layer (1) comprising at least one
photocatalyst, said layer being both permeable to the vapors of .at least one fumigating
compound and permeable to ultraviolet radiation capable of activating the photocatalyst.
2. The photocatalytic film as claimed in claim 1, wherein the photocatalyst is present in
10 the form of particles having an average particle size of between 0.5 nm and 200 nm, preferably
between 0.5 nm and 180 nm, more preferably between 0.5 nm and 100 nm, advantageously
between 1 nm and 50 nm, particularly between 10 nm and 40 nm and more particularly
between 15 nm and 30 nm.
IS 3. The photocatalytic film as claimed in claim 1 or claim 2, wherein the polymer layer (1)
is a polymer film comprising at least one polymer A chosen from polyolefins and polyesters,
preferably biobased and/or biodegradable polyolefins and polyesters.
4. The photocatalytic film as claimed in claim 3, wherein the polymer A is chosen from
20 polyolefins resulting from the polymerization or from the copolymerization of olefins which are
themselves chosen from ethylene, propylene, 1-butene, and the like, and also mixtures thereof,
the polymer A preferably being polyethylene.
5. The photocatalytic film as claimed in claim 3, wherein the polymer A is chosen from
• 25 biobased or biodegradable copolyesters, more preferably from poiylactides,
poly(hydroxyalkanoates), poly(alkylene succinates), thermoplastic starch, and the like, and also
mixtures thereof.
6. The photocatalytic film as claimed in any one of the preceding claims, wherein the
30 photocatalyst is chosen from titanium dioxide, silicon dioxide, zinc oxide, tungsten trioxide,
silicon carbide, iron II oxide or iron III oxide, cerium dioxide, zirconium dioxide, tin dioxide, zinc
sulfide, cadmium sulfide, silicon carbide, and the like, and also mixtures of two or more of them
in any proportions.
35 7. The photocatalytic film as claimed in any one of the preceding claims, wherein the
10
)^0^^^ -S •401®^^^
WO 2013/030513 PCT/FR2012/051960
— 34 £S Mtt
amount of photocatalyst is between 0.1% and 30% by weight of photocatalyst relative to the
total weight of the polymer layer (1), preferably from 0.1% to 20% by weight, more preferably
from 0.1% to 10% by weight of photocatalyst relative to the total weight of the polymer layer
(1).
8. The photocatalytic film as claimed in any one of the preceding claims, wherein the
thickness of the polymer layer (1) is between approximately 5 pm and approximately 100 pm,
preferably between 5 pm and 75 |jm, preferably between 5 pm and 60 pm and more preferably
between 5 pm and 50 pm.
9. The photocatalytic film as claimed in any one of the preceding claims, also comprising
at least one polymer layer (2) impermeable to the vapors of said at least one fumigant and
permeable to ultraviolet radiation.
15 10. The photocatalytic film as claimed in claim 9, wherein the polymer layer (2) is chosen
from nitrogenous and/or oxygen-containing polar resins, polyesters and copolyesters,
thermoplastic starches and mixtures of two or more of them in any proportions.
11. The photocatalytic film as claimed in claim 9 or claim 10, wherein the polymer layer
20 (2) is a polyamide or a copolyamide chosen from the products of condensation of one or more
amino acids, of one or more lactams, and of one or more diamines with one or more diacids,
and also mixtures of these monomers.
12. The photocatalytic film as claimed in any one of claims 9 to 11, also comprising at
25 least one compatibilizing agent in the layer (1) and/or the layer (2), preferably in the layer (1),
and/or a "compatibility" or "coupling" layer (C) between the layers (1) and (2).
13. The photocatalytic film as claimed in any one of the preceding claims, also comprising
one or more reinforcing layers and/or one or more colored layers.
30
14. The photocatalytic film as claimed in any one of the preceding claims, the total
thickness of which is between 10 pm and 300 pm, preferably between 20 pm and 150 pm.
15. A process for fumigating a soil, a cultivatable substrate or an item, comprising at least
35 the following steps:
14
35
sifare
WO 2013/030513 "^ '"^ ? PCT/FR2012/051960
a) application in said soil, substrate or item, and/or at the surface of said soil, subsfrafe or item,
of at least one fumigant, and
b) total or partial coverage of said soil, substrate or item with a photocatalyticfilm, as claimed in
any one of claims 1 to 14, before or after step a),
c) exposure of said photocatalytic film to ultraviolet radiation for. a period of time which can
range from a few days to several weeks; and
d) optional total or partial removal or simple perforation of said photocatalytic film.
16. The fumigation process as claimed in claim 15, wherein the fumigant is chosen from
10 methyl bromide, methyl iodide, methyl isothiocyanate (MiTC), 1,3-dichloropropene,
chloropicrin, sulfuryl fluoride (SO2F2), phosphine, tetrathiocarbonate or other MITC-generating
compounds, alkyl sulfides, dialkyi disulfides, dialkyi polysulfides, thiosulfinates and the like, and
also mixtures of two or more of them in any proportions.
15 17, The process as claimed in claim 16, wherein the fumigant is chosen from the sulfurcontaining
volatile pesticidal compounds of general formula (I):
R-S(0)n-Sx-R' (I)
in which R represents an alkyl or alkenyl, preferably alkyl, radical containing from 1 to 4 carbon
atoms, n is equal to 0, 1 or 2, x takes the values ranging from 0 to 4, limits included, and R',
20 represents an alkyl or alkenyl, preferably alkyl, radical,
preferably the volatile pesticidal compound is chosen from the compounds of formula (I'):
R-S-Sx-R' (I')
in which R and R', which may be identical or different, preferably, identical, each represent,
independently of one another, an alkyl or alkenyl, preferably alkyl, radical containing from 1 to
25 4 carbon atoms, and x represents 1, 2, 3 or 4, more preferably the fumigant is dimethyl
disulfide.
18, A fumigation treatment kit comprising at least one photocatalytic film as claimed in any
one of claims 1 to 14, and at least one fumigant, preferably at least one sulfur-containing
30 volatile organic compound, preferably of formula (I) as claimed in claim 16 or formula (I') as
claimed in claim 17, said fumigant more preferably being dimethyl disulfide.