Technical field:
The present invention relates to a polyhydroxyalkanoate
(PHA) composition with improved impact strength.
Prior art:
Polymers of polyhydroxyalkanoate or polyhydroxyalkanoic
acid (PHA) type, such as polylactic acid (PLA), are
polymers that may be obtained from a monomer of plant
origin. They are of major interest on account of their
biodegradable properties. However, they are
particularly fragile polymers, which require
reinforcing with respect to impacts.
In the prior art, mention may be made of document
JP H09-316310 which describes PLA compositions
containing ethylene-glycidyl methacrylate copolymers
grafted with polystyrene or polydimethacrylate, or
alternatively polyolefins grafted with maleic
anhydride.
More recently, WO 2005/059031 describes a PLA
composition comprising from 3% to 40% by mass of a
copolymer of ethylene, of a carboxylic acid ester and
of a glycidyl ester.
Document US 2008/0071008 discloses a polyhydroalkanoic
acid composition comprising from 0.2% to 10% of coreshell
compound with a refractive index of less than 1.5
and not comprising any vinyl aromatic monomer.
These compositions do indeed show improved impact
strength, but this strength is not entirely
satisfactory, especially at a temperature below 20°C.
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Moreover, some of these compositions have a fluidity
that is markedly inferior to that of PHA. This
substantial reduction in fluidity hampers the use, most
particularly for thin and large-sized injection-molded
parts.
The aim of the present invention is to propose a novel
PHA composition that has good impact strength,
especially at low temperature.
Summary of the invention:
The present invention relates to a polyhydroxyalkanoate
(PHA) composition also comprising a core-shell
elastomeric compound (A) and an olefinic copolymer (B)
comprising an ethylenic monomer bearing an epoxy
function.
This particular composition comprising an impact
modifier combining a core-shell compound with an
olefinic copolymer has exceptional impact properties
that are, surprisingly, much better than those of the
compositions of the prior art and in particular much
better than compositions comprising an impact modifier
consisting of an olefinic copolymer comprising an
ethylenic monomer bearing an epoxy function or a coreshell
compound.
The composition also has the advantage of having
excellent fluidity during its use.
The ethylenic monomer bearing an epoxy function is
preferentially glycidyl (meth)acrylate.
The copolymer (B) may be a copolymer of ethylene, of
glycidyl methacrylate and optionally an alkyl acrylate
and/or methacrylate in which the alkyl chain comprises
from 1 to 30 carbon atoms, the latter monomers being
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combined under the term alkyl (meth)acrylate in the
present description. The amount of alkyl (meth)acrylate
may be within the range from 0 (i.e. containing none)
to 40% relative to the total mass of said olefinic
copolymer (B), advantageously from 5% to 35% and
preferably from 20% to 30%.
The amount of ethylenic monomer bearing an epoxy
function in said olefinic copolymer (B) is, for
example, in the range from 0.1% to 20% relative to its
total mass, advantageously from 2% to 15% and
preferably from 5% to 10%.
The composition may also comprise an additional
olefinic polymer (C) other than the olefinic copolymers
comprising an ethylenic monomer bearing an epoxy
function. Preferentially, this additional olefinic
polymer (C) is a copolymer of ethylene and of an alkyl
(meth)acrylate, a copolymer of ethylene and of a vinyl
ester of a carboxylic acid, a copolymer of ethylene and
of a (meth)acrylic acid or an ionomer, most
preferentially a copolymer of ethylene and of an alkyl
acrylate with an alkyl chain ranging from 1 to 20, for
instance methyl acrylate, ethylene acrylate or n-butyl
acrylate. In this case, the composition advantageously
has a mass ratio (B)/(C) within the range from 90/10 to
10/90 and preferentially from 75/25 to 40/60.
Advantageously, the mass ratio (A)/((B) + optional (C))
is within the range from 90/10 to 10/90, for example
85/15 to 40/60, more advantageously from 80/20 to 50/50
and preferentially from 75/25 to 60/40.
The amount of modifier ((A) + (B) + optional (C)) may
be within the range from 1% to 30% by mass of the total
composition, advantageously from 2% to 15% and
preferentially from 3% to 9%.
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The amount, in polymerized form, of ethylenic monomer
comprising an epoxy function may be within the range
from 0.01% to 2%, advantageously from 0.02% to 1% and
preferentially from 0.03% to 0.7% relative to the mass
of the total composition.
As regards the elastomeric core-shell compound (A), the
glass transition temperature of the core polymer is
preferentially less than 20°C, for example between
-140°C and 0°C. Preferentially, the glass transition
temperature of the core polymer is greater than 20°C,
for example between 30°C and 250°C.
As regards the elastomeric core-shell compound (A), its
shell part preferentially comprises, in polymerized
form:
􀂃 an alkyl methacrylate in which the alkyl chain
comprises from 1 to 12 and preferably from 1 to
4 carbon atoms;
􀂃 and/or a vinyl aromatic organic compound
comprising from 6 to 12 carbon atoms, such as
styrene;
􀂃 and/or acrylonitrile;
this shell part possibly being crosslinked.
The core part of the core-shell compound (A)
advantageously comprises, in polymerized form:
􀂃 a conjugated diene comprising from 4 to 12 and
preferably from 4 to 8 carbon atoms;
􀂃 or an alkyl acrylate in which the alkyl chain
comprises from 1 to 12 and preferably from 1 to
8 carbon atoms.
The core-shell compound (A) may be chosen from:
􀂃 a compound with a core comprising butadiene and
a shell comprising methyl methacrylate, ethyl
acrylate, butyl acrylate, methacrylic acid
and/or styrene;
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􀂃 a compound with a core comprising butyl
acrylate, n-octyl acrylate and/or 2-ethylhexyl
acrylate and a shell comprising methyl
methacrylate;
􀂃 a compound with a core comprising butadiene and
a shell comprising a mixture of acrylonitrile
and styrene.
As regards the core-shell compound, the mass amount of
core is advantageously within the range from 10% to
99%, for example from 60% to 95%, of the total mass of
the core-shell compound.
The size of the core-shell compounds is advantageously
between 50 and 600 nm.
Preferentially, the PHA is chosen from polylactic acid
(PLA) and polyglycolic acid (PGA).
A subject of the invention is also a process for
preparing the modified PHA composition, in which the
mixture of PHA, of (A), of (B), of the optional (C)
with, optionally, one or more additives such as a
nucleating agent, is prepared by extrusion.
According to one preferred process of the invention,
the following are performed:
􀂃 mixing of (A), (B) and optional (C) to form an
impact modifier in a first step, and then
􀂃 in a second step, mixing of the impact modifier
obtained from the first step with PHA.
According to another process for preparing the
abovementioned composition that is the subject of the
present invention, the following are performed:
- a first step of manufacturing the impact
modifier by mixing at a temperature at which the
copolymer is in molten form and at a maximum
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temperature within the range from 60 to 180°C;
- a second step of manufacturing the polyhydroxyalkanoic
acid (PHA) composition by extrusion or by
mixing the impact modifier obtained in the first step
and said PHA.
Advantageously, the step for manufacturing the impact
modifier of the first step is performed such that the
maximum temperature is within the range from 70 to
140°C.
According to one embodiment, the step for manufacturing
the abovementioned impact modifier of the first step is
performed by extrusion in a twin-screw or single-screw
extruder, preferentially a single-screw extruder.
According to one embodiment, the step for manufacturing
the impact modifier of the first step is performed by
mixing in molten form in a co-rotating twin-screw
extruder or a counter-rotating twin-screw extruder or a
co-kneader or an internal mixer or a single-screw
extruder, preferentially in a single-screw extruder. It
is understood that all the steps for manufacturing the
impact modifier, including mixing in melt form, are
considered herein as extrusions.
Preferentially, the residence time of the impact
modifier in the first step is within the range from 10
to 300 seconds.
According to one embodiment, the second step for
manufacturing the mixture of the impact modifier
obtained in the first step and of the abovementioned
PHA may be performed such that the mixing temperature
is within the range from 180 to 320°C.
One subject of the invention is a part or object, for
instance wrapping, comprising the modified PHA
composition.
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The invention also relates to a process for
manufacturing the part or object, comprising a step of
forming said composition, for example by injectionmolding,
pressing or calendering, said part or said
object optionally undergoing an annealing step.
Detailed description of the invention
The present invention relates to a polyhydroxyalkanoate
(PHA) composition also comprising a core-shell compound
(A) and a polymer comprising an ethylenic monomer
bearing an epoxy function (B).
According to the invention, when one of the polymers of
the composition or a composition “comprises a monomer”,
this means that it is present in polymerized form in
said polymer or one (or more) polymer(s) of said
composition.
Polymers of PHA type are biodegradable polymers. Some
of them are also biorenewable, the monomers being
produced by bacterial fermentation processes or
alternatively extracted from plants. The term
“biodegradable” applies to a material if it can be
degraded by microorganisms. The result of this
degradation is the formation of water, CO2 and/or CH4
and, optionally, of byproducts (residues, new biomass)
that are not toxic to the environment. It is possible,
for example, to use standard EN13432 to determine
whether the material is biodegradable. To determine
whether a polymer is “biorenewable”, standard ASTM D
6866 may be used. Biorenewable polymers are
characterized in that they comprise carbon of renewable
origin, i.e. 14C. Specifically, all the carbon samples
taken from live organisms and in particular from the
plant material used to form the biorenewable polymers
are a mixture of three isotopes: 12C, 13C and 14C in a
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14C/12C ratio that is kept constant by continuous
exchange of the carbon with the environment and which
is equal to 1.2 × 10-12. Although 14C is radioactive and
its concentration thus decreases over time, its halflife
is 5730 years, and as such it is considered that
the 14C content is constant from the time of extraction
of the plant material up to the manufacture of the
biorenewable polymers and even up to the end of their
use. For example, it may be considered that the polymer
is biorenewable when the 14C/12C ratio is greater than or
equal to 1 × 10-12.
The 14C content of biorenewable polymers may be
measured, for example, according to the following
liquid scintillation spectrometry or mass spectrometry
techniques. These methods for measuring the 14C content
of materials are described precisely in standards ASTM
D 6866 (especially D6866-06) and in standards ASTM D
7026 (especially 7026-04). These methods measure the
14C/12C ratio of a sample and compare it with the 14C/12C
ratio of a reference sample of 100% renewable origin,
to give a relative percentage of carbon of renewable
origin in the sample.
The measuring method preferentially used in the case of
biorenewable polymers is mass spectrometry described in
standard ASTM D6866-06 (accelerator mass spectroscopy).
PHAs are polymers comprising hydroxyalkanoic acid
units, for example containing from 2 to 10 carbon
atoms. Examples that may be mentioned include the
polymer comprising 6-hydroxyhexanoic acid known as
polycaprolactone (PCL), polymers comprising 3-hydroxyhexanoic
acid, 4-hydroxyhexanoic acid or 3-hydroxyheptanoic
acid. Polymers containing 5 carbon atoms or
less, for example polymers comprising glycolic acid
(PGA), lactic acid (PLA), 3-hydroxypropionate,
2-hydroxybutyrate, 3-hydroxybutyrate (PHB), 4-hydroxyWO
2011/007092 - 10 - PCT/FR2010/051471
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butyrate, 3-hydroxyvalerate, 4-hydroxyvalerate and
5-hydroxyvalerate may be noted in particular. Preferred
polymers are PGA, PCL, PLA and PHB. The PHAs may be
aliphatic.
PHAs may also be copolymers, i.e. they may comprise a
first hydroxyalkanoic acid and another unit that may be
either a second hydroxyalkanoic acid different than the
first, or another monomer such as diols, for instance
ethylene glycol, 1,3-propanediol and 1,4-butanediol or
diacids such as succinic acid, adipic acid and
terephthalic acid.
The compositions of the invention may also comprise
mixtures of these polymers.
PHAs are often polymerized in bulk. A PHA may be
synthesized by dehydration and condensation of the
hydroxyalkanoic acid. It may also be synthesized by
dealcoholization and condensation of an alkyl ester of
a hydroxyalkanoic acid or by polymerization by ring
opening of a cyclic derivative of the corresponding
lactone or of the dimer of the cyclic ester. Bulk
polymerization is generally performed via a batch or
continuous process. As examples of continuous processes
for manufacturing PHA, mention may be made of the
processes in patent applications JP-A 03-502115, JP-A
07-26001 and JP-A 07-53684. Patents US 2 668 162 and
US 3 297 033 describe batch processes.
As regards the core-shell copolymer (A), it is in the
form of fine particles with a core made of soft polymer
and at least one shell made of hard polymer and the
size of the particles is generally less than a
micrometer and advantageously between 50 and 600 nm.
Preferentially, the polymer of the core has a glass
transition temperature of less than 20°C, for example
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between -140°C and 0°C and preferentially between
-120°C and -30°C. Preferentially, the polymer of the
shell has a glass transition temperature of greater
than 20°C, for example between 30°C and 250°C.
The glass transition temperatures of the polymers of
the composition may be measured according to standard
ISO 11357-2:1999.
Examples of core polymers that may be mentioned include
isoprene or butadiene homopolymers, isoprene-butadiene
copolymers, copolymers of isoprene with not more than
98% by weight of a vinyl monomer and copolymers of
butadiene with not more than 98% by weight of a vinyl
monomer. The vinyl monomer may be styrene, an alkylstyrene,
acrylonitrile, an alkyl (meth)acrylate,
butadiene or isoprene. The core polymer may also
comprise siloxane, optionally copolymerized with an
alkyl acrylate. The core of the core-shell copolymer
may be totally or partially crosslinked. To do this, it
suffices to add at least difunctional monomers during
the preparation of the core, and these monomers may be
chosen from poly(meth)acrylic esters of polyols such as
butylene di(meth)acrylate and trimethylolpropane
trimethacrylate. Other multifunctional monomers are,
for example, divinylbenzene, trivinylbenzene, vinyl
acrylate and vinyl methacrylate, and triallyl
cyanurate. The core may also be crosslinked by
introducing therein, by grafting or as comonomer during
the polymerization, unsaturated functional monomers
such as unsaturated carboxylic acid anhydrides,
unsaturated carboxylic acids and unsaturated epoxides.
Examples that may be mentioned include maleic
anhydride, (meth)acrylic acid and glycidyl
methacrylate. Crosslinking may also be performed using
the intrinsic reactivity of monomers, for example
dienes.
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The shell(s) are homopolymers of styrene, of an alkylstyrene
or of methyl methacrylate or copolymers
comprising at least 70% by weight of one of the
preceding monomers and at least one comonomer chosen
from the other preceding monomers, another alkyl
(meth)acrylate, vinyl acetate and acrylonitrile. The
shell may be functionalized by introducing therein, by
grafting or as comonomer during the polymerization,
unsaturated functional monomers such as unsaturated
carboxylic acid anhydrides, unsaturated carboxylic
acids and unsaturated epoxides. Examples that may be
mentioned include maleic anhydride, (meth)acrylic acid,
glycidyl methacrylate, hydroxyethyl methacrylate and
alkyl(meth)acrylamides. Examples that may be mentioned
include core-shell copolymers with a shell made of
polystyrene and core-shell copolymers with a shell made
of PMMA. The shell may also contain imide functions,
either by copolymerization with a maleimide, or by
chemical modification of the PMMA with a primary amine.
Advantageously, the molar percentage of imide functions
is from 30% to 60% (relative to the shell as a whole).
Core-shell copolymers containing two shells also exist,
one made of polystyrene and the other on the exterior
made of PMMA. Examples of copolymers and of processes
for preparing them are described in the following
patents: US 4 180 494, US 3 808 180, US 4 096 202,
US 4 260 693, US 3 287 443, US 3 657 391, US 4 299 928,
US 3 985 704, US 5 773 520.
The core represents, for example, in this invention, 5%
to 95% by weight of the core-shell compound, and the
shell 95% to 5% by weight.
An example of a copolymer that may be mentioned is the
one consisting of (i) from 50 to 95 parts of a core
comprising, in moles, at least 93% butadiene, 5%
styrene and 0.5% to 1% divinylbenzene and (ii) from 5
to 50 parts of two shells essentially of the same
WO 2011/007092 - 13 - PCT/FR2010/051471
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weight, the inner one made of polystyrene and the outer
one made of PMMA.
Preferentially, core-shell compounds with a core made
of butyl acrylate copolymer and a shell made of PMMA
may be used. These compounds have the advantage of
being particularly transparent.
All these core-shell compounds are occasionally
referred to as soft/hard on account of the elastomeric
core. It would not constitute a departure from the
context of the invention to use core-shell copolymers
such as hard/soft/hard copolymers, i.e. copolymers
which have in this order a hard core, a soft shell and
a hard shell. The hard parts may consist of polymers of
the shell of the preceding soft/hard copolymers and the
soft part may consist of polymers of the core of the
preceding soft/hard copolymers.
Examples that may be mentioned include those described
in EP 270 865, and those consisting of, in this order:
a core made of a copolymer of methyl methacrylate
and of ethyl acrylate,
a shell made of a copolymer of butyl acrylate and
of styrene,
a shell made of a copolymer of methyl methacrylate
and of ethyl acrylate.
Other types of core-shell copolymer also exist, such as
hard (core)/soft/semi-hard copolymers. Compared with
the preceding copolymers, the difference lies in the
“semi-hard” outer shell which consists of two shells:
one intermediate and the other outer. The intermediate
shell is a copolymer of methyl methacrylate, of styrene
and of at least one monomer chosen from alkyl
acrylates, butadiene and isoprene. The outer shell is a
PMMA homopolymer or copolymer.
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Examples that may be mentioned include those consisting
of, in this order:
a core made of a copolymer of methyl methacrylate
and of ethyl acrylate,
a shell made of a copolymer of butyl acrylate and
of styrene,
a shell made of a copolymer of methyl
methacrylate, of butyl acrylate and of styrene,
a shell made of a copolymer of methyl methacrylate
and of ethyl acrylate.
Compounds (A) are sold by the Applicant under the brand
names Biostrength®, Durastrength® and Clearstrength®.
The polymer (B) comprises an ethylenic monomer bearing
an epoxy function. Preferentially, it is a statistical
copolymer. The ethylenic monomer bearing an epoxy
function may be an unsaturated epoxide such as:
􀂃 aliphatic glycidyl esters and ethers such as
allyl glycidyl ether, vinyl glycidyl ether,
glycidyl maleate and itaconate, and glycidyl
(meth)acrylate, and
􀂃 alicyclic glycidyl esters and 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 endocis-bicyclo-
(2.2.1)-5-heptene-2,3-diglycidyl dicarboxylate.
Glycidyl methacrylate is preferred as ethylenic monomer
bearing an epoxy function.
Preferentially, the polymer (B) is an olefinic
copolymer comprising an ethylenic monomer bearing an
epoxy function, i.e. it is a copolymer of the
abovementioned ethylenic monomer and of at least one
α-olefin, which may comprise from 2 to 20 carbon atoms,
such as ethylene or propylene, preferentially ethylene.
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The olefinic copolymer may also comprise at least one
monomer different than the abovementioned α-olefins and
than the ethylenic monomer bearing an epoxy function.
Nonlimiting examples that may be mentioned include:
- a conjugated diene, for instance 1,4-hexadiene;
- carbon monoxide;
- an unsaturated carboxylic acid ester, for instance
alkyl (meth)acrylates;
- a saturated carboxylic acid vinyl ester, for
instance vinyl acetate or vinyl propionate.
According to one advantageous mode, the olefinic
copolymer comprises an alkyl (meth)acrylate. The alkyl
chain may contain up to 24 carbons. Those in which the
alkyl chain comprises from 1 to 12, advantageously from
1 to 6 or even from 1 to 4 carbon atoms are preferred.
Advantageously, the alkyl (meth)acrylates are n-butyl
acrylate, isobutyl acrylate, 2-ethylhexyl acrylate,
ethyl acrylate and methyl acrylate. Preferentially, the
alkyl (meth)acrylates are n-butyl acrylate, ethyl
acrylate and methyl acrylate. Most preferably, it is
methyl acrylate.
The polymers that are most preferred are ethylene-alkyl
acrylate-glycidyl methacrylate copolymers and ethyleneglycidyl
methacrylate copolymers.
The amount of monomer other than the ethylenic monomer
bearing an epoxy function and than the α-olefins, for
instance alkyl (meth)acrylate, may be within the range
from 0 (i.e. it does not comprise any) to 40% relative
to the total mass of said olefinic copolymer (B),
advantageously from 5% to 35% and preferably from 20%
to 30%.
The amount of ethylenic monomer bearing an epoxy
function in said olefinic copolymer (B) is, for
example, in the range from 0.1% to 20% relative to its
WO 2011/007092 - 16 - PCT/FR2010/051471
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total mass, advantageously from 2% to 15% and
preferably from 5% to 10%.
Copolymers (B) are sold by the Applicant under the
brand name Lotader®.
The composition of the invention may also comprise an
additional olefinic polymer (C), for instance ethylene
copolymers other than (B), i.e. not comprising any
monomer bearing an epoxy function. These may be chosen
from copolymers comprising ethylene and a vinyl ester
or copolymers comprising ethylene and an alkyl
(meth)acrylate, such as copolymers consisting of
ethylene and an alkyl (meth)acrylate. The alkyl chain
of the (meth)acrylate may contain up to 20 carbons.
Those in which the alkyl chain comprises from 1 to 12,
advantageously from 1 to 6 or even from 1 to 4 carbon
atoms are preferred. Advantageously, the alkyl
(meth)acrylates are n-butyl acrylate, isobutyl
acrylate, 2-ethylhexyl acrylate, ethyl acrylate and
methyl acrylate. Preferentially, the alkyl
(meth)acrylates are n-butyl acrylate, ethyl acrylate
and methyl acrylate. Preferentially, the amount of
alkyl (meth)acrylate ranges from 1% to 40% relative to
the total mass of said olefinic copolymer (C),
advantageously from 5% to 35% and preferably from 20%
to 30%.
Copolymers (C) are sold by the Applicant under the
brand name Lotryl®.
The amounts of the various monomers present in the
various polymers of the invention may be measured by
infrared spectroscopy, for example using the method
described in standard ISO8985.
The processes for manufacturing the copolymers (B) and
(C) are known. They may be manufactured via highWO
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pressure radical polymerization, for example in a
tubular or autoclave reactor.
According to a most preferred mode of the invention,
the polyhydroxyalkanoic acid (PHA) composition also
comprises:
(A) an elastomeric compound of core-shell type;
(B) a copolymer chosen from copolymers of
ethylene and of glycidyl methacrylate; and
(C) a copolymer of ethylene and of an alkyl
(meth)acrylate in which the alkyl chain
comprises from 1 to 20 carbon atoms.
The composition may also comprise additives for
improving certain properties of the PHA composition,
such as nucleating agents, plasticizers, dyes, UV
absorbers, stabilizers, antioxidants, fillers, flame
retardants, lubricants, antiblocking agents, moldrelease
agents or additives for facilitating the
process, commonly known as “processing aids”.
The composition according to the invention may be
manufactured by mixing the various constituents via
standard thermoplastic processing means, for instance
extrusion or blending. Internal mixers with paddles or
rotors, an external mixer, and co-rotating or counterrotating
single-screw or twin-screw extruders may be
used. Preferentially, the composition is prepared at a
temperature greater than or equal to the glass
transition temperature of the PHA, or even above. The
composition may be prepared, for example, at a
temperature within the range from 160°C to 260°C.
According to a preferred process of the invention, a
step of mixing of an impact modifier into the PHA is
performed, said impact modifier being a mixture
comprising (A), (B) and the optional (C).
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Since compound (A) is pulverulent, the process for
manufacturing the PHA composition is facilitated by
mixing (A) with (B) and the optional (C), the impact
modifier thus obtained then possibly being in the form
of granules that are easier to manipulate during the
PHA transformation process.
Another subject of the invention is a part or an
object, such as a wrapping, a film or a sheet,
manufactured from the composition according to the
invention.
To manufacture this part or this object, the known
molding techniques may be used, such as a press or an
injection-molded press, or alternatively the known
extrusion-blow molding techniques. The films or sheets
may also be manufactured via the techniques of castfilm
extrusion, blown-film extrusion or calendering.
The process for manufacturing this part may also
comprise an annealing step for crystallizing the PHA
and thus for improving its mechanical properties.
Examples of compositions will now be described in the
examples that follow; these examples are given as
illustrations and do not in any way limit the scope of
the claimed invention.
Examples
To prepare examples of the composition and the
structures according to the invention, the following
products were used:
(a1): core-shell compound based on butadiene,
methyl methacrylate, ethyl acrylate and butyl acrylate;
(a2): core-shell compound based on butyl acrylate
and methyl methacrylate;
(a3): core-shell compound comprising acryloWO
2011/007092 - 19 - PCT/FR2010/051471
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nitrile, butadiene and styrene;
(b): ethylene-methyl acrylate-glycidyl methacrylate
copolymer comprising, by weight, 25% acrylate
and 8% glycidyl methacrylate (Lotader® AX 8900) whose
melting point measured by DSC (ISO 11357-03) is 65°C;
(c): ethylene-butyl acrylate copolymer comprising,
by weight, 30% acrylate (Lotryl® 30BA02) whose melting
point measured by DSC (ISO 11357-03) is 78°C;
(d): polylactic acid 2002D sold by NatureWorks®.
Compositions (4) and (5) according to the invention and
comparative compositions (1), (2) and (3) comprise the
constituents (a), (b1), (b2), (b3), (c) and (d) in the
proportions given in Table 1.
Compositions (1) to (5) were prepared in a single step.
The mixing of the constituents in the ratio given in
Table 1 is performed by extrusion. The extrusion is
performed in an extruder of co-rotating twin-screw type
with a diameter of 16 mm and an L/D ratio of 25 (Haake
PTW16/25). The maximum mixture temperature is 240°C.
Since the constituents (b1), (b2) and (b3) are powders
and the extruder mentioned previously is equipped with
only one metering device, it is necessary to mill the
constituents (a) and (d) by cryomilling until a fine
powder is obtained, so as to obtain correct metering of
the constituents into the extruder for the preparation
of the mixtures (2) to (5).
The compositions are then injected at 200°C into a mold
regulated at 30°C by means of an injector press of
Krauss Maffei 60-210 B1 type.
The notched Charpy impact properties are measured
according to standard ISO 179:2000 after annealing the
samples for 1 hour at 110°C to crystallize the
polylactic acid. The higher the Charpy impact value,
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the better the impact strength. These properties were
measured at room temperature (23°C) and under cold
conditions (0°C and/or -40°C). The values obtained are
collated in Table 2.
The notched Charpy impact properties are also measured
at room temperature according to standard ISO 179:2000
without annealing. The values obtained are collated in
Table 3.
Table 1
Table 2
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Table 3 (without annealing)
The compositions prepared according to the invention
have improved impact properties when compared with
those obtained from the prior art.
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We Claim:
1. A polyhydroxyalkanoic acid (PHA) composition also
comprising:
(A) an elastomeric compound of core-shell type;
(B) and an olefinic copolymer comprising an
ethylenic monomer bearing an epoxy function.
2. The composition as claimed in claim 1,
characterized in that the ethylenic monomer
bearing an epoxy function is glycidyl
(meth)acrylate.
3. The composition as claimed in either of the
preceding claims, characterized in that (B) is a
copolymer of ethylene, of glycidyl methacrylate
and optionally of an alkyl (meth)acrylate in which
the alkyl chain comprises from 1 to 30 carbon
atoms.
4. The composition as claimed in one of the preceding
claims, also comprising an additional olefinic
polymer (C) other than the olefinic copolymers
comprising an ethylenic monomer bearing an epoxy
function.
5. The composition as claimed in the preceding claim,
in which the additional olefinic polymer (C) is a
copolymer of ethylene and of an alkyl
(meth)acrylate, a copolymer of ethylene and a
carboxylic acid vinyl ester, a copolymer of
ethylene and of a (meth)acrylic acid or an
ionomer, preferentially a copolymer of ethylene
and of an alkyl acrylate with an alkyl chain
ranging from 1 to 20, for instance methyl
acrylate, ethylene acrylate or n-butyl acrylate.
6. The composition as claimed in either of claims 4
and 5, in which the mass ratio (B)/(C) is within
the range from 90/10 to 10/90 and preferentially
from 75/25 to 40/60.
7. The composition as claimed in one of the preceding
claims, in which the mass ratio (A)/((B) +
optional (C)) is within the range from 90/10 to
10/90, for example 85/15 to 40/60, advantageously
from 80/20 to 50/50 and preferentially from 75/25
to 60/40.
8. The composition as claimed in one of the preceding
claims, in which the amount of ((A) + (B) +
optional (C)) is within the range from 1% to 30%
by mass of the total composition, advantageously
from 2% to 15% and preferentially from 3% to 9%.
9. The composition as claimed in one of the preceding
claims, in which the amount, in polymerized form,
of ethylenic monomer comprising an epoxy function
is within the range from 0.01% to 2%,
advantageously from 0.02% to 1% and preferentially
from 0.03% to 0.7% by mass of the total
composition.
10. The composition as claimed in one of the preceding
claims, in which the polymer of the core of the
core-shell compound (A) has a glass transition
temperature of less than 20°C and the polymer of
the shell has a glass transition temperature of
greater than 20°C.
11. The composition as claimed in one of the preceding
claims, in which the mass amount of core is within
the range from 60% to 95% of the total mass of the
core-shell compound.
12. The composition as claimed in one of the preceding
claims, in which the size of the core-shell
compounds is between 50 and 600 nm.
13. The composition as claimed in one of the preceding
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claims, in which the PHA is chosen from polylactic
acid (PLA) and polyglycolic acid (PGA).
14. A process for preparing the composition as claimed
in any one of the preceding claims, in which the
mixture of PHA, of (A), of (B), of the optional
(C) and optionally of additives such as a
nucleating agent is prepared by blending or
extrusion.
15. A process for preparing the composition as claimed
in one of claims 1 to 13, in which the following
are prepared:
- in a first step, a mixture of (A), (B) and
optional (C) to form an impact modifier, and
then
- in a second step, the mixture of the impact
modifier obtained from the first step with PHA.
16. A part or object, such as a wrapping, comprising a
composition as claimed in one of claims 1 to 13 or
a composition derived from the process as claimed
in claim 14 or 15.
17. A process for manufacturing a part or object as
claimed in claim 16, comprising a step of forming
the composition, for example by injection-molding,
pressing or calendering, said part or said object
optionally undergoing an annealing step.