USE OF HYDROGEN PEROXIDE IN SOLID FORM TO MODIFY THE RHEOLOGY OF A THERMOPLASTIC POLYMER WHEN MELTED

The present invention relates to the use of at least one hydrogen peroxide in solid form for modifying the rheology in the molten state of a thermoplastic polymer, in particular of a polyolefin, in particular of a polymer comprising at least one pattern derived from propylene, and more particularly polypropylene.

The invention also relates to a process for modifying the rheology in the molten state, in particular for reducing the viscosity in the molten state, of a thermoplastic polymer as defined above comprising at least one mixing step. of at least one hydrogen peroxide in solid form and of said polymer.

The invention also relates to the thermoplastic polymer capable of being obtained by the process as defined above.

The present invention also relates to a premix composition comprising at least one hydrogen peroxide in solid form, at least one thermoplastic polymer as defined above and optionally at least one organic peroxide intended to be used in the method according to the invention.

The controlled preparation of different grades of polyolefins, generally implemented following their polymerization, has the advantage of leading to polymers having molar masses, viscosities in the molten state, densities or even mass distributions. specific molars which are suitable for the type of technical application envisaged without adversely affecting the quality of the product obtained. Such a preparation is generally carried out by implementing conventional methods, for example an extrusion or injection molding process.

The control of the rheology in the molten state of the polyolefins, and in particular of their viscosity, can be carried out in particular, during the extrusion or injection molding step, by adding compounds capable of generating free radicals .

More precisely, the use of compounds capable of generating free radicals, such as organic peroxides, for example dialkyl peroxides, makes it possible to lead to a controlled degradation in the molten state, by cleavage of chains, in particular of viscosity, polyolefins, in particular polymers comprising at least one unit derived from propylene, such as polypropylene.

In fact, polypropylene is a polyolefin most often obtained by polymerization of propylene monomers in the presence of catalysts during the Ziegler Natta reaction (also called Ziegler Natta catalysis) followed by a step of controlled degradation in the presence of peroxides of Dialkyl added, in liquid or solid form, during an extrusion or injection molding step at temperatures above 180 ° C. Under these operating conditions, the dialkyl peroxides thus generate free radicals which will have the function of cutting the polypropylene chains by inducing reactions called beta-scission. As a result of such reactions, polypropylenes having lower molecular weights will be obtained.

In particular, the controlled degradation of polypropylene makes it possible to lead to products having in particular a lower molecular weight, a narrower molecular weight distribution, a higher melt flow index (Melt Flow Index). , referred to as MFI) as well as a lower melt viscosity. Such degradation can be obtained by implementing in particular a visbreaking process (called visbreaking process in English). This visbreaking process consists in carrying out, in a controlled manner, the cutting of chains in the molten state of a thermoplastic polymer. The polypropylene thus obtained can then be easily processed to make molded articles, films or fibers.

However, the organic peroxides regularly used during the stage of controlled degradation of polyolefins, in particular polyolefins capable of being obtained by Ziegler Natta catalysis, have the drawback of generating organic compounds.

undesirable volatiles in high contents even within the polyolefins obtained. In other words, the use of organic peroxides leads to polyolefins having rheological properties degraded in the molten state which have a residual content of undesirable volatile organic compounds which may be high and harmful for the envisaged application.

Furthermore, organic peroxides also have the drawback of being very unstable species when they are heated. In fact, in the event of an uncontrolled rise in temperature, certain organic peroxides can undergo a self-accelerated exothermic decomposition and risk igniting and / or exploding violently, which has the consequence of complicating their transport and / or their storage in polyolefin production units, in particular polypropylene. In other words, the use of organic peroxides requires special precautions to be taken when handling them.

In order to overcome these various drawbacks, it has already been proposed in the state of the art to use other compounds capable of generating free radicals such as hydrogen peroxide in aqueous solution in order to degrade one or more rheological properties. in the molten state of polyolefins.

In this regard, the scientific article published in the journal Polymer Dégradation and Stability in the edition 117 (2015) on pages 97-108 (G. Moad et al) describes a process making it possible to increase the melt index at l 'molten state (MFI), ie to reduce the viscosity in the molten state, of polypropylene in the presence of aqueous hydrogen peroxide. In particular, this document describes an extrusion process in which an aqueous solution of hydrogen peroxide is injected into the extruder in order to reduce the viscosity in the molten state of the polypropylene.

Likewise, patent application DE 1495285 describes the use of aqueous hydrogen peroxide in methanol to reduce the viscosity in the molten state of polyolefin, in particular of polypropylene.

However, the use of aqueous hydrogen peroxide also proves to have a certain number of drawbacks.

In fact, aqueous hydrogen peroxide does not mix well with polyolefins, which are hydrophobic compounds, in the absence of an additional additive such as a wetting agent or a surfactant. Thus, a heterogeneous product is generally obtained having a low melt flow index (MFI) which is liable to fluctuate significantly during extrusion. In other words, the use of aqueous hydrogen peroxide results in polyolefins having a generally low and unstable melt flow index.

To overcome this drawback, a large amount of aqueous hydrogen peroxide is necessary to achieve performance levels, in terms of controlled degradation of the rheological properties in the molten state of polyolefins, in particular in terms of their melt index. 'molten state (MFI), similar to those obtained with organic peroxides. In other words, a greater quantity of aqueous hydrogen peroxide is used to lead to the same results as those obtained with organic peroxides without, however, improving the reproducibility of the extrusion process using them.

In addition, the injection of aqueous hydrogen peroxide, in particular in large quantities, into the extruder can cause extrusion defects, for example the presence of moisture bubbles or the release of volatile bodies, which require setting up additional degassing and / or deaeration operations, which makes extrusion more tedious to implement.

Thus, one of the objectives of the present invention is to use one or more compounds capable of effectively modifying one or more rheological properties in the molten state of polymers, which do not exhibit the aforementioned drawbacks.

In other words, there is a real need to provide compounds, easy to handle and / or prepare, capable of leading to a homogeneous polymer having a content of volatile organic compounds lower than that obtained, under the same conditions, with organic peroxides in which one or more rheological properties in the molten state have been modified, in particular by reducing their viscosity in the molten state.

In view of the above, the object of the invention is more particularly to reduce the viscosity in the molten state, that is to say to increase the melt flow index (MFI), by polymers efficiently and stably.

A subject of the present invention is therefore in particular the use of at least one hydrogen peroxide in solid form for modifying the rheology in the molten state of a thermoplastic polymer, in particular of a polyolefin.

Hydrogen peroxide in solid form has the advantage of efficiently and stably modifying one or more rheological properties in the molten state of thermoplastic polymers, in particular by leading to a high melt flow index (MFI). , ie a low viscosity in the molten state, capable of remaining stable throughout the extrusion process.

In particular, hydrogen peroxide in solid form makes it possible to lead, under the same conditions, to a higher melt index (MFI), ie a lower melt viscosity, than peroxide. hydrogen in aqueous form.

More particularly, for the same level of melt flow index, hydrogen peroxide in solid form makes it possible to significantly reduce the effective amount of hydrogen peroxide capable of modifying the rheological properties in the solid state. melt of thermoplastic polymers relative to hydrogen peroxide in aqueous form.

Furthermore, the melt flow indices (MFI) obtained with hydrogen peroxide in solid form are stable, in particular more stable than those obtained with aqueous hydrogen peroxide.

In addition, hydrogen peroxide in solid form also has the advantage of leading to a homogeneous polymer comprising a content of volatile organic compounds (VOCs) which is significantly lower than that obtained, under the same conditions, with organic peroxides.

Thus, hydrogen peroxide in solid form makes it possible to reduce the residual content of undesirable volatile organic compounds (VOCs) in the polymer, one or more rheological properties of which in the molten state have been modified.

A subject of the invention is also a process for modifying the rheology in the molten state of a thermoplastic polymer comprising at least one step of mixing at least one hydrogen peroxide in solid form and said polymer.

The process according to the invention makes it possible in particular to modify one or more rheological properties in the molten state of a thermoplastic polymer, in particular by effectively reducing their viscosity in the molten state.

Furthermore, the process according to the invention also makes it possible to increase the melt flow index (MFI) of the thermoplastic polymer.

The method according to the invention also has the advantage of modifying in a reproducible manner one or more rheological properties in the molten state of a thermoplastic polymer.

In particular, the process results in a reproducible manner in thermoplastic polymers which in particular exhibit low melt viscosities and high melt indexes, more particularly compared to processes using peroxide. aqueous hydrogen.

Thus, the process according to the invention makes it possible to effectively control the rheology of thermoplastic polymers, in particular polyolefins, at the outlet of a polymerization reactor.

Another subject of the invention relates to a thermoplastic polymer capable of being obtained by the process as defined above.

The thermoplastic polymer capable of being obtained by the process as described above has the advantage of being homogeneous, of exhibiting a high and stable melt flow index (MFI) and of having a content of compounds. organic vo latils (VOCs) undesirable lower than that contained in the same polymer obtained under the same conditions with an organic peroxide.

Likewise, the present invention relates to a composition comprising at least one hydrogen peroxide in solid form and at least one organic peroxide.

The composition according to the invention is particularly advantageous for reducing the defects which may occur during the process described above while reducing the residual content of undesirable organic compounds in the polymer compared with the use of organic peroxide alone.

The invention also relates to a premix composition comprising:

- at least one thermoplastic polymer,

- at least one hydrogen peroxide in solid form, and

- optionally at least one organic peroxide.

The premix composition according to the invention is used to be used in the process according to the invention in order to modify the rheology in the molten state of a thermoplastic polymer obtained after polymerization and lead to a homogeneous polymer having notably a lower melt viscosity and a higher melt flow index.

In particular, the premix composition according to the invention is intended for use in an extruder for modifying the rheological properties of the thermoplastic polymer.

Other characteristics and advantages of the invention will emerge more clearly on reading the description and the examples which follow.

In what follows, and unless otherwise indicated, the limits of a domain of values ​​are included in this domain.

The expression "at least one" is equivalent to the expression "one or more".

use

As indicated above, the invention relates to the use of one or more hydrogen peroxides in solid form for modifying the rheology in the molten state of a thermoplastic polymer.

Preferably, the hydrogen peroxide (s) in solid form is or are used to modify one or more rheological properties in the molten state of a thermoplastic polymer.

In particular, the hydrogen peroxide (s) in solid form is or are used to carry out in a controlled manner the splitting of chains in the molten state of a thermoplastic polymer.

The rheological property (s) of the thermoplastic polymer thus modified is (or are) chosen in particular from the group consisting of the melt flow index (MFI), melt viscosity, molecular weight, molecular weight distribution and polydispersity index, preferably to decrease the melt viscosity of said thermoplastic polymer.

Thus the hydrogen peroxide (s) in solid form is or are used in particular to reduce the molecular mass and the molecular mass distribution of a thermoplastic polymer.

The hydrogen peroxide (s) in solid form is or are used in particular to reduce the polydispersity index of a thermoplastic polymer.

More preferably, the hydrogen peroxide (s) in solid form is or are used to reduce the viscosity in the molten state of a thermoplastic polymer.

In other words, the hydrogen peroxide (s) in solid form is or are used in particular to increase the melt flow index (MFI) of a thermoplastic polymer.

The melt flow index (MFI) of a thermoplastic polymer is measured according to the methods commonly used to characterize thermoplastic materials allowing to obtain information on the extrudability as well as the shaping possibilities of the material. such as those described in standard ASTM D 1238, standard NF T5 1 -01 6 or standard ISO 1 133.

The MFI values ​​referred to are determined according to the ISO 1133 standard at a temperature of 190 ° C. and 230 ° C. under a load of 2.16 kg (units expressed in g / 10 min).

Preferably, the hydrogen peroxide (s) in solid form is or are used to modify the molten rheology of a polyolefin.

The polyolefin is preferably chosen from the group consisting of polymers comprising in their structure at least one unit derived from propylene, that is to say having in their structure at least one unit derived from propylene.

In other words, the polyolefin is preferably chosen from the group consisting of polymers based on propylene.

Thus, preferably, the thermoplastic polymer is a polymer comprising at least one unit derived from propylene.

The polymer comprising at least one unit derived from propylene can be chosen from the group consisting of polypropylene, that is to say a homopolymer of propylene, or copolymers of propylene comprising in their structure at least 50% by mo les of units derived from propylene, that is to say that at least 50%> by mo les of the copolymer consists of polymerized propylene moieties.

The propylene copolymers also comprise in their structure one or more copolymerizable monomers, in particular one or more ethylenically unsaturated monomers chosen from the group consisting of ethylene, butylene, hexene, o ctene, vinyl esters. and (meth) acrylics.

Thus, preferably, the thermoplastic polymer is chosen from the group consisting of polypropylene and copolymers of

propylene comprising in their structure at least 50% by moles of units derived from propylene and at least one unit derived from an ethylenically unsaturated monomer other than propylene, preferably chosen from the group consisting of ethylene, butylene, hexene, octene, vinyl esters and (meth) acrylics.

Preferably, the propylene copolymers comprise in their structure from 50 to 90% by moles, more preferably from 60 to 80% by moles, of units derived from propylene, the remainder consisting of at least one unit derived from at least a copolymerizable monomer, in particular one or more ethylenically unsaturated monomers chosen from the group consisting of ethylene, butylene, hexene, octene, vinyl esters and (meth) acrylics.

The thermoplastic polymer is advantageously polypropylene, ie a propylene homopolymer, or a propylene copolymer comprising at least 50%> by moles of units derived from propylene and at least one unit derived from a comonomer chosen from the group consisting of ethylene, 1-butylene, 1-hexene and 1-octene.

More preferably, the polymer comprising at least one unit derived from propylene is polypropylene.

According to one embodiment, the invention relates to one or more hydrogen peroxides in solid form for reducing the viscosity in the molten state of a polyolefin.

According to one embodiment, the invention relates to one or more hydrogen peroxides in solid form for reducing the viscosity in the molten state of a polypropylene.

In accordance with the present invention, the hydrogen peroxide used to modify the rheology in the molten state of the thermoplastic polymer is a product which is solid at room temperature containing at least hydrogen peroxide.

For the purposes of the present invention, by ambient temperature is meant a temperature ranging from 10 to 30 ° C, in particular from 15 to 25 ° C.

Hydrogen peroxide is thus a solid product which is dry to the touch and can be in the form of a powder.

Advantageously, the solid hydrogen peroxide is in powder form.

Preferably, the solid hydrogen peroxide can be a solid adduct or a solid material in which aqueous hydrogen peroxide is adsorbed on a solid support.

For the purposes of the present invention, the term adduct denotes the product of an addition reaction between hydrogen peroxide and another molecular entity.

Preferably, the solid hydrogen peroxide is chosen from the group consisting of sodium percarbonate (2Na 2 C0 3 , 3H 2 0 2 ), urea-hydrogen peroxide (H 2 0 2 -CO (NH 2 ) 2 ), hydrogen peroxide adsorbed on a solid support and mixtures thereof.

In particular, the hydrogen peroxide powder can be obtained by precipitation of a hydrogen peroxide adduct, preferably sodium percarbonate or urea-hydrogen peroxide, or by mixing an aqueous solution of hydrogen peroxide. hydrogen and a solid support.

According to one embodiment, the solid hydrogen peroxide is an adduct.

According to this embodiment, the adduct can result from the addition reaction between:

- hydrogen peroxide (H 2 0 2 ) and sodium carbonate

(Na 2 C0 3 ) to form sodium percarbonate, or

- hydrogen peroxide (H 2 0 2 ) and urea to form carbamide peroxide (urea-hydrogen peroxide (H 2 0 2 - CO (NH 2 ) 2 )).

According to another embodiment, the solid hydrogen peroxide is a solid material obtained by mixing an aqueous solution of hydrogen peroxide and a solid support.

The solid support used is capable of adsorbing hydrogen peroxide in liquid form while remaining dry to the touch. Thus the solid material obtained is dry to the touch.

The solid support can be organic or inorganic.

By way of example, superabsorbent polymers, such as those obtained from acrylic acid sold under the name Aquakeep® and produced by the company SUMITOMOSEIKA CHEMICAL, can be used as an organic support.

Alternatively, the inorganic support can be obtained from different types of silica.

The silicas used are preferably amorphous and can be of precipitated origin or of pyrogenic origin.

The original precipitated silica is thus obtained by precipitation, in particular by reaction of a mineral acid with solutions of alkali metal silicates, preferably sodium silicate. In particular, a sulfuric acid solution and a sodium silicate solution are simultaneously added with stirring in water. The precipitation of the silica is carried out under alkaline conditions.

The properties of precipitated silica can be controlled and manipulated depending on the reaction conditions. Indeed, the duration and the type of agitation, the duration of the precipitation, the rate of addition of the reagents as well as their temperature and their concentration, as well as the pH of the reaction medium are all parameters likely to influence the values. properties of the precipitated silica thus obtained. The formation of a gel is in particular avoided by mixing the solutions described above at an elevated temperature (for example, a temperature ranging from 85 ° C. to 95 ° C.). Conversely, the fact of carrying out the precipitation at a low temperature (for example at a temperature ranging from 20 ° C to 30 ° C) can lead to the formation of a silica gel.

The white precipitate thus obtained is then filtered, washed and then dried.

The original precipitated silica is porous and therefore has the capacity to be able to absorb liquid. The original precipitated silica can be sold under the trade name Sipernat® 500 LS and Sipernat® 22LS by the company Evonik or under the name Syloid® 244FP by WR Grace.

Silica of fumed origin (also called fumed silica) can also be used as an inorganic support. Such a

silica has a very different morphology from the original precipitated silica.

Silica of pyrogenic origin (or fumed silica), such as those sold under the trade name Aerosil® by the company Evonik and CAB-O-SIL® by the company Cabot, is a product characterized by an amorphous structure and a range of primary particle sizes.

Such a silica is of pyrogenic origin due to its production in an oxyhydrogen flame. It consists of microdroplets (primary particles) of amorphous silica which merge to form three-dimensional chain-branched aggregates (secondary particles) which can then agglomerate into tertiary particles. The individual microdroplets are essentially non-porous.

Fumed silica is generally obtained by first carrying out a step of hydrolysis in a continuous flame of a substance such as silica tetrachloride (SiCU) in the presence of hydrogen and oxygen in the air. Thus the formation of silica can be described as being an oxyhydrogen reaction in the presence of water. In fact, the hydrolysis of silica tetrachloride with water is carried out in a continuous flame so as to produce the silica in a few fractions of a second.

As a result of this reaction, a mixture of hot gases and silica particles also containing hydrochloric acid is obtained in the form of an aerosol.

The aerosol is then cooled before carrying out a step of separating the gas phase and the solid phase. After separation, the solid phase still contains significant amounts of hydrochloric acid adsorbed on the surface of the silica particles.

A deacidification step is then implemented in order to remove the hydrochloric acid so as to obtain untreated hydrophilic fumed silica.

After this deacidification step, the fumed silica has a high density of silano ls (Si-OH) groups free at the surface, giving it an extremely hydrophilic character. So the

surface of fumed silica particles is easily wettable in the presence of water. Without being bound by any theory, since the primary particles of fumed silica are non-porous, when liquid addition is made, such liquid is not adsorbed into the silica particles (as is case for precipitated silica which is porous) but remains on the surface three-dimensional aggregates or branched secondary particles in a chain, which leads to the formation of a large number of agglomerates. Even though the agglomerates are formed from individual aggregates, it can be seen that the surface morphology of the aggregates and agglomerates is sufficiently complex to retain large amounts of liquid if the latter is able to wet the surface.

The surface of hydrophilic fumed silica can be modified by a variety of post-treatments. In this way, the fumed silica can be chemically modified at the surface by a chemical reaction by transforming the silano I (Si-OH) groups into hydrophobic groups. In other words, the density of the free silano ls groups is reduced.

The amount of liquid hydrogen peroxide adsorbed on the silica while ultimately forming a powder depends in particular on the type of silica. Generally, the weight ratio between silica and aqueous hydrogen peroxide varies from 5/95 to 70/30, preferably from 5/95 to 50/50 and more preferably from 8/92 to 30/70.

The aqueous solution of hydrogen peroxide adsorbed on the solid may comprise a hydrogen peroxide content ranging from 5 to 70% by weight, in particular from 35 to 70% by weight, relative to the total weight of the solution. .

Preferably, the hydrogen peroxide in solid form is sodium percarbonate (2Na 2 CC "3, 3H 2 0 2 ).

According to one embodiment, the invention relates to the use of a hydrogen peroxide powder for modifying one or more rheological properties as defined above of a thermoplastic polymer as defined above.

According to one embodiment, the invention relates to the use of sodium percarbonate for reducing the viscosity in the molten state of a polyolefin, in particular of a polymer comprising at least one unit derived from propylene, in particular from polypropylene.

Advantageously, the hydrogen peroxide in solid form can be used as a mixture with one or more organic peroxides as defined below in order to modify the rheology in the molten state of a thermoplastic polymer as defined below. after.

More advantageously, sodium percarbonate is used in combination with 2,5 -dimethyl-2,5 (di (tert-butylperoxy) hexane to modify one or more rheological properties as defined above, in particular to reduce the viscosity in the molten state, of a thermoplastic polymer as defined above.

In this case, the use of hydrogen peroxide in solid form also makes it possible to significantly reduce the amount of organic peroxide (s) to be used to effectively modify one or more rheological properties in the molten state. of a thermoplastic polymer.

The fact of reducing the quantity of organic peroxide (s) is in particular advantageous given the unstable nature of this type of compound and the precautionary measures to be taken to store and use it.

In other words, the use of such a mixture makes it possible in particular to result in a thermoplastic polymer having one or more rheological properties in the molten state similar to that (s) obtained with peroxide. organic alone while having in its structure a lower amount of volatile organic compounds.

Preferably, the solid hydrogen peroxide as defined above is used without a water-soluble catalyst, more preferably without a catalyst.

Preferably, the solid hydrogen peroxide as defined above is used at a temperature ranging from 50 to 350 ° C, and more particularly ranging from 100 to 300 ° C.

Indeed, if the mixing is carried out at a temperature above 350 ° C., there is a risk of oxidizing and coloring the final product, which is not desirable in the context of the present invention.

Preferably, the use according to the invention is not intended to oxidize the thermoplastic polymer as defined above.

Thus, the present invention relates to the use of at least one hydrogen peroxide in solid form for modifying the rheology in the molten state of a thermoplastic polymer, without increasing its rate of oxidation. Preferably, the thermoplastic polymer obtained has an oxidation rate of less than 6 mg of oxygen / g of thermoplastic polymer, preferably less than 5 mg / g, more preferably less than 4 mg / g, more preferably less than 3 mg. / g, more preferably less than 2 mg / g, and more preferably less than 1 mg / g of thermoplastic polymer.

Process

As indicated above, the process according to the invention for modifying the rheology in the molten state of the thermoplastic polymer as defined above comprises at least one stage of mixing between at least one hydrogen peroxide in solid form such as defined above and said polymer.

Preferably, the process according to the invention is a process for modifying one or more rheological properties in the molten state of the thermoplastic polymer as defined above.

In particular, the process according to the invention is a process for controlled chain cutting in the molten state of the thermoplastic polymer as defined above.

Preferably, the rheological properties thus modified (s) of the thermoplastic polymer is (or are) as described (s) previously.

More preferably, the process according to the invention is a process for reducing the viscosity in the molten state of a polymer.

thermoplastic, in particular of a polyolefin as defined above.

As a variant, the process according to the invention is a process for increasing the fluidity, in particular the melt index (MFI), of a thermoplastic polymer as defined above.

According to one embodiment, the process according to the invention is a process for reducing the distribution of molecular masses of a thermoplastic polymer as defined above.

According to another embodiment, the process according to the invention is a process for reducing the polydispersity index of a thermoplastic polymer as defined above.

In accordance with the present invention, the process is in particular a visbreaking process.

The thermoplastic polymer can be a polyolefin, in particular polypropylene.

In particular, the process according to the invention results in a polymer in which the hydrogen peroxide in solid form represents from 0.001 to 15% by weight, preferably 0.01 to 10%>, and more preferably from 0.02. at 5% by weight, even more preferably from 0.05 to 2% by weight relative to the weight of the thermoplastic polymer.

Preferably, the active concentration of pure hydrogen peroxide varies from 0.001 to 4.5% by weight, preferably from 0.005 to 0.6% by weight, relative to the weight of the thermoplastic polymer.

The mixing step of the process according to the invention can also comprise at least one organic peroxide.

Preferably, the organic peroxide has a half-life temperature at one minute greater than 150 ° C, more preferably greater than 160 ° C, and even more preferably greater than 170 ° C.

Preferably, the organic peroxide is not a peracid. Indeed, peracids can cause odor problems and undesirable acidity in the product obtained by the process according to the invention.

Preferably, the organic peroxide is chosen from the group consisting of cyclic ketone peroxides, dialkyl peroxides, monoperoxycarbonates, poly (t-butyl) peroxycarbonates, di-peroxyketals, peresters and their mixtures, more preferably still. the organic peroxide is chosen from the group consisting of cyclic ketone peroxides, dialkyl peroxides and mixtures thereof.

Preferably, the cyclic ketone peroxide is selected from the group consisting of 3, 6,9-triethyl-3, 6,9-trimethyl-1, 4,7-triperoxonane and 3, 3, 5, 7.7 -pentamethyl- 1,2,4-trioxepane.

Preferably, the monoperoxycarbonate is selected from the group consisting of tert-butyl isopropyl monoperoxycarbonate, 00-tert-amyl-0- (2-ethylhexyl) -monoperoxycarbonate and OO-tert-buty 1- O- (2 -ethylhexyl) ) -monoperoxycarbonate.

Preferably, the di-peroxyketal is selected from the group consisting of 1,1 -di (tert-butylperoxy) -3, 3, 5 -trimethylcyclohexane, 1,1 -di (tert-butylperoxy) cyclohexane, 4, N-butyl 4-di (tert-amylperoxy) valerate, ethyl 3, 3 -di (tert-butylperoxy) butyrate, 2,2-di (tert-amylperoxy) propane, 3, 6,6, 9,9-pentamethyl-3 -ethoxycarbonylmethyl- 1,2,4,5 -tetra-oxacyclononane, 4,4-bis (tert-butylperoxy) den-butyl valerate and 3, 3 -di (tert-amylperoxy) butyrate ethyl.

Preferably, the perester is chosen from the group consisting of tert-amyl peroxy3, 5, 5 trimethylhexanoate, tert-butyl amyl peroxy3, 5, 5 trimethylhexanoate, tert-butyl peroxyacetate, 2,2-di (tertamylperoxy) -butane and tert-butyl peroxybenzoate,

Preferably, the organic peroxide is a dialkyl peroxide.

Dialkyl peroxide comes in the following classic crude forms:

ROOR or R-OO-R'-OO-R

The R or R ′ segments can consist of aliphatic components but also optionally of branches carrying aromatic or cyclic functions.

Preferably, the compounds belonging to the family of dialkyl peroxides are chosen from 2,5-dimethyl-2,5-di (tert-butylperoxy) -hexyne-3 (Luperox ® 130), ditert-butyl peroxide (Luperox ® DI), ditert-amyl peroxide (Luperox ® DTA), 2,5-dimethyl-2,5 (di (tert-butylperoxy) hexane (Luperox ® 101), tert-butyl cumyl peroxide, di (tert -butylperoxy-isopropyl) -benzene, di-cumyl peroxide and mixtures thereof. More preferably, dialkyl peroxide corresponds to 2,5-dimethyl-2,5 (di (tert-butylperoxy) hexane sold under the trade name Luperox ® 101.

In particular, the organic peroxide used in the process according to the invention represents from 0.001 to 15% by weight of the polymer, preferably represents from 0.01 to 10%>, more preferably from 0.02 to 5% by weight, and even more preferably from 0.05 to 2%> by weight of the polymer.

Said organic peroxide may or may not be adsorbed on the solid support of hydrogen peroxide. In a particular embodiment, the organic peroxide is not adsorbed on the solid support of the hydrogen peroxide.

The mixing step can also comprise one or more functional additives intended to provide the polymer to which the hydrogen peroxide is added particular properties / characteristics.

Thus, as regards the additive, it can be chosen from the group consisting of antioxidants; UV protection agents; processing agents, the function of which is to improve the final appearance during its implementation, such as fatty amides, stearic acid and its salts, ethylene bis-stearamide or fluoropolymers; anti-fog agents; anti-blocking agents such as silica or talc; fillers such as calcium carbonate and nanofillers such as, for example, clays; coupling agents such as silanes; crosslinking agents such as peroxides other than those mentioned above; antistatic agents; nucleating agents; pigments; the colors; plasticizers; fluidizers and flame retardant additives such as aluminum or magnesium hydroxides; lubricants such as waxes, in particular waxes of oxidized or not oxidized polyethylene, esters of fatty acids, salts of fatty acids, ethylene bis stearamide, etc.

In particular, said additive can be an antioxidant. This antioxidant prevents possible oxidation which is not desirable in the context of the present invention.

Preferably, the process according to the invention is carried out without a soluble catalyst in water, more preferably it is carried out without a catalyst.

In particular, the mixing step of the process according to the invention is carried out for a time sufficient to allow the hydrogen peroxide in solid form to generate free radicals capable of breaking the chains of the thermoplastic polymer.

Preferably, the mixing step of the process according to the invention is carried out for a period ranging from 0, 1 and 30 minutes, preferably for a period ranging from 0.5 to 5 minutes.

More preferably, the step of mixing the polymer and the hydrogen peroxide in solid form takes place at a temperature ranging from 50 to 350 ° C., and more particularly ranging from 100 to 300 ° C. Preferably, the step mixing is a step of extrusion or injection by molding the thermoplastic polymer in the presence of at least one hydrogen peroxide in solid form and of said thermoplastic polymer.

More preferably, the step of extrusion or injection by molding of the thermoplastic polymer takes place at a temperature ranging from 50 to 350 ° C, and more particularly ranging from 100 to 300 ° C, in the presence of at least one. hydrogen peroxide in solid form and said thermoplastic polymer.

Even more preferably, the mixing step is an extrusion step.

According to one embodiment, the process according to the invention is a process for modifying the rheology in the molten state of a polyolefin, in particular of a polymer comprising at least one unit derived from propylene, in particular polypropylene, comprising at least one step of extrusion or injection by molding of the thermoplastic polymer in the presence of at least one hydrogen peroxide in solid form and of said thermoplastic polymer.

According to one embodiment, the process according to the invention is a process for modifying the rheology in the molten state of a polyolefin, in particular polypropylene, comprising at least one step of extrusion or injection by molding of said polyolefin in the presence:

- at least one hydrogen peroxide in solid form chosen from the group consisting of sodium percarbonate (2Na 2 C0 3 , 3H 2 0 2 ), urea-hydrogen peroxide (H 2 0 2 -CO (NH 2 ) 2 ), hydrogen peroxide adsorbed on a solid support and their mixtures,

- at least one organic peroxide chosen from the group consisting of dialkyl peroxides, and

- of said polyolefin.

More preferably, the hydrogen peroxide in solid form is sodium percarbonate (2Na 2 C0 3 , 3H 2 0 2 ).

More preferably, the dialkyl peroxide is 2,5-dimethyl-2,5 (di (tert-butylperoxy) hexane.

In accordance with this embodiment, the process according to the invention is a process for reducing the viscosity in the molten state of a polyolefin as defined above.

According to this embodiment, the extrusion or injection step preferably takes place at a temperature ranging from 50 to 350 ° C, and more particularly ranging from 100 to 300 ° C.

Preferably, the process according to the invention does not include an oxidation step.

In order to avoid this oxidation step, during the extrusion step, the residence time is preferably less than 5 minutes, preferably less than 3 minutes, and even more preferably less than 1 minute.

Preferably, the extrusion step is carried out under nitrogen.

Polymer

As indicated above, the invention relates to a thermoplastic polymer that can be obtained by the process according to the invention.

The thermoplastic polymer according to the invention has the advantage of having a residual content of volatile organic compounds that is lower than the thermoplastic polymers obtained under the same conditions with an organic peroxide.

The thermoplastic polymer has the advantage of having a more homogeneous composition than the thermoplastic polymers obtained with an aqueous hydrogen peroxide.

Preferably, the thermoplastic polymer is a polyolefin, in particular a polymer comprising at least one unit derived from propylene.

More preferably, the thermoplastic polymer is polypropylene.

Preferably, the thermoplastic polymer exhibits an oxidation rate of less than 6 mg of oxygen / g of thermoplastic polymer, preferably less than 5 mg / g, still more preferably less than 4 mg / g, still more preferably less than 3 mg / g. g, more preferably less than 2 mg / g, and more preferably less than 1 mg / g of thermoplastic polymer.

The oxidation rate can for example be measured by elemental analysis, for example using an Elementar Vario Micro Cube type analyzer.

The thermoplastic polymer obtainable by the process according to the invention is advantageously used to manufacture molded articles, films or fibers.

Composition

As indicated above, the invention relates to a composition comprising at least one hydrogen peroxide in solid form and at least one organic peroxide as defined above.

The composition according to the invention is particularly advantageous for reducing the defects which may arise during the process described above while reducing the content of residual undesirable organic compounds in the polymer compared with the use of organic peroxide alone.

In particular, the invention relates to a composition comprising at least one hydrogen peroxide in solid form and at least one organic peroxide as defined above, said organic peroxide not being a peracid.

In particular, the composition according to the invention makes it possible to reduce the bubbles and the release of volatile compounds which may occur during the extrusion of the thermoplastic polymer. In other words, the composition makes it possible to reduce the number of degassing and deaeration operations capable of being implemented during the process according to the invention.

Preferably, the hydrogen peroxide in solid form is chosen from the group consisting of alkali metal or alkaline earth metal percarbonates, in particular alkali metal percarbonates.

More preferably, the hydrogen peroxide in solid form is sodium percarbonate (2Na 2 CC ″ 3, 3H 2 O 2 ).

Preferably, the organic peroxide is chosen from the group consisting of cyclic ketone peroxides, dialkyl peroxides, monoperoxycarbonates, poly (t-butyl) peroxycarbonates, di-peroxyketals, peresters and their mixtures, more preferably still. the organic peroxide is chosen from the group consisting of cyclic ketone peroxides, dialkyl peroxides and mixtures thereof, again preferably said organic peroxide is a dialkyl peroxide.

Preferably, the compounds belonging to the family of dialkyl peroxides are chosen from 2,5 -dimethyl-2,5 -di (tert-butylperoxy) -hexyne-3 (Luperox ® 1 30), ditert-butyl peroxide ( Luperox ® DI), ditert-amyl peroxide (Luperox ® DTA), 2,5 -dimethyl-2,5 (di (tert-butylperoxy) hexane (Luperox ® 101), tert-butyl cumyl peroxide, di ( tert-butylperoxy-isopropyl) -benzene, di-cumyl peroxide and mixtures thereof.

More preferably, the dialkyl peroxide corresponds to 2,5 -dimethyl-2,5 (di (tert-butylperoxy) hexane sold under the trade name Luperox® 1 01.

According to one embodiment, the composition comprises:

- at least one hydrogen peroxide in solid form chosen from the group consisting of alkali metal or alkaline earth metal percarbonates, in particular alkali metal percarbonates,

- at least one organic peroxide chosen from dialkyl peroxides.

Premix composition

As indicated above, the invention also relates to a premix composition comprising at least one thermoplastic polymer, at least one hydrogen peroxide in solid form and optionally at least one organic peroxide as defined above.

Preferably, said premix does not comprise a water soluble catalyst, more preferably does not contain a catalyst.

In fact, the use of a catalyst risks leading to too rapid a reaction and to a colored end product, which is not desirable in the context of the present invention.

For the purposes of the present invention, the term “premix” is understood to mean the composition intended to be used by the process according to the invention.

In other words, the premix composition comprises a thermoplastic polymer whose rheological properties in the molten state have not yet been modified due to the presence of hydrogen peroxide in solid form.

In particular, the premix composition comprises a thermoplastic polymer having a lower melt index than the thermoplastic polymer obtained by the process according to the invention, that is to say after having been mixed with hydrogen peroxide in solid form.

The premix composition is in particular intended to be used in an extruder to produce a polymer according to the invention.

Preferably, the premix composition comprises at least one organic peroxide as defined above.

Preferably, the premix composition comprises:

- at least one thermoplastic polymer chosen from the group consisting of polyolefins,

- at least one hydrogen peroxide in solid form chosen from the group consisting of sodium percarbonate (2Na 2 C03, 3H 2 0 2 ), urea-hydrogen peroxide (H 2 02-CO (NH 2 ) 2), hydrogen peroxide adsorbed on a solid support and mixtures thereof,

- at least one organic peroxide chosen from dialkyl peroxides.

Preferably, the premix composition comprises:

- at least one thermoplastic polymer chosen from the group consisting of polymers comprising at least one unit derived from propylene, in particular polypropylene,

- le percarbonate de sodium (2Na2C03 , 3H202),

- at least one organic peroxide chosen from dialkyl peroxides.

The following examples serve to illustrate the invention without, however, being limiting in nature.

EXAMPLES

Example of preparation of polymer compositions

In the examples below, various additives were tested in order to modify the rheology in the molten state, in particular by reducing the viscosity in the molten state, of polypropylene (PP).

The polymer compositions, described below, were thus produced by mixing polypropylene (PP) with an additive chosen from:

- an organic peroxide (95% pure 2,5 -dimethyl-2,5 (di (tert-butylperoxy) hexane sold under the trade name Luperox ® 101 by the company ARKEMA),

- hydrogen peroxide in liquid form (aqueous solution of hydrogen peroxide at 35% by weight sold under the name Albone ® 35 by the company ARKEMA),

- sodium percarbonate (sold under the trade name ALDRICH and having a hydrogen peroxide equivalent of 28.5%> by weight),

- a mixture of these additives.

The various compositions are prepared in a powder mixer (Caccia CP0010G) at a temperature not exceeding 45 ° C. at a mixing speed of 2300 ± 200 rpm for a period of 5 to 10 minutes.

The additive concentrations are given in ppm for the organic peroxide or as a percentage by mass of pure hydrogen peroxide, or as a percentage of sodium percarbonate (with the equivalent of pure hydrogen peroxide as a percentage by weight) relative to the polypropylene.

A process for visbreaking the compositions, described below, is then implemented.

After mixing, the powder obtained is then extruded in the form of granules on a counter-rotating twin-screw extruder of the Brabender KDSE type at a material temperature in the die of 230 ° C. and a flow rate of 7 kg / h.

Fluidity Index Test (MFI)

The melt flow index (MFI) is measured according to ISO standard 1,133 at a temperature of 190 ° C. under a load of 2,160 grams. The die has a length of 8 mm and an internal diameter of 2.095 mm.

The temperature for carrying out the test at 190 ° C. was supplemented in the results tables by a measurement at a temperature of 230 ° C. (the other test conditions remaining identical).

The higher the melt flow index (MFI), the lower the melt viscosity.

Example 1

The melt index (MFI) was determined for the following compositions at a temperature of 190 ° C and 230 ° C in accordance with ISO standard 1,133.

The results are grouped together in the table below:

Table 1: Comparison of hot melt indices with hydrogen peroxide or organic peroxide.

During the extrusion of compositions 3 and 4, bubbles and gas evolved phenomena were observed as well as an irregularity of extrudability (feed into the unstable hopper).

Results - discussion

It is found that a significant amount of aqueous hydrogen peroxide is necessary to achieve the same level of performance, measured by the MFI value of the polypropylene, as in the presence of the organic peroxide.

Furthermore, it is observed that the melt index fluctuates significantly with aqueous hydrogen peroxide. This phenomenon is due to the irregularity of the supply of polypropylene in the presence of aqueous hydrogen peroxide.

Example 2

The melt index (MFI) was determined for the following compositions at a temperature of 190 ° C and 230 ° C in accordance with ISO standard 1,133.

The results are grouped together in the table below:

Table 2: Comparison of hot melt indices with organic peroxide alone or in the presence of sodium percarbonate.

By comparing the melt indexes (MFI) of compositions 10 and 3, a greater efficiency of sodium percarbonate is observed compared with aqueous hydrogen peroxide.

Indeed, composition 10 exhibits a significantly higher melt flow index (MFI) and more stable than composition 3 at a temperature of 190 ° C and 230 ° C. Therefore, Composition 10 also has a lower melt viscosity than Composition 3 at these temperatures.

In addition, composition 10 exhibits a melt flow index (MFI) identical to composition 7 at a temperature of 190 ° C and above a temperature of 230 ° C.

It also results from Table 2 that the MFI measurements have the same reproducibility whether in the presence of organic peroxide alone or in the presence of a mixture of organic peroxide and sodium percarbonate.

Composition 9 has a melt index similar to composition 7 using half the amount of organic peroxide which has been replaced with an amount of solid hydrogen peroxide in the form of sodium percarbonate much lower than the amount required in the mixture. 'example 10.

Thus the emp law of sodium percarbonate makes it possible to reduce the quantity of organic peroxide to be used to obtain a thermoplastic polymer having a similar viscosity.

Furthermore, the mixture of organic peroxide and sodium percarbonate has the advantage of reducing the bubbles in the extruded polypropylene, which makes it possible to minimize the number of degassing operations during the extrusion.

Example 3

The amount of volatile organic compounds (in μgC / g) in the following compositions was determined after the visbreaking process.

The content of the volatile organic compounds was measured under the analytical conditions used for the GC / MS and GC / FID analyzes and correspond to those detailed in standard VDA 277.

The chromatographic conditions used are as follows:

- Co lonne : ZB-WAX plus, 30m x 0.25mm, 0.25 μιη

- Temperature programming: 50 ° C (3 minutes) then 12 ° C / min up to a temperature of 200 ° C (19.5min)

- Carrier gas flow rate (helium): l ml / min

- Split : 20ml/min

2.6 grams of each sample is placed in a headspace type sample vial which is then crimped. The samples are then heated for a period of 5 hours at a temperature of 120 ° C.

The skies of the samples are taken and then analyzed by GC / MS or GC / FID. Analyzes are performed in duplicate for each sample.

The results are grouped together in the table below:

Compositions Volatiles

( gC/g)

PP only 1 10

PP+507 ppm 320

Luperox® 101

PP+ 1013 ppm

Luperox® 101 475

PP + 507 ppm

Luperox® 101 +

0.2% percarbonate

sodium 290

(+ 0.057% peroxide

hydrogen)

PP + 507 ppm

Luperox® 101 +

0.4% percarbonate 280

sodium

(+0. 1 14% peroxide

hydrogen)

PP + 1 .2%

percarbonate de

10 sodium (+0.34% 135

peroxide

hydrogen)

Table 3: Measurements of veil materials according to VDA 277

Composition 9 has a melt index similar to composition 7 using half the organic peroxide and also has the advantage of generating a significantly lower level of veil materials.

The results show that the composition according to the invention makes it possible both to increase the melt index at temperatures of 190 ° C. and 230 ° C. while significantly reducing the content of residual volatile organic compounds in the polypropylene.

For an identical melt index level, the composition of the invention also makes it possible to considerably reduce the quantity of useful hydrogen peroxide compared with a composition comprising only aqueous hydrogen peroxide.

CLAIMS

1. Use of at least one hydrogen peroxide in solid form for modifying the molten rheology of a thermoplastic polymer.

2. Use according to claim 1 for modifying one or more rheological properties in the molten state of a thermoplastic polymer.

3. Use according to claim 2, characterized in that the rheologic property (s) is (or are) chosen from the group consisting of the melt flow index. (MFI), melt viscosity, molecular weight, molecular weight distribution and polydispersity index, preferably to decrease the melt viscosity of said thermoplastic polymer.

4. Use according to any one of claims 1 to 3, characterized in that the thermoplastic polymer is a polymer comprising at least one unit derived from propylene.

5. Use according to any one of the preceding claims, characterized in that the thermoplastic polymer is chosen from the group consisting of polypropylene and propylene copolymers comprising in their structure at least 50% by mo the units derived from propylene and at least one unit derived from an ethylenically unsaturated monomer other than propylene, preferably chosen from the group consisting of ethylene, butylene, hexene, octene, vinyl esters and (meth) acrylics.

6. Use according to any one of the preceding claims, characterized in that the thermoplastic polymer is polypropylene.

7. Use according to any one of the preceding claims, characterized in that the hydrogen peroxide in solid form is chosen from the group consisting of sodium percarbonate (2Na 2 C03, 3H 2 0 2 ), urea- hydrogen peroxide (H 2 0 2 -CO (NH 2 ) 2 ), hydrogen peroxide adsorbed on a solid support, and mixtures thereof.

8. Use according to any one of the preceding claims, characterized in that the hydrogen peroxide in solid form is sodium percarbonate (2Na 2 CC "3, 3H 2 0 2 ).

9. Use according to any one of the preceding claims, characterized in that the solid hydrogen peroxide is used without a water-soluble catalyst, more preferably without a catalyst.

10. Use according to any one of the preceding claims, characterized in that the solid hydrogen peroxide is used at a temperature ranging from 50 to 350 ° C, and more particularly ranging from 100 to 300 ° C.

1 1. Process for modifying the rheology in the molten state of a thermoplastic polymer as defined in any one of claims 1 or 4 to 6 comprising at least one step of mixing said polymer and hydrogen peroxide in solid form. as defined in any one of claims 1, 7 or 8.

12. The method of claim 1 1 visbreaking the thermoplastic polymer.

13. The method of claim 1 1 or 12, characterized in that the hydrogen peroxide in solid form represents from 0.001 to

15% by weight, preferably represents from 0.01 to 10%> by weight, more preferably from 0.02 to 5% by weight, and even more preferably from 0.05 to 2% by weight of the thermoplastic polymer.

14. Method according to any one of claims 1 1 to 13, characterized in that the mixing step further comprises at least one organic peroxide, preferably selected from the group consisting of cyclic ketone peroxides, peroxides of dialkyl, monoperoxycarbonates, polyethers poly (t-butyl) peroxycarbonates, di-peroxyketals, peresters and their mixtures, more preferably the organic peroxide is chosen from the group consisting of cyclic ketone peroxides, dialkyl peroxides and their mixtures, preferably is dialkyl peroxide.

15. The method of claim 14, characterized in that the dialkyl peroxide is selected from the group consisting of 2,5 -dimethyl-2,5 -di (tert-butylperoxy) -hexyne-3, ditert-butyl peroxide , ditert-amyl peroxide, 2,5 -dimethyl-2,5 (di (tert-butylperoxy) hexane, tert-butyl cumyl peroxide, di (tert-butylperoxy-isopropyl) -benzene, di-cumyl peroxide and their mixtures.

16. The method of claim 14 or 15, characterized in that the organic peroxide represents from 0.001 to 15% by weight, preferably from 0.01 to 10%, more preferably from 0.02 to 5%> by weight, and even more preferably from 0.05 to 2%> by weight of the thermoplastic polymer.

17. Method according to any one of claims 1 1 to 16, characterized in that the mixing step is an extrusion step.

1 8. A thermoplastic polymer obtainable by the process as defined in any one of claims 1 1 to 17.

19. Composition comprising at least one hydrogen peroxide in solid form as defined according to any one of claims 1, 7 or 8 and at least one organic peroxide as defined according to any one of claims 14 to 16.

20. Premix composition comprising:

- at least one thermoplastic polymer as defined according to any one of claims 1 or 4 to 6,

- at least one hydrogen peroxide in solid form as defined in claim 1, 7 or 8, and

- optionally at least one organic peroxide as defined according to any one of claims 14 to 16.