EP1175449A1

EP1175449A1 - Crosslinking of vinyl acetate polymers or copolymers, preparation of dynamically crosslinked compositions and hybrid organic-inorganic compositions preserving a thermoplastic character

Info

Publication number: EP1175449A1
Application number: EP00910952A
Authority: EP
Inventors: Alain Michel; Agnès VERBOIS; Michel Bert; Christophe Angelloz; Patrice Blanc; Xavier Pages; Daniel Milesi; Philippe Cassagnau
Original assignee: Multibase SA
Current assignee: Multibase SA
Priority date: 1999-03-15
Filing date: 2000-03-15
Publication date: 2002-01-30
Also published as: CA2364574A1; JP2002539296A; FR2791062A1; WO2000055213A1; FR2791062B1

Abstract

The invention concerns a method for crosslinking a thermoplastic polymer or copolymer with vinyl acetate units, which consists in reacting, during the implementing processes, at a temperature ranging between 80 °C and 280 °C: the polymer or copolymer with vinyl acetate units, and a polyfunctional alcoholate, in the presence of a catalyst. The crosslinking of polymers or copolymers with vinyl acetate units in the presence of a second thermoplastic polymer or copolymer enables to prepare TPV materials. The method for obtaining a hybrid organic-inorganic material consists in: dispersing and grafting an inorganic network on a thermoplastic polymer or copolymer with vinyl acetate units inducing hydrolysis-condensation of the polyfunctional alcoholate pertaining to the network based on polymer or copolymer with vinyl acetate units and of the excess polyfunctional alcoholate. Said dispersion and said grafting can be carried out in the presence of a second thermoplastic polymer or copolymer for producing hybrid organic-inorganic TPV materials.

Description

CROSS-LINKING OF VINYL ACETATE POLYMERS OR CQPQLYMERS. ELABORATION OF DYNAMICALLY CROSSLINKED COMPOSITIONS AND ORGANIC-INORGANIC HYBRID COMPOSITIONS CONSERVING A THERMOPLASTIOUS CHARACTER

The present invention relates to a process for crosslinking a thermoplastic polymer or copolymer with vinyl acetate units by an alcoholate in the presence of a catalyst.

The invention also relates to a process for the preparation of dynamically crosslinked compositions and retaining, after crosslinking, their thermoplastic character for their subsequent applications, these compositions initially comprising a thermoplastic phase which will not be crosslinked and another phase which will be crosslinked, this phase being constituted by a thermoplastic polymer or copolymer with vinyl acetate units, which can be an elastomer, and an alcoholate as crosslinking agent and a catalyst.

The invention also relates to a process for dispersing and grafting an inorganic network onto a thermoplastic polymer or copolymer with vinyl acetate units, by coupling the crosslinking reaction with the alcoholate in the presence of a catalyst and a reaction of hydrolysis of this alcoholate after crosslinking. The invention finally relates to a process for the preparation of organic-inorganic hybrid compositions retaining, after crosslinking and hydrolysis-condensation, a thermoplastic character for their subsequent applications, these compositions initially comprising a thermoplastic phase which will not be crosslinked and another phase constituted by a polymer or copolymer with vinyl acetate units, which can be an elastomer, and an alcoholate as crosslinking agent and a catalyst, leading to the crosslinking of the polymer or copolymer with vinyl acetate units followed by hydrolysis-condensation of the alcoholate.

The development of dynamically crosslinked compositions retaining, after crosslinking, a thermoplastic character (TPV) for their subsequent applications is experiencing considerable development. A TPV is composed of a crosslinked phase and dispersed in a continuous thermoplastic phase. In the case where the crosslinked phase is an elastomer, the TPV is known by the name TPE-V. A TPE-V presents with on the one hand a thermoplastic character in the molten state allowing its subsequent shaping and on the other hand has the characteristic properties of crosslinked elastomers.

To crosslink the elastomeric phase, the dynamic crosslinking process is generally used. This process consists in crosslinking an elastomeric phase in the presence of a thermoplastic under special mixing conditions (temperature and shear), thus generating a morphology of the final material, such that fine particles of crosslinked elastomer are dispersed in a thermoplastic matrix.

State of the art

US-4, 116,914 discloses a TPV in which the thermoplastic phase is a semi-crystalline polyolefin of PP type and the elastomer phase is an EVA.

US-4,348,502 describes PA-elastomer mixtures. EVN with a mass content of vinyl acetate of between 40 and 70%, is used to constitute the elastomer phase of these mixtures. The weight compositions are 15 to 75% of PA for 85 to 25% of EVA respectively.

A disadvantage of the prior techniques is that the crosslinking system used to crosslink the elastomer phase of PP / elastomer or PN / elastomer mixtures often involves organic peroxides: this type of crosslinking involves radical reactions, which, in the case of PP, induce secondary reactions of chain cuts causing its degradation and alteration of its properties, and, in the case of PE or PN, crosslinking reactions making TPV thermoset.

In addition, the development of POS can be done by discontinuous and continuous processes. However, there are no examples of the development of EVN / PP type POS during an extrusion operation.

Statement of the invention

According to the invention, it is possible to crosslink the polymers or copolymers with vinyl acetate units by a transesterification reaction, between an ester function of the polymer or copolymer with vinyl acetate units and an alcoholate function, in the presence of a catalyst. This reaction is not radical. This crosslinking chemistry of polymers or copolymers with vinyl acetate units can be applied to the preparation of dynamically crosslinked compositions which, after their crosslinking, a thermoplastic character for their subsequent applications (TPV) by discontinuous and / or continuous processing operations. By coupling the crosslinking reaction of the polymer or copolymer with vinyl acetate units by an alcoholate in the presence of a catalyst and the hydrolysis-condensation reaction of this alcoholate, it is possible to obtain organic-inorganic hybrid compositions. These organic-inorganic hybrid compositions produced in the presence of a second thermoplastic phase lead to organic-inorganic hybrid TPVs.

According to a first aspect of the invention, a process for crosslinking a thermoplastic polymer or copolymer with vinyl acetate units, consists in reacting, during the processing operations, at a temperature between 80 ° C. and

280 ° C the polymer or copolymer with vinyl acetate units, and a multifunctional alcoholate of type M (OR) _x , in the presence of a catalyst.

The transesterification reaction used is an exchange reaction between the ester functions of the thermoplastic polymer or copolymer with vinyl acetate units, and the alcoholate functions of the crosslinking agent in the presence of a catalyst, according to reaction scheme 1.

All these reactions are carried out in the molten phase, in the total absence of solvents.

For crosslinking, the crosslinking temperature is preferably from 110 ° C to 230 ° C. Preferably, the polymer or copolymer with vinyl acetate units is chosen from the group of ethylene-vinyl acetate copolymers.

Among these copolymers, use is preferably made of copolymers of ethylene and vinyl acetate having between 28% vinyl acetate and 60% vinyl acetate which are elastomers. However, copolymers of ethylene and vinyl acetate having a vinyl acetate content of less than 28% can also be crosslinked according to the method of the invention.

Other polymers or copolymers with vinyl acetate units can also crosslink, such as polyvinyl acetate, the copolymer of vinyl chloride and vinyl acetate, the copolymer of styrene and vinyl acetate and the copolymer of l ethylene, vinyl acetate and carbon monoxide. The multifunctional alcoholate of type M (OR) _x can be a trifunctional alcoholate of general formula R'-M (OR) ₃ , or bifunctional of general formula R'R "-M (OR) ₂ , or very advantageously a tetrafunctional alcoholate , of general formula M (OR) ₄ , M possibly being very preferably Si. In this particular case, a tetraalkylorthosilicate (or tetralkoxysilane) of general formula Si (OR) _{4 is used} , in which R is an aromatic or aliphatic group of 1 with 20 carbon atoms, R preferably being a methyl, ethyl, propyl or butyl group, R can also be an aromatic group, M can also be Ti [titanate, Ti (OR) ₄ ], Al, [aluminate, Al (OR ) ₃ ] or Zr [zirconate, Zn (OR) ₄ ], or others The initial concentration of multifunctional alcoholate, expressed by the molar ratio, number of moles of vinyl acetate functions of the polymer or copolymer with acetate units of vinyl on the number of moles of fon ctions alcoholate of the multifunctional alcoholate (AV / OR), is substantially between 0.1 and 30, preferably between 0.3 and 10. The catalyst can be an organometallic compound. We choose a tin derivative, preferably an alkyl tin oxide, especially for its performance. Bu ₂ SnO (dibutyl tin oxide: DBTO) gave particularly interesting results.

The catalyst concentration, expressed in parts by mass per hundred parts by mass of polymer or copolymer with vinyl acetate units, is substantially between 0.1 and 3 parts by mass (pcr), preferably between 0.5 and 1.5 parts by mass (pcr).

^ CH ₂ - CH ₂ - C Si (OR) ₄

_ _{V Δ} tetraalkoxysilane

O 11 v VO _C H ₂ - CH ₂ -CH ₂ -CH ~ CH ₂ -CH ₂ ^ + CH ₃ -C— OR

Where i

RO-Si-OR crosslinked EVN

O

CH ₂ - CH ₂ - CH ₂ - CH— CH ₂ - CH ₂

Reaction diagram 1

The process also has real flexibility of use, making it possible to separate the shaping step and the crosslinking step. A mixture of the reagent composition can be produced at a temperature of 50 to 100 ° C corresponding to the melting temperature of the polymer or copolymer with vinyl acetate units without causing crosslinking. This composition is subsequently taken up and implemented, for example, by rotational molding, then by increasing the temperature, crosslinking is caused.

According to a second aspect of the invention, a method for preparing a TPV consists in carrying out, during the implementation operations, at a temperature between 80 ° C. and 280 ° C., dynamic crosslinking of a reactive mixture comprising a first polymer or copolymer with vinyl acetate units, a multifunctional alcoholate, a catalyst, and in the presence of a second thermoplastic polymer or copolymer.

The crosslinking reaction is carried out in the presence of another thermoplastic polymer in the molten state, and not crosslinkable by the multifunctional alcoholate under the conditions mentioned above. This second thermoplastic polymer or copolymer can be chosen from the group of polyolefins, or olefin copolymers, or polyamides, or thermoplastic polyurethanes (TPU). Preferably, polyolefins are used from which polypropylene (PP) and polyethylene (PE) can be particularly chosen.

According to a third aspect of the invention, a process for producing a hybrid organic-inorganic composition, by dispersing and grafting an inorganic network of the M _y O _{z type} onto the thermoplastic polymer or copolymer with vinyl acetate units comprises the steps consisting in: a) cross-linking the thermoplastic polymer or copolymer with vinyl acetate units, by reacting, during the processing operations, at a temperature between 80 ° C. and 280 ° C., the polymer or copolymer with vinyl acetate units, and a multifunctional alcoholate, in the presence of a catalyst, to obtain an organic network; b) cause the hydrolysis-condensation of the multifunctional alcoholate belonging to the organic network obtained in step a) and of the excess multifunctional alcoholate, in the presence of water, to obtain the inorganic network.

The inorganic network of M _y O _{z type} is preferably a network of silica SiO ₂ .

The synthesis of a particularly advantageous organic-inorganic hybrid material of the polymer-silica type is carried out in two main stages, according to reaction scheme 2. First, the polymer is crosslinked with an alkoxysilane in the presence of the catalyst. Then, the crosslinked material is hydrolyzed, for example in the presence of acidulated water. In short, we speak of hydrolysis-condensation. The silanol groups resulting from the hydrolysis of the alkoxysilanes will condense to form silica in situ. The cohesion of the material is then ensured by silica-polymer interactions and probably by non-hydrolysed Si-O- (polymer) bonds. The SiO ₂ silica network is grafted onto the crosslinking bridges by the hydrolysis-condensation of the OR bonds. The inorganic network is grafted onto the organic network. A nanometric dispersion of the filler is then obtained in an already crosslinked thermoplastic polymer. -Si - OR + H ₂ O Si OH + ROH

- Si - OH + HO -Si- ^" - Si - O - Si - + H ₂ O

Silica network

Reaction scheme 2

The limiting step being the diffusion of water in the polymer network, to accelerate the hydrolysis reaction it is possible to incorporate, in situ, hydrated molecules so as to eliminate the problems of diffusion. However, the crosslinking of the material implies that the molecule in question does not release its water too early, so that there is first crosslinking of the polymer or copolymer with vinyl acetate units by the alkoxysilanes in the presence of the catalyst, then hydrolysis-condensation of alkoxysilanes, leading to a network of silica grafted on the organic network. This entity must, on the other hand, be chemically inert with respect to the reactive groups present, that is to say not to generate side reactions. In order to accelerate the reaction, a hydrating filler can be added, for example trisodium citrate dihydrate, or alumina trihydrate, or others still. According to a fourth aspect of the invention, a method for preparing a material

Organic-inorganic hybrid TPV comprises the steps consisting in: a) dynamically cross-linking a first thermoplastic polymer or copolymer with vinyl acetate units, by reacting, during the processing operations, at a temperature between 80 ° C. and 280 ° C: the first polymer or copolymer with vinyl acetate units, and a multifunctional alcoholate, in the presence of a catalyst, to obtain an organic network; and b) causing the hydrolysis-condensation of the multi-functional alcoholate belonging to the organic network obtained in step a) and of the excess multi-functional alcoholate, in the presence of water, to obtain the inorganic network; in the presence of a second thermoplastic polymer or copolymer. Any dynamic crosslinking is carried out during a batch processing operation, for example in an internal mixer, and / or is carried out during a continuous processing operation such as, for example, in an extruder.

According to the invention, it is possible to control the final physical properties of the various materials by introducing a compatibilizing agent and / or a plasticizing agent for the polymer or copolymer with vinyl acetate units, for example diesters of phthalic acids, for example phthalate of dioctyl, and trimellitic and diesters of aliphatic diacids, for example of the methyl adipate, octyl adipate type.

Conventionally, it is also possible to add various additives to thermoplastic polymers, such as stabilizers, anti-UV, colored pigments (carbon black, titanium dioxide, etc.), fibers, agents facilitating the setting. work, etc.

Other advantages according to the invention will appear on reading the detailed description of the invention, with reference to the graphics, in which:

- Figure 1 shows the crosslinking kinetics of EVA 28% and EVA 40% for different temperatures; - Figure 2 shows the crosslinking kinetics for two EVA formulations

28%, at 170 ° C;

- Figure 3 shows the evolution of the crosslinking of 40% EVA in the absence and presence of PP;

- Figure 4 shows the influence of the addition of a plasticizer and its moment of introduction;

- Figure 5 shows the evolution of the elastic modulus as a function of temperature for an EV A-silica hybrid material; and

- Figure 6 shows the kinetics of formation of a hybrid EVA-silica material in the absence and in the presence of added hydrating filler, with 2 different concentrations. Detailed description of the invention

For all the formulations given, the initial concentration of tetrafunctional alcoholate of tetrapropylorthosilicate or tetrapropoxysilane (TPOS) type is given by the molar ratio AV / OR (number of moles of vinyl acetate functions of the copolymer with vinyl acetate EVA units over the number of moles of propoxysilane functions of TPOS). In addition, the initial concentration of DBTO catalyst is expressed in parts by mass (pcr) per 100 parts by mass of EVA.

EVA 28% is, for example, marketed by Elf-Atochem under the trade name Evatane® 28-03. Its melting point is around 75 ° C and its degree of crystallinity is around 20%. EVA 40% is, for example, marketed by Elf-Atochem under the trade name Evatane® 40-55, or by DuPont under the trade name Elvax® 40W. Its melting temperature is around 50 ° C and its degree of crystallinity is less than 10%. The TPOS is, for example, marketed by the company Lancaster or the company Roth-Sochiel. DBTO is, for example, marketed by the company Sigma-Aldrich or the company Goldschmidt.

The methods according to the invention are not limited by the details of the embodiments and of the examples chosen to illustrate it. Modifications can be made without departing from the scope of the invention. The latter therefore includes all the means constituting technical equivalents of the means described as well as their combination.

The products produced by means of the thermoplastic polymers or copolymers with vinyl acetate units produced according to the methods of the invention, as well as their subsequent applications in fields such as the automobile, cables, flame retardants, in particular for building , household appliances, also belong to the invention.

Example 1:

The chemical kinetics of crosslinking of an EVN by TPOS in the presence of DBTO was studied by a gas chromatography technique, following the release of propyl acetate (in accordance with reaction scheme 1). The amount of propyl acetate released at a given time is determined. The total number of moles of propyl acetate formed over time is calculated, which makes it possible to know the progress of the crosslinking reaction at all times. The AP / AV conversion rate is noted, the total number of moles of propyl acetate formed reduced to the initial number of moles of AV functions. Figure 1 gives the crosslinking kinetics of a 28% EVA formulation and a 40% EVA formulation at 180 ° C, 200 ° C and 220 ° C. The following formulations were produced and studied:

- EVA28% + TPOS (AV / OR = 10) + DBTO (0.5 pcr)

- EVA40% + TPOS (AV / OR = 10) + DBTO (0.5 pcr)

The results confirm, as might be expected, that we can play on the temperature factor to increase the kinetics of the crosslinking reaction of an EVA by TPOS in the presence of DBTO and to make it compatible with time. of implementation processes such as extrusion.

Figure 2 gives the crosslinking kinetics of two 28% EVA formulations at 170 ° C.

The following formulations were produced and studied: - EVA 28% + TPOS (AV / OR = 5) + DBTO (0.5 pcr)

- EVA 28% + TPOS (AV / OR = 10) + DBTO (0.5 pcr)

The results confirm, as might be expected, that one can play on the concentration of TPOS crosslinking agent to increase the kinetics of the reaction of crosslinking of an EVA by TPOS in the presence of DBTO. Temperature, TPOS crosslinking agent and catalyst concentrations

DBTO are all factors that can be varied to obtain the kinetics of crosslinking of a given EVA, by the TPOS in the presence of DBTO, as quickly as possible. These results therefore make it possible to grasp all of the experimental conditions (temperature, concentrations of TPOS crosslinking agent and of DBTO catalyst) making it possible to adjust the crosslinking kinetics for each EVA with the residence times, compatible with processes. batch (for example Banbury type internal mixer, or rotational molding) and continuous processes (for example extrusion).

The characterization of the thermomechanical behavior of polymers or copolymers with crosslinked vinyl acetate units in accordance with the method according to the invention, using a Dynamic Mechanical Spectrometer (RMS 800), has shown that these materials no longer have a zone of flow past their melting point. Example 2:

The dynamic crosslinking of a reactive EVA / PP / mixture (TPOS + DBTO) has been carried out and studied. To these reaction mixtures was used a homopolymer PP, sold by the company Appryl under the reference PP Appryl ^® 3120 MΝ1 (PP grade 12).

Using the Haake plastograph equipped with an internal Rheomix 600 type mixer, the crosslinking of 40% EVA (grade 55) was studied by TPOS in the presence of DBTO, in the absence and in the presence of PP. For each of the plastograph mixtures

Haake, the operating conditions are 180 ° C for the temperature setpoint and 50 rpm for the speed of rotation of the blades.

Figure 3 shows the evolution of the torque and the material temperature over time for the following mixtures:

- EVA 40% (grade 55) + TPOS (AV / OR = 10) + DBTO (0.5 pcr)

- 60% EVA 40% + TPOS (AV / OR = 10) + DBTO (0.5 pcr) + 40% PP (grade 12)

During the crosslinking of 1ΕVA in the absence of PP, a first peak is observed corresponding to the introduction of the EVA / (TPOS + DBTO) mixture and to its fusion. After the fusion, after a certain time, the crosslinking causes an increase in the torque, which goes through a maximum, before decreasing very quickly. This sudden drop corresponds to the passage to the pulverulent state of the crosslinked EVA, which has become mechanically fragile, and therefore transformed into the powder state under the effect of shearing.

During the dynamic crosslinking of a reactive EVA / PP / mixture (TPOS + DBTO), a first peak is observed corresponding to the introduction and melting of the EVA / PP / mixture (TPOS + DBTO). The crosslinking then causes an increase in the torque, which goes through a break in slope (start of a plateau) before reaching a maximum. However, unlike the crosslinked EVA reference mixture without PP, for the reactive EVA / PP / mixture (TPOS + DBTO), the torque does not drop suddenly after reaching this maximum, on the contrary it decreases to tend more or less quickly towards a constant value. In the presence of PP, a pulverulent state of the material is not obtained at the outlet of the internal mixer.

In order to assess the thermoplastic nature of the final mixture recovered at the outlet of the Haake plastograph, the formability was studied with a plate press (200 ° C, under pressure, for a few minutes). Getting back into shape material is satisfactory. The dynamically crosslinked EVN / PP final material has a thermoplastic character in the molten state for its subsequent shaping.

Measurements of the level of soluble EVA and of the swelling rate of the mixture (in toluene, at 40 ° C., for several days) have shown that, for a reactive EVA / PP / mixture (TPOS + DBTO), the soluble fraction of EVA decreases continuously and gradually as a function of the mixing-kneading time until the moment when the torque reaches its maximum value. After the maximum, the rate of soluble EVA is around 20%. Likewise, the volume swelling rate of the mixture decreases between the start of the torque increase and the maximum value reached by the latter. These results show that the rate of swelling of the mixture varies with the rate of progress of the dynamic crosslinking reaction of EVA in the presence of PP and also suggest that the crosslinking of the EVA phase begins with the increase in torque to end when the latter reaches its maximum.

The dynamic crosslinking of the reactive EVA / PP / mixture (TPOS + DBTO) leads to a final material which has a thermoplastic character in the molten state with an insoluble EVA level of the order of 80%. It is therefore possible to use the crosslinking chemistry of an EVA by transesterification reaction with TPOS catalyzed by DBTO to develop TPV materials of the EVA / PP type by batch processes.

Example 3:

An EVA PP / (TPOS + DBTO) reactive mixture was extruded (LEISTRITZ LSM 30-34 twin-screw extruder) with the following compositions:

- 70% EVA 40% (grade 55) + TPOS (AV / OR = 10, 5 and 2.5) + DBTO (1 pcr) + 30% PP (grade 12) Operating conditions for mixing:

- 220 ° C in temperature;

- 160 and 220 rpm for the screw rotation speed.

It has been found that crosslinking is done well in the extruder. The crosslinking kinetics of EVA by a transesterification reaction with TPOS, catalyzed by DBTO, is compatible with the residence times in an extruder, of the order of a few minutes. The crosslinking chemistry of EVA by the crosslinking system (TPOS + DBTO) can be used to develop EVA / PP type PV materials by continuous processes, such as extrusion.

Example 4:

A TPV contains many additives in addition to the two polymers constituting the thermoplastic and elastomeric phases. In particular, these TPV materials contain a non-negligible amount of plasticizer. The plasticizer was taken and studied during the dynamic crosslinking of a reactive EVA / PP / mixture (TPOS + DBTO). The plasticizer used is DOP (DiOctyl Phthalate).

Using the Haake plastograph, three mixtures were produced which differ only in the instant of introduction of the DOP during the dynamic crosslinking of the reactive EVA / PP / mixture (TPOS + DBTO).

- mixture 1: addition of DOP after the maximum reached by the couple - mixture 2: addition of DOP to the maximum reached by the couple

- mixture 3: addition of DOP to the start of the plateau reached by the couple 50% by mass of DOP was added relative to the amount of VA. The composition of the mixture studied is as follows:

- 60% EVA 40% (grade 55) + TPOS (AV / OR = 10) + DBTO (0.5 pcr) + 40% PP (grade 12)

Figure 4 shows the evolution of the torque and the material temperature as a function of time for the three plasticized mixtures and for a reference mixture of equivalent composition without plasticizer.

When the plasticizer DOP is introduced, respectively after, during and before the maximum of the torque, a sudden and very significant drop in the torque is observed (lubricating effect of the DOP relative to the overall mixture). Then the torque gradually increases to reach a constant value, representative of the overall viscosity of the final EVA PP mixture dynamically crosslinked and plasticized. The increase in torque after its sudden fall during the introduction of DOP is due to the diffusion of the plasticizer in the more or less crosslinked EVA. The final constant value is reached more quickly by the plasticized mixture in comparison with the mixture produced without plasticizer. A higher final constant torque value is obtained for mixture 3 than for mixture 1. At the outlet of the Haake plastograph, a dynamically crosslinked and plasticized EVA / PP mixture is obtained, a homogeneous material which has a thermoplastic character and a greater flexibility in comparison with the mixture of equivalent composition but not plasticized.

These results show that it is possible to introduce a plasticizer during the development of a TPV (EVA / PP type) and to regulate the final properties of this TPV not only by varying the composition of the mixture but also by function of the crosslinking density reached at the time of the introduction of the plasticizer. In other words, the introduction of the plasticizer can be regulated both in a discontinuous and continuous process, by separating the crosslinking step and the introduction of the plasticizer, the two operations being sequential.

Example 5: In order to prepare an organic-inorganic hybrid material based on EVA-silica, the following composition was crosslinked under press (at about 200 bars), at 150 ° C., for 45 min:

EVA 28% + TPOS (AV / OR = 0.5) + DBTO.

After 45 minutes, the crosslinking is almost complete because the swelling rate no longer decreases.

The hydrolysis was then carried out at 80 ° C. in an acidic aqueous medium (1 M HCl, pH = 2), by bringing a sample into contact with water, over a period of 6 days.

For crosslinked materials, the swelling rate makes it possible to characterize the crosslinking density very precisely. Qualitatively, when the swelling rate is low, the crosslinking density of the material is important. The volume swelling rate is given by the relation: Gv = 1 + (G _p - 1) x (pι / p ₂ ) with G _p : swelling rate by weight (weight of the swollen reticulate / weight of the dried reticulate) pi : density of solvent p ₂ : density of dry polymer When hydrolysis is complete, each sample is placed in toluene (toluene is a 28% EVA solvent). The samples are swollen for 24 hours at 80 ° C. To have the weight of the swollen sample, follow the weight loss and extrapolate at time t = 0. The density of the EVA is 0.95 and that of the toluene is 0.895. The calculation of the volume swelling rate is therefore as follows:

Gv = 1 + [(swollen sample mass / dried sample mass - 1) x (0.95 / 0.895)] The results of the evolution of the swelling rate as a function of the duration of hydrolysis are as follows:

Table 1

After hydrolysis, the swelling rate remains of the same order of magnitude as after crosslinking: the hybrid material EV A-silica remains crosslinked.

In order to study the influence of crosslinking on the mechanical properties of crosslinked materials prepared before and after hydrolysis, tensile tests were carried out.

This study was carried out with an INSTRON dynamometer allowing the measurement of the force supported by a material subjected to a deformation, at constant traction speed.

The tests were carried out in accordance with standard T 51-034. The plotting of the stress = f (deformation) curves makes it possible to determine the following characteristics:

- E = σ / ε: modulus of elasticity (Young's modulus);

- σnipture: breaking stress; - ε _pture : strain at break (expressed as a percentage of the initial length of the test piece: nominal strain).

Table 2

By way of comparison for the EVA: E = 31 ± 1 MPa; σ _r = 28 ± 1 MPa; and ε _r - 810 ± 30%.

It appears that the modulus of elasticity (E) measured after hydrolysis is dependent on the time of prior cooking treatment. In fact, an increase in the modulus is observed with the cooking time, which is not the case before the hydrolysis. In addition, the cooking time prior to hydrolysis regulates the crosslinking density of the EVA and influences the elastic modulus of the organic-inorganic hybrid material. In particular, the modulus of elasticity increases considerably to become greater than that of 1ΕVA. This gives the material obtained a reinforcing effect and good resistance to creep. Regarding the breaking stress, it increases significantly compared to the material after baking, but remains lower than that of EVA. After hydrolysis, the organic-inorganic hybrid material retains good elongation properties at break.

The dynamic thermomechanical properties of a hybrid EVA-silica material were evaluated using a Dynamic Mechanical Spectrometer (RMS 800). According to Figure 5, the evolution of G '(elastic modulus) as a function of the temperature shows that there is no flow beyond the melting temperature of the EVA, and up to 200 ° C. These materials can therefore be used in thermal environments above 100 ° C. Example 6:

To shorten the hydrolysis time, a hydrating charge was added. Trisodium citrate dihydrate (Na ₃ C ₆ H ₅ 0 ₇ , 2H ₂ 0) generates water quickly and quantitatively from 160 ° C. Under these conditions, it is possible to separate the crosslinking step (temperature range 80 ° C - 150 ° C) from the hydrolysis step, by varying the temperature.

The TPOS hydrolysis step leads to the formation of propanol, which can be determined by gas chromatography, which makes it possible to follow the hydrolysis reaction. FIG. 6, giving the number of moles of propanol relative to the number of moles of propoxysilane function introduced as a function of time at 160 ° C., shows the effectiveness of the trisodium citrate dihydrate. In a ^soul 20 minutes, the rate of hydrolysis reached 40% for a moisturizing load with a concentration 23.7 phr.

Under these conditions, the hydrolysis time goes from a few hours, or even several days, to the ten minute scale. The swelling rates of the organic-inorganic hybrid material remain of the same order of magnitude as those of the crosslinked material before hydrolysis.

Example 7:

Different reaction mixtures were extruded which included the following components:

- polymer of the crosslinkable phase: copolymer of ethylene and vinyl acetate (ELVAX® 40W from DUPONT): EVA 40% (grade 55)

- polymer of the non-crosslinkable phase: polypropylene homopolymer (APPRYL® 3120 MN1 of APPRYL): PP (grade 12) - cross-linking agent multi-functional alcoholate: tetrapropylorthosilicate, TPOS

(DYNASIL® P from ROTH-SOCHIEL)

- catalyst: dibutyl tin oxide, DBTO (TEGOKAT® 248 from GOLDSCHMIDT)

These different reactive mixtures (numbered tests 7-1, 7-2, 7-3) were developed in a twin-screw extruder (CLEXTRAL BC 21) in co-rotary configuration

The length of the screws was 36 D (D = 25 mm) For each of the tests, the components of each reactive mixture [the two polymers, the crosslinking agent, the catalyst and, optionally, a plasticizing oil such as dioctyl phthalate (DOP)], are introduced at the same time into the volumetric metering device in the feeding zone.

After two passages in the extruder, according to an adequate temperature profile along the sheath, a suitable speed of rotation of the screws and an appropriate flow rate, a final mixture was obtained which is thermoplastic (subsequent shaping of the final mixture by extrusion and injection-molding) and a crosslinked EVA phase whose crosslinking rate is expressed by the percentage of insoluble EVA.

All the characteristics of the reactive mixtures used, the extrusion conditions and the characteristics of the thermoplastic mixtures resulting from the dynamic crosslinking are brought together in Table 3 below.

Table 3

TESTS

Characteristics 7-1 7-2 7-3

Composition of the reactive mixtures:

- crosslinkable phase EVA concentration 40% grade 55 60% 60% 60%

- non-crosslinkable phase concentration of PP grade 12 40% 40% 40%

- alcoholate crosslinking agent TPOS: AV / OR 10

- catalyst

DBTO compared to the EVA phase 1 pcr 1 pcr 1 pcr

- plasticizing oil

DOP compared to the EVA phase 50%

EXTRUSION

- average temperature profile 220 ° C 200 ° C 200 ° C

- screw rotation speed: first pass 160 rpm 160 rpm 160 rpm 160 rpm second pass 320 rpm 160 rpm 160 rpm

- extrusion rate first pass 6.5 kg / h 5 kg / h 5 kg / h second pass 2.5 kg / h 3 kg / h 4 kg / h

Final mixture after second pass:

- thermoplastic yes yes YES

- crosslinking rate of the EVA phase, expressed in% of insoluble matter 40% to 50% 70% to 80% 70% to 80%

Thus, it is confirmed that each mixture is well crosslinked and retains its thermoplastic character after crosslinking for its subsequent shaping such as extrusion or injection molding. Example 8:

A reaction mixture which had the following components was extruded:

- polymer of the crosslinkable phase: copolymer of ethylene and vinyl acetate, EVA 40% (grade 55): 60% (ELVAX® 40W from DUPONT)

- polymer of the non-crosslinkable phase: polypropylene homopolymer, PP (grade 12): 40%

(APPRYL® 3120 MN1 from APPRYL)

- multifunctional alcoholate crosslinking agent: tetrapropylorth osilicate, TPOS

(DYNASIL® P from ROTH-SOCHTEL)

AV / OR: 5

- catalyst: dibutyl tin oxide, DBTO (TEGOKAT® 248 from GOLDSCHMIDT) compared to the EVA phase: 1 pcr

- plasticizer: dioctyl phthalate (DOP) compared to the EVA phase: 50%

This reactive mixture was produced in a twin-screw extruder (MARIS TM 40 MW), in a co-rotary configuration, operating under degassing. The length of the screws was 44 D with D = 40 mm.

The components of the reactive mixture comprising the two polymers and the catalyst were introduced into the volumetric metering device in the feed zone while the TPOS crosslinking agent was injected by means of a pump. As for the plasticizer (DOP), it was introduced (injection using a second pump) into a zone of the extruder where the crosslinking reaction of the EVA phase was well advanced.

The temperature profile along the barrel was of the order of 220 ° C., while the speed of rotation of the screw was of the order of 160 RPM and the flow rate of the mixture at the outlet of the extruder was of the order of 20 kg / h.

A single passage of the reactive mixture through the extruder was carried out. The material obtained was well crosslinked. The rate of crosslinking of the EVA phase was such that the percentage of insoluble VA was about 80%.

The material obtained after crosslinking had a thermoplastic character for its subsequent applications.

Claims

1. Method for crosslinking a thermoplastic polymer or copolymer with vinyl acetate units, in which the reaction is carried out, during processing operations, at a temperature between 80 ° C and 280 ° C:

- the polymer or copolymer with vinyl acetate units, and

- a multifunctional alcoholate, in the presence of a catalyst.

2. Method for preparing a dynamically crosslinked composition and retaining, after crosslinking, its thermoplastic character (TPV), in which a crosslinking is carried out, during the processing operations, at a temperature between 80 ° C. and 280 ° C. dynamics of a reactive mixture comprising:

- a first thermoplastic polymer or copolymer with vinyl acetate units,

- a multifunctional alcoholate,

- a catalyst, and

- in the presence of a second thermoplastic polymer or copolymer.

3. A method for dispersing and grafting an inorganic network onto a thermoplastic polymer or copolymer with vinyl acetate units comprising the steps consisting in: a) crosslinking the thermoplastic polymer or copolymer with vinyl acetate units, by reacting, during the setting operations in use, at a temperature between 80 ° C and 280 ° C:

- the polymer or copolymer with vinyl acetate units, and

- a multifunctional alcoholate, in the presence of a catalyst, to obtain an organic network; and

b) causing the hydrolysis-condensation of the multi-functional alcoholate belonging to the organic network obtained in step a) and of the excess multi-functional alcoholate, in the presence of water, to obtain an inorganic network; in order to develop an organic-inorganic hybrid material.

. Process for preparing an organic-inorganic hybrid TPV comprising the steps consisting in: a) dynamically cross-linking a thermoplastic polymer or copolymer with vinyl acetate units, by reacting, during the processing operations, at a temperature of between 80 ° C. and 280 ° C:

- the polymer or copolymer with vinyl acetate units, and

b) causing the hydrolysis-condensation of the multi-functional alcoholate belonging to the organic network obtained in step a) and of the excess multi-functional alcoholate, in the presence of water, to obtain the inorganic network;

in the presence of a second thermoplastic polymer or copolymer.

5. Method according to claim 3 or 4, wherein a hydrating filler is added.

6. The method of claim 5, wherein the concentration of hydrating filler expressed in parts by mass per hundred parts by mass of polymer or copolymer with vinyl acetate units is substantially between 5 and 75 parts by mass.

7. The method as claimed in claim 2 or 4, in which the second thermoplastic polymer or copolymer is chosen from the group of polyolefins, or olefin copolymers, or thermoplastic polyurethanes or polyamides, and is preferably polypropylene, polyethylene.

8. Method according to one of claims 1 to 7, in which the copolymer with vinyl acetate units is chosen from the group of ethylene-vinyl acetate copolymers.

. Process according to Claim 8, in which the copolymer with vinyl acetate units is preferably chosen from elastomers having between 28% vinyl acetate and 60% vinyl acetate

10. Method according to one of claims 1 to 9, in which the multifunctional alcoholate is of the M (OR) _{N type} , where M is chosen from the group consisting of silicon, titanium, aluminum, zirconium, where R is an aromatic or aliphatic group comprising from 1 to 20 carbon atoms, and preferably a methyl, ethyl, propyl, butyl group and where "x" takes a value between 2 and 4.

11. The method of claim 10, wherein the multifunctional alcoholate is chosen from the group of bifunctional alcoholates of type R'R "-M (OR), trifunctional of type R'-M (OR) ₃ , tetrafunctional of type M (OR) ₄ .

12. Method according to one of claims 10 or 11, wherein the multifunctional alcoholate is a tetraalkylorthosilicate or tetraalkoxysilane Si (OR) ₄ , where R is an aromatic or aliphatic group of 1 to 20 carbon atoms, and preferably R is chosen from methyl, ethyl, propyl and butyl groups.

13. Method according to one of claims 10 to 12, wherein the initial concentration of multifunctional alcoholate, expressed by the molar ratio, number of moles of vinyl acetate functions of the polymer or copolymer with vinyl acetate units over the number of moles of alcoholate functions of the multifunctional alcoholate, is substantially between 0.1 and 30, preferably between 0.3 and 10

14 Method according to one of the preceding claims, in which the catalyst is chosen from the group of organometallics, and in particular a tin derivative is chosen, preferably an alkyl tin oxide, and very preferably, l dibutyl oxide

15. The method of claim 14, wherein the catalyst concentration, expressed in mass parts per hundred mass parts of polymer or copolymer with vinyl acetate units, is substantially between 0.1 and 3 mass parts, preferably between 0, 5 and 1.5 mass parts.

16. Method according to one of the preceding claims, in which the crosslinking temperature is preferably from 110 ° C to 230 ° C.

17. Method according to one of the preceding claims, in which the dynamic crosslinking is carried out during a discontinuous and / or discontinuous implementation operation.

18. The method of claim 17, wherein the dynamic crosslinking is preferably carried out in an internal mixer when it is discontinuous, and is carried out in an extruder when it is continuous.

19. Method according to one of the preceding claims, in which a compatibilizing agent is introduced, and / or a plasticizing agent of the polymer or copolymer with vinyl acetate units, preferably diesters of phthalic and trimellitic acids and diesters of aliphatic diacids. .

20. Products produced using thermoplastic polymers or copolymers with vinyl acetate units according to the methods of claims 1 to 19.

21. Applications of the products according to claim 20 in the automotive, cable, flame retardant and household appliance fields.