THERMOPLASTIC ELASTOMERS AND PROCESS FOR THEIR PREPARATION

Abstract: Composition of thermoplastic elastomers comprising: (a) from 95 to 65 % by weight, preferably from 90 to 70 % by weight, of block copolymers; (b) polyethyleneterephtalate, in a quantity of 5 to 35 % by weight, preferably from 10 to 30 % by weight; (c) acrylate having general formula (I) wherein R is selected from H and CH3, n is an integer from 0 to 4, R is preferably CH3 and n = 1, in a quantity of 0.05 to 1 % by weight.

Description: THERMOPLASTIC ELASTOMERS AND PROCESS FOR THEIR PREPARATION The present invention relates to new thermoplastic elastomers and the process for their prepa- ration. Thermoplastic elastomers consist of "soft" polymeric chains of a varying chemical nature, bound to each other by means of thermolabile bonds. These thermolabile bonds can be of different origins (for example vitreous, crystalline, ionic, hydrogen-bridge) and generally define groups of thermoelastomers (for example block copolymers, polyesters, olefinic copolymers, acrylates, polyu- rethanes) and, together with the "soft" phase, de- termine the characteristics of thermoelastomers. Thermoelastomers of the block copolymer group are characterized by the presence of bonds of a vitreous nature deriving from the presence of polystyrene chain blocks, whereas the "soft" part, forming part of the same polymeric chain, generally consists of polybutadiene or polyisoprene or buta- diene-styrene copolymers. A general characteristic of the synthesis of this group of thermoelastomers is of forming poly- meric chains in which the vitreous ("hard") part can be situated at the chain-ends. As a result of this, the central "soft" part, consisting of the polydiene, may be very long, consequently guaranteeing the elasticity of the prod- uct even at high deformations. This characteristic cannot be obtained with other groups of thermoelastomers as the various and specific syntheses provide products in which the polymeric chain contains the thermolabile bonds internally (and not at the ends) , causing alternating sequences with a very small average length of the "soft" chain. Another characteristic of block thermoelastomers derives from the fact that the "soft" part of the chain can consist of polydienes, extremely valid for maintaining the elasticity even at low temperatures. The problems of this group of thermoelastomers derive from the high temperatures where, on the contrary, the other groups are generally better. These problems are of a double nature arising on the one hand from the presence of double bonds along the "soft" chain, and the low T 3 of polystyrene on the other. A new group of thermoplastic elastomers has now been found, which at least partly overcomes the above drawbacks. In accordance with this, the present invention relates to a composition of thermoplastic elastomers comprising: (a) from 95 to 65% by weight, preferably from 90 to 70% by weight, of block copolymers; (b) polyethylene terephthalate, in a quantity of 5 to 35% by weight, preferably from 10 to 30% by weight; ( c) acrylate having general formula (I) CH = C(R) -COO- (CH ) r -CH-CH (I) \/ 0 wherein R is selected from H and CHj, n is an integer from 0 to 4, R is preferably CH ? and n = 1, in a quantity of 0.05 to 1% by weight, preferably from 0.1 to 0.7% by weight; the sum of (a), (b) and (c) being equal to 100. The block copolymers (a) consist of a "hard" phase and a "soft" phase. The "hard" phase usually consists of a polyvinylarene, preferably polysty- rene, whereas the "soft" phase usually consists of a polydiolefin, preferably selected from polybuta- diene and polyisoprene . These block copolymers are ordered either in a sequential (linear) or branched (stellar) manner, with usually from 2 to 4 blocks and a varying number of branchings. The blocks, also when repeated, can have varying molecular weights. In any case the total molecular weights vary from 70,000 to 250,000. In the preferred embodiment the block copolymers (a) are sty- rene/butadiene/styrene block copolymers (SBS rubber) . Polyethylene terephthalate (PET) is the polymer deriving from the polycondensation (esterifica- tion) between terephthalic acid and ethylene gly- col. In the present invention recycled PET deriving from recuperated bottles, was used. As far as the acrylate (I) is concerned, in the preferred embodiment this is glycidyl methac- rylate (R = CH 5 , n = 1) . In the preferred embodiment, the molar ratio between compound (c) in general formula (I) and polyethylene terephthalate (b) ranges from 0.5 to 4, preferably from 0.7 to 3.1. A further object of the present invention re- lates to a process for the preparation of the composition of thermoplastic elastomers of the present invention by means of extrusion under vacuum with a twin-screw extruder, which comprises: (i) feeding (a) , (b) and (c) into an extruder and maintaining the three components in the ex- truder at a temperature ranging from 220 °C to 280°C, preferably from 240°C to 260°C, with residence times ranging from 20 to 80 seconds, preferably from 30 to 60 seconds, thus obtaining a thermo- plastic elastomer; (ii) rapidly cooling the thermoplastic elastomer obtained in step (i) and its subsequent recovery. In the preferred embodiment, it is preferable to carry out a treatment step of the rubber and PET, prior to the above steps, in order to eliminate the humidity possibly present in the polymers, and disperse the acrylate as much as possible. The process described above allows the PET to be grafted to the SBC rubber. This probably occurs (step i) by means of a first functionalization step of the rubber with the acrylate and subsequent reaction of the rubber thus functionalized with the PET chain-ends (-OH and -COOH) . Step (ii) comprises rapid cooling, to 120-160°C to avoid secondary reactions . The process of the present invention allows the production of thermoplastic elastomers having excellent elastic properties (the best within the group of thermoplastic rubbers) and good tensile characteristics, with a considerable improvement in resistance to fatigue, temperature and exposure to UV rays . The following examples provide a better under- standing of the present invention. It should be noted that the compositions are antioxidant-free . EXAMPLES The polyethylene terephthalate used is characterized by a number average molecular weight (Mn) of about 25, 000. SOL T 166 ® is a block copolymer (SBC) of the SBS group having the following characteristics: (a) it is linear, (b) it consists of 3 blocks in sequence (polystyrene - polybutadiene - polystyrene) where the two polystyrene blocks are more or less the same, (c) it has a molecular weight (Mn) of about 77,000, (d) the polybutadiene represents about 70% by weight of the polymer. The method used for the preparation of these elastomers can be subdivided into two steps. In the first step the rubber is "prepared" for the subsequent phase by means of two successive operations : a) drying (forced ventilation oven, 6 hours at 50°C) in order to eliminate the humidity present in the rubber; b) dispersion of the GMA in the rubber treated in step (a) and its "digestion" initially using a fast mill for 5 minutes at a low tempera- ture and subsequently a drum rotator for 24 hours; the purpose of this operation is to ensure the optimum dispersion of the GMA and absorb it onto the rubber granules . For the preparation of the samples indicated in the table, three different compositions were prepared by dispersing three different quantities of GMA in the rubber, in order to obtain rubber compositions containing 0.2, 0.3 and 0.5% by weight of GMA. The PET on the other hand is dried in an air circulation oven for 2 hours at 120°C. In the second phase (reactive blending in the extruder) , the polymers thus treated are charged into weight distributors situated at the first in- let of the twin-screw laboratory extruder characterized by a screw having a diameter of 35 mm with 1/d equal to 32, adopting the following conditions: thermal profile: brief initial thermal shock to speed up the reaction (255°C set) , fol- lowed by cooling the material to 150°C (set) at the head of the extruder; flow-rate of 10 kg/nour; screw revs: 180/mm.; extrusion carried out under vacuum. Under the above conditions, the machine allows a contact time of the materials (residence m the machine) of about 40 seconds. The different percentage compositions of the tests indicated were obtained by varying the per- centage flow-rate of the single (2) weight distributors, so as to obtain 4 compositions with 4 different composition ratios, wherein the PET is present m quantities of 10, 15, 20 and 30% by weight, respectively. The table measurements were effected according to techniques well known m the field. The measurements with the Vicat apparatus, on the contrary, were effected using internal methods. The following considerations can be obtained from the data of the table: 1) The tensile properties (modulus, ultimate tensile stress, ultimate elongation) are comparable to those of the starting product and m some cases even higher (examples with a low PET content) . 2) The elasticity is more or less analogous or slightly lower: in fact the tension measurement set after deformation (deformation percentage which the sample is not able to recover) is similar. When measured on the other hand as the bounce of a fal- ling body, the elastic response deteriorates slightly even with low PET contents. 3) The aging resistance by exposure to ultravio ¬ let rays (WOM) in some cases (20% and 30% of PET) is triplicate: in fact more than triple the time (over 48 hours against 16 hours of the rubber as such) is necessary for causing an analogous percentage decrease in characteristics. Up to 15% of PET, the improvements are not significant. 4) The temperature resistance (VICAT measure- ents) increases with an increase in the percentage content of PET, which means that it is the modulus of the modified rubbers which has a better resis ¬ tance to temperature increases, with an increase in their PET content. 5) There is a considerable increase in the tear strength and repeated flexural strength: the former increases with an increase in the PET % up to al ¬ most triple values, whereas the latter already has a maximum peak with low PET contents (after 100,000 cycles the incision has not moved - from 3 mm it has become 3.1 mm) and then drops again, with high PET contents, to values which are still much higher (the worst test-sample - 30% PET - breaks after over 25,000 cycles against the 1,500 cycles of the rubber as such) . In conclusion, the tensile and elastic properties of the compositions of the present invention substantially remain unvaried and there is a significant improvement in the resistance to fatigue, temperature and exposure to UV rays. TABLE 1

Claims: CLAIMS 1. A composition of thermoplastic elastomers comprising: (a) from 95 to 65% by weight of block copoly- mers; (b) polyethyleneterephthalate, in a quantity of 5 to 35% by weight; (c) acrylate having general formula (I) CH ^ = C(R)-COO-(CH_) r -CH-CH_ (I) \/ o wherein R is selected from H and CH 3 , n is an integer from 0 to 4, in a quantity of 0.05 to 1% by weight; the sum of (a) , (b) and (c) being equal to 100. 2. The composition according to claim 1, compris ¬ ing: (a) from 90 to 70% by weight of block copoly- mers; (b) polyethyleneterephthalate, in a quantity of 10 to 30% by weight; (c) glycidyl methacrylate, in a quantity of 0.1 to 0.7% by weight. 3. The composition according to claim 1, wherein the copolymers (a) are polyvi- nylarene/polydiene block copolymers. 4. The composition according to claim 3, wherein the polyvinylarene is polystyrene and the polydiene is polybutadiene. 5. The composition according to claim 1, wherein in the compound having general formula (I) R = CH 3 , n = 1. 6. The composition according to claim 1, wherein the molar ratio between (c) and (b) ranges from 0.5 to 4. 7. The composition according to claim 6, wherein the molar ratio between (c) and (b) ranges from 0.7 to 3.1. 8. A process for the preparation of the composition of thermoplastic elastomers according to claim 1, which comprises: (i) feeding (a) , (b) and (c) into an extruder and maintaining the three components in the extruder at a temperature ranging from 220°C to 280°C, with residence times ranging from 20 to 80 seconds, thus obtaining a thermoplastic elastomer; (ii) rapidly cooling the thermoplastic elas- tomer obtained in step (i) and its subsequent recovery. 9. The process according to claim 8, characterized in that the three components are maintained in the extruder at a temperature rang ¬ ing from 240°C to 260°C with a residence time ranging from 30 to 60 seconds.

Inventors: BIGGI AROLDO, MASI FRANCESCO, PAVANELLO DONATO, TACCIOLI ATTILIO, BIGGI, AROLDO, MASI, FRANCESCO, PAVANELLO, DONATO, TACCIOLI, ATTILIO
Applicants: BIGGI AROLDO, ENICHEM SPA, MASI FRANCESCO, PAVANELLO DONATO, TACCIOLI ATTILIO, BIGGI, AROLDO, ENICHEM S.P.A., MASI, FRANCESCO, PAVANELLO, DONATO, TACCIOLI, ATTILIO
Application year: 2000
Main classification: C08F279
IPC codes: C08L53