MODIFIED POLYETHYLENE TEREPHTHALATE

Abstract: A description follows of a polyethylene terephthalate modified with functionalized SBS rubber, in a quantity ranging from 1 to 15 % by weight, preferably from 2 to 7 % by weight. The polyester thus modified has: a) a considerably improved shock resistance with respect to PET as such (over ten times higher); b) an impact strength which is also 50-100 times higher than PET; c) modulus and transmittance only slightly influenced by rubber. The process for the preparation of the above modified polyester is also described.

Description: MODIFIED POLYETHYLENE TEREPHTHALATE The present invention relates to polyethylene terephthalate modified with rubbers essentially consisting of polyvinylarene/conjugated polydiene block copolymers. In various industrial applications of polyethylene terephthalate (PET) (for example in the field of fine plates), the ever-increasing necessity is felt for improving the properties of PET, in par ¬ ticular the impact strength, shock resistance and processability, without reducing some of the prop ¬ erties of polyester, such as transparency. For this purpose the market has resorted to various types of polyester characterized by high costs and low productive capacities installed, or to the use of PET modifiers. Recently, in fact, two chemical groups of PET modifiers, extremely different from each other, have appeared: the first consists of elastoplastic copolymers based on functionalized polyolefins, the second of copolymers with a core-shell structure based on MBS ( ethacrylate-butadiene-styrene) rub- ber (core) and functionalized acrylic copolymers (shell) . The former offer, at a convenient price with respect to the use of other polyesters, the possi ¬ bility of modifying PET without however conserving its transparency, the latter maintain the transpar ¬ ency of PET but are off-market from the point of view of economic convenience and are inferior to the former as impact modifiers of PET. A modified polyethylene terephthalate has now been found which overcomes the disadvantages de ¬ scribed above. In accordance with this, the present invention relates to a modified polyethylene terephthalate which comprises: (a) polyethylene terephthalate in a quantity rang ¬ ing from 80°ό to 99.5° 0 , preferably from 85% to 98%, even more preferably from 95% to 97%; (b) functionalized rubber in a quantity ranging from 20% to 0.5%, preferably from 15% to 2%, even more preferably from 5% to 3%; the above functionalized ruboer (b) being selected from polyvinylarene/conjugated polydiene block copolymers functionalized with an unsaturated epoxide having general formula (I) CH^C(R)-COO-(CH 2 ) n -CH-CH 2 ( I ) \ / O wfierein P is selected from H and CH , n is an inte ¬ ger from 0 to 4, R is preferably CH and n = 1. In the latter case, the unsaturated epoxide (I) is glycιd\l methacrylate (GMA, . Polyethyleneterephthalate (PET) is the polymer deriving from polycondensation (esteπfication) between terephthalic acid and ethylene glycol. In the present invention recycled PET deriving from bot- ties recovery, was used. Block copolymers consist of a hard phase and a soft phase. The hard phase usually consists of a polyvmylarene, preferably polystyrene, whereas the soft phase normally consists of a polydiolefm, preferably selected from polyoutadiene and polyiso- prene . These block copolymers can be sequentially ordered (linear) or branched (star), with a number of blocks normally ranging from 2 to 4 and a vary ¬ ing number of branches. Tne blocks, and also those which are repeated, can have a different molecular weight. In any case, the total molecular weights range from 70,000 to 250,000. In the preferred embodiment, the block copolymers are sty- rene/butadiene/styrene block copolymers, also known as SBS rubber. The block copolymers are functionalized with an acrylate having general formula (I), preferably with the acrylate having general formula (I) wherein R=CH ^ , n=l, or glycidyl methacrylate. In the preferred embodiment, the block copolymers are functionalized with a quantity of acrylate having general formula (I) ranging from 0.2% to 6% by weight, even more preferably from 1% by weight to 3% by weight. A further object of the present invention re ¬ lates to a process for the preparation of modified PET which comprises: (i) a first extrusion of a mixture essentially consisting of (a) one or more elastomers selected from polyvinylarene/conjugated polydiene block copolymers, preferably a styrene-butadiene-styrene block copolymer, and (b) an unsaturated epoxide having general formula (I), preferably glycidyl methacrylate, at a temperature ranging from 180°C to 220°C, preferably from 195°C to 205°C, thus ob- taining a functionalized rubber (c) ; (ii) a second extrusion under vacuum of a mixture essentially consisting of PET and the functionalized rubber (c; obtained in step (i), at a tempera- ture ranging from 260°C to 300°C, preferably from 270°C to 290°C, thus obtaining modified PET; (iii) recovery of the modified PET obtained in step (ϋ) - All the materials are preferably as damp-free as possible. It is therefore advisable to effect a pretreatment of the materials, in particular of the PET and rubber, in order to eliminate any humidity possibly present in the above products. In the preferred embodiment, in order to ob- tain a homogeneous functionalized rubber, it is preferable to carry out a preliminary mixing step of the acrylate (b) and rubber (a) , thus obtaining an optimum dispersion of the acrylate in the rubber. In step (i) , a functionalized rubber is obtained by the grafting of the epoxide on the rubber itself. The grafting of the epoxide in the rubber presumably takes place by means of radicalic reac ¬ tion. In step (ii), a second extrusion of the mix- ture, essentially consisting of PET and functionalized rubber, is carried out, thus obtaining the modified PET of the present invention. In this second step an ionic reaction between the PET ester groups and the epoxide groups of formula (I) presumably takes place. It should be pointed out that the conditions of the two different extrusions (i 1 and (ii) are critical in that the first extrusion should be carπed out at a lower temperature than the second. As can be seen from the following experimental tests, the modified PET obtained according to the process of the present invention has, with respect to PET as such, a distinctly improved shock resis- tance and above all impact strength, without there being a substantial loss in the optical character ¬ istics typical of PET as such. Furthermore the modified PET of the present invention has a decisively higher processability than PET as such. All these properties of modified PET can be conveniently exploited in the preparation of various kinds of materials, particularly in the prepa ¬ ration of fine transparent plates. The following examples are provided for a bet- ter understanding of the present invention. EXAMPLES The polyethylene terephthalate used is a recycled PET characterized by a number molecular weight (Mn) of about 25,000. SOL S 142 ® is a block copolymer (SBC) of the SBS (styrene-butadiene-styrene ; family having the following characteristics: Number molecular weight (Mn) equal to 75,000; 70% by weight of styrene of which 50% forms polystyrene blocks (hard phase) and the remaining styrene alternates with butadiene (30% by weight) forming the soft phase. Preparation of modified PET The preparation of the modified PET of the present invention is effected in two steps: (a) grafting of the GMA onto the block copolymer, thus obtaining modified rubber; (b) extrusion of PET and the modified rubber obtained in step (a) . A dispersion of GMA in the previously dried rubber (ventilation oven at 50°C for 6 hours) is carried out before step (a) , followed by a subse ¬ quent "digestion" initially using a fast mill for 5 minutes at a low temperature and subsequently a drum-rotator for 24 hours. The purpose of this treatment is to obtain an optimum dispersion of the GMA and absorb it onto the rubber granules. The first step (a) consists in "reactive blending" with grafting of the GMA onto the rubber. The dispersion of GMA in the rubber is charged into a weigher situated on the first inlet of the laboratory twin-screw extruder characterized by a screw having a diameter of 35 mm with 1/d equal to 32, under the following conditions: ** + thermal profile: 200°C are set in the first half of the screw length, -whereas in the second half the temperature gradually drops to 120°C at the head of the extruder; *** flow-rate 2.5 kg/h; *** screw revs of 200/min. Under these conditions the machine allows a contact time (machine holdup) of the materials (rubber and GMA) of about 160 seconds. Three different compositions of modified rub- ber containing respectively 1%, 2% and 3% by weight of GMA were prepared with the process described above . The second step (b) of the process of the pre ¬ sent invention consists in the extrusion of the modified rubber of step (a) and PET. The modified rubber and PET are charged into two different weighers situated at the first inlet of the laboratory twin-screw extruder characterized by a screw having a diameter of 35 mm with 1/d equal to 32, under the following conditions: *** thermal profile: 280°C are set in the first half of the screw length, whereas in the second half the temperature gradually drops to 250°C at the head of the extruder; *** flow-rate 11 kg/h; *** screw revs of 300/min; *** extrusion carried out under vacuum. Under these conditions, the machine allows a contact time (machine holdup) of the materials (modified rubber and GMA) of about 35 seconds. The different percentage compositions of the various tests indicated hereunder were obtained by varying the percentage flow-rate of the single per ¬ centage weighers, so as to obtain compositions in which the rubbers used are present at 3, 5 and 15% by weight. The characteristics of the various modified PET obtained are specified in Table 1. All the modified PET obtained have a combina- tion of characteristics which are better than those expected. All the examples described generally show improvements with respect to the starting PET, but the best results are obtained with low levels (from 3% to 5%) of Sol 142 modified with a weight quan- tity of GMA ranging from 1 to 3% by weight. This unexpected improvement consists in the fact that the characteristics which were expected to improve are all in all better than expected, without there being any significant losses in the PET properties (modulus and transparency) . In particular: 1) the shock resistance properties (charpy and izod without notch) are much higher than PET as such (over ten times higher) and, even if to a lesser degree, the izod with notch is also improved; 2) there is an incredible increase in the ulti ¬ mate elongation (from 50 to 100 times); 3) the impact strength of the material is also 50-100 times higher than that of PET; 4) the modulus and transmittance of the material are not particularly influenced by the rubber, above all in the optimum quantity (3%-5%); there is a slight deterioration in the haze. The processability of the materials was evalu- ated, not only by observation (both in tne extrus- tion and "stretching" phase of the extruded prod ¬ ucts ana m the injection moulding phase of 3.2 mm thick test samples) but also by means of standard deviation measurements of the average viscosities of the products under injection moulding conditions (the result is automatically provided by the injection press) . In both cases there is a distinct improvement, on the one hand m the greater regularity of the geometry of the moulded test samples and m the high reduction m mould detaching problems, and on the other, m the standard deviation value of the viscosities which increases 5 times, going from the mixture with 5% of rubber containing 2% of GMA to PET as such, whereas the viscosity values are similar. PET from bottle recovery Influence of Sol S 142 rubber modified with 1%, 2% and 3% of GMA

Claims: CLAIMS 1. Modified polyethylene terephthalate which comprises: (a) polyethylene terephthalate in a quantity rang- ing from 80% to 99.5%; (b) functionalized rubber in a quantity ranging from 20% to 0.5%; the above functionalized rubber (b) being selected from polyvinylarene/conjugated polydiene block co- polymers functionalized with an unsaturated epoxide having general formula (I) CH^C(R)-COO-(CH 2 )n-CH-CH 2 (I) \ / O wherein R is selected from H and CH 3 , n is an inte- ger from 0 to 4. 2. The modified polyethylene terephthalate ac ¬ cording to claim 1, which comprises: (a) polyethylene terephthalate in a quantity rang ¬ ing from 85% to 98%; (b) functionalized rubber in a quantity ranging from 15% to 2%. 3. The modified polyethylene terephthalate ac ¬ cording to claim 2, which comprises: (a) polyethylene terephthalate in a quantity rang- ing from 95% to 97%; (bj functionalizeα rubber m a quantity ranging from 5% to 3%. 4. The modified polyethylene terephthalate ac- cordmσ to claim 1, wherein the functionalized rub- ber (b) is selected from polysty- rene/polybutadiene/poiystvrene blocκ copolymers. 5. The modified polyethylene terephthalate ac ¬ cording to claim 1, wherein m the epoxide having general formula (I), R is CH and n = 1. b. Tne moαified polyethylene terepntnalate according to claim 1, wherein the block copolymers are functionalized with a quantity of epoxide having general formula (I) ranging from 0.2% by weight to 6% by weight. 7. The modified polyethylene terephtnalate according to claim 6, wherein the block copolymers are functionalized with a quantity of acrylate hav ¬ ing general formula (I) ranging from 1% by weight to 3% by weight. 8. A process for the preparation of modified PET according to claim 1, which comprises: (I) a first extrusion of a mixture essentially consisting of (a) one or more elastomers selected from polyvinylarene/conjugated polydiene block co- polymers, and (b) an unsaturated epoxide having general formula (I, at a temperature ranging from 180"C to 220°C, thus obtaining a functionalized rubber (c) ; (ii) a second extrusion under vacuum of a mixture essentially consisting of PET and the functionalized rubber (c) obtained in step (i), at a temperature ranging from 260°C to 300°C, thus obtaining modified PET; (in) recovery of the modified PET obtained m step (ii) . 9. The process according to claim 8, character ¬ ized m that the elastomers are selected from sty- rene-butadiene-styrene block copolymers. 10. The process according to claim 8, character- ized in that the unsaturated epoxide having general formula (I) is glycidyl methacrylate. 11. The process according to claim 8, characterized m that the first extrusion is carried out at a temperature ranging from 195°C to 205°C. 12. The process according to claim 8, character ¬ ized m that the second extrusion is carried out at a temperature ranging from 270°C to 290°C.

Inventors: BIGGI AROLDO, MASI FRANCESCO, TACCIOLI ATTILIO, BIGGI, AROLDO, MASI, FRANCESCO, TACCIOLI, ATTILIO
Applicants: BIGGI AROLDO, ENICHEM SPA, MASI FRANCESCO, TACCIOLI ATTILIO, BIGGI, AROLDO, ENICHEM S.P.A., MASI, FRANCESCO, TACCIOLI, ATTILIO
Application year: 2001
Main classification: C08L67
IPC codes: C08L67