Mechanical Properties of Photoaged In Situ Polymerized PS/EPDM Blends Emerson Lourenc ¸o, Maria Isabel Felisberti Instituto de Quı ´mica, Universidade Estadual de Campinas, Caixa Postal 6154, 13084-862 Campinas, Sao Paulo, Brazil Received 6 March 2007; accepted 17 April 2007 DOI 10.1002/app.26630 Published online 29 August 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: In this study, the mechanical properties of in situ polymerized PS/EPDM blends with different composition were evaluated before and after accelerated photoaging and compared with the properties of com- mercial HIPS submitted to similar aging conditions (ASTM G53). The mechanical properties of the PS/EPDM blends as well as their photochemical stability are influ- enced by the polymerization temperature and blend com- position. Although the initial mechanical properties of HIPS are superior in comparison with the in situ poly- merized PS/EPDM blends, a pronounced drop of them was observed already for short time exposure. For exam- ple, after the aging period, all PS/EPDM blends showed higher strain at break than HIPS. Because PS/EPDM blends present higher resistance to photoaging stability than HIPS, the mechanical properties of the HIPS become worse than the other blends as the aging time increases. Ó 2007 Wiley Periodicals, Inc. J Appl Polym Sci 106: 3617–3623, 2007 Key words: blends; photoaging; mechanical properties; polystyrene; EPDM INTRODUCTION Rubber toughening is one of the key inventions of plastics industry. The incorporation of dispersed elastomeric particles in a rigid polymer matrix has attracted significant attention because of its indus- trial importance. 1–3 High impact polystyrene (HIPS) is one of the most important toughened commercial systems in which the brittle polystyrene (PS) becomes more ductile. 4,5 However, aging is a serious problem for HIPS and for other rubber-toughened plastics, especially those based on polybutadiene (PB). The major contribution to photodegradation of HIPS is usually attributed to the PB phase, which is constituted of different isomers that present different stabilities to degradation, although the degradation also affects the PS matrix. 6 Exposure to sunlight causes a drastic drop in impact resistance attributed to the photooxidation of the unsaturated rubber phase induced by UV radiation, limiting the lifetime of molded parts in outdoor applications. 4,7 To over- come this problem, it has been suggested that PB be replaced in the polymer composition by a saturated rubber such as poly(ethylene-co-propylene-co-2-ethyl- idene-5-norbornene), EPDM. 8 Aging of polymeric materials may be defined as a progressive deterioration of the physical properties because of the action of heat, oxygen, UV radiation, or mechanical work, either separately or in combina- tion. Degradation of polymers includes all changes in chemical structure and physical properties of poly- mers because of external chemical or physical stresses leading to materials with characteristics different from those of the starting material. Usually, degrada- tion means worsened properties. Degradation because of mechanically induced thermal processes takes place during melt processing of polymers at high temperatures in an oxygen deficient atmosphere and accounts for chemical changes in the polymer structure. Consequently, it modifies mechanical prop- erties and weathering resistance of the final material. 9 After the polymerization step of styrene-based poly- mers the temperature is increased to between 200 and 2508C for short times, to remove residual mono- mers and any low molar mass compounds. Problems with vacuum conditions during this step may lead to oxidation of the polymer. 10 The thermal and pho- todegradation of PS in the presence of oxygen occurs through a typical radical chain mechanism and is well described in the literature. The hydrogen bonded to the same carbon as the phenyl group is labile and its loss occurs by the absorption of energy producing a radical group that undergoes subse- quent reactions such as depolymerization and oxida- tion, resulting in low molar mass compounds. 6,11,12 Differences in sensitivity to individual degradation processes arise from the effects of low amounts of structural polymeric inhomogeneities (e.g., unsatura- Correspondence to: M. I. Felisberti (misabel@iqm. unicamp.br). Contract grant sponsor: FAPESP; contract grant number: 03/04,246-2. Contract grant sponsor: CNPq. Journal of Applied Polymer Science, Vol. 106, 3617–3623 (2007) V V C 2007 Wiley Periodicals, Inc.