Influence of thermo-oxidative aging on the mechanical and yellowing properties of polystyrene blends with recycled styrene-butadiene rubber (SBR)

ABSTRACT The objective of this study was to evaluate thermo-oxidative aging in the mechanical properties and yellowing index (YI) of polystyrene blends with compatibilized recycled rubber (SBRr). The blends were initially prepared in a co-rotating double screw extruder, after which the extruded granules were injection molded; high-impact polystyrene (HIPS) was processed under the same conditions for comparison. The SBRr characterization results revealed composition fillers of silica, calcium carbonate, talc, and zinc oxide, while thermogravimetry demonstrated two thermal decomposition stages. It was found that impact strength decreased significantly during the initial 15 days of aging and then showed a tendency to stabilize with small oscillations. Properties related to the modulus of elasticity, strength, and elongation at tensile rupture were similar to those of impact strength: a marked reduction in the initial 15 days followed by stabilization with aging. When a blend was compatibilized with 5% styrene-butadiene-styrene (SBS), optimal properties were observed before and after aging, indicating impact resistance comparable to HIPS. The blends’ loss of mass suggested volatile component extraction. In terms of the YI, the blends showed a sudden increase in the first 15 days of aging before stabilizing at a practically constant yellowing rate. Up to 30 days of aging, HIPS presented a low yellowing rate, after which point the YI intensified. In general, the blends obtained via mechanical mixing exhibited behavior similar to HIPS; for the blend compatibilized with SBS, however, the impact behavior was identical to that of HIPS.

摘要：本研究旨在评估经相容化处理的再生丁苯橡胶（SBRr）共混聚苯乙烯的热氧老化对其力学性能与黄变指数（YI）的影响。该共混物初始通过同向双螺杆挤出机制备，随后将挤出所得粒料进行注塑成型；为便于对照，高抗冲聚苯乙烯（HIPS）采用相同工艺进行加工。对SBRr的表征结果显示，其填料成分为二氧化硅、碳酸钙、滑石粉与氧化锌；热重分析则表明其存在两个热分解阶段。研究发现，冲击强度在老化初始15天内显著下降，随后呈现小幅波动并趋于稳定的趋势。与弹性模量、拉伸强度及拉伸断裂伸长率相关的性能变化规律与冲击强度一致：均在初始15天内出现明显下降，随后随老化进程趋于稳定。当共混物以5%的苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）进行相容改性后，无论老化前后均表现出最优性能，其抗冲击性能可媲美高抗冲聚苯乙烯（HIPS）。共混物的质量损失现象表明存在挥发性组分的析出。就黄变指数（YI）而言，共混物在老化初始15天内黄变程度骤增，随后趋于以近乎恒定的速率保持稳定。老化时长不超过30天时，高抗冲聚苯乙烯（HIPS）的黄变速率较低；30天后其黄变程度显著加剧。总体而言，通过机械共混制备的共混物性能表现与HIPS相近；而经SBS相容改性的共混物，其冲击性能则与HIPS完全一致。