Keywords: PS; Wide-temperature-range Toughening; SEBS, SEPSKeywords: PS; Wide-temperature-range Toughening; SEBS, SEPS Outdoor PS sheets are required to meet the core performance criteria: no embrittlement at -30℃, and no deformation or aging at 50℃. The selection of its toughening system and optimization of molding process must be precisely tailored to the complex outdoor working conditions. I. Core Toughening Agent Selection PS is inherently brittle with a narrow temperature resistance range, making conventional toughening agents incompatible with outdoor high-low temperature environments. Although traditional SBS can improve toughness, SBS-modified PS materials have a narrow temperature tolerance range. Their toughness deteriorates significantly at -20℃, and they tend to age, soften and deform easily at 50℃, thus SBS must be ruled out. It is recommended to use medium-to-high molecular weight SEBS or SEPS, with the addition level controlled between 5%–8%: 1. Performance Compatibility Both are hydrogenated to eliminate unsaturated double bonds, boasting far superior aging resistance than SBS. They can resist outdoor UV radiation, temperature and humidity variations for long periods, preventing aging and embrittlement. Their medium-to-high molecular weight structure ensures excellent compatibility with the PS matrix, without compromising the mechanical strength or molding processability of the sheets. SEBS offers a higher cost-performance ratio and can be prioritized for cost control in outdoor environments with relatively mild temperature differences. 2. Differentiated Advantages SEPS features a wider temperature resistance range and better retention of low-temperature toughness. It maintains elasticity even at the extreme low temperature of -30℃, effectively preventing embrittlement. It also exhibits more outstanding high-temperature stability, remaining non-softening and non-migrating at 50℃. When combined with the PS matrix, it achieves the requirement of no deformation at high temperatures, making it more suitable for outdoor scenarios with large temperature fluctuations. II.Optimization of Molding Process Toughening agents alone cannot fully resolve the high-temperature warpage issue of outdoor PS sheets. Residual stress generated during injection molding or extrusion is the key cause of deformation in outdoor high-temperature conditions. Stress elimination requires the following process adjustments: 1. Increase Melt Temperature Reasonably raise the molding temperature (generally controlled at 200–220℃, with specific values subject to fine-tuning based on PS grades) to reduce melt viscosity, minimize the shearing effect of materials in the mold cavity or screw, and avoid internal stress caused by uneven shearing. Meanwhile, ensure sufficient plasticization of the melt to improve the structural uniformity inside the sheets. 2. Reduce Shear Orientation Optimize screw speed and feeding rate to lower the shear rate, preventing internal stress induced by orientation differences during material flow. Adjust the mold gate design by adopting multi-point gates or enlarging gate size to achieve uniform mold filling and reduce local stress concentration. 3. Extend Cooling Time and Optimize Cooling Method Appropriately extend mold cooling time and adopt a staged cooling strategy to avoid excessive temperature differences between the internal and external layers of sheets caused by rapid cooling. Ensure uniform distribution of cooling water channels, with focused cooling on sheet edges and areas with uneven thickness to prevent stress induced by uneven cooling. 4. Finished Product Annealing Treatment Molded PS sheets shall undergo annealing treatment: place the sheets in a constant temperature environment of 70–80℃ for heat preservation for 2–4 hours, followed by slow cooling to room temperature. Annealing can release residual internal stress generated during molding, fundamentally reducing the risk of warpage deformation in outdoor high-temperature environments while further improving the dimensional stability of the sheets. III. Supplementary Optimization Suggestions Formula Synergistic Modification Blend 0.2%–0.5% of antioxidants (e.g., hindered phenolic antioxidant 1010) and ultraviolet absorbers (e.g., benzotriazole UV absorber 326) to enhance the long-term weather resistance of sheets, avoiding aging, yellowing, and performance degradation caused by outdoor exposure. For further improvement of rigidity, a small amount (1%–3%) of glass fiber reinforcement can be added, which works synergistically with SEBS/SEPS to balance the toughness and rigidity of the material.