PVC型材发黄的原因

测试了用于生产型材A（合格品）和型材B（颜色发黄）的PVC树脂的原始白度、老化白度、热稳定时间、分子质量及其分布和型材A、型材B的凝胶化度，结果表明：①与型材A相比，用于生产型材B的PVC树脂的原始白度、老化白度、热稳定时间、分子质量及其分布都合格；②型材B外壁的凝胶化度比型材A外壁高约10％，表明挤出型材B时口模处的温度偏高，从而造成型材B表面颜色发黄。另外，还进行了模拟试验，验证了分析结果。

Reasons for the yellowing of PVC profiles

The original whiteness, aging whiteness, thermal stabilization time, molecular weight and its distribution of PVC resins used for producing profiles A（qualified product） and B（yellowing） and gelification degree of A and B were measured. The results showed that （1） comparing with profiles A,the whiteness, aging whiteness, thermal stabilization time and molecular weight and its distribution of PVC resins used for producing profiles B were all qualified; （2）the gelification degree of the outer wall of profiles B was 10% higher than that of profiles A,which showed that the temperaturc of dic during the extrusion of profiles B was high,leading to the yellowing of the sur face of profiles B. Furthermore, simulation tests were carried out to verify the obtained analysis results.