Generally speaking, Huang Dou of plastic products is caused by aging or degradation of materials, and PP is generally caused by aging (degradation). Due to the existence of side groups on polypropylene, its stability is not good, especially in the case of light. Light stabilizers are usually added. As for PE, because there is no side group, there are not many cases of yellowing in general processing or first use. PVC will turn yellow, which is related to the formula of the product. To put it bluntly, it is oxidation. The surface of some masterbatch is easy to be oxidized, so it is necessary to carry out surface treatment on the masterbatch. Besides the bad additives and impurities in the system, I think it is mainly caused by aging. Adding proper antioxidant system and anti-ultraviolet agent can improve the yellowing of PE and PP, but many hindered phenolic antioxidant systems themselves will bring slight yellowing. There are also some antioxidant systems and anti-ultraviolet agents that have resistance, so be careful when using them. Adding polymer lubricant to form a flowable fluoropolymer film on the machine wall can improve the extrusion processability, extrusion pressure and processing temperature of polyolefin resin, improve product quality and productivity, reduce production cost, reduce or eliminate melt fracture and reduce rejection rate.