The principle of the role of processing aids: PVC melt malleability, easy to cause the melt broken; PVC melt slack slow, easy to cause the product surface roughness, no gloss and sharkskin. Therefore, PVC processing often need to add processing aids to improve the above defects of its melt. Processing aids are a class of additives that can improve the processability of resins, and their main modes of action are three: promoting resin melting, melt rheology modification and imparting lubrication function. When PVC resin is heated under shear force, the processing modifier first melts and adheres to the surface of PVC resin particles. Based on its compatibility with resin and high molecular weight, the viscosity and friction of PVC increase, thus effectively transferring shear stress and heat to the whole PVC resin and accelerating the rheological modification of PVC melt. PVC melt has the disadvantages of poor strength, poor ductility and melt fracture, the processing modifier can improve the above problems of the melt. The mechanism of action is to increase the viscoelasticity of PVC melt, thereby improving the expansion of the mold and improving the melt strength. The compatible part of the processing modifier and PVC is first melted to promote melting, while the incompatible part with PVC migrates to the outside of the molten resin system, thus improving the release.