What is the difference between PVC processing aids ACR and AIM?

AIM (acrylate impact modifier) is a high-quality and environmentally friendly plastic modifier, primarily used in rigid PVC products such as pipes and fittings, plastic-steel doors and windows, sheets, and containers. AIM generally consists of a core made of cross-linked n-butyl acrylate polymer, with a shell of methacrylate polymer that has good compatibility with PVC, forming a core/shell structure. AIM is dispersed in the PVC continuous phase matrix in particle form; when subjected to external impact, tiny cracks form in the PVC, which affect the ACR elastic particles and cause them to compress and deform. This process absorbs the impact energy, preventing further propagation of the cracks and thereby enhancing the material’s impact strength. At the same time, AIM also endows PVC products with good processability and weather resistance; therefore, it is particularly suitable for outdoor applications, and is currently the PVC toughening modifier with the best overall performance.

ACR is a copolymer of monomers such as methyl methacrylate and acrylates; it is one of the best impact modifiers developed in recent years, capable of increasing the impact strength of materials by several dozen times. ACR is an impact modifier with a core-shell structure: a shell composed of methyl methacrylate-ethyl acrylate polymers, with chain segments formed by the crosslinking of butyl acrylate-based compounds acting as a rubbery elastomer core distributed in the inner layer of the particle. It is particularly suitable for the impact modification of PVC plastic products used outdoors. When used as an impact modifier in PVC plastic doors and windows profiles, ACR offers advantages such as good processability, a smooth surface, excellent aging resistance, and high strength at weld corners; however, its price is about 1/3 higher than that of CPE. Commonly used grades abroad such as K-355 are generally used in amounts of 6–10 parts. Currently, there are few manufacturers in China that produce ACR impact modifiers, and few companies that use them as well.

Basically the same, but the focus differs during use.