Polyvinyl chloride (PVC), as one of the world's largest-produced general-purpose plastics, is widely used in construction, packaging, wire and cable, medical devices, and daily consumer goods due to its abundant raw materials, low cost, and ease of processing. However, pure PVC resin suffers from poor thermal stability, insufficient impact strength, poor processing flowability, and limited weather resistance during processing and use, necessitating the addition of various functional additives. Therefore, PVC additives have become a core supporting system determining the quality and applicability of its products.
Among the many additives, heat stabilizers are paramount. PVC is prone to dehydrochlorination during heat processing, leading to molecular chain cross-linking or breakage, resulting in discoloration, embrittlement, and even loss of usability. Metal soaps, organotin compounds, and calcium-zinc composite stabilizers effectively extend the resin's thermal stability time by absorbing or neutralizing the generated hydrogen chloride, replacing unstable chlorine atoms, or blocking chain reactions, ensuring the stability of processes such as extrusion, injection molding, and calendering.
Plasticizers are key components for improving the flexibility and processing flowability of PVC. Phthalate esters were once commonly used, but with increasing environmental and health requirements, citrate esters, epoxidized soybean oil, and polyester plasticizers have seen their applications expand due to their low toxicity and migration resistance, especially in food packaging, children's products, and medical products. The type and amount of plasticizer directly affect the hardness, elasticity, and low-temperature performance of the finished product.
Impact modifiers are used to overcome the brittleness of rigid PVC. Acrylic copolymers, chlorinated polyethylene (CPE), and methyl methacrylate-butadiene-styrene copolymer (MBS) can form micro-tough regions within the matrix, absorbing impact energy and inhibiting crack propagation, thus significantly improving the impact strength of the product and enhancing its reliability in applications such as door and window profiles, pipes, and sheets.
Processing aids primarily improve the flow and plasticizing behavior of PVC melt. Acrylic polymers can promote particle melting, reduce melt viscosity, and eliminate surface defects such as sharkskin, improving production efficiency and product surface finish, and are particularly suitable for profile extrusion and film blow molding.
Lubricants are divided into two categories: internal lubricants and external lubricants. Internal lubricants reduce friction between resin molecules, promoting uniform plasticization; external lubricants reduce adhesion between materials and equipment surfaces, ensuring smooth processing and preventing overheating and decomposition. Proper formulation can avoid quality fluctuations caused by poor plasticization or excessive melting.
Furthermore, antioxidants, light stabilizers, flame retardants, fillers, and colorants are selected according to the intended use of the product. Antioxidants and light stabilizers can delay aging and extend the lifespan of outdoor products; flame retardants improve the safety of electrical and building materials; fillers can improve dimensional stability and rigidity while reducing costs; and colorants provide products with rich color expression.
Overall, the PVC additive system is characterized by its diverse functions and strong synergistic effects. The scientific compounding of different additives can not only compensate for the inherent defects of PVC but also achieve a comprehensive improvement in processing performance, mechanical strength, durability, and safety and environmental performance. With the advancement of green manufacturing and the demand for high performance, additives are developing towards low toxicity, high efficiency, and multifunctional integration, providing solid support for the expansion of PVC in high-end and emerging fields.