The function of ACR processing aid in PVC PROCESSING
ACR processing aid is a kind of thermoplastic graft polymer prepared by seed emulsion polymerization of methyl methacrylate and Butyl acrylate (BA) , which has dual functions of impact resistance modification and processing modification It is mainly used in hard and semi hard polyvinyl chloride products, especially chemical building materials, such as profile, pipe fittings, plates, foamed materials, etc. .
It can not only improve the impact resistance of high PVC products, but also improve the melt fluidity, thermal deformation, weatherability and surface gloss of the products. In addition, ACR processing AIDS can also be used in engineering plastics such as polycarbonate (PC) , polyester (PET) and their blends. It is one of the main PVC impact modifiers in the world.
In recent years, with the rapid growth of the processing consumption of polyvinyl chloride, especially for hard products made by polyvinyl chloride, the demand of ACR processing AIDS has been growing rapidly and has broad prospects for development.
Classification of ACR PROCESSING AIDS
ACR processing aid is a kind of thermoplastic graft polymer prepared by seed emulsion polymerization of methyl methacrylate and Butyl acrylate, which can be divided into processing modifier and anti-impact modifier. The additives used to improve the impact properties of plastics are called impact modifiers. IMPACT ACR is usually prepared by methyl methacrylate polymerization of Acrylic Ester elastomers with a "core-shell" structure. Its "core" is a kind of low cross-linking acrylic rubber polymer, "Shell" is a good compatibility with PVC methyl methacrylate polymer. Processing ACR is designed to improve the processability of PVC, which is usually produced by graft copolymerization of methyl methacrylate with methacrylate and acrylate. The melt fluidity, thermal deformability and surface gloss of PVC resin can be improved by adding ACR
Application of ACR processing aid in PVC PROCESSING
1. PROMOTE THE MELTING OF PVC
Generally used by suspension polymerization and bulk polymerization of PVC, particle diameter of about LOOPM, particle size of the primary particles about Ljun. In order for PVC to be processed into a useful molten state, it is necessary to heat and increase the shearing force to disperse the PVC particles into primary particles and to form a melt through the interdiffusion of the primary particles between the Molecules But granular PVC to heat and shear transfer is not good, so that the formation of the melt is not uniform, some parts have all melted, while the other part may remain granular state.
ACR processing aid accelerates the melting of PVC by increasing the heat and shear transfer. Because the processing aid and PVC have mixed melt and high molecular weight, its particles increase friction in PVC system, so the melting process is accelerated The melt is more uniform, the defects of molded products are reduced, the surface state and appearance are improved, and the physical and mechanical properties of PVC products are improved.
2. Improve the RHEOLOGIC PROPERTIES OF DAZZLE MELT
PVC MELT system is a viscoelastic fluid, both viscous, block the flow of melt, and elastic, the tendency to return to the initial state after deformation. Both of these properties depend to a great extent on the entangled state of polymer molecules in PVC system. ACR processing aid molecules inserted between the PVC molecular chains, playing a "tangle" and "cross-linking" role. Therefore, the viscosity and elasticity of PVC melt can be increased obviously.
3. Improve Lubrication
Many polymers, because of their chemical property, tend to stick to hot metal surfaces during processing, and adding lubricants can reduce or avoid such problems. There are already a number of conventional lubricants available. But ACR not only promoted the processing modification of PVC, but also promoted the external lubrication. The use of ACR had no effect on the transparency of PVC and no migration after processing. In addition, the impact on the melt of PVC will not exceed the impact of conventional lubricants.
4. IMPACT RESISTANCE
ACR impact modifier is a core-shell copolymer composed of MMA and some crosslinked monomers of low alkyl acrylate. Its core is a light cross-linked acrylate rubber component, which acts as a stress concentration point in PVC products. By inducing a large number of crazes to form, the shear band absorbs the impact energy, thus improving the impact strength; Its Shell, which was grafted onto the rubber core with PMMA as the main plastic component, had good compatibility with PVC resin, could promote the uniform dispersion in the base resin of the modifier, and improve the adhesion between rubber particles and PVC resin. The prominent feature of the core-shell structure is that the size of the rubber particles has been determined at the time of preparation, and is fixed in a certain position during processing, and its shape is kept, so the impact resistance is very outstanding.
Compared with other kinds of impact modifiers, ACR has the following application characteristics: (1) easy to disperse and has strong processing adaptability; (2) high impact efficiency and does not reduce the vicat temperature of products; (3) no saturated and double bond groups Excellent weather resistance, suitable for doors and windows profiles and pipes and other outdoor applications of products; (4) both a certain degree of processing modification, improve the processing properties of products.
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