PVC Modification additives

1. PVC Processing modification AIDS

1.1 Principle of processing modification AIDS

Due to the poor ductility of PVC melt, it is easy to break the melt. PVC melt relaxation slow, easy to lead to the product surface rough, dull and so on. Therefore, when PVC is processed, it is often necessary to add processing AIDS to improve the above defects in its melt.

PVC Processing AIDS are auxiliaries that can improve the processing performance of resin, and there are three main ways of action: promoting the melting of resin, improving the rheological properties of melt and giving lubrication function. Promote resin melting: PVC resin in the state of heating, under the action of a certain shear force melting, processing modifier first melt and adhere to the surface of PVC resin particles, its compatibility with the resin and its high molecular weight, so that PVC viscosity and friction increase, thus effectively the shear stress and heat transfer to the entire PVC resin, accelerate PVC melting. Improve the rheological properties of melt: PVC melt has shortcomings such as poor strength, poor ductility and melt rupture, and processing modifiers can improve the rheological properties of melt. The mechanism of action is as follows: increase the viscoelasticity of VC melt, thus improve the mold expansion and increase the melt strength. Giving lubricity: the compatible part of the processing modifier and PVC is first melted to promote melting; The parts incompatible with PVC migrate outside the molten resin system, thereby improving the release property.

1.2 Commonly used processing modifier ACR

Acrylic Processing Aids is a copolymer of methyl methacrylate and acrylate styrene monomers. Can be used as processing AIDS, can also be used as impact modifier. ACR can be divided into ACR201, ACR301, ACR401, ACR402, and foreign brands are: K120N, Kl25, Kl75P530, P501, P551, P700, PA100 and so on.

The important role of ACR processing modifier is to promote the plasticization of PVC, shorten the plasticization time, improve the uniformity of melt plasticization, and reduce the plasticization temperature. In PVC plastic door and window profiles, ACR201 or ACR401 is generally used, and the dosage is 1.5-3 dosage.

2. PVC Impact modifier

An important content of polymer material modification is to improve its impact resistance, PVC resin is a polar non-crystalline polymer, there is a strong force between molecules, is a hard and brittle material; Low impact strength. After the impact modifier is added, the elastomer particles of the impact modifier can reduce the total stress induced by the silver stripe, and use the deformation and shear band of the particles themselves to prevent the expansion and growth of the silver stripe, and absorb the impact energy in the incoming material, so as to achieve the purpose of impact resistance. The particles of the modifier are small, so as to increase the number of modifiers per unit weight or per unit volume, so that the number of effective volumes is increased, thus enhancing the ability to disperse stress. At present, the organic impact modifier is widely used. According to the internal structure of organic impact modifiers, they can be divided into the following categories.

2.1 Predetermined elastomer (PDE) type impact modifier

It belongs to the core-shell structure of the polymer, the core is a soft elastomer, giving products high impact resistance, the shell is a polymer with high glass transition temperature, the main function is to isolate the modifier particles between each other, the formation of free flow of component particles, promote its uniform dispersion in the polymer, enhance the interaction and compatibility between the modifier and the polymer. The modifiers of such structures are: MBS, ACR, MABS and MAC R, etc., which are excellent impact modifiers.

2.2 Non-predetermined elastic shape (NPDE) impact modifier

The impact modifier with non-predetermined elastic shape belongs to network polymer, and its modification mechanism is to modify plastics by solvation (plasticization) mechanism. Therefore, the NPDE must form a network of resin-coated structures, which are not very compatible with the resin. The modifiers of such structures are: chlorinated Polyethylene CPE &EVA, etc.

2.3 Excessive PVC impact modifier

Its structure is between two structures, such as ABS. The specific varieties of PVC resin are:

(1) Chlorinated polyethylene (CPE) . CPE is the dominant impact modifier in China, especially in the production of PVC pipes and profiles, and most factories use CPE. The serving size is usually 5-15 dosage. CPE can be used in conjunction with other toughening agents, such as rubber, EVA, etc., the effect is better, but the rubber additives are not resistant to aging.

(2) Acrylic Processing Aids. ACR is an impact modifier of core-shell structure. The shell is composed of methyl methacrylate and ethyl acrylate polymer, and the chain segments of rubber elastomer formed by butyl acrylate crosslinking are distributed in the inner layer of particles. Especially suitable for the impact modification of PVC plastic products used outdoors, the use of ACR as an impact modifier in PVC plastic door and window profiles has the characteristics of good processing performance, smooth surface, good aging resistance and high welding Angle strength compared with other modifiers, but the price is about 1/3 higher than CPE.

(3) MBS is a copolymer of methyl methacrylate, butadiene and styrene. The solubility parameter of MBS is between 9.4-9.5, which is close to the solubility parameter of PVC, so it has good compatibility with PVC, and its biggest feature is that it can be made into transparent products after adding PVC.

(4) SBS is a ternary block copolymer of styrene, butadiene and styrene, also known as thermoplastic styrene butadiene rubber, which is a thermoplastic elastomer, and its structure can be divided into two types: star and linear.

(5) ABS is styrene (40%-50%), butadiene (25%-30%), acrylonitrile (25%-30%) terpolymer, mainly used as engineering plastics, but also used as PVC impact modification, low temperature impact modification effect is also very good.

(6) EVA is a copolymer of ethylene and vinyl acetate, the introduction of vinyl acetate has changed the crystallinity of polyethylene, the content of vinyl acetate is a lot of poor, and EVA and PVC refractive index is different, it is difficult to get transparent products, therefore, EVA is often used with other impact resins. The amount of EVA added is less than 10 dosage.

2.4 Rubber impact modifier

It is an excellent toughening agent, the main varieties are: Ethylene-propylene rubber (EPR), EPDM (EPDM), nitrile butadiene rubber (NBR) and styrene butadiene rubber, natural rubber, butadiene rubber, neoprene rubber, polyisobutene, butadiene rubber, etc., of which EPR, EPDM, NBR three are most commonly used, which is to improve low temperature impact resistance is superior, but not resistant to aging. PVC Plastic door and window profiles generally do not use such impact modifiers.