Classification and selection of PVC modifiers

PVC modifiers can be divided into 6 groups according to their functions and modification characteristics for glassy amorphous PVC modifiers:

① Effective impact modifier: used in opaque impact mixture.

② Transparent impact modifier: When optical properties and impact resistance are required, this modifier is used.

③ Thermal deformation modifier: used to improve the processing temperature range of PVC mixture.

④ Common modifiers: used to improve impact resistance, high temperature strength and low temperature flexibility.

⑤ Weather resistant modifier: The use of this modifier in outdoor applications can prevent UV photodegradation.

Processing AIDS: Improve the melt performance of PVC by reducing the melting time.

1 Highly effective impact modifier

The highly effective impact modifiers such as ABS and MBS have a synergistic effect on the improvement of PVC impact resistance. Therefore, adding a small amount of modifier to PVC can obtain high impact resistance and increase the flexibility of PVC without significantly changing the mechanical properties of the mixture. The molecular weight of PVC determines the amount of impact modifier. The higher the molecular weight, the less modifier is required. The end use of the product determines the molecular weight required for the PVC mixture. For example, low molecular weight PVC is best processed by living molding; And high molecular weight PVC is selected tubular extrusion processing. Typical applications of highly effective impact-resistant modifiers are for PVC pipes, injection mixtures, and calendering opaque films and sheets.

2 Transparent impact modifier

Transparent impact modifiers in PVC mixtures can provide some additional properties like opaque modifiers, such as light propagation, light fog, yellowness index. Optical properties such as low break white and discoloration. In the process of preparing the emulsion of ABS and MBS modifiers, the optical properties required for maintaining transparency are obtained by making the refractive index of PVC and the modifier equal. The impact resistance effect was obtained by controlling the particle size of the rubbery matrix within a narrow distribution range of 1000-3000 A. A balance of compatibility/incompatibility (impact resistance) is obtained by grafting S/AN or MMA/S solubility parameters. Typical applications of these modifiers are transparent calendered films, packaging sheets and blown PVC bottles.

3. Heat deformation modifier

The thermal deformation modifier can increase the effective thermal service temperature of PVC. IT can be increased approximately with each addition of modifier. The addition of thermal deformation modifiers to PVC can also increase the stiffness, so that the impact of tensile strength is minimal, but often weakens the impact strength. Such modifiers are usually composed of polyalpha-methylstyrene/acrylonitrile (AMSAN) or glutarimide. For AMS polymer, the thermal deformability of PVC is increased due to the steric hindrance of the methyl group attached to styrene. Because of its heterocyclic structure, glutarimide polymer can increase the polymer chain stiffness, and thus increase the thermal deformation of PVC parent. Applications of thermal deformation modifiers include vinyl siding, heat-resistant profiles, and automotive instrument liners that require molding fastness.

4. Common modifiers

Common modifiers are semi-rigid modifiers for semi-rigid PVC mixtures, which are typical ABS modifiers, containing less butadiene and more ungrafted fully rigid polyS/AN. These modifiers have two phases of rigidity and rubbery, which can make semi-hard mixtures have a variety of properties. Butadiene rubber phase can increase the low temperature cracking resistance, high molecular weight rigid S/AN has thermal formability and good performance retention and other processing properties. Typical uses of ordinary modifiers include automotive dashboard sheet, luggage ABS cover plate material and automotive profiles.

5. Weather resistant modifier

Weather-resistant impact-resistant modifiers prevent UV photodegradation. Like MBS and ABS, butadiene modifiers are not suitable for outdoor use unless their outer layer is protected by an anti-ultraviolet layer. At the double-chain site of butadiene, ultraviolet light can break its unsaturated carbon chain skeleton and make the modification brittle through oxidation and other degradation reactions. Modifiers with strong resistance to UV-degradation function similar to MBS and ABS, but they have acrylate or 2-ethylhexyl acrylate bonding phases, and the polymer chains of these components do not contain double chains, and there is no site where the degradation reaction begins. These modifiers are usually called acrylic modifiers, and are mainly used in PVC siding, window profiles and other applications that require weather resistance. They have some impact resistance when used outdoors, but the effect is not as effective as ABS or MBS.

Another weather-resistant modifier that can be used outdoors is CPE (chlorinated polyethylene). This modifier is not very effective, the modification effect is not very good. The toughness of the PVC matrix is increased by a mechanism similar to plasticization (or a network of interpenetration).

6 Processing AIDS

Adding processing AIDS to the PVC compound can increase the melting and melt properties. Typical processing AIDS are polymers with very high molecular weight, such as MMA/EA, styrene, MMA/ S/AN or S/AN. It is mainly used in PVC blends, and its dosage is generally 1 or less for PVC dry mixes. Its function is to promote the melting of the mixture by increasing the friction between the PVC and the inner surface of the mixing equipment metal. In PVC foam, due to the high molecular weight poly SAN and poly MMA/S/AN control of melt viscosity is very effective. In the plastics industry, these different modifiers have their own roles, and each specific polymer requires impact resistance. Only by comparing fluidity, cost, stability and particle size control can the modifier be selected correctly.