Modification Method Of PVC Resin

PVC resin is a polar non-crystalline high polymer, density: 1.380 g/cm3, glass transition temperature: 87 ℃, so it has poor thermal stability and is not easy to process. It cannot be used directly. It must be modified and compounded, and related additives and fillers can be added before it can be used. Due to the different types and fractions of related additives and fillers added, this determines that the properties and requirements of the prepared PVC materials are different. We usually call it PVC formulations, strictly speaking, PVC modified formulations, and PVC can only be used after modification. This category is often classified as polymer modified materials. The modification of polymer materials mainly focuses on the research on the high performance of general-purpose plastics, the transformation of single-component materials to multi-component composite materials (alloys, blends, and composites), functionalization of materials, and optimization of performance and price. The modification methods are mainly chemical modification, filling modification, reinforcement modification, blend modification and nanocomposite modification. The basic principle of modification is to impart functions or improve certain properties to materials through additives. Therefore, the level of PVC formulation technology determines the level of technology and production capacity of a factory.

PVC generally needs to be modified and granulated first. After being prepared into granules with a screw extruder, the plasticization is more sufficient and the processing is easier, especially for products that are injection-molded. Screw extruder is one of the most important equipment for plastic molding processing. It carries out solid conveying, compaction, melting, shearing and extrusion molding of plastics through external power transmission and heat transfer from external heating elements. The screw extruder plays an important role as a plasticizing and granulating machine or a molding and processing machine. Strictly speaking, PVC products with special requirements and PVC modified formulations are tailored according to customer requirements. There are also copolymerization derivatives in the PVC production process. Such modified varieties include vinyl chloride copolymers, polyvinyl chloride blends and chlorinated polyvinyl chloride.

Polyvinyl chloride has poor thermal stability and light resistance. At 150 ° C, hydrogen chloride begins to decompose, and adverse reactions occur with the amount of plasticizer. In addition, the influence of pigment on PVC is reflected in whether the pigment reacts with PVC and other components that make up PVC products, as well as the migration resistance and heat resistance of the pigment itself. Certain ingredients in colorants may contribute to resin degradation. Such as iron ions and zinc ions are catalysts for the degradation of PVC resins. Therefore, the use of iron oxide (red, yellow, brown and black) pigments or white pigments like zinc oxide, zinc sulfide and lithopone will reduce the thermal stability of PVC resins. Certain colorants may interact with PVC resin degradation products. For example, ultramarine pigments have poor acid resistance, so in the process of PVC coloring, they will interact with the hydrogen chloride generated by the decomposition of PVC and lose their proper color. Therefore, in terms of PVC coloring, considering the characteristics of the resin and related additives used, combined with the characteristics of the pigment. The following issues should be paid attention to when selecting colorants.

1. Some metal ions in the pigment will promote the thermal oxidative decomposition of polyvinyl chloride resin as shown in Figure 1.

The measurement method is the hue change of pigmented polyethylene when heated to 180°C. Due to the metal ions contained in the pigment, the decomposition of PVC is accelerated, resulting in a hue change. At the same time, it should also be noted that the same addition of lake red can make the color difference of PVC different. If it contains calcium, the color difference is small; if it contains manganese, the color difference is large. This is due to the promotion of dehydrochlorination of PVC by metals such as manganese.

Sulfide colorants (such as cadmium red, yellow, etc.) are used for coloring PVC, and hydrogen sulfide may be released due to the decomposition of colorants. Such colorants should not be mixed with lead stabilizers to avoid the formation of black lead sulfide.

2. The influence of pigments on the electrical insulation of PVC

As a cable material, PVC, like polyethylene, should consider the electrical properties after coloring. In particular, polyvinyl chloride has poorer insulation properties than polyethylene, so the influence of pigments is greater. It is indicated that choosing inorganic pigments to color PVC has better electrical insulation than organic pigments (except furnace black and anatase titanium dioxide).