·Introduction to PVC
Polyvinyl chloride (PVC) is one of the five main general-purpose plastics and ranks second in global sales among thermoplastics, following polyethylene (PE).
While PVC has an amorphous structure that limits its light and heat stability and lacks a fixed melting point, it offers excellent mechanical properties, good insulation, flame retardancy, and strong cost-performance characteristics, making it versatile for various applications.
·Types of PVC
PVC applications
·Formula analysis–selection of PVC resin
1. According to the polymerization method
There are three main types of PVC resin: suspension PVC resin, bulk PVC resin, and emulsion PVC resin. Among these, suspension PVC resin is the most frequently chosen option. Emulsion PVC paste, on the other hand, is primarily utilized in applications such as artificial leather, wallpaper, and flooring materials.
2. According to the type of dispersant
Two types: loose type (XS) and compact type (XJ). Currently, loose type is more commonly used.
3. According to toxicity
PVC can be categorized based on its toxicity into two distinct grades: ordinary grade, which is classified as toxic , and sanitary grade, recognized as non-toxic. The sanitary grade is required to maintain a vinyl chloride (VC) content of less than 10 x 10^-6, thereby rendering it suitable for applications in food and medicinal products.
4. According to molecular weight
PVC is classified according to its molecular weight into eight types, designated SG1 through SG8. In this classification system, a lower designation signifies a higher degree of polymerization, resulting in increased molecular weight and strength. However, this correlation also leads to greater challenges in melt flow and processing of the material.
·Formula analysis-selection of additives
When selecting additives, it is important to choose based on the desired outcome. The chosen additives should be effective and meet specified performance criteria. Below is a detailed guide for selecting additives based on their intended purpose:
①Increase Toughness: Choose elastomers, thermoplastic elastomers, and rigid toughening materials.
② Increase Mechanical Strength: Select from glass fiber, carbon fiber, whiskers, and organic fibers.
③ Flame Retardants: Options include bromine (both traditional and environmentally friendly), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardants, antimony trioxide, and hydrated metal hydroxide.
④ Antistatic Agents: Utilize various antistatic additives.
⑤ Conductive Materials: Consider carbon sources (such as carbon black, graphite, carbon fiber, and carbon nanotubes), metal fibers, metal powders, and metal oxides.
⑥ Magnetic Additives: Include ferrite magnetic powder and rare earth magnetic powders, such as samarium cobalt (SmCo or SmCon), neodymium iron boron (Nd-FeB), samarium iron nitrogen (SmFeN), as well as aluminum nickel cobalt magnetic powder.
⑦ Thermal Conductivity: Select materials like metal fibers, metal powders, metal oxides, nitrides, carbides, and carbon-based materials (including carbon black, carbon fiber, graphite, and carbon nanotubes). Also, consider semiconductor materials such as silicon and boron.
⑧ Heat Resistance: Use glass fiber, inorganic fillers, and heat-resistant agents like substituted maleimides and B crystalline nucleating agents.
⑨ Transparency: Explore nano-modification methods, graphite, molybdenum dichloride, and copper powder for enhancing transparency.
⑩ Wear Resistance: Choose calcined kaolin.
⑪ Insulation: Look for insulating materials such as mica, montmorillonite, and quartz.
⑫ Barrier Materials: Use mica, montmorillonite, and quartz as effective barrier additives.