PVC physical and chemical properties
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PVC physical and chemical properties
The natural color is yellowish translucent and shiny. Transparency is better than polyethylene, polypropylene, and is different from polystyrene. It is divided into soft and hard polyvinyl chloride according to the amount of additives. The soft products are soft and tough, and the hand feels sticky. The hardness of hard products is higher than that of low density polyethylene. Below polypropylene, whitening occurs at the bend. Stable; not easily corroded by acid or alkali; more resistant to heat.
Polyvinyl chloride has flame retardancy (flame retardancy value of 40 or more), high chemical resistance (concentrated hydrochloric acid, 90% sulfuric acid, 60% nitric acid and 20% sodium hydroxide), mechanical strength And the advantages of good electrical insulation.
Polyvinyl chloride has poor stability to light and heat. The softening point was 80 ° C and decomposition began at 130 ° C. Without heating the stabilizer, the polyvinyl chloride starts to decompose at 100 ° C, and decomposes faster at 130 ° C or higher. It is decomposed by heat to release hydrogen chloride gas (hydrogen chloride gas is a toxic gas) to discolor, from white → light yellow → red → brown → black. The ultraviolet rays and oxygen in the sunlight cause photo-oxidative decomposition of the polyvinyl chloride, thereby lowering the flexibility of the polyvinyl chloride and finally becoming brittle. It is not difficult to understand from here why some PVC plastics turn yellow and become brittle after a long time.
It has stable physicochemical properties, is insoluble in water, alcohol, gasoline, and has low gas and water vapor leakage. It can withstand any concentration of hydrochloric acid, 90% or less sulfuric acid, 50-60% nitric acid and 20% or less at normal temperature. The caustic soda solution has certain chemical resistance; it is quite stable to salts, but can be dissolved in organic solvents such as ethers, ketones, chlorinated aliphatic hydrocarbons and aromatic hydrocarbons.
Industrial polyvinyl chloride resin is mainly amorphous structure, but also contains some crystalline regions (about 5%). Therefore, PVC has no obvious melting point, and starts to soften at about 80 °C. The heat distortion temperature (under 1.82 MPa load) is At 70-71 ° C, the flow started at 150 ° C under pressure and began to slowly release hydrogen chloride, causing the polyvinyl chloride to change color (from yellow to red, brown, or even black).
The weight average molecular weight of industrial polyvinyl chloride is in the range of 4.8-4.8 million, and the corresponding number average molecular weight is 2-179,500. The weight average molecular weight of most industrial resins is between 100,000 and 200,000, and the number average molecular weight is between 4.55 and 64,000. Rigid polyvinyl chloride (without plasticizer) has good mechanical strength, weather resistance and flame resistance. It can be used alone as a structural material for chemical processing of pipes, plates and injection molded products. Rigid polyvinyl chloride can be used with reinforcing materials.