The methyl group is arranged on the same side of the ma […]
The methyl group is arranged on the same side of the main chain of the molecule as isotactic polypropylene. If the methyl groups are disorderly arranged on both sides of the main chain of the molecule, it is called atactic polypropylene. When the methyl groups are alternately arranged on both sides of the molecular main chain, Gauge polypropylene. In general industrial production of polypropylene resin, the isotactic structure content is about 95%, and the rest is random or syndiotactic polypropylene. Industrial products are based on isotactic substances. Polypropylene also includes copolymers of propylene and a small amount of ethylene. Usually a translucent, colorless solid, odorless and non-toxic. The melting point can be as high as 167 ° C due to the high degree of crystallisation due to structural regularity. Heat-resistant, corrosion-resistant, steam-sterilizable products are its outstanding advantages. The low density is the lightest general purpose plastic. The disadvantage is that it is poor in low temperature impact resistance and easy to age, but can be overcome by modification.
The copolymer type PP material has a lower heat distortion temperature (100 ° C), low transparency, low gloss, low rigidity, but has stronger impact strength, and the impact strength of PP increases as the ethylene content increases. . The Vicat softening temperature of PP is 150 °C. Due to the high degree of crystallinity, this material has excellent surface stiffness and scratch resistance. There is no environmental stress cracking problem in PP.
The melt mass flow rate (MFR) of PP is usually from 1 to 100. Low MFR PP materials have better impact resistance but lower elongation. For materials of the same MFR, the impact strength of the copolymerization type is higher than that of the homopolymer type. Due to crystallization, the shrinkage rate of PP is quite high, generally 1.6 to 2.0%.
Non-toxic, odorless, low density, strength, stiffness, hardness and heat resistance are better than low-pressure polyethylene, can be used at around 100 °C. It has good dielectric properties and high-frequency insulation and is not affected by humidity, but becomes brittle at low temperature, not wear-resistant and easy to age. Suitable for making general mechanical parts, corrosion resistant parts and insulating parts. Common organic solvents such as acids and bases have little effect on it and can be used in food utensils.
Polypropylene has many excellent properties:
1. The relative density is small, only 0.89-0.91, which is one of the lightest varieties in plastics.
2, good mechanical properties, in addition to impact resistance, other mechanical properties are better than polyethylene, molding processing performance is good.
3. It has high heat resistance and the continuous use temperature can reach 110-120 °C.
4, good chemical properties, almost no water absorption, and does not react with most chemicals.
5, the texture is pure, non-toxic.
6, electrical insulation is good.
7. The transparency of polypropylene products is better than that of high density polyethylene products.