What kinds of plastic properties can be divided into thermal properties?
A. thermoplastic(a) polyvinyl chloride (PVC)Is the most widely used plastic varieties. Polyvinyl chloride resin is made from poly (vinyl chloride) monomer. According to the amount of plasticizer, it is divided into hard PVC and soft PVC. The former adds 30~70 phr of plasticizer <5 in 100 heavy resins, and the latter adds plasticizers.Physical properties: the relative density of hard PVC is 1.35 to 1.60, which is 1 / 5 of carbon steel; the relative density of soft PVC is 1.2 ~ 1.4.The water absorption rate of hard PVC is very low. The water absorption rate in long-term immersion in water is <0.5%; the soaking water is 24h, and the water absorption is 0.05%. The permeability of PVC is very low.The glass state temperature of PVC is 80~85 DEG C, the viscosity is 180 DEG C, the decomposition temperature is 240~260 DEG C (including stabilizer), and the brittleness temperature is -50 ~ -60 DEG C.The recommended temperature range of hard PVC is, in principle, maintained in terms of brittleness and glass temperature. If it is used above 50 degrees, necessary measures should be taken.The pure PVC, without stabilizers, begins to decompose at 150 C, releases hydrogen chloride, and further accelerates its decomposition. It decomposes faster than 180 DEG C. The polyvinyl chloride with the stabilizer decomposes the temperature to 240~260 degrees centigrade, but breaks down hydrogen chloride if used for 220 years. The material changes from dark grey to yellow brown, or even black. Therefore, in welding, we should try to avoid this phenomenon, the linear expansion coefficient of hard polyvinyl chloride is (5~6) X10-5 / DEG, 5-6 times larger than carbon steel. Therefore, when installing polyvinyl chloride pipes, expansion joints or bracing shall be installed to prevent deformation. When polyvinyl chloride is used as lining or bonding with other materials, the peeling phenomenon may be considered when heated.
Residual stress in the process of pressing and forming of pvc. Therefore, when heated, the shrinkage rate is relatively large, the longitudinal direction is about 1% to 6%, and the transverse direction is 1% to 2%, which should be taken into account when cutting down the material.Chemical properties of PVC do not contain active groups on the molecular chain, so they have higher chemical stability.Unplasticized polyvinyl chloride is under 50 degrees; it is capable of corrosion of most acids, bases, salts, in addition to strong oxidizing agents such as fuming sulphuric acid and nitric acid of mass fraction >50%. The concentrated sulfuric acid and nitric acid above 50 DEG C make the polyvinyl chloride first form carboxyl group, and then oxidize and crack to form carbonyl group or aldehyde group, thus being destroyed.
Classification of plastics (100 million nylon)There are many kinds of plastics. There are many kinds of classification methods. They are usually divided into two categories: thermoplastic and thermosetting plastics according to the change of their properties after heating.
