Views:223 Author:Site Editor Publish Time: 2020-03-16 Origin:Site
PVC is thermally degraded in air, and the commonly used melt index cannot be used to characterize the molecular weight of polymers. In practice, it is expressed by the relative viscosity K value, which is measured by the ratio of the viscosity of the diluted polymer solution to the pure solution. The K value increases with the increase of relative molecular weight. The K value of industrially produced PVC is generally 50 ~ 70.
PVC contains a lot of highly polar chlorine atoms in the molecule, which increases the intermolecular force, so it has higher mechanical strength and hardness than polyolefin. Mechanical strength is related to molecular weight, plasticizer variety and quantity, and external conditions. Generally, as the molecular weight increases, the tensile strength and elongation at break increase. When the molecular weight reaches a certain value, the increase is not obvious. With the addition of plasticizers, the mechanical properties of PVC can vary over a wide range. PVC is divided into hard and soft according to the amount of addition. Generally, the content of hard PVC plasticizer is less than 5 parts, and the content of soft PVC is more than 25 parts. Rigid PVC has high tensile strength, low elongation at break and impact strength, indicating poor toughness. Therefore, toughening is an important issue for modified PVC, while soft PVC has lower tensile strength and Higher elongation at break indicates higher toughness and elastomeric properties. The hardness of hard and soft PVC varies widely.
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