The shrinkage control of PPplastics is an important aspect of PP modification. Good shrinkage control is of great significance to the popularization and application of PP modified materials. Especially, it is very important to use modified polypropylene to replace traditional engineering plastics.
In the modification process, what factors affect the shrinkage of PP plastics?
One
1, Mineral filling
The mineral additives used in PP modification mainly include calcium carbonate, talcum powder, mica powder, etc., which have obvious influence on the shrinkage of PP plastics.
It is mainly reflected in three aspects
1. The mineral additive itself does not shrink, and its addition reduces the shrinkage of polypropylene modified material from the overall proportion.
2. The addition of mineral additives will inevitably affect the crystallinity of polypropylene, thus affecting the shrinkage.
3. The addition of fine mineral agent can act as a nucleating agent, which changes the structure of polypropylene, the formation of enlarged spherulites and the shrinkage of polypropylene.
Two
2, Glass fiber reinforced
Glass fiber reinforcement is an important means of PP plastic modification, and glass fiber has the greatest impact on the shrinkage of PP modified materials. When the content of glass fiber is more than 30%, the molding shrinkage of PP plastics decreases from 1.8 to 0.5, and the effect of surface treated glass fiber on molding shrinkage is greater than that of untreated glass fiber.
The addition of glass fiber destroys the crystallinity of PP and affects the shrinkage. At the same time, glass fiber limits the crystallization shrinkage of PP.
Three
3, Addition of polyethylene
Polyethylene is also a kind of plastic with high crystallinity, and its molding shrinkage rate is also very large. However, when it is added into polypropylene, the crystallinity of each other is destroyed to some extent, and the overall molding shrinkage is reduced.
4,Change of mi (melt index) of PP plastics
The shrinkage of polypropylene is affected by its crystallinity, which is also affected by its molecular weight. When Mi increases, the molecular weight decreases, the crystallization rate increases and the molding shrinkage increases. The change of MI also has some effect on the shrinkage of PP.
