Four factors affecting the shrinkage of modified PP Material
Control of the shrinkage of PP plastic is an important aspect of PP modification. Good shrinkage control / manufacturing has great significance for the promotion and use of polypropylene modified materials. Especially the application of modified polypropylene to replace traditional engineering plastics, the shrinkage rate is very important. What are the factors that affect the shrinkage of PP plastics during the modification process?
I. Mineral filling
The mineral additives used in the modification of PP plastics are mainly calcium carbonate, talc, mica powder, etc., which have a significant effect on the shrinkage of PP plastics.
It is mainly reflected in three aspects: one is that the mineral additive itself does not shrink, and its addition reduces the shrinkage rate of the polypropylene modified material as a whole; the second is that the addition of the mineral additive necessarily affects the crystallinity of polypropylene , Which affects the shrinkage rate; third, after the addition of fine mineral agents, it acts as a nucleating agent, changing the structural state of polypropylene, the formation of enlarged spherulites, and also affecting the shrinkage rate of polypropylene molding.
Glass fiber reinforced
Glass fiber reinforcement is an important method for the modification of PP plastics. Glass fiber has the greatest influence on the shrinkage of PP modified materials. When the glass fiber content reaches 30% or more, the molding shrinkage of PP plastic decreases from 1.8 to 0.5, and the surface-treated glass fiber has a greater impact on the molding shrinkage than the glass fiber without treatment.
The addition of glass fiber destroys the crystallinity of PP and affects the shrinkage rate. At the same time, glass fiber limits the crystal shrinkage of PP plastic.
Third, the addition of polyethylene
Polyethylene is also a high crystallinity plastic, and the molding shrinkage is also very large, but after adding polypropylene to each other, they destroy the crystallinity to a different degree, which reduces the overall molding shrinkage.
Fourth, the change of the MI (melt index) of PP plastic itself
The molding shrinkage of polypropylene is affected by its crystallinity, and the crystallinity is affected by its own molecular weight. When MI increases, molecular weight decreases, crystallization speed increases, and mold shrinkage increases. The change of polypropylene MI also has a certain effect on the molding shrinkage.