Shrinkage control of PP plastic is an important aspect of PP modification, good shrinkage control/control is of great significance to promotion and use of polypropylene modified materials. Especially when using modified polypropylene to replace traditional engineering plastics, shrinkage is very important. In modification process, what are factors that affect shrinkage of PP plastic?

Mineral additives used for PP plastic modification mainly include calcium carbonate, talc powder, mica powder, etc., which have a significant impact on molding shrinkage rate of PP plastics.
It is mainly reflected in three aspects: one is that mineral filler itself does not shrink, its addition reduces shrinkage rate of polypropylene modified material from overall ratio; second is that addition of mineral additives will inevitably affect crystallinity of polypropylene, thereby affecting shrinkage rate; third, after addition of fine mineral agent, it acts as a nucleating agent, changing structure of polypropylene, formation of enlarged spherulites, and also affecting molding shrinkage rate of polypropylene.

Glass fiber reinforcement is an important means of PP plastic modification, and glass fiber has the greatest impact on molding shrinkage of PP modified materials. When content of glass fiber reaches more than 30%, molding shrinkage rate of PP plastic decreases from 1.8 to 0.5, surface-treated glass fiber has a greater impact on molding shrinkage rate than untreated glass fiber.
Addition of glass fiber destroys crystallinity of PP and affects shrinkage rate. At the same time, glass fiber limits crystal shrinkage of PP plastic.

Polyethylene is also a kind of high crystallinity plastic, and its molding shrinkage rate is also very large. However, after being added to polypropylene, crystallinity of each other is destroyed to different degrees, which reduces overall molding shrinkage rate.

Molding shrinkage rate of polypropylene is affected by its crystallinity, and crystallinity is affected by its own molecular weight. When MI increases, molecular weight decreases, its crystallization speed increases, and molding shrinkage increases. Change of polypropylene MI also has a certain effect on molding shrinkage.