Four factors affecting the shrinkage of modified PP plastics

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

1. Mineral filling

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

2. Glass fiber reinforced

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

Three, the addition of polyethylene

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

Fourth, the change of PP plastic's MI (melt index)

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