The shrinkage rate control of PP plastic is an important aspect of PP modification. Controlling the shrinkage rate is very important for the promotion and use of PP modified materials. In particular, the use of modified PP to replace traditional engineering plastics, shrinkage is particularly important. What are the factors affecting the shrinkage of modified PP plastics during the modification process?
First, mineral filling
The mineral additives for PP plastic modification mainly include calcium carbonate, talc powder and mica powder, which have obvious effects on the shrinkage of PP plastics. Mainly reflected in three aspects: First, the mineral filler itself does not shrink, its addition reduces the shrinkage of the polypropylene modified material from the overall proportion; second, the addition of mineral fillers will inevitably affect the crystallinity of polypropylene Therefore, the shrinkage rate is affected; thirdly, after the fine mineral agent is added, it acts as a nucleating agent, changes the structural state of the polypropylene, and the formation of the enlarged spherulites also affects the molding shrinkage rate of the polypropylene.
Second, glass fiber reinforcement
Glass fiber reinforced is an important means of PP plastic modification. Glass fiber has the greatest influence on the molding shrinkage of PP modified materials. When the content of the glass fiber reaches 30% or more, the molding shrinkage of the PP plastic decreases from 1.8 to 0.5, and the surface-treated glass fiber has a greater influence on the molding shrinkage than the untreated glass fiber. The addition of glass fiber destroys the crystallinity of PP and affects its shrinkage. 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 rate is also large. However, after being added to the polypropylene, the respective crystallinity is destroyed to different degrees, and the overall molding shrinkage rate is lowered.
4. Changes in PP plastic's own MI (melt index)
The molding shrinkage of polypropylene is affected by its crystallinity, which in turn is affected by its own molecular weight. When MI is increased, the molecular weight is decreased, the crystallization rate is increased, and the molding shrinkage rate is increased. When the polypropylene MI changes, it also has a certain influence on the molding shrinkage rate.
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