The white substance on the surface of TPE/TPR products is small molecules caused by migration and precipitation.
Sometimes, certain low molecular weight additives, such as brighteners, releasing agents, may be added into the modification process of TPE/TPR products. Owing to the poor compatibility with substrates, these additives are generally added by 2~3‰. If excessive additives are added, the migration of small molecules will occur as time goes by.
The temperature is high while blending and modifying TPE/TPR. Hence, the additives show relatively even dispersed state (unstable) in the blending system. As time goes by, the oversaturated additives will migrate to the surface of TPE/TPR products owing to the low solubility of low molecular weight additives in the blending system. In daily life, we may find white substance exists on the surface of TPE/TPR finished products after a period of time, which can be rubbed off by hand. This is the migration of excessive low molecular weight additives.
Acidification, frosting, whitening and other phenomena commonly found in the production of TPE/TPR products are all caused by the migration of constituents that have poor compatibility in the blending system.
As a result, the amount of added additives with low solubility should be strictly controlled in the modification process, to prevent TPE/TPR products from consequent migration. In the actual production process, the migration of additives also occur in other modified engineering plastics and rubber products in addition to TPE/TPR products.
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