Gradual degradation of high temperature resistant foam: […]
Gradual degradation of high temperature resistant foam:
This degradation is mainly at the high temperature of processing, and the foamed polymer contains trace moisture, acid or alkali, etc. for selective degradation. The degradation generally occurs at the carbon-heterochain. This is because the carbon-heterochain bond can The reason is small and poor stability. Degradation has the characteristics of a gradual reaction, each step is independent, the intermediate product is stable, and the chance of chain scission increases with the increase of molecular weight, so as the degradation reaction progresses gradually, while the molecular weight of the polymer gradually decreases, its The molecular weight dispersion also gradually decreases.
The higher the temperature, the faster the degradation; the longer the residence time at high temperature, the more severe the degradation. There is often oxygen in the processing process. Oxygen can oxidize the polymer to form a peroxide structure at high temperature. The peroxide is easily decomposed to generate free radicals, which triggers a chain degradation reaction, called thermal oxygen degradation, which mainly degrades the polymer. course.
During the processing, the polymer is subjected to repeated stress. When the energy of the shear stress exceeds the bond energy, it will cause the chemical bond to break and cause degradation. The shearing effect and the heat effect together play a strong role in promoting the degradation of high temperature resistant foam. Trace moisture is the main factor for the degradation of some polymers, such as PC, nylon, ABS, polyester and so on. Therefore, drying before processing is a necessary process.