Insight into the Influence of Properties of Poly(Ethylene-co-octene) with Different Chain Structures on Their Cell Morphology and Dimensional Stability Foamed by Supercritical CO2

Poly(ethylene-co-octene) (POE) elastomers with different copolymer compositions and molecular weight exhibit quite distinctive foaming behaviors and dimensional stability using supercritical carbon dioxide (CO2) as a blowing agent. As the octene content decreases from 16.54% to 4.48% with constant melting index of 1, both the melting point and crystallinity of POE increase, due to the increase in fraction of ethylene homo-polymerization segment. the foaming window of POE moves to a narrow higher temperature zone from 20-50 degrees C to 90-110 degrees C under 11 Mpa CO2 pressure, and CO2 solubility as well as CO2 desorption rate decrease, so that the average cell diameter becomes larger. POE foams with higher octene content have more serious shrinkage problem due to lower compression modulus, weaker crystal structure and higher CO2 permeability. As POE molecular weight increases at similar octene content, there is little effect on crystallization and CO2 diffusion behavior, the foaming window becomes wider and cell density increases, mainly owing to higher polymer melt strength, the volume shrinkage ratio of their foams is less than 20% because of similar higher polymer modulus. In addition, when the initiate expansion ratio is over 17 times, POE foams with longer and thinner cell wall structures are more prone to shrinkage and recovery during aging process, due to more bending deformation and less compression deformation.

Automated summary

POE elastomers composition and molecular weight affect its foaming behaviors and dimensional stability. Lower octene content leads to higher melting point and crystallinity, resulting in a higher foaming temperature and larger cell diameter under high CO2 pressure.