Supercritical CO2 Foaming of Lightweight Polyolefin Elastomer/trans-Polyoctylene Rubber Composite Foams with Extra-Soft and Anti-Shrinkage Performance

Lightweight polyolefin elastomer (POE) foams are of great interest in numerous fields. However, POE is difficult to foaming and obtaining the ideal cellular structures before cross-linking. Herein, low-molecular-weight trans-polyoctylene rubber (TOR) with lots of double bonds and low molecular weight was introduced into the POE matrix to improve their vulcanizing and foaming process. Then, a series of lightweight POE/TOR composite foams with adjustable cellular structures and outstanding performance were prepared by supercritical CO2 foaming. It was worth noting that the gel content and foaming temperature windows were greatly improved under the action of TOR, and a record-breaking density as low as 0.036 g/cm3 for POE-based composite foams was harvested. In addition, the as-prepared elastomer foams exhibited rapid shrinkage but slow recovery feature due to the diffusivity difference of gas and cross-linking nature of materials, and its recovery ratio could reach 91.3%. More interestingly, the conversion law of the corresponding density change between hard and soft materials was discovered, and extra-soft POE-based composite foams (like Shore C below 10) were obtained, which could be twisted, folded, compressed, stretched, bent, and rolled with ease. Furthermore, the residual strain and hysteresis loss ratio of as-prepared elastomer foams were as low as 1.56 and 12.95%, respectively. These distinct advantages together with the green foaming process make the composite elastomer foams very promising toward high-performance flexible cellular polymeric materials.

Automated summary

In this study, low-molecular-weight trans-polyoctylene rubber (TOR) was introduced into the POE matrix to improve its vulcanizing and foaming process, and a series of lightweight POE/TOR composite foams with adjustable cellular structures and outstanding performance were prepared. These foams have potential applications as high-performance flexible cellular polymeric materials due to their extremely low density and excellent properties.