Abstract
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 °C to 90–110 °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.
Highlights
POE has easy processing, good chemical stability, good aging recyclability, and acoustic insulation performance [1,2,3,4], and POE foams are mainly used as cushioning and sealing materials
Zhai et al [8] used batch foaming process to prepare microcellular POE foams blown by supercritical CO2, and found that the increase of POE molecular weight can significantly inhibit the coalescence of bubble and increase cell density during bubble growth, due to increased melt strength
POE foams with different compositions and molecular weights were prepared with cell density range from 6.6 × 106 to 6.2 × 108 and average cell diameter from 4.3 to 57.9 um using supercritical CO2 as a blowing agent
Summary
POE has easy processing, good chemical stability, good aging recyclability, and acoustic insulation performance [1,2,3,4], and POE foams are mainly used as cushioning and sealing materials. The elastomer is in a rubbery state at room temperature and has a low modulus, so that its cells are difficult to resist this negative pressure and the shrinkage will happen It has found the linear shrinkage degree of TPU foam can reach 17–19% [16]. Since the difference in octene content and molecular weight for POE could significantly affect polymer crystallization and mechanical properties as well as cell morphology [8,10], POE foams with different chain structures blown with CO2 should exhibit different shrinking behavior, which has not been reported until now. Commercial POEs with same melting index (MI) but different octene content, or with the same octene content but different molecular weight and melting index, were chosen The effect of their rheological, melting and crystallization, mechanical properties as well as CO2 solubility on cell morphology were systematically investigated, Polymers 2021, 13, 1494. CO2 (purity: 99.99 wt%) was purchased from Air Liquide Co., Ltd. (Shanghai, China)
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