Stress and Optical Behavior of Polymers under Supercritical Carbon Dioxide

我们设计了一套拉伸测试系统，可以测量聚合物薄膜在超临界二氧化碳条件下拉伸过程中的应力-应变行为。结果表明，高密度聚乙烯在超临界二氧化碳中的应力和弹性模量低于常压空气中的应力和模数。应力和弹性模量的降低归因于二氧化碳在非晶区的塑化作用。由于拉伸旋转后片层之间的距离变宽，且二氧化碳不会溶解到片层中的结晶区，因此，超临界二氧化碳下力学性能的变化可能是由于片层间或片层之间非晶区的链密度降低而引起的片层的变形。在5 Mpa以上的高压下，随着二氧化碳压力的增加，无定形聚合物聚碳酸酯由韧性转变为脆性，而在较低温度下溶解二氧化碳，其应力降低，断裂应变增大。

We designed a tensile testing system in which we can measure the stress-strain behavior of polymer films during the elongation under supercritical carbon dioxide. The stress and modulus of high density polyethylene were found to be lowered under supercritical carbon dioxide than that under air at ambient pressure. The decrease of stress and modulus is attributed to the plasticization effect of carbon dioxide in the amorphous region. Since the distance between the lamellar stack becomes wider after the rotation of the lamellar stack by elongation and the carbon dioxide is not dissolved into the crystalline region in the lamellar stacks, the change in the mechanical property under supercritical carbon dioxide might be attributed to the deformation of lamellae due to the decrease of the chain density in the amorphous region between the lamellar stack or lamellae. The amorphous polymer polycarbonate was found to be changed from ductile to brittle with increasing the pressure of carbon dioxide at high pressure above 5 MPa, while the stress decreased and the strain at break increased by dissolving carbon dioxide at lower temperature.