Stress and Optical Behavior of Polymers under Supercritical Carbon Dioxide

我们设计了一套拉伸试验系统，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，在超临界二氧化碳中，高密度聚乙烯的应力和模量比在常压空气中低。应力和模量的降低归因于二氧化碳在非晶区的增塑作用。由于在片层堆叠体通过伸长旋转之后片层堆叠体之间的距离变宽，并且二氧化碳没有溶解到片层堆叠体中的结晶区域中，因此在超临界二氧化碳下的机械性质的变化可能归因于由于片层堆叠体或片层之间的非晶区域中的链密度的降低而引起的片层的变形。结果表明，当压力高于5 MPa时，随着CO2压力的增加，无定形聚碳酸酯由韧性向脆性转变;当温度较低时，CO2溶解使无定形聚碳酸酯的应力降低，断裂应变增加。

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.