Effect of Unexpected CO2’s Phase Transition on the High-Pressure Differential Scanning Calorimetry Performance of Various Polymers

详细信息    查看全文

• 作者：Erbo Huang ; Xia Liao ; Chongxiang Zhao ; Chul B. Park ; Qi Yang ; Guangxian Li
• 刊名：ACS Sustainable Chemistry & Engineering
• 出版年：2016
• 出版时间：March 7, 2016
• 年：2016
• 卷：4
• 期：3
• 页码：1810-1818
• 全文大小：601K
• ISSN：2168-0485

文摘

We used a high-pressure differential scanning calorimeter (HP-DSC) to study polymer plasticization by compressed gases at pressures of up to 30 MPa for polylactide (PLA), polycarbonate (PC), isotactic polypropylene (iPP), and polystyrene (PS). The pressure reached values twice as high as the previously published data. We found that the polymer/carbon dioxide (CO₂) system’s heating curves have an unidentified endothermic peak above 5 MPa, which turns out to be from CO₂’s phase transition. The HP-DSC could accurately determine the depression of the glass transition temperature (T_g), crystallization temperature (T_c), and melting temperature (T_m) of various polymers at low pressures by simply starting at a higher temperature to avoid CO₂’s phase transition; however, the increased plasticization effect of the dissolved CO₂ lowered the T_g to the level of overlapping with CO₂’s phase transition phenomena at elevated pressures, and therefore, the depressed T_g could not be measured above 6 MPa for PLA, PC, or PS. On the other hand, the T_c of iPP decreased with an increase in pressure, whereas T_m values of PLA and iPP decreased slightly with an increase in pressure and then remained almost unchanged above a certain pressure, which may indicate an increased hydrostatic pressure effect at elevated pressures.