超临界CO_2发泡工艺对聚乳酸微孔纳米复合材料泡孔结构的影响

Effects of Supercritical Carbon Dioxide Foaming Process on the Microcellular Morphology of Polylactic Acid Microcellular Nanocomposites

利用超临界CO_2作为物理发泡剂,采用高压釜间歇发泡法,制备了聚乳酸/聚丁二酸丁二醇酯/氧化锌(PLA/PBS/ZnO)微孔纳米复合材料,研究了超临界CO_2微孔发泡过程中,发泡温度、保压压力和释压速率对PLA/PBS/ZnO微孔纳米复合材料泡孔结构的影响。结果表明:发泡温度对微孔纳米复合材料泡孔结构的影响显著且与纳米复合材料熔体强度密切相关,温度相对过高或过低,都会引起聚合物熔体强度和表面张力的变化而导致无法得到均匀密集的泡孔,当体系的发泡温度为90℃时,复合材料的泡孔平均直径最小,泡孔密度最大,泡孔尺寸分布最集中;保压压力对泡孔结构的影响体现在超临界CO_2的溶解度和发泡体系的黏度上,保压压力较低时得到的泡孔平均尺寸较大且分布不均匀,当保压压力为16 MPa时,复合材料的泡孔平均直径最小,泡孔密度最大,泡孔尺寸分布最集中;释压速率决定着发泡初始阶段的成核效率,随着释压速率的升高,复合材料的泡孔平均直径减小,泡孔密度显著增大,泡孔数量增多且尺寸分布更集中。

Using supercritical carbon dioxide(CO2)as the physical foaming agent,polylactic acid/poly(butylenesuccinate)/zinc oxide(PLA/PBS/ZnO)microcellular nanocomposites were prepared by batch foaming method.Theeffects of foaming temperature,holding pressure and depressurization rate on the microcellular morphology of PLA/PBS/ZnO microcellular nanocomposites during the supercritical CO2microcellular foaming process were investigated.The results showed that the influence of foaming temperature on the microcellular morphology was mainly reflectedin the melt strength.With the foaming temperature being too high or too low,well-distributed and dense microcellularcould not be formed due to the change of the melt viscosity and surface tension.With the foaming temperature ataround90℃,the minimum average cell diameter,the maximum cell density,and the most concentrated distributionof microcellular were achieved.The effect of holding pressure on the microcellular morphology was confined to thesolubility of the supercritical CO2and the viscosity of foaming system.When holding pressure was too low,the largesize and uneven distribution in microcellular were resulted.With the holding pressure being around16MPa,themaximum cell density,and the most concentrated distribution in microcellular were achieved.Depressurization ratedetermined the nucleation efficiency at the initial stage of foaming process.With the increase in depressurization rate,the average cell diameter decreased,while the cell density increased,with the increase in the number of cells,and moreconcentrated size distribution.