Intellectual Textile Systems Research Center (ITRC) and RIAM School of Materials Science and Engineering, College of Engineering, Seoul National University, Shillim9dong 56-1, Kwanakku, Seoul, 151-744, Korea.
Phys Chem Chem Phys. 2013 Jul 14;15(26):11061-9. doi: 10.1039/c3cp51068a. Epub 2013 May 29.
For the preparation of nanocomposites, we conducted environmentally benign foaming processing on polypropylene (PP) copolymer/clay nanocomposites via a batch process in an autoclave. We investigated the dispersion and the exfoliation of the nanoclay particles. Full exfoliation was achieved by the foamability of the matrix PP copolymer using supercritical carbon dioxide (sc CO2) and subcritical carbon dioxide (sub CO2). More and smaller cells were observed when the clay was blended as heterogeneous nuclei and sc CO2 was used. Small angle X-ray scattering showed that highly dispersed states (exfoliation) of the clay particles were obtained by the foaming process. Since the clay particles provided more nucleating sites for the foaming of the polymer, a well dispersed (or fully exfoliated) nanocomposite exhibited a higher cell density and a smaller cell size at the same clay particle concentration. Expansion of the adsorbed CO2 facilitated the exfoliation of the clay platelets; thus, sc CO2 at lower temperature was more efficient for uniform foaming-cell production. Fully dispersed clay platelets were, however, re-aggregated when subjected to a further melting processing. The reprocessed nanocomposites still had some exfoliated platelets as well as some aggregated intercalates. The dual role of the nanoclay particles as foaming nucleus and a crystallization nucleus was confirmed by cell growth observation and nonisothermal crystallization kinetics analysis. A low foaming temperature and a high saturation pressure were more favorable for obtaining a uniform foam. The PP copolymer was found to be foamed more easily than polypropylene. A small amount of other olefin moieties in the backbone of the polymer facilitated better foamability than the neat polypropylene.
为了制备纳米复合材料，我们通过高压釜中的间歇过程对聚丙烯共聚物/粘土纳米复合材料进行了环境友好的发泡处理。我们研究了纳米粘土颗粒的分散和剥离情况。通过使用超临界二氧化碳（scCO2）和亚临界二氧化碳（subCO2）使基质聚丙烯共聚物具有可发泡性，实现了完全剥离。当将粘土作为异质核并使用 scCO2 混合时，观察到更多和更小的孔。小角度 X 射线散射表明，通过发泡过程获得了粘土颗粒的高度分散状态（剥离）。由于粘土颗粒为聚合物的发泡提供了更多的成核位点，因此在相同的粘土颗粒浓度下，分散良好（或完全剥离）的纳米复合材料表现出更高的细胞密度和更小的细胞尺寸。吸附的 CO2 的膨胀促进了粘土片层的剥离；因此，在较低温度下使用 scCO2 更有利于均匀发泡细胞的生产。然而，当经受进一步的熔融加工时，完全分散的粘土片层会重新聚集。重新加工的纳米复合材料仍然具有一些剥离的片层以及一些聚集的插层。纳米粘土颗粒作为成核剂和结晶核的双重作用通过孔生长观察和非等温结晶动力学分析得到证实。较低的发泡温度和较高的饱和压力更有利于获得均匀的泡沫。发现聚丙烯共聚物比聚丙烯更容易发泡。聚合物主链中少量的其他烯烃部分比纯聚丙烯具有更好的可发泡性。
