Material design of high performance polypropylene containing nucleating agent pp.1043-1058
Authors: (Masayuki Yamaguchi, School of Materials Science, Japan Advanced Institute of Science and Technology, Japan)
Abstract: High performance isotactic polypropylene (PP) is designed by using novel types of nucleating agents with processing techniques. Specific sorbitol derivatives which act as an α-form nucleating agent are dissolved into a molten PP and appear as nanofibers by self-organization during cooling process. Fine dispersion of the nanofiber leads to no spherulite texture or small size of spherulites. Consequently, the products exhibit high level of transparency. Further, thin plaques produced by injection-molding show marked transparency as compared with compression-molded ones for PP containing the sorbitol derivatives. Detailed characterization revealed that enhanced molecular orientation in the skin layer is responsible for the reduction of light scattering. The aggregation state of the sorbitol derivative, which can be controlled by applied flow field and thermal history, also affects the crystalline texture of PP and thus the transparency. When injection-molded products having the nanofibers of the sorbitol derivative are reprocessed at 180 ºC, i.e., lower temperature than the dissolution temperature of the sorbitol derivative, transparent products are obtained, although it has been believed that sorbitol derivatives have to be melted and dissolved into a molten PP at high temperature, e.g., 240 ºC.