Effects of Nanocrystallization on Surface Migration of Polypropylene/slip Agent Composites in Accelerated Aging

The accelerated thermal aging of plastics causes the migration of additives onto specimen surfaces. This is commonly called the “blooming” or “whitening” phenomenon and has long been an issue in the automotive applications of thermoplastic composites. Still, there is a lack of scientific reports regarding crystallization behavior to our best knowledge. This study investigates the mechanism and characteristics of slip agent migration onto injection-molded composite surfaces depending on the behavior of nanocrystallization with thermal aging and develops a method to evaluate the correlation between the internal and external crystallization size and migration of the composites. Slip agent migration was investigated by increasing the spherulite size of PP/slip agent composites, as measured by X-ray diffraction analysis at different periods. It was found that as the crystalline area increased, the low molecular weight slip agents present in the amorphous region migrated to the specimen surface owing to the absence of interactions with the polymer. In addition, surface elemental analysis, lightness, and roughness confirmed that the slip agents migrated to the surface in accelerated thermal aging conditions. The findings of this work provide a better understanding of the correlation between thermal aging and the migration phenomenon of slip agents on the surfaces of thermoplastic composites. Graphical abstract