Modified Polypropylene Microcellular Foaming And Cell Morphology Control Study

Nano-TiO2 and bamboo fiber were added into the bulk of PP to increase its mechanic property. The diffusity and solibility of CO2 in polymer were investigated in this paper. Microcellular plastics were manufactured which blown with supercritical CO2 during rapid pressure reduction process. The main experiment results and conclusions are as follows:1. The content of nano-TiO2 affects the crystallinity of PP significantly. As nano-TiO2 content increased from 0wt% to 5wt%, the crystallinity of PP firstly increased, and then decreased.Meanwhile, the micro-structure and the sensile strength of PP blended with bamboo fiber have been charetertied by the SEM and universal testing machine. Results show uniformity to improve the mechanical properties.2. The diffusity and solibility of CO2 in polymer obey the Fick law. The trend of Ms of CO2 firstly decreased, and then increased as TiO2 content from 0 wt% to 5wt%. However, for the bamboo fiber/PP, the Ms of CO2 increased as bamboo fiber content from 0 wt% to 50 wt%. The effects of sorption time, temperature and pressure on Ms of CO2 were studied by gravimetric method. The mechanism of the sorption and desorption of supercritical CO2 in the nano-TiO2/PP and bamboo fiber/PP were also discussed. In order to improve the Ms of CO2 in bamboo fiber/PP, SC-CO2/alcohol were used.3. With the increase of nano-TiO2 conten, the cell diameter reduced and the cell density increased, the cell distribution was uniformly. For nano-TiO2 content for nano-TiO2 (3wt%) /PP materials, when the saturation pressure increased, both the cell diameter and the cell density increased. The cell diameter increased and the cell density decreased with the elevated temperature. However, for the bamboo fiber/PP, bamboo fiber content is less than 30% which can improve the foaming behaviors of PP, with the bamboo fiber content increasing, the cell density increased, and the cell distribution was more uniform. It is impossible for PP to be foamed when the bamboo fiber content is up to 50%. Both the cell diameter and the cell density increased when the saturation pressure increased in bamboo fiber(30wt%)/PP. However, the cell will became thin, and also, few cell combined at 25MPa. The cell diameter increased and the cell density decreased with the elevated temperature. As temperature rised from 175℃to 190℃, the cell diameter increased, the cell density decreased. Compared with using SC-CO2, in SC-CO2/ethanol, bamboo fiber (30wt%)/PP foaming materal has gigger cell diameter, less cell density, a few cell combined.