In this study, carbon dioxide was used as a foaming agent for common
plastics, such as acrylonitrile–butadiene–styrene (ABS) polymer, polystyrene (PS),
polypropylene (PP), high-density polyethylene (HDPE), and high impact polystyrene
(HIPS). Carbon dioxide was first absorbed by the sample plastics placed within
a pressure vessel at various pressure levels and absorption time intervals. The
Henry’s constant of the absorbed carbon dioxide in the plastics was determined. The
diffusion coefficient of carbon dioxide in polymer was also identified by curve-
fitting with the relationship between the absorbed amount and time. The results
showed that ABS, PS, and HIPS absorbed more gas than did PP and HDPE, because
PP and HDPE exhibit higher crystallinity. Generally, a polymer can take up saturation
absorption of gas under higher pressure. After absorption, the foaming process
occurred at various temperatures and time intervals. The cell structure, density,
and size of the plastic foams were then investigated using scanning electron
microscopy. A longer foaming period and higher temperature increase the size of
the cell and decrease the cell density (the number of bubbles per unit volume). A
dense skin layer without bubbles appeared directly adjacent to the surface of the
foamed plastics. Its thickness decreased if the foaming process took place at higher
temperatures.
關聯:
Research on Chemical Intermediates 40(6), pp.2259-2269
