A study of foam extrusion using a chemical blowing agent



An experimental study of foam extrusion was carried out to determine the effect of processing variables on the quality of the foam produced. For the study, the chemical blowing agent azodicarbonamide was used, together with an activator and a nucleating agent, to produce thermoplastic foams of low-density polyethylenes. The quality of foam was determined from photomicrographs and the tensile properties of extrudate samples. It was found that the percent elongation correlates with the foam density and that the cell structure (cell size and its distribution) correlates with the ultimate tensile properties of the foam produced. Also, an experimental study was carried out to observe the growth of gas bubbles as the polymer melt containing a blowing agent flows through a rectangular channel constructed of quartz. This experiment helped us to interpret the curved pressure profile of the polymer melt containing a blowing agent as the melt approaches the die exit, whereas the polymer without a blowing agent shows a linear pressure profile.