| The primary goal of this thesis was to produce low density foams, using different blowing agents, having a density less than 0.3 g/cc of the base resin, a smooth skin, a closed cell structure and without losing more than 50% of the tensile properties as compared to the base resin.;A number of blowing agents is commercially available on the market today. Like all new materials it is important to know what the material's strengths, uses and limitations are. The purpose of this study was to evaluate expandable microballoons and chemical blowing agents as a means to lower the specific gravity of the foamed extrudate. The other variables consisted of changing the barrel temperature profile, the percentage of blowing agent and screw speed.;The different blowing agents lowered the specific gravity of the extrudate to different extents and valuable properties were also obtained. The expandable microballoon results in foams having the lowest density and the smoothest skin surface. Blends of exothermic blowing agent and the expandable microballoon produces foams of acceptable properties. A reverse barrel temperature profile in the produces foams with a good surface finish and a reasonable reduction in density. The strands produced using the blend of blowing agents and a reverse temperature profile gave the broadest processing window. |
