| Two high temperature exothermic chemical blowing agents, polyphenylene sulfoxide (PPSO) and a modified azodicarbonamide (M-Az) were evaluated for their ability to produce structural foams from three glass-filled semi-crystalline materials, polyphenylene sulfide (PPS), polybutylene terephthalate (PBT), and nylon-6,6. The polyphenylene sulfoxide was far better suited to high temperature foams and gave an ideal density reduction in PPS foams when the concentration was 2%. While the modified azodicarbonamide was incompatible with PPS, it produced acceptable foaming with nylon-6,6 and PBT. The maximum viable concentrations of 0.5 and 1.5% provided a less-than-ideal density reductions and higher loadings produced excessive drooling.; The tensile and flexural properties of the resultant foams were entirely dependent on part density reduction, but Izod impact resistance remained constant, suggesting that glass fiber content controlled impact resistance in these foams. Since PPSO-foamed PPS produced a more uniform cell structure and fewer voids, the foams exhibited better mechanical properties than the M-Az-foamed PBT. |
