Rheological Characteristics of Compact of Plastic Powders

Abstract

Powdered polystyrene was compacted into the specimens having various void fractions at 100°C. In order to compare with these compaction-molded specimens, injection-molded specimens having no void were prepared too. The rheological characteristics of these specimens were examined by the vibration test method, that is, the temperature dependences of dynamic storage modulus E' and dynamic loss modulus E" were investigated. The results obtained were summarized as follows:
(1) The value of E' was found to increase with decreasing void fraction at various temperatures, which was mainly attributable to the effect of void volume.
(2) Glass transition temperature T_g, which corresponded with the temperature where the value of E" took the maximum, was found to rise with decreasing void fraction.
(3) The values of E' and T_g of the compaction-molded specimens having the least void fraction were different from those of the injection-molded specimens, because both differed in the history of heat and strain.
(4) From the results of temperature and frequency dependences of E" at 95∼100°C, the relaxation mechanism of polystyrene powder compact was presumed not only to be dominated by the response of polymer segments but also to be influenced by the macroscopic mechanism due to the unstematic strain recovery of predeformed particles.