Processing Conditions of Expandable Graphite in PP and PA Matrix and their Performance

Abstract

Polypropylene (PP) and polyamide (PA) polymers are used in different situations where they provide a flame retarding effect to meet safety standards. The expandable graphite as an additive for polymer materials has a good flame retardant effect and it does not harm the environment. The processing of this additive is presented for those two different polymers. Compounds with proportions of 10, 20, 30% of this additive were prepared in order to investigate the processability and flame retarding effect of PP and PA samples. The results show that the process conditions differ greatly between the polymers used in higher proportions. The improvement of the flame retarding effect was observed for both polymer compounds with expandable graphite. The plastics flammability standard UL 94 V0 could be achieved for the PP compound in all additive proportions and for the PA compounds only above 20%. The processing of the PP compound with co-rotating twin-screw extruder and an injection moulding machine takes place works well and provides a good homogenous mixture. The PA compound could not be processed at a higher additive content by the extruder. Special screw configuration is necessary to process this polymer compound. Also the flame retardant effect was inferior to the PP compound. The mechanical properties of the compounds decrease with the increasing additive content, particularly the impact strength of the samples.