The Influence of the Aging Process on the Change of Selected Strength Properties of Polypropylene Compositions with Mineral Fillers

The goal is to understand the influence of minerals fillers on the course and performance of process of injection molding polypropylene compounds as well as on the mechanical properties of the obtained products. Three types of mineral fillers, derived from post-production waste, were used for testing. It was aluminosilicate (zeolite), fly ash and gypsum powder, all in powder form. The minerals fillers were introduced into the tested PP in a mechanical mixing process prior to the processing. During the injection molding process, inorganic fillers are subject to the same steps as plastic processing, compression, homogenization, transport. Organic fillers used in the injection process were introduced into the processed PP in the amount of 30% by weight. The test stand consists of a screw injection molding machine, Arburg AllRounder 320C. The research on the structure of manufactured materials, mechanical strength, impact resistance and hardness are presented. The laboratory tests of accelerated aging were conducted using an aging chamber. The aging temperature in the heat chamber was set to even amount of 63 oC and irradiance 0,51 W/m2. According to the standard, the aging time has been applied accordingly: 120, 240, 360 h, which conform to degradation at room temperature for 4 month, 8 month and one year. It was found that the type of mineral fillers used did not have a significant influence on the hardness of the surface of the moldings. The changes in hardness shown in the figures are primarily influenced by the properties and type of polymers used during the injection process. During the tests, differences in the mechanical strength of composites for injection molded parts made of PP with mineral fillers were observed. Filling PP with zeolite in the tested value causes a decrease in mechanical strength by an average of 10% from 24 to 21.6 MPa. Different mechanical interactions are shown by flying ash and gypsum powder fillers, increasing mechanical resistance of the composition. Flying ash increases mechanical strength by 30% on average, from 24 to 31.2 MPa. In case of gypsum powder application the resistance of PP composition increases analogically, but on average 20 %, to 29,5 MPa.