In the frame of injection moulding production process not all raw material creates the final products and a waste material is generated (defective and rejected products, cold runners, etc.). This technological waste is very often reused in production, which reduces the final production costs, however, this regrind or regranulated material affects the final properties of the part. The negative impact of recycled material presence depends on the degree of chain cleavage of the polymer macromolecules caused by high temperature load. The deterioration of the product end-use properties does not have to be demonstrated immediately (or in a short time period) after the removal of the part from injection mould. However, the product service life can be dramatically reduced which is simulated in the technical practice as exposure of the product to elevated temperature for prolonged time periods. This paper is focused on experimental methods for detection of heat-damaged recycled material incorporated to the non-filled moulded parts made of polypropylene. For the purpose of the analyses the multipurpose test specimens type A (specified by ISO 3167 standard) were prepared under the conditions defined in ISO 1873-2 and ISO 294-1 standard (melt temperature, mould temperature, injection rate, holding time, cycle time, etc.). Subsequently, the melt was overheated within the injection unit which caused the heat-induced macromolecule cleavage. This material was used for production another specimens that were then grinded and added to the original (virgin) raw material in the wide range of concentrations (from 10 to 100 wt%). These final specimens were analyzed using the physical methods modified for engineering practice to determine morphological, rheological, thermal and physical-mechanical properties of the moulded parts.
Science Journal 