Feasibility study of recycled polypropylene through multi response optimization of injection moulding parameters using grey relational analysis

Abstract

The present investigation is aimed at the feasibility of recyclability of polypropylene (PP) in injection moulding based on grey relational analysis. According to ISO 15270:2008, the recommended percentage of recyclability is maintained upto 25% by weight depending upon requirements. To qualify the products made up of polypropylene, besides rudimentary tensile strength at break and percentage elongation at break [ASTM: D638-03]; density [ASTM: D-792] and VSP (Vicat Softening Point) [ASTM: D-1525] were also considered, which are also very much needed to qualify products made up of PP. Virgin to recycled material ratio (V:R), injection pressure (IP), injection temperature (IT) and injection speed (IS) were the parameters dictating the product's quality and they all were taken at three levels. A Box-Behnken model of design of experiment was adopted to reduce the numbers of experiments instead of adopting full factorial layout. The raw material used for the experiments was Injection Grade Polypropylene Homomer (Grade: M-110) manufactured by M/s Haldia Petrochemicals Ltd. The specimens for the optimization were made as per ASTM-D 638-03-TYPE-I. To ascertain tensile strength and elongation at break, Universal Testing Machine (H100KS-0081) made by Hounsfield Test Equipment was used. VSP was determined by using microprocessor controlled HDT/VSP apparatus (model-MP3 Eod100/002, 20008305), made by Atsfaar, Italy. Density of PP sample is measured by using Dhona (200D, 29048). Grey Entropy method was adopted to ascertain the weights of the responses. It has been found that the V:R-1-IT-1-IP-1-IV+1 yielded for the best quality product. Confirmatory tests were conducted to adjudge the response qualities. In abreast the authors conducted another experiment with 100% virgin material at IT-1-IP-1-IV+1 and they found upto 5% recycle material adulteration gives the similar response characteristics.