Optimizing the blending ratio and processing parameters for ternary blends of recycled polypropylene with recycled high and virgin linear low-densities polyethylene

Abstract

The thermoplastic polymer of polypropylene (PP) is employed in many different applications. A huge amount of PP waste is produced by using its discarded parts. Recycled polypropylene (rPP) does not provide virgin properties and further reuse causes more loss of properties. This study investigates experimentally the effect of adding different ratios of recycled high-density polyethylene (rHDPE) and virgin linear low-density polyethylene (vLLDPE) with different process variables on the rPP's tensile strength. The most significant injection factors of melt temperature, injection pressure, holding pressure, holding time, and cooling time with the ternary blend ratio were proposed with three levels. Also, three different compositions of I, II and III with 85/12/3, 85/3/12, and 85/8/7 wt percent are considered respectively to the levels of the rPP/rHDPE/vLLDPE blend. Accordingly, 18 experiments are designed based on Taguchi's orthogonal array (OA) of L18. An injection molding die is designed and manufactured to produce tensile test samples. Scanning electron microscopic (SEM) is applied to show the microstructure of the blends. The response data of ultimate tensile stress are transmitted to signal-to-noise ratio (S/N) to facilitate their analysis by analysis of variance (ANOVA). Finally, the optimum set of parameters that provides the optimal blend with the highest ultimate stress of 21.62 MPa was defined. Additionally, according to the P-values the most significant parameters are holding pressure, injection pressure, and cooling time, respectively.