Ali Bakhshi - Department of Chemical Engineering, Polymer group, Isfahan University of Technology,Isfahan ۸۴۱۵۶-۸۳۱۱۱, Iran
Mahmood Masoomi
Rohollah Bagheri - Department of Chemical Engineering, Polymer group, Isfahan University of Technology

In this study, blends of virgin polypropylene (PP) and recycled PP used in lead-acid battery cases at various weight ratios were prepared by a single screw extruder. Melt flow index (MFI) and carbonyl index were measured for evaluation of the changes in chemical structure of the blends during the extrusion process. Oxidative induction time (OIT), was also tested to determine the thermal resistance of the samples. Mechanical properties of the samples were studied by tensile and charpy impact tests. To stabilize the compounds during the extrusion process, combinations of a phenolic (Primary Antioxidant, P-AO) and phosphite (Secondary Antioxidant, S-AO) thermal stabilizers with a metal deactivator (Calcium Stearate, CaSt) were used. An optimum composition of stabilizers in the 40:60 (virgin: recycled) PP blend was obtained by using the Taguchi method design of experiments (DOE). This optimum combination of stabilizers was 1 wt% P-AO, 0.2 wt% S-AO, and 0.5 wt% CaSt. In addition, DOE results showed that the primary antioxidant has the biggest influence on stabilization of PP during the extrusion process. Measurement of OIT parameter of the samples containing optimum combination of stabilizers proved that the thermal resistance of these samples was better than the virgin PP. Carbonyl index measurements of these blends indicated that a little degradation occurred in the extrusion process. The results of impact tests showed that the stabilized 40:60 (virgin: recycled) PP blend containing the optimum combination of stabilizers has the same impact strength as the virgin PP. The tensile test results showed that the stabilization of PP blends with the optimum combination of antioxidants led to the higher elongation at breaks and yield strength as compared to the sample without stabilizers.

Recycled polypropylene, Thermal stabilizer, Antioxidant, Metal deactivator, Design of experiments