In this study, blend of virgin polypropylene (PP) and recycled PP used in lead-acid battery casewith different weight ratios (20, 40, 60, 80,100 wt %) was prepared by a single screw extruder. Melt flow index (MFI) andcarbonyl index were selected for evaluation of blends degradation during the extrusion process. method design of experiments (DOE) was used. Also,the effect of process conditions such as screw speed and extruder temperature profile on the degradation of blends was studied. The results of measuring the MFI and carbonyl indexhowed that,in the non-stabilized blend, adding the virgin PP to the recycled PP not only didot decrease of polymer degradation during the extrusion process, but also addinga small amountofrecycled to the virgin PP causedto polymer degraded rapidly. Three metal deactivators, zinc and calcium stearate (CaSt) and a commercial metal deactivator, were used. The results showed that the combinations of CaSt with thermal stabilizers was more effective ireducing of polymerdegradatioduring theextrusion process .Commercial metal deactivator and zinc stearate did not decrease the PP degradation. By design of experiments, the optimum combination of stabilizer was obtained as: 1 wt% P-AO, 0.2 wt% S-AO, and 0.5 wt% CaSt. Also, DOE resulthowedthatthe primary antioxidant hathe most influence on reducing the degradation of PP during theextrusion process. Measurement of OIT parameter of the samples which stabilized with optimum combination of stabilizers proved that the thermal resistance of these samples was similar to virgin PP. Similarly, from a measurement of carbonyl index of these blends, it was found that a little degradation was happened in the extrusion process. It was found that the increasing of screw speed provided higher shear rate and hence resulted in the more degradation of PP during recycling. The results showed that the best screw speed was about 100 rpm. Investigation of different extruder temperature profiles showed that increasing extruder temperature profiles from 200?C caused an increase of polymer degradation during recycle process. The resultofimpact tests showed that the stabilized 40:60 (virgin: recycled) PP blend with theoptimum combinatioof stabilizers have impact strength similar to virgin PP, while the impact strength of this sample in the absence of stabilizer is near to the impact strength of recycled PP. Moreover, the tensile test results showed that the stabilization of PP blends with optimum combination of antioxidant had higher yield strength and elongation at break.
