Welding studies on polypropylene

This project involves background work on butt-welding of injection moulded polypropylene ASTM bars followed by a programme on the welding of extruded polypropylene strapping tape. In the butt-welding study, the effects of processing conditions of the bars, welding variables, and annealing treatments, on the morphology and strength of the welds, were investigated. Light and scanning electron microscopy have been used for the analysis of morphological structure and fracture surface texture. Tensile tests have been used to assess the weld strength either at room temperature and at sub-zero temperature. In the strapping tape programme the influence of the tape orientation and the welding temperature on weld efficiency was analysed. The orientation of the tapes, obtained by means of five different draw ratios in the manufacturing plant, was assessed by doing shrinkage and optical measurements. Shear and peeling tests have been used to study the weld efficiency. From the butt-welding study was concluded that the microstructure of the injection moulded bars affected the weld zone morphology. The annealing at l52 degrees C before and after welding caused a reduction in weld strength. However the oriented zones were apparently unaffected by these thermal treatments. In that the strapping tape welding is concerned, an optimum welding tool temperature could be identified. The draw ratio of the tapes seems not to affect the optimum weld temperature, but it influences the efficiency of the welds.