Morphology and Mechanical Behavior of Polypropylene Hot Plate Welds

Abstract

This chapter explores the production of bars that were hot plate welded under a wide range of conditions with an injection molding grade of polypropylene. The welding experiments were carried out with parts cut from ISO type tensile test bars. The bars were injection molded from polypropylene homopolymer of MFI 4.4g/600s, and cut in half. The welds were prepared with a purposely built semi-automatic hot plate welding machine. The weld morphology depends on the welding parameters and on the previous microstructure of the parts. The influence of the morphological features of the welds is enhanced differently by the various tests. The tensile test on hole-notched specimens enhances the central zone while the creep rupture test enhances the beads. In the tensile-impact test the fracture behavior is affected by the overall morphology. The optimum welds are void and orientation free at the central zone, and have detached beads with the central V-notches outside the bar plane. The characterization of the weld morphology, in complement with mechanical testing, is of great value on predicting the quality of welded joints.