The Relationship between Interfacial Structure and Welding Strength of Hot Plate Welding Crystalline Polymer

The effects of welding conditions on the interfacial microscopic structure and welding strength of hot plate welded polypropylene (PP) were investigated, and were obtained welding conditions that resulted in high welding strength. The following main results have been obtained. (1) The interface structure of welded specimen consists of an oriented flowing layers and sandwiched in between, a recrystallization layer. (2) In general, high heating temperature, high welding pressure and relatively high indentation speed leads to a perfect welding interface, therefore to enhance the welding strength. (3) It is important to completely remove air bubbles during the welding process. (4) The flowing melting resin will cause the flowing layer to have extremely high orientation, thus will easy lead to cracks along the orientation direction of the flowing layer. Especially, we can speculate the fatigue crack easily along the crystallographic orientation direction for expansion in the fatigue load, which will reduce fatigue life.