Welding Behavior of Semicrystalline Polymers. 1. The Effect of Nonequilibrium Chain Conformations on Autoadhesion of UHMWPE

The effect of the overall crystallinity and the initial crystal morphology on the welding behavior of semicrystalline polymers was investigated by means of T-peel testing above and below the melting point using ultrahigh-molecular-weight polyethylene (UHMWPE) as a model polymer. Different crystal morphologies were generated by either crystallizing UHMWPE from the melt or from dilute solutions. The initial crystal morphology was found to have a large influence on the adhesive fracture energy as measured above the melting temperature. In the case of two melt-crystallized films, the adhesive fracture energy above the melting temperature, , developed only slowly, and did not reach the fracture energy of the bulk material, even after 65 h of welding at 145 °C. However, welding two (completely wetted) solution-cast films above the melting temperature resulted in an almost instantaneous increase of to the level of the fracture energy of the bulk material. The adhesive fracture energy at room temperature increased almost instantaneously to the fracture energy of the bulk material upon welding above the melting point, irrespective of crystal morphology.