Morphology of fractured polymer surfaces self-bonded below the glass transition temperature

Previosly noncontact surfaces of polystyrene (PS) and poly(2,6-dimethyl 1,4-phenylene oxide) (PPO) were self-bonded in a lap shear joint geometry below the glass transition temperature T-g. The joints were then fractured in tension at room temperature and the contact area was analyzed by means of scanning electron microscopy. Zones of plastic deformation were revealed on the surfaces of PS and PPO which had been bonded at T-g - 33 and T-g - 70 degrees C, respectively, thus indicating interdiffusion across the interface. This result points to the lower T-g of the surface layer as compared with that of the bulk sample, in agreement with our previous studies. The unusually high self-bonding ability of PPO (at very low temperatures related to the built T-g) is presumably due to the low depth of penetration required to establish entanglements.