1 The Danish Polymer Centre, Department of Chemical and Biochemical Engineering, Technical University of Denmark2 Department of Chemical and Biochemical Engineering, Technical University of Denmark3 Abraham F. Ioffe Institute
Amorphous bulk samples of high-molecular-weight (HMW) polystyrene (PS) with a weight-average molecular weight M-w of 102.5 kg/mol and a number-average molecular weight M. of 97 kg/mol and of ultra-high-molecular-weight PS (UHMWPS) with M-w=1110.5 kg/mol and M-n = 965.6 kg/mol were brought into contact to themselves below the glass transition temperature T-g of the bulk Tg-bulk, in a lap-shear joint geometry, at a constant healing temperature T-h for a healing time t(h) of 10 min to 24 h. The lap-shear strength sigma of the symmetric HMWPS-HMWPS and UHMWPS-URMWPS interfaces has been measured at the ambient temperature. Larger values of sigma have always been measured for the HMWPS-HMWPS interface after healing at the same conditions. However, the difference between the values of a, for the HMWPS-HMWPS and UHMWPS-UHMWPS interfaces observed at T-h = Tg-bulk - 33 degreesC and T-h = Tg-bulk - 23 degreesC became negligible at T-h = Tg-bulk - 13 degreesC at long times. The kinetics of strength evolution at the two interfaces involved at T-h = Tg-bulk - 33 degreesC and T-h = Tg-bulk - 23 degreesC was found to follow the form sigma proportional to (t(h))(1/4)(M-n)(-1/4), in accordance with the minor chain reptation model, suggesting that the build-up of the interface structure develops via the diffusion of chain segments above T-g of the interface layer Tg-interface. (C) 2004 Elsevier Ltd. All rights reserved.