Self-bonding in an amorphous polymer below the glass transition: A T-peel test investigation

Films of amorphous polystyrene (PS) with a weight-average molecular weight (M-w) of 225 X 10(3) g/mol were bonded in a T-peel test geometry, and the fracture energy (G) of a PS/PS interface was measured at the ambient temperature as a function of the healing time (t(h)) and healing temperature (T-h). G was found to develop with (t(h))(1/2) at T-h = Tg-bulk -33 degreesC (where Tg-bulk is the glass-transition temperature of the bulk sample), and log G was found to develop with 1/T-h at Tg-bulk -43 degreesC less than or equal to T-h less than or equal to Tg-bulk -23 degreesC. The smallest measured value of G = 1.4 J/m(2) was at least one order of magnitude larger than the work of adhesion required to reversibly separate the PS surfaces. These three observations indicated that the development of G at the PS/PS interface in the temperature range investigated (<Tg-bulk) was controlled by the diffusion of chain segments feasible above the glass-transition temperature of the interfacial layer, in agreement with our previous findings for fracture stress development at several polymer/polymer interfaces well below Tg-bulk. Close values of G = 8 -9 J/m(2) were measured for the symmetric interfaces of polydisperse PS [M-w = 225 X 10(3), weight-average molecular weight/number-average molecular weight (M-w/M-n) = 3] and monodisperse PS (M-w = 200 X 10(3), M-w/M-n = 1.04) after healing at T-h = Tg-bulk -33 degreesC for 24 h. This implies that the self-bonding of high-molecular-weight PS at such relatively low temperatures is not governed by polydispersity. (C) 2004 Wiley Periodicals, Inc.