Mechanical properties developing at the interface of amorphous miscible polymers, below the glass transition temperature: Time-temperature superposition

The bonding of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was conducted over a broad range of time and temperatures, but always below the (bulk) glass transition temperature (T-g). Stress-strain properties developing at the symmetric (PS/PS and PPO/PPO) and asymmetric interfaces (PS/PPO), in a lap-shear joint geometry, were measured at room temperature as a function of contact time and bonding temperature. Master curves of shear strength and modulus, obtained by time-temperature superposition, were constructed over several decades of time. Arrhenius apparent activation energies calculated for shear strength are 99, 81, and 144 kcal/mol for, respectively, PS/PS, PPO/PPO, and PS/PPO interfaces. A higher value of 191 kcal/mol was calculated for the shear modulus at the PS/PS interface, suggesting that the development of the strength and modulus is controlled by different molecular factors, that is, the modulus is controlled by the number of chains across the interface and the strength by the depth of penetration. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 825-830, 1999.