Abstract
Two bulk samples of one and the same or of different amorphous polymers were brought into contact and held for a chosen period of time at a constant healing temperature (T) over the interval of T from below the bulk glass transition temperature (Tgbulk) by ~50 °C to above Tgbulk by ~10 °C. As formed adhesive joints were shear-fractured in tension at room temperature, and lap-shear strength (σ) was measured as a function of T. It has been found that σ develops with T as logσ ~ 1/T both at symmetric and asymmetric interfaces of polystyrene, poly (methyl methacrylate) and poly (2,6-dimethyl-1,4-phenylene oxide). This behaviour implies that there is no discontinuity in the evolution of σ when going through Tgbulk, and that this process is controlled by one and the same diffusion mechanism both below and above Tgbulk. The results obtained indicate that the contact layer of the polymers investigated is in the viscoelastic state at T well below Tgbulk and support the concept of a decrease in the Tg of a near-surface layer with respect to Tgbulk.
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