Stress dissipation glass transition temperature

Hygroscopic stresses are interrelated with ambient temperature [11, 20]. They also depend heavily on the glass transition temperature (T ) of the coating [24]. In immersion studies, Perera and Vanden Eynde examined the stress of an epoxy coating whose Tg was near — even below — the ambient temperature [25]. The films in question initially had tensile stress from the film formation. Upon immersion, this stress gradually disappeared. As in the previously cited studies, compressive stresses built up. The difference was that these stresses then dissipated over several days even though immersion continued. Hare also noted dissipation of compressive... 

An added benefit of exposing the bottle to temperatures above the glass transition is that molecular relaxation takes place at the same time crystallinity is building up. Both depend on molecular movement freedom for a molecule to either get into the crystalline structure or slip by other molecules out of the oriented state. This facilitates the dissipation of the orientation and the residual stresses associated with it. Residual stresses are ultimately responsible for any deformation of a product on reheating above the glass transition temperature, like shrinkage or warp-age in hot filled bottles. 

We assign the sharp rise in friction at elevated RH to the glass-to-rubber transition. It is well known that both PVOH and gelatin are plasticized by absorbed water. ] At approximately 60% RH a moisture content of 8% is expected in PVOH. This would shift the glass transition from around 80 C in anhydrous PVOH to 20-22°C, i.e. room temperature, as used in the present experiment. Thus above 60% RH, large-scale molecular motions in response to shear and compressive stresses (tip) will dissipate strain energy. Enhanced energy dissipation is measurable as an abrupt... 

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