Storage stability, glass temperature influence

Roos (1995) has used a combined sorption isotherm and state diagram to obtain critical water activity and water content values that result in depressing Tg to below ambient temperature (Figure 1-25). This type of plot can be used to evaluate the stability of low-moisture foods under different storage conditions. When the Tg is decreased to below ambient temperature, molecules are mobilized because of plasticization and reaction rates increase because of increased diffusion, which in turn may lead to deterioration. Roos and Himberg (1994) and Roos et al. (1996) have described how glass transition temperatures influence nonenzymatic browning in model systems. This deteriorative reaction... 

It is generally believed that plasma treating processes provide surfaces with greater stability than chemical etch, corona, flame or other common polymeric treatment processes. Plasma-treated parts can be stored for weeks or longer in a clean, dry storage area, whereas it is normally recommended that corona- or flame-treated polymers be bonded immediately after surface preparation. Exposure to temperatures near the polymer s glass transition temperature will deteriorate any surface treatment. Once bonded, the surfaces of treated polymers are relatively stable, excluding the effects of outside environmental influences. 

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