Glass transition temperature water content effect

The typical differential scanning colorimetric (DSC) traces shown in Figure 9.2 compare the thermal transitions of similar low-DEG-content PEN and PET resins. The fact that the glass transition temperature (Tg) of PEN is 45-50 °C higher than that of PET has a major influence on the processing and performance of PEN applications. In addition, the fact that PEN S Tg is 20-25 °C above the boiling point of water has a significant effect on the thermal stability potential of many hot, aqueous exposure applications. 

Fig. 4.8.12. Diagram showing the effect of degree of acetylation and water content on the glass transition temperature, Tx, of dioxane lignin. (Hatakeyama and Hatakeyama 1983)...

A continuous effect is the decrease in water content and void volume with Increasing temperature. Water is lost from the primary gel during annealing, both because of the formation of virtual crosslinks and because of the decrease in hydrogen bonding and cluster size in the water Itself. An example of a discontinuous effect is the dramatic increase in permselectivity (salt rejection) observed when cellulose acetate membranes are heated above the glass transition temperature 68.6 C. In fact, not one but two... 

Water acts as a plasticizer for soy flour (Yildiz and Kokini, 2001). Therefore, increase in water content will plasticize the matrix causing an increase in available free volume for molecular transport. Moisture diffusion as a result will be effected from the water activity of the system. The relationship between moisture content and a can be established using the moisture sorption isotherm (MSI) of soy flour. The glass transition temperature is a very important concept in the diffusion process. At the vicinity of the glass-transition temperature the diffusion process increases at a higher rate. Figure 46.1 shows the plasticization effect of moisture on soy flour and Gordon-Taylor prediction of Tg vs. moisture content (Yildiz and Kokini, 2001). 

The Water Content Effect on the Glass-Transition Temperature of Low Calory Candy Formulations... 

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