Glass transition temperatures relative humidity

The effect of physical aging on the crystallization state and water vapor sorption behavior of amorphous non-solvated trehalose was studied [91]. It was found that annealing the amorphous substance at temperatures below the glass transition temperature caused nucleation in the sample that served to decrease the onset temperature of crystallization upon subsequent heating. Physical aging caused a decrease in the rate and extent of water vapor adsorption at low relative humidities, but water sorption could serve to remove the effects of physical aging due to a volume expansion that took place in conjunction with the adsorption process. 

The glass transition temperatures ofthe polyimides are 195-250 °C their 10% weight loss temperamres (dynamic thermogravimetric analysis, air, AT = 4.5 °C/min) are 390-422 °C. Of particular interest are the dielectric constants of these polyimides. At a relative humidity of 50% these constants are 2.70-2.90 and are comparable with constants of the best fluorinated polyimides [21, 50-55]. The lowest dielectric constant (2.70) was observed for polyimide based on 6F dianhydride, containing the highest amount of fluorine. Thermal treatment of this polymer film at 280-290 °C for 1 hour led to a decrease (2.45) of dielectric constant due to the possible formation of nanofoams [56]. 

Figure 7. Glass transition temperature Tt against silica content at four levels of relative humidity indicated on the plot...

Glass transition temperature 106°C for Plasdone S-630. Hygroscopicity at 50% relative humidity, copovidone gains less than 10% weight. 

Water Content and Glass-Transition Temperatures for Model Systems at Various Relative Humidities... 

RH relative humidity (%), Gel. St. gelatinized starch, W.C. water content (% dry basis), Nat. St. native starch, T. glass transition temperature (°C), Lact. lactose. 

Experimental glass-transition temperature (onset) values (closed symbols) and water contents (open symbols) for amorphous maltodextrin MlOO (circles) and M180 (triangles) matrices as a function of storage relative humidity at 25°C. The glass-transition temperatures and water contents for maltodextrin MlOO and M180 matrices stored at relative humidities of 66 and 54%, respectively, are shown by straight lines. 

Glass transition temperature K Dependent on relative humidity 320-330 (1)... 

To characterize the materials after extrusion, the beads were conditioned for one week at 20°C at different relative humidity values to obtain various moisture contents. Characteristics were obtained using differential scanning calorimetry (DSC) and X-ray measurements. DSC measurements are performed to determine the glass transition temperature of the beads. X-ray measurements provide an indication about the degree and, if present, the type of crystallinity in the extruded materials. 

Table 38-4. Properties of Some High Modulus and High Temperature Fibers. p. Density Tm, Melting Temperature Tg Glass Transition Temperature ob. Tensile Strength at Break b, Elongation at Break E, Modulus of Elasticity AFP, Water Uptake C

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