Thermal expansion glassy state

Transition region or state in which an amorphous polymer changed from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one. Transition occurs over a narrow temperature region similar to solidification of a glassy state. This transformation causes hardness, brittleness, thermal expansibility, specific heat and other properties to change dramatically. 

Both of these are equations are approximate and are useful only for giving estimates of the value of the of the polyblend or copolymer. To calculate values of more accurately requires additional information such as the coefficients of thermal expansion of both components in both their liquid and glassy states. Given the uncertainty in the numerical value of T, which as we have seen depends on the method by which has been determined, there is little point in developing such arithmetical refinements. 

The glass transition of the polymer Is Tg. while that of the plasticizer is Te the volume fraction of plasticizer is Fi(b), and its weight fraction js Wg. Typical values of TA are betvaen -50 and - 100°0. To calculate more accurate values of Tg additional information must be available, such as the Tg value of a known mixture or the coefficients of thermal expansion (aA and a ) of the pure components in both their liquid and glassy states (51,95). For each Component i... 

Polymers above their Tg are in a state of equilibrium much like simple liquids. However, upon cooling below Tg, polymers are not able to achieve an equilibrium state since the polymer chain segments lack sufficient mobility to reach this state in realizable time scales. Thus, glassy polymers exist in a nonequilibrium state that is a function of the prior history of the sample. It is useful to think of simple volumetric thermal expansion where at equilibrium the specific volume at a given temperature and pressure is Veq(T,p) the specific volume of a rubbery polymer is given by Veq. The... 

If this hypothesis is right, the specific volumes that characterize the RAF and MAF have to be essentially different below the crystallization temperature. Figure 17 exhibits a sketch to illustrate this point. This sketch basically shows a hypothetical thermal-expansion behavior associated with the RAF and MAF for PET, crystallized at some arbitrary crystallization temperature, Tc. Above Tc, in the equilibrium melt, only one phase occurs, i.e. the specific volumes for the RAF and MAF are the same. If vitrification of the RAF occurs at Tc, the slope of specific volume versus temperature for this fraction should change at Tc, and become characteristic of the glassy state in the temperature interval below Tc. In the same manner for the MAF, the slope of specific volume versus temperature, below Tc, should continue to be the same as for the equilibrium melt and change only at the real Tg. Therefore, if room temperature (25 °C) is considered as the reference, the specific volume for the RAF at 25 °C must be larger than that for the MAF. The same reasoning would lead to the anticipation that the specific volume of the RAF will be a direct function of Tc. 

The kink observed around 367 K corresponds to a change of the thermal expansion coefficient from a glassy to a liquid-like state and, by that, marks the position of the glass transition temperature. Usually, the 7g is calculated as a intersection point between two linear dependencies. Nevertheless, a more convenient method is the calculation of the first and second numerical derivatives of the experimental data (Fig. 15b,c). In this case, the Tg is defined as the minimum position in the second numerical derivative plot (Fig. 15c). Down to a thickness of 20 nm, no shifts of 7g as determined by capacitive scanning dilatometry were found (Fig. 16). 

Figure 5 (a, b) shows typical heat capacities and thermal expansion coefficient curves for some epoxy-aromatic amine networks. Table 1 gives some numerical values for networks with different component ratios P Cp and P values for the glassy state do not practically depend on the chemical composition of networks and are very... 

Thermal mechanical analysis was utilized by Ophir 174) to study the densification of Bisphenol-A-based epoxies. The glass transition temperature can easily be characterized by a slope change as the resin transits from the glassy state to the rubbery state (see Fig. 25). Hence, in glassy material, it is typically represented by two thermal expansivity parameters, one below T (glassy thermal expansivity) and one... 

Fig. 27. Glassy state thermal expansivity of Fiberite 934 epoxies as a function of thermal history...

With 10 minutes of sub-T annealing at 140 °C, thermal expansivity below T decreased to 4.78 x 10-5 K-. This parameter decreased throughout the 140 °C aging experiment. After 10s minutes of aging, the value decreased to 4.30 x 10 s K-1. The free volume decrease evidently dictates the thermal expansivity in the glassy state during sub-T annealing. 

Figure 28 shows the thermal expansivity of epoxy above its Tg as a function of thermal history. Rubbery-state expansivity is generally an order of magnitude larger compared to the glassy-state expansivity (see Table 2). As-cast epoxy has an expansivity above Tg of 3.22 x 10-4 K-1. With postcuring and quenching, this parameter tends... 

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