Aging rate, physical

Fig. 17. Calculated dependence of the physical aging rate on temperature for three glassy polymers...

In the vicinity of glass transition, both Eqs. (47) and (48) become Eqs. (42) and (43), respectively. The calculated dependence of the physical aging rate on temperature for polystyrene (PS), poly(vinyl chloride) (PVC), and poly(vinyl acetate) (PVAc) is shown in Fig. 17. There are five parameters (e, p, f xr, 7 ) in Eqs. (23), (2), (15) and (19). We have chosen p = 1/2. ft = 1/30, and xr = 30 min for these linear polymers in our theoretical calculation. The other two parameters r. = h and Tr are listed in Table 1. The calculation reveals that the Struik exponent (p) increases from zero above 7 to a constant below Tg, and then decreases to zero at 200 K below Tg. The three polymers all show a similar type of temperature dependence of physical aging rate, which compares well with the reported observations (see Fig. 15 of Ref. 2). 

The master curves and shift factors of transient and dynamic linear viscoelastic responses are calculated for linear, semi-crystalline, and cross-linked polymers. The transition from a WLF dependence to an Arrhenius temperature dependence of the shift factor in the vicinity of Tg is predicted and is related to the temperature dependence of physical aging rate. 

The physical aging rates increase from zero above Tg to a constant below T and then decrease to zero at 200 K below Te. In contrast to all the published expressions, the new equations also predict increasingly smaller activation energies with decreasing temperature in the glassy state. 

It appears, therefore, that formaldehyde emission rate from a given large panel may be controlled by chemical processes within the board or by diffusion either in the board-air interface or within the board. Which of these predominates depends upon the board s age, composition, physical structure, and exposure conditions. 

T JTg = 1.20 0.05 Boyer high melt transition temperature, rLL 50 a(1.35 0.1)x melting and reference temperature temperature at which the physical aging rate is the highest... 

Physical aging effects have practical implications and need to be considered when assessing the long-term stabihty of polymers and polymer-polymer mixtures. This chapter focuses on a discussion of the effect of blending on physical aging and gives a review of the different experimental methods that can be used to compare aging rates in blends to those of the individual components. 

To apply the Arrhenius equation is to presume that the rate of plastics aging is determined by one (dominant) chemical reaction or one (dominant) physical process with corresponding dependency of aging rate on temperature. The relation found by Arrhenius for gas reactions between the reaction rate constant and absolute temperature T states that ... 

The general issue is that a ten degree temperamre increases doubles the aging rate, issue which may be surpassed only by calculating E of aging from Eq. (13). This aspect also brings forth the issue of ambient temperature value, which must be selected in such a manner as not to initiate previously mentioned chemical or physical processes, thus a generaUzation of the empiric law is required. 

In 2002, the effect of film thickness on the physical aging rate of spin-cast poly (iso-butyl methacrylate) (PiBMA) films supported on silicon substrates was... 

Fig. 3.4 a Time dependence of the normalized fluorescence intensity of the dye molecule TCI chemically labeled to PiBMA in a thin film geometry (film thickness = 39 nm) when annealed at 343 K (circles) and after quenching to 298 K (diamonds) and 323 K (squares). The inset show the TCI molecule, b Thickness dependence of the fluorescence physical aging rate as dehamined by eq. 3.21 for TCl-labeled PiBMA. Reproduced with permission from Ref. [120]... 

Fig. 3.7 Temperature dependence of the physical aging rate, as determined by elhpsometry...

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