Modulus glassy state

Fig. 19. Generalized modulus—temperature curves for polymeric materials showing the high modulus glassy state, glass-transition regions for cured and uncured polymers, plateau regions for cross-linked polymers, and the dropoff in modulus for a linear polymer.

At very short times the modulus is on the order of 10" ° N m comparable to ordinary window glass at room temperature. In fact, the mechanical behavior displayed in this region is called the glassy state, regardless of the chemical composition of the specimen. Inorganic and polymeric glasses... 

In the uniaxially oriented sheets of PET, it has been concluded that the Young s modulus in the draw direction does not correlate with the amorphous orientation fa or with xa "VP2(0)> 1r as might have been expected on the Prevorsek model37). There is, however, an excellent correlation between the modulus and x,rans,rans as shown in Fig. 15. It has therefore been concluded 29) that the modulus in drawn PET depends primarily on the molecular chains which are in the extended trans conformation, irrespective of whether these chains are in a crystalline or amorphous environment. It appears that in the glassy state such trans sequences could act to reinforce the structure much as fibres in a fibre composite. 

Researchers smdied the effect of fullerene in rubber composites with different temperature range [52]. There was no substantial influence of fullerene on Tg, tan 8, and G-modulus within the temperamre range from — 150°C to —50°C (glassy state), and properties increase at mbbery state (0°C-150°C). At temperamres between — 150°C and —50°C when rubber is rigid, G-modulus is virtually independent of the fullerene concentrations between 0.065 and 0.75 phr and a single major peak in Figure 28.26 shows that the fullerene does not influence the glass transition. 

The glassy-state modulus is very high and E shows no sign of approaching a "rubbery" value even at 300°C. 

At low temperature the material is in the glassy state and only small ampU-tude motions hke vibrations, short range rotations or secondary relaxations are possible. Below the glass transition temperature Tg the secondary /J-re-laxation as observed by dielectric spectroscopy and the methyl group rotations maybe observed. In addition, at high frequencies the vibrational dynamics, in particular the so called Boson peak, characterizes the dynamic behaviour of amorphous polyisoprene. The secondary relaxations cause the first small step in the dynamic modulus of such a polymer system. 

A value for E of about 3 GPa is normal for an amorphous polymer in the glassy state, unless below Tg a strong secondary transition occurs such as with PC, so that the E-modulus at ambient temperature is significantly lower. 

Fig. 21. Effect of the volume fraction vd of ethylene glycol on the decrease in the shear storage modulus in the transition from the glassy to rubberlike state. Gg is the modulus of the glassy state (140 K), G represents the boundary between the /8d and a dispersions (cf. Fig. 14), Ge is the modulus in the rubberlike state...

The glassy state modulus is of the order of 1 GPa just below Tg. One can imagine the case of a very highly crosslinked polymer in which the rubbery modulus would be equal to the glassy one (no gap at Tg). The corresponding Me value would be (at 500 K for instance) Me 16 g mol-1, which is an unrealistic value. 

Figure 11.4 Typical shape of the temperature variation of the bulk (K) and shear (G) modulus in the glassy state, around a relatively intense p transition.

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