Glass transition and the factors that influence it

In the case of rubbers, aU of which have Tg s that are sub-ambient and, in some cases as low as 120°C (e.g. silicone rubber), the experiments have to start at very low temperatures, e.g. -150°C [67, 68]. 

Sample ID sample 3 - failed near gate Operator ID CDP 

Comment CCA -20°C, 10 iL pans Project no. BM0236 Sample weight 6.180 mg Date collected 11/10/2005 12 46 24 

With respect to the effects that additives have, ones that are not soluble in the polymer (glass fibres, inorganic fillers, carbon black, etc.) do not increase free volume and so do not reduce the energy required for main chainmotion i.e. the 7 is not reduced in temperature. It is possible, though, for such additives to increase the temperature of 7 if they are intimately mixed with the polymer molecules and inhibit their ability to rotate. 

Cassel and Li [72] have described how developments in DSC have improved its ability to characterise semi-crystalline thermoplastics and mixed recyclates. The techniques covered show the influence of impurities on the glass transition, crystallinity and crystallisation. It is also possible to use this effect to investigate the degree to which two compatible polymers are blended - the greater the degree of mixing the nearer to merger the 7 s for the individual polymers become [73]. 

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