Composite properties glass-rubber transition

The mechanical behavior of isomorphic macromolecular systems would be expected to be quite different from the behavior observed in bicomponent or biconstituent systems. Indeed, isomorphic systems would be expected to behave in many respects like crystalline homopolymers, except that such properties as 7 and lattice spacings may be dependent on composition. Because of the single-phase situation, the glass-rubber transition and related properties may be expected to behave as if a random copolymer... 

The glass-rubber transition temperature, Tg, of cellulose whisker filled polymer composites is an important parameter, which controls different properties of the resulting composite such as its mechanical behavior, matrix chain dynamics, and swelling behavior. Its value depends on the interactions between the polymeric matrix and cellulosic nanoparticles. These interactions are expected to play an important role because of the huge specific area inherent to nanosize particles. For semicrystalline polymers, possible alteration of the crystaUine domains by the cellulosic filler may indirectly affect the value of Tg. 

There are several ways in which the impact properties of plastics can be improved if the material selected does not have sufficient impact strength. One method is by altering the composition of the material so that it is no longer a glassy plastic at the operating temperature of the product (Chapter 6). In the case of PVC this is done by the addition of an impact modifier which can be a compatible plastic such as an acrylic or a nitrile rubber. The addition of such a material lowers the glass transition temperature and the material becomes a rubbery viscoelastic plastic with much improved impact properties. This is one of the methods in which PVC materials are made to exhibit superior impact properties. 

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. 

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