Polymer00051 - cooperative movement when the polymer...

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40 In contrast, T-G displayed the opposite effect on the vulcanization of the elastomer. The addition of T-G increased Ea from 81.0 kJ/mol to 127.0 (2% T-G) and 124.8 kJ/mol (4% T-G), indicating that T-G hindered elastomer vulcanization. This result was consistent with the mixing torque results which showed that the FC 2660/T-G blend has the lowest mixing torque among all the samples (Figure 2.2). The reason for T-G’s hindrance to the elastomer vulcanization is not clear yet. 2.4.3 Dynamic Mechanical Properties DMA measurements are often used to evaluate polymer stiffness under dynamic mode, molecular segment mobility, and maximum damping temperature ( T g ) (Chartoff, et al. 2009). The glass transition temperature, T g , represents a critical transition temperature for many polymers, as physical properties change drastically when the material transit from a hard glassy state to a rubbery state. Large segments of polymer chains start
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Unformatted text preview: cooperative movement when the polymer reaches its glass transition temperature. In general, more heavily crosslinked rubber leads to higher T g because the structure of three dimensional network hinders large scale chain movement. The T g of highly crosslinked materials can not be easily detected by DSC since the amount of heat exchange is small during the transition, but can be easily measured by DMA because DMA is 10 to 100 times more sensitive than DSC to the movement of polymer chains under dynamic bending mode (Menard 2008). Figure 2.4 shows the effects of various nanofillers on the storage modulus of FC2260 nanocomposites. Figure 2.4a compares the effects of the two types of clay on the modulus of the nanocomposites. The modulus plummeted at ca. -10 o C due to glass transition of the fluoroelastomer. The modulus increased with the...
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