Dynamic Mechanical Behavior at Thermal Transitions

Tg from static measurements or the maximum in the loss modulus-temperature curve. 

The development of a maximum in tan 5 or ihe loss modulus at the glass-to-rubber transition is explained as follows. At temperatures below Tg the polymer behaves elastically, and there is little or no flow to convert the applied energy into internal work in the material. Now It, the energy dissipated as heat per unit volume of material per unit time because of flow in shear deformation, is 

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Reaction of kenaf with succinic anhydride were done in xylene at 120°C and WPGs up to 80% were achieved [32]. Dynamic mechanical analysis was done on acetone-extracted esterified fibers in the WPG range of 30-80. The data showed that there was a reduced transition temperature from about 170°C down to about 135°C and that there was no change in this first transition temperature as the WPG increases. The data showed that complete modification of that melting species had taken place at a WPG of m35. This thermal behavior is similar to reported trends observed for water-plasticized lignin in wood. 

Based on "equilibrium" dynamic mechanical results of Figure 2a, tan 6 properties associated with network thermal behavior at 20 C should be greater than comparable behavior at the 50 C thermal state. The difference in relative magnitudes stems from the relative positions of the 20 C and 50 C thermal states with respect to the low temperature 8 transition for this epoxy. This difference for the transient data is best observed in Figure 8. Equilibrated 20°C tan 5 and loss property values for the 20°C hygrothermal state are greater than the subsequent 50°C hygrothermal state measurements. 

There are several other thermal analysis techniques. In thermomechanical analysis (TMA), mechanical changes are monitored versus temperature. Expansion and penetration characteristics or stress-strain behavior can be studied. In dynamic mechanical analysis (DMA), the variations with temperature of various moduli are determined, and this information is further used to obtain fundamental information such as transition temperatures. In thermogravimefric analysis (TGA), weight changes as a function of temperature or time (at some elevated temperature) are followed. This information is used to assess thermal stability and decomposition behavior. 

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