Moisture Content Effects on Polymers Molecular Relaxations

DSC defines the glass transition as a change in the heat capacity as the polymer matrix goes from the glassy state to the rubbery state. This is a second-order endothermic transition (requires heat to go through the transition), and so in DSC the transition appears as a step transition and not a peak such as might be seen with a melt transition. DSC is the classic and official way to determine even though in some cases there are polymeric materials that do not exhibit a sharp by DSC this has been the case of chitin and CS as well as cellulose [12, 39]. 

Erom the practical point of view, fundamental information on the processability of polymers is usually obtained through thermal analysis, which provides knowledge of the main polymer transitions (melting and glass-to-rubber transition to the crystalline and amorphous phases, respectively). In addition to the well-established calorimetric techniques, experimental methods capable of revealing the motional phenomena occurring in the solid state have attracted increasing attention. 

The a-relaxation is related to the glass transition of the systems and for that reason this relaxation is also called dynamic glass transition. In general, the a-relaxation and the related glass transition phenomenon are not well understood, and the actual microscopic description of the relaxation remains unsolved besides it is a current problem in polymer science [41]. However, it is well accepted that the dynamics of the glass transition is associated with the segmental motion of chains being cooperative in nature 

In the a-process, the viscosity and consequently the relaxation time increase drastically as the temperature decreases. Thus, molecular dynamics is characterized by a wide distribution of relaxation times. A strong temperature dependence presenting departure from linearity or non-Arrhenius thermal activation is present, owing to the abrupt increase in relaxation time with the temperature decrease, thus developing a curvature near T. This dependence can be well described by the Vogel-Fulcher-Tammann-Hesse (VFTH) equation [40, 41], given by Equation 2.1  

4 MOISTURE CONTENT EFFECTS ON POLYMER S MOLECULAR RELAXATIONS 

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