No abstract

Neutralized and nonneutralized chitosan films subject to different thermal treatments were studied by dielectric relaxation spectroscopy from -130 to +150 degrees C in the frequency range between 20 Hz and 1 MHz. Two main relaxation processes, both arrhenian type, were detected: process I at temperatures below 0 degrees C with a mean activation energy of 49 +/- 1 kJ mol(-1), which has the characteristics of a secondary relaxation process related with local chain dynamics, and process II observable at higher temperatures with an activation energy of 94 +/- 2 kJ mol(-1), correlated with dc conductivity, which is found in dried polysaccharides systems. Process I is always observed in neutralized chitosan, but it is strongly depleted in the wet nonneutralized form. Although the location of process I is independent of NH2/NH3+ side group, process II deviates to higher temperatures with dryness in both chitosan forms, being located at lower temperatures in nonneutralized chitosan.

The properties of the amorphous component in poly(l-lactic acid), PLLA, depend on its crystalline structure, where the nanoconfinement effects may be monitored using dielectric relaxation spectroscopy. In this work this technique is used to monitor isothermal crystallization in PLLA by probing the evolution of the loss peak with crystallization time. It was found, for two different molecular weight materials and by crystallization from either the glassy or melt states, that the data could be given by a linear combination of three loss processes, where just their intensities vary:  the α-process of the amorphous material, the constrained α-process present in the fully crystallized material, corresponding to the segmental motions of the amorphous phase confined by the crystalline lamellae, and the sub-glass β-relaxation. The appearance of the confined process was detected in the earlier stages of the crystallization, suggesting that the confinement effects are effective during primary crystallization. In this case, the cooperative segmental motions are restricted by the primary lamellae, leading to a dynamics characterized by a broader relaxation time distribution shifted to higher values. It was observed that the crystallization, as investigated by monitoring the evolution of the amorphous phase, is quicker for lower molecular weight PLLA and is slower for the material crystallized from the melt with respect to the cold crystallization. It was found that the confined dynamics is not very dependent on the thermal history prior to the crystallization step. The features of the β-relaxation were found to be similar for amorphous and semicrystalline systems, indicating that the sub-glass process in PLLA is not influenced by the crystalline confinement.