Study of the glass transition on viscous-forming and powder materials using dynamic mechanical analysis

The investigation of the glass transition in materials that become too viscous or are difficult to prepare in a solid compact form, is not straightforward using dynamic mechanical analysis, DMA. In this work, metallic pockets are used to envelop samples in order to resolve the loss factor peak, tan 6, in the region of T-g. Experiments with indium were carried out at different heating rates in order to correct the temperature in such isochronal measurements. The proof of concept of the utility of such methodology was done by investigating the glass transition dynamics of poly(D,L-lactic acid), PDLLA, a biodegradable amorphous polyester widely investigated for biomedical applications. The glass transition peaks obtained at scanning rates below 4 degrees C min(-1) shifted to the same temperature region after correction. DMA tests on PDLLA at different frequencies allowed construction of a relaxation plot where the glass transition dynamics followed Vogel-Fulcher-Tamman-Hesse behaviour. Inclusion complexes, ICs, of PDLLA with alpha-cyclodextrin were obtained, exhibiting a very organized arrangement at the nano-scale level. DMA experiments on the ICs powder packed in the metallic pocket revealed a loss factor peak located at a higher temperature as compared with PDLLA, indicating that the segmental mobility of the polymer chains is highly restricted in this supra-molecular organization. (C) 2008 Elsevier Ltd. All rights reserved.