Abstract

DIAZ-CALDERON, Paulo et al. Effect of sorbitol on structural relaxation of gelatin fi lms in the glassy state. Rev. ion [online]. 2015, vol.28, n.2, pp.93-101. ISSN 0120-100X.  https://doi.org/10.18273/revion.v28n2-2015008.

The objective of this work was to study the effect of sorbitol on the kinetic of enthalpy relaxation of gelatin fi lms stored at temperatures below the glass transition temperature (Tg). Bovine gelatin and sorbitol fi lms were prepared by cold casting method. Sorbitol was added at weight fraction (Qs) of 0.0, 0.06 and 0.10. Films were equilibrated in environment of 44% relative humidity using a saturated salt solution of potassium carbonate, giving a moisture weight fraction in samples (Qw) of 0.18, 0.16 and 0.18 respectively. Enthalpy relaxation (ΔH) was measured by differential scanning calorimetry (DSC). Tg values of the samples tested were observed at 48°C (Qs=0.0), 35°C (Qs=0.06) and 30°C (Qs=0.10). After the thermal history deletion (30°C above Tg, 15 minutes), samples were annealed from 2 to 80 hours at 10°C below Tg_onset. The addition of sorbitol showed a significant reduction (p<0.05) in structural relaxation kinetic. The linearization of relaxation enthalpy (ΔH) versus log of annealing time showed a reduction of the slope in samples plasticized with sorbitol. The reduction in structural relaxation kinetic could be related to the effect of molecular packing by the presence of polyol in polymer matrix as has been recently reported by Positron Annihilation Spectroscopy (PALS).

Keywords : gelatin; plasticizers; glassy state; physical aging.

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