Abstract
In this work is presented the complete thermal analysis of polyols by direct methods such as simultaneous thermogravimetric and differential thermal analyzer (TGA-DTA), differential scanning calorimetry (DSC), modulated DSC (MDSC), and supercooling MDSC. The different thermal events in the temperature range of 113–553 K were identified for glycerol (GL), ethylene glycol (EG), and propylene glycol (PG). Boiling temperature (TB) decreased as GL > EG > PG, but increased with the heating rate. GL showed a complex thermal event at 191–199 K, identified as the glass transition temperature (Tg) and devitrification temperature (Tdv), and a liquid–liquid transition (TL-L) at 215–221 K was identified as the supercooling temperature. EG showed several thermal events such as Tg and Tdv at 154 K, crystallization temperature (Tc) at 175 K, and melting temperature (Tm) at 255 K. PG also showed a complex thermal event (Tg and Tdv) at 167 K, a second devitrification at 193 K, and TL-L at 245 K. For PG, crystallization was not observed, indicating that, during the cooling, the liquid remained as an amorphous solid.
Highlights
In the field of food products, comestible films have been well accepted in applications related to the extension of the shelf life of products [1]
The results reported in this work agree with those values reported by Duo et al based on the simultaneous thermogravimetric and differential thermal analyzer (TGA-Differential Thermal Analysis (DTA)) results, the identification of the thermal event corresponded to the evaporation of liquids rather than to the decomposition as indicated by Duo et al Agarwal and Lattimer [36] reported the complete evaporation of GL and ethylene glycol (EG)
The thermal events of three polyols were determined by direct characterization techniques such as simultaneous thermogravimetric analysis and differential thermal analysis (TGA-DTA), differential scanning calorimetry (DSC), modulated DSC (MDSC), and super cooling MDSC (S-MDSC)
Summary
In the field of food products, comestible films have been well accepted in applications related to the extension of the shelf life of products [1]. This type of films is employed for conserving the quality and stability of products, acting as a selective transfer barrier for environmental gases and moisture, preventing the degradation of nutrients and the loss of volatile compounds responsible of imparting specific properties to the product [2]. Different materials are employed in the production of comestible films. These materials are typically based in biopolymers such as polysaccharides, cellulose, starch, gums, carrageenan and alginate [3]. Plasticizers are low Polymers 2018, 10, 467; doi:10.3390/polym10050467 www.mdpi.com/journal/polymers
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