Drying conditions highly influence the characteristics of glycerol-plasticized alginate films

This paper focusses on the characteristics of Na-alginate films (using glycerol as the plasticizer) produced under different drying conditions. Response surface methodology (RSM) was applied to study the effects of drying temperature (25-90 degrees C) and air flow rate (0-12 L/s) on the drying rate, glycerol content, sorption isotherm, physical, morphological, mechanical and barrier properties of the films. All aspects of the films properties except for color were significantly depended on the drying temperature; while the effect of air flow rate was not significant. The glycerol content of the films decreased with increasing the drying temperature, that subsequently influenced the other properties of the films. Drying rate, elastic modulus, and tensile strength increased; while thickness, elongation at break, water vapor permeability, opacity and monolayer moisture content of the films decreased with increasing the drying temperature. SEM and AFM observations showed more compact cross-section and more smooth surface with increasing the drying temperature. According to the X-ray diffraction results, the degree of crystallinity of the films increased with drying temperature. Differential thermal gravimetric analyses showed three distinct peaks. Water loss and glycerol loss peaks shifted to lower temperatures, while the third thermal decomposition maxima were not considerably different. The results of this study proved that the drying of glycerol-plasticized alginate films at higher temperatures, considerably reduces the drying time and highly influences and improves the overall film characteristics while imposing no defects.