A thermodynamic study of water vapour sorption in hydrocolloids/MMT nanocomposite based films

SLAVUTSKY, ANIBAL M.; BERTUZZI, MARÍA A.

Milán

Congreso; European Polymers Congress; 2013

Water transport in edible films based on hydrocolloids is a complex phenomenon due to the strong interaction of sorbed water molecules with polymeric structure of polysacharides. Edible films based on corn starch (CS) and brea gum (BG) were obtained. In order to improve water resistance, films based on nanocomposites of hydrocolloids and nanoclay (montmorillonite, MMT) were prepared. Moisture sorption isotherms of hydrocolloid based films and nanocomposites based films, were obtained at 5, 25, 35 and 45¨¬C through the gravimetric method. The entropy changes, ¥ÄS , Gibb¢¥s energy changes, ¥ÄG and isosteric heat of sorption, Qs, were calculated. Water vapour sorption experimental data showed an exothermic process and were well described by GAB model in all samples. Isotherm curves showed an exponential increase of water uptake above aw=0.6, producing film structural changes which allow a facilitated water transport phenomenon and deteriorate mechanical resistance. MMT addition decreased water uptake of CS and BG films in all the studied temperatures. The water content values of the monolayer calculated with GAB equation reduced with MMT incorporation in both cases. Entropy changes and net isosteric heat of sorption showed a well defined peak at monolayer water content and in both cases indicated a more stable and ordered structure when MMT was added. Gibb¡¯s energy changes showed the process spontaneity and that final structure of CS/MMT and BG/MMT films has less affinity with water than the CS and BG films respectivelly. The results indicated that nanoclay incorporation produce a decrease of water uptake at all temperatures analyzed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the polysacharide matrix. producing film structural changes which allow a facilitated water transport phenomenon and deteriorate mechanical resistance. MMT addition decreased water uptake of CS and BG films in all the studied temperatures. The water content values of the monolayer calculated with GAB equation reduced with MMT incorporation in both cases. Entropy changes and net isosteric heat of sorption showed a well defined peak at monolayer water content and in both cases indicated a more stable and ordered structure when MMT was added. Gibb¡¯s energy changes showed the process spontaneity and that final structure of CS/MMT and BG/MMT films has less affinity with water than the CS and BG films respectivelly. The results indicated that nanoclay incorporation produce a decrease of water uptake at all temperatures analyzed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the polysacharide matrix. producing film structural changes which allow a facilitated water transport phenomenon and deteriorate mechanical resistance. MMT addition decreased water uptake of CS and BG films in all the studied temperatures. The water content values of the monolayer calculated with GAB equation reduced with MMT incorporation in both cases. Entropy changes and net isosteric heat of sorption showed a well defined peak at monolayer water content and in both cases indicated a more stable and ordered structure when MMT was added. Gibb¡¯s energy changes showed the process spontaneity and that final structure of CS/MMT and BG/MMT films has less affinity with water than the CS and BG films respectivelly. The results indicated that nanoclay incorporation produce a decrease of water uptake at all temperatures analyzed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the polysacharide matrix. w=0.6, producing film structural changes which allow a facilitated water transport phenomenon and deteriorate mechanical resistance. MMT addition decreased water uptake of CS and BG films in all the studied temperatures. The water content values of the monolayer calculated with GAB equation reduced with MMT incorporation in both cases. Entropy changes and net isosteric heat of sorption showed a well defined peak at monolayer water content and in both cases indicated a more stable and ordered structure when MMT was added. Gibb¡¯s energy changes showed the process spontaneity and that final structure of CS/MMT and BG/MMT films has less affinity with water than the CS and BG films respectivelly. The results indicated that nanoclay incorporation produce a decrease of water uptake at all temperatures analyzed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the polysacharide matrix.