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Effects of glycerol, sorbitol, xylitol and fructose plasticisers on mechanical and moisture barrier properties of pullulan–alginate–carboxymethylcellulose blend films


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The effects of glycerol, sorbitol, xylitol and fructose plasticisers on water sorption, mechanical properties, water vapour permeability (WVP) and microstructure of pullulan–alginate–carboxymethycellulose (PAC) blend films were investigated. At low plasticiser concentrations (below 7% w/w dry basis), antiplasticisation effect was observed, causing an increase in tensile strength (TS) but a decrease in the equilibrium moisture content. As glycerol concentration increased from 0% to 7%, TS increased from 68.1 to 69.6 MPa, whereas equilibrium moisture contents at 0.84 aw decreased from 0.37 to 0.3 g H2O g−1 dry basis. At higher plasticiser concentrations (14–25% w/w), an opposite trend was observed on the PAC films, resulting in the reduction of TS and elevation of moisture content. Among the four plasticisers tested, the fructose-plasticised films were the most brittle, showing the highest TS, but had the lowest elongation at break (EAB), WVP and equilibrium moisture content values than films plasticised with other polyols. On the other hand, glycerol resulted in the most flexible film structure, exhibiting opposite materials' properties as compared with the fructose-plasticised films. For instance, at 25% (w/w) plasticiser concentration, EAB and WVP values of fructose-plasticised films were 33.5% and 3.48 × 10−6 g m Pa−1 h−1 m−2, which were significantly lower than that of glycerol-plasticised films (58.6% and 4.86 × 10−6 g m Pa−1 h−1 m−2, respectively). Scanning electron microscopy showed that the plasticised PCA films were less homogeneous and more porous than the unplasticised counterparts, indicating that plasticisers had an effect on the microstructural morphology of the film matrix.