| The edible film which made by the food macromolecular materials is a kind of green packaging material without any pollution to the environment. In this paper, pullulan was blended respectively with chitosan and carboxymethyl chitosan (cmch) to form the edible film. Glycerol was used as plasticizer. The influence of different blend ratios, acetic acid concentration, pH value, relative humidity and storage temperature on the properties of the blend films has been investigated.Pullulan and chitosan/carboxymethyl chitosan was blended with different (1:3, 2:2, 3:1) ratios. Significant improvements in the mechanical and oxygen barriers properties of pullulan films have been observed especially when the chitosan and pullulan blend ratio was 2:2, tensile strength was increased by 29.2% and the oxygen permeability rate has been decreased by 23% compared with pullulan film. The characteristics of the pul-chitosan blend film (2:2) were tested: film thickness 60.3μm, tensile strength 61.5 Mpa (increased by 26% compared with chitosan film), elongation at break 2.78%, water vapor permeability 0.42 g.mm/m2.h.kPa (decreased by 35.4% compared with chitosan film), water solubility 34.47% (results were expressed by the percentage of the dissolved film), oxygen barrier 88.24 meq/kg (results were expressed by the peroxide value of oil), FTIR and XRD results have proved the existence of strong hydrogen bonding between pullulan and chitosan, pullulan and carboxymethyl chitosan. The phase separation has been proved when the pul: chitosan blend ratio was 1:3. pH value and the solvents of the film-forming solutions are two important factors which affect the film forming property as well as the film properties. The influence of the acetic acid concentration (1%,2%,5%,10%) and the pH values (3,3.5,4,4.5, 5) have been studied.With the increase of the acetic acid concentration the tensile strength of the pul-chitosan decreased while the E% increased. The results showed that when the acetic acid concentration was 2%, the pul-chitosan blend film showed the best barrier properties.Tensile strength of the pul-chitosan blend film reached maximum (69.3 Mpa) when pH=3.5. With the reducing of pH value, E% decreased, water solubility increased, while the water vapor permeability and moisture content reduced, the pul-chitosan blend film showed worst oxygen barrier property when pH values was 4.5 (106.67 meq/kg). Experimental results of the rheology tests, FTIR and XRD proved that the acetic acid concentration and pH affected the chitosan chain stretching state, thereby affecting the interaction between the polysaccharides.The effect of the storage temperature (4℃, 25℃, 45℃, 65℃) and RH (0.113, 0.328,0.530, 0.708, 0.90) on the properties of the two blend films have been studied. The tensile strength of both the two blend films reached the maximum when the RH was 0.328. With the increase of the RH, the water solubility of the pul-chitosan and pul-cmch blend films decreased, while the WVP values increased, the transparency reduced and color deepened. The pul-cmch blend film was much easier been effected than the pul-chitosan film by the RH. The results showed that storage at low temperature (4°C) was conducive to enhancing the film's flexibility (the elongation at break of the pul-chitosan and pul-cmch blend films respectively are 10.18% and 6.53%); polysaccharide blend film preserved under 25°C have a low water vapor permeability and good mechanical properties. FTIR results showed that with increasing temperature, the reaction of carboxylic acids and amino amide in the blend films eventually led to the change of the properties of the blend films, the higher the temperature, more obvious the reaction was. At the same time, the XRD results showed that the increase in storage temperature increased the crystallinity of the polysaccharide blend film. |
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