Study On The Film Prepared By Using Grafted Starch For Fresh-keeping Packaging Material

The grafted starch/PVA packaging films and grafted starch/PVA films with excellent mechanical properties and moderate oxygen permeation flux are prepared by tape casting method in this paper,using grafted starch/PVA as basic materials and glutaraldehyde as crosslinker with amount of antistaling agent.First of all,the effects of different process factors on grafting degree and grafting efficiency of grafted starch were discussed.The characterization of FTIR and DSC shows that the grafting degree and grafting efficiency of grafted starch increase with the increase of the concentration of MA,but the grafting efficiency decreases when the concentration reaches 0.6mol/L because the probability of homopolymerization reaction increases.The grafting degree and grafting efficiency of grafted starch increase with the increase of the concentration of CAN,when the concentration reaches 5.5×10^-3mol/L,Ce⁴⁺ ion reacts with free radicals and the termination reaction and homopolymerization reaction increase,which results in the decrease of degree grafting and grafting efficiency.As a result,the best formulation of grafted starch is that concentration of MA is 0.6mol/L,concentration of MA is 5.5×10^-3mol/L,reaction temperature is 33℃,reaction time is 3h,proportion of starch and monomer is 3:1.The grafted starch/PVA packaging films were prepared by using the grafted starch and PVA.The results show that because of the hydrogen bonds increase,mechanical properties of films increase with PVA proportion increasing,but the oxygen permeation flux of the films decrease,when PVA proportion reaches 60%,PVA proportion decreases slightly; crosslinking degree increases with the concentration of glutaraldehyde increasing,tensile strength and elongation ratio increase,but the oxygen permeation flux of the films decrease, when the concentrate of glutaraldehyde reach 0.6%,the gel will appear and influence the maintaining of reaction;with the increase of the glycerol,the tensile strength and oxygen permeation flux of the films increase and the elongation ratio decreases,but the excessive amount of glycerol will affect the mechanical properties of films,as a result,the content of glycerol is controlled about at 15 percent.The optimum process parameters of the films preparation can be gained:PVA proportion is 55%,concentration of glycerol is 15%,concentration of glutaraldehyde is 0.6%,reaction temperature is 85℃,and reaction time is 25min.The preservation experiments of strawberries with grafted starch/PVA films with different preservative were done.The results show that strawberries mildew which were packaged by grafted starch/PVA films at 1.5 days at room temperature,and the strawberries mildew which were packaged by grafted starch/PVA keep-fresh packaging films at 2 days, the weight-loss of the strawberries decrease 1.9%and 7.57%and the content of the V_C of the fruits increase 4.64%and 6.02%compared with the grafted starch/PVA films at 1.5 days.At 4℃,the weight-loss of the strawberries decrease 7.18%and 1.92%and the content of the V_C of the fruits increase 7.04%and 6.22%compared with the grafted starch/PVA films after 4 days.From the above data,it can be concluded that the grafted starch/PVA fresh-keeping packaging films have a certain degree of effect to keep strawberry fresh.