| At present,petroleum-based materials that are the main material of the packaging films not only accelerated oil consumption,but also causeed“white pollution”,which made the demand for biodegradable materials more urgent.Starch and polylactic acid,as biodegradable materials,have the advantages of wide source and reproducible characteristics.Therefore,the production of monolaye packaging films using biodegradable materials such as starch and polylactic acid has become a hot spot for research today,but the monolayer films were affected by moisture inside and outside t.To better solve this problem,this paper prepared a starch/polylactic acid bilayer films with starch and polylactic acid.The hydrophilic starch layer was used as the inner layer to absorb the internal moisture,and the hydrophobic polylactic acid layer was used as the outer layer to prevent the external moisture in order to improve the preservation of the film.The main findings are as follows:A pea starch/polylactic acid bilayer film was prepared by solution casting method,using pea starch and polylactic acid as raw materials and the optimum technological conditions for the preparation of the starch layer were explored.When the dosage of polylactic acid layer was50%,the water absorption?37.43%?,solubility?20.67%?and water vapor transmission coefficient(0.27×10-10 g·cm/?cm2·s·Pa?)of the pea starch/polylactic acid ilayer film were the lowest.And the minimum elongation at break?16.11±0.16%?,maximal tensile strength?13.47MPa?and tensile modulus?0.848 GPa?was achived.FT-IR analysis confirmed the two components were fited together by mechanical bond result to not tightly connecte.Based on the above problems,pea starch was hydrophobically modfied by octenyl succinic anhydride,and the modified starch was added as an intermediate layer to the composite films.A starch/modified starch/polylactic acid composite membrane was prepared by solution casting method.The optimum reaction conditions for the modification reaction were confirmed by scanning electron microscopy and infrared spectroscopy of the modified starch.Compared with the performance of the pea starch/polylactic acid bilayer film,the addition of the modified starch layer resulted in the water absorption,dissolution rate,water vapor transmission coefficient,and mechanical properties of the starch/polylactic acid composite film all decreased slightly.Importantly,the starch/modified starch/polylactic acid composite film had only one break point in the stretching process.The results showed that the addition of the modified starch layer contributed to the polylactic acid layer to bind more tightly with the starch layer.The prepared starch/modified starch/polylactic acid composite film was used as a preservative film for packaging cherry tomatoes.The PS/MPS/PLA films substantially reduced the rate of weightlessness,rotting rate,and the content of soluble solids of cherry and maintained the total acid content,vitamin C content and hardness. |
PDF Full Text Request