Preparation And Study On Polylactic Acid Film For Food Preservation Packaging

After producing and processing,food was extremely vulnerable to environmental impacts during transportation and sales.Food packaging could effectively prevent further spoilage of food.In order to effectively ensure the safety of food and extend the shelf life,this paper used polylactic acid as the substrate to prepare polylactic acid breathable films,polylactic acid antibacterial films,and polylactic acid degradation films.We investigated the effects of functional substances on the morphology,thermal properties,and mechanical properties of polylactic acid composite films.We tested the permeability of polylactic acid breathable films,the antibacterial properties of polylactic acid antibacterial films,and the degradation properties of polylactic acid degradation films.Finally,we investigated the fresh-keeping effect of polylactic acid breathable films and polylactic acid antibacterial films on vegetables,fruits and meat.The main results were as follows:1.A series of polylactic acid permeable films with different N-methylpyrrolidone(NMP)additions were prepared by non-solvent induced phase separation method.The results of scanning electron microscopy showed that the addition of NMP could cause a porous structure inside the film.The test results of the permeability of the polylactic acid breathable film also proved that when the NMP addition amount was 10%,the water vapor transmission rate and air permeability of the film reached the maximum,while the light transmittance gradually decreased with the increase of the NMP addition.Through the test of thermal properties,it was found that the addition of NMP had a small effect on the melting temperature of the film,and the thermal decomposition temperature slightly increased.However,both T_g and T_c showed a trend of increasing first and then decreasing with the increase of the NMP addition.The results of mechanical properties showed that the addition of NMP made the tensile strength of the film continuously decrease,and the elongation at break increase first and then decrease.The test results of the freshness-preserving effect of vegetables,fruits and meat showed that the polylactic acid breathable film can extend the shelf life of vegetables and fruits by 2-3 days and the shelf life of meat products by 3 days compared with the plastic wrap.2.A series of polylactic acid antibacterial films were prepared by blending chitosan,tea polyphenols,MgO and silver as antibacterial agents with polylactic acid solution,respectively.These composite films showed strong antibacterial effects on E.coli.The thermal performance test found that the addition of each antibacterial agent had little effect on the melting temperature of the composite films.The transmittance of the composite films were generally reduced,and tea polyphenols had the largest effect on the transmittance.As the content of antibacterial agent increased,the tensile strength of each polylactic acid antibacterial films decreased,and the elongation at break increased.Among them,silver had the smallest effect on tensile strength,and MgO had the largest effect on elongation at break.Using polylactic acid antibacterial films for meat packaging,the test results showed that the meat packaged with polylactic acid antibacterial films could generally extend the shelf life of 5 days compared with plastic wrap packaging.3.Four different polylactic acid composite films were prepared by blending polylactic acid with starch,polyethylene glycol,and sodium carboxymethyl cellulose in different proportions and combinations.Tests on the degradation performance of the composite films found that the degradation rate of the four composite films were higher than that of the pure PLA film,and the degradation performance was better with the increase of the amount added.The results of thermal performance tests showed that polyethylene glycol(PEG)improved the compatibility of polylactic acid with starch,resulting in a lower melting point and no significant change in the remaining composite films.The addition of starch,sodium carboxymethylcellulose and PEG all affected the light transmittance of polylactic acid films,of which starch had the largest impact and PEG had the smallest.The results of the mechanical properties of each composite film showed that the tensile strength of the composite film continued to decrease with the increase of the addition amount,while the elongation at break was increased to a certain extent.