Preparation Of Polylactic Acid-based Nanocomposite And Its Application In Food Packaging

Polylactic acid（PLA）is a kind of green and environmental friendly thermoplastic polyester with good biodegradability and biocompatibility.It has good optical properties,convenient processing and simple operation.It is currently the most promising biodegradable polymer in the market.However,its application is greatly limited due to its brittleness,low strength and poor barrier properties.In this paper,epoxy soybean oil was selected as plasticizer,nano-CaCO₃ and zeolite in different proportions were blended with PLA by melt blending,and the effect of nano-CaCO₃ and zeolite on the properties of PLA blown film were studied.The specific research contents are as follows:Firstly,he PLA blown film molding process was studied by using the controlled single factor method,so that it can be successfully extruded and blowed into a film.The effects of processing temperature,screw speed,blowing ratio and traction ratio on the mechanical properties of PLA blown film were investigated.The results showed that the mechanical properties of PLA blown film was the best when the processing temperature is 155,170,175,185°C,the screw speed is 35 rpm,the blowing ratio is 2.6,and the traction ratio is 5.0.Secondly,epoxy soybean oil was used as plasticizer to improve the flexibility of the material.Nano-CaCO₃ and zeolite with different proportions were blended with PLA by melt blending method to study the effect of nano-CaCO₃ and zeolite on the physical properties of PLA composites.The results found that the tensile strength and elongation at break of the films both increased first and then decreased with the increase of CaCO₃/zeolite mass fraction.When the mass fraction of CaCO₃ was 6%,the tensile strength and elongation at break of the composite film was 65.35 MPa and 11.73%,which was 24.69%and 160.67%higher than those of pure PLA respectively.When the mass fraction of zeolite was 8%,the maximum tensile strength was 76.23 MPa and the elongation at break was 9.27%,which increased by 45.45%and 106.00%respectively.The results showed that both CaCO₃ and zeolite as nucleating agents could play the role of strengthening and toughening,but the effect of zeolite filled and modified PLA were better,and the physical properties were better.Finally,the cross-section morphology of the zeolite/PLA composite was observed by SEM.It was found that when the mass fraction of zeolite was less than 4%,it could be more evenly dispersed in the matrix.DSC analysis showed that Tg decreased slightly,Tc moved to the low temperature direction,the crystallization temperature range was widened,and the crystallinity increased from 34.63%to 42.76%,indicating that zeolite promoted the crystallization process of PLA.The results showed that when the content of zeolite was 8%,the barrier performance of the composite were the best,and the oxygen permeability coefficient,carbon dioxide permeability coefficient and water vapor transmission coefficient reach the lowest,which was 0.59×10^-8 cm³·cm/（cm²·s·Pa）、1.95×10^-8 cm³·cm/（cm²·s·Pa）and 2.79×10^-7 g m/（m²·h·Pa）,which was 11.94%,8.45%and 21.63%lower than those of pure PLA respectively,The results showed that the zeolite/PLA composite had excellent air and moisture blocking effect and played an important role in the application of modified atmosphere packaging for food.In conclusion,when epoxy soybean oil was used as a plasticizer,zeolite was used as a filler and the mass fraction of zeolite was 8%,it could improve the defects of PLA’s brittleness,low strength,and poor barrier properties,and obtained blow molding with excellent mechanical properties and barrier properties film.