Study On The Properties And Degradation Behavior Of Polylactic Acid/Gelatin Blends

The use of plastic products not only brings convenience to human beings,but also poses a great threat to human living environment.With the improvement of environmental awareness and the urgent need to improve the environment,biodegradable plastics have gradually gained more and more attention.Polylactic acid(PLA)not only comes from renewable natural resources,but also forms starch substances after being completely decomposed into carbon dioxide and water through plant photosynthesis,which again provides raw materials for PLA synthesis and realizes carbon cycle.It is an environmentally friendly and sustainable biodegradable plastic with great potential to replace petroleum-based polymer materials.However,the low toughness and high cost limit its application in industrial production.Therefore,it is not only necessary to toughen PLA,but also to introduce biodegradable and low-cost materials to reduce the cost of PLA blends while ensuring that the biodegradability of PLA blends is not affected.It is a simple and effective way to improve the elongation at break and impact strength of PLA blends by toughening PLA blends with plasticizers,but it still cannot ensure the biodegradability of PLA blends on the basis of reducing the cost.Therefore,this project aims to reduce the cost of the blend material and improve its biodegradability by melting and blending low-cost biological macromolecular gelatin with PLA.Then,plasticizers are used to toughen and modify the blend material,making it have excellent comprehensive properties.And the degradability of the blend material was studied through alkaline solution degradation and biological composting degradation.The research content of this topic is as follows:1.The 20 phr plasticizer acetyltributyl citrate(ATBC),epoxy soybean oil(ESO),low molecular weight polyethylene glycol(PEG)and low molecular weight polypropylene glycol(PPG)were melted and blended with PLA and polylactic acid/gelatin(PLA/GEL)blends by torque rheometer to explore the effects of different plasticizers on the mechanical properties,melt fluidity,and crystallization behavior of PLA.The results show that after the introduction of gelatin in the system,the toughening effect of the four plasticizers is: ATBC>PPG> PEG>ESO.The addition of plasticizer increases the elongation at break,notched impact strength and melt flow rate of the blended material,and increases the crystallinity while reducing the glass transition temperature of the blended material.2.ATBC was selected to toughen and modify PLA and PLA/GEL blends.The results show that with the increase of ATBC content,the toughness of modified PLA and modified PLA/GEL blends increases.The addition of gelatin can improve the bending strength and bending modulus of the blend,but the poor compatibility of PLA and gelatin,and the high content of gelatin is not conducive to the improvement of the toughness of the blend.When the content of ATBC in modified PLA and modified PLA/GEL blends increases from 15 phr to 20 phr,the "brittle ductile transition" occurs because ATBC undergoes a phase transition and forms a cocontinuous phase with PLA.Gelatin promotes the crystallization of the blend through heterogeneous nucleation and improves its crystallinity.At the same time,due to the good hydrophilicity of gelatin,it can promote the degradation of blends.3.In the modified PLA/GEL blend,homemade compatibilizer polylactic acid grafted maleic anhydride(PLA-g-MAH)and polylactic acid grafted glycidyl methacrylate(PLA-g-GMA)were added.The compatibility of PLA and gelatin was improved by chemical methods,thereby improving the toughening effect of ATBC.The results showed that the addition of PLA-g-MAH improved the plasticization efficiency of ATBC(reducing the ATBC content of the "brittle ductile transition" of the blend)and had an inhibitory effect on the decrease in tensile strength of the blend.This is because the chemical reaction between PLA-g-MAH and gelatin improved the compatibility of PLA and gelatin.The addition of PLA g-GMA did not change the ATBC content of the "brittle ductile transition" of PLA/GEL blends,but it significantly improved the tensile strength of PLA/GEL blends.The compatibilizer PLA-g-MAH increased the degradation rate of the blend in alkaline solution,while PLA-g-GMA reduced the degradation rate of the blend in alkaline solution.