Study On Preparation And Properties Of Starch-based Biodegradable Materials

Starch is the most promising natural biodegradable material at present.Starch has the advantages of abundant sources and low price,but its water resistance is poor,and due to the the crystalline structurepart of starch,there are a lot of hydrophilic hydroxyl groups and hydrogen bonds between the molecular chains.So the melting temperature of starch is very high,making the thermal process difficult.Theromplastic starch(TPS)is prepared through plasticizing by plasticizer to destroy the crystalline structure of starch,so as the melting temperature of starch,makingthe thermal process of starch possible.The choice of plasticizer requires no pollution to the environment and no harm to the human body.In the past,many plasticizers with small molecular weight were used,but the choice of plasticizers was always the key to the performance of thermoplastic starch.At the same time,although thermoplastic starch can be formed by hot processing,its poor processing and use performance limits its application.Most of the researches took biodegradable polyester as matrix material and added a small amount of starch as filler to reduce the production cost,but starch-based plastics still need to be further studied.In this paper,glycerol and epoxidized soybean oil(ESO)were used as plasticizers to prepare glycerol thermoplastic starch(GTPS)and epoxy soybean oil thermoplastic starch(ETPS).To improve traditional thermoplastic starch processing and mechanical properties,water resistant properties,thermal stability and so on,retaining the starch biodegradable properties in the meantime,poly(butyl diacid butyl glycol ester(PBS)was usedto toughen and modify the GTPS.The effects of PBS and glycerol on GTPS/PBS blend system of rheological properties,mechanical properties,hydrophilic properties were studied.GTPS/PLA and ETPS/PLA blends were prepared by melt-blending polylactic acid(PLA)with two kinds of thermoplastic starches.The different crystallization behaviors of the two blends and the differences in rheological properties,mechanical properties,hydrophilic properties and heat resistance of the two plasticizers were compared.The main research results are as follows:By increasing the distance between the starch molecules and breaking the hydrogen bond between the starch hydroxyl groups,the small-molecule glycerol reduced the force between the starch molecular chains and destroyed the crystalline structure of the starch.However,ESO reacted with the hydroxyl group in the starch chain through the epoxy group in the molecular structure to destroy the intramolecular forces and the crystalline structure.Meanwhile,in the ETPS/PLA blend system,starch accumulation in the"microzone"of ESO was observed,and the crystal structure was gradually destroyed.Comparing the plasticizing efficiency of the two plasticizers,ESO was better than glycerol,and the epoxy soybean oil had less effect on the mechanical properties of starch,and had toughening effect.PBS can significantly improve the processing properties,mechanical properties and thermal stability of starch.Starch particles were dispersed in PBS phase during thermal processing,and then further plasticized under the action of heat and force field.When the addition amount of PBS was 25 wt%,the tensile strength of GTPS/PBS blend reached 18.46 MPa,which was 116.4%higher than that of pure GTPS.The elongation at break reaches 156.52%,which is 536.8%higher than pure GTPS,and the impact strength reached 2.3 KJ/m~2.Meanwhile,the thermal stability and hydrophilicity of the system were improved by PBS.According to the POM results,GTPS can promote the crystal growth of PLA in the crystallization process,while ESO can promote the cold crystallization process of PLA to a certain extent,and ETPS can promote the crystal nucleation of PLA.Compared with the two blends,ETPS/PLA blends have better compatibility,and ESO had less influence on the hydrophilicity of the blends,which can improve the thermal stability of the blends and show toughening effect.When two plasticizers were compounded,it can make up for the shortcomings of low plasticizing efficiency,poor hydrophilicity and thermal stability due to the glycerol’s plasticizing,and improved the toughness and heat endurance of blends.At the same time,formulation can reduce the amount of ESO,avoiding the unconvience of the storeage of ESO under the environment of high temperature and sunlight.