Preparation And Properties Of Starch/Lactic Graft Copolymer And Starch-based Film

With the over development and utilization of petroleum,energy shortages and environmental pollution have become one of the most serious issues facing humanity.Starch,as a natural macromolecular compound,has received extensive research attention because of its abundance,good biocompatibility and reproducibility.However,due to the strong water-solubility,complex processing procedures,as well as poor mechanical properties the applications of starch-based materials have been greatly restricted.Currently,starch-based materials are mainly used in the food industry or as fillers.In order to improve the mechanical properties and hydrophobicity of starch-based polymers,complexing of starch and lactic acid is a good solution.Lactic acid is another kind of renewable biodegradable compound possessing excellent mechanical properties.Modification of starch with lactic acid through grafted-copolymerization is promising to obtain fully-biodegradable starch/ lactic acid copolymers with improved mechanical properties.In this thesis,amylopectin is selected as the starch matrix and lactic acid is grafted onto it.Three kinds of catalysts,HCl,NaOH,and NaAC,are used to catalyze the grafted-copolymerization of starch and lactic acid,respectively.The obtained copolymers(St-g-PLA)were branched and the reaction conditions of three catalytic systems were optimized.The structures and morphologies of St-g-PLA were characterized by FT-IR,DSC,XRD,and SEM.Starch-based films(St-g-PLA/starch films)were prepared from the mixtures of St-g-PLA obtained through different catalytic systems and plasticized starch.The preparation processes were optimized.The mechanical properties of St-g-PLA/starch films under different experimental conditions were explored.The thermal performance and surface morphology of St-g-PLA/starch films were tested by DSC and SEM,respectively.The grafting degree of St-g-PLA obtained under the catalysis of HCl was 65%.The St-g-PLA/starch film obtained shows good mechanical properties.The tensile strength and elastic modulus were 8 MPa and 1073.5 MPa,respectively.The elongation at break is 3%.Under the catalysis of NaOH,the grafting degree of St-g-PLA was 117.4%.The St-g-PLA/starch film obtained shows better mechanical properties.The tensile strength and elastic modulus were 10 MPa,and 1905.8 MPa,respectively.The elongation at break was 3%.Under the catalysis of NaAC,the grafting degree of St-g-PLA was 121%.The St-g-PLA/starch film obtained shows the best mechanical properties.The tensile strength and elastic modulus were 12 MPa and 2040.2 MPa,respectively.The elongation at break was 3%.A reinforced starch-based composite film was prepared by adding carboxymethyl cellulose(CMC)as the reinforcing agent to the St-g-PLA/starch film.The reinforced composite film shows excellent mechanical properties,with tensile strength of 14 MPa,elastic modulus of 1810.7 MPa and elongation at break of 4%.