Study On The Preparation And Properties Of Corn Nano-starch Based Composite Film

In this paper,corn nano-starch(CNS)was used as film-forming matrix and glycerol as plasticizer to prepare com nano-starch based film by casting.The preparation process of nano-starch based film was studied,and on the basis of single factor,the preparation conditions were optimized by the Analysis of Variance(ANOVA)and Response Surface Methodology(RSM).Cellulose nanocrystals(CNC)with different raw materials was obtained by sulfuric acid hydrolysis of the bleached kraft hardwood pulp,bleached kraft softwood pulp and cotton pulp.And the effects of CNC from different raw materials on the physical properties,mechanical strength and barrier properties of corn nano-starch based composite films were studied.The modified CNC(MCNC)with esterificationof citric acid and amideation of chitosan was obtained.And the effects of MCNC on the mechanical strength,barrier properties and antimicrobial activity of corn nano-starch based composite film were studied.Also the surface morphology,microstructure,crystal structure,chemical composition,thermal stability and hydrophobicity of CNC,MCNC and corn nano-starch based composite films were characterized by Transmission electron microscopy(TEM),Fourier transform infrared analysis(FTIR),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction spectroscopy(XRD).The results showed that the optimal process conditions for the preparation of corn nano-starch film were as follows:the concentration of corn nano-starch of 13.0%,the dosage of glycerol of 13.0%and the gelatinization temperature of 67?.The tensile strength of the film was 10.9 MPa and the elongation at break was 9.8%.XRD showed that the crystalline types of the film were A and V-mixed crystals;DSC showed that the thermal stability of corn nano-starch based film was higher than that of corn nano-starch.The yields of softwood-CNC,hardwood-CNC and cotton-CNC were 40.16%,42.48%and 50.39%,respectively.Three kinds of CNC can enchance the mechanical and barrier properties of corn nano-starch based composite film.When the dosage of hardwood-CNC was 4.0%,the tensile strength,elongation at break,water absorption and water vapor transmission rate(WVP)of CNS/CNC composite film were 16.3MPa,6.8%,19.4%and 3.48×10-10 g/(m·s·Pa),respectively;when the dosage of softwood-CNC was 6.0%,the tensile strength,elongation at break,water absorption and WVP of CNS/CNC composite film were 12.2MPa,5.2%,16.1%and 3.20×10-10 g/(m·s·Pa),respectively;when the dosage of cotton-CNC was 8.0%,the tensile strength,elongation at break,water absorption and WVP of CNS/CNC composite film were 16.5 MPa,3.0%,13.6%and 2.61×10-10 g/(m·s·Pa),respectively.The tensile strength of the CNS/CNC composite film increased by 334.0%,226.0%and 342.0%,respectively,compared with the corn nano-starch-based film.And the WVP decreased by 28.0%,39.0%and 41.0%,respectively,compared with the corn nano-starch based film.The results showed that the hardwood-CNC and cotton-CNC improved the mechanical strength and barrier properties of CNS/CNC composite films more significantly;XRD and DSC showed that CNC increased the crystallinity of nano-starch based composite film and improved the thermal stability of composite film.FTIR and XPS showed that CNC was successfully modified by citric acid and chitosan by two-step method.And MCNC improved the properties of corn nano-starch based composite film.When the dosage of MCNC was 8%,the solubility,transmittance,tensile strength,elongation at break,water absorption,WVP and water contact angle of CNS/MCNC composite film were 49.7%,41.2%,11.3 MPa,5.6%,23.8%,0.56×10-10 g/(m·s·Pa)and 60.0°,respectively.Compared with the pure corn nano-starch base film,the tensile strength increased by 200.0%,WVP decreased by 87.0%,water contact angle increased by 26.0%.The antibacterial activity test showed that CNS/MCNC composite film had good antibacterial effect against Staphylococcus aureus and Escherichia coli,especially for the Staphylococcus aureus.