Preparation Of Antibacterial Starch-ZnO Nanoparticles And Starchbased Antibacterial Film

Starch film is a biodegradable,renewable,economical and environmentally-friendly,but its mechanical properties and barrier properties are poor.Addition of zinc oxide（ZnO）nanoparticles can solve the above problems and provide the starch film with antibacterial properties.However,ZnO nanoparticles have extremely high reactivity and poor compatibility with starch film and are easy to aggregate,resulting in the decrease or even loss of the effect of ZnO nanoparticles on starch film.It was found that addition of polysaccharides in the preparation system of ZnO nanoparticles could effectively prevent aggregation of ZnO nanoparticles.Among these polysaccharides,starch performed best,which might be due to that the helical cavity structure of starch could encapsulate ZnO nanoparticles,thereby further restricting aggregation of ZnO nanoparticles.In addition,the side chain length of amylopectin is shorter than that of amylose,and amylopectin contains branches,which hinders the formation of helical cavity structure.Therefore,the complexing ability of amylose with guest molecules is stronger than that of amylopectin.It was speculated that the higher the amylose content in starch,the stronger the dispersion and stability of ZnO nanoparticles.Therefore,in this paper,starches with different amylose contents were used as stabilizer to prepare antibacterial agent ZnO nanoparticles,and the effect of amylose content of starch on the structure and properties of ZnO nanoparticles was studied.The obtained ZnO nanoparticles were used in the preparation of starch films to explore the effects of ZnO nanoparticles stabilized by starches with different amylose contents on the properties of starch films.Finally,the addition amount of ZnO nanoparticles with the best effect was optimized.The main research contents and results are as follows.Firstly,ZnO nanoparticles,the antibacterial agent,were prepared by the chemical precipitation method with zinc acetate as the precursor,sodium hydroxide as the precipitant and starches with different amylose contents as the stabilizer.Scanning electron microscope analysis suggested that ZnO particles were hexagonal wurtzite crystals,and the optimal addition of starch,the stabilizer,was 2.0%.X-ray diffraction analysis suggested that ZnO particles were successfully prepared in the absence and presence of starch.Transmission electron microscopy analysis demonstrated that when starch was added into the preparation system of ZnO nanoparticles,the prepared ZnO particles were coated with starch,which indicated that ZnO nanoparticles prepared in the presence of starch were starch-ZnO hybrid nanoparticles.However,in the presence of waxy corn starch,some starch particles appeared around the waxy corn starch-ZnO nanoparticles.In addition,the average particle size of high-amylose corn starch-ZnO hybrid nanoparticles,normal corn starch-ZnO hybrid nanoparticles,waxy corn starch-ZnO hybrid nanoparticles and pure ZnO nanoparticles was 7.7 nm,34.6 nm,148.3 nm and 204.0 nm,respectively.This result proved that starch with high amylose content had stronger ability to disperse and stabilize ZnO nanoparticles.Thermogravimetric analysis showed that the starch content in high-amylose corn starch-ZnO hybrid nanoparticles,normal corn starch-ZnO hybrid nanoparticles,and waxy corn starch-ZnO hybrid nanoparticles was 19.1%,12.4%,and 28.9%,respectively.According to the results of transmission electron microscopy,some starch particles appeared around the waxy corn starch-ZnO hybrid nanoparticles,which might lead to the highest starch content in the waxy corn starch-ZnO hybrid nanoparticles.Moreover,it was found that the high-amylose corn starch-ZnO hybrid nanoparticles had the strongest crystallinity,ultraviolet absorption ability and antibacterial ability.In summary,high-amylose corn starch has the strongest ability to disperse and stabilize ZnO nanoparticles.Secondly,effects of four kinds of ZnO nanoparticles prepared above on the mechanical properties,barrier properties,antibacterial ability and micromorphology of starch films were investigated.Firstly,the basic formulation of the starch film was obtained,including 3.0%starch,0.3%citric acid,and 1.0%glycerin.In addition,it was found that addition of pure ZnO nanoparticles,high-amylose corn starch-ZnO hybrid nanoparticles,normal corn starch-ZnO hybrid nanoparticles,and waxy corn starch-ZnO hybrid nanoparticles significantly enhanced the mechanical properties,barrier properties and antibacterial properties of starch films.Among them,addition of high-amylose corn starch-ZnO hybrid nanoparticles had the best effect on the improvement of starch film properties.When high-amylose corn starch-ZnO hybrid nanoparticles were added,the tensile strength of the starch film was increased from 0.86 MPa to14.01 MPa,the water vapor permeability was decreased from 15.48×10^-11 gm^-1s^-1Pa^-1to 8.63×10^-11 gm^-1s^-1Pa^-1,and the antibacterial properties were also significantly improved.In addition,scanning electron microscopy analysis showed that four kinds of ZnO nanoparticles had good compatibility with starch film,and the high-amylose corn starch-ZnO hybrid nanoparticles had the best compatibility with starch film.Finally,using the mechanical properties,barrier properties and antibacterial properties of starch films as indexes,the addition amount of high-amylose corn starch-ZnO hybrid nanoparticles was optimized.It was found that the optimum addition amount of high-amylose corn starch-ZnO hybrid nanoparticles was 10.0%,which might be due to that when the particle content was not more than 10.0%,the high-amylose corn starch-ZnO hybrid nanoparticles had good compatibility with the starch film.However,when the nanoparticle content was more than 10.0%,nanoparticles aggregated and particles appeared on the surface of starch film.