Preparation And Characterization Of Lignocellulosic Antibacterial Film For Fresh-keeping Packaging

Food quality and safety has been a big issue of closely concerned by food manufacturers and consumers.The development of various packaging technologies and packaging materials for the purpose of keeping freshness became the forefront and hotspot in current scientific research.Degradable fresh-keeping film based on cellulose matrix is considered non-toxic,harmless,cheap and easy to obtain,owning incomparable advantages versus traditional plastic cling film.In addition,it is of great significance to choose a suitable antibacterial agent,develop a cellulose-based fresh-keeping film with high antibacterial ability without harmful to the human body.In this paper,wood chips from low-cost and fast-growing poplar were used as raw materials.high polymerization and purity cellulose were obtained through environmental-friendly treatment.The cellulose was then dissolved and cast to the regenerated cellulose film.Three kinds of antibacterial agents including organic phase silver nanoparticles solution,N-benzyl-N,N-diethyl chitosan quaternary ammonium salt and quaternized cellulose were prepared by different methods.The antibacterial agents were then used as fillers blended with the obtained cellulose to fabricate cellulose-silver nanoparticles composite film,quaternized chitosan-cellulose composite film and cellulose-cellulose quaternary ammonium salt composite film.The morphology,chemical structure and performance of the obtained cellulose,antibacterial agent and cellulose antibacterial film were comprehensively characterized and systematically studied by scanning electron microscopy,transmission electron microscopy,Fourier transform infrared spectroscopy,X-ray diffraction,nuclear magnetic resonance,high performance liquid chromatography,thermogravimetry and other technical means.The antibacterial performance of antibacterial agents and films were characterized by using the minimum bacteriostatic concentration text,the minimum bactericidal concentration text,the inhibition zone text,the"film cover method" and the "immersion culture method".The residual solvent rate and biosafty of the films were detected by inductively coupled plasma chromatography,gas chromatography-mass spectrometry,and inverted microscope.The obtained films were then used to packaged blueberry to verify their fresh-keeping effects,differences and principles.The main research contents can be summarized as follows:The nitro acid-ethanol treatment cooperate with mechanical dispersion was used to treated poplar wood chips.And the cellulose samples with different degrees of treatment were obtained by controlling the treatment time.The mechanical dispersion treatment helped to the soften lignocellulosic raw material fibers,promoted the surface layer fibers fell off,in order to make the inner layer fibers exposed to the solution.Thus,all fibers are fully infiltrated by the solution and participation in the reaction during the subsequent processing.The content of the remaining components in the fiber declined with the degree of treatments increase.Most of the lignin was nitrated and oxidized by nitric acid,and hemicellulose was hydrolyzed in a short period of treatment time,which make the fiber behave superior dispersibility.After third treatment,the obtained cellulose sample preformed the highest α-cellulose content and average degree of polymerization.It also showed good crystallinity and thermal stability compared to other samples.Therefore,the sample was more suitable as a raw material for film formation.Silver nanoparticles solution,N-substituted quaternized chitosan quaternized cellulose were prepared and their structures and properties were studied.An organic phase uniform dispersed silver nanoparticles solution with good stability was prepared by reducing silver ions through the organic phase system.Various coordination bonds between polyvinylpyrrolidone and silver nanoparticles(N:Ag:O and O:Ag:O)makes it stable in N,N-dimethylacetamide solution.The quaternized chitosan with good water and organic solubility was prepared.Characterization results revealed that chitosan formed chitosan Schiff base intermediate,and then it was reduced to produce a chitosan derivative,and the desired product was produced through quatemization.Using the obtained cellulose as a polymer base,a cellulose quatemized ammonium salt was produced through a three-step reaction.After 8 h of homogeneous ATRP polymerization between cellulose-BiBBr and 2-(Dimethylamino)ethyl methacrylate(DMAEMA),the growth trend of the reaction product quality was nearly flat.And the degree of polymerization of the modified cellulose particles obtained through the quaternization reaction was relatively uniform.The antibacterial results show that all three products can be used as antibacterial fillers for the fabrications of antibacterial cellulose films.The obtained cellulose was dissolved and regenerated to cellulose film.In addition,cellulose was blended with three antibacterial agents to produce three types of cellulose composite films.The uniformity,light transmittance and thermal stability of all cellulose films were remarkable.The addition of the antibacterial agent caused the physical and chemical structure change of the film,resulting in changs in film properties.The tensile strength of the films are higher compared with some of the antibacterial films obtained in recent studies.Thereby,the obtained cellulose-based composite films present high application potential in antibacterial film fields.The antibacterial ability and cytotoxicity of the antibacterial cellulose films were characterized,and the antibacterial mechanism and safty were studied.The antibacterial mechanism of the silver-loaded cellulose film can be summarized as:The silver nanoparticles on the film surface adsorbed bacteria and destroy the bacterial cell membrane,and a small amount of antibacterial agent was diffused into the bacterial solution to adsorbed bacteria as well.This prompted the film to exhibit the fastest sterilization rate.While,the effect of quaternized cellulose film and quatemized chitosan-cellulose film sterilization only through adsorption process.Thus,the sterilization rate of two films are slower.The low content of cellulose solvent system remains and good biosafety in the four types of films revealed that the films could be applied in the fresh-keeping packaging field.The fresh-keeping packaging experiments of cellulose films on blueberry were conducted,the difference and mechanism of antibacterial cellulose film on the fresh-keeping effect of blueberries were investigated.The results of packaging at 20℃ showed that the silver-loaded cellulose film,quatemized cellulose film and quatemized chitosan-cellulose film present antibacterial activities that effectively slowed down the growth of microorganisms in blueberries.The silver-loaded cellulose film presents the highest effect on inhibit the respiration and oxidation of blueberry.The quaternized cellulose film has the best effect on nutrient retention of blueberry.