Preparation And Characterization Of Functional Nanoparticle Modified Protein-Based Composite Films

Biomass materials,which have the advantages of abundant yield,renewable and biodegradation,can solve the problems of energy shortage and environmental pollution to a certain extent,and become an important direction of scientific research.Soy protein,as a product of agricultural and forestry products processing,is the most abundant plant protein in nature.It has a huge output in China,and its development and utilization are of great significance.In this paper,soy protein isolate was used as the main raw material,and modified by functional metal nanoclusters and graphene nanomaterials.A series of high-performance SPI-based composite films were developed and applied in food packaging and active antimicrobial materials,providing new ideas and methods for expanding the use and added value of soy protein.The main research contents and conclusions are as follows:1.Soy protein isolate composite films were prepared by modification of metal nanoclusters.The dispersions of water-soluble copper nanoclusters and zinc nanoclusters were designed and synthesized by complexing soybean protein isolate with copper sulfate and zinc chloride containing divalent cations.The morphological characteristics of metal nanoclusters were analyzed by transmission electron microscopy and ultraviolet absorption spectroscopy,which showed that the size of copper nanoclusters in the solution was about 5 nm,while that of zinc nanoclusters was about 5 nm.The tensile strength of the modified composite films increased to 4.91 MPa,while the elongation at break of the zinc nanocluster modified composite films increased to 304.05%.The release of metal elements from the modified soybean protein isolate composite films was confirmed to meet the national food safety standards by metal release measurement.2.The composite film of soybean protein isolate was further modified by chitosan and microcrystalline cellulose.The surface morphology of the composite films was characterized by scanning electron microscopy.It was found that metal nanoclusters could significantly improve the biocompatibility between chitosan and soybean protein isolate,and make the composite films have more uniform structural characteristics.The water contact angle of the composite films modified by chitosan and zinc nanoclusters was significantly increased,which proved that they could further improve the hydrophobicity of the composite films.The tensile strength and Young's modulus of the composite films modified by chitosan and copper nanoclusters increased to 5.01 MPa and 197.50 MPa,respectively.3.Composite films of soybean protein isolate were prepared by modification of graphene/cellulose nanocrystals.A stable graphene aqueous dispersion was prepared by ultrasonic treatment in bovine serum albumin solution.Cellulose nanocrystals were modified by cationic polyethyleneimine.The modified positive-charged cellulose nanocrystals could generate strong charge with negatively charged graphene nanosheets,which effectively improved the compactness of the composite films of soybean protein isolate.The tensile strength of the modified composite films increased to 7.49 MPa,and the water vapor permeability and absorption were improved.Water-solubility decreased by 13.49%and 47.18%respectively.4.Soybean protein isolate composite films were prepared by dopamine modification.According to the biomimetic principle inspired by mussel adhesion protein,carbon nanotubes were chemically modified by dopamine,and soybean protein isolate films were modified by graphene nanosheets with unique functionality and carbon nanotubes with interfacial reinforcement.High-performance protein-based composite films were prepared.Because amino acids in soybean protein isolate and benzene ring structure in polydopamine molecule contain conjugated double bonds,the modified nanocomposite film exhibits stronger absorption to ultraviolet radiation;the tensile strength of the composite film increases to 10.15 MPa;the hydrophobicity of the composite film is improved,and the water contact angle increases from 38.150 to 52.78°;the maximum thermal degradation rate of the composite film increases from 38.15° to 52.78°.The temperature also increased from 308? to 312?,indicating that the modified protein-based nanocomposite film has better thermal stability,and is expected to be used in the preparation of heat-resistant packaging materials.5.Protein-based composite films were prepared by modification of silver nanoparticles.Silver nanoparticles were synthesized by in situ reduction of dopamine with strong reducibility and coordination between catechol and silver in dopamine,and were used to modify protein-based composite films.The water vapor transmittance and water absorption of the modified composite films decreased by 51.60%and 30.98%respectively,showing excellent barrier properties and water resistance;the tensile strength and breaking elongation of the composite films increased to 35.99 MPa and 71.31%respectively;and the temperature at the maximum thermal degradation rate increased from 310? to 319?,which proved that the thermal stability of the composite films was significantly enhanced;at the same time,the antibacterial properties of the composite films were remarkable.It shows obvious antimicrobial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli,and is expected to be applied to new active antimicrobial materials.