Hui Chen

Despite the recent advances in protein-based adhesives, the poor water resistance and unsatisfactory mechanical property limit the industrial application of soybean protein adhesive. It is challenging to achieve strong adhesion and high water resistance. In this work, chitosan, tannic acid and silver ion were used to modify soybean protein adhesive. Through chelation, redox reaction and hydrogen bonding, a dynamic crosslinking network structure was constructed, so as to prepare a bio-based adhesive with high water resistance and high bonding strength. It was revealed that when the tannic acid and silver nitrate were mixed at the same concentration of 10 mg/mL and the volume ratio of 1:1, silver nanoparticles with the highest content were produced. When the mass of soybean protein, chitosan, tannic-silver solution and distilled water was 15, 0.3, 30 and 55 g, respectively, the enhancement effect was the best. The dry shear strength increased by 171% to 3.03 MPa, and the wet shear strength increased by 93% to 1.29 MPa. The water resistance, thermal stability, hydrolysis stability, and the toughness and viscosity of the soybean protein adhesive were greatly improved. This study developed a new bio-based adhesive and expanded its potential application in wood products manufacturing.

The demands for strong integrated biopolymer materials have substantially increased across various industries. In this study, a biomimic strategy was proposed to prepare the poly(dopamine)‐functionalized carbon nanotubes (PDCNTs) via mussel‐inspired chemistry. The graphene dispersion was prepared in aqueous bovine serum albumin solution by ultrasonic treatment through a facile and green approach. Inspired by the excellent integration of mechanical properties and hierarchical nano/microscale structure of natural nacre, we fabricated soy isolate protein (SPI)‐based nanocomposite film with 2D graphene nanosheets and 1D surface‐functionalized PDCNTs through a layer‐by‐layer assembly process. The morphology and thickness of graphene nanosheets were analyzed by atomic force microscopy. The successful surface modification of PDCNTs was confirmed by X‐ray photoelectron spectroscopy and transmission electron microscopy. The cross‐linking hierarchical structure of the SPI hybrid film was observed in scanning electron microscopy images. A combination of multiple interfacial interactions and enhanced adhesion between the PDCNTs‐graphene conjugation and SPI matrix resulted in a remarkable improvement in the mechanical properties of the SPI‐based nanocomposites. When compared with the unmodified film, the tensile strength and elongation at break of the hybrid film were simultaneously increased by 158.93 and 78.67%, respectively. As a result of the enhanced tortuosity effect, the water vapor permeability was significantly reduced by 33.65%. In addition, the resultant film also possessed favorable water resistance, thermal stability, and ultraviolet–visible light barrier behavior. This work provided a novel bio‐inspired interfacial toughening strategy for constructing high performance biopolymer nanocomposites. POLYM. COMPOS., 40:E1649–E1661, 2019. © 2018 Society of Plastics Engineers

Wood composites used in indoor living environments often pose formaldehyde emission and fire hazard problems. In this study, magnesium oxychloride cement-based (MOC) inorganic adhesives are presented as an effective and sustainable binder for plywood applications. The phase composition, microstructure, and thermal stability of the adhesives prepared with different ratios of MgO/MgCl₂ were investigated. In addition, the dry and wet shear strength and the combustion behavior of the plywood were also examined. The results indicated that the limiting oxygen index (LOI) values of the plywood bonded by the MOC adhesives were higher than those of the plywood bonded by urea-formaldehyde resin. The active MgO/MgCl₂ molar ratio of 7 was the optimal ratio for the dry and wet shear strength of the plywood with values of 1.02 and 0.88 MPa, respectively, which meet the interior use panel (Type II plywood) requirements. These improvements were ascribed to the increasing ratio of MgO/MgCl₂ that facilitated the formation of an excellent microstructure. Meanwhile, the continuous hydration phase strengthened the interaction between the MOC adhesive and the wood. With these improved properties, MOC adhesive is expected to be widely used for industrial applications in plywood fabrication.

A facile, inexpensive, and green approach for the production of stable graphene dispersion was proposed in this study. We fabricated soy protein isolate (SPI)-based nanocomposite films with the combination of 2D negative charged graphene and 1D positive charged polyethyleneimine (PEI)-modified cellulose nanocrystals (CNC) via a layer-by-layer assembly method. The morphologies and surface charges of graphene sheets and CNC segments were characterized by atomic force microscopy and Zeta potential measurements. The hydrogen bonds and multiple interface interactions between the filler and SPI matrix were analyzed by Attenuated Total Reflectance–Fourier Transform Infrared spectra and X-ray diffraction patterns. Scanning electron microscopy demonstrated the cross-linked and laminated structures in the fracture surface of the films. In comparison with the unmodified SPI film, the tensile strength and surface contact angles of the SPI/graphene/PEI-CNC film were significantly improved, by 99.73% and 37.13% respectively. The UV–visible light barrier ability, water resistance, and thermal stability were also obviously enhanced. With these improved functional properties, this novel bio-nanocomposite film showed considerable potential for application for food packaging materials.

This study applied a facile and green approach to synthesize a stable graphene aqueous dispersion, and the graphene aqueous dispersion was employed to modify the renewable, compatible and biodegradable soy-protein-isolated (SPI) films to enhance their thermal stability, mechanical properties and water resistance. Atomic force microscopy (AFM) images confirmed the monolayer structure of graphene. The hydrogen bonds and π–π interactions between graphene and the SPI molecules were showed with the attenuated total reflectance Fourier transform infrared (ATR FT-IR) spectroscopy, and X-ray diffraction (XRD). As expected, compared to the pure SPI film, the tensile strength (TS) of the film with 74% graphene increased by 27.22% and the total soluble matter (TSM) of the film with 93% graphene decreased by 11.30%.

Soy protein isolate (SPI) based films have received considerable attention for use in packaging materials. However, SPI-based films exhibit relatively poor mechanical properties and water resistance ability. To tackle these challenges, chitosan (CS) and endogenous Cu nanoclusters (NCs) capped with protein were proposed and designed to modify SPI-based films. Attenuated total reflectance-Fourier transform infrared spectroscopy and X-ray diffraction patterns of composite films demonstrated that interactions, such as hydrogen bonds in the film forming process, promoted the cross-linking of composite films. The surface microstructure of CS/SPI films modified with Cu NCs was more uniform and transmission electron microscopy (TEM) showed that uniform and discrete clusters were formed. Compared with untreated SPI films, the tensile strength and elongation at break of composite films were simultaneously improved by 118.78% and 74.93%, respectively. Moreover, these composite films also exhibited higher water contact angle and degradation temperature than that of pure SPI film. The water vapor permeation of the modified film also decreased. These improved properties of functional bio-polymers show great potential as food packaging materials.

Soy protein isolate (SPI)-based materials are abundant, biocompatible, renewable, and biodegradable. In order to improve the tensile strength (TS) of SPI films, we prepared a novel composite film modified with microcrystalline cellulose (MCC) and metal nanoclusters (NCs) in this study. The effects of the modification of MCC on the properties of SPI-Cu NCs and SPI-Zn NCs films were investigated. Attenuated total reflectance-Fourier transformed infrared spectroscopy analyses and X-ray diffraction patterns characterized the strong interactions and reduction of the crystalline structure of the composite films. Scanning electron microscopy (SEM) showed the enhanced cross-linked and entangled structure of modified films. Compared with an untreated SPI film, the tensile strength of the SPI-MCC-Cu and SPI-MCC-Zn films increased from 2.91 to 13.95 and 6.52 MPa, respectively. Moreover, the results also indicated their favorable water resistance with a higher water contact angle. Meanwhile, the composite films exhibited increased initial degradation temperatures, demonstrating their higher thermostability. The results suggested that MCC could effectively improve the performance of SPI-NCs films, which would provide a novel preparation method for environmentally friendly SPI-based films in the applications of packaging materials.

Eco-friendly films containing soy protein isolate (SPI), gelatin, and microcrystalline cellulose (MCC) were made by casting. Effects of MCC content on mechanical and thermal properties of MCC-reinforced SPI–gelatin (MSG) films were studied. With the increase of MCC content, thickness and tensile strength (TS) of MSG films increased, and the elongation at break (EB) decreased. MSG films containing 3.5% MCC (MSG3.5) had limit values of the thickness, TS, and EB of 108%, 351%, and 27% of those of films without MCC, respectively, while all MSG films exhibited lower moisture content and total soluble matter compared to SPI–gelatin film. The film with 1.5% MCC (MSG1.5) had the minimum value of moisture content as 16.41%, and film with 2.5% MCC (MSG2.5) had the minimum value of total soluble matter as 24.87%. Scanning electron microscope photomicrographs showed that MCC dispersed well in the SPI–gelatin matrix, and the films had a relatively smooth surface. Blending of 2.5% MCC caused a rough and uneven surface, resulting in a more ductile failure of MSG2.5 films. Attenuated total reflectance-Fourier transform infrared spectroscopy revealed that there was no intermolecular association via chemical bonds between MCC and SPI–gelatin. Thermo-gravimetric analysis showed that the thermal degradation of MSG films initiated at higher and ended at lower temperature than the SPI–gelatin film. Data from differential scanning calorimetry scans indicated that MSG films had a smaller degree of crystallinity, which was also confirmed by test results of a dynamic mechanical analyzer. Blending MCC with SPI–gelatin film has been successful in obtaining better mechanical and thermal properties as well as reduced moisture sensitivity. In addition, the films became more transparent, and transmittance was improved.