Waterborne Polyurethane Dispersions Research Articles

Degradable, anticorrosive, and fluorescent waterborne polyurethanes from vegetable oil internal emulsifiers for adhesives and strain sensor

In this work, three soybean oil internal emulsifiers with different −OH functionalities (203.03 ∼ 219.45 mg KOH·g−1) were prepared via the ring-opening reaction of epoxidized soybean oil (ESO) attacked by phosphoric acid. The soybean oil internal emulsifiers and castor oil (C.O) were employed to produce an array of DMPA- (dimethylol propanoic acid-) free anionic waterborne polyurethane dispersions (PUDs) with high bio-based content (69.2%) by utilizing the phosphoryl groups in ionic form. The curing films exhibited good mechanical properties, thermal stability, and multifunctionality (degradability, fluorescence, and anticorrosion). The films (WPU-P5, WPU-P10, and WPU-P15) can be completely degraded in 4.5 wt% NaOH solution for 10 h at room temperature. In addition, the films also displayed fluorescence under 365 nm UV irradiation, and the change of fluorescent intensity during material stretching and damage, which hence could be used to detect material tensile behavior and material damage. Due to the corrosion inhibition performance of the phosphoryl group and its excellent adhesion to the metal substrate, the WPU-P15 film had the best corrosion resistance. The adhesive capacity of the films as pressure sensitive adhesive was characterized by the shear strength test, hanging weight time and peeling test. The WPU-P10 film had a shear strength of 1.66 MPa, a hanging time of 1 kg weight up to 10 h, and a peel stress of 0.67 MPa. The WPU-P15 film was also applied in strain sensing to detect human activity. These studies are bound to further expand the application range of vegetable oil-based WPU materials.

Antibacterial waterborne polyurethane coatings impregnated with in-situ formed and capped silver nanoparticles via p-sulfonatocalix[4]arene

The development of antibacterial nanocomposite coatings has been well studied in response to antibiotic resistance concerns. In this regard, silver nanoparticles incorporated waterborne polyurethanes (WPUs) are among the most attractive area due to their unique properties such as biocompatibility, reduced use of volatile organic compounds (VOC), easy construction, low viscosity, high adhesion to various surfaces, and rapid film formation. In this project, silver nanoparticles (AgNPs) were in-situ formed and simultaneously stabilized in the presence of sodium p-sulfonatocalix [4]arene (p-SC4A) as both reducing and stabilizing agents. Subsequently, the p-SC4A-stabilized AgNPs (p-SC4A/Ag) were incorporated into waterborne polyurethane, which was synthesized by the prepolymer mixing method. Examination of the structure and morphology of p-SC4A/Ag nanostructures using FT-IR, XRD, UV, SEM, and TEM analyses confirmed the synthesis of p-SC4A/Ag NPs with a smaller size than 50 nm. In addition, the various properties of WPU films with and without SC4A/Ag were evaluated by ATR-FTIR, XRD, SEM, ICP, TGA, and contact angle tests. The results showed that using p-SC4A macrocycles not only solves the agglomeration problem of silver nanostructures in waterborne polyurethane dispersions but also significantly improves bacteria-killing efficiency against the gram-positive S. aureus and gram-negative E. coli bacteria relative to pure WPU. The biocompatibility of WPU films was also evaluated, and the results showed that samples containing SC4A/Ag NPs have good biocompatibility in contact with L929 fibroblast cells.

Preparation and optimization of WPU dispersion from polyether/polyester polyols for film and coating applications

BackgroundCastor oil and polytetramethylene ether glycol (PTMG) are used as polyester and polyether polyols. The waterborne polyurethane (WPU) resin is synthesized from polyether/polyester polyols following a ketone and catalyst-free pre-polymerization process. MethodsWPU resins are prepared from PTMG/castor oil with various hydroxyl molar ratios, such as 1/0, 3/1, 1/1, 1/3, and 0/1. Significant findingsThe results indicate that the WPU dispersions has a long shelf-life, high colloidal stability, and narrow distribution of molecular size. The addition of castor oil can increase the proportion of the cross-linking density, hard segments and hydrogen bonds of the WPU molecular chain. The addition of PTMG/castor oil increases from the molar ratio 1/0 to 1/1, the tensile strength of WPU film increases from 17.1 MPa to 25.6 MPa; the T5% increases from 250°C to 262°C; the water swelling ratio at 24 h decreases from 33.2 g/g to 19.4 g/g. The results indicate the using PTMG/castor oil can improve the mechanical strength, water resistance, and thermal stability of WPU film. The WPU could be applied to wood coatings with high properties. This study provides a cleaner process for optimizing the performance of WPU resin, which can replace conventional ketone- and organotin-based films and coatings.

Structural and adhesion properties of waterborne polyurethane adhesives containing nanosilica dispersion obtained with different physical mixing procedures

Nanosilica dispersion was added to waterborne polyurethane dispersion by using three different physical mixing procedures differing in the flow regime (tangential, laminar, radial) and the stirring rate (300–2400 rpm). The influence of the physical mixing procedure on the structural, thermal, rheological, mechanical, surface and adhesion properties of the polyurethanes (PUs) containing 1 wt% nanosilica was evaluated. The nanosilica in the dispersion was functionalized with acrylic moieties and showed high surface tension and negative Z potential values. The PU + nanosilica blend made with higher shear rate and laminar flow regime showed high homogeneous dispersion of the nanosilica particles and greater extent of intercalation between the soft segments of the polyurethane, this led to higher thermal stability. Unexpectedly, the better dispersion of the nanosilica in the PU matrix decreased the wettability of the PU + nanosilica materials due to the migration of acrylic moieties from the nanosilica particles to the surface. As a consequence, a decrease of the final T-peel strength was found. However, the single lap-shear strength did not change by adding nanosilica because of the scarce improvement of the mechanical properties in the PU + nanosilica materials.

Design, Preparation and Properties of Polyurethane Dispersions via Prepolymer Method.

A waterborne polyurethane dispersion for foamed synthetic leather base was designed and prepared using prepolymer method. There are many variables in the emulsification and chain-extension process of waterborne polyurethane (WPUR) dispersions prepared by prepolymer method. This work thoroughly evaluated the impacts of the steps of adding emulsified water, the temperature of the prepolymer and emulsified water, and concentration of ammonia water on WPUR dispersions by investigating the particle sizes/distributions and the mechanical stability. Changes in the temperature of the prepolymer and emulsified water, the concentration of ammonia water, and the step of adding emulsified water showed great impacts on the appearance and particle size of dispersions. Decreasing the temperature of the prepolymer and emulsified water and increasing the dilution ration of H2O to ethylenediamine (EDA) led to safe emulsification and dispersions with good appearance and narrow particle size distributions can be prepared. Surprising results were obtained by adding emulsified water in two steps, WPUR dispersions with a small particle size, narrow particle distribution and excellent tensile properties can be obtained. The optimized WPUR1 was applied to prepare water-based synthetic leather base after mechanical foaming, and the base presented the desired high performance, such as high folding resistance and peel strength.

Waterborne Polyurethane Dispersion Synthesized from CO2 Based Poly(Ethylene Carbonate) Diol with High Performance

Waterborne Polyurethane Dispersion Synthesized from CO2 Based Poly(Ethylene Carbonate) Diol with High Performance

Synthesis and Study of Properties of Waterborne Polyurethanes Based on β-Cyclodextrin Partial Nitrate as Potential Systems for Delivery of Bioactive Compounds

Eco-friendly waterborne polyurethanes (WPU) find wide application in agriculture as pesticide carriers, which enhances their efficiency. To provide better control of the retention time and capacity of pesticides, WPU can be modified by cyclodextrin derivatives able to form supramolecular assemblies with bioactive substances. Synthesis of WPU containing up to 15 wt.% of covalently bound β-cyclodextrin partial nitrate (CDPN) is reported in this work. Covalent bonding of CDPN to a polyurethane matrix has been proved by IR spectroscopy and size exclusion chromatography. The particle size and viscosity of the WPU dispersion have been determined. The introduction of CDPN affects molecular weight and thermal properties of WPU films. The presence of CDPN in WPU is shown to provide higher average molecular weight, wider molecular weight distribution, and larger average size of dispersed particles, compared with WPU reference samples containing 1,4-butanediol. The analysis of the rheological behavior of the obtained WPU dispersions shows that they can be classified as pseudoplastic liquids. The analysis of the thermal parameters of WPU films indicates that the introduction of 15.0 wt.% CDPN shifts the value of the glass transition temperature from -63 °C to -48 °C compared with reference samples. We believe that the results of the present study are sufficiently encouraging in terms of using CDPN-modified eco-friendly WPU as potential systems for developing the delivering agents of bioactive compounds. The application of such systems will allow the long-term contact of pesticides with the plant surface and minimize the possibility of their release into the environment.

Preparation of waterborne polyurethane with high surface activity for regulating the interfacial properties of carbon fiber/polyamide 6 composite

The poor wetting and spreading performances of waterborne polyurethane dispersion (WPUD) on carbon fiber (CF) surface limited its application in regulating the interfacial properties of CF reinforced polyamide 6 (PA6) composites. Unlike previous studies, this work diversified into improving the film-forming property of WPUD on CF surface. Two novel WPUD sizing agents named WPUD-Y1 and WPUD-F1 were synthesized by introducing block polyether and organic fluorine into the molecular chain. Results showed that surface energies of the elaborately designed WPUD-Y1 (35.5 mN/m) and WPUD-F1 (32.7 mN/m) were significantly lower than that of ordinary WPUD (40~55 mN/m). Especially, both sizings formed a complete and uniform film on CF surface. Interfacial shear strength (IFSS) analysis from micro-droplet test showed that sizing relieved the thermal residual stress at composite interphase by over 40%, at the cost of reducing its interfacial strength by 20%. More importantly, although sizing had not enhanced interfacial adhesion, the IFSS values between the sized CF and PA6 were still 20% higher than the maximum interlaminar shear strength (ILSS) values reported in literatures.

Multifunctional Waterborne Polyurethane Microreactor-Based Approach to Fluorocarbon Composite Latex Coatings with Double Self-Healing and Excellent Synergistic Performances.

In this article, chlorotrifluoroethylene (CTFE)-based fluorocarbon composite latexes and their coatings are successfully fabricated by an environmentally friendly preparation method based on a new multifunctional waterborne polyurethane (MFWPU) dispersion. It is worth noting that the MFWPU acts as the sole system stabilizer as well as microreactor and simultaneously endows the composite coating with excellent double self-healing performance and adhesion. Moreover, the introduction of a dynamic disulfide bond in the polyurethane dispersion entrusts the coating with excellent scratch self-healing performance. Simultaneously, carbon-carbon double bonds in the polyurethane dispersion increase the compatibility between the core polymer and shell polymer. The fluorine-containing chain segments can be distributed in the coating evenly during the self-assembly film-forming process of composite particles so that the original element composition of the worn coating surface can restore the original element composition after heating, and the coating presents a regeneration ability, which further and verifies the usefulness of the double self-healing model of the coating. Afterward, efficient recovery and durability, which are two contradictory properties of scratch self-healing polymers, are optimized to obtain a composite coating with excellent comprehensive performance. The research results regarding the composite system may provide a valuable reference for the structural design and application of waterborne fluorocarbon functional coatings in the future.

Waterborne hybrid polyurethane coatings containing Casein as sustainable green flame retardant through different synthesis approaches

Waterborne polyurethane (WPU) dispersions were prepared for flame retardant coatings. Specifically, alkoxysilane-capped polycaprolactone-based WPUs were synthesized employing the acetone process, and Casein, as a green and sustainable flame retardant additive, was added by two different methods (in situ and ex situ). These two strategies made possible to evaluate the effect of the Polyurethane/Casein interaction in the final properties of the dispersions and films. FTIR and solid-state 29Si NMR, confirmed the formation of the siloxane network during film generation process. The addition of Casein during the synthesis (in situ) resulted in a covalent bonding between the polyurethane and Casein, which significantly increased the particle size. However, the incorporation after phase inversion of the WPU (ex situ), did not change the particle size. Tensile tests revealed that the covalent bond promoted an increase in the brittleness of the material compared to ex situ approach due to a better dispersion of the Casein in the system. TGA results showed that Casein increased the thermal stability of all the coatings, especially of those obtained by the ex situ route. Moreover, and according to the microscale combustion calorimeter (MCC) and vertical burning test (UL-94) measurements Casein delayed the combustion of the material. Consequently, due to their characteristics, these Casein-WPU dispersions could potentially be used as combustion retardant coatings, where good physicochemical properties are essential for effective performance.

Functional properties of coatings based on novel waterborne polyurethane dispersions with green cosolvents

Three green sustainable cosolvents were used to produce polyurethane waterborne coatings. The effect of dihydrolevoglucosenone, gamma valerolactone and propylene carbonate on the performance of different coatings from a range of polyurethane structures with different hard segment content and different chain extender (a diol and a diamine) was studied. Properties of both synthesised polymers and water dispersions, like particle size distribution, stability, and pH, were carefully examined. The key properties of obtained coatings, including Koning hardness, specular gloss, hydrophobicity, abrasion resistance, adhesion or chemical resistance were detailly investigated to validate the use of these alternative green solvents in industrial coatings. The results indicated that the performance of materials based on sustainable cosolvents were equivalent to that of PUD coatings from commonly used cosolvent, N-methyl-2-pyrrolidone (NMP) maintaining a high gloss finished, as the properties of the dispersions keep optimal. Monomodal water dispersions with particle's diameter below 180 nm and stable for at least one month were achieved.

Enhanced Mechanical and Thermal Properties of Chain-Extended Waterborne Polyurethane Coatings with Cellulose Acetate Butyrate.

A series of waterborne polyurethane (WPU) dispersions were prepared by chain-extending a prepolymer made of polyester diol, isophorone diisocyanate, and dimethylol propionic acid using cellulose acetate butyrate (CAB). The particle size and viscosity of the WPU dispersion were measured. In addition, we investigated the effects of CAB on the thermal, mechanical, and optical properties of WPU films. The use of CAB effectively improved the crosslinking degree of the WPUs, increasing the thermal stability and water resistance of the corresponding films. In particular, CAB increased the tensile strength of the WPU films up to 67%, while maintaining their elongation at break unchanged. In addition, CAB improved the optical transmittance by reducing the microphase separation between the soft and hard segments of PU. The rough surface structure of the WPU films formed by CAB led to improved matting properties.

Novolac-based microcapsules containing isocyanate reagents for self-healing applications

Microcapsules (MCs) containing isocyanate compounds for use as self-healing materials in waterborne polyurethane coatings have been synthesized, in the presence of modified Novolac resins. With modification of Novolac resin, it is succeeded partial or total protection (Benzylation and Acetylation) of its hydroxyl groups. The idea here is to use a protected Novolac resin as the organic substrate for the encapsulation of the less reactive Isophorone isocyanate (IPDI) while the more reactive one, Methylene diphenyl diisocyanate (MDI), is used for the shell formation. Based on that strategy microcapsules of different morphologies and sizes were obtained, depending on the agitation conditions, as revealed using SEM and optical microscopy. Selective extraction was performed to determine the amount of the less reactive isocyanate (IPDI) stored inside the capsules through FTIR-ATR spectroscopy and isocyanate titration as well as the stability of IPDI inside the capsules over time. As determined, microcapsules based on Acetyl-modified Novolac resin encapsulated 96 wt% of IPDI monomer; this amount is about five and ten times higher than that encapsulated in MCs based on by Benzyl-modified Novolac resin or unprotected Novolac resin, respectively. At the same time, MCs based on Acetyl-modified Novolac resin were stable, maintaining approximately 80 % of the initial isocyanate content after two months of storage under inert conditions. Finally, the self-healing ability of the microcapsules was tested by adding selected IPDI-loaded microcapsules in waterborne polyurethane dispersions. It was proven that the Acetyl-modified Novolac-based MCs showed efficient healing behavior, in the absence of any catalyst, on the polyurethanes’ surfaces when scratched artificially.

Synthesis of Jatropha-Oil-Based Polyester Polyol as Sustainable Biobased Material for Waterborne Polyurethane Dispersion.

The utilization of vegetable oil in the production of polymeric material has gained interest due to its proven ability to replace nonrenewable petroleum sources, as it is readily modified via chemical reaction to produce polyol and subsequently for polyurethane production. Jatropha oil (JO), a second-generation feedstock, is one of the suitable candidates for polyester polyol synthesis because it contains a high percentage of unsaturated fatty acids. In this study, jatropha-based polyester polyols (JOLs) with different hydroxyl values were successfully synthesized via a two-step method: epoxidation followed by oxirane ring-opening reaction. Ring-opening reagents; methanol, ethanol, and isopropanol were used to produce polyol with hydroxyl number of 166, 180, and 189 mg/KOH, respectively. All the synthesized JOLs exhibited a Newtonian to shear thinning behavior in the measured shear rate ranges from 10 to 1000 s−1 at 25 °C. The viscosity of a JOL ring-opened with methanol, isopropanol, and ethanol was 202, 213, and 666 mPa·s, respectively, at 20 °C and 100 s−1, which is within the range of commercially available polyols. Successively, the JOLs were reacted with isophorone diisocyanate (IPDI) to produce polyurethane prepolymer by utilizing 2,2-dimethylol propionic acid (DMPA) as an emulsifier. The prepolymer was then dispersed in water to produce a waterborne polyurethane dispersion. Colloidal stability of the jatropha-based polyurethane dispersions (JPUDs) were investigated by particle size analysis. A JPUD with a small particle size in the range of 6.39 to 43.83 nm was obtained, and the trend was associated with the soft segment of the polyol in the formulation. The zeta potentials of the JPUs ranged from −47.01 to −88.9 mV, indicating that all synthesized JPUs had high dispersity and stability. The efficient synthesis procedure, low cost, and excellent properties of the resulting product are thought to offer an opportunity to use jatropha oil as a sustainable resource for polyester polyol preparation.

Impact of Diisocyanates on Morphological and In Vitro Biological Efficacy of Eco-Friendly Castor-Oil-Based Water-Borne Polyurethane Dispersions.

The search for renewable resources that can replace petroleum products is not only nerve-wracking, but also perplexing, as there is an abundance of plants that have yet to be explored. In this project, virgin castor oil was converted to polyol in two steps: epoxidation and hydroxylation. The resulting polyol was used to synthesize two series of water-borne polyurethane dispersions (WPUDs). The effects of the diisocyanates on the final product were evaluated. Isophorone diisocyanate (IPDI) and dicyclohexylmethane-4,4′-diisocyanate (H12MDI) were used as the hard segment (HS) up to 72 wt%, along with 1–4 butanediol (BD) as the chain extender, for the dispersions. Fourier transform infrared spectroscopy (FTIR) confirmed the bonds required for the synthesis of the dispersions. Thermogravimetric analysis (TGA) showed the multistep degradation for both series: maximum degradation took place at 500 °C for IPDI and 600 °C for H12MDI-based series. Scanning electron microscopy (SEM) showed phase-segmented morphology. Hemolytic activity was observed at biologically safe levels of up to 7.5% for H12MDI-based series. Inhibition of biofilm formation showed comparable results against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus): up to 46%. The results were also confirmed by phase contrast microscopy.

Polyurethane dispersions prepared from vegetable oil and their application as textile finishes

One of the major challenges facing the polymer industry now is finding sustainable and renewable alternatives to petroleum-based raw materials. To overcome such challenges, these novel water-borne polyurethane dispersions were prepared from bioresources (vegetable oil). Vegetable oil-based polyol is synthesized by epoxidation and hydroxylation methods from vegetable oil. Consequently, polyurethane dispersions are prepared by reacting the vegetable oil-based polyol with isophorone diisocyanate and dimethylol propionic acid to form the polyurethane prepolymer, which further reacts with 1,4-butanediol, and the final product is obtained by the addition of water. Fourier transform infrared analysis is used for the structural confirmation of the prepared vegetable oil-based polyol and polyurethane dispersions. A number of textile tests, including mechanical (tear strength (ASTM 1424) and tensile strength (ASTM D-5034)) and antibacterial, were conducted on poly/cotton plain weave fabrics after applying the synthesized dispersions by pad dry-cure methods. The hemolytic test method was used to check the biocompatibility of the synthesized dispersions. Results reveal that these finishes effectively increase the tensile strength of the treated fabric samples, such as white fabric samples, which show tensile strength values of (248, 255, 268 and 325 N from untreated 240 N) in the warp direction. The biological outcomes show the antibacterial and hemolytic activity of the dispersions are influenced by the presence of natural polyols in the dispersions. These results indicate that covering poly/cotton fabrics with vegetable oil-based polyurethane dispersions improve their tensile strength and antibacterial properties and they can replace petroleum-based polyurethane finishes.

The influence of hydrogen bond and electrostatic interaction on the mechanical properties of the WPU/modified SiO2 nanocomposites

A variety of nano SiO2 microspheres with negative charge or positive charge were prepared by hydrochloric acid treatment or/and γ-mercaptopropyltrimethoxysilane modification respectively. The obtained modified SiO2 with different content of -OH or -SH and different charges were physically introduced into water-borne polyurethane (WPU) dispersion to fabricate the WPU/modified SiO2 nanocomposites with interfacial interaction of hydrogen bond and electrostatic interaction. The influence of interfacial interaction (hydrogen bond and electrostatic interaction) between WPU and modified SiO2 on the interface structure and mechanical properties of the WPU/modified SiO2 nanocomposites were investigated. The results showed that when both hydrogen bond and electrostatic interaction were present between WPU and modified SiO2, the microstructure and the tensile strength of the WPU/modified SiO2 nanocomposite were mainly affected by the electrostatic interaction, while the elongation at break was mainly affected by the hydrogen bond interaction. Overall, a methodology of the combination of molecular dynamics simulation and experiment study was established to reveal the influence of surface characteristic of SiO2 on the interface interaction and mechanical properties of the WPU/modified SiO2 nanocomposites.

The role of the electrical percolation threshold on the anticorrosion performance of an aqueous polyurethane dispersion containing polyaniline

In this study, the anticorrosion properties of a waterborne polyurethane dispersion (WPU) containing polyaniline (PAni) were investigated and discussed considering the electrical percolation threshold (EPT) of this mixture. For that, easily dispersible poly(styrene sulfonic acid)-doped PAni (PAni:PSS) was incorporated into an anionic WPU at contents ranging from 1 to 8 wt%. Free-standing films of PAni:PSS/WPU reached the EPT at 6 wt% (4.8 v.%) of PAni:PSS. The mixtures remained stable and without signs of PAni dedoping. Based on the electrical behavior curve, PAni:PSS/WPU coatings were prepared below (1, 2, 3 wt%), close to (5 wt%), at (6 wt%) and above the EPT (8 wt%). The coatings were applied on ground low-carbon steel panels and evaluated regarding their contact angle, adhesion, and anticorrosion performance in electrochemical tests. The coatings prepared below the EPT presented higher hydrophobicity, good wet adhesion, and higher open circuit potential (OCP) and impedance modulus in the low frequency range (|Z|10 mHz). The best overall performance was achieved at 3 wt% of PAni:PSS which presented OCP values in the range of 34 ± 11 mV for 144 h and initial |Z|10 mHz of 108 Ω.cm2. These coatings also presented a colorimetric feature of changing color as the corrosion progressed. Meanwhile, the coatings containing PAni:PSS quantities close, at and above the EPT, i.e., at 5, 6 and 8 wt% presented high porosity, poor wet adhesion, and intense blistering. They also presented OCP values in the region of active corrosion and impedance spectra typical of coatings with poor barrier properties. These results indicate that, the formation of conducting networks within the insulating matrix is not necessarily a condition that must be met for a coating containing PAni achieve an optimal anticorrosion performance.

UV resistance, anticorrosion and high toughness bio-based waterborne polyurethane enabled by a Sorbitan monooleate

Sorbitan monooleate (SP) is considered to be a promising renewable polyol with unique molecular structures for the development and design of bio-based waterborne polyurethane (WPU) with versatility and excellent mechanical properties. In this study, SP was used as a bio-based polyol in combination with castor oil to design and prepare a series of bio-based WPU with anti-ultraviolet, corrosion resistance and excellent mechanical properties. The influence of the hydroxyl ratios between SP and castor oil on the chemical structures and properties of bio-based WPU dispersions and the resulting WPU films was systematically studied. The resulting WPU films exhibited excellent mechanical properties and thermo-physical properties due to the presence of large amounts of hydrogen bonding and rigid furan ring, and high crosslinking densities. The bio-based WPU films could lift heavy objects 10,330 times their own weight. The resulting WPU coatings could resist ultraviolet radiation in the region (200–400 nm) and exhibited excellent UV resistance in outdoor practical application tests. In addition, these WPU coatings demonstrated effectively anticorrosive effect in which the anticorrosion period of the coating on the tinplate outdoors could be as long as 6 months in terms of corrosion potential, corrosion current and corrosion protection efficiency of the coating reached −0.507 V, 2.92 × 10−6 A, and 95.39%, respectively. This study provides a new and simple method for preparing bio-based WPU with excellent anti-ultraviolet performance, anti-corrosion performance and excellent mechanical properties.

Bioinspired dual-crosslinking strategy for fabricating soy protein-based adhesives with excellent mechanical strength and antibacterial activity

Plant-derived biomass adhesives are increasingly in demand to replace traditional non-biodegradable petrochemical materials. However, the insufficient mechanical strengths and poor antibacterial activities of biomaterials severely limit their applicability. Inspired by the amphiphilic characteristics of mussel protein, a dual-crosslinking strategy is reported here for preparing soy meal (SM)-based adhesives with excellent adhesion and antibacterial properties. Specifically, castor oil containing abundant hydroxyl groups was used to prepare the cationic waterborne polyurethane (WPU) dispersion. Subsequently, the dynamic glue bridges were synthesized from the tannic acid-functionalized borax (TA@BA) complexes via multiple coordination bonds. Finally, the enhanced cross-linking network system was then constructed in the protein matrix based on the synergy of dynamic covalent bonds, electrostatic interactions, and hydrogen bonds. As a result, the wet strength of the resultant adhesive significantly increased by 154.77% compared to the SM adhesive. Additionally, the resultant adhesive exhibited remarkably enhanced thermal stability, flame retardancy, and water resistance. Based on the synergistic effect of the cationic WPU, polyphenol components, and borate groups, the SM/WPU/TA@BA adhesive exhibited desirable anti-mildew and antibacterial properties. This biomimetic dual-crosslinking design therefore provides a novel and facile strategy for the preparation of high-performance biopolymer adhesives used in the fields of biology and engineering.