Increase In Crosslink Density Research Articles

VISCOELASTICITY AND DYNAMIC FATIGUE CRACK GROWTH BEHAVIOR OF NATURAL RUBBER/CIS-POLYBUTADIENE RUBBER COMPOSITES

ABSTRACT Because cis-polybutadiene rubber (BR) can improve the fatigue crack growth (FCG) resistance of natural rubber (NR) in the low-tearing-energy (G) range, a blending system of NR/BR is often used in tire materials. In this study, based on relationship of (FCG rate (dc/dN) − G) established from the perspective of fracture mechanics and then inspired by Persson's theory and starting from the perspective of viscoelasticity, the FCG behavior and mechanism of NR/BR were investigated. NR/BR with different blending ratios were prepared, and dc/dN under different G inputs (500/1500 J/m2) was measured. According to the viscoelastic parameters (storage modulus E′, loss factor tan δ, and loss compliance modulus J″) recorded in situ, energy dissipation distribution at the crack tip (energy consumption for FCG inside crack tip: G0 and energy loss in linear viscoelastic zone near crack tip: G0f [v, T]) was determined, and the relationship of (viscoelasticity − dc/dN) was finally set up. When G = 500 J/m2, blending BR can reduce dc/dN as compared with pure NR. On one hand, with a higher BR fraction, an increased cross-linking density and enhanced filler network provided greater rigidity, which increased E′; on the other hand, a low glass transition temperature and flexible chain of BR reduced hysteresis, which decreased tan δ. The joint action led to a decrease in J″, which caused more G0f (v, T) and less G0, resulting in the ultimate reduction of dc/dN. In contrast, for G = 1500 J/m2, when the BR content was >50 phr, dc/dN showed a significant increase. Although more BR evidently decreased J″ and then led to a large amount of G0f (v, T), due to absence of strain-induced crystallization, the chain orientation of BR was hard to resist FCG when G increased. Finally, the morphology of the crack tip propagation path was captured to corroborate the different orientation characteristics of NR and BR and their effects on FCG behavior.

Improvement in toughness and flame retardancy of bismaleimide/diallyl bisphenol A resin with a eugenol allyl ether-grafted polysiloxane

Despite bismaleimide/2,2′-diallyl bisphenol A (BD) resin has been successfully used as a high-performance thermosetting resin, it is needed to further improve its toughness and flame retardancy to meet the requirements of application in harsh environments. In this study, we synthesized a eugenol allyl ether grafted polysiloxane (PMES-Allyl), and used it as an allyl compound to modify BD resin to obtain a new BDPA resin. The eugenol structure helped to improve the compatibility of the polysiloxane with the BD resin. When the addition amount of PMES-Allyl was 15 wt%, PMES-Allyl could be well dispersed in the resin matrix, leading to a significant increase of crosslinking density. As a result, the cured BDPA15% resin had better toughness than the cured BD resin, with the impact strength and flexural strength reaching 17.9 kJ/m2 and 177.1 MPa, respectively. Compared to the cured BD resin, the cured BDPA15% resin showed a comparable glass transition temperature and thermal stability, while an improved char yield. The active role of PMES-Allyl in helping the resin form an expanded, dense and stable char during heating, further made the cured BDPA15% resin exhibit an excellent flame retardancy. Compared with the cured BD resin, the cured BDPA15% resin showed a decrease of peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) by 58.6 %, 33.1 %, and 41.9 %, respectively, as well as a reduced release amount of the gasified pyrolysis products. This study provides a new insight and method for improving the properties of BD resin.

Study on properties of copolymers based on different types of benzoxazines and branched epoxy resins

Previous studies on linear epoxy (bisphenol A epoxy) resin/benzoxazine composites showed that with the addition of epoxy (EP) resin, the resulting copolymers exhibited an increased glass transition temperature ( Tg) ( Tg reached a maximum value at a specific content), improved flexural strength, lower heat resistance, and reduced tensile strength. Herein, branched EP resin (AG-80)/benzoxazine copolymers featuring novolac (N-box) and siloxane (Si-box) chains were prepared without any external curing agent. In both systems, the EP resin endowed the copolymers with an increased crosslinking density; however, Tg continued to increase with increasing EP content. In addition, the heat resistance of the copolymers gradually enhanced. Different types of benzoxazines have various effects on the properties of copolymers. In terms of mechanical properties, AG-80/N-box copolymers exhibited brittle fracture characteristics; with increasing EP content, the flexural strength of the copolymer decreased while the tensile strength increased. AG-80/Si-box copolymers exhibited ductile fracture characteristics, with gradual increases in flexural and tensile strengths. Furthermore, with increasing EP content, the molecular chain migration ability and network homogeneity of the AG-80/N-box copolymers decreased gradually. Alternatively, in the case of the AG-80/Si-box copolymers, the molecular chain migration ability remained unchanged and network homogeneity improved. Hence, the developed copolymers can be used as resin matrices for the fabrication of advanced composites.

Sustainable lignin precursors for tailored porous carbon-based supercapacitor electrodes

Sustainable materials are attracting a lot of attention since they will be critical in the creation of the next generation of products and devices. In this study, hydrogels were effectively synthesized utilizing lignin, a non-valorised biopolymer from the paper industry. This study proposes a method based on utilizing lignin to create highly swollen hydrogels using poly(ethylene) glycol diglycidyl ether (PEGDGE) as a crosslinking agent. The influence of different crosslinker ratios on the structural and chemical properties of the resultant hydrogels was investigated. Pore size was observed to be lowered when the amount of crosslinker was increased. The inclusion of additional hydrophilic groups in the hydrogel network decreased the swelling capacity of the hydrogels as the crosslinking density increases. These precursor materials were carbonised and electrochemically tested for application as electrodes for supercapacitors with capacitance characterized as a function of crosslinker ratio.

Effects of glutaric anhydride functionalization on filler-free benzoxazine/epoxy copolymers with shape memory and self-healing properties under near-infrared light actuation

We have developed new types of thermosets from bio-based benzoxazine/epoxy copolymers with shape memory and self-healing properties that could be triggered by using near-infrared (NIR) light, without using any filler. The copolymers were prepared from bio-based raw materials, including vanillin, furfurylamine, and epoxidized castor oil, along with functionalized with glutaric anhydride (GA), due to which self-healing properties of the copolymers were enabled through dynamic covalent bonds. Effects of GA content (0.00, 0.02, 0.04, 0.06, 0.08, and 0.10 mol) on molecular structure, mechanical properties, dynamic mechanical properties, and thermal stability of the copolymers were investigated. The results from infrared spectroscopy showed the formation of ester linkages and free carboxylic acids upon functionalization of copolymers with GA. The increased crosslinking density by GA was observed from increased tensile strength (from 11 to 16 MPa), glass transition temperature (72–150 °C), and degradation temperature at 5% weight loss (382–405 °C) of the copolymers. However, excess contents (0.08 and 0.10 mol) of GA might result in the existence of free components, hindering the formation of the copolymer network and diminishing the mechanical properties of the copolymers. Shape memory properties of GA-functionalized V-fa/ECO copolymers were investigated under NIR actuation; the results showed a 100% of shape recovery ratio within 20 s of actuation. Self-healing properties of GA-functionalized V-fa/ECO copolymers were investigated under NIR actuation; the results showed 94% of restored storage modulus after 20 min of actuation. Lastly, the self-healing mechanism under NIR actuation was proposed that NIR photothermal effects of the copolymers induced the crack closing due to their shape memory effects. Consequently, the copolymer chains could diffuse across the crack interface along with transesterification through GA functionalities, leading to crack healing. The findings of this study suggested a new way to produce NIR light-responsive self-healing polymer without using NIR photothermal filler. • Filler-free benzoxazine/epoxy copolymers with shape memory and self-healing effects triggered by NIR light were developed. • Copolymers were synthesized from bio-based raw materials and functionalized with glutaric anhydride (GA). • Copolymers showed 100% shape recovery within 20 s and 94% restored storage modulus after 20 min of NIR light actuation. • Self-healing mechanism involved shape memory effects and transesterification induced by NIR photothermal effects.

Improving Mechanical Properties of Starch-Based Hydrogels Using Double Network Strategy.

This work aims to improve the mechanical properties of starch-based hydrogels using a double-network (DN) strategy. The single network (SN) starch hydrogel was first prepared using glutaraldehyde as a crosslinker. The compressive properties of the SN hydrogels were influenced by both crosslinker content and crosslinking time. The SN starch hydrogel possessing the best mechanical properties was then fabricated into DN hydrogels. Poly(vinyl alcohol) (PVA) and borax were used as a secondary polymer and a crosslinker, respectively. The PVA–borax complexation partly enhanced the DN hydrogel’s compressive modulus by 30% and its toughness by 39%. DN hydrogels were found to have denser microstructures than SN hydrogels. To be specific, their walls thickened and grew more continuous while their pores shrank. The increased crosslinking density resulted in changes to the microstructure, which were well correlated with their porosity and water uptake capacity. An in vitro cytotoxicity test of the DN hydrogels revealed that they were non-toxic to chondrocytes. This work demonstrated that double networking is a simple but effective strategy for improving mechanical properties of starch-based hydrogels without sacrificing their biocompatibility. This approach can be used to tailor hydrogel properties to fulfill requirements for biomedical applications, such as tissue engineering and other related fields.

Study on Thermo-oxidative Aging Mechanism of Air Spring Rubber Cord Composites

To study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, study the thermo-oxidative aging mechanism of air spring rubber cord composites, observe the changes in surface micro-morphology, infrared spectrum, quality, hardness, and mechanical properties during the process of thermo-oxidative aging, and analyze the aging mechanism. The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface The results show that the micro-morphological changes of the rubber surface of the rubber cord composites go through two stages: at 0-72 h, the rubber surface develops from no cracks to a large number of cracks; at 96-336 h, the rubber surface changes from a cracked state. The size of the crack on the rubber surface affects the rate of change of IRHD hardness. The larger the crack, the greater the hardness growth rate, otherwise the opposite. In the aging process, the rubber is in a state of dynamic development. The increase of cross-linking density causes changes in microscopic The increase of cross-linking density causes changes in microscopic morphology and accessible volume, which affects the IRHD hardness. The aging mechanism is more complicated. Material failure is dominated by the failure of the rubber matrix.

A phosphaphenanthrene‐based derivative for simultaneously improving flame retardant and smoke suppression of epoxy resin composites

AbstractEpoxy resin (EP) have the disadvantage of high flammability and large amount of smoke, which greatly restricts its wide application in basic material. In order to obtain EP with excellent smoke inhibition and flame retardance, the flame retardant called as PBO, which with both condensed phase and gas phase flame‐retardant effects, was synthesized by the reaction among p‐phenylenediamine, DOPO, and indole‐3‐carboxaldehyde. From combustion results, EP containing PBO obtained V‐0 grade with a significantly improvement from 22.5% to 30.2% in limiting oxygen index. In comparison with EP, total smoke production, total heat release and the peak of heat release of EP/PBO‐1.0 were declined by 32%, 41.5%, and 37.4%, respectively. Besides,Tgof EP composites also had a certain degree of improvement, which due to the increase of rigidity and crosslinking density of EP caused by the addition of PBO. Meanwhile, the analysis of chars and pyrolysis products of PBO presented that the improvement was assigned to two phase synergy through barrier effect of chars in condensed phase and interrupt chain reaction in gaseous phase.

Use of Self-Assembled Colloidal Prodrug Nanoparticles for Controlled Drug Delivery of Anticancer, Antifibrotic and Antibacterial Mitomycin.

Herein we present the synthesis of a polymeric prodrug nanomaterial capable of spontaneous, self-assembled nanoparticle formation and of the conjugation (encapsulation) of drugs with amino and/or carboxyl and/or hydroxyl groups via ester and/or amide linkage. Mitomycin C (MMC) a versatile drug with antibiotic, antibacterial and antineoplastic properties, was used to prove this concept. The in vitro drug release experiments showed a fast release for the pure MMC (k = 49.59 h−n); however, a significantly lower MMC dissolution rate (k = 2.25, 1.46, and 1.35 h−n) was obtained for the nanoparticles with increased cross-link density (3, 10, 21%). The successful modification and conjugation reactions were confirmed using FTIR and EDX measurements, while the mucoadhesive properties of the self-assembled particles synthesized in a simple one-pot reaction were proved by rheological measurement. The prepared biocompatible polymeric prodrugs are very promising and applicable as a drug delivery system (DDS) and useful in the area of cancer treatment.

Super-strong and anti-tearing poly(vinyl alcohol)/graphene oxide nano-composite hydrogels fabricated by formation of multiple crosslinking bonding network structure

As load-bearing material in biomedical-applications as cartilage replacement, artificial meniscus and tendons, etc., poly(vinyl alcohol) (PVA)/graphene oxide (GO)-tannic acid (TA) nano-composite hydrogels with multiple-crosslinking network were fabricated by establishing freezing/thawing-annealing-swelling method. By TA anchoring, PVA molecules were grafted onto GO surface efficiently, and strong interfacial interaction led to exfoliation and uniform distribution of GO in matrix. By introducing annealing process, the crystallinity and crystallite size of PVA increased and introducing GO-TA led to more perfect and denser crystalline structure, while physical crosslinking network centered on GO-TA and hydrogen bond-abundant crystalline phase formed, resulting in increasing crosslinking density of hydrogel. By further swelling in CaCl2 aqueous solution, hydroxyl-Ca2+ coordination formed, and multiple-crosslinking network was constructed with high crosslinking density. The tensile strength and fracture toughness of composite hydrogel were remarkably improved, reaching 14.38 MPa/27.93 MJ/m3, approximately 11-/26-fold higher than those of neat PVA hydrogel, while tearing strength was significantly enhanced, attributed to high energy dissipation through unzipping multiple interactions.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Poly‐cardanol as plasticizer and compatibilizer on styrene butadiene rubber with improved processability and silica dispersion

AbstractNatural products used as plasticizer can inhibit its migration in rubber and improve the dispersion of inorganic power. Herein, styrene butadiene rubber (SBR) was plasticized by poly‐cardanol (PCA) originated from the Friedel–Crafts alkylation without solvent of cardanol which was extracted from abandoned cashew nut shell. Results show that the Mooney viscosity of SBR/PCA compounds decreases from 45.8 to 34.7 and Tg from −52°C to −56.3°C when PCA is added from 0 to 30 phr. Moreover, the elongation at break of SBR contained 30 phr PCA increases by 515% compared with SBR. PCA also shows amphiphilic, which is verified by the improved dispersion of SiO2 in SBR/PCA compounds. The swelling ratio of SBR/PCA/SiO2 vulcanized rubber decreases and the crosslinking density increases. Meanwhile, the elongation at break of SBR70‐40 vulcanized rubber is 17.3%, which is higher than that of SBR100‐40 vulcanized rubber. PCA, acted as plasticizer and compatibilizer, provides a simple and green way for the application of natural products in the rubber industry.

Subdiffusive High-Pressure Hydrogen Gas Dynamics in Elastomers

Elastomeric rubber materials serve a vital role as sealing materials in the hydrogen storage and transport infrastructure. With applications including O-rings and hose liners, these components are exposed to pressurized hydrogen at a range of temperatures, cycling rates, and pressure extremes. High-pressure exposure and subsequent rapid decompression often lead to cavitation and stress-induced damage of the elastomer due to localization of the hydrogen gas. Here, we use all-atom classical molecular dynamics simulations to assess the impact of compositional variations on gas diffusion within the commonly used elastomer ethylene–propylene–diene monomer (EPDM). With the aim to build a predictive understanding of precursors to cavitation and to motivate material formulations that are less sensitive to hydrogen-induced failure, we perform systematic simulations of gas dynamics in EPDM as a function of temperature, gas concentration, and cross-link density. Our simulations reveal anomalous, subdiffusive hydrogen motion at pressure and intermediate times. We identify two groups of gas with different mobilities: one group exhibiting high mobility and one group exhibiting low mobility due to their motion being impeded by the polymer. With decreasing temperatures, the low-mobility group shows increased gas localization, the necessary precursor for cavitation damage in these materials. At lower temperatures, increasing cross-link density led to greater hydrogen gas mobility and a lower fraction of caged hydrogen, indicating that increasing cross-link density may reduce precursors to cavitation. Finally, we use a two-state kinetic model to determine the energetics associated with transitions between these two mobility states.

The role of natural rubber endogenous proteins in promoting the formation of vulcanization networks

Abstract Non-rubber components are critical in the formation of the natural rubber (NR) vulcanization network, which leads to outstanding mechanical properties of NR. This study reports the effect of NR endogenous proteins (C-serum protein/lutoid protein [CSP/LP]) on the formation of vulcanization networks at the molecular level. Results indicate that CSP/LP has a positive effect on vulcanization. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses demonstrate that the decrease in vulcanization time of CSP/LP is ascribed to coordination interaction between Zn2+ and amide bond. The interaction increases the availability of ZnO in the matrix, thereby promoting the formation of the vulcanized network. CSP/LP also participates in the construction of the vulcanization network as a new crosslinking point, thus increasing crosslinking density and improving the mechanical properties of the NR. This study provides new research ideas for studying the relationship among component–structure–property of NR materials and developing high-strength and high-toughness elastomer materials.

Investigation of Structural and Thermal Properties of Graphene Oxide Reinforced Epoxy Nanocomposites

The nanocomposites thin film was prepared by adding exfoliated GO in epoxy-hardner solution in different weight ratio. We investigate the thermal and surface properties of epoxy-graphene oxide (GO) nanocomposites using differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and contact angle measurement method. AFM and contact angle results are supporting that graphene oxide provides the best reinforcement in epoxy. AFM is investigated the dispersion of GO and structural morphology of epoxy nanocomposites. The FTIR results show that exfoliated GO of two-dimensional (2D) shape favors the hardening process of the epoxy matrix, increasing its reaction rate by observing an epoxy stretching frequency at 907 cm−1. The GO modified with amino group of epoxy lead to the increase of crosslinking density. FTIR absorption peak in 1700–1500 cm−1 regions is due to amino group. This attributes the significant increase of glass transition temperature of epoxy/GO nanocomposites . The contact angle and surface roughness increases with increase in concentration of GO in epoxy shows roughness induced hydrophobic surface. The solid surface energy was calculated by contact angle favors the good dispersion of GO in epoxy matrix.

The effect of temperature and peroxides content on cross-linking and properties of EPDM-based rubber matrix

In this work, dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), di(tert-butylperoxyisopropyl)benzene (DTBPIB), and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (DDTBPH) were used for cross-linking of rubber matrix based on Ethylene-propylene-diene monomer rubber (EPDM). The aim was to investigate the influence of curing temperature and the type and content of peroxide on curing process of rubber compounds, cross-link density, and physical-mechanical properties of vulcanizates. The results revealed that higher curing temperatures promote faster decomposition of organic peroxides, leading to the faster reactions of peroxide radicals with rubber chains. The increase in temperature resulted also in the increase of cross-linking degree. Although, side reactions as chain scission take over the main cross-linking reactions at very high temperatures resulting in the decrease of cross-link density. The increasing content of peroxides resulted in the acceleration of curing reactions and to increase of cross-link density. The fastest curing kinetics exhibited rubber compounds cured with DCP. However, vulcanizates cured with DCP were found to have the lowest cross-link density. In generally, the dependences of modulus, hardness, and elongation at break of vulcanizates were in line with the dependences of the cross-link densities, while higher tensile strength were found to have vulcanizates cured at higher temperatures and lower peroxides content.

Negatively charged poly(N-isopropyl acrylamide-co-methacrylic acid)/polyacrylamide semi-IPN hydrogels: Correlation between swelling and compressive elasticity

A series of thermoresponsive semi-interpenetrating polymer network (semi-IPN) based on linear polyacrylamide (PAAm), N-isopropylacrylamide (NIPA) and methacrylic acid (MA) were synthesized by varying linear polymer content via free radical polymerization. An interpenetrated network of P(NIPA-MA)/PAAm was designed to modulate elasticity by varying inner composition and to improve rate of swelling-deswelling phenomenon. Correlation between swelling and compression elasticity was demonstrated. Inclusion of linear PAAm chains with high molecular weight (Mw = 9.639 × 105 g/mol) into P(NIPA-MA) network induced physical entanglements, increased apparent crosslinking density νeand enlarged compressive elasticity. Dependence of νeon linear polymer content was expressed as a cubic polynomial function. Extent of swelling of semi-IPN P(NIPA-MA)/PAAm gels was sensitive to presence of linear PAAm chains. Existence of linear polymer decreased apparent ionic group density and increased crosslinking density compared to that of copolymer P(NIPA-MA) network which in turn decreased equilibrium swelling. A significant increase in swelling/shrinking rate was observed in the presence of linear PAAm. Due to ionization of carboxylic acid groups in P(NIPA-MA) network, semi-IPN P(NIPA-MA)/PAAm gels showed different degrees of swelling depending on linear PAAm content and temperature of swelling medium. Semi-IPNs exhibited phase transition temperatures shifted higher temperature, suggesting physical entanglements between P(NIPA-MA) network and linear PAAm. Increasing swelling temperature resulted in an increase in Flory-Huggins interaction parameter. Entropic contributionχSincreased and enthalpic contribution χH decreased with PAAm content. The results showed that the prepared semi-IPNs are a suitable adsorbent for adsorption of the cationic dye Methyl violet (MV). Adsorption kinetics followed a pseudo-second-order model and exhibited a two-stage intra-particle diffusion. A detailed understanding of physicochemical properties of negatively charged thermoresponsive semi-IPNs in relation to structural architecture is an important criterion in many biomedical and pharmaceutical applications.

The microwave-absorption properties and mechanism of phenyl silicone rubber/CIPs/graphene composites after thermal-aging in an elevated temperature

Recently, the application and development of flexible microwave-absorption composites based on silicone rubber have gradually become a research hot spot. In this study, methyl vinyl phenyl silicone rubber (MPVQ)/carbonyl iron particles (CIPs)/graphene (GR) composites were prepared by mechanical blending, and the effects of thermal-ageing temperature on the microwave-absorption properties of the composites were investigated. The mechanism of the thermal-ageing temperature’s effects on microwave-absorption behaviour was identified. The results show that unaged composites have superior microwave-absorption properties, with a minimum reflection loss (RLmin) of − 87.73 dB, a lowest thickness of 1.46 mm, and an effective absorption bandwidth (EAB, RL < − 10 dB) reaching 5.8 GHz (9.9–15.7 GHz). With ageing at 240 °C for 24 h, the RLmin at a frequency of 5.48 GHz is − 45.55 dB with a thickness of 2.55 mm, and the EAB value reaches 2 GHz (range 4.6–6.6 GHz). In the thermal-ageing process, a crosslinking reaction occurs in MPVQ with an increase in crosslinking density from 5.88 × 10−5 mol g−1 (unaged) to 4.69 × 10−4 mol g−1 (aged at 240 °C). Simultaneously, thermal degradation of the composites leads to a reduction in the rubber concentration. In addition, a small amount of CIPs are oxidized to Fe3O4, and the remaining CIPs aggregate to generate more electrically conductive pathways. Consequently, the dielectric loss of the composites will be significantly improved, resulting in poor impedance matching. The microwave-absorption properties of the composites gradually decrease with increasing thermal-ageing temperature from 200 to 240 °C.

Bio-based epoxy resins derived from diphenolic acid via amidation showing enhanced performance and unexpected autocatalytic effect on curing

Bisphenol A (BPA) is the main precursor in the synthesis of epoxy resins. However, because of its toxic and nonrenewable nature, BPA is unsuitable in the sustainable preparation of epoxy resins. In contrast, Diphenolic acid (DPA) is renewable but its carboxyl group limits its applications in bio-based thermosets. In this study, we report a novel amidation route to tailor DPA to produce epoxide monomers that present epoxy resins with a high performance. The diphenolic amides exhibited very low toxicities when compared with that of BPA, and also provided an unexpected autocatalytic effect on the curing reactions when succinic anhydride (SA) was used as the hardener. Dynamic mechanical analyses (DMA) and tensile test results confirmed the remarkable thermomechanical properties of the cured epoxy resins, which may be attributed to the increased cross-linking density and enhanced hydrogen bonding by the amide groups. Among the SA-cured epoxy resins, diglycidyl ether of diphenolic ethylamide exhibited the best performance, which included a high Tg of 114 °C, char yield (CY) of 20%, tensile strength of 60.2 MPa, and toughness value of 185 MPa. In addition, the DPA-derived epoxy resins have great potential in the preparation of bio-based composites because they act as excellent interfaces between the resin and cotton fibers (CoFs). Our study presents a new strategy to prepare bio-based epoxy resins with a high performance, emphasizing the greater potential of amidated DPA derivatives to replace BPA in the epoxy resin market.

A hair fiber inspired bio-based adhesive with high bonding strength and mildew tolerance

Soybean protein (SP)-based adhesives present low adhesive strength, poor water resistance and low mildew resistance, which generally limit their practical industrial applications. Inspired by the interesting phenomenon that the strength of hair fiber was affected by the breaking and reuniting of disulfide bonds during perming, in this study, a new biomimetic strategy was proposed to construct a soybean meal (SM)-disulfide bonds-chitosan (CS) structure to achieve enhanced adhesive strength, improved water resistance and higher mold resistance. The introduction of sulfhydryl chitosan (CSSH) with high sulfhydryl content provided sufficient reaction sites, endowing the resultant high-strength and mold resistant bio-based adhesive with increased crosslinking density and numerous hydrogen bonds. The dry shear strength and the wet shear strength for 3 h soaking at 63 °C of SM-CSSH was improved by 61.31% and 365.6% to 2.71 MPa and 1.49 MPa, respectively. The increase in residual rate and decrease in moisture absorption of adhesive illustrated the excellent water resistance of the material. More importantly, the antibacterial property of chitosan prolonged the storage time of the adhesive, which benefits to its industrial applicability. This study provided a new biomimetic strategy to prepare high-strength adhesives from agricultural and fishery wastes, exploring for green and sustainable development concept.