Applications of eco-friendly soy protein (SP) adhesives in the wood industry are restricted by their poor wet bonding strength and mold resistance. In this study, we noted that epoxy crosslinking agents not only have cross-linking properties, but also antifungal properties and can be used as cross-linkable antifungal agents to simultaneously improve the mold resistance and strength of SP adhesives. In order to develop sustainable and highly active epoxy cross-linkable antifungal agents, biomass-derived oxalic acid (OA) was converted into epoxy oxalic acid (EOA) with two electron-withdrawing ester groups, with 99.93% antifungal activity. The 1% ultra-low amount of EOA (when used as crosslinking agent) was uniformly dispersed in the uncured adhesive, prompting the anti-mold life of the adhesive to increase from 2 to 26 days. After curing, the tighter and more stable cross-linked network structure of the adhesive was constructed by the reaction of low reactive groups such as amide II bonds with ultra-low amounts of EOA, and the dry and wet shear strengths were increased by 49.0% and 139.7%, respectively, compared with pure adhesives. In addition, the anti-mold life of the cured adhesive increased from 4 to more than 30 days under the action of residual EOA. This work demonstrates the novel antifungal effect of epoxy crosslinkers, providing a controllable, green, and sustainable idea for the high-efficient improvement of mold resistance and strength of bio-based adhesives.

There is an increasing demand for high-performance adhesive joints in the fields of aerospace, civil engineering and automobile engineering. However, stress concentrations at the edge of adhesive joints could result in pre-failure and make the joints unreliable. In this work, functionally graded adhesives (FGA) are utilized to solve the above-mentioned issues. We incorporate graphene nanoplatelets (GNP) into the epoxy resin to produce composite adhesives with high modulus. These high-modulus adhesives, together with neat epoxy with medium-modulus, are placed in the center and edge of the bondline respectively, to create a modulus gradient. The as-produced FGA joints deliver superior mechanical performances over the mono adhesive joints, and highly tunable properties could be achieved by adjusting the relative sizes of the high-modulus and medium-modulus regions. For example, the FGA with the lateral size of high-modulus edge region: medium-modulus center region: high-modulus edge region of 1:3:1 exhibit significant 210.1%, 350%, and 1118.58% improvements in failure load, elongation at break and toughness, respectively. Such exceptional mechanical properties of FGA come from the rearranged stress distributions at the overlap. According to the numerical analysis, the gradient modulus in FGA can effectively decline the peel stress concentrations. In addition, based on the linear elastic material models for adhesive and adherends, it is found that the stress concentrations at the edge of the overlap could be suppressed by the medium-modulus region, while the GNP reinforced high-modulus region mainly provide load-bearing capacity of the joints, resulting in delayed adhesive joints failure.

Cross-linked acrylate latex pressure sensitive adhesives (PSAs) were synthesized via unseeded semi-batch emulsion polymerization processes with butyl acrylate (BA), acrylic acid (AA), 2-hydroxyethyl acrylate (HEA) and difunctional cross-linker, ethylene glycol dimethacrylate (EGDMA). The influences of EGDMA on the comprehensive properties of the acrylate latex PSAs were investigated. The results indicated that both viscosity and particle size of the latexes were independent of the amount of EGDMA in the pre-emulsion feed when unseeded semi-batch emulsion polymerization process was employed. It was also found that water resistance of the latex PSA was improved with increasing EGDMA content, further confirmed by water contact angle measurements. DSC and TGA results showed that Tg of the copolymer was elevated, plus thermal stability was increased with introduction of EGDMA. Besides, with the increase of EGDMA content, the gel content of the polymer increased. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncross-linked counterparts.

Epoxy adhesives for concrete cracks repair may necessitate the addition of reactive diluent to decrease their viscosity. However, research on the effect of different reactive diluents on the various properties of epoxy adhesives remains insufficient. In this paper, three reactive diluents, including monofunctional alkyl C12–C14 glycidyl ether (AGE), butyl glycidyl ether (BGE) and difunctional 1,4-butanediol diglycidyl ether (BDDE) are utilized to comparatively study the different effects on the viscosity, exothermic temperature, mechanical properties, and bond strength with cement mortar of the adhesives. The results show that the addition of BDDE increases the maximum curing temperature of the adhesives, whereas AGE and BGE both causes a decrease. The epoxy adhesive with AGE or BGE shows greater ultimate tensile strain, but a more obvious reduction in Young's modulus than that with BDDE at the same concentration. BDDE improves the bond strength of the adhesive-mortar interface whereas AGE and BGE both decrease it. Moreover, the bond strength shows a positive correlation with the hydroxyl content on the surface of cured epoxy. Comparing with AGE and BGE, BDDE increases the hydroxyl content, resulting in the strongest bond strength.

To deepen the research on the surface treatment technology of bonding matrix of composite materials, carbon fiber reinforced polymer (CFRP) was selected as the research object, and the research status at home and abroad were reviewed from three aspects: matrix characteristics, durability and bonding and stripping effect before and after surface treatment. Because of the effects of existing surface treatments on the surface roughness, surface wettability, surface morphology, fatigue characteristics, shear strength, and tensile section morphology of CFRP, the influence mechanism of surface treatments on the bonding properties of CFRP was summarized, and the future research focus and direction prospected. The results show that the bonding effect depends on the good mechanical interlocking and adsorption/chemical bonding between the adhesive and CFRP surface. The surface treatment can remove the surface pollutants of CFRP, optimize the surface topography characteristics, and enhance the spreading ability of the adhesive on the substrate surface, thereby enhancing the bonding ability between CFRP and the adhesive. The combination of different surface treatments can significantly improve the preparation quality of the CFRP surface, and avoid the defects of the single surface treatment itself to a certain extent. The surface treatment technology of the bonding matrix is developing in the direction of precision, refinement, and accuracy.

In this paper, we establish a failure criterion for aluminum alloy polyurethane bonded joints under extreme service conditions. Firstly, we analyze the mechanical properties of the bonded joints at different service temperatures after exposure to a hygrothermal environment, and determine the extreme service conditions (120 aging cycles and 80 °C service temperature) of the bonded joints based on their changing trends. We then construct a finite element model of the bonded joint using ABAQUS software, and divide the four corner points of the adhesive layer into failure areas. We extract the stresses of the adhesive elements in these areas, linearly combine them, and check if the combined stresses satisfy the screening conditions. The combined stresses that meet the conditions are defined as the allowable equivalent stresses [σeq]. Finally, to check the validity of the failure criterion, we embed it in the finite element model and compare it with mechanical experiments. The results show that the failure criteria can accurately simulate the failure process of bonded joints and can be used to calibrate the strength of bonded joints, providing a useful reference for joint strength design.

Rational design of environmentally friendly and sustainable bio-based wood adhesives is of great significance to people's health, environmental protection, high value-added utilization of crop resources and national economic development. In this work, we develop new cellulose-based wood adhesives and explore the differences in the spatial structure of branched polyamines and linear binary amines after cross-linking with dialdehyde cellulose (DAC). The bio-based wood adhesives DAC-2N (adhesives obtained from the reaction of DAC with diethylenetriamine) and DAC-3N (adhesives obtained from the reaction of DAC with tris(2-aminoethyl)amine) are prepared by the cross-linking reaction between DAC and linear amines (2N)/branched amines (3N). The effects of spatial cross-linking degree, mass ratio of amine to DAC and solid content of adhesives on the bonding performance are systematically studied, and the mechanical properties of wood specimens are also tested by universal mechanical tests. Results show that the best formulation of DAC adhesive is a 1:1 mass ratio of DAC to 3N, and the optimal solid content is 40%. Compared with the pristine DAC adhesive, the dry bonding strength of the DAC-3N adhesive increased by 103% from 1.35 MPa to 2.74 MPa, and the wet bonding strength increased from 0 MPa to 1.81 MPa. DAC-3N adhesive with dense network structure has stronger glue and water-proof properties than DAC-2N adhesive, and the shear strength test of the three plywood shows the failure mode of the substrate rather than the failure mode of bonding or cohesion. Therefore, this study might offer a prospective strategy for future research, especially the rational design and potential application of bio-based adhesives with branched structure.

This research attempts to create a pressure-sensitive adhesive (PSA) from cardanol as an outset material. The two kinds of formulations were established; the first scheme followed the epoxidation of cardanol, dihydroxylation, and PSA development. In the latter system, cardanol was pretreated with dichlorodimethysilane (DCDMS) in the second scheme, continuing the same procedure to obtain PSA resin. The chemical nature and structure confirmation were done using FTIR and NMR spectroscopy, hydroxyl value, epoxy equivalent weight (EEW), etc. To evaluate PSA resin's crystallinity, thermal stability and hydrophilicity the film was separately obtained for both the schemes by curing whereas to obtain PSA tapes the obtained PSA and tackifying resins were applied onto PET sheets. XRD analysis showed a decrease in the degree of crystallinity after incorporating DCDMS. The gel content values decreased, whereas the water absorption values increased, which could be related to the increase in the hydrophilic nature of PSA with an increasing number of tacky sites. TGA and DSC showed the formation of a high amount of char yield (∼31%) and a higher Tg (−37.72 °C) in Si containing film. The probe tack, peel strength, and shear strength values were high for the formulation with equal amounts of PSA and tackifying resin. Finally, the contact angle measurements showed that the hydrophobicity of film was also improved after incorporating DCDMS. The materials resembling PSA tape and including only small amounts of tackifying resins and crosslinkers displayed the ideal characteristics with satisfactory results.

This work compares for the first time the efficacy of using different ionic liquids (ILs) as epoxy hardeners in epoxy-based adhesives. Several phosphonium and imidazolium-based ionic liquids were tested as epoxy hardeners, and the thermal and mechanical properties and the lap shear strength of the cured epoxy resins were studied at different IL concentrations. Both the chemical structure and the concentration of ILs were found to impact the final properties of the epoxy resin, but among the ten different ILs studied, three of them cured the epoxy resin effectively and produced similar and even better mechanical properties and lap shear strength than those obtained with traditional amine-based curing agents. These results constitute an important step towards sustainability thanks to the non-volatility of ILs and the significantly lower amount needed for effectively curing epoxy resins.

The development of cellulose-substrate remedies remains a technological challenge owe to their inability to self-heal and excessive dependence on petroleum-based adhesives, which is further hindered by the significant drawbacks of commercially unavailable welding materials and inconvenient manipulation. We herein describe a cellulose-substrate bonding technique achieved through partial dissolution using a low dosage of ZnCl2 aqueous solvent (ZS) and its dissolved cellulose (ZDC) gel as adhesives. This method demonstrates strong joint areas between strips without any failure, while shrinkage in the diffusion area remains the main cause of breakage. This shrinkage phenomenon can be alleviated by using ZDC instead of ZS, due to the water retention of hydrophilic hydroxyls on the macromolecular chains of dissolved cellulose. The well-maintained tensile strength of the ZDC-bonded strip (5.0% lower than the control) indicates that partially dissolved cellulose fills gaps between fibers, providing evidence for a mechanical interlocking adhesive mechanism in strip connections. ZDC gels exhibit favorable adhesive behavior for hand-sheets, art paper, and corrugated board, with welded joints demonstrating robust mechanical performance even after soaking in water for 6 h.

The bonding potential of as-printed additively manufactured stainless steel is largely unknown, and the use of additional hierarchical bio-inspired surface texture has not yet been explored or characterized. In this study, it is demonstrated with the use of Selective Laser Melting (SLM) that a hierarchy of three surface features at different length scales can greatly improve the shear strength of metal-metal adhesive joints. The intrinsic stochastic texture of the SLM as-printed surface showed a high contact angle and a mixed failure with a dominance of adhesive failure. However, enhancing the as-printed surface with the Tree Frog (TF) and Fish Scale (FS) bio-inspired textures produced super-wetting surfaces, significantly improving the shear strength due to the synergistic effect of mechanical interlocking and physical adsorption adhesion mechanisms, resulting in mixed failure. The results indicated that the interfacial bonding performance was in line with the super-wetting behavior and was higher for the samples with a hierarchy of three surface features. The highest increase in bond strength was found for the tree frog hierarchical hexagonal texture (+70% compared to the as-printed texture). In contrast, abrasion of the as-printed surface with P1000-grit paper significantly reduced the surface roughness and increased the water contact angle, resulting in the lowest shear strength.

Photovoltaic (PV) is a sustainable energy source and an efficient tool towards CO2 neutrality. However, recycling of PV modules remains challenging due to the strong connection of the multi-material assembly. The present work aims at the development of disbonding concepts for adhesive connections used in PV modules to enable improved recyclability and repairability of such modules. To achieve stimuli-responsive adhesive connections, thermally expandable fillers were implemented in a condensation-curing alkoxy-based silicone adhesive. 10–50 wt% of expandable graphite (EG) as well as 10–50 wt% of thermally expandable microspheres (TEM) were incorporated to obtain a controlled expansion of the adhesive at elevated temperature. The expansion ratio in dependence on time and temperature was examined. Furthermore, nanoscale magnetite (Fe3O4) passivated with a layer of SiO2 was added to the formulation to trigger the expansion of TEMs, and therefore separation of adhesive bonds by inductive heating. In this approach an efficient heating and expansion of the adhesive layers was feasible by applying an external alternating magnetic field with a ring coil. Aging stability, influence of filler content and expansion of the adhesive layers were further evaluated in lap shear tests. The addition of functional fillers decreased the bond strength by approximately 50% for adhesive layers containing 50 wt% EG. In contrast, adhesives with 50 wt% TEM exhibited a higher bond strength (by 10%) compared to the unfilled silicone system. Thermally triggered expansion significantly lowered the bond strength (20–30%) for TEM-filled adhesives and led to separation for EG-filled adhesives. Temperature cycling tests had no influence on the filled and unfilled adhesive's strength, whereas after damp heat tests all samples exhibited a lower (less than 40% of the unaged, pristine reference samples) but similar bond strength.

In this research the interactions and structural changes induced by NaOH:urea mixtures on cassava starch suspensions as well as their adhesive capacity were studied. Cold gelatinization of 10–20% w/w cassava suspensions was induced by adding different NaOH:urea mixtures (0.5–2:1). Chemical modification of cassava starch was analyzed through optical microscopy as well as SEC-HPLC and size particle determinations, ATR-FTIR spectral and chemometric analysis were also carried out.Cassava starch treatment with NaOH:urea mixtures generated structural disorganization, induced cold gelatinization and promoted the hydrolysis of the polymeric chains. SEC-HPLC and ATR-FTIR results showed that the modifications induced in the adhesive formulations depend both on the starch content and the NaOH:urea ratio. All tested formulations exhibited adhesive capacity, being effective for Kraft paper substrate bonding. Thus, this simple and low-cost procedure was effective to chemically modify cassava starch allowing to obtain derivatives with tailor-made adhesive properties.

The road infrastructure condition, which can be easily damaged by the occurrence of potholes due to the weak adhesion between asphalt and aggregate, disrupts economic activity and requires high maintenance costs. This problem needs to be overcome by adding adhesive to modify the asphalt. Lignin is a sustainable biopolymer that can serve as a natural asphalt binder. Lignin isolated from mahogany sawdust combined with diphenylmethane 4,4′-diisocyanate has never been used to modify asphalt mixtures. This modification can improve the properties of the asphalt mixture, which is very important in road pavement engineering. This study aims to modify asphalt mixtures with lignin isolated from mahogany sawdust combined with diphenylmethane 4,4′-diisocyanate and investigate their physical, mechanical, and thermal characteristics. The isolated lignin was prepared for a modified asphalt mixture by reacting with diphenylmethane 4,4-diisocyanate and adding asphalt. Next, the asphalt mixture was mixed with sand aggregate in an extruder at 150 °C. The results showed an improvement in mechanical, physical, and thermal properties. The optimum composition of asphalt and lignin was 60:40 with a compressive strength value of 3.107 MPa, a water absorption value of 0.246%, and a melting point of 238 °C. The Fourier-transform infrared spectroscopy (FT-IR) spectrum showed a small band at 1715 cm−1, indicating the CO carbonyl group of the NH–CO–O urethane bond. The morphology showed that the surface structure of the modified asphalt mixture becomes more homogeneous due to the interaction between asphalt and polyurethane, which is the result of the reaction of lignin isolate with diphenylmethane 4,4′-diisocyanate.

ObjectivesTo evaluate Wettability, pH and Microtensile bond strength (immediate and after thermocycling) of a universal adhesive after incorporation of 0.5% and 1% bulk-chitosan or nanochitosan.MethodsAll-bond universal adhesive was used to obtain five groups according to the type of additive; CONTROL, CHITOSAN (0.5), CHITOSAN (1%), NANOCHITOSAN (0.5%) and NANOCHITOSAN (1%). Contact angle and pH of the adhesives were tested with n = 7 for each test. for Microtensile bond strength testing, premolars teeth (N = 50) were used; twenty-five teeth for immediate bond strength and the other twenty-five were tested after thermocycling.ResultsCONTROL and CHITOSAN (0.5%) groups showed significantly higher contact angle measurements (30.78 ± 3.71 and 27.77 ± 4.63 respectively) compared to all other groups. CONTROL group showed significantly higher pH value (3.17 ± 0.05), followed by NANOCHITOSAN (0.5%) and NANOCHITOSAN (1%) and the least pH values were for 0.5% CHITOSAN group and CHITOSAN (1%). Bond strength results revealed that NANOCHITOSAN (0.5%) and NANOCHITOSAN (1%) had the highest bond strength (52.99 ± 16.14, 55.80 ± 16.11). CONTROL, CHITOSAN (0.5%) and CHITOSAN (1%) had no significant difference. After thermocycling, NANOCHITOSAN (0.5%) and NANOCHITOSAN (1%) had the highest bond strength values (38.58 ± 7.01 and 40.07 ± 11.40), followed by CHITOSAN (0.5%) and CHITOSAN (1%), and the least bond strength value was obtained by the control group. Hybrid layer micrographs showed that NANOCHITOSAN (1%) has intense resin infiltration before and after aging compared to all other groups.ConclusionIncorporation of nanochitosan (0.5% and 1%) improved the universal adhesive microtensile bond strength and bond durability.

Enhancement of the fracture resistance for sintered silver joints has been one of the critical issues that considered frequently in engineering practice. In this paper, different micropatterned sintered silver joints were fabricated. Through end notch flexural test, the load displacement curves for various kinds of micropatterned joints are presented. The shearing fracture toughness and shearing fracture characteristics for different micropatterned joints are also given. The maximum shearing fracture toughness is obtained under the grid groove samples with the highest shearing fracture toughness obtained at 356.95 ± 27.45 J/m2, which is about 7.8 times of that without micropatterned joints. It is also found that the shearing fracture toughness is strongly dependent on the groove depth of the micropatterns. The cracking morphology shows that the crack extension was mainly in a cohesive mode but was also associated with locally interfacial debonding failure that occurred at the groove locus. Although the micropatterns lead to the increase of shearing fracture toughness of adhesively bonded joints and even some of the tested P-δ curves shows the ductile fracture manner, the macro fracture morphology of the crack in sintered silver shows that the cracking in micropatterned joints still presents brittle fracture manner.

Developing a bonded prestressed solution for strengthening structures utilizing an iron-based shape memory alloy (Fe-SMA), is of significant interest. This study is the first systematic investigation of adhesively-bonded Fe-SMA joints to achieve complete cohesive failure, which is an essential prerequisite for bond integrity. The Fe-SMA surface was prepared by combining UV/ozone exposure (UV), sol–gel (SG), and primers (PC, PNC), and the failure mode of the joint was investigated using the floating-roller peel test. Furthermore, the joint durability was studied through artificial aging using a salt spray cabinet. Cohesive failure was obtained for all investigated adhesives, and the effect of every surface preparation step was described. The application of sol–gel was found to be a crucial step in obtaining complete adhesive failure.

ObjectiveTo evaluate the effect of SDF-based treatments following delayed bonding and surface treatment approaches on resin-dentin bonding efficiency of a universal adhesive under different application modes.MethodsMid-coronal dentin surfaces from sound third molars were randomly treated with 38% silver diamine fluoride (SDF) and/or additionally with potassium iodide (SDF/KI). Untreated dentin served as control. SDF-treated teeth were assigned to groups according to surface treatment approaches (air-abrasion and water rinsing), the application mode of a mild universal adhesive (etch-and-rinse or self-etch) and delayed bonding (immediate, 7, 15 or 30 days). Microtensile bond strength (n = 5), SEM analyses of hybrid layer formation and dentin etching patterns and dentin permeability were evaluated. Data were analyzed with factorial ANOVA.ResultsSDF-based treatments affected dentin bonding depending on application mode and surface treatment approaches (p15 days apart) potentialize mineral deposition improving caries control and service life of composite restorations.

As a way of reducing the formaldehyde emission and improving the properties of medium density fiberboard (MDF), this study investigated the effects of nanoclay and modified nanoclay with 3-aminopropyltriethoxysilane (APTES) and l-Lysine (Lys) on the MDF. The XRD, FTIR, and CHN anaLyses showed that nanoclay was successfully modified with APTES and Lys. 1.5, 2, and 2.5% of nanoclay and modified nanoclay were added into UF resin (based on the dry weight), and the mixtures were used to produce MDF. Changes in formaldehyde emissions were determined by the desiccator method. In addition, the modulus of rupture (MOR), modulus of elasticity (MOE), internal bonding (IB), thickness swelling (TS), and water absorption (WA) of the boards were measured. The results showed that adding nanoclay (5–25%) and modified nanoclay with APTES (42–61%) and Lys (38–50%) reduced formaldehyde emission. Meanwhile, the mechanical and physical properties of the boards also improved by adding nanoclay and modified nanoclay.

Adhesive bonding is widely used for joining light weight structures and surface preparation methods play a significant role in improving the bonding quality. Bond quality assessment of thermoplastic composites can be challenging due to the highly inhomogeneous structure. This article explores the use of ultrasonic testing to nondestructively characterize the bond state between thermoplastic composites with different surface preparation methods. Classification of bond states was carried out using a physics-based statistical method and machine learning based method. The results suggest that machine learning methods show a higher classification accuracy. The ultrasonics results were validated using destructive lap-shear testing.