Polyurethane adhesives containing functionalized nanoclays

The development and commercialization of nanoclays (NCs) offers new possibilities to tailor adhesives on the nanoscale range. Three types of functionalized nanoclays were included in the current study, two novel ones and one commercial nanoclay. The novel ones were based on aminosilane and amidoamine hyperbranched polymer, and the commercial nanoclay possessed hydroxyl functionality. All the three functionalities were expected to react with the polyurethane (PU) based thermoset adhesive. Fourier transform infrared (FT-IR) spectroscopy was used to follow the disappearance of the isocyanate group of the polyurethane thermoset adhesive. Thermo-mechanical properties were studied using dynamic mechanical analysis (DMA). Shear and peel properties of adhesively-bonded joints were evaluated using the appropriate test standards. Atomic force microscopy (AFM) was used to analyze the nanoscale morphology of cryogenically fractured surfaces. DMA measurements indicated that the glass transition temperature (T _g) of neat PU was 32°C. Incorporation of nanoclays in concentrations of 1, 3 and 5 wt% affected the glass transition temperature significantly. The functionalized nanoclays increased the T _g gradually to the range of 60 to 62°C for 5 wt% loading. The incorporation of functionalized nanoclays into PU improved the shear strength by 170, 160 and 195% for the hydroxyl-, aminosilane- and hyperbranched-treated NCs, respectively. The functionalized nanoclays exhibited higher peel strength compared to the neat PU by 30% for the hydroxyl modified clay and by 40% for aminosilane-modified clay (at 1 wt% concentration) and almost no change for the hyperbranched modified one. AFM analysis indicated that different fracture mechanisms occurred with respect to the type and concentration of nanoclay used.     

The effect of grafted caged silica (polyhedral oligomeric silesquioxanes) on the properties of dental composites and adhesives

With the emergence of commercial grafted caged silica (Polyhedral Oligomeric Silesquioxanes, POSS) having a three-dimensional (3D) morphology with peripheral functionality, new opportunities have been created for formulating dental adhesives and composites with enhanced mechanical and physical properties. The objective of the present study was to investigate the properties obtained by incorporating grafted caged silica into acrylate based dental composite and adhesive systems. Two commercial POSS materials (methacrylated and octaphenyl grafted) were added to dental restorative-glass-filled pre-polymers, based on BisGMA (bis-phenol A-glycidyldimethacrylate), HEMA (2-hydroxyethylmethacrylate) and TEGDMA (tetraethylglycidylmethacrylate). The nanostructured organic/inorganic hybrid compounds exhibited enhanced mechanical and thermal properties in cases where the POSS added was in concentrations up to 2 wt%. Beyond this threshold concentration, properties decreased due to agglomeration. In the case of the acrylated POSS, the T _g increased by 5°C, the composite compressive strength by 7%, and the bond shear strength by 36% and the shrinkage was reduced by 28% compared with neat dental composites and adhesives. Furthermore, in the case of octaphenyl grafted POSS, the compressive strength was reduced by 20%, the adhesive shear bond strength decreased by 49% and the shrinkage was reduced by 67%. It was concluded that the type of the grafted functional group of the caged silica was the dominant factor in nano-tailoring of improved dental composites and adhesives.     

Polyester hot-melt adhesives. I. Factors affecting adhesion to epoxy resin coatings

The peel strength and tensile shear strength of polyester hot-melt adhesives on metals coated with epoxy resins are affected by four characteristics of the polyester: (1) inherent viscosity, (2) glass transition temperature (T_g), (3) degree of crystallinity, and (4) melting point. The inherent viscosity affects the strength, toughness, and crystallinity of the adhesive. The T_g and degree of crystallinity affect the low-temperature adhesive properties; the peel strength is relatively low when the T_g is appreciably above the use temperature. The T_g, degree of crystallinity, and melting point affect the high-temperature adhesive properties. A hot-melt adhesive with high peel and tensile shear strengths from 0° to 120°C is the polyester of 1,4-butanediol and trans-1,4-cyclohexanedicarboxylic acid.     

The effect of tungsten disulphide nanoparticles on the properties of polyurethane adhesives

Thermoset-elastomer polyurethane (PU) nanocomposites were prepared using two types of tungsten disulphide (WS₂) nanoparticles: inorganic fullerene-like (IF) and inorganic nanotubes (INT) through an in-situ polymerization process. The quality of dispersion was evaluated using scanning electron microscope (SEM) and the thermomechanical properties were analyzed using dynamic mechanical analysis (DMA). Addition of 1% and 3?wt.%. IFs resulted in enhancement in storage modulus of 45 and 100%, respectively, compared to the neat polymer. The enhancement using only 0.5% wt. INTs was more than 100% and then decreased with additional amount of nanotubes. While no significant change in the composite’s glass transition temperature (T_g) was observed with IF-WS₂, 0.5% INT-WS₂ showed a 20?°C increase of T_g. In both cases, analysis of the chemical structure using an attenuated total reflectance- Fourier transform infrared spectroscopy showed no effect of the nanoparticles on the chemical structure of the PU and wide-angle X-ray diffraction showed no change in morphology. In the case of IF-WS₂ the highest peel strength was obtained with 1% wt. demonstrating a 44% improvement in peel strength. However, in the case of INT-WS₂, incorporating 0.5% wt. improved the peel strength by more than 1000%. SEM analysis showed a unique development of a nodular morphology and a failure mechanism dominated by nanotube pull-out. It was concluded that the geometry of the nanoparticles (nanotubes or fullerene) has a dominant effect on the final PU nanocomposite properties.     

Microsphere pressure sensitive adhesives—acrylic polymer/montmorillonite clay nanocomposite materials

In this study, the synthesis and characterization of acrylic polymer/montmorillonite (MMT) clay nanocomposite pressure sensitive adhesives (PSA) are presented. Different types and amounts of modified and unmodified montmorillonite clays were dispersed in ethyl acrylate (EA)/2-ethylhexyl acrylate (2-EHA) monomer mixture, which was then polymerized using a suspension polymerization technique. Polymerization was monitored in-line using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The adhesion properties of the synthesized nanocomposite materials were determined using standard measurements of tack, peel and shear strength. Viscoelastic properties of dried adhesive films were analyzed using dynamic mechanical analysis (DMA). The results showed that the kinetics of suspension polymerization was independent of the addition of MMT clays. On the other hand, adhesive properties were strongly influenced by the type and the amount of MMT clay added. While peel strength and tack gradually decreased with higher amount of modified MMT clay, a substantial increase in shear strength was determined with a maximal value at 1 wt% of added MMT clay. Moderate influence on tack, peel and shear strength was observed when the unmodified type of MMT clay was used. DMA analysis showed an increase in storage modulus (G′) for adhesives synthesized with MMT clay addition, but no significant differences were determined between particular types of MMT clays. A decrease in tan δ value for adhesives with 1 wt% of added MMT clay was observed, which also concurs with higher shear strength and implies to the improved cohesion of adhesive.     

Melt Synthesis and Characterization of Aliphatic Low-Tg Polyesters as Pressure Sensitive Adhesives

Polyesters, which are readily synthesized in the absence of solvent, are excellent candidates for a new generation of pressure sensitive adhesives (PSAs) due to their low cost and potential biodegradability. In this study, linear, all-aliphatic polyesters with low glass transition temperatures (T_g) were synthesized using a solvent-free, environmentally friendly melt polycondensation methodology. Polyesters of various compositions were synthesized from different diol and diester monomers to adjust the glass transition temperature and achieve optimum adhesive properties. Melt polycondensation of an isomeric mixture of dimethyl-1,4-cyclohexane dicarboxylate (DMCD), dimethyl adipate (DMAP), diethylene glycol (DEG), and triethylene glycol (TEG) generated a series of linear low-T_g polyesters. The synthesized polyesters were characterized using size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and ¹H NMR spectroscopy. The frequency- and temperature-dependent properties of the low-T_g polyesters were characterized using dynamic mechanical analysis (DMA). The adhesive performance of the polymers was evaluated using tack, peel, and shear strength measurements at ambient humidity and temperature. The low-T_g polyesters exhibited peel and tack properties comparable with commercial acrylic adhesives.     

Mechanistic studies in tackified acrylic emulsion pressure sensitive adhesives

Twenty‐three wt % aqueous tackifier dispersion based on glycerol ester abietic acid (T_g = 64°C, M_w = 940) was added to emulsion polymer 50/32/15/3 poly(2‐ethyl hexyl acrylate‐co‐vinyl acetate‐co‐dioctyl maleate‐co‐acrylic acid) pressure sensitive adhesive (PSA). From these latices, 25 μm thick films were cast. The films were dried at 25°C for 24 h or at 121°C for 5 min. Dynamic mechanical analysis (DMA) of the films included measuring elastic modulus (G′) and damping factor (tan δ). Under the above drying conditions, the films did not produce significant differences in their DMA and PSA properties as measured by loop tack, peel, and shear holding power. DMA of the tackified acrylic film showed thermodynamic miscibility between the tackifier and polymer regardless of the drying conditions. Microgels formed during emulsion polymerization of the acrylic PSA brought inherent weakness to the tackified film properties. In the neat acrylic PSA film, these discrete networks entangled with the uncrosslinked chains while in the tackified film, these networks could not form entanglements due to the increased molecular weight between entanglements for the uncrosslinked chains. This lack of network entanglements caused shear holding power of the tackified acrylic PSA film to be 4× lower than that of the neat acrylic PSA film. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1965–1976, 2000     

Preparation and properties of in‐situ polymerized polyurethane/stearate intercalated layer double hydroxide nanocomposites

The present work deals with the effect of stearate intercalated layered double hydroxide (St‐LDH) loadings on the morphological, mechanical, thermal, adhesive and flame retardant properties of polyurethane (PU)/St‐LDH nanocomposites prepared by the in situ polymerization method. X‐ray diffraction and transmission electron microscopy studies confirmed that exfoliation takes place at 3 wt% loading followed by intercalation at higher filler loadings in the PU matrix. The exfoliated structure has been further verified by atomic force microscopy. The measurements of stress‐strain, thermogravimetric analysis, dynamic mechanical analysis, lap shear strength and peel strength analysis showed that the nanocomposites containing 3 wt% St‐LDH exhibit excellent improvement in tensile strength (ca 175%) and log storage modulus (ca 14%), while PU/St‐LDH (5 wt%) possesses optimum improvement in glass transition temperature (ca 6 °C), lap shear strength (200%) and peel strength (130%) over neat PU. In addition, the gradual improvements in limiting oxygen index value with St‐LDH loading indicated the higher effectiveness in providing better barrier properties as well as better flame retardant behavior. Copyright © 2012 Society of Chemical Industry     

Preparation and properties of environment-friendly acrylic latex laminating adhesives applied in plastic/plastic composite films

Acrylic latex laminating adhesives (ALLAs) were successfully prepared via a monomer-starved seeded semi-continuous emulsion polymerization with butyl acrylate (BA), methyl methacrylate (MMA), styrene (St), acrylamide (Am), and methacrylate glycidyl ether (GMA) as monomers. Impacts of GMA on the final latex, the dried latex films and the adhesive properties of ALLAs were investigated, respectively. The results indicated that the increase of GMA contents in the pre-emulsion feed has no apparent effect on the final latex average particle size and size distribution, while the gel contents, glass transition temperature (T_g) and water contact angle of the ALLAs gradually increased, and the molecular weight (M_n, M_w) obviously increased. Additionally, as the amount of GMA increased from 0 to 10?wt%, the maximum peel strength of the composite films reached 3.72 N/15mm with 5?wt% GMA contents. When heated to 65?°C, the peel strength of the composite films with 5?wt% of GMA can still maintain an acceptable peel strength (2.51 N/15mm) for application, showing excellent adhesive performance and heat resistance properties.     

Adhesive strength of steel–epoxy composite joints bonded with structural acrylic adhesives filled with silica nanoparticles

This paper reports a study on the effect of silica nanoparticles on the adhesion strength of steel–glass/epoxy composite joints bonded with two-part structural acrylic adhesives. The introduction of nano-silica in the two-part acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strengths of the adhesive joints increased with addition of the filler content up to 1.5 wt%, after which decreased with addition of more filler content. Also, addition of nanoparticles caused a reduction in the peel strength of the joints. Differential scanning calorimeter analysis revealed that T_g values of the adhesives rose with increasing the nanofiller content. The equilibrium water contact angle was decreased for adhesives containing nanoparticles. Scanning electron microscope micrographs revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.     

Synthesis and characterization of UV-curing epoxy acrylate coatings modified with organically modified rectorite

Epoxy acrylate (EA) coatings modified with organically modified rectorite (OREC) were synthesized employing the ultraviolet-curing technique. Two kinds of alkyl ammonium ions, octadecyltrimethylammonium chloride (OTAC) and [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MAOTMA), were used to modify rectorite (REC). The methacrylate functionalities of MAOTMA were capable of reacting with the acrylate groups of EA. The structure of OREC was characterized by FTIR and XRD and the results indicated that the surfactants were successfully intercalated into the REC interlayers via cation exchange process. The morphology of nanocomposites was investigated by SEM and TEM. OREC showed better dispersion in EA matrix compared with unmodified REC. The T _g of neat EA obtained by DMA was 75.6°C, while for 5 wt% EA/MAOTMA-REC and EA/OTAC-REC nanocomposites it increased to 76.5 and 80.8°C, respectively. The nanocomposite with 3 wt% loading of OTAC-REC had the highest T _g (89.7°C). TGA revealed that the thermal stability of nanocomposites was enhanced by OTAC-REC and MAOTMA-REC and the thermal stability of EA/MAOTMA-REC nanocomposites was better than that of EA/OTAC-REC nanocomposites. The mechanical properties of nanocomposites containing OTAC-REC and MAOTMA-REC were better than those of nanocomposites containing unmodified REC. With increasing OREC content, the adhesive force of nanocomposites decreased slightly and the flexibility increased significantly.     

Influence of symmetry/asymmetry of the nanoparticles structure on the thermal stability of polyhedral oligomeric silsesquioxane/polystyrene nanocomposites

The thermal degradation of two polyhedral oligomeric silsesquioxane/polystyrene (POSS/PS) nanocomposites of formula R₈(SiO_1.5)₈ POSS/PS and R′₁R₇(SiO_1.5)₈ POSS/PS (where R′ = Phenyl and R = Cyclopentyl), at 5% of POSS concentration, was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres. Compounds were prepared by the polymerization of styrene in the presence of POSS. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates, and the obtained thermogravimetric (TG) curves were discussed and interpreted. The initial decomposition temperature (T_i), the temperature at 5% mass loss (T_5%), the glass transition temperature (T_g), and the activation energy (E_a) of degradation of nanocomposites were determined and compared with each other and with those of unfilled PS. The T_i, T_5%, and degradation E_a values of nanocomposites were higher than those of neat PS, thus indicating a better heat resistance and lower degradation rate, and then a better overall thermal stability. The use of POSS with a symmetric structure, in the synthesis of PS based nanocomposite, showed a decrease of T_g value not only in respect to asymmetric POSS/PS nanocomposite but also in respect to neat polymer, thus suggesting an influence of filler structure in the thermal properties of the materials. POLYM. COMPOS., 33:1903–1910, 2012. © 2012 Society of Plastics Engineers     

Morphology,thermal and mechanical properties of epoxy adhesives containing well-dispersed graphene oxide

Graphene oxide (GO) is prepared and introduced into epoxy resins through a wet-transfer migration technique using a three-roll mill. The results of TEM, XRD and digital microscope observation show that good dispersion of GO is achieved without using any additives. The mechanical and thermal properties of GO/epoxy (GO/EP) adhesives are enhanced with GO incorporated. A 10.2% increase in Young's modulus and a 56.3% increase in elevated-temperature (120 °C) lap shear strength (LSS) was observed on addition of 1.0 wt% GO, compared to the neat epoxy adhesive. Increased glass transition temperature and improved thermal stability of the GO/EP adhesives are also observed in the DMA and TG analysis. Moreover, the toughness of the GO/EP adhesives is improved and much rougher fracture surface can be observed compared with the neat epoxy adhesive. No GO agglomeration can be observed in the SEM images of GO/EP adhesive with 1.0 wt% loading.     

Physical gelation in ethylene-propylene copolymer melts induced by polyhedral oligomeric silsesquioxane (POSS) molecules

The rheological behavior of ethylene-propylene (EP) copolymers containing polyhedral oligomeric silsesquioxane (POSS) molecules was investigated by means of wide-angle X-ray diffraction (WAXD), oscillatory shear, stress and strain controlled rheology in the molten state and dynamic mechanical analysis (DMA) in the solid state. WAXD results showed that the majority of POSS molecules in the EP melt were present in the crystal form. Oscillatory shear results showed that the EP/POSS nanocomposites exhibited a solid-like rheological behavior compared with the liquid-like rheological behavior in the neat resin, i.e. POSS caused physical gelation in EP. While POSS exhibited only a minimum effect on the flow activation energy of EP, the high POSS concentration samples were found to induce higher yield stress than the neat resin. This behavior was similar to the Bingham rheology, indicative of a structured fluid. DMA results indicated that the presence of POSS increased the Young's modulus as well as the T_g of the EP copolymer. These results suggested that two types of interactions contributed to the physical gelation in EP/POSS melts were present: the strong particle-to-particle interactions between the POSS crystals and the weak particle-to-matrix interactions between the POSS crystals and the EP matrix.     

Viscoelastic and adhesive properties of single‐component thermo‐resistant acrylic pressure sensitive adhesives

Poly(butyl acrylate‐vinyl acetate‐acrylic acid) based acrylic pressure sensitive adhesives (PSAs) were synthesized by solution polymerization for the fabrication of high performance pressure sensitive adhesive tapes. The synthesized PSAs have high shear strength and can be peeled off substrate without residues on the substrate at temperature up to 150°C. The PSAs synthesized in the present work are single‐component crosslinked and they can be used directly once synthesized, which is convenient for real applications compared to commercial multi‐component adhesives. The results demonstrated that the viscosity of the PSAs remained stable during prolonged storage. The effects of the preparation conditions such as initiator concentration, cross‐linker amount, organosiloxane monomer amount and tackifier resin on the polymer properties, such as glass transition temperature (T_g), molecular weight (M_w), surface energy and shear modulus, were studied, and the dependence of the adhesive properties on the polymer properties were also investigated. Crosslinking reactions showed a great improvement in the shear strength at high temperature. The addition of tackifier resin made peel strength increase compared to original PSAs because of the improvement of the adhesion strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40086.     

Effect of organoclay and chain-transfer agent on molecular parameters and adhesion performance of emulsion pressure-sensitive adhesives

Organoclay-reinforced pressure-sensitive adhesives (PSAs) based on poly(butyl acrylate-co-vinyl acetate-co-acrylic acid) were prepared in the presence of an organically modified montmorillonite, that is, Cloisite15A (C15A), via in situ batch emulsion polymerization. The effect of C15A and chain transfer agent (CTA) level on the molecular parameters and adhesion properties of resulting reinforced PSA were investigated. Small-angle X-ray scattering (SAXS), gel permeation chromatography (GPC), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), and differential scanning calorimetry (DSC) were used to determine the characteristics of the neat and reinforced PSAs. The adhesion test results showed that the incorporation of C15A up to 1 wt% considerably increased the peel strength, shear and probe tack due to increasing the entanglement density of the PSA copolymer, while further increase lowered the peal and tack properties. Interestingly, the addition of 0.25 wt% CTA in the presence of 1 wt% C15A silicate layers resulted in PSA nanocomposite with the highest peal strength and probe tack. Although the CTA remarkably decreased the shear resistance of the neat PSA, the existence of C15A layers or tactoids in the reinforced PSAs decreased the rate of shear resistance decay due to the good interaction between the C15A and adhesive copolymer chains.     

Montmorillonite nanoclay filler effects on electrical conductivity,thermal and mechanical properties of epoxy‐based nanocomposites

Epoxy‐based nanocomposites with 2, 5, and 7 wt% of montmorillonite (MMT) nanoclay were prepared using high shear melt mixing technique. The microstructural features of the nanocomposites were investigated by transmission electron microscopy (TEM). The thermal and mechanical properties were measured using differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), and dynamic mechanical analyzer (DMA). Further, the effect of voltage, temperature, seawater aging on the electrical conductivity (σ_DC) of the nanocomposites was also measured. To understand the free volume behavior upon filler loading, and to observe the connectivity between microstructure and other properties, positron annihilation lifetime spectroscopy was used. The TEM results revealed that MMT nanoparticles were uniformly dispersed in the epoxy matrix. Experimental results showed that the inclusion of 2 wt% MMT nanofiller increased the T_g, electrical conductivity, thermal stability, modulus, free volume of the epoxy nanocomposite significantly. This is well explained from the results of T_g (DSC and DMA), thermal stability, TGA residue, free volume analysis, and electrical conductivity. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Cellulose nanocrystals (CNCs) reinforced acrylic pressure- sensitive adhesives (PSAs) prepared via miniemulsion polymerization

In this study, poly (n-butyl acrylate-co-2-ethyl hexyl acrylate) (P(nBA-co-2EHA)) pressure sensitive adhesives (PSAs) were successfully synthesized in the presence of cellulose nanocrystals (CNCs) via in-situ miniemulsion polymerization. First, the CNCs were prepared via acid hydrolysis of cellulose microcrystals (CMCs) at various temperatures, 42–54 °C, and characterized using atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) apparatus. The results showed that hydrolysis of MCCs at 45 °C resulted in CNCs with a well-defined aspect ratio, average length of 206 nm and thickness of 3.9 nm, and the highest crystallinity. Adding further CNC to the copolymer adhesive enhanced the mean particle size of the composite latex and decreased the glass-rubber transition temperature (T_g) of the copolymer matrix. Molecular weights and viscoelastic properties of the resultant PSAs were determined using gel permeation chromatography (GPC) and dynamic mechanical thermal analysis (DMTA), respectively. Adhesion performance of the neat and reinforced PSAs containing 1–5 wt% CNCs was evaluated at room temperature. The results showed that the incorporation of CNCs up to 4 wt% in the copolymer adhesive increased the shear resistance by 518%, peel strength by 176% and probe tack by 13%, while further addition, 5 wt%, lowered the adhesion performance due to a lack of surface wettability.     

Preparation and performance of urethane-modified polytriazole adhesives

Polytriazole adhesives are a new type of adhesives with excellent heat resistance, but the lap shear strength at room temperature is not ideal, which is about 15 MPa. In order to improve its adhesion performance at room temperature, a series of urethane-modified polytriazole (UPTA) adhesives were successfully synthesized via 1, 3-dipolar cycloaddition reaction between azides, and alkynes. Firstly, an alkynyl-terminated urethane monomer di(but-3-yn-1-yl) (1,3-phenylenebis(methylene)) dicarbamate (DBPMD) was synthesized and characterized. Then DBPMD was reacted with biphenyl dibenzyl azide (BPDBA) and N′,N′,N′,N′-tetrapropargyl-p,p′-diaminodiphenyl methane (TPDDM) to prepare UPTA adhesives. Curing behavior, thermal properties, bonding performance, and resistance to damp heat aging of UPTA adhesives were studied. The results show that the introduction of urethane group has almost no effect on the curing behavior. The glass transition temperature (T_g) and the 5% thermal weight loss temperature (T_d5) gradually decreased with the increased proportion of DBPMD added. T_g of UPTA adhesives ranged from 185 to 215°C and T_d5 of UPTA adhesives were all above 300°C, which indicated its outstanding thermal stability. The lap shear strength at room temperature of UPTA adhesives increased first and then decreased with the increasing amount of DBPMD, which ranged from 13.9 to 19.9 MPa. The highest lap shear strength of UPTA adhesives can reach 19.9 MPa, which was 31.8% higher than PTA adhesive. The lap shear strength retention rate of UPTA adhesives at 180°C was all over 75%. Lap shear strength retention rate of UPTA adhesives under 168 h damp heat aging time was all over 80%. UPTA adhesives have good bonding performance, heat resistance, and damp heat aging resistance, which can meet many complex construction requirements.     

Mechanically robust,electrically and thermally conductive graphene-based epoxy adhesives

This study develops a facile approach to fabricate adhesives consists of epoxy and cost-effective graphene platelets (GnPs). Morphology, mechanical properties, electrical and thermal conductivity, and adhesive toughness of epoxy/GnP nanocomposite were investigated. Significant improvements in mechanical properties of epoxy/GnP nanocomposites were achieved at low GnP loading of merely 0.5?vol%; for example, Young’s modulus, fracture toughness (K_1C) and energy release rate (G_1C) increased by 71%, 133% and 190%, respectively compared to neat epoxy. Percolation threshold of electrical conductivity is recorded at 0.58?vol% and thermal conductivity of 2.13?W m^?1 K^?1 at 6?vol% showing 4 folds enhancements. The lap shear strength of epoxy/GnP nanocomposite adhesive improved from 10.7?MPa for neat epoxy to 13.57?MPa at 0.375?vol% GnPs. The concluded results are superior to other composites or adhesives at similar fractions of fillers such as single-walled carbon nanotubes, multi-walled carbon nanotubes or graphene oxide. The study promises that GnPs are ideal candidate to achieve multifunctional epoxy adhesives.