The effects of modified zinc oxide nanoparticles on the mechanical/thermal properties of epoxy resin

Characterized by its strength, durability, and thermal properties, epoxy resin has been widely used as an adhesive, paint, and coating in many applications in the aerospace, civil and automotive industries. Despite this, the thermoset polymer resin has been known for its brittleness and low fracture resistance. This study focuses on the reinforcement of an epoxy resin system (diglycidyl ether of bisphenol A) with zinc oxide (ZnO) nanoparticles in their pristine form and a further modified form. The modification took place in two ways: coating with polydopamine (PDA) and covalently functionalizing them with (3-aminopropyl)triethoxysilane (APTES) and (3-glycidoxypropyl)trimethoxysilane (GPTMS). Therefore, four different types of nanoparticles were used: pristine ZnO, ZnO/PDA, ZnO/GPTMS, and ZnO/APTES aiming to improve the interfacial bonding between the polymeric matrix and the reinforcement. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, and scanning electron microscopy characterization and imaging techniques were used to prove that the ZnO nanoparticles were successfully modified prior to manufacturing the epoxy composites. While tensile testing showed that using pristine ZnO increases the composite's strength by 32.14%, the fracture toughness of the resin was improved by 9.40% when reinforced with ZnO functionalized with APTES. TGA showed that the addition of functionalized nanoparticles increases the material's degradation temperature by at most 7.31 ± 4.9°C using ZnO/APTES. Differential scanning calorimetry and dynamic mechanical analysis testing proved that the addition of any type of nanoparticles increases the resin's glass transition temperature by as much as 7.83°C (ZnO/APTES).     

Effect of nanoparticles on the performance of thermally conductive epoxy adhesives

Microsized or nanosized α‐alumina (Al₂O₃) and boron nitride (BN) were effectively treated by silanes or diisocyanate, and then filled into the epoxy to prepare thermally conductive adhesives. The effects of surface modification and particle size on the performance of thermally conductive epoxy adhesives were investigated. It was revealed that epoxy adhesives filled with nanosized particles performed higher thermal conductivity, electrical insulation, and mechanical strength than those filled with microsized ones. It was also indicated that surface modification of the particles was beneficial for improving thermal conductivity of the epoxy composites, which was due to the decrease of thermal contact resistance of the filler‐matrix through the improvement of the interface between filler and matrix by surface treatment. A synergic effect was found when epoxy adhesives were filled with combination of Al₂O₃ nanoparticles and microsized BN platelets, that is, the thermal conductivity was higher than that of any sole particles filled epoxy composites at a constant loading content. The heat conductive mechanism was proposed that conductive networks easily formed among nano‐Al₂O₃ particles and micro‐BN platelets and the thermal resistance decreased due to the contact between the nano‐Al₂O₃ and BN, which resulted in improving the thermal conductivity. POLYM. ENG. SCI., 50:1809–1819, 2010. © 2010 Society of Plastics Engineers     

Electroconductive Adhesives: Comparison of Three Different Polymer Matrices. Epoxy,Polyimide and Silicone

Electrically conductive organic adhesives are used in the microelectronics manufacturing industry for the attachment of silicon dies. These adhesives are composite materials which owe their conductivity to the incorporation of silver flakes. Several polymers have been formulated into electrically-conductive adhesives to meet different applications in the microelectronics industry; these are an epoxy resin, a polyimide and a silicone polymer. The purpose of this paper is to examine properties of these die-bonding adhesives in order to determine the advantages or disadvantages of these materials. This study offers a comparison of hardening chemistry, chemical purity, processing, electrical, thermal, and mechanical properties of three conductive adhesives based on an epoxy, a polyimide and a silicone polymer. We discuss correlation of composite properties with the structure of each matrix. The results indicate that the choice of the matrix is dictated by the application for which the electronic grade conductive adhesive is to be used and the desired properties for best reliability and performance.     

Electroconductive Adhesives: Comparison of Three Different Polymer Matrices. Epoxy, Polyimide and Silicone

Electrically conductive organic adhesives are used in the microelectronics manufacturing industry for the attachment of silicon dies. These adhesives are composite materials which owe their conductivity to the incorporation of silver flakes. Several polymers have been formulated into electrically-conductive adhesives to meet different applications in the microelectronics industry; these are an epoxy resin, a polyimide and a silicone polymer. The purpose of this paper is to examine properties of these die-bonding adhesives in order to determine the advantages or disadvantages of these materials. This study offers a comparison of hardening chemistry, chemical purity, processing, electrical, thermal, and mechanical properties of three conductive adhesives based on an epoxy, a polyimide and a silicone polymer. We discuss correlation of composite properties with the structure of each matrix. The results indicate that the choice of the matrix is dictated by the application for which the electronic grade conductive adhesive is to be used and the desired properties for best reliability and performance.     

水性环氧树脂包覆有机蒙脱土制备木材胶粘剂

摘要：水性环氧树脂通常含有水溶性分子或分子链，导致在高温和潮湿条件下作为木材胶粘剂时耐水性及力学性能较差。采用有机改性的纳米蒙脱土改性水性环氧树脂增强水性环氧树脂胶粘剂的耐水性及力学性能。并通过乳液包覆蒙脱土的方法与直接共混的方法对比，研究了不同添加量有机蒙脱土（0%，3%，6%，9%）对胶粘剂性能的影响。胶粘剂的耐水性及力学性能通过测量胶粘剂在干燥及潮湿条件下的剪切强度来表示。通过TGA、SEM、TEM、DSC研究了复合胶粘剂的热稳定性和结构。结果表明，在水性环氧树脂中添加有机改性的纳米蒙脱土，可以有效地提高胶粘剂的粘结强度，此外，采用乳液包有机覆蒙脱土的方法比直接共混的方法制备得到胶粘剂，有机蒙脱土在胶粘剂中分布更均匀，具有更优异的力学性能，说明有机蒙脱土在复合材料中的分散质量是影响复合胶粘剂性能的主要原因。     

Enhanced mechanical,thermal and adhesion properties of polysilsesquioxane spheres reinforced epoxy nanocomposite adhesives

ABSTRACT

Epoxy-based systems serve as excellent adhesives to join a wide range of substrates such as metal, ceramics, plastics, etc. The mechanical properties of such systems can be improved considerably by the addition of filler to the epoxy matrix. Herein, polymethylsilsesquioxane (PMS) and poly(methyl/vinyl)silsesquioxane (PMVS) nanosphere were synthesised by hydrolytic condensation of oraganosilane as a precursor in aqueous phase. The epoxy nanocomposite adhesives were prepared by adding different weight percentages (1–4 wt%) of the PS nanospheres. Tensile and compressive strength of the adhesive formulations were studied using the universal testing machine (UTM) and it was observed that the mechanical properties of the composites showed an increasing trend on increasing the filler loading. Adhesive strength of the epoxy composites on mild steel substrate was studied by conducting the lap shear test and EPV-4 exhibited a 31% increase in adhesive strength on the mild steel compared to the neat epoxy. Surface morphology of the epoxy composites were visualised from the SEM images and the composites also showed enhanced thermal conductivity. Higher mechanical and adhesive strength indicates the potential of the prepared nanocomposites to be used as an effective formulation in adhesive-based systems.     

Preparation and Characterization of Electroconductive Adhesives of NanoG/Polyurethane-Epoxy IPNs

Polyurethanes (PU) based on toluene diisocyanate (TDI) and polypropylene glycol 2000 (PPG) were reacted with an epoxy resin (EP) to prepare interpenetrating polymer networks (IPNs). Three kinds of electroconductive adhesives were prepared by dispersing nano-graphite (NanoG) into different matrices, i.e., pure PU, crosslinked PU/EP, and pure EP. The effects of epoxy content on morphological structure, conducting properties, thermal stability, and adhesive properties of the electroconductive adhesives were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, standard digital multimeter, dynamic mechanical thermal analysis, and lapshear tests. The results indicate that epoxy in the polyurethane-epoxy IPN adhesives plays an important role in clanging the morphological structure and improving conductivity properties, thermal stability, and adhesive properties of the electroconductive adhesives of PU.     

Lap shear strength and thermal stability of diglycidyl ether of bisphenol a/epoxy novolac adhesives with nanoreinforcing fillers

Nanoreinforcing fillers have shown outstanding mechanical properties and widely used as reinforcing materials associated to polymeric matrices for high performance applications. In this study, a series of multiwalled carbon nanotubes (MWCNTs)‐, nano‐Al₂O₃‐, nano‐SiO₂‐, and talc‐reinforced epoxy resin adhesives composites were developed. The influence of different types and contents of nanofillers on adhesion, elongation at break, and thermal stability (under air and nitrogen atmospheres) of diglycidyl ether of bisphenol A (DGEBA)/epoxy novolac adhesives was investigated. A simple and effective approach to prepare adhesives with uniform and suitable dispersion of nanofillers into epoxy matrix was found to be mechanical stirring combined with ultrasonication. Transmission electron microscopic and scanning electron microscopic investigations revealed that nanofillers were homogeneously dispersed in epoxy matrix at optimized nanofiller loadings. Adhesion strength was measured by lap shear strength test as a function of nano‐Al₂O₃ and MWCNTs loadings. The results indicated that the lap shear strength was significantly increased by about 50% and 70% with addition of MWCNTs and nano‐Al₂O₃ up to a certain level, respectively. The highest lap shear strength was reached at 1.5 wt % of nano‐Al₂O₃ loading. MWCNTs at all loadings (except 3 wt %) and nano‐Al₂O₃ have enhanced onset of degradation temperature and char yield of the adhesives. By combined incorporation of 0.75 wt % nano‐Al₂O₃ and 0.75 wt % MWCNTs into the epoxy novolac/DGEBA blend adhesives a synergistic effect was observed in the thermal stability of the adhesives at high temperatures (800°C). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40017.     

Bond behavior of epoxy resin–polydicyclopentadiene phase separated interpenetrating networks for adhering carbon fiber reinforced polymer to steel

The performance of bonded joints of carbon fiber reinforced polymer (CFRP) and steel relies on the mechanical properties of the adhesive used. Despite the high strength and modulus of epoxy adhesives, their brittleness limits their application to defect-sensitive structures. The development of interpenetrating polymer networks (IPNs), either homogeneous or phase separated, provides a route to toughen the epoxy while maintaining its high strength and modulus. Microphase separated IPNs consisting of a diglycidyl ether of bisphenol A-based epoxy resin and a thermoset with high toughness, polydicyclopentadiene (PDCPD), has been previously shown to demonstrate superior combinations of strength and toughness. This work investigates the most critical adhesive properties that affect bond strength by characterizing CFRP-steel double-lap shear joints containing the epoxy resin–PDCPD blend as the adhesive, using a wet lay-up manufacturing technique. The epoxy resin–PDCPD blend adhesives realized much higher bond strengths compared to either neat epoxy or neat PDCPD. Correlations between the bond strength and the bulk material properties are presented. Theoretical calculation of the bond strength indicates that the higher bond strength that can be achieved by using the epoxy resin–PDCPD blend adhesive is due to the increased shear toughness of the new formulations. POLYM. ENG. SCI., 60:104–112, 2020. © 2019 Society of Plastics Engineers     

Toughening of Epoxy Adhesives by Nanoparticles

With the emergence and commercialization of nanoparticles, new opportunities have emerged for toughening of epoxy adhesives using nanoparticles without sacrificing strength, rigidity and glass transition temperature, as is the case with conventional elastomeric tougheners. Inorganic Fullerene-like tungsten disulfide (IF-WS₂) nanoparticles and functionalized nano-POSS (Polyhedral-Oligomeric-Sil-Sesquioxane) were used to study the effects of nanoparticles on the toughening and mechanical properties of low and high temperature curing epoxy systems. Experimental results indicated that IF-WS₂ increased the fracture toughness by more than 10 fold in both epoxy systems at very low concentrations (0.3–0.5 wt%) while increasing its storage modulus and preserving its glass transition temperature. Epoxy functionalized POSS demonstrated an increase in toughness in addition to preserving rigidity and thermal properties at higher concentrations (3 wt%). It was postulated that chemical interaction of the sulfide and the epoxy matrix and the inherent properties of WS₂ were the decisive factors with respect to the outstanding nano-effect in the case IF-WS₂.     

Hybridizing MWCNT with nano metal oxides and TiO2 in epoxy composites: Influence on mechanical and thermal performances

In this study, the effects of multi‐walled carbon nanotubes (MWCNT), and its hybrids with iron oxide (Fe₂O₃) and copper oxide (CuO) nanoparticles on mechanical characteristics and thermal properties of epoxy binder was evaluated. Furthermore, simultaneous effects of using MWCNT with TiO₂ as pigment and CaCO₃ as filler for epoxy composites were determined. To investigate effects of nano‐ and micro‐particles on epoxy matrix, the samples were evaluated by TGA and DTA. It was found that the hybrid of MWCNT with nano metal oxides caused considerable increment in the tensile and flexural properties of epoxy samples in comparison to the single MWCNT containing samples at the same filler contents. Significant improvement in the thermal conductivity of epoxy samples was obtained by using TiO₂ pigment along with MWCNT. The TiO₂ pigment also caused considerable improvement in mechanical properties of the epoxy matrix and the MWCNT containing nanocomposite. The best mechanical and thermal properties of epoxy nanocomposites were obtained at 1.5 wt % of MWCNT and 7 wt % of TiO₂ that it should be attributed to particle network forming of the particles which cause better nano/micro dispersion and properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43834.     

Accelerated-curing epoxy structural film adhesive for bonding lightweight honeycomb sandwich structures

Accelerating the curing of epoxy/aromatic amine adhesives and improving their toughness are challenges in heat-resistant epoxy structural adhesives. Herein, we report an epoxy/aromatic amine adhesive accelerated curing system with an oxo-centered trinuclear (chromium III) complex, which is toughened using a thermoplastic block copolymer (TPBC). The reaction characteristics, heat resistance, microstructure, and bonding properties of the accelerated epoxy adhesives were analyzed. The reaction peak temperature of the epoxy with 3% catalyst was 113.1°C, which was 113.6°C lower than that of epoxy without catalyst, and the modified epoxy resin demonstrated a potential for rapid curing at medium temperature. The glass transition temperature of the TPBC-toughened epoxy adhesive was 125°C after curing, indicating excellent thermal stability after medium temperature curing. The introduction of the TPBC increased the single-lap shear strength of the epoxy adhesive without reducing its heat resistance. The shear strength at room temperature and 120°C of the modified epoxy adhesive with 50 phr of TPBC was 25.2 and 10.9 MPa, respectively. Moreover, the epoxy film adhesive exhibited outstanding bonding properties when used in the bonding of lightweight honeycomb sandwich structures.     

Transmission and Mechanical Properties of Optical Adhesives

The optical, mechanical and durability performance of selected epoxy, polyester, UV-curable acrylic, cyanoacrylate and silicone adhesives were evaluated and measured for bonding applications of optically transparent glasses in the visible and infra-red regions of the electromagnetic spectra.

From the initially selected adhesives only the UV-curable modified acrylic, two-component silicone and room temperature cured epoxy, were found to be of high performance characteristics, having good transmission properties and enhanced endurance in a combination of heat and humidity and following thermal cycling.

Sodium chloride substrates served as adherends for the transmission characterization of the optical adhesives, due to their high transmission properties in the 0.4-10 m μ spectral range. A modified lap shear specimen was designed for studying the mechanical properties and failure mechanisms of the adhesives and their durability in a humid and not environment. Finally, a two-piece glass doublet was used for investigating the optomechanical characteristics of the optical adhesive following environmental conditioning and thermal shock cycling.

Due to the inherent C-C bond, polymer adhesives are limited in utility, as far as transparency is concerned, close to 3.5 μm and in most of the 8-12 μm spectral range.     

Toughening structural adhesives via nano- and micro-phase inclusions

It has been clearly demonstrated that the addition of low concentrations of nanosilica particles to a typical rubber-toughened adhesive, based upon a two-part epoxy formulation, leads to very significant increases in the toughness of the adhesive and also to increases in the glass transition temperature and the single-lap shear strength. The nano-SiO 2 particles have an average particle diameter of 20 nm and are very well dispersed in the epoxy adhesive, and only a concentration of about 1% to 8% by mass of such nanoparticles are needed to achieve significant improvements in the mechanical and thermal performance of the rubber-toughened two-part epoxy adhesive.     

Development of Polypyrrole/Epoxy Composites as Isotropically Conductive Adhesives

As a possible replacement for lead bearing solders, metal filled isotropically conductive adhesives (ICAs) have shown a lot of potential recently. But still they have to come a long way and overcome their limitations like low impact strength and moisture instability. The current paper attempts to address the limitations of these ICAs by using intrinsically conducting polymer as a filler in place of metals. Conducting polymer (CP) polypyrrole (PPy) was incorporated as a filler in an epoxy/anhydride (EP) system and its application as an isotropic conductive adhesive was studied. PPy was synthesized by chemical polymerization using dodecyl-benzene sulphonic acid (DBSA) as dopant. The composites with varying PPy concentrations were studied for curing behavior and thermal degradation properties using DSC and TGA, respectively. The composites show good impact properties and conductivity at very low filler concentrations. SEM observations established that PPy particles were dispersed in the epoxy matrix uniformly. The overall characteristics of these conductive adhesives establish that they can be used as conductive adhesives in the electronics industry.     

Thermally and mechanically enhanced epoxy resin‐silica hybrid materials containing primary amine‐modified silica nanoparticles

In this article, a series of hybrid materials consisted of epoxy resin matrix and well‐dispersed amino‐modified silica (denoted by AMS) nanoparticles were successfully prepared. First of all, the AMS nanoparticles were synthesized by performing the conventional acid‐catalyzed sol–gel reactions of tetraethyl orthosilicate (TEOS), which acts as acceded sol–gel precursor in the presence of 3‐aminopropyl trimethoxysilane (APTES), a silane coupling agent molecules. The as‐prepared AMS nanoparticles were then characterized by FTIR, ¹³C‐NMR, and ²⁹Si‐NMR spectroscopy. Subsequently, a series of hybrid materials were prepared by performing in situ thermal ring‐opening polymerization reactions of epoxy resin in the presence of as‐prepared AMS nanoparticles and raw silica (RS) particles (i.e., pristine silica). AMS nanoparticles were found to show better dispersion capability in the polymer matrices than that of RS particles based on the morphological observation of transmission electron microscopy (TEM) study. The better dispersion capability of AMS nanoparticles in hybrid materials was found to lead enhanced thermal, mechanical properties, reduced moisture absorption, and gas permeability based on the measurements of thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and gas permeability analysis (GPA), respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Effect of Modification of an Epoxy Resin Adhesive with ATBN on Peel Strength

The effects of rubber content, rate of peel and temperature on peel strength of ATBN modified DGEBA based epoxy resin adhesives have been investigated. The fracture surfaces of peel test specimens and the distribution of rubber particles in cured bulk epoxy resin have been observed with SEM and TEM, respectively. The mechanical properties of bulk rubber modified epoxy resin have been also measured. The peel strengths increased with increasing rubber content, peel rate, and decreasing temperature. The peel strengths were superposed as a function of rate and temperature. Plots of the shift factors against temperature gave two straight lines, which followed an Arrhenius relationship. The region of temperature below the intersection of the two straight lines, temperature somewhat lower than T_g of epoxy adhesive, gave markedly high peel strengths and a stick-slip failure due to plastic deformation of the adhesive, and a number of micro holes produced by the rupture of rubber micro particles on the fracture surface. The region of temperature above the intersection gave lower peel strengths and an apparent interfacial failure with ductile fracture of the adhesive, and larger, shallow holes or no holes. From these results, the marked increase of peel strength was concluded to be mainly attributed to the plastic or viscoelastic deformation of epoxy matrix, the strong bond at the interface between rubber particles and epoxy matrix, and the dilation and rupture of a number of rubber particles.     

Investigation of the Mechanical Properties of Interphases in Adhesively Bonded Epoxy-Aluminum Joints by Localized Micro Extensometry

In recent papers it has been reported that epoxide-based adhesives form so-called interphases in adhesive joints. The properties of these interphases play an important role concerning the performance and durability of structural adhesive joints under detrimental service conditions. In this paper, the formulation of a basic epoxy adhesive and a methodology for gaining insight into the local mechanical properties of polymer interphases in structural adhesive joints made with ambient temperature curing epoxy adhesive are presented. The localized strain analysis in the cross-section of shear-loaded adhesive joints is accomplished by combining a high precision micro tensile tester with a digital microscope and by developing a method for preparing, marking, and digitally tracking the local deformations in a micro shear specimen.     

Silica aerogel/epoxy nanocomposites: Mechanical,vibrational, and morphological properties

The present study was an attempt to examine the effects that adding silica aerogel (SA) nanoparticles to epoxy would exert on its mechanical, vibrational, and morphological properties. Neat epoxy was consecutively combined with 1, 2, and 4 wt% of SA nanoparticles. A number of tests of mechanical properties were then performed on the samples, including tests of tensile, bending, compressive, dynamic mechanical thermal, hardness, and Izod impact. Vibration and water uptake tests were also conducted on the samples. The highest modulus and strength values were found in the nanocomposite sample with 4 wt% of SA, and the highest toughness and elongation values were detected in the sample with 1 wt% of SA. Furthermore, adding the SA nanoparticles to the epoxy improved the energy absorption and hardness of the epoxy matrix. The findings from the tests of dynamic mechanical thermal and vibration properties demonstrated that, with an increase in the nanoparticles content in the samples, the values of storage modulus and natural frequency increased while the values of tan δ and damping ratios decreased. A comparison between the values of natural frequency from the vibration test and the values from the Euler–Bernoulli beam theory showed a good agreement between the theoretical and experimental results.     

Enhancing the Anhydrous Proton Conductivity of Sulfonated Polysulfone/Polyvinyl Phosphonic Acid Composite Membranes With Hexagonal Boron Nitride

Hexagonal boron nitride (h-BN) particles have attracted increasing interest due to mechanical properties, chemical stability, electrical features, thermal stability, and good lubrication property. In this work hexagonal boron nitride were used as inorganic fillers, which increase the mechanical and thermal stabilities of the membrane. The proton conducting polymer membranes were prepared by blending of sulfonated polysulfone, polyvinyl phosphonic acid, and boron nitride. Scanning electron microscopy indicated the homogeneous distribution of hBN nanoparticles in the polymer matrix. hBN increased the proton conductivity and in the anhydrous state the maximum proton conductivity was determined as 7.9 × 10^?3 S/cm at 150°C for PVPA-SPSU-5hBN.