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.     

Modification of Glass Fiber-Reinforced Epoxy with Amine Functional Aniline Formaldehyde Condensate (AFAFC)

Unmodified epoxy glass fiber laminates are brittle by nature. In this study, an improvement of the mechanical properties, such as impact, tensile and flexural strengths of the reinforced glass fiber diglycidyl ether of bisphenol-A based epoxy laminate, was carried out by incorporating an amine functional aniline formaldehyde condensate (AFAFC) modifier. AFAFC was synthesized by reacting aniline and formaldehyde in an acid medium (pH 4) and was characterized by FT-IR and 1-H NMR spectroscopy, viscosity measurements, elemental analysis and potentiometric titration. The fracture energies of the modified glass fiber composite were vastly improved and the improvement depended on the concentration of the modifier. The optimum properties were obtained by adding 10 phr (parts per hundred parts of epoxy resin) of the modifier. Furthermore, the fracture energies of the modified glass fiber composite increased with increasing the number of glass fiber layers. Scanning electron microscopy showed that round shaped AFAFC oligomer domains were formed in the matrix. These oligomer domains led to improved strength and toughness due mainly to the 'rubber toughening' effect in the brittle epoxy matrix. The thermal stability of the modified epoxy composites by thermogravimetric analysis was also reported.     

环氧树脂胶粘剂的增韧填充改性

研究增韧剂、填料对环氧树脂胶粘剂剪切强度和冲击强度性能的影响。结果表明，随聚硫橡胶加入量的增加，剪切强度和冲击强度呈先增加然后降低的趋势。加入经偶联剂处理的石英粉，剪切强度和冲击强度都有很大的提高。加入二氧化锰后冲击强度提高约250％。     

环氧胶粘剂增韧改性研究进展

概述了关于近些年环氧树脂以及环氧树脂胶粘剂增韧改性的研究进展情况,简单地介绍了以无机刚性填料(颗粒)增韧改性环氧胶粘剂的情况,比较详细地叙述了以橡胶弹性体和热塑性树脂增韧改性环氧胶粘剂的一些重要研究情况及相关的增韧机理,指出了国内外之间环氧胶粘剂发展的差距,同时提出了环氧胶粘剂将来的重点和发展趋势。     

Rheological Behaviour of Nanoreinforced Epoxy Adhesives of Low Electrical Resistivity for Joining Carbon Fiber/Epoxy Laminates

Epoxy resins reinforced with carbon nanofibers (CNF) and nanotubes (CNT) were prepared and evaluated as adhesives of carbon fiber/epoxy laminates. Different percentages of nanofiller (0.1–3 wt%) have been tested. The viscosity of the non-cured nanoreinforced epoxy mixtures increased with the nanofiller content. On the other hand, the thermal treatment at high temperatures of the mixtures of amino-functionalized CNTs and epoxy monomer also caused an increase of their viscosity — this is likely due to the chemical reaction between the oxirane groups of the epoxy and the amine groups of the nanofiller. The joint strength of the carbon fiber/epoxy laminates bonded with nanoreinforced epoxy adhesives was analyzed by means of the single lap shear test. The shear strength of these joints was similar to that of the one made with unfilled epoxy resin. However, observation by Scanning Electron Microscopy of the fracture surfaces of the adhesive joints confirmed that the incorporation of carbon nanofillers caused the cohesive fractures inside the laminates (light-fiber tear failure). The electrical conductivity was drastically increased by the addition of nanofillers, especially CNTs.     

The Effect of Accelerated Weathering on the Mechanical Properties of Alkali Treated Hemp Fibre/Epoxy Composites

In this study, 65 wt% aligned untreated long hemp fibre/epoxy (AUL) and aligned alkali treated long hemp fibre/epoxy (AAL) composites cured at 70°C using compression moulding were subjected to accelerated weathering using an accelerated weathering chamber with UV-irradiation and water spray at 50°C for four different time periods (250, 500, 750 and 1000 h). After accelerated weathering, tensile strength (TS), flexural strength, Young's modulus (YM), flexural modulus and fracture toughness (K _Ic) were found to decrease and impact energy (IE) was found to increase for both AUL and AAL composites. AUL composite had greater overall reduction in mechanical properties than that for AAL composite upon exposure to accelerated weathering environment. FTIR, TGA and WAXRD analyses of the accelerated weathered composites support the results of the deterioration of mechanical properties upon exposure to accelerated weathering environment.     

The Miscibility of Novel Bisphenol-Propylene Epoxy Resin With Liquid NBR

A novel kind of bisphenol-type epoxy resin with a vinyl side-chain was developed and its miscibility behavior with liquid nitrile-butadiene rubber (NBR) was investigated. The diglycidyl ether of bisphenol propylene (DGEBP) was prepared by the condensation of phenol with acrolein in the presence of an acid catalyst and the subsequent epoxidization with epichlorohydrin (ECH). The structures of the bisphenol and corresponding epoxy resin were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectral analyses and the epoxy value was determined to be 0.34 mol/100 g by titration. The mixture of DGEBP with the liquid NBR containing diglycidyl ether of bisphenol acetone (DGEBA) was prepared and cured with diaminodiphenylmethane (DDM). The miscibility and morphology of the mixture system were studied by dynamic mechanical thermal analysis (DMTA) and transmission electron microscopy (TEM), respectively. The cured mixture of DGEBP/NBR/DDM exhibited good miscibility and, therefore, no separation, along with a transparent appearance at rubber contents of 10 wt% and 30 wt%. For cured DGEBP/DGEBA/NBR/DDM systems at 20 wt% rubber content, the dispersed rubber phase and rubber particles were not observed by DMTA or TEM at DGEBP content above 40 wt%. The DMTA plot showed a single peak related to the glass transition temperature (T _g) which decreased with increasing DGEBP content. The appearance of the system varied from transparent to opaque and the rubber separated from the epoxy matrix to form two phases when the DGEBP content decreased. The T _g values of the rubber- and epoxy-rich phases were strongly dependent on the DGEBP content in the mixed system. The miscibility of epoxy resin with liquid NBR can be altered by varying the ratio of DGEBP to DGEBA.     

The effect of silica (SiO2) nanoparticles and ammonia/ethylene plasma treatment on the interfacial and mechanical properties of carbon-fiber-reinforced epoxy composites

A nanoparticle dispersion is known to enhance the mechanical properties of a variety of polymers and resins. In this work, the effects of silica (SiO₂) nanoparticle loading (0–2 wt%) and ammonia/ethylene plasma-treated fibers on the interfacial and mechanical properties of carbon fiber–epoxy composites were characterized. Single fiber composite (SFC) tests were performed to determine the fiber/resin interfacial shear strength (IFSS). Tensile tests on pure epoxy resin specimens were also performed to quantify mechanical property changes with silica content. The results indicated that up to 2% SiO₂ nanoparticle loading had only a little effect on the mechanical properties. For untreated fibers, the IFSS was comparable for all epoxy resins. With ethylene/ammonia plasma treated fibers, specimens exhibited a substantial increase in IFSS by 2 to 3 times, independent of SiO₂ loading. The highest IFSS value obtained was 146 MPa for plasma-treated fibers. Interaction between the fiber sizing and plasma treatment may be a critical factor in this IFSS increase. The results suggest that the fiber/epoxy interface is not affected by the incorporation of up to 2% SiO₂ nanoparticles. Furthermore, the fiber surface modification through plasma treatment is an effective method to improve and control adhesion between fiber and resin.     

The Effect of WS2 Nanotubes on the Properties of Epoxy-Based Nanocomposites

In this paper we evaluated the effect of embedding inorganic nanotubes (INT) of tungsten disulfide (WS₂) in an epoxy matrix, on the mechanical, thermal and adhesion properties of the resulting nanocomposites. The nanotube content spanned a range of values (0, 0.1, 0.3, 0.5 and 1.0 wt%), and the nanotube incorporation process consisted of a combination of both distributive (magnetic stirring) and dispersive (ultrasonic mixing) methods. The adhesion of the nanocomposites to an aluminum substrate was characterized by both a single lap shear and a T-peel test. The fracture toughness (K _IC) of the nanocomposites was characterized by a standard compact tension (CT) plane-strain fracture test. The thermal properties of the nanocomposites were determined by dynamic mechanical thermal analysis (DMTA). Overall, the addition of INT-WS₂ was found to improve the shear strength and peel properties of the nanocomposite, and to significantly improve its fracture toughness and glass transition temperature. The extent and character of the nanotube–epoxy interaction were examined by electron microscopy, as was the energy dissipation mechanisms during fracture.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

对环氧胶粘剂微观结构的新认识

本文叙述了国内外在环氧胶粘剂微观结构研究上的新进展。     

Fracture Toughness Enhancement of UV‐Cured Epoxy Coatings Containing Al2O3 Nanoparticles

Commercially available alumina powder (α‐Al₂O₃ nanoparticles with 150 nm diameter) is added up to 4 vol% into cycloaliphatic epoxy resins and cured using UV light. Chemical and physical investigations of these UV‐cured, reinforced epoxy resin are carried out. The FTIR analysis indicates decreasing effect of these nanoparticles on the curing rate. The FESEM study for the fracture surface of reinforced epoxy resins revealed increase in the surface roughness that might be a sign of toughness enhancement. Also, an improvement in the scratch resistance was noticed for samples containing alumina filler.

     

A Study on the Properties and Structure of polyether-Sulfone-Modified Epoxy Adhesives

Properties and morphology of PES-modified epoxy adhesives were studied in this paper. These systems have excellent mechanical properties and can be used as heat-resistant adhesives. SEM and EDX observations showed that the system has a two-phase structure. At lower PES content, there is a PES dispersed phase and a epoxy continuous phase. At higher PES content, there are two continuous phases. From these results, the relationship between structure and properties of this system were discussed.     

酞侧基聚芳醚砜／聚苯硫醚共混物的断裂韧性

本文通过有缺口和无缺口冲击试验、断裂韧性测试以及结合扫描电镜分析断面形貌，研究了酞侧基聚芳醚砜／聚苯硫醚共混物的断裂行为，讨论了聚苯硫醚增韧聚芳醚砜的机理。结果表明，共混物冲击强度的改善主要是由于其裂纹引发能的提高；共混物断裂韧性提高的原因是由于外加应力场在ＰＰＳ微纤附近产生应力集中，促使基体和微纤都发生塑性形变，从而吸收更多的能量所致。     

中温潜伏性固化剂在环氧胶黏剂中的研究进展

在环氧胶黏剂体系中,中温潜伏性固化剂以其优异的潜伏性和相对较低的固化温度而成为研究热点,符合当下提倡的绿色、环保、低碳生活理念。详细介绍了双氰胺、咪唑、酸酐、有机酰肼、BF3-胺络合物、微胶囊六种中温潜伏性固化剂及其改性方法。它们的改性方法主要是:通过改性活化或者加入活性促进剂降低双氰胺、酸酐、有机酰肼等高温固化剂的固化温度;通过改性钝化咪唑的固化活性,延长室温储存期;将BF3等路易斯酸室温固化的固化剂与胺络合降低其固化活性,提高室温储存期;将活性固化剂用壁材包裹形成微胶囊使其在室温时稳定,较高的温度时壁材破裂释放出活性固化剂,迅速固化。     

水中固化环氧树脂胶黏剂制备与性能研究

以固化剂、偶联剂及水泥用量,填料种类及其用量、促进剂及其用量等因素为考察对象,进行正交实验设计,考察了环氧胶黏剂中各组分用量对其剪切粘接强度的影响,并测试了其粘接性能及动态黏弹力学性能,同时进行了傅立叶红外光谱(FTIR)结构表征和热重(TGA)分析。通过粘接性能测试,得到了自制固化剂复配环氧树脂及不同助剂的最优配方:环氧树脂100份、固化剂30份、偶联剂5份、水泥120份、填料10份、促进剂2.8份,该环氧胶黏剂的剪切粘接强度为22.0MPa左右,拉伸强度为12.50MPa左右,冲击强度为9.41kJ/m2。TGA表明:环氧胶黏剂在低于335℃时,热稳定性比较好,保留率为90%以上。DMA测试得到:该胶玻璃化温度Tg为50℃左右。通过探索,混凝土哑铃型试件水中固化环氧胶黏剂的拉伸粘接强度达2.5MPa以上。     

Synergic Effect of Acrylate Liquid Rubber and Bisphenol A on Toughness of Epoxy Resins

The synergic effect of acrylate liquid rubber with pendant epoxy group and bisphenol A on the toughness of epoxy resins was presented in this paper. The addition of bisphenol A enhances the impact strength and elongation at break of epoxy resin and actually increases the ductibility of epoxy resin matrix. Much higher toughness efficiency can be achieved for the ALR modified epoxy resins by the incorporation of bisphenol A at the same time. The synergic promotion effect of acrylate liquid rubber and bisphenol A on the toughness efficiency of epoxy resins is attributed to the two-phase morphology and high ductibility of matrix, and the resultant large stress white zones and high shear yielding during the fracture process.     

聚醚胺对高弹性-高伸长率环氧树脂胶粘剂力学性能影响的研究

用聚醚胺(D230,D400,T403)和聚醚胺(D2000)作为混合固化剂,用浇铸成型法制备了系列环氧树脂结构胶粘剂。目的是通过配方设计、简化工艺研制出系列具有高弹性-高伸长率的环氧树脂胶粘剂。并与普通改性脂肪胺(593#)和聚醚胺(D2000)作为混合固化剂,聚醚多元醇(HF220)作为改性剂的环氧树脂体系进行了比较。实验用SEM法对树脂浇铸体断面微观形貌进行了观察,用动态DMTA法对树脂玻璃化转变温度(Tg)进行了测定,并对固化物的拉伸强度、断裂伸长率、以及断面形貌进行了测定,考察了聚醚胺相对分子质量、结构、官能度对拉伸强度、断裂伸长率和应力-应变的影响。动态力学分析法(DMTA)结果显示:体系的玻璃化转变温度(Tg)随着聚醚胺(D2000)加入量的增加而降低,当m(D400)∶m(D2000)=35∶100,Tg为16.63℃,达到最低,说明材料在低温也具有较好的柔弹性。通过扫描电镜(SEM)观察,证明聚醚胺对环氧树脂具有优异的相容性,对环氧树脂起到了增柔-弹性化的作用。     

The Effect of Moisture on Polyurethane Adhesives

Polyurethane adhesives predominate for bonding shoe soles but the moisture resistance of the adhesive polymer has been questioned. A typical polymer was hydrolytically degraded at 120°C for up to 29 hours and at 20, 30 or 37°C for up to one year and changes in physical and bonding properties monitored. Considerable degradation was necessary before bonding was seriously impaired due to cohesive failure of the adhesive, although heat resistance declined more rapidly. Joints made with undegraded adhesive on exposure to moisture showed rapid loss of strength and cohesive failure at 60 or 70°C, but little loss of strength and failure at or near the interface at 30 or 40°C.