Effect of reinforcements at different scales on mechanical properties of epoxy adhesives and adhesive joints: a review

Improvement of the mechanical properties of adhesives and adhesive joints has been a subject of great interest in recent years. Up to now, several methods have been presented such as modifying substrate shapes, adding microparticles (MPs) and nanoparticles (NPs), and embedding micro and macrofibers in the adhesive layer. This review aims to investigate how these reinforcements of different scales in the adhesive layer influence the mechanical properties of adhesive joints and adhesives. Characteristics and applications of reinforcements are introduced in the first part. In the second part, the effects of several parameters commonly investigated by researchers on the strength, stiffness and fracture toughness improvement of polymeric materials are reviewed for reinforcements of different scales. Finally, damage mechanisms involved in increasing or decreasing the mechanical properties are reviewed and discussed.     

The effect of moisture on the strength of polycarbonate-cyanoacrylate adhesive bonds

The effect of humid ageing on the bond strength of polycarbonate-polycarbonate and steel-steel joints bonded with cyanoacrylate adhesive has been investigated. The superior moisture resistance of the bond between the polymer adherends has been demonstrated. The improved stability can be attributed to the dissolution of the polycarbonate in the monomer during curing. The bond produced has no true adherend/adhesive interface. This prevents the entry of water into the joint and consequently precludes effects such as adhesive displacement or hydrolysis of the cured polymer.     

An experimental study on the dependence of the strength of adhesively bonded joints with thickness and mechanical properties of the adhesives

Adhesive bonding joints are widely applied in many engineering fields. Their overall strength is much dependent on the thickness of adhesive layers. Many previous experimental studies have found that the ultimate failure strength of the bonding structure increases with the decrease of the adhesive thickness. However, few of them consider the effect of adhesive intrinsic material parameters on the relation between the overall strength and adhesive thickness. In the present investigation, the effect of the adhesive thickness on the overall strength of the lightweight metallic adhesive bonding joints was experimentally studied, considering the effect of the adhesive toughness. The results show that the variations of overall strength resulting from the adhesive thicknesses have remarkable discrepancy due to the toughness of the adhesive, which is in agreement with the previous model prediction.     

Reactive hot melt polyurethane adhesives modified with pentaerythritol diacrylate: synthesis and properties

Pentaerythritol diacrylate (PEDA) was synthesized by direct esterification from acrylic acid and pentaerythritol, and the reactive hot melt polyurethane adhesives (PURs) with high green strength were prepared from Poly(1,6-hexamethyleneadipate), PHA-3000, two kinds of Poly(propylene glycol) (PPG-1000 and PPG-4000) and PEDA as well as terpene-phenolic resin. Five samples of PURs with different weight percent (α) of PEDA (α = 0, 3, 5, 7, and 10 wt%), were obtained. The rheological properties, thermal stability, and mechanical properties of the samples were investigated. The results showed that the melt viscosity (η) and the storage shear modulus of the samples increase with the increase in α, while the thermal stability changes little. The bonding strength of the samples after 10 min, 30 min, and 48 h was assessed by 180° peel tests of Fabric 6535/adhesives/Fabric 6535 stacks. The results showed that the green strength after 30 min increases with the increase in α when α is not higher than 7 wt%.     

Strength, deformation and relaxation of joints bonded with modified cyanoacrylate adhesives

The introduction of high molecular weight poly(methyl methacrylate) or poly(butadiene-co-acrylonitrile) into ethyl 2-cyanoacrylate produced viscous adhesives with a homogeneous or heterogeneous structure after cure. Steel joints bonded with these adhesives are shown to have improved tensile shear strength, deformability and stress relaxation of bonds compared with pure cyanoacrylate adhesive. Poly(methyl methacrylate)-modified adhesive is recommended for static load-bearing joints while poly(butadiene-co-acrylonitrile)-modified adhesive is more suited to cyclic or vibrating loads.     

支化型水性聚氨酯胶黏剂的合成及性能

采用异佛尔酮二异氰酸酯(IPDI)、聚四氢呋喃醚二醇2000(PTMG2000)为原料,二月桂酸二丁基锡、1,4-丁二醇和2,2-二羟甲基丙酸分别为催化剂、小分子扩链剂和亲水单体,制得水性聚氨酯预聚体(PPU);接着以丙烯酸甲酯、二乙醇胺和三羟甲基丙烷为原料合成了超支化聚(胺-酯)(HPAE);最后制备出不同HPAE含...     

Investigating the influence of the chamfer and fillet on the high-cyclic fatigue strength of adhesive joints of steel parts

This paper presents the results of research undertaken to determine the possibility of improving the fatigue properties of peel-loaded adhesive-bonded joints by the constructional modification of the adherend. Fatigue strength tests were carried out on the electromagnetic inductor at the resonance frequency of the adhesive-bonded joint specimens. The tests were carried out on the specimens bonded by means of Bison Epoxy and Epidian 57 epoxy compositions with poly-aluminium chloride hardener. The joined elements were modified by making the chamfer or fillet to enlarge the thickness of the adhesive layer with the aim of reducing the stress concentration in the frontal part of the joint. This modification is the result of a research that confirms the existence of a stress concentration on the short section of the frontal part of an adhesive joint. This phenomenon can lead to the rapid initiation of adhesive joint destruction. The fatigue strength tests revealed a significant improvement in fatigue endurance.     

Process variable effect on the strength of autoclave-bonded film adhesive joints

This study investigates the effect of five independently-controlled process variables and variable combinations on the shear strength of autoclave-bonded film adhesive joints. Studied variables include the cure temperature, cure pressure and their respective ramp rates, as well as the duration of cure time. A full factorial design of experiment (DoE) at two levels for each variable is conducted with 3 replicas of each test. Test coupons are made of two layers of polycarbonate lexan that are autoclave-bonded using aliphatic polyether film adhesive (Huntsman PE399). Two set of test joints are used for generating test data on shear strength and failure mode. Bonded joints in the first set are tested prior to any environmental cycling, in order to generate baseline data on joint shear strength and failure mode. However, samples from the second set of autoclave-bonded joints were heat-cycled, in an environmental chamber at high relative humidity, prior to testing for shear strength. Test data on shear strength and failure mode is statistically analyzed using ANOVA.     

溶剂型聚氨酯鞋用胶的合成

研究了溶剂型聚氨酯鞋用胶粘剂,探索了合成的最优工艺条件,并进行了性能测试。胶粘剂采用PBA2000、BDO、TD180／20在溶剂丁酮下合成预聚体。最优条件为:扩链剂BDO与PBA摩尔比为0．4,异氰酸酯指数R控制在0．98-0．99范围,丁酮为首选溶剂,以二乙烯三胺和二丁基二月桂酸锡作复合催化剂,反应温度为75-85℃,反应时间为3h。合成的溶剂型聚氨酯胶粘剂具有良好的剥离强度和综合性能,添加(0．2-0．3)％的固化剂JQ-6能提高胶粘剂的最终剥离强度(20-30)％。     

胶粘剂固化行为对性能的影响

研究了一种中温固化耐高温胶粘剂固化行为对胶粘剂力学性能和耐久性能的影响,表明胶粘剂只有达到一定的固化程度,才能获得一定的交联密度,耐热性能、粘接强度和耐久性能。同时胶粘剂的固化时间和温度存在等效性关系。     

聚氨酯丙烯酸酯的合成及紫外光固化压敏胶的性能研究

以二聚酸聚酯二元醇(Diol)、氢化蓖麻油(HCO)和异佛尔酮二异氰酸酯(IPDI)等为主要原料合成聚氨酯丙烯酸酯(PUA),制备了紫外光固化压敏胶PSA,并用FTIR表征了Diol、PUA和PSA固化前后的结构。研究考察了Diol与HCO摩尔比和增粘树脂与PUA质量比对压敏胶热性能(differentialscanningcalorimetric,DSC)、动态粘弹性(dynamicrheologicalspectrometer,DRS)和粘接性能的影响。结果表明,随着PUA中HCO含量的增加,PSA的贮能模量和复数粘度增强,剥离力减小,持粘力升高。增粘树脂含量增加,压敏胶的贮能模量和复数粘度快速下降,损耗角正切峰向低频方向移动,表明增粘树脂与PUA等压敏胶组分相容性良好。此外,随增粘树脂的增加,剥离力增大,但持粘力降低。     

表面处理方法对胶粘剂性能的影响

采用不同的表面处理方法处理粘接接头,在湿热老化条件下通过元素分析法测定了样品中碳、硅、氧的含量,以及对胶粘剂粘接接头剥离强度、吸水率,玻璃化温度等湿热老化性能进行了考查,得出最佳处理粘接接头的方法。     

Synthesis and properties of waterborne polyurethane adhesives: effect of chain extender of ethylene diamine,butanediol, and fluoro-butanediol

Waterborne polyurethane (WBPU) adhesives were prepared using poly(tetramethylene oxide glycol), 4,4’-dicyclohexylmethane diisocyanate (H₁₂MDI), hydrophilic agent dimethylol propionic acid and chain extender of 2,2,3,3-tetrafluoro-1,4-butanediol (TFBD), ethylene diamine (EDA), and 1,4-butanediol. All three chain extenders have been used as single and mixed (different ratio) content during synthesis, and the effect of chain extender and their content to the properties of tensile strength, Young’s modulus, water swelling (%), and adhesive strength was investigated. The adhesive strength value was higher using EDA as a single-chain extender; however, the potentiality of adhesive strength under water was improved using mixed-chain extenders of EDA and TFBD in WBPU adhesives. The maxima potentiality was observed with 6.31 mole% TFBD and 2.10 mole% EDA in WBPU adhesives.     

醇溶性聚氨酯胶粘剂的合成与性能研究

醇溶性聚氨酯(APU)胶粘剂是一种新型、环保的胶粘剂,它既克服了溶剂型聚氨酯(PU)胶粘剂毒性大的缺点,又克服了水性PU水挥发慢、影响生产效率和能耗大的缺点,是目前综合性能优良的新品种胶粘剂。采用聚醚二醇、甲苯二异氰酸酯、二羟甲基丙酸和三羟甲基丙烷为基本原料,用丙酮为溶剂合成了聚醚型阴离子APU胶粘剂。讨论了预聚反应-NCO/-OH的配比、交联体系、硅烷偶联剂KH-550的加料方式和扩链反应温度等因素对APU胶粘剂性能的影响。当初聚n(-NCO)/n(-OH)比值为6,扩链剂反应温度控制在(60±2)℃时,合成的聚醚型阴离子APU具有较好的力学性能和耐水性,而且贮存稳定性较好。     

提高鞋用聚氨酯胶粘剂剥离强度的几种途径

论述了提高聚氨酯胶粘剂剥离强度盼几种途径。包括选择具有结晶度高、结晶速度快的原材料合成聚氨酯胶粘剂,通过改性或添加增粘树盾提高聚氨酯胶粘剂的结晶度和结晶速度。选择合适溶剂、表面处理剂和配合异氰酸酯固化剂使用等,来提高聚氨酯胶粘剂对材质的剥离强度。     

Effects of salt spray on the mechanical properties of aluminum-epoxy adhesive joints

The aluminum bonding joints were aged in salt spray fog for various aging time from 0 to 1200?h. Uniaxial tensile tests were conducted for the joints to obtain the residual strength of the joints. The test results showed that the residual strength of the joints increases firstly and then decreases with the aging time in salt spray environment. The mechanism of the spray fog environment effect on the joint residual strength is analyzed by infrared spectral analysis and energy dispersive spectroscopy experiments. It is suggested the effect of aging time in the salt spray fog on the joint residual strength is the competing result of two mechanisms. One positive mechanism is that the adhesive expands after absorbing water in the early aging and reaches its saturation after a certain time, which leads to releasing of the internal stress in joints and consequently increases the joint residual strength. Another negative mechanism is that the water molecules permeating into the adhesive when aged in salt spray fog leads to the plasticization of the adhesive, which results in decreasing the joint residual strength as the aging time increases.     

Review on adhesive joints and their application in hybrid composite structures

Composites have been used extensively in various engineering applications including automotive, aerospace, and building industries. Hybrid composites made from two or more different reinforcements show enhanced mechanical properties required for advanced engineering applications. Several issues in composites were resolved during the last few years through the development of new materials, new methods and models for hybrid joints. Many components in automobile are joined together either by permanent or temporary fastener such as rivets, welding joint and adhesively bonded joints. Increasing use of bonded structures is envisaged for reducing fastener count and riveted joints and there by drastically reducing assembly cost. Adhesive bonding has been applied successfully in many technologies. In this paper, scientific work on adhesively bonded composites and hybrid composites are reviewed and discussed. Several parameters such as surface treatment, joint configuration, material properties, geometric parameters, failure modes, etc. that affect the performance of adhesive bonded joints are discussed. Environmental factors like pre-bond moisture and temperature, method of adhesive application are also cited in detail. A specific case of adhesive joints in hybrid bonded-bolted joints is elaborated. As new applications are expanding in the field of composites joining and adhesive joints, it is imperative to use information on multiple adhesives and their behaviour in different environmental conditions to develop improved adhesive joint structure in mechanical applications.     

一种氯丁胶粘剂拉伸粘接强度降低的原因分析

研究了影响氯丁胶粘剂拉伸强度主要因素,探讨了混炼胶、溶剂、树脂等对氯丁胶粘剂拉伸粘接强度的影响。     

Soy-oil-based waterborne polyurethane improved wet strength of soy protein adhesives on wood

Soy-oil-based waterborne polyurethane (WPU) is used to improve wet strength in shear test of wood bonded with an adhesive of soy protein isolate (SPI) by dispersing WPU into SPI slurry. WPU׳s effects on the physiochemical properties of WPU-SPI adhesives are characterized through Fourier transform infrared spectrum, transmission electron microscopy, thermal analysis, contact angle, and mechanical strength. Wet strength of the WPU-SPI adhesives increases by 65% compared to SPI control. Moreover, the microstructure of WPU has effects on the interactions between WPU and SPI. In this study, smaller and more uniform distributed WPU0002 is easier to interact and form stronger crosslinking network with protein than WPU0500. The stronger interaction between WPU0002 and protein results in increased viscosity and bond strength. The WPU-SPI blended adhesives show significantly improved wet strength, demonstrating their potential as wood adhesives.     

鞋用聚氨酯胶粘剂的研究

探讨了研制高性能鞋用聚氨酯胶粘剂的技术路线,并介绍了聚酯多元醇和聚氨酯胶粘剂的合成工艺和方法。以聚己内酯、1,4-丁二醇和MDI等原料合成的鞋用聚氨酯胶粘剂,具有结晶度高、结晶速度快、内聚强度大等特点。讨论了聚酯二元醇、扩链剂、聚氨酯胶粘剂的分子量、异氰酸酯指数等对胶粘剂性能的影响。