Improving Epoxy Adhesives with Zirconia Nanoparticles

Zirconia nanoparticles were synthesized by a sol–gel route and dispersed into an epoxy base for structural adhesives. Nanoparticles were used as-synthesized or after calcination. Moreover, the effect of silane functionalization was also investigated. According to preliminary tensile mechanical tests on bulk nanocomposite samples, calcined and untreated zirconia nanoparticles were selected for the preparation of adhesives with various filler contents. The glass transition temperature increased up to a filler content of 1 vol% and then decreased, probably due to the concurrent and contrasting effects of chain blocking and reduction of the crosslinking degree. Also tensile modulus, stress at break and fracture toughness of bulk adhesives samples were positively affected by the presence of an optimal amount of zirconia nanoparticles. Mechanical tests on single lap aluminium bonded joints indicated that zirconia nanoparticles led to relevant enhancements of the shear strength of the joints. In particular, the shear strength increased by about 60% for an optimal filler content of 1 vol%, and an adhesive failure mechanism was evidenced for all the tested specimens. Concurrently, a significant decrease of the equilibrium contact angle with water was observed for adhesives containing zirconia nanoparticles. It can therefore be concluded that the addition of zirconia nanoparticles can effectively improve epoxy adhesives, both by increasing their mechanical properties and by enhancing the interfacial wettability with an aluminium substrate.     

Castor Oil-Based Polyurethane/Epoxy Intercross-linked Polymer Network Adhesives for Metal Substrates

Castor oil based polyurethane (CO-PU) was first synthesized from castor oil and 4, 4’-diphenyl-methane-diisocyanate (MDI). Then, a series of CO-PU/epoxy (EP) intercross-linked polymer network (ICPN) adhesives for metal substrates were prepared by a sequential method. The functional groups, tack -free time, mechanical properties, adhesive properties, and thermal stability were studied. Fourier transform infrared spectroscopy analysis indicated that an ICPN structure was formed through the introduction of CO-PU into EP. Results of adhesive measurements showed that the maximal value of lap shear strength was achieved at the CO-PU content of 20%. Thermogravimetric analysis results indicated that thermal stability of the adhesive film decreased with increased CO-PU content.     

有机蒙脱土改性脲醛树脂的结构与纳米力学研究

蒙脱土(MMT)作为一种天然矿物质,在树脂胶粘剂的增强改性方面应用前景广阔。为了探明蒙脱土增强作用机理,本文采用有机蒙脱土改性脲醛树脂,利用傅里叶红外光谱仪(FTIR)和X射线衍射仪(XRD)分析蒙脱土和改性树脂的化学和晶体结构;并制造木质复合材料,采用纳米压痕技术(NI)比较研究复合材料界面区域树脂的纳米力学性能,测定复合材料的宏观胶合强度。FTIR和XRD分析表明,经十六烷基三甲基溴化铵分析纯(CTAB)改性后的蒙脱土在2 929和2 855 cm-1附近出现新的吸收峰,蒙脱土原土中的金属阳离子和有机阳离子实现有效交换,其(001)面强衍射峰向小角度移动,蒙脱土原土纳米片层的间距从1.51 nm增加至2.71 nm,有助于蒙脱土均匀分散于树脂体系中,并与体系中聚合物分子基团发生化学反应。蒙脱土片层的物理填充、化学反应形成的弹性体结构使得胶粘剂在加载过程中可以有效地分散应力,从而有利于提高脲醛树脂的力学性能,有机蒙脱土改性脲醛树脂的微观弹性模量和硬度分别增加了66.9%和24.2%。改性后树脂的耐水性能得到明显改善,木质复合材料的湿胶合强度增加了约97%。     

杂化溶胶改性紫外光固化胶粘剂的研究

 以自制的杂化溶胶对紫外光固化丙烯酸酯胶粘剂进行改性，得到了具有高粘接强度，对丙酮、乙醇、氯仿等具有明显的耐溶剂性的紫外光固化胶粘剂。实验发现：活性稀释剂中含有较多的羟基、羧基时，此胶粘剂对玻璃的粘接强度较高；胶层粘接力随杂化溶胶用量的增加先增大，后减小，当杂化溶胶中的固体质量为光敏树脂的60％时，胶粘剂的剪切强度达到最大（12MPa）。     

杂化溶胶改性紫外光固化胶粘剂的研究

以自制的杂化溶胶对紫外光固化丙烯酸酯胶粘剂进行改性,得到了具有高粘接强度,对丙酮、乙醇、氯仿等具有明显的耐溶剂性的紫外光固化胶粘剂。实验发现：活性稀释剂中含有较多的羟基、羧基时,此胶粘剂对玻璃的粘接强度较高;胶层粘接力随杂化溶胶用量的增加先增大,后减小,当杂化溶胶中的固体质量为光敏树脂的60％时,胶粘剂的剪切强度达到最大（12MPa）。     

利用傅里叶变换红外光谱分析高温对木材-胶粘剂界面性能的影响

胶合木层板间界面起传递应力的作用,是构件承载的重要参数,其高温胶合性能决定了构件的抗火性能。以兴安落叶松结构材,以及结构用间苯二酚-酚醛树脂胶粘剂(PRF)和三聚氰胺-脲醛树脂胶粘剂(MUF)为研究对象,研究了20～280 ℃中木材含水率、密度、顺纹弦向抗剪强度和木材-胶粘剂界面胶合性能等216个试件在高温中的物理力学性能变化规律,通过傅里叶变换红外光谱分析高温中胶粘剂官能团变化,揭示了高温对木材-胶粘剂界面性能的劣化机理。结果表明,20～150 ℃时,兴安落叶松主要发生由水分释放导致的木材密度降低等物理反应,木材颜色未发生明显变化;150～200 ℃时,木材热降解开始,密度下降速度变缓,木材颜色逐渐加深;温度继续升高时,木材热降解加剧,颜色急剧加深,木材密度损失快速增加;当温度升至280 ℃时,木材发生炭化、完全转化为黑色,密度降至常温的72.49%。高温对兴安落叶松顺纹弦向抗剪强度有明显的劣化作用;20 ℃时木材抗剪强度为9.654 MPa,20～110 ℃时木材抗剪强度下降较快,150 ℃时降至常温的60.68%;150～280 ℃时,木材顺纹抗剪强度急剧下降,280 ℃时降至1.054 MPa。木材-胶粘剂界面的高温性能与胶粘剂的耐热性能密切相关;常温时,兴安落叶松与PRF和MUF均有较好的胶合性能,其界面抗剪强度分别为9.071和9.619 MPa,木破率均在80%以上;随着温度的升高,两种胶粘剂的界面抗剪强度均明显降低,木材-PRF界面较木材-MUF具有更好的耐高温性能。20～150 ℃时,两种胶粘剂界面抗剪强度劣化规律与木材抗剪强度相似,150 ℃时木材-PRF和木材-MUF的界面抗剪强度分别为常温的60.61%和60.92%,木破率均高于70%。150～280 ℃时,木材-PRF界面抗剪强度劣化规律仍与木材顺纹抗剪强度相似,280 ℃时降至0.774 MPa;木材-MUF界面胶合性能受温度影响更大,220 ℃时其木破率为10%,280 ℃时界面抗剪强度降至0 MPa。傅里叶变换红外光谱图中,20～150 ℃时PRF化学结构无明显变化;温度高于150 ℃时主要发生胶粘剂的进一步交联,以及醚键和亚甲基桥的断裂,PRF开始热解,但化学结构仍较完整;20～150 ℃时MUF的化学结构无明显变化,温度高于200 ℃时,羟甲基特征峰减弱、异氰酸酯基团产生,热降解剧烈,PRF较MUF具有更高的耐热性能。研究结果将为木结构工程合理选择原材料提供数据支撑,并为完善木结构抗火设计理论和方法提供依据。     

Z箍缩动态黑腔负载装配用胶粘剂

由于Z箍缩动态黑腔负载中的低密度聚合物泡沫柱具有多孔结构和极低的力学强度,在装配过程中对胶粘剂有一定的特殊要求。实验以聚氨酯丙烯酸酯为主体树脂,丙烯酸异冰片酯为活性单体,配以光引发剂和偶联剂制得了适用于低密度泡沫粘接用的紫外光固化胶粘剂。测试表明,所研制的胶粘剂的体积收缩率仅为2.25%,且具有较高的固化速率和适当的粘接强度,能够满足稳固、快速装配的要求。通过对粘接界面的观测发现,胶粘剂在诊断孔内没有明显的扩散,且在低密度致密结构泡沫中的扩散厚度较小,均匀性好。     

Z箍缩动态黑腔负载装配用胶粘剂

由于Z箍缩动态黑腔负载中的低密度聚合物泡沫柱具有多孔结构和极低的力学强度,在装配过程中对胶粘剂有一定的特殊要求。实验以聚氨酯丙烯酸酯为主体树脂,丙烯酸异冰片酯为活性单体,配以光引发剂和偶联剂制得了适用于低密度泡沫粘接用的紫外光固化胶粘剂。测试表明,所研制的胶粘剂的体积收缩率仅为2.25%,且具有较高的固化速率和适当的粘接强度,能够满足稳固、快速装配的要求。通过对粘接界面的观测发现,胶粘剂在诊断孔内没有明显的扩散,且在低密度致密结构泡沫中的扩散厚度较小,均匀性好。     

Mechanical and Thermal Performance of High-Density Polyethylene/Alumina Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with pristine and vinyltrimethoxysilane (VTMS)-treated alumina nanoparticles of 2, 4, and 6 wt% were melt-compounded in a twin-screw extruder followed by injection molding. Their structure, thermal and mechanical behaviors were studied. Fourier transform infrared (FTIR) spectra showed that VTMS was successfully covalently grafted to the alumina nanoparticles. The X-ray diffraction (XRD) patterns indicated that the alumina nanoparticle additions broadened the characteristic peak width of HDPE, indicating that they reduced the crystallite size of HDPE. The heat deflection temperature and thermogravimetric analyses demonstrated that the dimensional and thermal stability of HDPE were enhanced markedly by adding pristine and silane-treated alumina nanoparticles. The alumina nanoparticle additions were also beneficial in enhancing Young's modulus and yield strength of HDPE. The reinforcing effect was particularly apparent in the silane-treated nanocomposites due to improved filler–matrix interactions.     

Microstructural evolution of SiC joints soldered using Zn–Al filler metals with the assistance of ultrasound

SiC ceramics were successfully soldered with the assistance of ultrasound. Two kinds of filler metals, namely non-eutectic Zn–5Al–3Cu and eutectic Zn–5Al alloys, were used. The effects of ultrasonic action on the microstructure and mechanical properties of the soldered joints were investigated. The results showed that ultrasound could promote the wetting and bonding between the SiC ceramic and filler metals within tens of seconds. For the Zn–5Al–3Cu solder, a fully grain-refined structure in the bond layer was obtained as the ultrasonic action time increased. This may lead to a substantial enhancement in the strength of the soldered joints. For the Zn–5Al solder, the shear strength of the soldered joints was only ∼102 MPa when the ultrasonic action time was shorter, and fractures occurred in the brittle lamellar eutectic phases in the center of the bond layer. With increasing ultrasonic action time, the lamellar eutectic phase in the bond layer of SiC joints could be completely transformed to a fine non-lamellar eutectic structure. Meanwhile, the grains in the bond layer were obviously refined. Those results led to the remarkable enhancement of the shear strength of the joints (∼138 MPa) using the Zn–5Al solder, which had approached that enhancement using the Zn–5Al–3Cu solder. The enhanced mechanical properties of the joints were attributed to the significant refinement of the grains and the change in the eutectic structure in the bond layer. Prolonged enhanced heterogeneous nucleation triggered by ultrasonic cavitation is the predominant refinement mechanism of the bond metals of the SiC joints.     

Measuring the critical energy release rate in mode II of tough,structural adhesive joints using the tapered end-notched flexure (TENF) test

This paper shows and discusses results of the Tapered End-Notched Flexure (TENF) test, investigating the fracture behaviour of high-strength structural adhesive joints under shear loading. The TENF test has been previously applied to brittle joints by different authors and has been re-designed to be applicable to ductile adhesives in the presented work. Furthermore, the tests are performed at two velocities, a quasi-static and a dynamic one, to investigate rate effects on the fracture behaviour of the joint. All experimental work has been performed using the structural adhesive DOW Betamate 1496V.     

正火和回火处理过程中W/Fe/RAFM钢接头W/Fe界面组织和剪切性能的演化

对热等静压(HIP)扩散焊制备的W/Fe/RAFM钢接头进行了正火和回火处理,以恢复其中RAFM钢的组织和性能.采用电子探针微分析器(EPMA)和掠入射X射线衍射(GIXRD)对W/Fe界面组织的演化进行了分析,采用剪切测试和扫描电镜(SEM)对接头连接性能的演化进行了测试和分析.结果表明,正火处理后,RAFM钢中的C...     

Thermosets as compatibilizers at the isotactic polypropylene film and thermomechanical pulp fiber interphase

The objective of this study was to improve interfacial adhesion properties at the interface of thermomechanical pulp (TMP) fiber and isotactic polypropylene (iPP) using thermoset adhesives such as phenol formaldehyde (PF) and urea formaldehyde (UF). This study also attempted to achieve fiber-to-fiber adhesion using thermoset adhesives before the molten iPP would flow into the fiber web. The fracture surfaces with thermoset adhesive showed identical differences in terms of fracture modes at the interface. An increased TMP fiber failure was observed with increased thermoset quantity at the interface. Using one percent resin content of weight fraction of TMP fiber handsheet, the tensile strength properties increased almost two fold higher than the strength of control samples. Additional adhesive contents of three and five percent showed gradual strength enhancement. However, the enhanced strength was statistically insignificant. UF resin showed slightly better strength performance over PF resin. This result may be caused by solid contents and additional pigments of resins.     

Propagation of ultrasonic guided waves in lap-shear adhesive joints: case of incident a0 Lamb wave

This paper deals with the propagation of ultrasonic guided waves in adhesively bonded lap-shear joints. The topic is relevant to bond inspection by ultrasonic testing. Specifically, the propagation of the lowest-order, antisymmetric a0 mode through the joint is examined. An important aspect is the mode conversion at the boundaries between the single-plate adherents and the multilayer overlap. The a0 strength of transmission is studied for three different bond states in aluminum joints, namely a fully cured adhesive bond, a poorly cured adhesive bond, and a slip bond. Theoretical predictions indicate that the dispersive behavior of the guided waves in the multilayer overlap is highly dependent on bond state. Experimental tests are conducted in lap-shear joints by a hybrid, broadband laser/air-coupled ultrasonic setup in a through-transmission configuration. The Gabor wavelet transform is employed to extract energy transmission coefficients in the 100 kHz 1.4 MHz range for the three different bond states examined. The cross-sectional mode shapes of the guided waves are shown to have a substantial role in the energy transfer through the joint.     

Attaching Planar Waveguide Dies to Aluminum Using Low-Stress Thermal Conductive Adhesives

We analyzed stress and heat transfer in attached planar waveguides. Die attaching adhesives were known to be the key to avoiding stress buildup in and dissipating heat from waveguides. When adhesives have a shear modulus of less than 1 MPa and a thermal conductivity of 2 w/mk, a 0.1-0.2-mm-thick layer of adhesive can eliminate stress-related effects and efficiently dissipate 30-50 mW/mm² of heat, even if aluminum is used as a substrate. Supersoft thermal conductive adhesives were thus developed and used to attach 60-mm-long AWG dies to aluminum with excellent results.     

Bonding Interface Imaging and Shear Strength Prediction by Ultrasound

The propagation of a longitudinal ultrasonic wave normally incident upon an adhesively bonded structure is studied. The structure consists of adherend and adhesive layers with finite thickness. Interfaces between adherend and adhesive are regarded as distributed springs. Theoretical and experimental results show that resonant frequencies of the bonded structure vary sensitively with the interface stiffness constants and adhesive thickness, and these interface characteristics are inversed by the simulation annealing (SA) method. Furthermore, the distribution image of interface stiffnesses is compared with the state of fracture interface, and quantitative prediction of shear strength is achieved based on the distribution of interface stiffnesses and adhesive thicknesses by using a back-propagation neutral network. The average relative error of the shear strength from prediction to real value is 10.7%.     

铝纳米晶的低温导电特性研究

采用真空热压技术将电磁感应加热-自悬浮定向流法制备的铝纳米粉末压制成块体样品.通过X射线衍射、透射电子显微镜、扫描电子显微镜及X射线能谱分析了铝纳米晶的微观结构,并用四探针法测量了不同温度下(8—300 K)样品的电阻率,研究了铝纳米晶的电阻率(ρ)随温度的变化规律.结果表明:由于晶界(非晶氧化铝)对电子的散射以及晶界声子对电子的散射效应,低温(40 K)下,铝纳米晶的本征电阻率随温度变化关系明显不同于粗晶铝,不仅呈现出T~4变化,还表现出显著的T3变化规律.因晶界等缺陷和非晶氧化铝杂质对电子的散射,铝纳米晶残余电阻率比粗晶铝电阻率大5—6个数量级.     

三层介质超声谐振模式随材料和界面粘接性能变化的演变规律

在用超声波谐振对粘接材料的粘接强度进行无损评估时, 不同模式对粘接强度的敏感程度受到众多因素和参数的影响, 对检测结果的可靠性至关重要. 基于多层介质中声传播和界面弱粘接边界条件的理论模型, 将一个上下非对称的金属-粘接剂-金属三层结构的平面波反射系数函数中的谐振模式看作是上下铝金属层各自的Lamb波频散模式通过夹心粘接剂层相互耦合后叠加组成. 改变影响结构粘接强度的因素, 即粘接剂的性能参数(声阻抗、密度、厚度)和界面切向劲度系数k_t来分析三层结构谐振模式耦合方式的变化,得出结论: 粘接结构粘接性能的变化基本上不改变与被粘铝层相关的固有部分的Lamb波模式, 而它们的耦合模式则在谐振频率上产生平移并会与固有模式进行交换和替代; 不同参数的变化引起的模式演变有各自的规律, 大多可彼此区分.     

Improved Dispersion of Carbon Nanoparticles Modified by Poly(Sodium 4-Styrenesulfonate) and Its Influence on the Properties of Natural Rubber Latex

A novel strategy of radical polymerization of sodium 4-styrenesulfonate on the surface of carbon black (CB) in the solid state was developed to prepare hydrophilic carbon nanoparticles (PNASS-CB). A high performance natural rubber latex (NRL)/PNASS-CB composite was produced by the latex compounding technique. Scanning electron microscope shows considerable improvement in the dispersion of PNASS-CB in rubber matrix. The lower degree of filler–filler networks and the stronger filler–rubber interaction of PNASS-CB in rubber matrix were confirmed by dynamic mechanical thermal analysis. Rheometric properties of NRL/PNASS-CB, like scorch time and optimum cure time, decreased. Tensile strength, tear strength, and elongation at break increased due to stronger interaction between the PNASS-CB and rubber matrix. Dynamic mechanical properties of the modified carbon nanoparticles further corroborated a significant contribution from the better dispersion and efficient load transfer of PNASS-CB on the static and dynamic mechanical properties of composites.     

Effect of interfacial slippage in peel test: Theoretical model

Peel test is an efficient method to assess the performance and characteristics of materials such as adhesives and adhesive tapes. Recent experiments evidenced that the measured adhesive strength is closely related to the shear-induced interfacial slippage near the delamination front due to the concomitant Poisson contraction effect of the adhesive. Based on the experimental observations, a theoretical model is presented in this paper to examine the effect of the shear-induced interfacial slippage in the peel test. The influence of the interfacial slippage, represented by the shear displacement in the cohesive zone, on the fracture energy of decohesive zone is analyzed. An implicit expansion method with a Gauss-Chebyshev quadrature scheme is used to derive the solution. It is found that the length of the slippage zone and the receding contact angle of adhesives are the two most significant contributors to the total fracture energy of the decohesive zone. These results demonstrate that the mechanism of interfacial slippage plays a significant role in the adhesion and peeling behaviors of adhesives.