新型高强度单组分环氧树脂胶粘剂的研制

采用新工艺制备了一种新型高强度单组分环氧树脂胶粘剂。实验结果表明,新型环氧树脂体系具有良好的力学性能、疏水性及耐热性。     

The effects of Al surface treatment,adhesive thickness and microcapsule inclusion on the shear strength of bonded joints

The influences of various Al surface treatments, adhesive thicknesses as well as the incorporation of synthesized microcapsules into epoxy adhesive on the shear strength of adhesive/ Al joints have been investigated using lap-shear tensile tests. First, the influence of adhesive thickness on the shear strength of joints has been presented. Then, the effects of various Al surface treatments on the surface roughness of Al and shear strength of joint have been researched. Atomic force microscopy was used to study the Al surface morphologies and textures. Finally the few micron-sized polymeric microcapsules were synthesized and the shear performances of microcapsule filled epoxy adhesives were inspected. It was observed that the HCl acid based etching increased both micro-roughness and nano-texture of the Al surface and led to the peak shear strength. Moreover, HCl-nitric acid treatment offered the maximum value for the cohesive failure. Capsule inclusions into the adhesive displayed different influences on the joint shear performances depending on the capsule morphology and the surface treatment of Al.     

Effect of adhesive thickness and surface roughness on the shear strength of aluminium one-component polyurethane adhesive single-lap joints for automotive applications

Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength‐to‐weight ratio. The bonding may be made between metal–metal, metal–composite or composite–composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.     

Influence of adhesive bond line thickness on joint strength

While the geometry of aerospace assemblies is carefully controlled, for many industrial applications such as marine structures bond line thickness can vary significantly. In this study epoxy adhesive joints of different thicknesses between aluminium substrates have been characterized using physico-chemical analyses (differential scanning calorimetry, DSC; dynamic mechanical analysis, DMA; spectroscopy), nano-indentation and mechanical testing. Thermal analyses indicated no influence of thickness on structure. Nano-indentation revealed no evidence of an interphase at the metal/epoxy interface, nor any change in modulus for different thicknesses, though Raman spectroscopy suggested there may be slight variations in composition close to the substrates. However, mechanical testing using the modified Arcan fixture indicated a significant drop in strength and failure strain under pure tension and a smaller reduction for tension/shear and pure shear loads as thickness increased. Examination of sections through joints did not indicate any physical reason for this, but numerical analysis of the stress state revealed larger stress concentration factors for tensile loading in thick joints, which may explain the thickness effect. It is recommended that joint thickness should be kept below 0.8 mm to avoid obtaining artificially low values with the Arcan test.     

Determination of traction-separation laws on an acrylic adhesive under shear and tensile loading

Structural acrylic adhesives are of special interest because those adhesives are cured at room temperature and can be bonded to oily substrates. To use those adhesives widely for structural bonding, it is necessary to clarify the methodology for predicting strengths of bonding structures with those adhesives. Recently, cohesive zone models (CZMs) have been receiving intensive attentions for simulation of fracture strengths of adhesive joints, especially when bonded with ductile adhesives. The traction-separation laws under mode I and mode II loadings require to estimate fracture toughness of adhesively bonded joints. In this paper, the traction-separation laws of an acrylic adhesive in mode I and mode II were directly obtained from experiments using Arcan type adhesively bonded specimens. The traction-separation laws were determined by simultaneously recording the J-integral and the opening displacements in the directions normal and tangential to the adhesive layer, respectively.     

Evaluation of different desensitizing agents effect on shear bond strength of adhesive resin cement to dentin

Desensitizing agents can inhibit the bonding strength between dentin and adhesive resin cement. This study evaluated the effects of different desensitizing agents on the shear bond strength of adhesive resin cement to dentin. Sixty freshly extracted and caries free teeth were classified into five experimental groups, randomly (n?=?12). Each group was treated with a different desensitizing agent (Teethmate, Shield Force Plus, Admira Protect and Ultra-Ez) respectively, except for an untreated control group. After desensitizing agents and adhesive resin cement were applied to each dentin surface, all specimens were stored in incubator at 37?°C for 24?h. The shear bond strength was tested with a Universal testing machine at a 0.5?mm/min crosshead speed. Data were analysed by using a statistical software (SPSS 22). The results of the measurements were analysed by Kruskal Wallis test with Bonferroni correction and multiple comparisons were made by Wilcoxon test (p???.01). Specimens were examined by a scanning electron microscope, additionally. The Shield Force Plus showed significantly the highest shear bond strength compared with other groups (p?<?.01). Ultra-Ez showed the lowest shear bond strength (p?>?.01). There was no significant difference among Teethmate and Admira Protect groups (p?>?.01). Desensitizing agents containing resin monomers increased the bonding strength, however desensitizers containing calcium phosphate, potassium nitrate and fluoride did not effect the bonding strength of resin cement to dentin.     

Polyacrylonitrile solution homogeneity study by dynamic shear rheology and the effect on the carbon fiber tensile strength

Poly(acrylonitrile‐co‐methacrylic acid) (PAN‐co‐MAA)/N,N‐dimethylformamide (DMF) solutions were prepared and dynamic shear rheology of these solutions were investigated. With increasing stirring time up to 72 h at 70°C, the polymer solution became less elastic (more liquid‐like) with a ～60% reduction in the zero‐shear viscosity. Relaxation spectra of the PAN‐co‐MAA/DMF solutions yield a decrease in relaxation time (disentanglement time, τ_d), corresponding to an about 8% decrease in viscosity average molecular weight. The log‐log plot of G′ (storage modulus) versus G″ (loss modulus) exhibited an increase in slope as a function of stirring time, suggesting that the molecular level solution homogeneity increased. In order to study the effect of solution homogeneity on the resulting carbon fiber tensile strength, multiple PAN‐co‐MAA/DMF solutions were prepared, and the precursor fibers were processed using gel‐spinning, followed by continuous stabilization and carbonization. The rheological properties of each solution were also measured and correlated with the tensile strength values of the carbon fibers. It was observed that with increasing the slope of the G′ versus G″ log‐log plot from 1.471 to 1.552, and reducing interfilament fiber friction during precursor fiber drawing through the addition of a fiber washing step prior to fiber drawing, the carbon fiber strength was improved (from 3.7 to 5.8 GPa). This suggests that along with precursor fiber manufacturing and carbonization, the solution homogeneity is also very important to obtain high strength carbon fiber. POLYM. ENG. SCI., 56:361–370, 2016. © 2016 Society of Plastics Engineers     

Experimental investigation into the effect of DC glow discharge pretreatment of HDPE on tensile lap shear strength

The present investigation aims to optimise the process parameters of DC glow discharge treatment through air in terms of discharge power and time of exposure for attaining best adhesive joint of high-density polyethylene (HDPE) to mild steel. The as- received and DC glow discharge exposed HDPE surfaces have been characterised by energy dispersive spectra (EDS). It is observed that with increasing power level up to 13 W, tensile lap shear strength of adhesive (Araldite AY 105) joint of HDPE to mild steel increases and then decreases. At 13 W power level, joint strength increases up to 120 s of exposure and then decreases. At the optimised condition for the surface modification, the effect of two different adhesives Araldite AY 105 and Araldite 2011 on the strength of polymer to mild steel, polymer to polymer and mild steel to mild steel joints have been examined. It is observed that tensile lap shear strength of HDPE–HDPE joint and HDPE–mild steel joint does not change with the change of adhesive and this could be possible as initiation of fracture takes place from subsurface layer of the polymer. This is confirmed by studies under optical microscopy and EDS, which shows when the polymer has been modified by exposure under glow discharge the failure is observed to initiate from subsurface layer of the HDPE, then within the adhesive cohesively and thereafter in the mild steel to adhesive interface.     

The effect of primers on adhesive properties and strength of adhesive joints made with polyurethane adhesives

The paper presents selected aspects of the effect of primers on adhesive properties and strength of aluminium sheet adhesive joints, made using polyurethane adhesives. The strength of adhesive joints was determined based on two cure time variants: 15 and 64 h. It was found that the longer cure time at a humidity of 33% is more desired, as it leads to a substantial increase in strength of the tested adhesive joints. In addition, two variants of surface preparation were applied: degreasing and degreasing followed by the application of a primer (a pro-adhesive agent). It was observed that the primer application prior to the application of an adhesive leads to a significant increase in strength compared to the variant where the adhesive application is preceded only by degreasing. Moreover, the aluminium sheet surface that was subjected to cataphoretic painting and priming exhibits better adhesive properties. It has a higher value of both surface free energy and its dispersion and polar components compared to the surface that was only subjected to degreasing.     

An eco-friendly and high shear strength adhesive from catechol-modified polyethyleneimine

Conventional adhesives often emit volatile organic compounds (VOCs), which have a negative impact on human health. In this paper, an environmentally-friendly supramolecular adhesive PD which has high adhesive and low VOCs emission is prepared by the reaction between polyethyleneimine (PEI) and 3,4-dihydroxybenzaldehyde (DBA). PD containing abundant catechol groups exhibit excellent adhesion to wood substrates and is able to reach a maximum shear strength of 5.20 ± 0.39 MPa. One factor is attributed to multiple reactions between PEI, and DBA and oxidation of DBA. These reactions construct a complex three-dimensional cross-linked structure which is very helpful to improve the bonding performance of the adhesive. Another reason refers to the fact that a large number of catechol groups in PD can form a lot of hydrogen bonds with the amino group in PEI and the hydroxyl group in the wood substrate. These hydrogen bonds play an important role in enhancing shear strength. PD adhesives have a stronger bond strength than commercial chloroprene rubber (CR, Pattex-PXL) and polyvinyl acetate adhesives (PVAc, JUJU-8708) and have lower emissions of VOCs. As an environmentally-friendly adhesive for wood-based substrates, this adhesive may have potential applications in the wood processing industry.     

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.     

聚酰亚胺胶粘剂的改性研究

介绍了聚酰亚胺(PI)胶粘剂改性的研究进展,详细讨论了缩合型PI胶粘剂、热塑性PI胶粘剂和加成型PI胶粘剂的发展现状、最新进展、性能(物理机械性能、耐热性、耐化学性和成型加工性)及其在各领域中的应用。总结了PI胶粘剂存在的具体问题和未来的发展趋势。     

高剪切高剥离强度单组分环氧树脂结构胶的研制

利用红外光谱确认了环氧树脂(EP)与端羧基丁腈橡胶(CTBN)的预聚反应机理是-COOH与环氧基进行酯化反应生成-OH基团,其最佳反应条件是70℃、3 h。在该预聚物中加入固化剂、促进剂及其他助剂,可制备出一种糊状EP结构胶;将该结构胶用于不锈钢的粘接时,其室温粘接强度为57 MPa,100℃剪切强度为34.5 MPa,150℃剪切强度为12 MPa,室温90°剥离强度为17 N/mm;该结构胶具有良好的耐环境老化性能,可以在-40～150℃范围内使用。     

Estimation of static strength of adhesively bonded single lap joints with an acrylic adhesive under tensile shear condition based on cohesive zone model

In this study, the tensile shear and bending tests of adhesively bonded single lap joints with the acrylic adhesive was evaluated experimentally and numerically. In the previous paper, the traction-separation laws in mode 1 and mode 2 for an acrylic adhesive were directly obtained from the observation of failure process using Arcan type adhesively bonded specimens: simultaneous measurements of the J-integral and the opening displacements in the directions normal, δ_n and tangential to the adhesive layer, δ_s respectively. The experimental results were compared with numerical simulations conducted in ABAQUS including cohesive damage model. The cohesive laws obtained in the previous paper were simplified to trapezoidal shape from the experimentally obtained ones which were indicated in the previous paper. A good agreement was found between the experimental and numerical results. Then, to investigate the damage evolution in the adhesive layer for some lap joints, microscopic video observation was conducted near the end of the adhesive layer, and the video image have been compared with the contours of damage variable obtained by FEM corresponding to the video images. The observed damage evolution also agrees with the trend of damage variable.     

The effect of surface modification of vulcanized rubbers on the adhesive strength

Results of a study are reported on the utilization of ground vulcanizate, which is a waste product of rubber prcoessing plants. Loaded stocks of various commercial rubbers act as objects for the study. Talc, kaolin, silicon dioxide, and furnace carbon black are used as fillers. According to the results of a study on the effect of the amount of rubber crumb, an increase in the content of unmodified crumb leads to a decrease in tear resistance that is associated with poor wettability. To increase wettability, we use organosilicon couplings. It is shown that the addition of vulcanizate to rubber stocks, together with highly dispersed fillers treated with organosilicon couplings, leads to a significant increase in tear resistance and makes it possible to significantly reduce the cost of production and utilization.     

Effects of a silane coupling agent on the tensile adhesive strength between resin and titanium

Adhesion of a cured dental opaquer, which masks metallic appearance and color, to sandblasted Ti aided by 3‐methacryloyloxypropyltrimethoxysilane (MPTS) is investigated. The tensile bond strengths of Ti and the opaquer are 43.3 and 45.9 MPa, respectively, when MPTS dissolved in ethanol (6 wt %) and premixed with the opaquer (3 wt %) are applied to the sandblasted Ti surface. Mirror finishing alone and sandblasting alone result in the bond strengths of 1.8 and 21.3 MPa, respectively. After thermal cycling (4 and 60°C for 5000 cycles), the bond strengths of the Ti with sandblasting and the MPTS treatment remain higher than that of the Ti with sandblasting only. Sandblasting and the MPTS treatment effectively promote the adhesion of the opaquer to Ti that rapidly forms an oxide surface layer. The silane‐aided adhesion of the opaquer to the sandblasted Ni? Cr, Co? Cr, and Au? Ag? Pd alloys attain adhesive strengths of 33.2, 31.9, and 31.6 MPa, respectively. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Influence of rheological properties of adhesive polymer on strain energy release rate of mode II and adhesive shear strength

It is well known that adhesive strength shows temperature and rate dependencies reflecting viscoelastic properties of an adhesive used. Specifically, a mechanical relaxation mechanism around the glass transition temperature (T_g) has a strong effect on the adhesive strength, which involves deformation of the adhesive layer. In addition, it is very interesting to know how viscoelastic properties of the adhesive affect the value of strain energy release rate since deformation and failure of the adhesive occur at the measurement of strain energy release rate for adhesive joints. In this study, adhesive tensile strength and strain energy release rate (G_IIC) in plain-shearing mode were measured under a constant experimental condition using adhesives consisting of two types of epoxy resins; the influence of viscoelastic properties on these two values was investigated, and we discuss the relationship between the adhesive shear strength and G_IIC. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 525–536, 1997     

Effect of adherend's rigidity on the shear strength of single lap adhesive joints

The present paper compares the tensile shear strength of single-lap joints with different adherends. Three materials were combined in the single lap joints: a carbon/epoxy laminated composite, a high elastic limit steel and the 6082-T6 aluminium alloy. The shear strength of joints was influenced by the adherend stiffness and the highest shear strengths were obtained using high stiffness adherend materials. The overlap length influenced the shear strength in different ways depending on the adherend materials. Numerical analysis concluded that the increase in the rigidity of the adherends decreases the rotation of the specimen and promotes a more uniform distribution of stresses in the glue. In joints with distinct materials, the less stiff material was found to determine the strength of the appropriate joint.     

The effect of sorption on the tensile creep and strength reduction of desiccated concrete

The influence of sorption of fluids of differing molecular size on the strength and tensile creep of desiccated concrete and mortar are investigated. It is shown that the desiccated tensile strength is significantly reduced by sorption in accordance with the molecular sieve concept; compressive and splitting tensile strengths are also reduced but to lesser extent. For specimens subjected to a constant applied tensile load, strength reduction increases the effective stress-strength ratio thereby contributing to creep. In some cases, the concomitant effect of strength reduction and sorption induced deformations results in specimen fracture.