Effect of silane coupling agent on the durability of epoxy adhesion for structural strengthening applications

In this article, the durability of the interfacial bonds between epoxy and concrete during hygrothermal exposure was investigated. Through the application of a silane coupling agent, we examined the hypothesis that hydrogen bonding plays a large role in the degradation of the interfacial bond between epoxy and concrete, in which displacement of epoxy with water induces the disruption of the interfacial hydrogen bond. This hypothesis suggests that durability can be enhanced with the use of a silane coupling agent by changing the interfacial hydrogen bonds to stronger covalent bonds. The slant shear test results show that the durability of the interfacial bond was significantly enhanced with the use of an epoxy‐functional silane coupling agent. Spectroscopic features using FTIR confirmed the changes in chemical nature of concrete after the silane modification. By calculating the percent contribution to the bond strength for each set of specimens, it was confirmed that the silane application improved the durability with exposure for all conditions; however, over time the improvement diminished. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Bonding between precipitated silica and epoxidized natural rubber in the presence of silane coupling agent

Results of Monsanto rheometic studies and measurements of physical properties reveal that precipitated silica interacts chemically with epoxidized natural rubber (ENR) during high temperature (180°C) molding and the extent of chemical interaction increases in the presence of silane coupling agent, namely N‐3(N‐vinyl benzyl amino) ethyl‐γ‐amino propyl trimethoxy silane monohydrogen chloride. Fourier transform infrared spectroscopic studies show that silica is bonded to ENR through formation of Si—O—C bond, whereas in the presence of silane coupling agent, silica is bonded to the coupling agent through Si—O—Si bond, and ENR is bonded to the coupling agent through C—N—C bond formation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 389–398, 1999     

In situ examination of water diffusion to the polypropylene-silane interface using FTIR-ATR

This study investigated the effect of moisture on a model silane coupling agent modified adhesive bond. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) spectroscopy was used to characterize the transport of moisture to a polypropylene-silane interphase and monitor the resulting chemical changes. The FTIR-ATR method offers the advantage of in-situ examination of the diffusion process, as well as the ability to characterize chemical changes that occur due to the presence of moisture. Experiments were conducted at ambient and elevated temperatures. The results of the real-time measurements demonstrated that moisture will migrate through the polypropylene to the silane interphase. The diffusion behavior was described well by a Fickian model. The apparent diffusion coefficients for water in the polypropylene-silane bilayer were on the order of the diffusion coefficients for water in polypropylene at both test temperatures. Furthermore, changes in the spectra were observed during the diffusion experiments. These changes were indicative of hydrolysis of the siloxane backbone in the silane layer while buried beneath the polypropylene film. This finding is significant as it presents direct evidence of a degradation mechanism in silane-modified adhesive bonds. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1971–1985, 1997     

Cathodic Delamination of an Epoxy/Polyamide Coating from Steel

X-ray photoelectron spectroscopy (XPS) has been used to determine the mechanism responsible for debonding of an epoxy/polyamide coating from steel during cathodic delamination in 3.5% aqueous NaCl solutions. Coating failure always occurred near the interface between the coating and the oxide. The nitrogen content of the free surface of the prepared coatings was about 10%. However, the nitrogen content of the free surface dropped to only 5% after exposure to 1 N NaOH for four weeks and that of the coating failure surface after cathodic delamination was only about 2%, implying that the failure involved degradation of the polyamide curing agent by hydroxide ions formed at the steel surface by reduction of oxygen. That conclusion was supported by results obtained from curve fitting of C(1s) and O(1s) spectra. The intensity of components in the C(1s) spectra due to C—N and C≡O bonds in amide functional groups decreased significantly after coatings were exposed to NaOH or subjected to cathodic delamination. Small amounts of organic materials characteristic of the coating were observed on the substrate failure surface, perhaps indicating that the failure was cohesive within the coating but very close to the interface or that some products from degradation of the curing agent precipitated on the substrate. Use of silane coupling agents to retard cathodic delamination was also investigated. Coupling agents were added directly to the coating or applied to the substrate as a primer before application of the coating. Significant reduction in the rate of cathodic delamination was seen only when the silane coupling agent was applied to the substrate and cured at elevated temperatures before the epoxy/polyamide coating was applied.     

Cathodic Delamination of an Epoxy/Polyamide Coating from Steel

X-ray photoelectron spectroscopy (XPS) has been used to determine the mechanism responsible for debonding of an epoxy/polyamide coating from steel during cathodic delamination in 3.5% aqueous NaCl solutions. Coating failure always occurred near the interface between the coating and the oxide. The nitrogen content of the free surface of the prepared coatings was about 10%. However, the nitrogen content of the free surface dropped to only 5% after exposure to 1 N NaOH for four weeks and that of the coating failure surface after cathodic delamination was only about 2%, implying that the failure involved degradation of the polyamide curing agent by hydroxide ions formed at the steel surface by reduction of oxygen. That conclusion was supported by results obtained from curve fitting of C(1s) and O(1s) spectra. The intensity of components in the C(1s) spectra due to C—N and C≡O bonds in amide functional groups decreased significantly after coatings were exposed to NaOH or subjected to cathodic delamination. Small amounts of organic materials characteristic of the coating were observed on the substrate failure surface, perhaps indicating that the failure was cohesive within the coating but very close to the interface or that some products from degradation of the curing agent precipitated on the substrate. Use of silane coupling agents to retard cathodic delamination was also investigated. Coupling agents were added directly to the coating or applied to the substrate as a primer before application of the coating. Significant reduction in the rate of cathodic delamination was seen only when the silane coupling agent was applied to the substrate and cured at elevated temperatures before the epoxy/polyamide coating was applied.     

Stresses associated with diffusion in polyimide and polyacrylics films

When a constrained polymeric thin film is immersed in a liquid medium, its state of stress changes because the diffusion of the liquid into the film causes it to swell. Polyimide and polyacrylics films are used in the laminated structures of inkjet printheads. Swelling behavior of the films in various ink component solutions are of great interest because they are closely related to the delamination problem. Swelling stress at constant strain was measured using an environmental tensile tester at both ambient and elevated temperatures. Two kinds of information were extracted. One is the extent of stress relaxation, which is the amount of stress decay between initial stress and equilibrium stress. The difference in the extent of stress relaxation could result in delamination if two different materials with different swelling characteristics are bonded together and exposed to a swelling agent. The other piece of information was the diffusion coefficients of the liquid agents into the polymer films. The magnitude of the diffusion coefficient indicates the rate of proceeding by the penetrant, i.e., the rate of swelling of the films. The results show that the extent of stress relaxation and diffusivity are different for two films. In addition, the diffusion in polyimide film is Fickian and the diffusion in polyacrylics film is pseudo‐Fickian. The changes in mechanical properties after swelling also differ. Among all the ink solutions tested, one component was identified as the most influential and detrimental agent. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Environmental aging of the Ti-6Al-4V/FM-5 polyimide. adhesive bonded system: implications of physical and chemical aging on durability

Ti-6A1-4V/FM-5 polyimide adhesively bonded double cantilever beam (DCB) specimens were aged for 12 months at elevated temperatures (177°C and 204°C) in one of three different environments: ambient atmospheric air pressure and reduced air pressures of 2 psi (13.8 kPa) and 0.2 psi (1.38 kPa), to assess bond durability. The FM-5 polyimide adhesive (Tg~ 250°C) is based on a polyimide developed by NASA Langley Research Center and is produced by Cytec Industries, Inc. Bonds aged for different times were tested to measure the critical strain energy release rate as a function of the temperature and environment. The greatest loss in bond strength occurred after aging in air at 204°C. Following thermal rejuvenation of the aged bonds at 300°C for 2 h, part of the strength loss could be recovered. This strength recovery was attributed to the reversal of physical aging in the adhesive resin. Further evidence for physical aging, which is a thermo-reversible phenomenon, was obtained from tests conducted on neat resin specimens using DMA (dynamic mechanical analysis) and DSC (differential scanning calorimetry). The unrecovered portion of the loss in bond strength following longer-term aging was attributed to chemical aging/degradation of the bonded 'system'. The 'system' in this study includes the adherends, the adhesive, the surface pretreatment (chromic acid anodization, CAA), and their respective interphase/interface regions. Evidence for chemical aging was also seen from weight loss, and Soxhlet extraction data on neat resin specimens.     

Promotion of Adhesion Between Resin and Silica-coated Titanium by Silane Monomers and Formic Acid Catalyst

Three bifunctional silane coupling agent monomers and their blends with a cross-linking silane were investigated as six experimental adhesion-promoters in vitro. Three organosilane monomers, 3-methacryloxypropyltrimethoxysilane, styrylethyltrimethoxysilane, and 3-(N-allylamino)propyltrimethoxysilane, were prepared as 1% (v/v) primers and also blended with a cross-linking silane, 1,2-bis-(triethoxysilyl)ethane at 0.5% (v/v), in a 95:5 solution of ethanol in deionized water. The silanes were allowed to hydrolyze using formic acid as catalyst and were applied to a substrate of silica-coated Ti. The control was a pre-hydrolyzed silane coupling agent that is commonly used in dentistry. An experimental unfilled bis-phenol-A-diglycidyldimethacrylate/methylmethacrylate resin was bonded by photo-polymerization as stubs to the prepared Ti. Half of the specimens were artificially aged by wet thermo-cycling and half were stored in dry conditions in a desiccator. Storage conditions and the type of primer silane or blend significantly affected shear bond strength values. 3-Methacryloxypropyltrimethoxysilane, alone or blended, produced significantly higher shear bond strength values than the control, both after dry storage and after thermo-cycling.     

High-performance poly(lactic acid)/starch materials prepared via starch surface modification and its in situ enhancement

High-performance modified poly(lactic acid) (PLA)/starch (ST) blends were prepared by incorporating silane coupling agent. The coupling agent acted as a bridge between PLA and ST components, enhancing their interfacial compatibility during the melt blending. The addition of epoxy-functionalized silane coupling agent improved the interfacial adhesion between PLA and ST phases, as evidenced by the decreased number and spacing of gaps between the ST particles and PLA matrix. The coupling agent also filled the surface crack of the ST particles, improving their dispersion in PLA matrix. The tensile strength of the modified PLA/ST blend increased from 19.6 MPa for the neat PLA/ST blend to 53.4 MPa, exceeding that of neat PLA. The modified blend also showed improved hydrophobicity and thermal stability. This research presented an effective approach to reducing the cost of PLA-based materials and improving the performance of ST-filled PLA materials by enhancing the interfacial adhesion between ST and PLA through surface modification with silane coupling agent. It provided a simple and feasible strategy for the high-performance modification of polyester/ST materials.     

硅烷偶联剂对复合水泥砂浆性能的影响

通过红外光谱分析及砂浆强度测试，研究了硅烷偶联剂对不同种类复合水泥砂浆的稠度、分层度、抗折强度及抗压强度的影响。结果表明，加入硅烷偶联剂能提高普通水泥砂浆、苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当硅烷偶联剂质量分数为0．5％时，普通水泥砂浆的抗折强度和抗压强度达到极大值，提高约10％；当硅烷偶联剂质量分数为1％时，苯丙胶乳改性水泥砂浆的抗折强度和抗压强度达到极大值，提高约20％；同时，硅烷偶联剂还能增大普通水泥砂浆和苯丙胶乳改性水泥砂浆的稠度，但砂浆的分层度略有增大。加入经硅烷偶联剂处理的钢纤维，能够提高普通水泥砂浆及苯丙胶乳改性水泥砂浆的抗折强度和抗压强度；当钢纤维用硅烷偶联剂质量分数为1％的硅烷偶联剂水溶液处理时，钢纤维增强砂浆的抗折、抗压强度达到极大值，提高10％以上。     

硅烷偶联剂改性阳离子水性聚氨酯的研究

以硅烷偶联剂γ-氨丙基三乙氧基硅烷(KH550)为封端剂对阳离子型水性聚氨酯进行杂化改性,并以KH550和γ-缩水甘油醚氧丙基三甲氧基硅烷(KH560)为原料合成新型偶联剂D,对聚氨酯进行复合改性,分别合成了纳米SiO2/PU杂化材料和纳米SiO2/PU复合材料.通过FT-IR、粒径分析、AFM对样品的结构进行表征,并对样品的力学性能和耐水性、耐溶剂性进行测试.结果表明:两种体系均生成了二氧化硅相,二氧化硅相在杂化体系中的分散性好于其在复合体系中的分散性.对提高产品性能而言,化学封端改性比物理共混改性更有效.     

硅烷偶联剂在环氧涂料中的应用

本文对硅烷偶联剂的水解特性，以及对硅烷偶联剂直接添加到环氧涂料中形成的涂层与钢铁基材的附着力进行了研究。研究发现硅烷偶联剂水解能力很强且容易在涂层与基材之间形成化学键作用；将硅烷偶联剂直接添加到环氧涂料中能够显著地提高涂层对钢铁基材的附着力。     

Silanisation of adhesively bonded aluminium alloy AA6060 with γ-glycidoxypropyltrimethoxysilane. I. Durability investigation

The wedge test was used to determine the durability of adhesively bonded joints of pretreated aluminium alloy AA6060 in a hydrothermal environment. Testing of joints bonded with the one-component epoxy adhesive XD4600 showed that the durability was higher for surfaces that were grit-blasted with alumina than for alkaline etched, FPL-etched, and sulphuric acid anodised surfaces. All these surfaces performed much better than those abraded with ScotchBrite®. It was discovered that increased surface roughness improved the durability, while increased surface contamination reduced the durability of the bonded joints. On a very rough surface such as the grit-blasted, the effects of surface contamination were more than outweighed by the effects of surface roughness. Treatment of some of the pretreated surfaces with a 1% aqueous solution of γ-glycidoxypropyltrimethoxysilane significantly improved the durability, but the ranking between the pretreatments was the same as before the silane treatment. The silane treatment also reduced the initial crack lengths of the wedge test specimens. The best performance was seen by the grit-blasting plus silane treatment, which performed much better than the well-established FPL-etch.     

硅烷偶联剂KH-570湿法改性TiO2的结构与性能研究

利用硅烷偶联剂(KH-570)对纳米二氧化钛(TiO2)进行湿法改性处理.采用静态沉淀法、亲油化度、接触角、X射线光电子能谱( XPS)和傅立叶红外光谱(FT-IR)等手段对改性效果进行分析表征,探析湿法改性机理.研究表明KH-570以化学链形式结合于TiO2表面,改性后TiO2的表面性质由亲水变为亲油.     

FDT: A technique for direct study of water attack at the silane-filler interface

A technique is presented for the direct study of water attack at the silane-filler interface. This technique, Filler Desorption Test (FDT), involves observations of surface tension changes which occur when a silane-treated filler is floated on a water surface. If all the silane has been appropriately cured to form one integral polymerized siloxane network, then the rate and degree of surface tension lowering are a sensitive measure of the adhering tendency of the polymerized silane film. Data are presented which suggest that, all other things being equal, the strength of the coupling agent (C.A.)-filler bond under water attack can be assessed by observation of the ease with which the first small amount of polymerized silane leaves the filler and the relative degree of hydrophobicity of the resulting surface. FDT is a new tool for fundamental studies of the coupling agent-filler interface and interphase. The method also allows rapid screening and evaluation of a wide range of chemical and physical modifications designed to improve C.A. response on various filler systems.     

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber-Reinforced Phenolic Resin Composite Joints

Energy-dispersive X-ray spectroscopy analysis (EDX) is an easy and exact method for determination of water diffusion coefficients and dynamics. Here we have calculated the water diffusion coefficients and dynamics in adhesive/carbon fiber-reinforced phenolic resin composite joints subjected to different surface treatments with both EDX and elemental analysis. The water diffusion coefficients and dynamics in the adhesive joints determined with EDX analysis are almost the same as those determined with elemental analysis. The durability of the adhesive joints with carbon fiber-reinforced phenolic resin composites subjected to silane coupling agent treatment is better than those subjected to sandpaper burnishing and chemical oxidation treatment.     

Bonding between epoxidized natural rubber and clay in presence of silane coupling agent

Based on the results of bound‐rubber determination, Monsanto rheometric studies, solvent swelling, measurement of physical properties, and infrared spectroscopic studies, it is revealed that epoxidized natural rubber (ENR) and hard clay interact chemically to form Si–O–C bond during high‐temperature (180°C) molding. It is also observed that addition of the silane coupling agent N‐3‐(N‐vinyl benzyl amino)ethyl‐γ‐amino propyl trimethoxy silane monohydrogen chloride enhances the extent of the chemical interaction with the formation of coupling bonds of Si–O–Si type between clay and the coupling agent and C–N bonds between ENR and the coupling agent. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1895–1903, 1999     

Surface characterization of silane-treated industrial glass fibers

The adsorption of silane coupling agents onto glass fiber surfaces has been investigated. The type of adsorption was elucidated using electron spectroscopy for chemical analysis (ESCA or XPS). The surface charging was recorded using streaming potential analysis. The silane bond strength was tested by boiling the silanized fibers in water for 2 h. Thereafter the conductivity of the water was measured in order to estimate the capability of the silane surface film to prevent ion dissolution from the glass. ESCA provided information on the amount adsorbed and indicated that substantial rearrangement in the surface film structure occurred as a function of the silane concentration. The aminosilane produced a strong positive charge on the glass fibers, while the nonionic silanes were only partly condensed, giving rise to a substantial enhancement of the negative charge. The conductivity measurements indicated that the silane films were present as a loose patchlike silane network on the surface of the E-glass fibers. This conclusion is in accordance with the results obtained with all the techniques used.     

Dynamic mechanical properties and hysteresis loss of epoxidized natural rubber chemically bonded to the silica surface

High‐temperature (180°C) molding of epoxidized natural rubber (ENR) filled with precipitated silica leads to chemical bond formation between epoxy groups of ENR and silanol groups of silica. The extent of chemical bond formation is further enhanced in the presence of the silane coupling agent N‐3‐N‐(vinyl benzyl amino)ethyl‐γ‐amino‐propyl trimethoxy silane mono hydrogen chloride (trade name Z‐6032). The results of hysteresis loss measurements show that hysteresis loss increases with increase in coupling agent loading as a result of the higher modulus of the compounds compared to that of the ENR–silica mix. The dynamic mechanical property measurements show that the addition of coupling agent increases the glass‐transition temperature. Whereas strain‐dependent dynamic mechanical properties show that filler structure breakdown increases with increasing loading of coupling agent. Sulfur‐cured systems show higher filler structure breakdown compared to that of nonsulfur systems. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2171–2177, 2002     

Effects of coupling agents on the rheological properties,processability, and mechanical properties of filled polypropylene

An experimental study was carried out to investigate the effects of coupling agents on the rheological properties, processability, and mechanical properties of highly filed polypropylenes (PP). Inorganic fillers used were CaCO₃ and glass beads, and coupling agents used were two silane coupling agents, N-octyl triethoxy silane and γ-aminopropyl triethoxy silane, and one titanate coupling agent, isopropyl triisostearoyl titanate. It was found that the addition of the coupling agents to the PP-CaCO₃ (50 wt percent) decreased the melt viscosity and increased the melt elasticity (first normal stress difference). However, the addition of the silane coupling agents to the PP-glass beads (50 wt percent) affected the rheological properties of the melts quite differently. The N-octyl triethoxy silane had relatively little effect on either the melt viscosity or the melt elasticity, whereas the γ-aminopropyl triethoxy silane increased the melt viscosity and decreased the melt elasticity. The CaCO₃- or glass bead-filled polypropylenes, with and without coupling agents, were injection-molded and the mechanical properties of the molded specimens were measured by the use of an Instron testing machine. It was found that the effect on the tensile strength and percent elongation of the filled polypropylenes depended upon the specific coupling agent utilized. A melt-spinning study was also carried out to investigate the effect of coupling agents on the spinnability (defined as the maximum draw-down ratio) of the PP-CaCO₃ system, and on the mechanical properties of the melt-spun fibers. It was found that the spinnability of the PP-CaCO₃ was enhanced considerably by the addition of the coupling agents, and that the tensile strength of the melt-spun fibers was also improved by their addition. Scanning electron micrographs were taken of the fracture surface of injection-molded specimens and an attempt was made, with the aid of photomicrographs, to explain the mechanical properties of molded specimens observed experimentally.