Use of the Blister Test to Study the Adhesion of Brittle Materials. Part II. Application

Using a modified form of the blister test, where the adhesive layer was between the substrate and a massive base, instead of as a continuous sheet on top of the substrate, we determined the interfacial fracture energy F for a series of interfaces where a brittle material (ice) was adhering to various substrates. Fracture energies obtained were compared with work of adhesion values measured for water on the same substrates. Fracture energy, which contains within it both a reversible contribution due to intermolecular interactions across the interface (work of adhesion) and an irreversible contribution due to collective dissipative processes, was found to rise rapidly with modest increases in work of adhesion. The observed relation suggests that the irreversible contribution to fracture energy is influenced strongly by the intermolecular interactions at the interface.     

Use of the Blister Test to Study the Adhesion of Brittle Materials. Part II. Application

Using a modified form of the blister test, where the adhesive layer was between the substrate and a massive base, instead of as a continuous sheet on top of the substrate, we determined the interfacial fracture energy F for a series of interfaces where a brittle material (ice) was adhering to various substrates. Fracture energies obtained were compared with work of adhesion values measured for water on the same substrates. Fracture energy, which contains within it both a reversible contribution due to intermolecular interactions across the interface (work of adhesion) and an irreversible contribution due to collective dissipative processes, was found to rise rapidly with modest increases in work of adhesion. The observed relation suggests that the irreversible contribution to fracture energy is influenced strongly by the intermolecular interactions at the interface.     

Crack Propagation in Polymer Adhesive/Glass Sandwich Specimens

Moisture-assisted crack growth in polymer adhesive/glass interfaces was measured as a function of the applied energy release rate, G, using a four-point flexure test coupled with an inverted microscope. The specimens consisted of two glass plates bonded together with an epoxy or an epoxy-acrylate adhesive. It was found that cracks formed and grew on both interfaces if the glass surfaces were both smooth; however, roughening the surface of one of the glass plates increased the fracture resistance of the interface sufficiently so that crack growth occurred only on the remaining “smooth” interface (top or bottom). Finite element analysis was used to determine the G and ψ (phase angle) appropriate for the different crack geometries. It was found experimentally that crack growth rates for all crack geometries depended on the applied G via a power law relationship and that for a given applied G, crack growth rates were sensitive to the crack geometry. The results indicate that the primary driving force for moisture-assisted crack growth at a polymer/glass interface is the applied G at the crack tip and that the effect of the phase angle for the different crack geometries (13° to 54°) is negligible.     

Crack Propagation in Polymer Adhesive/Glass Sandwich Specimens

Moisture-assisted crack growth in polymer adhesive/glass interfaces was measured as a function of the applied energy release rate, G, using a four-point flexure test coupled with an inverted microscope. The specimens consisted of two glass plates bonded together with an epoxy or an epoxy-acrylate adhesive. It was found that cracks formed and grew on both interfaces if the glass surfaces were both smooth; however, roughening the surface of one of the glass plates increased the fracture resistance of the interface sufficiently so that crack growth occurred only on the remaining “smooth” interface (top or bottom). Finite element analysis was used to determine the G and ψ (phase angle) appropriate for the different crack geometries. It was found experimentally that crack growth rates for all crack geometries depended on the applied G via a power law relationship and that for a given applied G, crack growth rates were sensitive to the crack geometry. The results indicate that the primary driving force for moisture-assisted crack growth at a polymer/glass interface is the applied G at the crack tip and that the effect of the phase angle for the different crack geometries (13° to 54°) is negligible.     

Effect of Interphase Structure on the Debonding of Polycarbonate from S-2 Glass Fibers

The effect of interphase structure on the debonding of polycarbonate from S-2 glass fibers has been studied. The shear strength, fracture toughness and hydrolyic stability of the interphases were measured in a single fiber composite of a continuous S-2 glass fiber embedded in a polycarbonate matrix. Polycarbonate oligomers were chemically grafted onto the glass fiber surfaces through use of a silicon tetrachloride intermediary and the properties of the resulting interphases were compared with those of two commercial sizings and ozone-cleaned surfaces. Evaluation was accomplished by measuring the stress transmission across the interphase, τ, by carrying the embedded single fiber fragmentation test to saturation and by using computer simulations and a finite element analysis to calculate the strain energy release rate, G, of the observed fiber-matrix debonding accompanying the first fiber fracture. The oligomer-grafted interphase exhibited improved stress transmissibility and toughness, after 24 hours in boiling water. The tenacity of the tightly bound oligomers was confirmed via DRIFT, TGA and GC/MS experiments on Soxhlet-extracted fibers.

The grafting reaction was modeled on a high surface area silica and studied using solid state NMR to determine reasons for the greater stability of the oligomer-treated surfaces. Measurements of chemical shifts and spin-lattice relaxation times indicate that the oligomers are chemically attached to the surfaces, providing for a well bonded, water resistant interphase. Parallel experiments on a monomeric Bisphenol A-primed silica surface provided evidence that chemical bonding was primarily responsible for the greater hydrolytic stability.     

Effect of Interphase Structure on the Debonding of Polycarbonate from S-2 Glass Fibers

The effect of interphase structure on the debonding of polycarbonate from S-2 glass fibers has been studied. The shear strength, fracture toughness and hydrolyic stability of the interphases were measured in a single fiber composite of a continuous S-2 glass fiber embedded in a polycarbonate matrix. Polycarbonate oligomers were chemically grafted onto the glass fiber surfaces through use of a silicon tetrachloride intermediary and the properties of the resulting interphases were compared with those of two commercial sizings and ozone-cleaned surfaces. Evaluation was accomplished by measuring the stress transmission across the interphase, τ, by carrying the embedded single fiber fragmentation test to saturation and by using computer simulations and a finite element analysis to calculate the strain energy release rate, G, of the observed fiber-matrix debonding accompanying the first fiber fracture. The oligomer-grafted interphase exhibited improved stress transmissibility and toughness, after 24 hours in boiling water. The tenacity of the tightly bound oligomers was confirmed via DRIFT, TGA and GC/MS experiments on Soxhlet-extracted fibers.

The grafting reaction was modeled on a high surface area silica and studied using solid state NMR to determine reasons for the greater stability of the oligomer-treated surfaces. Measurements of chemical shifts and spin-lattice relaxation times indicate that the oligomers are chemically attached to the surfaces, providing for a well bonded, water resistant interphase. Parallel experiments on a monomeric Bisphenol A-primed silica surface provided evidence that chemical bonding was primarily responsible for the greater hydrolytic stability.     

Influence of the fiber surface properties on the mechanical strength of unidirectional fiber composites

The influence of the thermodynamic adhesion between fibers and matrix on the mechanical properties of a continuous fiber reinforced composite is studied for two systems: carbon fiber reinforced poly(ether ether ketone) and glass fiber reinforced poly(ether imide). The fibers are modified chemically and characterized by measuring the contact angle formed by molten resin on the fibers. Various fiber treatments yield a wide range of contact angles, which are determined optically. Unidirectional fiber reinforced laminates are manufactured and transverse flexural strength is measured with the values reported as a function of the specific work of adhesion. It is shown that adhesion at the fiber-resin interface correlates with both the composite strength and the void morphology within the laminate after consolidation.     

Adhesion-induced deformations of polyurethane substrates in contact with spherical glass particles: the effect of particle size on the radius of contact

Spherical glass particles having radii between approximately 0.5 and 100 *m were deposited onto a polyurethane substrate and the radii of contact, resulting from the adhesion forces between the particles and the substrate, were determined using SEM. For particles having radii less than approximately 5 μm, it was found that the contact radius varied as the particle radius to the 0.75 power. In addition, large menisci, presumably resulting from tensile interations, were observed. For particles having radii between 5 and 60 μm, the contact radius varied as the particle raidus to the 2/3 power. Stretching of the substrate was also observed for particles having radii of approximately 100 μm. This is probably a harbinger of the impending separation of the particle from the substrate, due to gravitational forces. The thermodynamic work of adhesion was calculated from the data and the results were compared with the predictions of several theories of particle adhesion.     

Evaluation of Fracture Surfaces in Carbon Fiber/Epoxy Composites

We have investigated carbon fiber/resin debonding mechanisms using wetting force scanning to examine the fracture surfaces. The wettability of the site of a resin microdroplet (50-150 μm long) on a fiber after debonding is compared with that of the original fiber surface by scanning along the fiber with an appropriate probe liquid. For an HMS/Epon828 system, debonding seems to involve removal of a layer of carbon fiber, while for an AS4/Epon828 system, there is evidence for adhesive failure as well as cohesive failures in both fiber and resin. These contrasting failure mechanisms are consistent with the morphological structures of the carbon fibers studied.     

石墨烯/橡胶复合改性沥青-集料界面黏附性能及机理

为探究石墨烯/橡胶复合改性沥青与集料的界面黏附性能及黏附机理;采用光电比色法和接触角法对石墨烯/橡胶复合改性沥青与集料的界面黏附性能进行了研究。利用分子动力学软件MS构建了沥青与集料的界面模型;以黏附功对沥青与集料的界面黏附性能进行了量化。从原子尺度对沥青与集料间的黏附机理以及温湿敏感性进行了分析研究。结果表明:集料种类对于黏附性能的影响要明显大于沥青种类对于黏附性能的影响;在碱性集料缺乏的地区;石墨烯/橡胶复合改性沥青与花岗岩的黏附性效果最优;因此此类地区推荐使用石墨烯/橡胶复合改性沥青作为沥青胶结料;石墨烯/橡胶复合改性沥青可以明显改善沥青与集料的黏附性能;随着集料氧化物碱性增强;沥青中的极性分子在集料表面从“倾斜分布”转为“平行分布”;从而增强沥青与集料间的黏附性能。本研究在微细观层面揭示了石墨烯/橡胶复合改性沥青与集料的界面黏附机理;旨在为石墨烯/橡胶复合改性沥青路面的设计提供指导。     

Conceptualizing Physical and Chemical Interactions in the Compatibilized HDPE/PA6 and HDPE/EVOH Pairs: Theoretical and Experimental Analyses

Physical/chemical interaction in blends of high-density polyethylene with polyamide 6 and polyethylene-co-vinyl alcohol compatibilized with maleic anhydride-grafted high-density polyethylene was discussed. The performance of maleic anhydride-grafted high-density polyethylene was assessed by domain size variation and interfacial adhesion examination. Analysis of impact strength elucidated physical interaction improvement by compatibilization (entanglements and hydrogen bonding), while chemical reactions between ?OH and ?NH (from polyethylene-co-vinyl alcohol and polyamide 6, respectively) and ?COOH functional groups resulting from ring-opening of maleic anhydride determined interfacial adhesion reinforcement, where interfacial adhesion parameter changed from 0.75 for noncompatibilized to 0.96 compatibilized high-density polyethylene/polyamide 6, but remained unchanged for high-density polyethylene/polyethylene-co-vinyl alcohol blends, from 0.98 to 1.02.     

试验频率和温度对橡胶/纤维帘线复合材料动态粘合性能的影响

研究试验频率和温度对橡胶/纤维帘线复合材料动态粘合性能的影响,并通过扫描电镜分析粘合失效后纤维帘线的表面形貌。结果表明,降低试验频率和提高试验温度会加速橡胶/纤维帘线复合材料的粘合失效,这主要是由橡胶基体的破坏以及橡胶与纤维帘线的界面脱粘引起的。     

Effect of filler content and surface treatment on the tensile properties of glass‐bead‐filled polypropylene composites

The tensile properties of polypropylene (PP) filled with two A‐glass beads with the same size, PP/3000 (glass bead surface pretreated with a silane coupling agent) and PP/3000U (no surface pretreatment), have been measured by using an Instron materials testing machine at room temperature, to identify the effects of the filler surface pretreatment and its content on the tensile properties of these composites. The results show that the Young's modulus E_c of the composites increases non‐linearly with increasing volume fraction of glass beads ϕ_f, while the tensile yield strength σ_yc and tensile stress at break σ_bc of the composites decrease with an increase of ϕ_f, in the ϕ_f range 0–30%. Furthermore, the values of E_c and σ_bc of the PP/3000 system are somewhat higher than those of the PP/3000U system under the same test conditions, but this is in contrast to the tensile strain at break ε_bc and tensile fracture energy E_bc, especially at higher ϕ_f values. Good agreement is shown between the measured tensile strength and the predicted value by using an equation proposed in previous work. In addition, ε_bc and E_bc reach maximum values at ϕ_f = 25% for both systems. This indicates that there is a brittle–ductile transition for the composites in tension. © 2000 Society of Chemical Industry     

Mechanical effects in peel adhesion test

—Mechanical effects in the peel strength of a thin film have been studied both experimentally and theoretically. It has been found that the adhesion strength measured by the peel test is a practical adhesion (an engineering strength per unit width) and does not represent the true interface adhesion strength. The measured value may represent a multiplication of the true interface adhesion and other work expended in the plastic deformation of the thin film. The contribution of the latter to the peel strength is found to be, sometimes, of the order of 100 times higher than the former. It is found that the major controlling factors in the peel strength are the thickness, Young's modulus, the yield strength, the strain hardening coefficient of the film, and the compliance of the substrate as well as the interface adhesion strength. Even though the true interface adhesion strength is the same, a higher peel strength is obtained if the film is thinner or more ductile under the test conditions reported in this paper. The same effect can be obtained if the substrate is thinner in the case where the substrate is a soft elastic material, or if the substrate is thicker in the case where the substrate is a rigid material.     

Rheological, Interfacial and Thermal Control of Polymer Adhesion. I. Isothermal Theoryf

We have developed an isothermal theory of separation in polymer-solid adhering systems. The model used is based on the (observed) drawing of filaments between a bulk polymer and a solid. In the isothermal theory, a criterion is set up, demarcating filament elongation vs. detachment of the filament base from the solid. It employs a dimensionless parameter, ω, that relates free energy of adhesion, elongational viscosity or yield strength of the polymer, and filament size, to adhesive performance. The isothermal theory can be applied directly to the separation processes that occur with pressure-sensitive adhesives. Certain observations by Aubrey and Sherriff, by Gardon and by Kaelble are explained. The validity of the demarcation is believed to extend beyond pressure-sensitive systems, to all thermoplastic adhesives and/or coatings.     

玻纤长度及其含量对BMC力学性能影响

用正交试验设计的方法研究了玻纤／填料质量比、玻纤长度及混合时间等主要因素对BMC（预制整体模塑料）力学性能的影响。在系统地分析试验数据的基础上，以BMC的力学性能为参考值，得出了以上3个因素对BMC力学性能的影响趋势曲线；用扫描电镜讨论了3因素与BMC的微观结构及力学性能的关系，并获得了优化BMC的方案，所得的BMC的弯曲和冲击强度分别达到96．35MPa和21．82kJ／m^2。