汽车用单组分环氧结构胶性能的研究

对一种汽车用单组分环氧结构胶的固化行为、固化工艺和力学性能进行了研究。结果表明：黏度随温度升高而降低,在固化工艺为175℃/30min时,力学性能达到最佳,在固化时间20min时,剪切强度达到最大值28.9MPa,并对其耐水、耐湿热和耐热等老化性能进行了研究,结果表明试样的性能变化不大,说明该环氧结构胶具有良好的耐老化性能。     

Mixed-mode fatigue behavior of degraded toughened epoxy adhesive joints

Open-faced asymmetric double cantilever beam (ADCB) specimens of toughened epoxy-aluminum adhesive joints were aged either in a constant humidity environment or a cyclically changing environment to study the mixed-mode fatigue behavior. Under constant humidity environments, the fatigue threshold strain energy release rate initially decreased with aging time until it reached a constant minimum value for long times. In contrast, the crack growth rates continued to increase with aging time. It is hypothesized that at crack growth rates close to threshold the fatigue behavior is governed by the epoxy matrix, whereas at relatively high crack growth rates the fatigue behavior is governed by the loss of the rubber toughening mechanism. Increasing the aging temperature accelerated the degradation of the joints leading to a reduction in the time to reach the constant minimum value and increased the crack growth rates.Under a cyclic aging environment with intermittent salt spray, neither the threshold strain energy release rate nor the crack growth rates degraded until four weeks of aging. The superior fatigue performance of these joints compared to joints aged in constant humidity environments was due to the lower water concentrations in the adhesive while aging. This conclusion was supported by moisture uptake measurements of the adhesive in deionised and salt water environments that showed simple Fickian behavior at room temperature and dual-Fickian behavior at higher temperature. The salt water environment produced osmotic pressure that decreased the moisture concentration in the second stage of diffusion.     

Hygrothermal ageing effect of ADEKIT A140 adhesive on the J-integral of a plate repaired by composite patch

The effect of an hygrothermal ageing on the mechanical behavior of the bulk adhesive ‘Adekit A140 epoxy’ was investigated. The bulk test specimens of the adhesive were immersed in distilled water at various temperatures (20, 40 and 60 °C). Under these conditions, the tensile properties were determined and used in a numerical study about the behavior of bonded assemblies allowing to calculate the J-Integral. The obtained results illustrate the variation of the mechanical behavior of bulk adhesive depending on the immersion time and environmental temperature. The presence of water in the adhesive decreases the tensile strength and the elastic modulus but also increases the ductility of material. These changes in mechanical properties are more important when the percentage of water absorbed increases. The temperature increases the amount of absorbed water in the adhesive, consequently increases the degradation kinetics with the immersion time and directly affect the load transfer rate of the damaged area to the composite patch and therefore the value of the integral J.     

Hygrothermal aging of an adhesive reinforced with microparticles of cork

In the present study, natural microparticles of cork are used with the objective to increase the toughness of a brittle epoxy adhesive. The cork particles act as a crack stopper, leading to more energy absorption. This fact occurs because cork presents a remarkable combination of properties (low density, low cost and sustainability of the raw material). Adhesives are susceptible to the presence of moisture in the environment. There are several studies that refer that moisture can degrade the molecular structure of the adhesive, and, therefore, its mechanical properties. The main objective of this research is to investigate the effect of moisture on the degradation of an adhesive reinforced with micro cork particles, knowing that cork presents a great capability to absorb water. The water absorption and desorption characteristics have been studied, for specimens without cork and with 1% cork, 125–250 μm. The moisture uptake behaviour in the adhesive was studied to obtain the coefficient of moisture diffusion. The effect of water exposure on the mechanical properties and glass transition temperature was also investigated. It was observed that the presence of water alters the mechanical properties of the adhesive (with and without cork), but these changes are not permanent.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

The Effect of Moisture Content in Epoxy Film Adhesives on their Performance. III: Bulk Properties

Humidity absorbed by epoxy film adhesives during low temperature storage or exposure to atmosphere may result in reversible changes and irreversible modifications. Vacuum treatment may partially remedy the reversible changes. The consequences of vacuum drying are manifested in enhancement of both the peel and shear properties of bonded joints (Part I and Part II of this series of papers) and the thermal, physical and mechanical properties of the bulk adhesive, characterized in the present study.

Experimental results have shown that the bulk properties of structural epoxy based adhesives are highly correlated with the aging processes caused by water absorption in the prepolymerized adhesive. Applying the vacuum process is harmful to fresh unaged adhesive due to devolatization of low molecular species of the film adhesive.

The characterization of bulk properties for the purpose of following the aging and recovery processes is advantageous, since the bulk is independent of geometrical and interfacial effects which dominate in the case of property evaluation of the adhesive in a bonded joint.     

Creep behaviour of steel bonded joints under hygrothermal conditions

The aim of this research is to study the influence of moisture absorption at low moisture contents on the creep behaviour of an epoxy adhesive in steel bonded joints. Single lap joints were manufactured using high strength steel adherends and a two-component epoxy adhesive. The single lap joints were tested at load levels corresponding to average lap shear stresses of ± 5%, 15%, 30% and 45% of the dry lap shear strength in both 40 °C air and 40 °C distilled water. Specimens were not pre-aged to be able to analyse the coupled effect of moisture and loading. The test results show that an increase in the load level resulted in an increase in the instantaneous strain and in the creep strain rate. The creep strain of single lap joints loaded in water was generally larger than for the ones loaded in air. For joints loaded in water the creep behaviour was found to be dependent on the moisture concentration in the adhesive. At low moisture percentages creep was suppressed, resulting in a lower instantaneous strain. At higher moisture percentages creep was promoted, resulting in a larger strain rate. The suppression of creep at low moisture percentages is attributed to water molecules bonding to the epoxy macromolecules, resulting in a reduction in molecular mobility and a smaller creep strain. At higher moisture percentages the plasticizing effect of the water dominates, resulting in a larger creep strain. The Maxwell three-element solid model and Kelvin-Voigt three-element solid model were used to simulate the creep behaviour of the single lap joints loaded in air and water. The models gave good representations of the creep response across the different load levels in both water and air, they were however unable to give a correct representation of the instantaneous strain of the single lap joints loaded in water. This is attributed to the models being unable to account for the present short-term relaxation process that is dependent on the moisture concentration.     

Factors Affecting the Processing of Epoxy Film Adhesives II. Moisture Content

Dielectric and thermomechanical analysis, infrared spectroscopy, and mechanical testing were used to study the changes which occur in the cure behavior of a 178°C (350°F) epoxy film adhesive, Hysol EA-9649. The response of the system was compatible with the catalyst type employed. The overall effect of increasing moisture content was an increase in flow accompanied by lower T_g values in the cured film with no loss in ambient temperature tensile lap shear strength. These effects are interpreted in terms of the dicyandiamide portion of the adhesive catalyst system reacting with the absorbed moisture resulting in a cured adhesive of different structure but equivalent in bonded joint strength to those made with low moisture content adhesive.     

Influence of water immersion on the single-lap shear strength of aluminum joints bonded with aluminum-powder-filled epoxy adhesive

Durability of adhesively-bonded aluminum joints was investigated by measuring the joint strength using the single-lap shear test before and after exposure to distilled water and seawater. Fractured specimens were examined by photography and scanning electron microscopy to determine the failure modes. Addition of Al particles as much as 50 wt% did not cause any significant decrease in adhesive joint strength. Moreover, varying the Al filler content in the adhesive did not have a significant effect on adhesive behavior in either of the two environments studied. The unexposed adhesive joints failed almost completely in a cohesive (in the adhesive) failure mode. Some decrease in strength was observed in adhesive joints after exposure to both distilled water and seawater for 6 months. The decrease in adhesive joint strength was more significant for specimens immersed in distilled water than those immersed in seawater, probably due to the higher amount of moisture in the adhesive in distilled water than in seawater, as observed in a related moisture diffusion study. The joints exposed to distilled water or sea water failed in more than one mode. The interior part of the adhesive lap area failed in a cohesive mode while an adhesion failure mode was observed near the edges of the adhesive lap area, which is believed to be a result of moisture diffusion through the edges.     

Factors Affecting the Processing of Epoxy Film Adhesives II. Moisture Content

Dielectric and thermomechanical analysis, infrared spectroscopy, and mechanical testing were used to study the changes which occur in the cure behavior of a 178°C (350°F) epoxy film adhesive, Hysol EA-9649. The response of the system was compatible with the catalyst type employed. The overall effect of increasing moisture content was an increase in flow accompanied by lower T_g values in the cured film with no loss in ambient temperature tensile lap shear strength. These effects are interpreted in terms of the dicyandiamide portion of the adhesive catalyst system reacting with the absorbed moisture resulting in a cured adhesive of different structure but equivalent in bonded joint strength to those made with low moisture content adhesive.     

The durability of adhesive/carbon–carbon composites joints in salt water

This paper researches the durability of the adhesive/carbon–carbon (C–C) composites joints in salt water with infrared spectroscopy (IR), energy dispersive X-ray spectrosopy (EDX) and shear strength test methods. In salt water, Na⁺ and Cl⁻ ions can accelerate hydrolyzation of the adhesive and increase water ingress ability in the adhesive, although salt water cannot produce ionization potential between adhesive and C–C composites like adhesive/metal joints. The durability of the adhesive/C–C composites joints in salt water aging is lower than that in humidity aging by shear strength tests. EDX and IR spectra of the adhesive indicate that the salt water diffusion speed in the adhesive/C–C composites joints depend on not only temperature but also salt water aging time, i.e. time–temperature equivalence between temperature and salt water aging time. Shear strength tests also indicate that the rate of shear strength of the adhesive/C–C composites joints treated by silane coupling agent is lower than that treated by sand paper burnishing or by chemical oxidation in salt water aging.     

螺旋桨用榉木层板胶粘剂性能测试及工艺研究

为了解决木质螺旋桨的稳定性与变形问题,选用自制的聚氨酯(PU)胶粘剂对榉木层板进行胶接后再加工成螺旋桨。分别对胶接件的力学性能、耐热性、耐寒性、耐水性和耐湿热老化性能等进行了测定,探索了自制PU胶粘剂的最佳工艺条件,并进行了常温、高低温处理后的发动机试车试验。结果表明:自制PU胶粘剂具有较高的综合力学强度及稳定性能(其平均常温拉伸剪切强度和压缩剪切强度分别为8.13 MPa和15.00 MPa,平均高低温拉伸剪切强度和压缩剪切强度分别超过6.50 MPa和7.10 MPa;在水中浸泡20 h或湿热环境中放置24 h后,其平均压缩剪切强度分别为5.85 MPa和11.75 MPa),完全满足木质螺旋桨的使用要求。     

Physicochemical and mechanical degradation of polyamide 11 induced by hydrolysis and thermal aging

This article deals with the effect of both temperature and water activity on polyamide 11 physicochemical and mechanical properties. The purpose of this work is to describe the ductile–brittle transition of polyamides during aging in a wet environment using a mechanical behavior model. For that it is necessary to make physicochemical analyzes (DSC, FTIR, GPC, viscosity) and mechanical tests (uniaxial tensile test and dynamic mechanical thermal analysis). All of these tests were performed on unaged samples and on aged samples for until 60 days. Two types of aging conditions were performed: In water in an acidic medium at temperature, and in purely thermal conditions in a neutral environment. Changes in mechanical properties with aging were observed in the polymer and were correlated to morphological changes deduced from the physicochemical characterizations. An increase of the second yield stress related to the recrystallization and a decrease of the strain at break due to the decrease of the molecular weight were observed during aging. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47628.     

Shear strength of wood to wood adhesive based on palm kernel oil

A polyurethane adhesive system was prepared by reacting a resin consisting of palm kernel oil‐based polyester and dimethyl cyclohexanediamine with an aliphatic adduct based on 2,4‐diphenylmethane diisocyanate (MDI). Brushing technique was used for applying the adhesive (of thickness 0.05–0.10 mm) onto the wood substrate. Shear strength test for substrates that have been exposed to moisture and various degrees of heat was carried out. Collected data indicated that the adhesive exposed to heat at 70°C has the highest shear strength. At this point, the shear force was at the maximum of 2562 N with strength of 2.65 MPa. However, at higher testing temperature, there is a decrease in the shear force and strength of the adhesive. The presence of moisture, however, does not affect much on the shear strength. The morphological observations via optical microscope were made to explain the relationship of heat and moisture with the shear strength of the adhesive. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1759–1764, 2006     

JP-6新型导电胶的性能研究

对自制的JP-6新型导电胶性能进行了系统的研究,包括力学性能、电学性能以及耐热性和吸水性等。结果表明J:P-6新型导电胶是一种综合性能非常优异的导电胶黏剂体系,具有很高的拉伸剪切强度,高达21.1MPa;优良的导电性,其固化物的体积电阻率为2.32×10-4Ω·cm;良好的耐热性,其固化物的Tonset热分解温度高达375.6℃;很低的吸水性,只有0.5%;长的室温贮存期,高达3个月以上。而且具有优异的耐大气老化性能、耐热老化性能以及耐湿热老化性能等。     

Adhesive and flame resistance behavior of poly(arylene ether phosphine oxide) (PEPO) and PEPO‐modified epoxy resins

Poly(arylene ether phosphine oxide) (PEPO) with controlled molecular weights and amine end‐groups was synthesized, and used as an adhesive, a coating material for adherend or a modifier for diglycidyl ether of bisphenol A (DGEBA)‐based epoxy resins. Closely related poly(arylene ether sulfone) and commercial polyethersulfone, Udel® P‐1700, were also utilized for comparison purposes. Adhesive behavior was measured via single lap shear samples as a function of coated polymer type, test temperature (R.T. and 100°C), and aging condition in boiling distilled water or 5% salt water. Flame resistance of PEPO and PEPO‐modified epoxy resin was evaluated by TGA and a flame test. PEPO exhibited better adhesive properties than PES or Udel® P‐1700. PEPO coating on an Al adherend markedly improved adhesive property of PES and Udel® even at 100°C, and after aging study failure mode changed from adhesive to cohesive with the PEPO. Aminophenyl terminated PEPO‐modified epoxy resins also exhibited highly improved adhesive behavior and flame resistance, compared to control samples. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1198–1205, 2001     

Physical aging time scales and rates for poly(vinyl acetate) stimulated mechanically in the Tg-region

The physical aging behavior of poly(vinyl acetate), PVAc, in the T_g-region has been investigated using dynamic mechanical analysis (DMA). Tests in shear and flexure modes were performed for samples quenched from a stabilization temperature of 40°C to aging temperatures 35.0°C and 32.5°C (down-jumps), and from equilibrium at a stabilization temperature of 32.5°C to aging temperature 36.2°C (up-jump). Volume recovery was investigated for the same thermal histories using mercury-in-glass dilatometry. The time scales for the evolution of the storage and loss moduli during physical aging have been compared with the volumetric time scales. Aging rates, µ, have been calculated in the frequency and time domains. The evolution of dynamic mechanical properties during aging is found to be different from the volumetric behavior. In the case of the temperature down-jump, the evolution of the volume ceases earlier than that for the storage and loss moduli. In the up-jump experiment, the opposite is found. Aging rates for the storage and loss moduli are analyzed. A suggestion is offered that the evolution of dynamic mechanical properties during physical aging is retarded by the cyclic mechanical stimulus, and that this effect (rejuvenation) is more noticeable the higher is the damping; consequently rejuvenation in the T_g-region can be caused by small strains in dynamic mechanical analysis.     

The Effects of Molecular Weight on the Single Lap Shear Creep and Constant Strain Rate Behavior of Thermoplastic Polyimidesulfone Adhesive

The bonded shear creep and constant strain rate behavior of zero, one, and three percent end capped Thermoplastic Polyimidesulfone adhesive were examined at room and elevated temperatures. End capping was accomplished by the addition of phthalic anhydrides.

The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced.

The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive in the bonded form. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Crochet's relation was used to describe the experimental creep failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed.     

Strength and Durability of Epoxy-Aluminum Joints

The adhesive strength and durability of adhesively-bonded aluminum joints in wet environments was analyzed. A2024-T4 alloy was subjected to two different surface treatments based on etching with chromic-sulfuric acid (FPL) and with sulfuric acid-ferric sulfate (P2). Small differences were observed in the lap shear strength as a function of the applied surface treatment. However, durability in humid environments was higher for the joints whose adherends were treated with P2.

Although the amount of water absorbed by the epoxy adhesive is lower in saline environments, the effects on the glass transition temperature of the epoxy adhesive and on the lap shear strength of the joints are more marked than the effects caused by aging with distilled water.

Finally, a new epoxy adhesive with a siloxanic hardener was tested, obtaining good mechanical properties, high glass transition temperature, moderate values of lap shear strength, and high durability in wet environments.     

Twin‐screw compounding of poly(methyl methacrylate)/clay nanocomposites: effects of compounding temperature and matrix molecular weight

Poly(methyl methacrylate) (PMMA)/organoclay nanocomposites prepared by melt‐compounding using a co‐rotating twin‐screw extruder were intercalated nanocomposites. Commercially available PMMA resins of various molecular weights were used for comparison. The results showed an optimum compounding temperature for maximum intercalation with balanced shear and diffusion. Higher operating temperature reduced the shear mixing effect, and might have induced early degradation of the organoclay. Lower operating temperature, in contrast, reduced the mobility of the polymer molecules, which not only hampered the intercalation attempts, but also generated high torque in the extrusion. The mechanical behavior of the nanocomposites was studied. The tensile modulus, storage modulus and glass transition temperature of the nanocomposites increased with increasing clay content; however, an associated decrease in strength and strain at break was also observed. The notched impact strength also showed a slight decrease with clay content. Nanocomposites based on the lower molecular weight PMMA yielded more significant improvement in mechanical and thermal properties at the same clay content. Copyright © 2007 Society of Chemical Industry