The Effect of Cure Conditions on a Rubber-Modified Epoxy Adhesive

The effect of cure conditions on the mechanical properties of a piperidine-cured, rubber-modified epoxy is described. The results obtained reveal that variations in cure conditions (temperature and time) have a pronounced influence on the mechanical behaviour, in particular the fracture energy obtained in both bulk and adhesive joint form. Techniques such as dynamic mechanical spectroscopy and scanning electron microscopy have been employed in an attempt to explain the trends.     

Toughening of epoxy resins with thermoplastics. Ii. Tetrafunctional epoxy resin-polyetherimide blends

A series of blends has been prepared by adding a polyetherimide (PEI), in varying proportions, to a tetrafunctional epoxy resin, tetraglycidyl-diaminodiphenylmethane (TGDDM), cured with 4,4′-diaminodiphenylsulphone (DDS). All the materials exhibited two-phase morphologies which were characterised by dynamic mechanical thermal analysis and scanning electron microscopy. Addition of the thermoplastic gave a modest improvement in fracture properties (K_1c and G_1c), as determined by three-point bending experiments, although no obvious correlation with the marked morphological changes was observed.     

Toughening of Epoxy Resins with Thermoplastics: 3. An Investigation into the Effects of Composition on the Properties of Epoxy Resin Blends

Three different epoxy resins, based on the diglycidylether of bisphenol A (DGEBA), triglycidyl-p-aminophenol (TGPAP) and tetra-glycidyldiaminodiphenylmethane (TGDDM), which are di-, tri- and tetrafunctional, respectively, were mixed in varying proportions and cured with both 3,3′-diaminodiphenylsulphone and 4,4′-[1,4-phenylene(1-methylethylidene)]bis(2,6-dimethylbenzenamine) (EPON 1062-M from Shell). All the blends could be satisfactorily cured and gave homogeneous materials. The dynamic mechanical and fracture properties of the cured materials were measured. It was found that the glass transition temperature varied with composition systematically, whereas values of the strain energy release rate (G_1c) and the stress intensity factor (K_1c) showed relatively small variations with the blend composition. Toughened epoxy resins were prepared by adding a polyetherimide (PEI), in varying proportions, to the resin mixture. The ‘toughenabilities’ of different resins, or resin mixtures, were compared. This showed that the 75/25 TGPAP/DGEBA resin mixture was the most toughenable. Adding 20% of PEI led to a more than three-fold increase of the G_1c value. © of SCI.     

The Fracture Behaviour of a Rubber-Modified Epoxy Under Impact Fatigue

The fracture behaviour of a rubber-modified epoxy adhesive under impact fatigue has been investigated. An instrumented-impact test has been employed to apply multiple, “repeated-blow,” impacts to pre-cracked three-point-bend specimens at sub-critical energy levels. A fracture mechanics approach has been adopted to assess the effects of the impact-fatigue damage on the epoxy material.     

Off-Optimum Cure of Aerospace Epoxy Adhesives

Four epoxy film adhesives used in aircraft manufacture and repair have been examined to establish the effect of deviation from the cure cycle specified by the manufacturer. In addition to the variation of the cure cycle, two surface preparations of the aluminium adherends (chromic acid etch or grit blast followed by silane treatment) were evaluated. Thermal analysis was used to examine the cure envelope of the adhesive, and its extent of cure and glass transition temperature. The adhesive properties were assessed by shear strength (in both single lap joints and in Iosipescu configuration), durability (Boeing wedge test) and chemical resistance to selected aggressive fluids. The sensitivity of the performance of a particular adhesive to offoptimum cure conditions depends on its composition and needs to be determined, not predicted.     

Off-Optimum Cure of Aerospace Epoxy Adhesives

Four epoxy film adhesives used in aircraft manufacture and repair have been examined to establish the effect of deviation from the cure cycle specified by the manufacturer. In addition to the variation of the cure cycle, two surface preparations of the aluminium adherends (chromic acid etch or grit blast followed by silane treatment) were evaluated. Thermal analysis was used to examine the cure envelope of the adhesive, and its extent of cure and glass transition temperature. The adhesive properties were assessed by shear strength (in both single lap joints and in Iosipescu configuration), durability (Boeing wedge test) and chemical resistance to selected aggressive fluids. The sensitivity of the performance of a particular adhesive to offoptimum cure conditions depends on its composition and needs to be determined, not predicted.     

硅氧烷树脂改性环氧树脂胶粘剂性能的研究

通过差示扫描量热(DSC),热解重量分析(TGA)和粘接强度的测定,对硅氧烷树脂改性的环氧树脂胶粘剂的性能进行了研究。     

Differential Scanning Calorimetry Cure Studies of Tetra-N-glycidyldiaminodiphenylmethane Epoxy Resins 3 - Reaction with Dicyandiamide

Continuation of work on the curing characteristics of an epoxy resin which is widely used as a composite matrix is reported. Results are given of study of the cure of the resin with dicyandiamide as hardener and diuron as accelerator, using differential scanning calorimetry to monitor the cure. The effect of diuron on the cure of the resin with an aromatic amine curing agent is also described. Distinctive effects of composition are found and values of the apparent activation energy of the curing reaction are derived.     

The Effect of Adherends on the Curing of an Epoxy Adhesive

The effect of E-glass, cured vinyl ester resin, and silica gel on the curing of an epoxy-anhydride adhesive was examined. The techniques used were calorimetry in both isothermal and scanning modes and Fourier transform infrared spectroscopy in the attenuated total reflectance (ATR-FTIR) mode. Isothermal calorimetry was used to obtain the exotherm, conversion rate, and curing kinetic parameters, and scanning calorimetry was used to obtain the glass transition temperature. ATR-FTIR was used to study the curing kinetics and chemistry of the adhesive. The results suggest either the immobilization of a layer of the epoxy adhesive adjacent to inert solid surfaces or selective adsorption of the accelerator or both, each of which suppresses the cure reaction. This was reversed by the presence of adsorbed water. At least for this epoxy-anhydride system, adsorbed water seems to have had the beneficial effect of increasing the crosslink density in the interfacial region between the adhesive and adherend. Water seems also to change the overall cure reaction, causing more ether formation and less ester formation than without water. An additional finding was that the cured vinyl ester surface appeared to have a catalytic effect on the reaction, perhaps in conjunction with the accelerator, benzyldimethylamine.     

The Effect of Modification of an Epoxy Resin Adhesive with ATBN on Peel Strength

The effects of rubber content, rate of peel and temperature on peel strength of ATBN modified DGEBA based epoxy resin adhesives have been investigated. The fracture surfaces of peel test specimens and the distribution of rubber particles in cured bulk epoxy resin have been observed with SEM and TEM, respectively. The mechanical properties of bulk rubber modified epoxy resin have been also measured. The peel strengths increased with increasing rubber content, peel rate, and decreasing temperature. The peel strengths were superposed as a function of rate and temperature. Plots of the shift factors against temperature gave two straight lines, which followed an Arrhenius relationship. The region of temperature below the intersection of the two straight lines, temperature somewhat lower than T_g of epoxy adhesive, gave markedly high peel strengths and a stick-slip failure due to plastic deformation of the adhesive, and a number of micro holes produced by the rupture of rubber micro particles on the fracture surface. The region of temperature above the intersection gave lower peel strengths and an apparent interfacial failure with ductile fracture of the adhesive, and larger, shallow holes or no holes. From these results, the marked increase of peel strength was concluded to be mainly attributed to the plastic or viscoelastic deformation of epoxy matrix, the strong bond at the interface between rubber particles and epoxy matrix, and the dilation and rupture of a number of rubber particles.     

Deformation behavior of nanocrystalline titania particles accessed by complementary in situ electron microscopy techniques

The mechanical behavior of nanostructured spherical submicrometer titania particles was studied by in situ uniaxial compression experiments in the scanning and transmission electron microscope (SEM and TEM). Mesoporous and amorphous titania particles were prepared by a wet chemical sol‐gel approach. To obtain nanocrystalline (nc) single‐phase anatase and rutile particles the amorphous particles were crystallized by high‐temperature annealing. For each sample the deformation behavior of at least 50 particles was investigated by in situ compression experiments in the SEM. In all cases an elastic – predominantly plastic deformation behavior accompanied by crack initiation at exceptionally high engineering strain values of several percent were observed. Crack propagation presumably along grain boundaries and a Weibull distributed fracture stress was shown for all nc particles. Complementary in situ TEM experiments and ex situ analysis of focused ion beam prepared particle cross‐sections were carried out to identify the underlying deformation mechanisms. Grain rotations and grain sliding are observed for nc anatase particles during in situ compression and are further identified to be linked to a densification of the mesoporous particle structure. Our dedicated preparation and quantitative in situ characterization methodology provides an excellent basis for a better understanding of the mechanical behavior of advanced ceramics.     

Adhesive and Mechanical Properties of Reactive Polysulfone Modified Epoxy Resins

The diglycidyl ether of bisphenol-A epoxy resin (EPON 828®) was cured with 4,4'-diaminodiphenylsulfone (DDS) and, optionally, an animophenyl functional reactive polyethersulfone (R-PES, 〈 M_n 〉=10k) as a co-curing agent. Commercial polysulfone, Udel® P-1700, was also utilized to afford epoxy-Udel® blends (or semi-IPNs). Cured epoxy polymers were subjected to T_g determinations, plane strain fracture toughness (K_IC) tests, adhesive bond strength measurements, tensile tests and chemical resistance studies. The morphologies of the fractured samples were studied by SEM and correlated to the property changes. Only the reactive polysulfone modification improved both fracture toughness and adhesive properties without detracting from the good mechanical properties and chemical resistance.     

Adhesive and Mechanical Properties of Reactive Polysulfone Modified Epoxy Resins

The diglycidyl ether of bisphenol-A epoxy resin (EPON 828®) was cured with 4,4′-diaminodiphenylsulfone (DDS) and, optionally, an animophenyl functional reactive polyethersulfone (R-PES, ? M_n ?=10k) as a co-curing agent. Commercial polysulfone, Udel® P-1700, was also utilized to afford epoxy-Udel® blends (or semi-IPNs). Cured epoxy polymers were subjected to T_g determinations, plane strain fracture toughness (K_IC) tests, adhesive bond strength measurements, tensile tests and chemical resistance studies. The morphologies of the fractured samples were studied by SEM and correlated to the property changes. Only the reactive polysulfone modification improved both fracture toughness and adhesive properties without detracting from the good mechanical properties and chemical resistance.     

Effects of Accelerated Thermo-Oxidative Aging on Properties of a Damped-Encapsulating Epoxy Adhesive

The effects of accelerated thermo-oxidative aging treatment on structure, hardness, morphology of fractured surface, and dynamic mechanical properties of a damped-encapsulating epoxy adhesive were investigated. FT-IR indicated the formation of a small quantity of amide groups. The hardness increases rapidly at earlier stages and then tends to stabilize when the thermo-oxidative aging time is over 300 hours. SEM graphs indicated a change from some toughness to rigidity. DMA analyses revealed that the Tg of the aged samples gradually shifted to higher temperatures, the maximum value of tanδ fluctuated in a narrow range, the tanδ spectra were greatly temperature dependent, and the tanδ spectrum showed a tendency of horizontal displacement with increased thermo-oxidative aging time.     

Effect of Nonstoichiometry on Fracture Toughness and Hardness of Yttrium Oxide Ceramics

This work deals with the changes in mechanical properties of yttrium oxide ceramics induced by nonstoichiometry. The maximum fracture toughness, K_lc, is observed at the stoichiometric composition. For an oxygendeficient ceramic, a decrease of K_lc is observed from 3.5 to 2.3 MPa.m^1/2. On the other hand, the Vickers hardness seems to be less dependent on stoichiometry. These results are discussed in the frame of the evolution of the Y-O bond with the stoichiometry. They set in particular the problem of the role of electrostatic energy stored in a brittle material containing charged defects in the energy balance controlling crack propagation.     

Toughening of Diglycidyl Ether of Bisphenol-A Epoxy Resin Using Poly (Ether Ether Ketone) with Pendent Ditert-Butyl Groups

Poly(ether ether ketone) (PEEKDT), hydroxyl terminated poly(ether ether ketone) (PEEKDTOH) and fluorine terminated poly (ether ether ketone) (PEEKDTF) with pendent ditert-butyl groups were synthesized by the nucleophilic substitution reaction of 4,4′-difluorobenzophenone with 2,5-ditert-butylhydroquinone in N-methyl-2-pyrrolidone medium using anhydrous potassium carbonate as catalyst. Diglycidyl ether of bisphenol-A epoxy resin was blended with PEEKDT, PEEKDTOH, and PEEKDTF, and cured with 4,4′-diaminodiphenylsulfone (DDS). The polymers formed heterogeneous blends before curing, and upon curing the polymers got dispersed in the epoxy matrix. The mechanical properties of the cured blends were slightly lower than that of the unmodified resin. The fracture toughness increased with the addition of ditert-butyl PEEK into epoxy resin and the extent of improvement was dependent on the type of modifier used. Hydroxyl terminated polymers gave up to 40% increase in fracture toughness. The dynamic mechanical spectrum of the blends showed only a single T_g due to the proximity of the glass transition temperature of modified PEEK and DDS cured epoxy resin.     

一种高韧性耐湿性环氧树脂的合成及其性能研究

利用β-甲基环氧氯丙烷与双酚A在氢氧化钠的存在下合成了一种新的甲代双酚A型缩水甘油醚环氧树脂(BPA-MECH EP)预聚物,并通过FT-IR、1H NMR、GPC等手段对产物结构进行了表征。用盐酸-丙酮滴定法测定其环氧值为0.43 mol/100 g。用DDM作固化剂,利用DSC对其添加量为树脂质量的20%时体系的固化反应动力学以及最佳固化工艺条件进行了探讨。实验结果表明:BPA-MECH/DDM固化体系的反应级数n为1.30;表观活化能为15.37 kJ/mol;最佳固化工艺条件为:120℃/1 h→140℃/1 h→175℃/3 h→200℃/1 h逐步阶段升温固化。与E-44的DDM固化物进行了性能比较,结果表明:BPA-MECH与E-44固化产物的热变形温度无显著差别,但吸水率降低了47.6%,弯曲强度和弯曲模量分别提高了10.5%和7.8%,冲击强度上升了129.4%,拉伸强度、弹性模量以及断裂伸长率都有不同程度的提高,最大增幅分别为27.6%、25.9%和12.9%。研究结果表明,甲代双酚A型缩水甘油醚环氧树脂是一种性能优良的环氧树脂预聚物。     

室温固化柔性环氧胶黏剂的制备研究

以自制改性环氧树脂和改性胺类固化剂制备了双组份的室温固化柔性环氧胶黏剂。研究了固化剂种类、用量以及促进剂对胶黏剂粘接和力学性能的影响。还对该胶的固化行为进行了DSC分析,并采用FT-IR对固化过程中体系的官能团变化做了监测。结果表明:胶黏剂起始固化温度在70℃左右,体系中的氨基和环氧基对应的特征峰随着固化反应的进行有明显的减少,并最终消失;在室温下固化7d可获得优异的粘接和力学性能,常温剪切强度为30.5MPa,剥离强度为9.2k N/m,断裂伸长率为97%。