Fracture and mechanical properties of epoxy resins and rubber-modified epoxy resins

Fracture and mechanical property data on a wide range of epoxy resin systems are presented. The extent to which toughening can be induced by heterophase rubber inclusions depends more on the curing agent used than on the resin component. The greatest improvements in toughness were obtained by rubber modification of epoxy resins cured with an anhydride. A preformed ABS polymer can be used to toughen many epoxy resin systems. With one major exception (where a large improvement was found) only small changes in tensile properties occur when small amounts of rubber are present.     

含有聚醚多胺环氧树脂网络的形态及力学性能

不同相对分子质量聚醚多胺与环氧树脂于６０℃混合后,加入固化剂二乙烯三胺,在８０℃＊ｈ,１２０℃＊４ｈ下固化,可制备含聚醚多胺的固化环氧树脂网络。     

Morphology,thermal and mechanical properties of epoxy adhesives containing well-dispersed graphene oxide

Graphene oxide (GO) is prepared and introduced into epoxy resins through a wet-transfer migration technique using a three-roll mill. The results of TEM, XRD and digital microscope observation show that good dispersion of GO is achieved without using any additives. The mechanical and thermal properties of GO/epoxy (GO/EP) adhesives are enhanced with GO incorporated. A 10.2% increase in Young's modulus and a 56.3% increase in elevated-temperature (120 °C) lap shear strength (LSS) was observed on addition of 1.0 wt% GO, compared to the neat epoxy adhesive. Increased glass transition temperature and improved thermal stability of the GO/EP adhesives are also observed in the DMA and TG analysis. Moreover, the toughness of the GO/EP adhesives is improved and much rougher fracture surface can be observed compared with the neat epoxy adhesive. No GO agglomeration can be observed in the SEM images of GO/EP adhesive with 1.0 wt% loading.     

Synthesis and properties of phosphorus containing advanced epoxy resins

A series of advanced epoxy resins with various epoxy equivalent weights were synthesized from a reactive phosphorus‐containing diol, 2‐(6‐oxido‐6H‐dibenz[c,e][1,2]oxaphosphorin‐6‐yl)‐1,4‐dihydroxy phenylene and diglycidyl ether of bisphenol A and then cured with 4,4′‐diaminodiphenyl sulfone, phenol novolac, or dicyandiamide. The parameters of the polymerization reaction (such as reaction time, catalyst) are discussed in this article. Thermal properties of cured epoxy resins were studied using differential scanning calorimetry, dynamic mechanical analysis, and thermal gravimetric analysis. The flame retardancy of cured epoxy resins was tested by limiting oxygen index. The relations between thermal properties, flame retardancy, and epoxy equivalent weights were also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 429–436, 2000     

Morphology, thermal relaxations and mechanical properties of layered silicate nanocomposites based upon high-functionality epoxy resins

This paper investigates the possibility of improving the mechanical properties of high-functionality epoxy resins through dispersion of octadecyl ammonium ion-modified layered silicates within the polymer matrix. The different resins used are bifunctional diglycidyl ether of bisphenol-A (DGEBA), trifunctional triglycidyl p-amino phenol (TGAP) and tetrafunctional tetraglycidyldiamino diphenylmethane (TGDDM). All resins are cured with diethyltoluene diamine (DETDA). The morphology of the final, cured material was probed by wide-angle X-ray scattering, as well as optical and atomic force microscopy. The α- and β-relaxation temperatures of the cured systems were determined using dynamic mechanical thermal analysis. It was found that the presence of organoclay steadily decreased both transition temperatures with increasing filler concentration. Further, the effect of different concentrations of the alkyl ammonium-modified layered silicate on the toughness and stiffness of the different epoxy resins was analyzed. All resin systems have shown improvement in both toughness and stiffness of the materials through the incorporation of layered silicates, despite the fact that it is often found that these two properties cannot be simultaneously achieved.     

Bonding properties of epoxy resins containing two mesogenic groups

Liquid‐crystalline epoxy resins, with introduced aliphatic chains between two mesogenic groups, were synthesized and their adhesive bonding properties were compared to those of the bisphenol‐A–type epoxy resin and the liquid‐crystalline epoxy resin, previously reported. The bonding strength of the former resin system was higher than that of the two later systems. We suggest that the high bonding strength of the twin mesogenic epoxy resins, cured with an aromatic amine, was attributable to the large plastic deformation of the adhesive layer in the fracturing process. We also investigated the effects of the aliphatic chain length in the twin mesogenic epoxy resin on their dynamic mechanical and bonding properties. The bonding strength of the cured twin mesogenic epoxy resins increased with an increase in the aliphatic chain length. We suggest that the high bonding strength of the system introduced by the long aliphatic chain was attributable to the large plastic deformation of the adhesive layer because of the higher network mobility. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3721–3729, 2004     

Thermomechanical and morphological properties of epoxy resins modified with functionalized hyperbranched polyester

Thermomechanical and morphological properties of blends of epoxy monomers and hydroxyl and epoxy functionalized hyperbranched polyesters have been studied. Different properties of the blends were found by changing the cure cycles (a precure step followed by a postcure at higher temperature). All the blends showed phase separation with a particulate morphology. Through the addition of the hydroxyl‐ended modifiers, rather than the epoxy‐ended, an increase of the viscosity and of the reactivity of the uncured blends was obtained. The blends containing the epoxy functionalized polymer showed some liquid–liquid transitions in the rheological traces, probably because of the phase separation phenomena. POLYM. ENG. SCI., 46:1502–1511, 2006. © 2006 Society of Plastics Engineers     

Relationship between structure and mechanical properties in rubber-toughened epoxy resins

Toughened polymers were prepared by adding CTBN rubbers to DGEBA-type epoxy resins. Structure was varied by altering the type and concentration of hardener, the initial molecular weight of the resin, the amount of Bisphenol A added, and the conditions of cure. Electron microscopy showed that these factors affected both particle size and degree of phase separation: rapid curing inhibited phase separation, and produced small particles. Increasing the molecular weight of the resin, either directly or by reaction with Bisphenol A, improved phase separation. Dynamic mechanical measurements of rubber phase volume proved possible, although T_g of the CTBN rubber coincided with a β process in the epoxy resin. Fracture resistance, measured by G_IC, increased linearly with rubber phase volume. Creep and yield behaviour were also affected by the degree of phase separation.     

Preparation and mechanical properties of modified epoxy resins with flexible diamines

Diglycidyl ether of bisphenol A (DGEBA) is one of the most widely used epoxy resins for many industrial applications, including cryogenic engineering. In this paper, diethyl toluene diamine (DETD) cured DGEBA epoxy resin has been modified by two flexible diamines (D-230 and D-400). The cryogenic mechanical behaviors of the modified epoxy resins are studied in terms of the tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding properties at room temperature (RT). The results show that the addition of flexible diamines generally improves the elongation at break and impact strength at both RT and 77 K. The exception is the impact strength at 77 K filled with 21 wt% and 49 wt% D-400. Further, two interesting observations are made: (a) the cryogenic tensile strength increases with increasing the flexible diamine content; and (b) the RT tensile strength can only be improved by adding a proper content of flexible diamines. It is concluded that the addition of a selected amount namely 21–78 wt% of D-230 can simultaneously strengthen and toughen DGEBA epoxy resins at both RT and 77 K. However, only the addition of 21 wt% D-400 can simultaneously enhance the strength and ductility/impact strength of DGEBA epoxy resins at RT. The impact fracture surfaces are examined using scanning electron microscopy (SEM) to explain the impact strength results. Finally, differential scanning calorimetry (DSC) analysis shows that the glass transition temperature (T_g) decreases with increasing the flexible diamine content. The presence of a single T_g reveals that the flexible diamine-modified epoxy resins have a homogeneous phase structure.     

Time-dependent changes in mechanical properties of neat and reinforced epoxy resins

Several neat and reinforced epoxy resin formulations were prepared and investigated. Solid glass microspheres, with and without coupling agent, were used as reinforcement. After completion of post-cure all samples were quenched into an ice-water bath. Upon removal from the ice-water bath, dynamic mechanical and fracture properties of all samples were evaluated as a function of time elapsed after quenching. Electron microscopic evidence was obtained for the existence of nodular morphology in all cured systems. The changes in dynamic mechanical and fracture parameters, induced by the sub-T_g annealing, were described in terms of the model of inhomogeneous thermoset morphology.     

Morphology and mechanical properties of amine-terminated butadiene-acrylonitrile/epoxy blends

Morphology and mechanical properties of (amine terminated butadiene acrylonitrile rubber/diglycidyl ether of bis-phenol-A epoxy resin) blends of different compositions, cured in wide range of temperatures, are described. Curing at low temperature promoted formation of homogeneous materials with poor fracture resistance. On the contrary, at high temperature tough heterogeneous blends were obtained. Such blends showed phase inversion above 20 percent of rubber. The volume fraction of precipitated phase, determined on SEM micrographs, was higher than the amount of added rubber. A fracture mechanism to account for this is proposed. Extensive voiding and interface damage were observed in the low temperature cured materials. Such phenomena did not contribute to the fracture energy.     

Miscibilization of telechelic fluoroalkeneoxide oligomers in epoxy resins and effects on morphology and physical properties

Hydroxyterminated fluoroalkene oxide oligomers were reacted with chlorendic anhydride and subsequently with ?-caprolactone to produce carboxyterminated perfluoroethers prepolymers that were totally miscible with diglycidylether of bisphenol A. Curing the epoxy resin mixtures with hexahydrophthalic anhydride hardener and benzyl dimethylamine catalyst produced transparent products exhibiting a two-phase co-continuous morphology. Prereacting the fluoroalkeneoxide prepolymers with an excess of epoxy resin prior to the addition of hardener and catalyst, resulted in opaque products displaying a two-phase dispersed particles morphology. The dynamic mechanical spectra of the cured products confirmed the absence of any significant short-range network miscibility and revealed substantial enhancements in β-relaxations in all cases, which are normally associated with microdispersed morphologies. Both systems exhibited much higher flexural strength and ductility than the equivalent unmodified epoxy resins even at very low levels of addition. 3.5–5.0%. The surface energy was found to be much lower than that exhibited by the unmodified resin system, and the reduction in water absorption was relatively small. The above effects were much more pronounced for products exhibiting a particulate morphology than for systems that exhibited a co-continuous morphology. © 1994 John Wiley & Sons, Inc.     

Reactive blending of functionalized acrylic rubbers and epoxy resins

A high molecular weight acrylonitrile/butadiene/methacrylic acid (Nipol 1472) rubber is chosen to control processability and mechanical properties of a TGDDM (tetra glycidyl diphenyl methane) based epoxy resin formulation for aerospace composite applications. The physical blend of rubber and epoxy resin, achieved by dissolution of all the components in a common solvent, forms a heterogeneous system after solvent removal and presents coarse phase separation during cure that impairs any practical relevance of this material. A marked improvement of rubberepoxy miscibility is achieved by reactive blending (‘pre‐reaction’) the epoxy oligomer with the functional groups present in the rubber. The epoxy‐rubber ‘adduct’ so obtained appears as a homogeneous system at room temperature and also after compounding with the curing agent. Depending on the nature and extent of interactions developed between the rubber and the epoxy resin during ‘pre‐reaction,’ materials with different resin flow characteristics, distinctive morphologies and mechanical properties after curing were obtained. The effect of ‘pre‐reaction’ on the resin cure reaction kinetics has been also investigated.     

The preparation and properties study of methoxy functionalized silicone‐modified epoxy resins

In this work, a series of siloxane epoxy resins (E3074) were synthesized through reaction of poly(methylphenylsiloxane) (DC‐3074) with epoxy resin. The chemical structure of the resultant epoxy resin was determined by FTIR, GPC, and epoxy equivalent weight (EEW) tests. The mechanical measurements indicated that the tensile strength of E3074 was lower than that of neat epoxy resin after modification, while their elongations at break improved markedly when compared with that of epoxy resin. SEM revealed that the particle size of silicone had a significant effect on the mechanical properties of the modified epoxy resin. TGA results showed that the thermal stability of E3074 serials was better than that of epoxy resin. The char residue of E3074 at 600°C increased with the incremental content of silicone. DMA tests displayed that the addition of silicone effectively enhanced the damping properties of epoxy resin. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40212.     

Morphology and mechanical properties of rubber modified aromatic-ether bismaleimide matrix resins

An aromatic ether bismaleimide (BMI) was modified by copolymerization with various CTBN and ATBN liquid elastomers. Dynamic mechanical (DMA), flexural, and SEM fractography studies indicate that cured specimens containing various amounts of the different elastomers have widely varying morphologies and properties. The experimental parameters of interest in this study included the type of elastomer reactive end group, elastomer acrylonitrile content, elastomer concentration, and cure reaction conditions. The ATBNs are clearly more compatible than CTBNs. CTBN modified compositions show a distinct, low temperature rubber phase mechanical loss dispersion, reduced modulus and ultimate strength values, and only slight improvements in elongation. Cured compositions with small amounts of ATBN elastomers (5 phr), however, show no reduction in modulus but improved elongation and ultimate strength values. The “rubber” domains in these systems are small, typically < 5 μm, and consist of copolymerized BMI and elastomer. DMA data for these systems show no distinct low temperature elastomer peak but a broad “interphase” loss dispersion covering a wide range of temperatures. Failure in the ATBN modified BMIs involves initiation of numerous microcracks with obvious crack deflection at the rubber particles. No cavitation of rubber particles occurs, as is frequently the case with the CTBNs.     

Correlations between dynamic mechanical properties and nodular morphology of cured epoxy resins

Various epoxy resin formulations, based on the diglycidyl ether of bisphenol A (DGEBA) and cured with diethylene triamine (DETA) were studied. Dynamic mechanical measurements were used to characterize changes in mechanical properties as a function of temperature. The morphology of the cured resins was investigated by transmission electron microscopy. Correlations between dynamic mechanical properties and morphology were described and discussed by applying the concept of inhomogeneous (nodular) thermoset morphology. The elastic storage modulus in the glassy state was determined primarily by the internodular matrix, whereas the glass transition of cured resins depended upon the intranodular crosslink density.     

Thermal and mechanical properties of PPO filled epoxy resins compatibilized by triallylisocyanurate

A series of blends has been prepared by adding a poly(phenylene oxide) (PPO), in varying proportions, to an epoxy resin cured with dicyandiamide. All the materials show two‐phase morphology when characterized by SEM and DMA. SEM and DMA indicate that partial mixing exists in all the blends especially with high PPO content. This implies that the epoxy oligomer or low crosslinking density epoxy exists in the PPO phase after curing. The tensile strength and modulus of these blends are nearly independent of the PPO content, while the fracture toughness (G_IC) is improved by PPO. However, the two‐phase particulate morphology is not uniform. In order to improve the uniformity and miscibility, triallylisocyanurate (TAIC) has been used as an in situ compatibilizer for the polymer blends of epoxy and PPO. SEM and DMA reveal improvement of miscibility and solvent resistance for this system. The fracture toughness of these TAIC‐modified systems are also improved by adding TAIC (0–20 phr). © 2000 Society of Chemical Industry     

Morphology and mechanical properties of unidirectional sisal– epoxy composites

Plant fibers are of increasing interest for use in composite materials. They are renewable resources and waste management is easier than with glass fibers. In the present study, longitudinal stiffness and strength as well as morphology of unidirectional sisal–epoxy composites manufactured by resin transfer molding (RTM) were studied. Horseshoe‐shaped sisal fiber bundles (technical fibers) were nonuniformly distributed in the matrix. In contrast to many wood composites, lumen was not filled by polymer matrix. Technical sisal fibers showed higher effective modulus when included in the composite material than in the technical fiber test (40 GPa as compared with 24 GPa). In contrast, the effective technical fiber strength in the composites was estimated to be around 400 MPa in comparison with a measured technical fiber tensile strength of 550 MPa. Reasons for these phenomena are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2358–2365, 2002     

Structure and properties of novel epoxy resins containing naphthalene units and aliphatic chains

Two novel epoxy resins; namely, R1 and R2 were synthesized and characterized. These two resins were isomers and both contained naphthalene units and two symmetric flexible aliphatic ester chains terminated by epoxy groups. To investigate the influence of different structural isomers on the performance of these epoxy resins, they were both cured with various curing agents which results in the choosing of 4,4′-diaminodiphenylmethane (DDM) as the optimized curing agent. The curing technical temperature was obtained from extrapolated plots of T–β curve at different heating rates. The kinetic parameters, the activation energy (E _a) and the reaction order (n) were deduced by Kissnger’s isoconversional method and Crane equation. The moisture absorption and mechanical and thermal properties of the cured epoxy resins were investigated. Experimental results indicated that the R1/DDM and R2/DDM epoxy resins displayed improved mechanical performance without significant decrease in their important inherent properties, e.g., temperature of glass transition (T _g), moisture absorption and thermal properties when compared with the corresponding commercial biphenyl-type epoxy resins. The average inter-segment distances in R1/DDM and R2/DDM systems were 4.46 and 4.88 Å, respectively, which were measured by wide-angle X-ray diffraction. The result showed R1/DDM (1,5-di-substituted) was strongly hindered in comparison with R2/DDM (2,7-di-substituted) and E _a and T _g values of the R1/DDM were slightly higher than those of R2/DDM. Furthermore, mechanical properties and moisture absorption of the R1/DDM were lower than those of R2/DDM. Nevertheless, the position of the substituent only weakly affected the thermal properties and the reaction order (n).     

Influence of hydroxyl functionalized hyperbranched polymers on the thermomechanical and morphological properties of epoxy resins

Rheological, thermomechanical, and morphological properties of blends of two different epoxy resins with hydroxyl functionalized hyperbranched polymers have been studied. The hydroxyl functionalized hyperbranched polymers used in this work had different generation number and different number of terminal groups. The difunctional epoxy resin has been also mixed with a linear aromatic thermoplastic in order to compare its effects with that of the hyperbranched polymers. All the blends have been characterized by linear elastic fracture mechanics (LEFM) testing to evaluate the efficiency of the two types of toughening modifiers. In addition, the water uptake has been evaluated for all the formulations. POLYM. ENG. SCI. 45:225–237, 2005. © 2005 Society of Plastics Engineers