Fracture and adhesion behaviors of epoxy resins modified with poly(amine‐quinone)

An amine‐quinone monomer, i.e. 2,5‐bis(4,4′‐methylenedianiline)‐1,4‐benzoquinone (BB), was synthesized by the Michael addition of 4,4′‐diaminodiphenyl methane with 1,4‐benzoquinone. To evaluate the effect of BB content on the glass transition temperature (T_g) and crosslinking density (ρ) of cured diglycidyl ether of bisphenol A (DGEBA)/BB systems, storage modulus and loss factor measurements were obtained using dynamic mechanical analysis. The mechanical properties of the systems were determined in terms of the fracture toughness, impact strength, and adhesion strength. As a result, the ρ values of the systems were found to decrease systematically as the BB content increased. The fracture toughness and adhesion strength of the systems increased with increasing BB content. These results indicate that the addition of BB into epoxy resins increases the free volume of the epoxy network and absorbs the deformation energy, resulting in an improvement of the mechanical properties of the DGEBA/BB systems. Copyright © 2006 Society of Chemical Industry     

Preparation and properties of UV-autocurable BTDA-based epoxy-multiacrylate resins. Effects of the degree of polymerization and the epoxy type

A series of UV-autocurable epoxy-multiacrylate resins was synthesized, and the effects of degree of polymerization (DP) and epoxy type on their properties were investigated. These autocurable multiacrylate resins possess good pot life and are cured rapidly when exposed to ultraviolet (UV) without the addition of photoinitiator or photosensitizer. The curing rate of the autocurable resins was probably dependent on the number of abstractable hydrogen in epoxy resins. Stress-strain, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used to characterize the properties of cured multiacrylate resins. Increased crosslinking density of cured films improved tensile properties. Increasing the molar ratio of epoxy resin in the multiacrylate resins was found to decrease the effective acrylate concentration of resins and to depress crosslinking density of cured resins, which also resulted in an increased elongation at break but a decreased Young's modulus and breaking strength. Furthermore, the different structures of epoxy resins were used to give wide range properties of cured epoxy-multiacrylate resins with a glass transition temperature (T_g range from 74 to 102°C. The film properties of the multiacrylate resins coated on steel plates were also investigated.     

Synthesis and characterization of fluorinated poly(etherimide)s toughening for carbon fiber‐reinforced epoxy composites

Novel‐fluorinated poly(etherimide)s (FPEIs) with controlled molecular weights were synthesized and characterized, which were used to toughen epoxy resins (EP/FPEI) and carbon fiber‐reinforced epoxy composites (CF/EP/FPEI). Experimental results indicated that the FPEIs possessed outstanding solubility, thermal, and mechanical properties. The thermally cured EP/FPEI resin showed obviously improved toughness with impact strength of 21.1 kJ/m² and elongation at break of 4.6%, respectively. The EP/FPEI resin also showed outstanding mechanical strength with tensile strength of 91.5 MPa and flexural strength of 141.5 MPa, respectively. The mechanical moduli and thermal property of epoxy resins were not affected by blending with FPEIs. Furthermore, CF/EP/FPEI composite exhibited significantly improved toughness with Mode I interlaminar fracture toughness (G_IC) of 899.4 J/m² and Mode II interlaminar fracture toughness (G_IIC) of 1017.8 J/m², respectively. Flexural properties and interlaminar shear strength of the composite were slightly increased after toughening. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Preparation of epoxy-terminated poly(aryl ether sulfone)s and their use as modifiers for epoxy resins

Epoxy-terminated poly(aryl ether sulfone)s (PSE) were prepared by the reaction of epichlorohydrin with hydroxyethyl-terminated polysulfones, which were synthesized from chloro-terminated polysulfones (PSC) and diethanolamine. Both PSE and PSC were used as modifiers for toughening of bisphenol A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulfone. The mechanical, thermal, and dynamic viscoelastic properties of the modified resins were examined and compared to the parent epoxy resin. The effectiveness of PSC was larger than that of PSE. The fracture toughness, K_IC, for the modified resin increased 45% at slight expense of its mechanical properties on 20 wt % addition of PSC (M_w 5300). These results were discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system.     

Effect of the physical and mechanical properties of epoxy resins on the adhesion behavior of epoxy/copper leadframe joints

In this study, the adhesion strength of three epoxy resins, which are used as basic materials for epoxy molding compound (EMC) in microelectronics, to copper leadframe was determined using the peel test. The epoxy resins used were O-cresol Novolac (OCN), dicyclopentadiene (DCPD), and biphenyl sulfide (BIPHS) epoxy resins. It was found that DCPD showed the highest peel strength and OCN had the lowest value. The difference in the peel strength was explained by investigating the physical and mechanical properties, as well as the surface properties of the epoxy resins. These properties included the surface energy, viscosity and gelation time, fracture toughness, and the coefficient of thermal expansion. As a result of the lower viscosity of BIPHS and DCPD than OCN epoxy resin, BIPHS and DCPD have a better peel strength than OCN. The DCPD resin has a better peel strength than BIPHS because of its higher fracture toughness.     

Mode I and Mode II delamination resistance and mechanical properties of woven glass/epoxy–PU IPN composites

The effect of polyurethane on the mechanical properties and Mode I and Mode II interlaminar fracture toughness of glass/epoxy composites were studied. Polyurethanes (PU) synthesized using polyols and toluene diisocyanate were employed as modifier for epoxy resin by forming interpenetrating polymer network. The PU/Epoxy IPN was used as matrix material for GFRP. PU modified epoxy composite laminates having varying PU contents were prepared. The effect of PU content on the mechanical properties like interlaminar fracture toughness (Mode I, G_1c and Mode II, G_IIc), tensile strength, flexural strength, and Izod impact strength were studied. The morphological studies were conducted on the fractured surface of the composite specimen by scanning electron microscopy (SEM). Tensile strength, flexural strength, and impact strength of PU‐modified epoxy composite laminates were found to increase inline with interlaminar fracture toughness (G_1c and G_IIc) with increasing PU content to a certain limit and then it was found to decrease with increase in PU content. It was observed that toughening of epoxy with PU increases the Mode I and Mode II delamination toughness up to 17 and 120% higher than that of untoughened composite specimen, respectively. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Toughening of aromatic diamine-cured epoxy resins by modification with hybrid modifiers composed of N-phenylmaleimide–styrene copolymers and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers

Hybrid modifiers composed of N-phenylmaleimide–styrene copolymers (PMS), and N-phenylmaleimide–styrene–p-hydroxystyrene terpolymers (PMSH) containing pendent p-hydroxyphenyl groups as functionalities, were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p,p′-diaminodiphenyl sulphone. The hybrid modifiers were effective in toughening the epoxy resin. When using the modifier composed of 10 wt% PMS (M?_w 313000) and 2.5 wt% PMSH (2.5 mol% p-hydroxystyrene units, M?_w 316000), the fracture toughness (K_IC) for the modified resins increased 100% with no deterioration in the flexural properties and the glass transition temperature. The improvement in toughness of the epoxy resins was attained because of the co-continuous phase structure and the improvement in interfacial adhesion. The toughening mechanism is discussed in terms of the morphological characteristics of the modified epoxy resin systems.     

Toughening of aromatic diamine-cured trifunctional epoxy resins by modification with N-phenylmaleimide–styrene copolymers containing pendant p-hydroxyphenyl groups

N-Phenylmaleimide (PMI)–N-(p-hydroxy)phenylmaleimide (HPMI)–styrene (St) terpolymers (HPMS), containing pendant p-hydroxyphenyl (HP) groups, were prepared and used to improve the toughness of triglycidyl aminocresol epoxy resin cured with p,p′-diaminodiphenyl sulfone. HPMS was effective as a modifier for the toughening of the epoxy resin. When using 15 wt % of HPMS (1.0 mol % HP unit, M_w 129,000), the fracture toughness (K_IC) for the modified resin increased 190% with a medium loss of flexural strength. The toughening of epoxies could be attained because of the cocontinuous phase structure of the modified resins. The decrease in flexural strength was suppressed to some extent by introducing a functional group into the modifier. The toughening mechanism was discussed in terms of the morphological behavior of the modified epoxy resin system. © 1995 John Wiley & Sons, Inc.     

Crosslinking by etherification of bisepoxide with adducts of divalent metal salts of p-aminobenzoic acid and anhydride

Crosslinking by etherification of a large excess of bisepoxide with adducts of divalent metal salts of p-aminobenzoic acid and dicarboxylic acid anhydride was investigated. As the divalent metals, Mg and Ca were selected and hexahydrophthalic anhydride was the anhydride used. As the bisepoxide, bisphenol A diglycidyl ether was used. In the crosslinking reactions, the metal carboxylate groups showed catalytic action and the Ca carboxylate group showed higher catalytic activity than did the Mg carboxylate group. Therefore, the crosslinking reactions were supposed to proceed via an ionic mechanism in which the carboxylate anion is concerned. As for the physical and other properties of the metal-containing cured resins, the T_g determined by dynamic mechanical properties increased with increase in the metal content. Also, the heat-distortion temperature increased with increase in the metal content. Interestingly, the cured resins showed very high impact strength and the strength increased markedly with decrease in the T_g. Scanning electron micrographs for fracture surfaces of the cured resins with high impact strength showed uneven patterns, which suggests microphase separation. From TGA and DTA, it was suggested that the metal carboxylate groups accelerated thermal decomposition. In addition, the cured resins exhibited high boiling water and water resistances. © 1996 John Wiley & Sons, Inc.     

Toughening mechanism of rubber reinforced epoxy composites by thermal and microwave curing

The carboxyl terminated polybutadiene (CTBN) is utilized to improve the toughness of diglycidylether of bisphenol A epoxy cured by heat and microwave. The change of viscosity, chemical groups, and the glass transition temperature (T_g) of system are analyzed. The impact performance is characterized to evaluate the fracture toughness, and tensile properties also are investigated. The fracture morphologies are observed by the scanning electron microscopy for exploring toughening mechanism. The viscosity results indicate that viscosity of system increases with increasing of CTBN, demonstrating the formation of precrosslinking and interpenetrating network structure of two phases. The Fourier transform infrared spectrometer results show that effective chemical bonds are formed between CTBN and epoxy resins. The T_g decreases with introducing CTBN, indicating the decline of crosslinking density, which further suggests inherent three‐dimensional structure have been changed. The impact strength and energy increase with increasing of CTBN, and reach a maximum value of 5.92 kJ/m² and 0.13 kJ at 15% for thermal curing, respectively, increased by 36.8% and 23.1% relative to microwave curing system, while tensile strength and modulus reach the optimum at 5%. Scanning electron microscopy observation finds that “plastic tensile” and “microvoid” deriving from “sea‐island” structure exist, presenting the ductile fracture features. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45767.     

Synthesis and properties of urethane elastomer-modified epoxy resin having hydroxymethyl group

Synthesis and properties of urethane elastomer-modified epoxy resins were studied. The urethane elastomer-modified epoxy resins were synthesized by the reaction of a 4-cresol type epoxy compound having hydroxymethyl groups (EPCDA) with isocyanate prepolymer. The structure was identified by IR, ¹H NMR and GPC. These epoxy resins (EPCDATDI) were mixed with a commercial epoxy resin (DGEBA) in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′-diaminodiphenylmethane and 3-phenylenediamine (molar ratio 6:4) as a hardener. The curing behaviour of these epoxy resins was studied by DSC. The higher the concentration of EPCDATDI, the higher the onset temperature and the smaller the rate constant (k) of the exothermic cure reaction were. It was considered that the ratio of hydroxymethyl group to epoxide group was very small and the molecular weight of EPCDATDI was large. Therefore, the accelerating effect of the hydroxymethyl group on the epoxide–amine reaction was cancelled by the retardant effect of increased molecular weight and viscosity, and decreased molecular motion. Toughness was estimated by Izod impact strength and fracture toughness (K_1C). On addition of 10 wt% EPCDATDI with low molecular weight (M?_n 6710, estimated by GPC using polystyrene standard samples), Izod impact strength and K_1C increased by 70% and 60%, respectively, compared with unmodified epoxy resin. Glass transition temperatures (T_g) for the cured epoxy resins mixed with EPCDATDI measured by dynamic mechanical spectrometry were the same as those of unmodified epoxy resin. The storage modulus (E′) at room temperature decreased with increasing concentration of EPCDATDI. Toughness and dynamic mechnical behaviour of cured epoxy resin systems were studied based on the morphology.     

Synthesis of liquefied corn barn-based epoxy resins and their thermodynamic properties

The liquefied corn barn-based epoxy resin (LCBER) was synthesized through the glycidyl etherification reaction from liquefied corn barn (LCB), which has groups of bound phenol, and epichlorohydrin under alkali conditions. The average molecular weights of LCB and LCBER in various liquefaction conditions were examined. The thermodynamic properties of thermosetting resin cured by polyamide-650 (PA-650) were evaluated. It was found that the macromolecular chain and epoxy function of the resins would be a dominant factor for crosslinking density and properties of the cured LCBER. The cured liquefied CB-based epoxy resin (LCBER-30) using the corresponding LCB at 30 min (LCB-30) as raw materials had much macromolecular exhibited higher glass-transition and decomposition temperatures at 5% weight loss (T_d), but worse shear strength in comparison with the other LCBER ones. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Mechanical,thermal, and viscoelastic response of novel in situ CTBN/POSS/epoxy hybrid composite system

The present study focuses on the preparation of a novel hybrid epoxy nanocomposite with glycidyl polyhedral oligomeric silsesquioxane (POSS) as nanofiller, carboxyl terminated poly(acrylonitrile‐co‐butadiene) (CTBN) as modifying agent and diglycidyl ether of bisphenol A (DGEBA) as matrix polymer. The reaction between DGEBA, CTBN, and glycidyl POSS was carefully monitored and interpreted by using Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). An exclusive mechanism of the reaction between the modifier, nanofiller, and the matrix is proposed herein, which attempts to explains the chemistry behind the formation of an intricate network between POSS, CTBN, and DGEBA. The mechanical properties, such as tensile strength, and fracture toughness, were also carefully examined. The fracture toughness increases for epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems with respect to neat epoxy, but for hybrid composites toughening capability of soft rubber particles is lost by the presence of POSS. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the toughening mechanism. The viscoelastic properties of epoxy/CTBN, epoxy/POSS, and epoxy/CTBN/POSS hybrid systems were analyzed using dynamic mechanical thermal analysis (DMTA). The storage modulus shows a complex behavior for the epoxy/POSS composites due to the existence of lower and higher crosslink density sites. However, the storage modulus of the epoxy phase decreases with the addition of soft CTBN phase. The T_g corresponding to epoxy‐rich phase was evident from the dynamic mechanical spectrum. For hybrid systems, the T_g is intermediate between the epoxy/rubber and epoxy/POSS systems. Finally, TGA (thermo gravimetric analysis) studies were employed to evaluate the thermal stability of prepared blends and composites. POLYM. COMPOS., 37:2109–2120, 2016. © 2015 Society of Plastics Engineers     

Modification of epoxy resins with poly(aryl ether ketone)s

Poly(aryl ether ketone)s were used as modifiers for bisphenol-A diglycidyl ether epoxy resin (AER 331) cured with methyl hexahydrophthalic anhydride. Poly(phthaloyl diphenyl ether) (PPDE), soluble in the uncured epoxy resin without using solvents, was prepared by the Friedel-Crafts reaction of phthaloyl chloride and diphenyl ether. The mechanical, thermal, and dynamic viscoelastic properties of the modified resins with PPDE were examined and compared to the parent resin (AER 331). The fracture toughness, K_IC, for the modified resins increased at no expense to their mechanical and thermal properties on 10 wt % addition of PPDE with molecular weights of more than 17,000. The toughening mechanism is discussed based on the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system.     

Modification of Acid Anhydride-cured Epoxy Resins By N-Phenyl- maleimide–Styrene Copolymers and N-Phenylmaleimide–Styrene– p-Hydroxystyrene Terpolymers

N-Phenylmaleimide–styrene copolymers (PMS) and reactive N-phenylmaleimide–styrene–p-hydroxystyrene (HSt) terpolymers (PMSH) containing p-hydroxyphenyl groups were used to improve the toughness of bisphenol A diglycidyl ether epoxy resin cured with methyl hexahydrophthalic anhydride. PMS and PMSH were effective modifiers for epoxies. The morphologies of the modified resins depended on modifier structure and content. The most effective modification for the cured resins was attained because of the co-continuous structure of the modified resins in both PMS and PMSH modification systems. When using 15wt% of PMS (M¯_w 125000), the fracture toughness, K_IC, for the modified resin increased by 230%, with retention of flexural modulus and glass transition temperature, but with a loss of flexural strength, compared with the values for the unmodified epoxy resin. When using PMSH as the reactive modifier, the efficiency decreased with increase in HSt content, because of the increasing extent of dispersion of the PMSH-rich continuous phases. In the modification with 10wt% PMSH (1·0mol% HSt unit, M¯_w 294000), the modified resin had balanced physical properties. © of SCI.     

Functionalized liquid natural rubber and liquid epoxidized natural rubber: A promising green toughening agent for polyester

Toughened unsaturated polyester resins (UPRs) were prepared using two different reactive rubbers, namely, liquid natural rubber (LNR) and liquid epoxidized natural rubber (LENR). The effect of varying amounts of LNR and LENR on the morphology, thermal, and mechanical properties of UPR were evaluated. Fourier Transform Infrared spectroscopy was used to investigate the probable crosslinking reaction and changes in the functional groups on crosslinking. Field emission scanning electron microscopy and infinite focus microscopy were used to study the morphology of fracture surfaces. Tensile test showed that both the rubber‐modified resins (1.5 wt %) improved tensile strength. The viscoelastic properties and thermal stability of the toughened polyesters were evaluated using dynamic mechanical thermal analysis and thermogravimetric analysis, respectively. A slight reduction in the glass transition temperature (T_g) of the polyester was reported on the addition of both the rubbers. An increment in impact strength and fracture toughness was observed at 1.5 wt % for LNR and 4.5 wt % for LENR‐modified UPR. The results showed that both the liquid rubbers improved the mechanical properties of UPR. However, LENR‐modified UPR exhibited a more significant improvement in the mechanical properties compared to LNR‐modified UPR. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41292.     

Preparation and properties of high performance phthalide‐containing bismaleimide modified epoxy matrices

A series of intercrosslinked networks formed by diglycidyl ether of bisphenol A epoxy resin (DGEBA) and novel bismaleimide containing phthalide cardo structure (BMIPP), with 4,4′‐diamino diphenyl sulfone (DDS) as hardener, have been investigated in detail. The curing behavior, thermal, mechanical and physical properties and compatibility of the blends were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), notched Izod impact test, scanning electron microscopy (SEM) and water absorption test. DSC investigations showed that the exothermic transition temperature (T_p) of the blend systems shifted slightly to the higher temperature with increasing BMIPP content and there appeared a shoulder on the high‐temperature side of the exothermic peak when BMIPP content was above 15 wt %. TGA and DMA results indicated that the introduction of BMIPP into epoxy resin improved the thermal stability and the storage modulus (G′) in the glassy region while glass transition temperature (T_g) decreased. Compared with the unmodified epoxy resin, there was a moderate increase in the fracture toughness for modified resins and the blend containing 5 wt % of BMIPP had the maximum of impact strength. SEM suggested the formation of homogeneous networks and rougher fracture surface with an increase in BMIPP content. In addition, the equilibrium water uptake of the modified resins was reduced as BMIPP content increased. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Structure and viscoelastic properties of epoxy resins prepared from o-cresol novolacs

The relation between the structure and viscoelastic properties of the epoxy resins prepared from o-cresol novolacs was studied. Our model epoxy resins were two kinds of epoxy compounds synthesized from three-nuclei and four-nuclei o-cresol novolacs. In addition to these models, a commercially available o-cresol novolac-type epoxy resin was also studied. Each of the three epoxy compounds was cured with one of three kinds of novolacs, which were starting materials of the above-mentioned epoxy resins. Characteristic properties of the cured resins, such as glass transition temperature (T_g), average molecular weight between crosslinking points (M¯_c), and front factor (?) were obtained. It was concluded that the number of functional groups contained in the curing system almost dominated the viscoelastic properties of the cured resins.     

Toughening of epoxy systems by brominated epoxy

Blends of brominated epoxy (BE) and conventional epoxy resins were studied following curing with aliphatic triethylenetetramine (TETA), etheric (polyether diamine‐ PEA4), and aromatic (3,3′‐diamino diphenyl sulfone [DDS]) hardeners. The addition of BE resulted in an increase in T_g in all tested blends. Blends with 50 wt% BE cured with TETA demonstrated an increase in flexural modulus and flexural strength, while preserving the elongation. Blends with 40 wt% BE cured with PEA4 and 50 wt% BE cured with DDS resulted in a significant enhanced tensile elongation. The shear strength of all cured systems decreased moderately with the addition of BE exhibiting a mixed mode failure. Analysis of the fracture morphology using electron microscopy supported the increase of toughness levels as a result of incorporating BE to conventional epoxy. A unique nodular and rough fracture morphology was obtained, which is related to a toughening mechanism caused by the addition of BE. It was concluded that blends of BE and conventional epoxy could be used as structural adhesives having high T_g, enhanced mechanical properties and increased toughness. POLYM. ENG. SCI., 59:206–215, 2019. © 2018 Society of Plastics Engineers     

Influence of Skydrol immersion at elevated temperatures on the thermo-mechanical properties of a high-Tg anhydride epoxy resin toughened with a hydroxy-terminated polyester

Currently, the application of composites in aerospace parts exposed to higher temperatures and in aggressive media is still severely limited. To replace metal alloys, alternative resins systems with suitable long-term heat resistance are needed. In this study, the effect of the aviation hydraulic fluid Skydrol on the thermal and mechanical properties of a high-T_g, anhydride-cured epoxy resin in the unmodified and toughened state at elevated temperature is investigated. An aliphatic polyester diol was selected as an intrinsic toughener and its impact on the thermal, mechanical, and aging properties was determined. Experimental characterization of the aging effects is carried out with dynamic-mechanical characterization, infrared spectroscopy, and electron dispersion x-ray spectroscopy. In addition, the fracture toughness and the fatigue crack propagation behavior are determined. Initially, the toughened system shows an improved fracture toughness. Since oxidation is blocked by the Skydrol fluid only thermal degradation takes place as determined by the decrease in glass transition temperature T_g and network density. The thermal degradation leads to a tougher behavior, which is observed in both systems in static and dynamic mode with toughness decreasing with aging time again.