Thermal and mechanical properties of polysulfide/epoxy copolymer system: the effect of anhydride content

Polymerization of a ternary system containing polysulfide (PS), as a liquid elastomer, diglycidylether of bisphenol A resin, and phthalic anhydride was conducted using “design of experiment” technique. The polymerization progress with respect to concentration variations of components were studied by Fourier transform infrared spectroscopy. Fourier transform infrared spectroscopy studies showed that the anhydride plays a decisive role in curing reaction so that, in its absence, the epoxy/PS mixture becomes gel in about 2 hr, whereas, by addition of the anhydride, the pot life of the system can be extended to 48 hr. The cured samples were investigated by thermal gravimetry analysis and differential scanning calorimetry to evaluate thermal properties. Thermal gravimetry analysis and differential scanning calorimetry results indicated that two different soft and hard segments are formed, which have different thermal decompositions. The soft segment consists of loose etheric bonds, which are attributed to PS, and the hard segment is formed during the etherification and esterification reactions of the epoxy resin. Tensile strength test was performed to investigate the mechanical properties of PS/epoxy/anhydride‐cured systems. The results showed that the tensile strength, elongation‐at‐break, and the fracture energy of specimens are essentially dependent on PS/anhydride ratios. Two different segments impart high strength and ductility simultaneously. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of new nonionic curing agent on curing kinetics and mechanical properties of epoxy resin

The current research work presents a novel nonionic curing agent (AEDA) synthesized by utilizing ethylene glycol diglycidyl ether (EGDE), 3,4-dimethoxyaniline (DI), and triethylenetetramine (TETA). Infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structure of AEDA curing agent. Non-isothermal scanning calorimetry was used to determine the activation energy and curing conditions of epoxy resin in the curing process. An impact testing machine, a tensile testing machine and a scanning electron microscope (SEM) were used to analyze the impact strength, tensile strength, bending strength, and micromorphology of the AEDA/E-51 system with different mass ratios. The results show that AEDA is an effective high-temperature curing agent. For the AEDA/E-51 system with the optimal mass ratio of 10:100, the best curing temperature is 92.15°C, and the post-curing temperature is 135.65°C. Furthermore, the apparent activation energy (E_a) of 1670 J/mol, the pre-exponential factor (A) of 3.7 × 10^?4, and the reaction series (n) value of 0.76 are obtained for the AEDA/E-51 system. The impact strength of AEDA/E-51 epoxy resin polymer is 7.82 kJ/m², tensile strength is 14.2 MPa, and bending strength is 18.92 MPa. The micromorphological results of the AEDA/E-51 system are consistent with the results of DSC test and mechanical properties test. Hence, this study provides theoretical support for the practical applications of AEDA as curing agent.     

Curing kinetics,thermal, mechanical,and dielectric properties based on o‐cresol formaldehyde epoxy resin with polyhedral oligomeric (N‐aminoethyl‐γ‐amino propyl)silsesquioxane

The curing reaction and kinetics of o‐cresol formaldehyde epoxy resin (o‐CFER) with polyhedral oligomeric silsesquioxane of N‐aminoethyl‐γ‐amino propyl group (AEAP‐POSS) were investigated by differential scanning calorimetry (DSC). The thermal, mechanical, and dielectric properties of o‐CFER/AEAP‐POSS nanocomposites were investigated with thermogravimetric analysis (TGA), torsional braid analysis (TBA), tensile tester, impact tester, and electric analyzer, respectively. The results show that the activation energy (E) of curing reaction is 58.08 kJ/mol, and the curing reaction well followed the ?esták‐Berggren (S‐B) autocatalytic model. The glass transition temperature (T_g) increases with the increase in AEAP‐POSS content, and reaches the maximum, 107°C, when the molar ratio (N_s) of amino group to epoxy group is 0.5. The nanocomposites containing a higher percentage of AEAP‐POSS exhibited a higher thermostability. The AEAP‐POSS can effectively increase the mechanical properties of epoxy resin, and the tensile and impact strengths are 2.84 MPa and 143.25 kJ m^?2, respectively, when N_s is 0.5. The dielectric constant (ε), dielectric loss factor (tan δ), volume resistivity (ρ_v), and surface resistivity (ρ_s) are 4.98, 3.11 × 10^?4, 3.17 × 10¹² Ω cm³, and 1.41 × 10¹² Ω cm², respectively, similarly at N_s 0.5. Copyright © 2009 John Wiley & Sons, Ltd.     

Poly(ether ether ketone)‐bischromenes: Synthesis,characterization, and influence on thermal,mechanical, and thermo mechanical properties of epoxy resin

Poly(ether ether ketone) s with terminal propargyl groups (PEEK‐PR) were synthesized from hydroxyl terminated PEEK (PEEKTOH) and characterized. The heat‐triggered polymerization of PEEK‐PR to poly bischromenes having PEEK backbone was confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetric studies. PEEK‐PR was blended with a bisphenol based epoxy resin‐diamino diphenylsulphone system in different proportions and cured to form PEEK‐bischromene‐interpenetrated‐epoxy‐amine networks. Tensile strength and elongation of the cured blends increased up to 10‐phr loading of PEEK‐PR and then declined. Tensile moduli of all formulations were comparable. Fracture toughness increased by a maximum of 33%, and the fractured surface morphology showed a ductile fracture. The blends exhibited slightly lower glass transition temperature to that of the neat epoxy‐amine system. A reference sample of epoxy‐amine was processed with the optimum loading of the precursor polymer, PEEKTOH, and compared its properties with the PEEK‐PR incorporated epoxy systems. In this way, it is found that the incorporation of addition curable propargylated PEEK increases the strength characteristics with adequate thermal stability and fracture toughness for high‐performance structural applications.     

Diglycidyl ether of bisphenol‐A epoxy resin modified using poly(ether ether ketone) with pendent tert‐butyl groups

Bisphenol‐A‐based difunctional epoxy resin was modified with poly(ether ether ketone) with pendent tert‐butyl groups (PEEKT). PEEKT was synthesized by the nucleophilic substitution reaction of 4,4′‐difluoro benzophenone with tert‐butyl hydroquinone in N‐methyl‐2‐pyrrolidone. Blends with various amounts of PEEKT were prepared by melt‐mixing. All the blends were homogeneous in the uncured state. The glass transition temperature of the binary epoxy/PEEKT blends was predicted using several equations. Reaction‐induced phase separation was found to occur upon curing with a diamine 4,4′‐diaminodiphenyl sulfone. The phase morphology of the blends was studied using scanning electron microscopy. From the micrographs, it was found that PEEKT‐rich phase was dispersed in a continuous epoxy matrix. The domain size increased with the amount of PEEKT in the blends. The increase in domain size was due to the coalescence of the domains after phase separation. Dynamic mechanical analysis of the blends gave two peaks corresponding to epoxy‐rich phase and thermoplastic‐rich phase. The tensile strength and modulus of the blends remained close to that of the unmodified resin, while the flexural properties decreased with the addition of PEEKT to epoxy resin. The fracture toughness of the epoxy resin increased with the addition of PEEKT. Investigation of the fracture surfaces revealed evidences for local plastic deformation of the matrix, crack pinning, crack path deflection, and ductile tearing of PEEKT‐rich phase. Thermogravimetric analysis revealed that the initial decomposition temperature of the blends were close to that of the unmodified resin. Finally, the properties of the blends were compared with other modified PEEK/epoxy blends. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2481–2496, 2007     

Thermal and electrical behavior of hybrid thermosets based on epoxy and maleimide resins cured with p-aminobenzoic acid

Two thermoset systems based on maleimides and diglycidyl ether of bisphenol A (DGEBA) cured with p-aminobenzoic acid were characterized in terms of thermal and electrical behavior. Thermal characterization has been undertaken by means of thermogravimetric analysis in nitrogen atmosphere up to 600°C using simultaneous thermogravimetric/Fourier transform infrared/mass spectrometry (TG/FT-IR/MS) analysis. In the first stage of thermal degradation, the global kinetic parameters [activation energy (E_a) and preexponential factor (log A₁ (s⁻¹))] were calculated using the isoconversional method of Friedman. The energies variation as well as the shape of the differential thermal analysis curves suggests that the thermal decomposition process occurred in multiple stages. The evolved gases analysis was conducted by simultaneous TG/FT-IR/MS coupled techniques. Dielectric relaxation spectroscopy characterization was also made.     

Environmentally benign green composites based on epoxy resin/bacterial cellulose reinforced glass fiber: Fabrication and mechanical characteristics

Bio-based bacterial cellulose (BC) epoxy composites were manufactured and their mechanical properties were examined. The BC was initially fabricated from Vietnamese nata de coco by means of alkaline pretreatment followed by solvent exchange. The obtained fibers were dispersed in epoxy resin (EP) by both mechanical stirring and ultrasonic techniques. The resulting blend was used as the matrix for glass-fiber (GF) composite fabrication using a prepreg method followed by multiple hot-press-curing steps. The morphology, mechanical characteristics and mode-I interlaminar fracture toughness of the fabricated composites were investigated. With a 0.3-wt% BC content, the mode-I interlaminar fracture toughness for both crack initiation and crack propagation were improved by 128.8% and 1110%, respectively. The fatigue life was dramatically extended by a factor of 12, relative to the unmodified composite. Scanning electron microscopy images revealed that the BC plays a vital role in increasing the interlaminar fracture toughness of a GF/EP composite via the mechanisms of crack reflection, debonding and fiber-bridging.     

Novel nanocomposites based on epoxy resin and modified magnesium hydroxide: Focus on flame retardancy and mechanical properties

In this work, a novel multifunctional organic‐inorganic hybrid flame agent (AM‐MEL) was prepared from magnesium hydroxide nanosheets decorated by nitrilotrimethylene triphosphonic acid and melamine. Then, an intrinsic flame‐retardant epoxy resin (EP) was prepared by covalently incorporating AM‐MEL nanoparticles. Meanwhile, ammonium polyphosphate (APP) was added into EP to form an intumescent flame retardant system with AM‐MEL. The chemical structure of AM‐MEL was characterized by Fourier transform infrared spectra, X‐ray photoelectron spectroscopy, and scanning electron microscopy. With the incorporation of 5 wt% AM‐MEL and 15 wt% APP, EP/AM‐MEL/APP could reach a limiting oxygen index value of 32.0% and achieve UL‐94 V‐0 rating, along with 88.0%, 70.0%, 81.5%, and 87.3% decrease in the peak heat release rate, total heat release, total smoke production, and the peak CO production rate, respectively, with respect to that of pure EP. The mechanisms of its flame retardant and smoke suppression were investigated.     

Thermal and dynamic mechanical properties of epoxy resin/poly(urethane‐imide)/polyhedral oligomeric silsesquioxane nanocomposites

Linear isocyanate‐terminated poly(urethane‐imide) (PUI) with combination of the advantages of polyurethane and polyimide was directly synthesized by the reaction between polyurethane prepolymer and pyromellitic dianhydride (PMDA). Then octaaminophenyl polyhedral oligomeric silsesquioxane (OapPOSS) and PUI were incorporated into the epoxy resin (EP) to prepare a series of EP/PUI/POSS organic–inorganic nanocomposites for the purpose of simultaneously improving the heat resistance and toughness of the epoxy resin. Their thermal degradation behavior, dynamic mechanical properties, and morphology were studied with thermal gravimetric analysis (TGA), dynamic mechanical analysis (DMA), and transmission electron microscope (TEM). The results showed that the thermal stability and mechanical modulus was greatly improved with the addition of PUI and POSS. Moreover, the EP/PUI/POSS nanocomposites had lower glass transition temperatures. The TEM results revealed that POSS molecules could self assemble into strip domain which could switch to uniform dispersion with increasing the content of POSS. All the results could be ascribed to synergistic effect of PUI and POSS on the epoxy resin matrix. Copyright © 2010 John Wiley & Sons, Ltd.     

Correlation between nanohole volume and mechanical properties of amine‐cured epoxy resin blended with poly(ethylene oxide)

A set of diglycidylether of bisphenol‐A (DGEBA)/4,4′‐diaminodiphenylmethane (DDM) epoxy matrix modified with poly(ethylene oxide) (PEO), pre‐cured at two different temperatures, was examined by positron annihilation lifetime spectroscopy (PALS). The aim was to investigate the correlation between local free volume and mechanical properties. A negative deviation from the linear additivity rule of the local free volume is observed at both cure schedules. Using together the local free volume and mechanical results allows to conclude that the cure temperature makes small contribution to the flexural strength and modulus of blends but is responsible for the composition‐dependent rise of the fracture toughness. It is proposed that this behavior is a consequence of the nearest‐neighbor intrachain contacts or self‐association of the epoxy‐OH groups during cure leading to a non‐uniform space distribution of the DGEBA–PEO contacts, which causes the deflection of the crack path. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal degradation and evolved gas analysis: A polymeric blend of urea formaldehyde (UF) and epoxy (DGEBA) resin

A polymeric blend has been prepared using urea formaldehyde (UF) and epoxy (DGEBA) resin in 1:1 mass ratio. The thermal degradation of UF/epoxy resin blend (UFE) was investigated by using thermogravimetric analyses (TGA), coupled with FTIR and MS. The results of TGA revealed that the pyrolysis process can be divided into three stages: drying process, fast thermal decomposition and cracking of the sample. There were no solid products except ash content for UFE during combustion at high temperature. The total mass loss during pyrolysis at 775 °C is found to be 97.32%, while 54.14% of the original mass was lost in the second stage between 225 °C and 400 °C. It is observed that the activation energy of the second stage degradation during combustion (6.23 × 10⁻⁴ J mol⁻¹) is more than that of pyrolysis (5.89 × 10⁻⁴ J mol⁻¹). The emissions of CO₂, CO, H₂O, HCN, HNCO, and NH₃ are identified during thermal degradation of UFE.     

Thermal degradation behaviors of epoxy resin/POSS hybrids and phosphorus–silicon synergism of flame retardancy

Epoxy resin (EP)/polyhedral oligomeric silsesquioxane (POSS) hybrids were prepared based on octavinyl polyhedral oligomeric silsesquioxane (OVPOSS) and phosphorus‐containing epoxy resin (PCEP). The PCEP was synthesized via the reaction between bisphenol A epoxy resin (DGEBA) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO). The structure and morphology of PCEP/OVPOSS hybrids were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Differential scanning calorimetry revealed that the PCEP/OVPOSS hybrids possessed higher glass transition temperatures than that of PCEP. The thermal stability of the PCEP/OVPOSS hybrids was studied using thermogravimetric analysis (TGA). The TGA results illustrated the synergistic effect of phosphorus–silicon of flame retardancy: phosphorus promotes the char formation, and silicon protects the char from thermal degradation. The thermal degradation mechanism of the PCEP/OVPOSS hybrids was investigated by real time Fourier transform infrared spectra and pyrolysis/gas chromatogram/mass spectrometry (Py‐GC/MS) analysis. It was found that OVPOSS migrated to the surface of the matrix and then sublimed from the surface in nitrogen; whereas, the vinyl groups of OVPOSS were oxidated to form a radical trap which could react with pyrolysis radicals derived from PCEP to form the branched and crosslinked structure in air. The combustion behaviors of the hybrids were evaluated by micro combustion calorimetry. The addition of OVPOSS obviously decreased the value of peak heat release rate and total heat release of the hybrids. Moreover, scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy were used to explore the char residues of the PCEP and the hybrids. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 693–705, 2010     

Toughening of highly crosslinked epoxy resins by reactive blending with bisphenol A polycarbonate. II. Yield and fracture behavior

The yield and fracture behavior of highly crosslinked epoxy resin modified by a reactive blending process carried out in the presence of bisphenol A polycarbonate has been studied. It was found that the fracture toughness of this blend system increases markedly with increasing PC content in the blend. Scanning electron microscopy of the fractured surfaces indicated a crack blunting mechanism as the main source of energy dissipation in the various investigated blend compositions. No evidence of phase separation of the minor component during the curing and postcuring steps was observed. The yield data were correlated with the fracture toughness data to evaluate the extent of crack-tip blunting. © 1994 John Wiley & Sons, Inc.     

Synthesis of a novel epoxy resin containing diphenylether moiety and thermal properties of its cured polymer with phenol novolac

A new type of epoxy resin containing 4,4′-diphenylether moiety in the backbone (2) was synthesized, and was confirmed by gel permeation chromatography, infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. In addition, in order to evaluate the influence of 4,4′-diphenylether moiety in the structure, epoxy resins having 4,4′-biphenylene moiety (4) and having 1,4-phenylene moiety (6) in place of 4,4′-diphenylether moiety were synthesized. The cured polymer obtained through the curing reaction between the new diphenylether-containing epoxy resin and phenol novolac was used for making a comparison of its thermal and physical properties with those obtained from 4, 6, and bisphenol-A (4,4′-isopropylidenediphenol) type epoxy resin. The cured polymer obtained from 2 showed markedly higher anaerobic char yield at 700°C of 44.0 wt %, higher fracture toughness, and higher mechanical strength and modulus. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3687–3693, 1999     

Intractable high‐Tg thermoplastics processed with epoxy resin: Interfacial adhesion and mechanical properties of the cured blends

The intractable, high‐temperature‐resistant thermoplastics (TPs) polyphenylenether (PPE) and polyetherimide (PEI) were processed by dissolution into epoxy–amine precursors and a subsequent reaction of the precursors. Because the TP concentration was higher than the critical concentration, the phase separation produced a dispersion of crosslinked thermoset (TS) particles into a TP matrix. The morphology of the blends was examined with transmission electron microscopy and dynamic mechanical thermal spectroscopy, which showed completion of the phase separation. The interfacial adhesion at the TP‐matrix/TS‐particle interface was estimated on TP/TS bilayers to be 10 J/m² in PEI blends, whereas it was 70 J/m² in PPE blends, where there is strong evidence for in situ grafting between PPE phenolic chain ends and glycidyl functions of the reactive TS. Yielding in the compressive mode occurred at an intermediate yield stress between the components' values, and the anelastic deformation was separated from the plastic deformation. Fractures in the tensile mode occurred through debonding at the matrix/particle interfaces and coalescence of these defects, which led to microcrack formation and brittle failure. Mode I fracture toughness was, therefore, higher for PPE blends than for PEI blends, a result of the higher interfacial adhesion. However, a decrease from pure TP was observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 363–373, 2001     

Preparation and cryogenic mechanical properties of epoxy resins modified by poly(ethersulfone)

A thermoplastic, poly(ethersulfone) (PES) was used to modify a bisphenol‐F based epoxy resin cured with an aromatic diamine. The initial mixtures before curing, prepared by melt mixing, were homogeneous. Scanning electron microscopy (SEM) micrographs of solvent‐etched fracture surfaces of the cured blends indicated that phase separation occurred after curing. The cryogenic mechanical behaviors of the epoxy resins were studied in terms of tensile properties and Charpy impact strength at cryogenic temperature (77 K) and compared to their corresponding behaviors at room temperature (RT). The addition of PES generally improved the tensile strength, elongation at break, and impact strength at both RT and 77 K except the RT tensile strength at 25 phr PES content. It was interesting to observe that and the maximum values of the tensile strength, elongation at break, and impact strength occurred at 20 phr PES content where a co‐continuous phase formed. Young's modulus decreased slightly with the increase of the PES content. Moreover, the tensile strength and Young's modulus at 77 K were higher than those at RT at the same composition, whereas the elongation at break and impact strength showed the opposite results. Finally, the differential scanning calorimetry analysis showed that the glass transition temperature (T_g) was enhanced by the addition of PES. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 612–624, 2008     

Thermally conductive and electrically insulative nanocomposites based on hyperbranched epoxy and nano‐Al2O3 particles modified epoxy resin

Novel epoxy nanocomposites based on a diglycidyl ether of bisphenol A (DGEBA) epoxy, an epoxy functionalized hyperbranched polymer (HTTE) and nano‐Al₂O₃ were synthesized with the aim of determining the effect of the nano‐Al₂O₃ particles and HTTE on the structure and properties of epoxy nanocomposites. The mechanical properties, thermal conductivity, bulk resistivity, and thermal stability of the nano‐Al₂O₃/HTTE/DGEBA ternary composites were evaluated and compared with the corresponding matrix. The improvement in impact properties of these nanocomposites was explained in terms of fracture surface analysis by SEM. The results indicate that the incorporation of nanoparticles and hyperbranched epoxy effectively improved the toughness of epoxy composites without sacrificing thermal conductivity and bulk resistivity compared to the neat epoxy and Al₂O₃/DGEBA, obtaining a well dispersion of nanoparticles in epoxy matrix and solving the drawbacks for single fillers filled epoxy nanocomposite. Copyright © 2010 John Wiley & Sons, Ltd.     

A phosphate-based epoxy resin for flame retardance: synthesis, characterization, and cure properties

A phosphorus-containing oligomer, bis(3-hydroxyphenyl) phenyl phosphate (BHPP), was synthesized through the reaction of phenyl dichlorophosphate and 1,3-dihydroxybenzene, and characterized by elemental analysis, Fourier transform IR spectroscopy, and ¹H NMR and ³¹P NMR spectroscopy. Consequently, the phosphate-based epoxy resins with a phosphorus content of 1 and 2 wt % were prepared via the reaction of diglycidyl ether of bisphenol-A with BHPP and bisphenol-A, and were confirmed with Fourier transform IR spectroscopy and gel permeation chromatography. Phenolic melamine, Novolak, and dicyanodiamide were used as curing agents to prepare the thermoset resins with the control and the phosphate-based epoxy resins. Thermal properties and thermal degradation behavior of these thermoset resins were investigated by using differential scanning calorimetry and thermogravimetric analysis. The thermoset resins cured with phenolic melamine exhibited higher glass-transition temperatures than the other cured resins owing to the high rigidity of their molecular chain. Thermogravimetric analysis studies demonstrated that the decomposition temperatures of the thermoset resins cured with Novolak were higher than those of the others. A synergistic effect from the combination of the phosphate-based epoxy resin and the nitrogen-containing curing agent can result in a great improvement of the flame retardance for their thermoset resins.     

Highly efficient multielement flame retardant for multifunctional epoxy resin with satisfactory thermal,flame‐retardant,and mechanical properties

Multifunctional epoxy resins with excellent, thermal, flame‐retardant, and mechanical properties are extremely important for various applications. To solve this challenging problem, a novel highly efficient multielement flame retardant (PMSBA) is synthesized and the flame‐retardant and mechanical properties of modified epoxy resins are greatly enhanced without significantly altering their and thermal properties by applying the as‐synthesized PMSBA. The limiting oxygen index value reaches up to 29.6% and could pass the V‐0 rating in the UL‐94 test with even low P content (0.13%). Furthermore, cone calorimetry results demonstrate that 30.3% reduction in the peak heat release rate for the sample with 10.0 wt% PMSBA is achieved. X‐ray photoelectron spectroscopy and scanning electron microscopy indicate that Si‐C, Si‐N, and phosphoric acid derivative can be transformed into a multihole and intumescent char layer as an effective barrier, preserving the epoxy resin structure from fire. More importantly, mechanical properties such as impact strength, tensile strength, and flexural strength are also increased by 63.86%, 33.54%, and 15.65%, respectively, which show the incorporation of PMSBA do not deteriorate the mechanical properties of modified epoxy resins. All the results show that PMSBA is a promising strategy for epoxy resin with satisfactory, thermal, flame‐retardant, and mechanical properties.