Modification of epoxy resin by isocyanate‐terminated polybutadiene

Hydroxy‐terminated polybutadiene was functionalized with isocyanate groups and employed in preparation of a block copolymer of polybutadiene and bisphenol A diglycidyl ether (DGEBA)‐based epoxy resin. The block copolymer was characterized by Fourier transform infrared (FTIR) spectroscopy and size‐exclusion chromatography (SEC). Cured blends of epoxy resin and hydroxy‐terminated polybutadiene (HTPB) or a corresponding block copolymer were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMTA), and scanning electron microscopy (SEM). All modified epoxy resin networks presented improved impact resistance with the addition of the rubber component at a proportion up to 10 wt % when compared to the neat cured resin. The modification with HTPB resulted in milky cured materials with phase‐separated morphology. Epoxy resin blends with the block copolymer resulted in cured transparent and flexible materials with outstanding impact resistance and lower glass transition temperatures. No phase separation was discernible in blends with the block copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 838–849, 2002     

Cure kinetics and morphology of blends of epoxy resin with poly (ether ether ketone) containing pendant tertiary butyl groups

The cure kinetics and morphology of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin modified with a poly (ether ether ketone) based on tertiary butyl hydroquinone (PEEK-T) cured with diamino diphenyl sulphone (DDS) were investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic mechanical thermal analysis (DMTA). The results obtained from DSC were applied to autocatalytic and diffusion controlled kinetic models. The reaction mechanism broadly showed autocatalytic behaviour regardless of the presence of PEEK-T. At higher PEEK-T concentration, more diffusion controlled mechanism was observed. The rate of curing reaction decreased with increase in thermoplastic content and also with the lowering of curing temperature. The activation energies of the blends are higher than that of the neat resin. The blends showed a phase separated morphology. The dispersed phase showed a homogeneous particle size distribution. The T_g of the neat resin decreased with the decrease in cure temperature. Two T_g's corresponding to the epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum. The storage modulus of 10 and 20 phr PEEK-T blends are found to be greater than the neat resin.     

Bisphenol A dicyanate–novolac epoxy blend: Cure characteristics,physical and mechanical properties,and application in composites

Reactive blends of bisphenol A dicyanate (BACY) and a novolac epoxy resin (EPN) were investigated for their cure behavior and the mechanical, thermal, and physical properties of the cocured neat resin and glass‐laminate composites. Contrary to the apparent observation in DSC, the dynamic mechanical analysis confirmed a multistep cure reaction of the blend, in league with an established reaction path for similar systems. The cured matrix was found to contain both polycyanurate and oxazolidinone networks that existed in discrete phases exhibiting independent glass transitions in dynamic mechanical analysis (DMA). The flexible and less crosslinked oxazolidinone network contributed to enhanced flexural strength at the cost of the tensile strength of the neat resin. The increased resin flexibility was, however, not translated to the glass‐laminate composite for which the flexural strength decreased with the oxazolidinone content, although the latter was conducive for rendering a stronger interphase. The presence of oxazolidinone adversely affected the thermal stability of the cured resin and the high‐temperature performance of both neat resin and the composites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1675–1685, 1999     

Curing kinetics and reaction‐induced homogeneity in networks of poly(4‐vinyl phenol) and diglycidylether epoxide cured with amine

Mixtures of diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin with poly(4‐vinyl phenol) (PVPh) of various compositions were examined with a differential scanning calorimeter (DSC), using the curing agent 4,4′‐diaminodiphenylsulfone (DDS). The phase morphology of the cured epoxy blends and their curing mechanisms depended on the reactive additive, PVPh. Cured epoxy/PVPh blends exhibited network homogeneity based on a single glass transition temperature (T_g) over the whole composition range. Additionally, the morphology of these cured PVPh/epoxy blends exhibited a homogeneous network when observed by optical microscopy. Furthermore, the DDS‐cure of the epoxy blends with PVPh exhibited an autocatalytic mechanism. This was similar to the neat epoxy system, but the reaction rate of the epoxy/polymer blends exceeded that of neat epoxy. These results are mainly attributable to the chemical reactions between the epoxy and PVPh, and the regular reactions between DDS and epoxy. Polym. Eng. Sci. 45:1–10, 2005. © 2004 Society of Plastics Engineers.     

Morphology effect on the hydrothermal ageing of a thermoplastic modified epoxy thermoset

The hydrothermal ageing of an epoxy thermoset modified with different amounts of poly(vinyl acetate), PVAc, was studied by gravimetric analysis, dynamic mechanical thermal analysis, and scanning electron microscopy. Differences in the water uptake process were observed as a function of the PVAc content, these differences were related to the morphology. Samples with nodular morphology, having spheres of thermoplastic dispersed in the epoxy matrix, showed water absorption behavior similar to neat epoxy. However, samples with inverted morphology, in which the thermoplastic formed the continuous phase, were more susceptible to water absorption; they exhibited a continued water uptake that could be described by a two‐stage diffusion model. Samples with inverted morphology showed debonding between phases after hydrothermal ageing. Different dynamic‐mechanical behavior has been found for samples that had epoxy matrix and samples with inverted morphology, both before and after hydrothermal ageing. POLYM. ENG. SCI., 47:960–968, 2007. © 2007 Society of Plastics Engineers     

Assessment of morphological,thermal, and viscoelastic properties of epoxy vinyl ester coating composites: Role of glass flake and mixing method

In this work, glass flake (GF)/epoxy vinyl ester resin composites were fabricated with various compositions and mixing methods. The effect of GF on thermal and mechanical behavior of these composites was investigated using different techniques such as differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The results showed that the presence of GF in epoxy vinyl ester formulation could obviously affect the cure temperature, reaction enthalpy value, and degradation temperature. DMTA results also exhibited that the tan δ peak area decreased and storage modulus increased with increasing GF content and this effect seemed to be different depending on the initial epoxy vinyl ester compositions. The scanning electron microscopy (SEM) images showed that mixing method had a strong effect on the surface morphology, size, and distribution of glass flake. The effect of mixing method on properties of produced composite was also studied.     

Effect of hydroxyl content on the morphology and properties of epoxy/poly(styrene-co-allylalcohol) blends

Blends based on epoxy resin and random copolymers, poly(styrene-co-allylalcohol) (PS-co-PA), were studied. Two PS-co-PA copolymers, with different hydroxyl content, and a polyallylalcohol (PA) homopolymer were used to analyze the effect of polyalcohol content. The polymers presented similar values of molar mass. The miscibility of noncured mixtures and the thermal transition behavior of cured blends were investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Its morphology was studied using both scanning and transmission electron microscopy (SEM and TEM). While the epoxy/PA blends are homogenous materials, because of the epoxy/hydroxyl reaction, PS-co-PA/epoxy blends shows separated phases. In these blends, the presence of a third glass transition, whose value is an intermediate between those of pure components, and the presence of a well-defined interfacial layer between PS-co-PA domains and epoxy matrix indicates a secondary epoxy/hydroxyl reaction. The modification of epoxy resin with PS-co-PA provides significant increase in the storage modulus measured by DMTA. POLYM. ENG. SCI., 47:1580–1588, 2007. © 2007 Society of Plastics Engineers     

Properties of cyanate ester-cured epoxy/polyphenylene oxide blends as a matrix material for Kevlar fiber composites

Epoxy/polyphenylene oxide (PPO) blends were cured with multifunctional cyanate ester resin. The effects of the PPO content on the cure behavior in the cyanate ester-cured epoxy were investigated with Fourier transform infrared spectroscopy (FTIR). The cure reaction in the epoxy/PPO blends was faster than that of the neat epoxy system. FTIR analysis revealed that the cyanate functional group reactions were accelerated by adding PPO and that several co-reactions had occurred, such as cyanate-hydroxyl addition and epoxy-cyanate addition. This was caused by the reaction of cyanate ester with the PPO phenolic end-group and water yielding imidocarbonate and carbamate intermediate which can react with cyanate ester to form cyanurate. Then the cyanurate can react further with the epoxy resin. Thermal mechanical analysis showed that the thermal stability of the epoxy/PPO blends is improved by adding PPO. The morphology of the fiber-rich areas in the composite is different from that of the epoxy/PPO blend without Kevlar fiber. In the pure polymer blends with high PPO content (30 and 50 phr), phase separation and phase inversion were observed. In the composites, the majority of the epoxy resin migrates to the polar fiber surface, resulting in epoxy-coated fibers. So the interfacial shear strength (IFSS) between Kevlar fiber and the epoxy/PPO blends is almost the same as that between Kevlar fiber and neat epoxy. The presence of PPO does not affect the interfacial property in the epoxy/PPO/fiber composite. So the interlaminar shear strength (ILSS) increase with the PPO content is due to an increase in the composite's ductility or toughness.     

Phthalonitrile‐epoxy blends: Cure behavior and copolymer properties

Binary blends composed of 4,4′‐bis(3,4‐dicyanophenoxy)biphenyl (biphenyl PN) and diglycidyl ether of bisphenol A (epoxy resin) and oligomeric n = 4 phthalonitrile (n = 4 PN) and epoxy resin were prepared. The cure behavior of the blends was studied under dynamic and isothermal curing conditions using differential scanning calorimetry, simultaneous thermogravimetric/differential thermal analysis, infrared spectroscopy, and rheological analysis. The studies revealed that phthalonitrile‐epoxy blends exhibited good processability and that they copolymerized with or without the addition of curing additive. In the absence of curing additive, the blends required higher temperatures and longer cure times. The thermal and dynamic viscoelastic properties of amine‐cured phthalonitrile‐epoxy copolymers were examined and compared with those of the neat epoxy resin. The properties of the epoxy resin improved with increasing biphenyl PN content and with n = 4 PN addition. Specifically, the copolymers exhibited higher glass transition temperatures, increased thermal and thermo‐oxidative stabililty, and enhanced dynamic mechanical properties relative to the commercially available epoxy resin. The results showed that the phthalonitrile‐epoxy blends and copolymers have an attractive combination of processability and high temperature properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cure kinetics and properties of epoxy/dicyanate blends

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxilde groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The k₁₀ and E₁ values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.     

Influence of copolymer's end groups and molecular weights on the rheological and thermomechanical properties of blends of novel thermoplastic copolymers and epoxy resins

In this paper, we present a study on the properties of epoxy resins blended with copolyethersulfones. Several copolyethersulphones were synthesized by varying the molecular weights and the end groups. The obtained thermoplastics were then mixed with diglycidyl ether of biphenol A (DGBEA) (15% wt ratio), cured with methylene bis(2,6‐diethylanine) (MDEA), and the resulting blends characterized by the use of dynamic thermal mechanical analysis (DMTA), rheometry, and fracture mechanics tests. The morphology of the blends was studied by the use of scanning electron microscopy (SEM). The different molecular weights of the copolymers had a significant effect on the rheological and thermomechanical properties of the resins, as well as the different end groups on the reaction rate and on the thermomechanical properties of the blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 250–257, 2006     

Cure behavior,morphology, and mechanical properties of the melt blends of epoxy with polyphenylene oxide

Cure behavior, miscibility, and phase separation have been studied in blends of polyphenylene oxide (PPO) with diglycidyl ether of bisphenol A (DGEBA) resin and cyanate ester hardener. An autocatalytic mechanism was observed for the epoxy/PPO blends and the neat epoxy. It was also found that the epoxy/PPO blends react faster than the neat epoxy. During cure, the epoxy resin is polymerized, and the reaction‐induced phase separation is accompanied by phase inversion upon the concentration of PPO greater than 50 phr. The dynamic mechanical measurements indicate that the two‐phase character and partial mixing existed in all the mixtures. However, the two‐phase particulate morphology was not uniform especially at a low PPO content. In order to improve the uniformity and miscibility, triallylisocyanurate (TAIC) was evaluated as an in situ compatibilizer for epoxy/PPO blends. TAIC is miscible in epoxy, and the PPO chains are bound to TAIC network. SEM observations show that adding TAIC improves the miscibility and solvent resistance of the epoxy/PPO blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 26–34, 2000     

Acrylic‐based epoxy resin damping systems: Synthesis,characterization, and properties

Acrylate‐based epoxy resin (AE)/low molecular weight polyamine (LPA) composites were developed. The chemical structure, curing behavior, fracture morphology, damping properties, and mechanical properties were evaluated by Fourier transform infrared (FTIR), ¹H‐nuclear magnetic resonance (¹H‐NMR), gel permeation chromatography (GPC), Differential scanning calorimeter (DSC), scanning electron microscope (SEM), Dynamic mechanical thermal analysis (DMTA), and electro mechanical machine. Transmission electron microscope (TEM) and SEM pictures exhibited nanoscale micro‐phase separation between epoxy and acrylic segmers. DMTA results indicated that the loss factor of cured AE/LPA system could reach 1.84 and temperature range of tan δ > 0.5 was about 84 °C. Tensile strength and elongation at break of the cured AE samples can reach 6.5 MPa and 185%, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43654.     

Layered silicate nanocomposites based on various high‐functionality epoxy resins: The influence of an organoclay on resin cure

The influence of an organically modified clay on the curing behavior of three epoxy systems widely used in the aerospace industry and of different structures and functionalities was studied. Diglycidyl ether of bisphenol A (DGEBA), triglycidyl p‐amino phenol (TGAP) and tetraglycidyl diamino diphenylmethane (TGDDM) were mixed with an octadecyl ammonium ion modified organoclay and cured with diethyltoluene diamine (DETDA). The techniques of dynamic mechanical thermal analysis (DMTA), chemorheology and differential scanning calorimetry (DSC) were applied to investigate gelation and vitrification behavior, as well as catalytic effects of the clay on resin cure. While the formation of layered silicate nanocomposite based on the bifunctional DGEBA resin has been previously investigated to some extent, this paper represents the first detailed study of the cure behavior of different high performance, epoxy nanocomposite systems.     

Dynamically cured polypropylene/epoxy blends

The dynamic vulcanization process, usually used for the preparation of thermoplastic elastomers, was used to prepare polypropylene (PP)/epoxy blends. The blends had crosslinked epoxy resin particles finely dispersed in the PP matrix, and they were called dynamically cured PP/epoxy blends. Maleic anhydride grafted polypropylene (MAH‐g‐PP) was used as a compatibilizer. The effects of the reactive compatibilization and dynamic cure were studied with rheometry, capillary rheometry, and scanning electron microscopy (SEM). The crystallization behavior and mechanical properties of PP/epoxy, PP/MAH‐g‐PP/epoxy, and dynamically cured PP/epoxy blends were also investigated. The increase in the torque at equilibrium for the PP/MAH‐g‐PP/epoxy blends indicated the reaction between maleic anhydride groups of MAH‐g‐PP and the epoxy resin. The torque at equilibrium of the dynamically cured PP/epoxy blends increased with increasing epoxy resin content. Capillary rheological measurements also showed that the addition of MAH‐g‐PP or an increasing epoxy resin content increased the viscosity of PP/epoxy blends. SEM micrographs indicated that the PP/epoxy blends compatibilized with PP/MAH‐g‐PP had finer domains and more obscure boundaries than the PP/epoxy blends. A shift of the crystallization peak to a higher temperature for all the PP/epoxy blends indicated that uncured and cured epoxy resin particles in the blends could act as effective nucleating agents. The spherulites of pure PP were larger than those of PP in the PP/epoxy, PP/MAH‐g‐PP/epoxy, and dynamically cured PP/epoxy blends, as measured by polarized optical microscopy. The dynamically cured PP/epoxy blends had better mechanical properties than the PP/epoxy and PP/MAH‐g‐PP/epoxy blends. With increasing epoxy resin content, the flexural modulus of all the blends increased significantly, and the impact strength and tensile strength increased slightly, whereas the elongation at break decreased dramatically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1437–1448, 2004     

DSC and DMTA characterization of ternary blends

The phase behavior of ternary blends made of poly(epichlorohydrin) (PECH), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) has been investigated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). DMTA measurements have been shown to be more sensitive than DSC for the detection of a second phase, for the determination of the composition of each phase, and the distribution of PECH in each of them. About 70% PECH was required to obtain a single narrow T_g in the ternary system, which suggests a single homogeneous phase in the limit of sensitivity of DMTA. This study also emphasizes the importance of the composition of the immiscible polymer pair (i.e. the PVAc/PMMA pair in the PECH/PVAc/PMMA system), in addition to the thermodynamic interaction parameters, for controling the phase behavior of ternary systems.     

Ternary nanocomposites based on epoxy,modified silica,and tetrabutyl titanate: Morphology,characteristics, and kinetics of the curing process

In this study, the effects of unmodified nanosilica and nanosilica modified by an isopropyl tri[di(octyl) phosphate] titanate coupling agent (KR-12; m-nanosilica) on the structure, morphology, thermomechanical properties, and kinetics of the curing process of epoxy–tetrabutyl titanate (TBuT) nanocomposites were investigated. The viscosity, tensile strength, and flexural strength of the cured epoxy and cured epoxy–m-silica–TBuT nanocomposites were determined with a Brookfield viscometer and an Instron 5582-100KN universal machine. The morphology and gel fraction content of the nanocomposites were analyzed with transmission electron microscopy and scanning electron microscopy methods and Soxhlet extraction. The viscosity, mechanical properties, gel fraction content, and morphology results of the cured epoxy–m-silica–TBuT nanocomposites confirm that 5 wt % m-nanosilica was the most suitable for improving the dispersion of m-nanosilica in the epoxy matrix and the properties of these materials. The thermal behavior of the nanocomposites was determined by thermogravimetric analysis and differential scanning calorimetry (DSC) methods. On the basis of DSC data, the average value of the activation energy of the cured epoxy–TBuT system, calculated according to Flynn–Wall–Ozawa and Kissinger equations, was 67.893 kJ/mol. The calculation according to the Crane equation showed that the first-order kinetics complied with the curing reaction for the neat epoxy. When we introduced the unmodified nanosilica and modified nanosilica into the epoxy matrix, the order kinetics of the curing reaction for the nanocomposites also followed first-order kinetics, but the activation energy of their curing reaction decreased significantly. Some other properties were also investigated with dynamic mechanical analysis and Fourier transform infrared analysis and are discussed. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47412.     

Epoxy modification with poly(vinyl acetate) and poly(vinyl butyral). I. Structure,thermal, and mechanical characteristics

Efficiency of the application of high strength heat resistant thermoplastics for improving fracture toughness and impact properties of epoxy resins motivated authors to try large‐scale production thermoplastics for the same purpose. Epoxy/anhydride systems were modified by up to 8 wt % poly(vinyl acetate) (PVAc) and up to 6 wt % poly(vinyl butyral) (PVB). In epoxy–PVAc blends it was possible to obtain morphologies with continuous thermoplastic phase. However, only sea‐island morphologies with a very small size of PVB‐rich phase were observed in epoxy–PVB matrices. The former type of morphology allowed a notable 2.4‐fold increase in the fracture toughness of epoxy resin and simultaneous up to 30% decrease in its' impact strength. The latter type of morphology caused a notably lower (45%) enhancement of the epoxy fracture toughness combined with a 50% increase in its' impact strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44081.     

Epoxy resin containing the poly(sily ether): Preparation,morphology, and mechanical properties

The poly(sily ether) with pendant chloromethyl groups (PSE) was synthesized by the polyaddition of dichloromethylsilane (DCM) and diglycidylether of bisphenol A (DGEBA) with tetrabutylammonium chloride (TBAC) as a catalyst. This polymer was miscible with diglycidyl ether of bisphenol A (DGEBA), the precursor of epoxy resin. The miscibility is considered to be due mainly to entropy contribution because the molecular weight of DGEBA is quite low. The blends of epoxy resin with PSE were prepared through in situ curing reaction of diglycidyl ether of bisphenol A (DGEBA) and 4,4′‐diaminodiphenylmethane (DDM) in the presence of PSE. The DDM‐cured epoxy resin/PSE blends with PSE content up to 40 wt % were obtained. The reaction started from the initial homogeneous ternary mixture of DGEBA/DDM/PSE. With curing proceeding, phase separation induced by polymerization occurred. PSE was immiscible with the 4,4′‐diaminodiphenylmethane‐cured epoxy resin (ER) because the blends exhibited two separate glass transition temperatures (T_gs) as revealed by the means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). SEM showed that all the ER/PSE blends are heterogeneous. Depending on blend composition, the blends can display PSE‐ or epoxy‐dispersed morphologies, respectively. The mechanical test showed that the DDM‐cured ER/PSE blend containing 25 wt % PSE displayed a substantial improvement in Izod impact strength, i.e., epoxy resin was significantly toughened. The improvement in impact toughness corresponded to the formation of PSE‐dispersed phase structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 505–512, 2003     

Preparation and thermal properties of bismaleimide blends based on hydroxyphenyl maleimide

N‐(4‐hydroxyphenyl)maleimide was melt‐blended with the glycidyl ether of bisphenol‐A and various mole percentages of 4, 4′‐(diaminodiphenylsulfone) bismaleimide. The cure behaviour of the resins was evaluated by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The blends showed distinct reductions in the onset of cure (T_o) and peak exothermic (T_exo) temperatures. The blends cured at low temperatures exhibited glass transition temperatures (T_gs) higher than the cure temperatures. The cured blends showed high moduli, glass transition temperatures in excess of 250 °C and good thermal stabilities up to 400 °C. Copyright © 2005 Society of Chemical Industry