Diglycidyl Ether Of bisphenol-A Epoxy Resin Research Articles

Toughening of thermoset polymers by rigid crystalline particles

The toughening of an aromatic amine-cured diglycidyl ether of bisphenol-A epoxy with particles of crystalline polymers was studied. The crystalline polymers were poly (butylene terephthalate), nylon 6, and poly(vinylidene fluoride). Nylon 6 and poly(vinylidene fluoride) were found to toughen the epoxy about as well as did an equivalent amount of CTBN rubber. Poly(butylene terephthalate) was found to toughen the epoxy about twice as well as did the rubber. The toughness of poly(butylene terephthalate)-epoxy blends was independent of particle size for sizes in the range of tens of micrometres, but the toughness of the nylon 6-epoxy blends decreased with increasing particle size for sizes smaller than about 40 μm. There was no loss of either Young's modulus or yield strength of the epoxy with the inclusion of either nylon 6 or poly(butylene terephthalate) and less loss of these with the inclusion of poly(vinylidene fluoride) than with the inclusion of rubber. Toughness seems to have arisen from a combination of mechanisms. The poly(butylene terephthalate)-epoxy blends alone seem to have gained toughness from phase-transformation toughening. Crack path alteration and the formation of steps and welts and secondary crack bridging seem to have accounted for an especially large part of the fracture energy of the poly(vinylidene fluoride)-epoxy blends. Secondary crack nucleation contributed to the toughness of the nylon 6-epoxy blends.

Toughening of epoxy resins by modification with reactive elastomers composed of butyl acrylate and glycidyl (meth)acrylate

Acrylic elastomers with pendant epoxy groups were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with p, p′-diaminodiphenyl sulphone. The elastomers were prepared by copolymerization of butyl acrylate (BA) with glycidyl acrylate (GA) or methacrylate. These copolymers were effective for toughening of the epoxy resin system. The addition of 20 wt% of copolymer (74 mol% BA and 26 mol% GA) led to 60% increase in the fracture toughness of the cured resin at slight expense of its mechanical properties. The glass transition temperatures of cured resins were comparable to that of the parent epoxy resin. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviour of the modified epoxy resin system.

Toughening of epoxy resins by modification with reactive elastomers composed of butyl acrylate, glycidyl methacrylate and acrylonitrile or styrene

Acrylic elastomers with pendant epoxy groups were used to improve the toughness of bisphenol-A diglycidyl ether epoxy resin cured with p, p′-diaminodiphehyl sulphone. The elastomers were prepared by terpolymerization of butyl acrylate (BA), glycidyl methacrylate (GMA) and acrylonitrile (AN) or styrene (St). BA-GMA-AN terpolymers were more effective as modifiers for toughening of the epoxy resin system than those containing St. The use of the latter terpolymers tended to separate macroscopically because of poor compatibility with the epoxy matrix. The addition of 20 wt% of the terpolymer (66 mol% BA, 20 mol% GMA and 14 mol% AN units, M n 8700) led to a 40% increase in the fracture toughness ( K IC) of the cured resin at slight expense of its mechanical properties. The modified resins had two-phase morphologies in which the volume fraction and average diameter of the dispersed particles were dependent on the structure and concentration of the terpolymers. The glass transition temperatures of cured resins were equal to or less than that of the parent epoxy resin. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviours of the modified epoxy resin system.

Toughening of epoxy resins by modification with acrylic elastomers containing pendant epoxy groups

New acrylic elastomers with pendant epoxy groups were used to reduce the brittleness of bisphenol-A diglycidyl ether epoxy resin cured with p, p′-diaminodiphenyl sulphone. The elastomers were prepared by copolymerization of butyl acrylate (BA), vinylbenzyl glycidyl ether (VBGE) and styrene (St) or acrylonitrile (AN). These terpolymers were effective for toughening of the epoxy resin system. The addition of 20 wt% of the terpolymer (74 mol% BA, 18 mol% VBGE and 8 mol% St) resulted in an 80% increase in the fracture toughness ( K 1c) of the cured resin at the slight expense of its mechanical properties. The modified epoxy resins had two-phase morphology in which the volume fraction and average diameter of the dispersed elastomer particles were dependent on the structure and concentration of the terpolymer. The toughening mechanism is discussed in terms of the morphological and dynamic mechanical behaviour of the modified epoxy resin system.

Dielectric analysis of epoxy/amine resins using microwave cavity technique

AbstractDielectric properties (permittivity and dielectric loss factor) of stoichiometric mixtures of DGEBA (diglycidylether of bisphenol A) epoxy (DER 332) and amine (diaminodiphenyl sulfone; DDS) as a function of temperature and extent of cure have been measured at a microwave frequency of 2.45 GHz. Permittivity and dielectric loss factor of this resin increase with increasing temperature and decrease with increasing extent of cure. Dielectric loss factor is more dependent on temperature in the early stages of cure but becomes less dependent on temperature as the cure proceeds. Dielectric loss data can be related to extent of cure in order to monitor the cure process. Online measurements of temperature‐ and cure‐dependent dielectric loss factor show three material structure stages and significant changes in dielectric loss factor during the microwave cure process. Dielectric Joss factor is also found to be the same for both thermal and microwave cured samples.

Epoxy matrices for filament-wound carbon fiber composites

Epoxies suitable for filament-winding fibrous composites must be processible at ambient temperatures, nontoxic, chemically simple, undergo full cure at ≤ 100°C and, also, be tough and exhibit a Tg > 120°C. In this paper, we report the cure characteristics, processibility, toxicity, and mechnical and physical properties of a number of amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxide candidate systems suitable for filament-wound carbon fiber composites. 2,5-Dimethyl-2,5-hexane diamine (DMHDA)-cured DGEBA epoxy was found to be the most promising candidate. The good processibility and thermal properties, together with the low cure characteristics of the DGEBA–DMHDA epoxy system, are discussed in terms of molecular structure of the amine molecule. The network structural parameters that control epoxy toughness and subsequent embrittlement upon plastic flow are discussed. Evidence is presented for plastic flow-induced thermal and mechanical property deterioration of epoxies as a result of network chain scission.

Rubber-modified thermosets: Prediction of the particle size distribution of dispersed domains

A model predicting the particle size distribution of dispersed domains in rubber-modified thermosets was developed on the basis of a thermodynamic description of the variation of free energy of mixing with conversion and a phase-separation analysis through constitutive equations for nucleation and growth rates. The model includes experimental information illustrating its application to a bisphenol-A diglycidyl ether epoxy resin cured with diaminodiphenylsulphone and containing a carboxyl-terminated acrylonitrile-butadiene random copolymer. Reasonable agreement between predicted and experimental cumulative particle size distributions is shown. Most of the morphological characteristics of the rubber-modified thermoset depend on the location of the reaction extent at which phase separation begins to take place ( p c), with respect to gel conversion ( p gel). Increasing the span of the ( p gel – p c) range leads to: (a) an increase in the concentration of dispersed particles, (b) an increase in the volume fraction of the dispersed phase, (c) a decrease in the final amount of rubber remaining in the matrix, (d) a decrease in the average concentration of rubber in dispersed particles, and (e) an increase in the concentration of small particles in the overall distribution (a bimodal distribution may result).

Investigation of local order in unreacted DGEBA epoxy resin monomers by light scattering

AbstractThe existence of local order in two epoxy resins of the diglycidyl ether of bisphenol‐A (DGEBA) type has been investigated using Rayleigh scattering and Brillouin spectroscopy. The resins differ in their molecular weight distributions and their relative concentrations of epoxide and hydroxyl groups. The complementary use of both techniques in elucidating the thermal behavior of local order is illustrated, and the use of the latter technique to study thermal acoustic phonons and hypersonic relaxation is discussed. Both techniques independently show that molecular aggregates exist in each resin system. The scattering‐envelope dissymmetry shows that the resin with the high epoxide/hydroxyl group ratio contains aggregates up to 20 nm in size, and the low‐ratio resin exhibits sizes up to 70 nm. These aggregates are thermally unstable in the temperature range studied (293–443 K). Dissolution in chloroform shows that these aggregates are reduced in size and that further structural changes occur which are dependent on solvent concentration. Aggregate volume fractions were determined for a range of aggregate size. Brillouin spectroscopy indicated that both resins exhibit hypersonic relaxation in the temperature range studied. The complex longitudinal moduli of the resins were superimposable under a WLF temperature transformation comparable to the difference in their static glass transition temperatures. Molecular aggregate size, number, and stability are related to the epoxide/hydroxyl ratio of the resins and the degree of intermolecular hydrogen bonding.