Cured Epoxide Resins Research Articles

Determination of 137Cs and 85Sr transport parameters in fucoidic sand columns and groundwater system

Abstract The determination is based on the evaluation of experimentally obtained breakthrough curves using the erfc-function. The first method is founded on the assumption of a reversible linear sorption/desorption isotherm of radionuclides on solid phase with constant distribution and retardation coefficients, whereas the second one is based on the assumption of a reversible non-linear sorption/desorption isotherm described with the Freundlich equation, i.e., with non-constant distribution and retardation coefficients. Undisturbed cores of 5 cm in diameter and 10 cm long were embedded in the Eprosin-type cured epoxide resin column. In this study the so-called Cenomanian background groundwater was used as transport medium. The groundwater containing radionuclides was introduced at the bottom of the columns at about 4 mL h−1 constant flow-rate. The results have shown that in the investigated fucoidic sands: (i) the sorption was in principle characterized by linear isotherms and the corresponding retardation coefficients of 137Cs and 85Sr, depending on the type of sample, were approximately 13 or 44 and 5 or 15, respectively; (ii) the desorption was characterized by non-linear isotherms, and the retardation coefficients of the same radionuclides ranged between 23–50 and 5–25, respectively. The values of the hydrodynamic dispersion coefficients of these radionuclides varied between 0.43–1.2 cm2 h−1.

Effect of network structure on thermal and mechanical properties of cured epoxide resins

Dynamic mechanical properties and internal stress were investigated using several different kinds of epoxide resins with different chemical structures. Resin containing a tetramethyl biphenol structure showed a very high rubbery modulus, a low glassy modulus and a low internal stress, in addition to exhibiting a high glass transition temperature. Furthermore, the effect of the introduction of methyl branches into the biphenol skeleton on viscoelastic properties of cured epoxide resin was investigated by comparing with that of bisphenol-A type resin in detail. In the case of bisphenol-A type resin, the introduction of methyl branches slightly affected the modulus in the rubbery and the glassy regions and the glass transition temperature. These results show that the introduction of methyl branches into the resin does not significantly affect the mobility of network chains or the free volume of cured resins. In contrast, the introduction of methyl branches into biphenol type resin resulted in a decrease in modulus in the rubbery region and an increase in the peak height of tan δ. These results show that the introduction of methyl branches into biphenol type resin increases the mobility of network chains in the rubbery region. On the other hand, the modulus in the glassy region increased according to the introduction of methyl branches. This is due to the decrease in free volume in the glassy region with an increase in the mobility of network chains in the rubbery region.

シリコーンエラストマーで変性したエポキシ樹脂硬化物の内部応力

シリコーンエラストマーで変性したエポキシ樹脂硬化物の内部応力

Adhesive properties of cured epoxide resin containing the intermolecular compound of 2,4-diamino-6-vinyl-s-triazine and isocyanuric acid

The intermolecular compound of 2,4-diamino-6-vinyl-s-triazine and isocyanuric acid was synthesized, and the glass transition temperature and the adhesive properties of the cured epoxide resin containing the above compound were studied. Epoxide reacted with amino groups of 2,4-diamino-6-vinyl-s-triazine and isocyanuric acid at the curing conditions of 150 to 180°C for 60 min and formed the cured compounds. The infrared spectra showed that epoxide reacted with isocyanuric acid in the presence of imidazole compounds and converted to 2-oxazolidinone compound on the curing process. The glass transition temperatures of the cured compounds having isocyanurate and 2-oxazolidinone rings in their structures were higher than that of the epoxide resin cured with imidazole and rise as the curing temperature rises, but fall as 2-oxazolidinone ring content increases in their cured compounds. The tensile shear and peel strengths of the steel and steel bonded with the cured compounds and the cured epoxide resin were measured at 25 and 150°C. The adhesive strengths were improved due to isocyanurate and 2-oxazolidinone rings formed in their cured compounds.

Mechanical relaxation properties of spiro-type epoxide resins cured with acid anhydrides

Low-temperature relaxation behaviour has been investigated for a bisphenol-A type and three spiro-type epoxide resins cured with acid anhydrides. In the spiro-type resin systems, one new relaxation, denoted here as the β′ relaxation, is clearly observed near room temperature. It is suggested that the β′ relaxation is related to the motion of p-phenylene group adjacent to the spiro ring. The impact strength of epoxide resin systems that show the β′ relaxation is considerably higher than that of other cured systems and is proportional to the intensity of the β′ relaxation. Consequently, it is concluded that the existence of the room-temperature relaxation such as the β′ relaxation is associated with increased toughness of cured epoxide resins.

Effects of tertiary amine accelerators on curing of epoxide resins

AbstractThe effects of seven tertiary amine accelerators on curing of bisphenol‐type epoxide resins using azelaic acid as a curing agent have been investigated. The structure of the cured resins is characterized and reaction and structure schemes are proposed. The reaction mechanism and the resulting structure of the resin depend on the basicity of the accelerator. With increasing accelerator basicity crosslinking in the cured resin increases. Characterization results indicate that the network structure consists of ether bonds or a mixture of ether and ester bonds; the linear structure consists of only ester bonds. The structure and, therefore, the properties of the cured epoxide resin may thus be regulated by selection of the amine basicity.

Mechanical relaxation mechanism of epoxide resins cured with diamines

The mechanism of mechanical relaxation, which is observed between 50° and 90°C in epoxide resins cured with aromatic and alicyclic diamines, has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. This relaxation is denoted here as the α′ relaxation. The occurrence of the α′ relaxation depends on the existence of p-phenylene groups, and is independent of the degree of cure in the cured epoxide resins. Moreover, the intensity of the α′ relaxation increases linearly with increasing the concentration of p-phenylene groups in the networks. From these results, it is concluded that the α′ relaxation of the cured epoxide resins is attributed to the motion of p-phenylene groups in the network structures.

The environmental response of hybrid composites

Hybrid composite specimens containing a total of 60 or 75 vol % of unidirectional fibre were prepared from HT S-carbon fibre and E-glass fibre, HT S-carbon fibre and Kevlar 49 fibre, and E-glass fibre and Kevlar 49 fibre with a standard anhydride cured epoxide resin. The specimens were divided into four groups and subjected to the following environments: (A) room temperature and humidity; (B) soaked in water for 300 h at 95° C and then oven dried at 60° C to a constant weight; (C) thermally cycled 100 times between −196 and 95° C; (D) cycled 35 times between −196 and water at 95° C. The flexural properties of the samples were measured at room temperature after exposure. The modulus of the hybrid materials was not significantly affected by any of the treatments, although thermal cycling with or without water caused a large decrease in the modulus of all Kevlar fibre/resin and to a lesser extent all glass fibre specimens. The flexural strength of the unexposed carbon fibre/glass fibre and glass fibre/Kevlar fibre hybrids showed a positive deviation from the rule of mixtures behaviour at low volume loadings of the lower extension fibre. Wet thermal cycling or soaking in water caused a substantial reduction in the flexural strength of glass fibre/Kevlar fibre specimens. The interlaminar shear strength of all three fibre combinations was not affected by dry thermal cycling, but the effects of soaking in water and especially thermal cycling with water exposure were significant and irreversible.

Mechanical properties of acid‐cured epoxide resins with different network structures

AbstractStatic and dynamic mechanical properties of cured epoxide resins based on ester bonds, ether bonds, or a mixture of ester and ether bonds were investigated. Their network structures were estimated from the results of gel content before and after saponification, and conversion of functional groups. It was found that cured epoxide resins based on a mixture of ester and ether bonds indicate intermediate properties between the resins based on ester bonds and the resins based on ether bonds. Both dynamic and static mechanical properties were strongly affected by their network density and their segmental structures suggested in this paper.

Frictional behaviour of cured epoxide resins

The friction mechanisms for sliding between dicarboxylic-acid-cured epoxide resins and stainless steel were investigated by monitoring the changes in the coefficient of friction and the geometry of the sliding surfaces in the glassy, transition and rubbery regions of the cured resins. In the glassy region, a constant value of the friction coefficient was obtained in spite of the variation in contact pressure. A trace of shearing fracture was observed on the sliding surfaces, and a linear relationship existed between the friction coefficient and the shear modulus of the cured resins. In the transition region, the maximum values of the friction coefficient were observed at the glass transition temperatures of the cured resins. The maximum value increased as the magnitude of the damping of these resins increased. In this region it was found that the softened polymer adhered to the metal surface and was also deformed by the movement of the metal specimen. In the rubbery region, the friction coefficient remained constant in spite of the variation in contact pressure. It was shown that a good correlation exists between the friction coefficient and the concentration of network chains.

Mechanical relaxation mechanism of epoxide resins cured with aliphatic diamines

AbstractThe mechanism of low‐temperature relaxations in bisphenol‐A‐type epoxide resins cured with aliphatic diamines, with aliphatic diamines in the presence of salicylic acid as an accelerator, and with tertiary amines was investigated to compare the dynamic mechanical properties and the chemical structure of these networks. Mechanical relaxations are observed at about −140 and −60°C. The former relaxation is denoted the γ relaxation and the latter the β relaxation. The β relaxation of the cured epoxide resins containing hydroxyether groups is a sum of contributions from the relaxation of these groups and of other parts of the network structure. A new relaxation due only to the motion of the hydroxyether group can be estimated from the difference of tanδ curves between the aminecrosslinked and ether‐crosslinked systems. The γ relaxation is attributed to the motion of a polymethylene sequence consisting of at least four carbon atoms.

Radiation induced structural changes in an epoxide resin system—II: Aromatic amine cured system

The structural changes which occur on irradiation of an aromatic amine cured epoxide resin have been examined using UV and IR spectroscopy. The production of stable diphenyl ethylene and carbonyl groups, diphenyl cations and phenyl, phenoxyl and diphenyl radicals have been identified. Modifications to the resin system by the use of additives produces changes in the relative proportions of the species produced.