A Fundamental Approach to Resin Cure Kinetics

Chiao, Leroy; Lyon, Richard E.

doi:10.1177/002199839002400704

Cited by 45 publications

(28 citation statements)

References 12 publications

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“…The different ways the crosslinking reactions can occur due to the variation of the hardener to epoxy monomer ratio can lead to the formation of a more open structure, contributing to the diffusion of small molecules such as water, or a more compact structure, acting as barriers to the movement of molecules [29] . For the epoxy rich systems (phr 7, 9 and 11) the formation of a more open structure is likely, because after depletion of amine groups, secondary reactions such as homopolimerization and ether formation can occur [4,9] . This structure will favor higher diffusion rates (D) and will have smaller proportion of dense phase (V d ).…”

Section: Resultsmentioning

confidence: 99%

“…For non-stoichiometric formulations with excess of epoxy monomer the epoxy rings could, in principle react with these hydroxyls groups forming ether groups [1,4] . But this secondary reaction will not contribute to reduce the number of hydrophilic OH groups and its effect is very restricted for reactions taking place below 150 °C [9] . Besides, amines are also strongly hydrophilic groups, and when in excess could contribute to moisture up-take and to resin plasticization [10] .…”

Section: Introductionmentioning

confidence: 99%

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Effect of the hardener to epoxy monomer ratio on the water absorption behavior of the DGEBA/TETA epoxy system

Pereira

d’Almeida

2016

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SbstractThe water absorption behavior of the DGEBA/TETA epoxy system was evaluated as a function of the epoxy monomer to amine hardener ratio. Weight gain versus immersion time curves were obtained and the experimental points were fitted using Fickian and Non-Fickian diffusion models. The results obtained showed that for all epoxy monomer to hardener ratios analyzed water diffusion followed non-Fickian behavior. It was possible to correlate the water absorption behavior to the macromolecular structure developed when the epoxy/ hardener ratio was varied. All epoxy/hardener ratios present a two-phase macromolecular structure, composed of regions with high crosslink density and regions with lower crosslinking. Epoxy rich systems have a more open macromolecular structure with a lower fraction of the dense phase than the amine rich systems, which present a more compact two-phase structure.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of the hardener to epoxy monomer ratio on the water absorption behavior of the DGEBA/TETA epoxy system

Pereira

d’Almeida

2016

Polímeros

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“…The effect of this reaction is, however, restricted for reactions taking place below 150 °C 26 . Finally, homopolimerization reactions can be catalysed by steric hindered tertiary amines 27 , leading to the formation of the p-dioxane ring structure or to the step like structure.…”

Section: Introductionmentioning

confidence: 99%

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

2003

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An investigation was carried out on the room temperature ageing of off-stoichiometric DGEBA/TETA epoxy formulations. The results obtained show that the epoxy rich mixtures have their inherent brittleness increased by the ageing treatment due to recrystalization of the unreacted epoxy monomers, although homopolymerization could also play a minor role. The initial reaction steps dominated by the amine addition reactions control the macromolecular structure and the mechanical performance of the stoichiometric and near stoichiometric formulation with excess of epoxy monomer. Plasticization due to absorbed -OH results on a significant increase of the deformability of these formulations. The amine rich mixtures have the more stable structures, although plasticization due to moisture absorption from the surrounding environment also produces an increase on the deformability of all, but one, of the formulations investigated. keywords: epoxy resins, ageing, mechanical propertiesoff-stoichiometric mixtures. For the particular system made of the triethylene tetramine, TETA, hardener and the DGEBA monomer the variation of the hardener to monomer ratio promotes strong changes on the mechanical behavior [18][19][20][21] . Of particular interest with respect to these changes is the very sharp increase in the impact strength, when amine rich mixtures were used 21 . The problem of working with off-stoichiometric mixtures is that latent reaction sites could remain on the macromolecular structure developed and under the proper conditions the structure can evolve, resulting in changes on the mechanical performance of the material. Temperature is clearly one external parameter that could cause changes to the system, but, even at room temperature, ageing due to exposure of the epoxy resin to humid environments could also be important [22][23][24] . The changes observed on the mechanical properties when the epoxy monomer to hardener ratio is varied, and the possible changes due to aging, are a direct consequence of the different macromolecular structures that are developed and/or the possible reactions that could occur given a

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“…3,4 The crosslinked network obtained is also dependent on processing variables such as the time and the temperature of cure because these parameters will sensibly affect the degree of cure. [5][6][7][8] Dealing with a specific hardener, variations from the stoichiometric hardener to resin mixture can also bring important changes on the final properties of epoxy systems. 9 -12 A change on macroscopic mechanical properties as a function of the hardenerto-resin ratio was particularly observed for the epoxy system formed by the diglycidyl ether of bisphenol A, DGEBA, epoxy resin, and the triethylene tetramine, TETA, hardener.…”

Section: Introductionmentioning

confidence: 99%