Spectroscopical contributions to the regioselectivity of nucleophilic curing reactions in epoxy resins

Grob, Alfred; Kollek, H.; Schormann, Anette; Brockmann, Hans

doi:10.1016/0143-7496(88)90093-0

Cited by 16 publications

(5 citation statements)

References 4 publications

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“…Nevertheless, this reaction proceeds at a much slower rate than the amine-epoxy addition reaction [35][36][37] and it is not considered as a main reaction for room temperature cured systems. Unreacted DGEBA epoxies can, however, recrystallize in ambient cured epoxies, thus causing embrittlement 38 .…”

Section: Resultsmentioning

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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Section: Resultsmentioning

confidence: 99%

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

2003

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“…This characteristic is due to the presence of the very strained ethoxyline ring structure [1,2] . Therefore, given a specific epoxy monomer, the mechanical properties of the epoxy system can be varied over fairly high bounds by changing the curing agent.…”

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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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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“…It contains at the very least two epoxy groups per 1-3 molecule. An epoxy ring is made up of two carbon atoms joined by a single covalent bond to an oxygen atom with a C-O bond angle of 61° 24' [4,5]. Because of their excellent adhesive properties, reactive epoxy rings can be used in a wide range of applications.…”

Section: Introductionmentioning

confidence: 99%

Study of Polymeric Composite Reinforced with Natural Particles: Measurement and Evaluation

Oleiwi¹,

Hadi²

2022

I2M

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Natural particles and their composites are important in materials science, where a significant attentiveness is being displayed in the usage of natural particles as reinforcement in polymer composites. The purpose of this research is to investigate the effect of the walnut shell particles as reinforcing fillers in a matrix composite. So, the amount composite examples were advanced through varying the percentage by weight of filler (3, 5, 7, and 9%) in an epoxy and unsaturated polyester polymer. Composite samples were mechanically characterized by tensile tests, flexural tests, hardness tests, and the Izod impact test. The tensile strength and impact strength of epoxy resin were increased after adding organic waste filler. The highest values of tensile strength and impact strength happened at 7% wt. The flexural strength and hardness of shore D increased with the percentage of walnut shell particles. The highest values of flexural strength and hardness were found at 9% wt. The results show that the mechanical properties of epoxy composite are better than the mechanical properties of unsaturated polyester composite when walnut shell particles are added.

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Spectroscopical contributions to the regioselectivity of nucleophilic curing reactions in epoxy resins

Cited by 16 publications

References 4 publications

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

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

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

Study of Polymeric Composite Reinforced with Natural Particles: Measurement and Evaluation

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