Curing of off-stoichiometric amine–epoxy thermosets

Morancho, J. M.; Ramis, Xavier; Fernández‐Francos, Xavier; Salla, Josep María; Konuray, Osman; Serra, À.

doi:10.1007/s10973-018-7158-2

Cited by 29 publications

(37 citation statements)

References 29 publications

(42 reference statements)

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“…Fig. 5 shows that, in the case of the first curing process, the activation energy is fairly constant, between 50 and 60 kJ/mol, with a slightly decreasing trend, as reported for other aliphatic amines [14] or other off-stoichiometric amine-epoxy systems [10]. In the case of the second curing process, the activation energy is also fairly constant, with a value around 85 kJ/mol, which is higher than the values reported for the homopolymerization of excess epoxy groups after the thiol-epoxy reaction [3], but similar to the homopolymerization of excess epoxy groups after epoxy-amine addition [10].…”

Section: Preliminary Analysissupporting

confidence: 61%

Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity

et al. 2018

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Dual-curing, that is, the combination of two different polymerization processes taking place simultaneously or sequentially in a curing process, is a highly advantageous technology for the processing of thermosetting systems [1,2] because of its versatility and flexibility. A significant added value of sequential dual curing is possibility of controlling the curing process sequence and the intermediate and final network structures and properties [3-5]. This has potential application in multi-stage processing of one-pot formulations, where materials can be partially pre-cured before their storage, and with tailored material properties for the final application [4-7]. Processing or assembly and the final properties can be achieved whenever desired by using heat or UV light, depending on formulation chemistry, to initiate the final curing stage. Click-type reactions are commonly used in dual-curing formulations [1], in combination with other click [8,9] or non-click reactions [3,5]. Many dual-curable systems are based on acrylate reactions [2,5], although systems based on epoxy curing chemistries such as off-stoichiometric thiol-epoxy [3] or epoxyamine [4,10] formulations, or other epoxy systems [11], are also gaining interest in the recent years. We recently developed a novel off-stoichiometric epoxy-amine system, with excess epoxy groups and latent reactivity in the intermediate state [4]. The first curing reaction was a self-limiting epoxy-amine condensation that takes place at moderate temperatures until exhaustion of reactive amine groups. In the presence of a suitable initiator such as a nucleophilic tertiary amine [10], the excess of epoxy groups can undergo anionic homopolymerization at higher temperatures. However, in this recent work we employed a latent thermal base for the epoxy homopolymerization [4], which ensured at least 7 weeks of storage stability at 30 °C for intermediate materials after the completion of the epoxy-amine reaction. Different materials, coming from a wide range of formulations with different amine-epoxy ratios and tailored intermediate and final properties, were analyzed and characterized, but the curing kinetics of Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity Núria Areny

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Section: Preliminary Analysissupporting

confidence: 61%

Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity

et al. 2018

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“…In addition, one can use other epoxy monomers/resins and change the amount of initiator or type of catalyst to control the reactivity of the curing process. Other dual‐curing thermosetting systems such as off‐stoichiometric thiol–acrylate or epoxy–amine could be used as well, providing suitable catalysts or initiators were used to activate the curing reactions in a controlled way in order to achieve a SHR and therefore enable easy thermal management during processing. We recently reported a novel off‐stoichiometric epoxy–amine system with excellent stability in the intermediate state that could be useful for that purpose …”

Section: Resultsmentioning

confidence: 99%

Sequential heat release: an innovative approach for the control of curing profiles during composite processing based on dual‐curing systems

Romero

Fernández‐Francos

Ramis

2018

Polymer International

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The sequential heat release (SHR) taking place in dual‐curing systems can facilitate thermal management and control of conversion and temperature gradients during processing of thick composite parts, hence reducing the appearance of internal stresses that compromise the quality of processed parts. This concept is demonstrated in this work by means of numerical simulation of conversion and temperature profiles during processing of an off‐stoichiometric thiol–epoxy dual‐curable system. The simulated processing scenario is the curing stage during resin transfer moulding processing (i.e. after injection or infusion), assuming one‐dimensional heat transfer across the thickness of the composite part. The kinetics of both polymerization stages of the dual‐curing system and thermophysical properties needed for the simulations have been determined using thermal analysis techniques and suitable phenomenological models. The simulations show that SHR makes it possible to reach a stable and uniform intermediate material after completion of the first polymerization process, and enables a better control of the subsequent crosslinking taking place during the second polymerization process due to the lower remaining exothermicity. A simple optimization of curing cycles for composite parts of different thickness has been performed on the basis of quality–time criteria, producing results that are very close to the Pareto‐optimal front obtained by genetic algorithm optimization procedures. © 2018 Society of Chemical Industry

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“…As the secondary epoxy homopolymer network imparts high crosslink density to the pristine epoxy-amine network, this dual-curing strategy is useful to obtain materials with superior mechanical properties. Secondary epoxy homopolymerization, with well-defined curing kinetics, is usually carried out using anionic initiators such as imidazole derivatives [63,64]. Since the epoxy-amine reaction has a self-limiting character, the intermediate materials can be stored safely for more than 50 days.…”

Section: Preparation Of Thermosets By Nucleophilic Attack To Epoxy Rementioning

confidence: 99%

The Use of Click-Type Reactions in the Preparation of Thermosets

et al. 2020

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Click chemistry has emerged as an effective polymerization method to obtain thermosets with enhanced properties for advanced applications. In this article, commonly used click reactions have been reviewed, highlighting their advantages in obtaining homogeneous polymer networks. The basic concepts necessary to understand network formation via click reactions, together with their main characteristics, are explained comprehensively. Some of the advanced applications of thermosets obtained by this methodology are also reviewed.

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Curing of off-stoichiometric amine–epoxy thermosets

Cited by 29 publications

References 29 publications

Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity

Time-temperature-transformation (TTT) diagram of a dual-curable off-stoichiometric epoxy-amine system with latent reactivity

Sequential heat release: an innovative approach for the control of curing profiles during composite processing based on dual‐curing systems

The Use of Click-Type Reactions in the Preparation of Thermosets

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