Investigation of the thermal self-healing mechanism in a cross-linked epoxy system

Bai, Nan; Simon, George P.; Saito, Kei

doi:10.1039/c3ra43746a

Cited by 41 publications

(40 citation statements)

References 23 publications

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“…The main challenge connected with the preparation of a self-healing Diels-Alder (DA) functionalised resin is the activation of selective desired reactions (DA coupling) while avoiding undesired side reactions, such as Michael addition [17] or homo-polymerisation of BMI [18], that occur at high temperatures [19]. To ensure the resultant self-healing polymer had sufficient reactivity after processing careful considerations were taken during the synthesis with respect to the order of the reactions, by using stepwise synthesis and limiting the exposure to oxygen during high temperature processing.…”

Section: Resultsmentioning

confidence: 99%

Novel Diels-Alder based self-healing epoxies for aerospace composites

Coope¹,

Turkenburg²,

Fischer³

et al. 2016

Smart Mater. Struct.

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Epoxy resins containing Diels-Alder furan and maleimide moieties are presented with the capability to self-heal after exposure to an external heat source. A conventional epoxy amine system has been combined with furfuryl and maleimide functional groups in a two-step process, to avoid major sidereactions, and the concentration of a thermo-reversibly binding cross-linker was considered to balance thermoset and thermoplastic behaviours, and the subsequent self-healing performance.In the context of self-repair technologies an inbuilt 'intrinsic' self-healing system is deemed favourable as the healing agent can be placed in known 'hot spot' regions (i.e. skin-stringer run outs, ply drops and around drilled holes) where operational damage predominately occurs in load bearing aerospace structures. In this study, the mechanical and self-healing performance of furan functionalised epoxy resins containing varying amounts (10, 20, 30 or 40 pph) of bismaleimide were investigated using a bulk epoxy polymer tapered double cantilever beam (TDCB) test specimen geometry. Two forms, a thin film and a bulk material, were evaluated to account for future integration methods into fibre reinforced polymer (FRP) composites. The highest healing efficiency, with respect to the obtained initial load value, was observed from the 20 pph bulk material derivative. The polymers were successful in achieving consistent multiple (three) healing cycles when heated at 150 °C for 5 minutes.This novel investigated Diels-Alder material exhibits favourable processing characteristics for FRP composites as preliminary studies have shown successful coextrution with reinforcing fibres to form free standing films and dry fibre impregnation.

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Section: Resultsmentioning

confidence: 99%

Novel Diels-Alder based self-healing epoxies for aerospace composites

Coope¹,

Turkenburg²,

Fischer³

et al. 2016

Smart Mater. Struct.

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“…Recent methodologies for self‐healing polymers use covalent dynamic reactions which require external stimuli such as heat or light to heal damages. Different chemistries have been established to enable self‐healing for polymers such as Diels‐Alder reactions,, or imine,, alkoxyamine and disulphide exchange procedures ,…”

Section: Figurementioning

confidence: 99%

Light‐Switchable Self‐Healing Dynamic Linear Polymers: Reversible Cycloaddition Reactions of Thymine‐Containing Units

Abdallh

Hearn

et al. 2019

ChemPlusChem

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A dynamic linear polymer was formed by the [2π + 2π] reversible cycloaddition reaction of a thymine-based monomer under topochemical conditions and was used in self-healing applications. The reversible polymerisation of the thymine monomer was confirmed by UV and GPC analysis. Irradiation at 302 nm resulted in polymerisation of the monomer, and irradiation with wavelengths lower than 240 nm resulted in depolymerisation and the production of oligomeric units. This leads to a reduction in the glass transition temperature, and promoted healing of surface scratches due to the increased chain mobility. The self-healing ability of scratched samples was assessed based on the visual disappearance of the damage. In addition, the mechanical properties of the polymer before and after healing were found to be similar. [a] Dr. M. Abdallh, Mr. P. He, Prof. M. T.

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“…Since then, Liu et al., [ 22 ] Park et al., [ 23 ] Bai et al., [ 24,25 ] and Kuang et al. [ 26 ] also utilized the FA/BMI‐based DA bonds to modify epoxy to prepare a remendable epoxy resin, and results also suggested that the synthesized epoxy system can self‐heal its own cracks to some extent. But an unavoidable fact is that Michael addition side‐reaction would happen between FA and BMI, which would decrease the self‐healing efficiency.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Diels‐Alder Reaction‐Based Remendable Epoxy Matrix and Corresponding Self‐healing Efficiency to Fibrous Composites

Liu

2020

Macro Materials & Eng

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Thus, delamination and micro-cracks occurred within the FRPs become the potential safety risks of FRPs. Most importantly, with the increasing usages of FRPs, a serious problem is that the scrapping of a large number of FRPs will increase the negative impact on the environment. Therefore, self-healable FRPs have attracted much attention in recent years. [6] That is once dangerous cracks occur within the FRPs, they are immediately healed by applying reasonable external or internal excitations, which will significantly improve the reliability and service life of the FRPs. There are mainly two kinds of crack self-healing technologies proposed for FRPs, i.e., introducing of extrinsic microcapsules or micro-vessels injected with healing agents into FRPs [7-10] and developing of new epoxy matrix systems with intrinsic crack self-healing functions for FRPs. [11-14] The latter method mainly involves introducing some polymers possessing dynamic reversible chemical bonds into a mature epoxy resin to form a new epoxy system, and micro-cracks occurred within the cured products could be healed by the reversible bonds' dissociation and reassociation when applying proper thermal excitations. [15-18] In fact, Diels-Alder (DA) reaction is an important thermo-reversible dynamic covalent bond and currently is the most popularly studied one, possessing advantages of mild reaction conditions, few by-products and catalyst-free requirements. [19] The involved mechanism is that by incorporating a DA bond into a thermosetting epoxy resin (which is originally cured as insoluble and unmeltable), the cured DA bond-modified epoxy system will show somewhat thermoplastic characteristics such as thermal softening. Then the internal fractured molecular segments could re-crosslink at a certain temperature and so self-healing of micro-cracks can be realized. [6,19] Furthermore, taking the self-healing efficiency and manufacturing compatibility with epoxy resins into consideration, one most promising way is by introducing a special DA bond obtained from furan (FA) and bismaleimide (BMI) into a mature epoxy system and so it is possible to quickly develop an optimal epoxy system with high self-healing capability. [6] One of the earliest works carried out by Chen et al. [20,21] had demonstrated that the covalent crosslinked networks formed by thermo-reversible DA reaction between furfuryl (within a FA) and maleimide groups (within a BMI) show good crack A Diels-Alder (DA) thermo-reversible compound consisting of a furan (FA) and a bismaleimide (BMI) is synthesized and grafted to a general low-viscosity epoxy to prepare a self-healable epoxy matrix system. Results prove that the synthesized epoxy can completely self-heal its own cracks and the interlaminar shear cracks of a fiber reinforced plastic (FRP) due to the dissociation and reassociation of DA thermo-reversible covalent bonds under proper thermal excitations. Self-healing efficiencies of 108.5% for the first healing and 130.5% for the second healing are obtained to the mode II interlaminar fract...

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Investigation of the thermal self-healing mechanism in a cross-linked epoxy system

Cited by 41 publications

References 23 publications

Novel Diels-Alder based self-healing epoxies for aerospace composites

Novel Diels-Alder based self-healing epoxies for aerospace composites

Light‐Switchable Self‐Healing Dynamic Linear Polymers: Reversible Cycloaddition Reactions of Thymine‐Containing Units

Synthesis of Diels‐Alder Reaction‐Based Remendable Epoxy Matrix and Corresponding Self‐healing Efficiency to Fibrous Composites

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