Thermally reversible cross-links in a healable polymer: Estimating the quantity, rate of formation, and effect on viscosity

Nielsen, Christian; Weizman, Haim; Nemat‐Nasser, Sia

doi:10.1016/j.polymer.2013.12.030

Cited by 10 publications

(14 citation statements)

References 28 publications

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“…On one hand, a long heating of the network leads to the conversion of the endo-to exo DA adducts, 42,43 in accordance with the formation of stronger hydrogen bonds in the exo-type of the (thio)urethane network. The reason for the modulus recovery exceeding 100% is probably related to the better order in the hard phase, which is composed of hydrogen-bonded (thio)urethane and ester groups.…”

Section: Scratch-healing Behaviourmentioning

confidence: 98%

Healable shape memory (thio)urethane thermosets

et al. 2015

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Urethane-thiourethane networks combining shape memory properties and the ability to self-heal under mild temperature conditions via Diels-Alder (DA) chemistry were developed. As a result of the shape recovery effect, no external force was needed to bring the fracture surfaces into intimate contact during the healing process. Four network architectures with DA net-points were evaluated. Two systems were composed of either bismaleimidic or bisfuranic semi-crystallized polycaprolactone chains acting as shape memory switching segments (T trans = T m ), whereas the other two networks consisted of bis-/trismaleimidic and trisfuranic monomers and displayed glass transitions for initiating shape recovery behaviour (T trans = T g ). The formation of the DA cross-links, the DA reversibility and shape memory assisted scratch healing of the materials were studied by FTIR and 1 H-NMR spectrometry, differential scanning calorimetry, optical microscopy and tensile measurements. The results indicated that the healing efficiency of scratches depends strongly on the shape recovery ability, without which crack closure and thus the healing reaction could not occur. Two materials were found to feature good shape memory properties as well as efficient scratch-healing capacities, showing mechanical recoveries of 70-80% and the almost complete disappearance of scratches after healing at a mild temperature of 60°C for 1-3 days. These materials could find applications in diverse fields such as self-healing coatings.Scheme 1 Chemical structures of the (thio)urethane multi-maleimide and multi-furan monomers and schematic depiction of the SM networks reversibly cross-linked by the DA reaction. Polymer Chemistry PaperThis journal is

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Section: Scratch-healing Behaviourmentioning

confidence: 98%

Healable shape memory (thio)urethane thermosets

et al. 2015

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“…Several scientific articles have reported the ability of thermoset polymers to be repaired in different ways. These include the incorporation of low molecular weight additives in the form of capsules as healing agent after damage events (extrinsic self-repair) [12][13][14][15][16], but also the functionalization of raw non-reworkable polymers that can heal cracks as a consequence of an external stimuli like heat [17][18][19][20] and light [21][22][23][24][25] (intrinsic self-repair). The last approach relies on the chemical modification of the base polymer with functional groups able to undergo a reversible reaction as function of the presence/absence of the external stimulus.…”

Section: Introductionmentioning

confidence: 99%

Intrinsic self-healing thermoset through covalent and hydrogen bonding interactions

Araya-Hermosilla

Lima

Raffa

et al. 2016

European Polymer Journal

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The intrinsic self-healing ability of polyketone (PK) chemically modified into furan and/or OH groups containing derivatives is presented. Polymers bearing different ratios of both functional groups were cross-linked via furan/bis-maleimide (Diels-Alder adducts) and hydrogen bonding interactions (aliphatic and aromatic OH groups). The resulting thermosets display tuneable softening points (peak of tan (δ)) from 90 to 137 °C as established by DMTA. It is found that the cross-linked system containing only furan groups shows the highest softening temperature. On the other hand, systems displaying the combination of Diels-Alder adducts and hydrogen bonding (up to 60 mol % of -OH groups) do not show any change in modulus between heating cycles (i.e. factually a quantitative recovery of the mechanical behaviour). It is believed that the novelty of these tuneable thermosets can offer significant advantages over conventional reversible covalent systems. The synergistic reinforcement of both interactions resists multiple heating/healing cycles without any loss of mechanical properties even for thermally healed broken samples

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“…Each sample was formed from prepreg layers containing either Toray T300 carbon fiber or AGY S-2 glass fiber. The properties of each composite constituent are given in Table 1. The prepreg process was developed as an extension of the small-sample 2MEP4FS processing method outlined by Nielsen et al (2014). This method allows small quantities of polymer to be produced with precise monomer ratios and minimal wasted material.…”

Section: Sample Preparationmentioning

confidence: 99%

“…The glass transition temperatures of the carbon fiber and glass fiber composites were 94.7 °C and 100.8 °C respectively. Applying the previously determined model for 2MEP4FS cross-linking as a function of (Nielsen et al, 2014) gives conversions of 0.956 and 0.998, where 1 indicates a fully cured sample. The relatively low final conversion of the carbon fiber composite may be due to the increased surface area of the smaller diameter carbon fibers and more sizing transferring into the polymer and acting as a plasticizer.…”

Section: Differential Scanning Calorimetrymentioning

confidence: 99%

Crack healing in cross-ply composites observed by dynamic mechanical analysis

Nielsen

Nemat‐Nasser

2015

Journal of the Mechanics and Physics of Solids

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Cross-ply composites with healable polymer matrices are characterized using dynamic mechanical analysis (DMA). The [90,0] s samples are prepared by embedding layers of unidirectional glass or carbon fibers in 2MEP4FS, a polymer with thermally reversible covalent cross-links previously shown to be capable of healing internal cracks and fully recovering fracture toughness under ideal conditions. After fabrication, cracks in the composites' transverse plies are observed and attributed to residual thermal stresses introduced during processing.Single cantilever bending DMA measurements show the samples exhibit periods of increasing storage moduli with increasing temperature. These results are accurately modeling using simple one-dimensional composite and beam analyses. The effect of cracks on the measured stiffness is considered using a shear lag model, and the predicted crack density of the glass fiber composite falls within a range estimated by microscopy observations. Crack healing is assumed to occur as a function of temperature, and rationales for the onset and conclusion of healing are given.

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Thermally reversible cross-links in a healable polymer: Estimating the quantity, rate of formation, and effect on viscosity

Cited by 10 publications

References 28 publications

Healable shape memory (thio)urethane thermosets

Healable shape memory (thio)urethane thermosets

Intrinsic self-healing thermoset through covalent and hydrogen bonding interactions

Crack healing in cross-ply composites observed by dynamic mechanical analysis

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