Multiple welding of long fiber epoxy vitrimer composites

Chabert, Erwan; Vial, Jérôme; Cauchois, Jean-Pierre; Mihaluta, Marius; Tournilhac, François

doi:10.1039/c6sm00257a

Cited by 162 publications

(154 citation statements)

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“…The temperature dependence of the stress relaxation is illustrated in Figure 3B for cured p X2.4 and it is immediately clear that an increase in temperature leads to a faster stress relaxation. Analogous to what has been done in other vitrimer studies, [1][2][3]17,18,[22][23][24][25][26][27]35,36] we use the relaxation time τ, which is defined as the time it takes for the modulus to relax to 1/e of its original value, as a characteristic measure for stress relaxation. The data in Figure 3B show that an increase in temperature from 230 to 260 °C leads to a Figure 3C.…”

Section: Doi: 101002/marc201800356mentioning

confidence: 99%

In Situ Network Formation in PBT Vitrimers via Processing‐Induced Deprotection Chemistry

Zhou

Goossens

Bergen

et al. 2018

Macromol. Rapid Commun.

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in the solid state. [38,45] In general, the terminal relaxation behavior of PBT vitrimers above the melting temperature was rarely observed at angular frequencies down to 10 −2 s −1 in the temperature range from 250 to 270 °C. [37,38,45] Considering that typical shear rates during injection molding are as high as 10 000 s −1 and the viscosity of PBT vitrimers can be up to 10 7 Pa s at 250 °C, these PBT vitrimers cannot be processed like neat PBT during the short residence times typical for extrusion and injection molding. [52] Here, we propose a controllable way to process PBT vitrimers (based on transesterification exchange reactions) via controlling the network formation with the help of protection-deprotection chemistry. In this way, we can overcome the relatively long relaxation times and high viscosities associated with PBT vitrimers and maintain the high production rates of final parts by injection molding as for neat PBT. The strategy is schematically shown in Scheme 1: pentaerythritol is first converted into 5,5-bis(hydroxymethyl)-2-phenyl-1,3-dioxane (BPO, melting point 135-137 °C) via benzaldehyde protection chemistry. [53] Subsequently, this diol is incorporated into the PBT backbone via solid-state (co)polymerization to form a linear copolyester in line with earlier work from our group on PBT modification in the solid state. [54][55][56][57][58][59][60] The linear polymer chain is then transformed into a network via deprotection of the benzal group to afford a linear polymer chain with pendent-free hydroxyl groups for further thermal transesterification of the linear copolyester catalyzed by the Zn(II) catalyst. If deprotection and subsequent cross-linking takes place during processing, we can combine an initial low viscosity with final vitrimer characteristics.Normally, the deprotection step to obtain the linear copolyester with pendent hydroxyl groups, as shown in Scheme 1, involves an acid-promoted deprotection of the benzal group at room temperature and an acid used often is trifluoroacetic acid (TFA). [53] Accidentally we discovered that compression molding of the linear copolyester with benzal protection groups resulted in a cross-linked material with vitrimer characteristics, even without deprotection with TFA. This observation is in contrast to results previously reported by Collard et al., [53] who obtained thermoset materials after incorporation of BPO into PBT and poly(ethylene terephthalate) (PET) and repeated subsequent cycling to 300 °C in differential scanning calorimetry (DSC). Driven by this intriguing result and its practical relevance, we investigated the in situ network formation in more Vitrimers Although the network dynamics and mechanical properties of poly(butylene terephthalate) vitrimers can to some extent be controlled via chemical and physical approaches, it remains a challenge to be able to process PBT vitrimers with the same processing conditions via, for example, injection molding as neat PBT. Here, it is shown that the use of protected pentaerythritol as a latent cross...

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Section: Doi: 101002/marc201800356mentioning

confidence: 99%

In Situ Network Formation in PBT Vitrimers via Processing‐Induced Deprotection Chemistry

Zhou

Goossens

Bergen

et al. 2018

Macromol. Rapid Commun.

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“…Unlike permanently cross-linked elastomers or gels, these bond swaps allow vitrimers to release internal stresses without losing shape. Their versatility shines particularly in smartly designed materials, where bond swapping provides a welding strategy [6], or responsiveness to light, pH, voltage, metal ions, redox chemicals and mechanical stimuli [7][8][9].The unusual molecular interaction in vitrimers renders current theories of polymer performance of limited use. Neither a conventional static model nor a fully dynamic one can coherently address the exchange dynamics.…”

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confidence: 99%

Dynamics of Vitrimers: Defects as a Highway to Stress Relaxation

2018

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We propose a coarse-grained model to investigate stress relaxation in star-polymer networks induced by dynamic bond-exchange processes. We show how the swapping mechanism, once activated, allows the network to reconfigure, exploring distinct topological configurations, all of them characterized by complete extent of reaction. Our results reveal the important role played by topological defects in mediating the exchange reaction and speeding up stress relaxation. The model provides a representation of the dynamics in vitrimers, a new class of polymers characterized by bond-swap mechanisms which preserve the total number of bonds, as well as in other bond-exchange materials.

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“…2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27 Other studies explored the properties of vitrimer composites and the addition of nondynamic cross-links to the network. 14,28,29,30,31,32,33,34,35 These research efforts established that modifying vitrimer chemistry provides a pathway for tuning mechanical properties, 36,37,38 stress relaxation, 39,40,41,42 shape memory, 43,44,45 and the ability to self-heal and adhere to other materials. 21,46 Due to this versatility, vitrimers are now being tested for a variety of high-end applications.…”

Section: Introductionmentioning

confidence: 99%

Linear Viscoelasticity and Flow of Self-Assembled Vitrimers: The Case of a Polyethylene/dioxaborolane System

Ricarte

Tournilhac²,

Cloître³

et al. 2019

Preprint

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For vitrimer systems obtained by dynamic cross-linking of polymer chains, incompatibility effects between the cross-links and polymer backbone can lead to microphase separation, resulting in a network made of cross-linked aggregates. Additionally, when there is a wide distribution of the number of cross-links per chain, macrophase separation can occur. Here, we investigate the linear viscoelasticity and flow of a polyethylene (PE) vitrimer that has cross-linkable dioxaborolane maleimide grafts, which aggregate into a hierarchical nanostructure. To elucidate the role of selfassembly, noncross-linked graft functionalized PE was first studied. It had a terminal relaxation time that was orders of magnitude larger than both neat PE and partially peroxide cross-linked PE.When dioxaborolane cross-linker was added to form the vitrimer, the resulting material could not achieve terminal relaxation within 8 hr. The graft-poor soluble and graft-rich insoluble portions of the PE vitrimer were then isolated and characterized. The soluble portion expressed similar flow behavior as neat PE, while the insoluble portion -which is a network of cross-linked aggregatesrelaxed very little over 8 hr. When the insoluble and soluble portions were blended, the rheological behavior of the original vitrimer was basically recovered, showing that the soluble portion acts as a lubricant. When the insoluble portion was blended with neat PE, the material relaxed much more stress, but still did not reach steady-state flow within 8 hr. When high stresses were applied, however, PE vitrimer flowed. Nonlinear rheology experiments revealed melt fracture at high strains and suggested that flow is enabled by rapid healing, which follows fracture events. The presence of macroscopic phase separation facilitated flow.

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Multiple welding of long fiber epoxy vitrimer composites

Cited by 162 publications

References 50 publications

In Situ Network Formation in PBT Vitrimers via Processing‐Induced Deprotection Chemistry

In Situ Network Formation in PBT Vitrimers via Processing‐Induced Deprotection Chemistry

Dynamics of Vitrimers: Defects as a Highway to Stress Relaxation

Linear Viscoelasticity and Flow of Self-Assembled Vitrimers: The Case of a Polyethylene/dioxaborolane System

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