Effect of mechanical damage and wound healing on the viscoelastic properties of stems of flax cultivars (Linum usitatissimum L. cv. Eden and cv. Drakkar)

As plant fibres are increasingly used in technical textiles and their composites, underlying principles of wound healing in living plant fibres are relevant to product quality, and provide inspiration for biomimetic healing in synthetic materials. In this work, two Linum usitatissimum cultivars differing in their stem mechanical properties, cv. Eden (stems resistant to lodging) and cv. Drakkar (with more flexible stems), were grown without wound or with stems previously wounded with a cut parallel or transversal to the stem. To investigate wound healing efficiency, growth traits, stem biomechanics with Dynamic Mechanical Analysis and anatomy were analysed after 25-day recovery. Longitudinal incisions formed open wounds while transversal incisions generated stem growth restoring the whole cross-section but not the original stem organisation. In the case of transversal wound healing, all the bast fibre bundles in the perturbed area became lignified and pulled apart by parenchyma cells growth. Both Linum cultivars showed a healing efficiency from 79% to 95% with higher scores for transversal healing. Morphological and anatomical modifications of Linum were related to mechanical properties and healing ability. Alongside with an increased understanding of wound healing in plants, our results highlight their possible impact on textile quality and fibre yield

Self-Healing Fiber-Reinforced Composites with Tailored Supramolecular Matrices

Fiber Reinforced Composites (FRCs), due to their intrinsic heterogeneity, are generally affected by complex multi-scale failure mechanisms leading to the formation of matrix cracks that are difficult to detect and repair. FRCs with the ability to heal and recover at least part of their initial properties after damage could present a solution to extend their lifetime and reliability. A possible approach is to introduce external healing agents in the matrix of the composite, through capsules or micro-channels, but this is often difficult to achieve in a high volume fraction reinforcement composite. An alternative approach is to rely on intrinsic self-healing polymers as matrices, which alleviates the need for additional phases beyond matrix and reinforcement. The present work investigated this second approach, by exploring for the first time the feasibility of processing glass fabric reinforced composites based on supramolecular hybrid network self-healing matrices and analysing their resulting properties and transfer of the self-healing ability to the composite. Hybrid networks based on epoxy chemistry, combining covalent cross-links and cooperative reversible hydrogen bonds, were selected as benchmark materials. These systems were charac- terized, in particular in terms of processing parameters and self-healing ability, and showed to be a-priori compatible with FRCs manufacturing techniques and demonstrated higher healing efficiency by increasing the H-bonds content in the polymer network, from none to 50%. On the other hand, networks characterized by large number of physical cross-links exhibited limited solvent and creep resistance, hindering their potential application. These issues were addressed by modifying the average functionality of the monomers through the combination of bifunctional and tetrafunctional epoxy resins in the compositions while keeping the use of a catalyst, leading to better controlled networks, both in terms of kinetics and final structure, and to propose a range of materials with several levels of compromise between self-healing efficiency, mechanical strength, creep resistance, and damping properties. In particular, 50% to 100% self-healing recovery of tensile properties were observed after one day, depending on the tetraepoxide content. In parallel, since the Tg of benchmark supramolecular hybrid net- works was in the range from 11-16 âŠC, an aliphatic diepoxide was introduced in the synthetic procedure to propose materials with a Tg down to -10 âŠC, to reach applications closer to those of elastomers. In view of FRCs development, the ability of partially supramolecular self-healing polymers to bond to inorganic reinforcements and to heal interfacial failure was then investigated: two dedicated butt joint-like and tack-like test methods were developed. Adhesion strength of the polymers cured on glass substrates decreased with increasing H-bonds content in the polymer networks (from 0 to 50 %) as the mechanical strength of the polymer also decreased, while the failure mechanism shifted from adhesive to cohesive due to the possibility to form hydrogen bonds with the glass substrates. Interface restoration through healing of the polymer matrices however increased from none to a strength recovery up to 70 % after 1 h healing time for the 50% H-bond polymer..

Processing and damage recovery of intrinsic self-healing glass fiber reinforced composites

Glass fiber reinforced composites with a self-healing, supramolecular hybrid network matrix were produced using a modified vacuum assisted resin infusion moulding process adapted to high temperature processing. The quality and fiber volume fraction (50%) of the obtained materials were assessed through microscopy and matrix burn-off methods. The thermo-mechanical properties were quantified by means of dynamic mechanical analysis, revealing very high damping properties compared to traditional epoxy-based glass fiber reinforced composites. Self-healing properties were assessed by three-point bending tests. A high recovery of the flexural properties, around 72% for the elastic modulus and 65% of the maximum flexural stress, was achieved after a resting period of 24 h at room temperature. Recovery after low velocity impact events was also visually observed. Applications for this intrinsic and autonomic self-healing highly reinforced composite material point towards semi-structural applications where high damping and/or integrity recovery after impact are required

Adhesion and interfacial healing between supramolecular hybrid networks and glass substrates

Adhesion towards glass and interfacial healing of partially supramolecular hybrid polymer networks featuring a range of H-bdnds content were investigated through two dedicated adhesion test methods. In a first series of tests, adhesion strength was measured by separating two substrates containing a cured inner resin layer, and shown to decrease with increasing H-bonds content in the polymer network (from 0 to 50%) as the mechanical strength of the polymer also decreased while the failure mechanism shifted from adhesive to cohesive due to the possibility to form hydrogen bonds with glass substrates. In a second step, the test was used to evaluate interface restoration through healing of the polymer matrices and results showed an increased from none to a tensile strength recovery up to 70% after 1 h healing time for the 50% H-bond polymer. Then, self-adhesion of freshly cut polymer surfaces to glass substrates was investigated, showing increasing tack with increasing H-bonds content. The influence of glass surface treatments on adhesion and interfacial recovery properties was also explored: while aminosilanes did not influence the interfacial behavior of partially supramolecular self healing polymers towards glass, trimethoxy (octadecyl)silane (ODS) modification strongly hindered their adhesion abilities, further highlighting the fundamental role of hydrogen bonds interaction with the substrates

Insights into the fabrication of sub-100 nm textured thermally drawn fibers

The preform-to-fiber thermal drawing process has been recently proposed for the fabrication of fibers and microchannels with submicrometer surface textures. To better control the final architecture and reach small feature size down to tens of nanometers however, a proper understanding and modeling of the fluids dynamics at play during the fabrication of the texture is needed. Here, we present an analytical model describing comprehensively the reflow of periodic polymer micropatterns of arbitrary shape in isothermal annealing as well as in a fiber drawing process. Experiments on square-grooved thermoplastic plates subjected to both treatments show excellent agreement with the calculated theoretical values. Based on this model, we could identify a strategy and the corresponding materials to fabricate sub-100 nm surface-patterned fibers. These results deepen the understanding and control of thermal-based approaches for polymer surface texturing and open novel opportunities for textured fibers and microchannels in bioengineering, microfluidics, or smart textiles. Published under license by AIP Publishing

Design of Self-Healing Supramolecular Rubbers with a Tunable Number of Chemical Cross-Links

Supramolecular rubbers incorporating a large number of physical cross-links through cooperative hydrogen bonds display high self-healing properties but limited solvent and creep resistance due to the lack of chemical cross-links. Increasing both chemical cross-links and H-bonding is therefore desirable but limited by the functionality of monomers. The present work thus devises a convergent chemical platform permitting to increase the number of chemical cross-links without changing the concentration of hydrogen-bonding groups. Starting from a single reactive prepolymer, functionalized with a defined number of hydrogen-bonding groups, a series of networks presenting different ratios of diepoxide and tetraepoxide were prepared. The curing process (controlled by 2-MI catalyst), thermomechanical behavior, and tensile properties recovery of the cured materials were investigated. Gelation state was quantified and compared to theoretical predictions. The introduction of tetrafunctional epoxide in the presence of 2-MI gave rise to gelled materials characterized by higher rigidity and strength and significantly improved creep resistance. Self-healing was observed for all materials, with 50% to 100% complete recovery in a day depending on tetraepoxide content

Advanced Multimaterial Electronic and Optoelectronic Fibers and Textiles

The ability to integrate complex electronic and optoelectronic functionalities within soft and thin fibers is one of today's key advanced manufacturing challenges. Multifunctional and connected fiber devices will be at the heart of the development of smart textiles and wearable devices. These devices also offer novel opportunities for surgical probes and tools, robotics and prostheses, communication systems, and portable energy harvesters. Among the various fiber-processing methods, the preform-to-fiber thermal drawing technique is a very promising process that is used to fabricate multimaterial fibers with complex architectures at micro- and nanoscale feature sizes. Recently, a series of scientific and technological breakthroughs have significantly advanced the field of multimaterial fibers, allowing a wider range of functionalities, better performance, and novel applications. Here, these breakthroughs, in the fundamental understanding of the fluid dynamics, rheology, and tailoring of materials microstructures at play in the thermal drawing process, are presented and critically discussed. The impact of these advances on the research landscape in this field and how they offer significant new opportunities for this rapidly growing scientific and technological platform are also discussed

Edible fiber

The invention provides an edible fiber comprising a biopolymer and a plasticiser; wherein the weight ratio of biopolymer to plasticiser is about 1:0.25 to about 1:3; and wherein the fiber has a diameter of about 0.5 μm to about 1 mm