Eric Devaux

Efficient thermal management is essential for the energy balance and thermal comfort. In this context, the design of textiles, which can modulate the infrared radiation emitted by the human body, is attractive. These fabrics will manage the microclimate between the skin and fabric. The proposed textile design consists of the coating of commercial woven fabrics based on polyamide 6–6 by a dip‐coating process. The coating is based on the incorporation of fine spherical silica particles with a submicron size within thermosensitive poly(N‐isopropylacrylamide) hydrogels. Neat commercial fabrics reflect 12% of the radiation, while the addition of silica particles leads to a reflection of 24% of the infrared radiation in the 5–15 μm wavelengths range. The infrared radiation reflection capacity of the coated fabrics can be increased by managing the size and the content of the silica particles, which allows reaching 36% of reflected radiation. Our findings open opportunities for warming up fabrics and thus reduce energy consumption in heating close space.

In many textile fields, such as industrial structures or clothes, one way to detect a specific liquid leak is the electrical conductivity variation of a yarn. This yarn can be developed using melt spun of Conductive Polymer Composites (CPCs), which blend insulating polymer and electrically conductive fillers. This study examines the influence of the proportions of an immiscible thermoplastic/elastomer blend for its implementation and its water detection. The thermoplastic polymer used for the detection property is the polyamide 6.6 (PA6.6) filled with enough carbon nanotubes (CNT) to exceed the percolation threshold. However, the addition of fillers decreases the polymer fluidity, resulting in the difficulty to implement the CPC. Using an immiscible polymers blend with an elastomer, which is a propylene-based elastomer (PBE) permits to increase this fluidity and to create a flexible conductive monofilament. After characterizations (morphology, rheological and mechanical) of this blend (PA6.6_CNT/PBE) in different proportions, two principles of water detection are established and carried out with the monofilaments: the principle of absorption and the short circuit. It is found that the morphology of the immiscible polymer blend had a significant role in the water detection.

Poly(vinylidene fluoride) (PVDF) fibres used to develop sensors or energy harvesters have great potential in the sector of portable electronic devices and especially in the development of smart textiles. This polymorphic polymer is known for several years for its excellent piezoelectric properties related to its different crystalline phases and more particularly to the polar β‐phase is the subject of studies dedicated to the development, optimization, and characterization of β‐PVDF fibres. The presence and the evolution of the different crystalline phases are linked to different factors and can be controlled for example by changing some parameters during the process. In the case of the spinning process, the influence of the operating conditions, such as temperature and drawing on the crystalline structure is currently determined by post‐mortem analyses. Development of ‘mimetic’ tests to characterize in situ the evolution of the crystalline structure of a mechanically stretched polymer is a possible way. Nevertheless, this cannot totally reproduce a real process. For the first time, phase transformations and evolutions of PVDF during a melt‐spinning process were studied online thanks to in situ Raman spectroscopy measurements. Performed at different stages of the spinning line, this method allows us to follow the evolution of the crystalline phases in real time, during the key steps of the process and to conclude on the conditions for obtaining the piezoelectric phase. The successful online characterization of PVDF crystalline phases by Raman spectroscopy opens new perspectives for the optimization of these fibres by controlling the evolution of the structure when changing process parameters.

This work presents the effect of a melt-spinning process on the degradation behavior of bioresorbable and immiscible poly(d,l-lactide) (PLA) and polycaprolactone (PCL) polymer blends. A large range of these blends, from PLA₉₀PCL₁₀ (90 wt% PLA and 10 wt% PCL) to PLA₆₀PCL₄₀ in increments of 10%, was processed via extrusion (diameter monofilament: ∅ ≈ 1 mm) and melt spinning (80 filaments: 50 to 70 µm each) to evaluate the impact of the PCL ratio and then melt spinning on the hydrolytic degradation of PLA, which allowed for highlighting the potential of a textile-based scaffold in bioresorbable implants. The morphologies of the structures were investigated via extracting PCL with acetic acid and scanning electron microscopy observations. Then, they were immersed in a Dulbecco’s Modified Eagle Medium (DMEM) media at 50 °C for 35 days and their properties were tested in order to evaluate the relation between the morphology and the evolution of the crystallinity degree and the mechanical and physical properties. As expected, the incorporation of PCL into the PLA matrix slowed down the hydrolytic degradation. It was shown that the degradation became heterogeneous with a small ratio of PCL. Finally, melt spinning had an impact on the morphology, and consequently, on the other properties over time.

By incorporating electrically conductive yarns into a waterproof membrane, one can detect epoxy resin cracking or liquid leakage. Therefore, this study examined the electrical conductivity variations of several yarns (metallic or carbon-based) for cracking and water detection. The first observations concerned the detectors’ feasibility by investigating their conductivity variations during both their resin implementation processes and their resin cracking. Throughout this experiment, two phenomena were detected: the compression and the separation of the fibres by the resin. In addition, the resin cracking had an important role in decreasing the yarns’ conductivity. The second part of this study concerned water detection. Two principles were established and implemented, first with yarns and then with yarns incorporated into the resin. First, the principle of absorption was based on the conductivity variation with the yarns’ swelling after contact with water. A short circuit was established by the creation of a conductive path when a drop of water was deposited between two conductive, parallel yarns. Through the influence of the yarns’ properties, this study explored the metallic yarns’ capacity to better detect water with a short circuit and the ability of the carbon-based yarns to detect water by the principle of absorption.

In many application fields, such as medicine or sports, heating textiles use electrically conductive multifilaments. This multifilament can be developed from conductive polymer composites (CPC), which are blends of an insulating polymer filled with electrically conductive particles. However, this multifilament must have filler content above the percolation threshold, which leads to an increase of the viscosity and problems during the melt spinning process. Immiscible blends between two polymers (one being a CPC) can be used to allow the reduction of the global filler content if each polymer is co-continuous with a selective localization of the fillers in only one polymer. In this study, three immiscible blends were developed between polypropylene, polyethylene terephthalate, or polyamide 6 and a filled polycaprolactone with carbon nanotubes. The morphology of each blend at different ratios was studied using models of co-continuity and prediction of fillers localization according to viscosity, interfacial energy, elastic modulus, and loss factor of each polymer. This theoretical approach was compared to experimental values to find out differences between methods. The electrical properties (electrical conductivity and Joule effect) were also studied. The co-continuity, the selective localization in the polycaprolactone, and the Joule effect were only exhibited by the polypropylene/filled polycaprolactone 50/50 wt.%.

Composites of polypropylene (PP) and water soluble poly(vinyl alcohol) (PVA) can become an environmentally friendly precursor in preparing porous material, and their biphasic morphology needs to be manipulated. In this work, PP-PVA extrudates were prepared with a twin-screw extruder, and different PP/PVA ratios were employed to manipulate the morphology of the blends. Afterwards, different silicas were imbedded within the blends to further regulate the biphasic microstructure. PVA continuity, as a vital parameter in obtaining porous material, was determined by selective extraction measurement, and PP-PVA biphasic morphology was characterized by scanning microscopy analyses (SEM). Rheological measurement was also performed to correlate the microstructure evolution of the blends. First, it was found that with the increment of PVA proportion, PVA continuity is raised gradually, and the microstructure of blends containing 40–50 wt % of PVA is approaching co-continuous. Second, the localization of silicas was predicted based on the wettability of silica and polymers, and it was also confirmed by TEM that different silicas showed selective distribution. It is inspiring that R972 nanoparticles were found mainly distributed at the interface, which gives a possibility in preparing a surface-modified porous material. The shape distribution and average size of PVA nodules were examined by analyzing the SEM images. It is indicated that silicas with different wettabilities play disparate roles in tuning the biphasic microstructures, leading to heterogeneous PVA continuity.

Microencapsulation has been proved to be an efficient technic to entrap and protect active substance in variety fields of application. This process implies two consecutive stages, that is, the emulsion stage, which can be described as a limiting step since it determines the diameter and size distribution of the microcapsules and need to remain stable long enough to allow the membrane to form in the second one. Pickering emulsions are used to improve the stability of the emulsions and to limit the exudation of the active ingredient during membrane formation. The first part of this chapter deals with the description of the Pickering emulsion stabilized with solid particles. The second part focuses on the use of this kind of emulsion in a microencapsulation process, and the last part concerns a study of the influence of the nanosilica particles on microparticle formation obtained from a sol-gel process.

A first study focused on the realization of a 100% Polyvinylidene fluoride woven fabric. The multi-filaments produced by melt spinning and studied by FTIR, X-Ray and DSC, were optimized in the β-phase, 97%, thanks drawing ratio of λ=5, and the processing temperature, 90°C. When the polar β-phase achieves a certain level in PVDF, the woven material is poling with fields up to about 6kV. DMA tests coupled to a Keithley voltmeter allow the solicitation of PVDF fabrics. A variation of voltage is obtained in compression, with a maximum output voltage of up to 2,3V. The other part of the study explains premises of a tricomponent fibre development, PEHD/PVDF/PA12. Two layers of conductive polymers acting as electrodes are placed on either side of the PVDF layer. The interfacial adhesion between the three different layers is analysed by SEM. The maximum stretch on melt spinning was fixed at 2.5 and the β-phase of the PVDF measured by X-Ray.