Polyvinylidene fluoride (PVDF) is among the most attractive piezo-polymers due to its excellent piezoelectricity, lightweight, flexibility, high thermal stability, and chemical resistance. PVDF can exist under different forms of films, membranes, and (nano)fibers, and its piezoelectric property related to its β phase content makes it interesting for energy harvesters and wearable applications. Research investigation shows that PVDF in the form of nanofibers prepared by electrospinning has more flexibility and better air permeability, which make them more suitable for these types of applications. Electrospinning is an efficient technique that produces PVDF nanofibers with a high β phase fraction and crystallinity by aligning molecular dipoles (–CH2 and –CF2) along an applied voltage direction. Different nanofibers production techniques and more precisely the electrospinning method for producing PVDF nanofibers with optimal electrospinning parameters are the key focuses of this paper. This review article highlights recent studies to summarize the influence of electrospinning parameters such as process (voltage, distance, flow rate, and collector), solution (Mw, concentration, and solvent), and ambient (humidity and temperature) parameters to enhance the piezoelectric properties of PVDF nanofibers. In addition, recent development regarding the effect of adding nanoparticles in the structure of nanofibers on the improvement of the β phase is reviewed. Finally, different methods of measuring piezoelectric properties of PVDF nanofibrous membrane are discussed.

Using bio-based polymers to replace of polymers from petrochemicals in the manufacture of textile fibers is a possible way to improve sustainable development for the textile industry. Polylactic acid (PLA) is one of the available bio-based polymers. One way to improve the fire behavior of this bio-based polymer is to add an intumescent formulation mainly composed of acid and carbon sources. In order to optimize the amount of bio-based product in the final material composition, lignin from wood waste was selected as the carbon source. Different formulations of and/or ammonium polyphosphate (AP) were prepared by melt extrusion and then hot-pressed into sheets. The thermal properties (thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC)) and fire properties (UL-94) were measured. The spinnability of the various composites was evaluated. The mechanical properties and physical aspect (microscopy) of PLA multifilaments with lignin (LK) were checked. A PLA multifilament with up to 10 wt % of intumescent formulation was processed, and the fire behavior of PLA fabrics with lignin/AP formulation was studied by cone calorimeter.

Lignin is a highly abundant bio-polymeric material that constitutes cellulose one of major component in cell wall of woody plants. Alternatively, large quantity of lignin is yearly available from numerous pulping and paper industries; this is the key point that justifies its large use for industrial applications. Lignin could be one of the most essential and sustainable bio-resources as raw material for the development of environmentally friendly polymer composite. Owing to its huge chemical structure, lignin can provide additional functionality such as filler, reinforcing agent, compatibilizer, stabilizer, etc. In this study, the fire retardant functionality of lignin has been employed in polymeric materials. Due to high charring capability, lignin is effectively used as carbon source in combination with other flame retardants for designing the intumescent system for polymeric materials. Further in this, several articles related to lignin-based intumescent are reviewed and interesting work formulation as well as meaningful results achieved in the flame retardancy are discussed. More attention is given to the studies concerning the use of current intumescent systems for textile applications by means of coating on fabric/nonwoven and melt blending in bulk polymers.

Piezoelectric textile structures based on 100% poly(vinylidene fluoride) (PVDF) were developed and characterised. Multifilaments of 246 tex were produced by melt spinning. The mechanical stretching during the process provides PVDF fibres with a piezoelectric β-phase of up to 97% has been measured by FTIR experiments. Several studies have been carried out on piezoelectric PVDF-based flexible structures (films or textiles), the aim of the study being the investigation of the differences between 2D and 3D woven fabrics from 100% optimised (by optimising piezoelectric crystalline phase) piezoelectric PVDF multifilament yarns. The textile structures were poled after the weaving process, and a maximum output voltage of 2.3 V was observed on 3D woven under compression by DMA tests. Energy harvesting is optimised in a 3D interlock thanks to the stresses of the multifilaments in the thickness. The addition of a resistor makes it possible to measure energy of 10.5 μJ.m−2 during 10 cycles of stress in compression of 5 s each.

This study investigates the influence of various lignins and their content on the thermal stability and fire retardancy of biobased polyamide 11 (PA). Microcomposites based on PA and containing 5, 10, 15, and 20 wt % different lignins were prepared with a twin-screw extruder. Morphological analysis showed good interfacial interaction and uniform distribution of lignin particles within the resulting microcomposites. Further, thermogravimetric analyses carried out in inert atmosphere indicated that, unlike kraft lignin, which is able to give rise to the formation of lower char residue (41–48 wt % at 600 °C), the sulfonated counterpart provides a higher thermal stability as well as a higher char residue (55–58 wt %). Furthermore, vertical flame spread tests clearly showed that 15 wt % is the optimum of kraft or sulfonated lignin loading to achieve improved flame retardant properties and a V1 rating. In addition, a cone calorimeter was exploited to study forced combustion behavior; in particular the microcomposites containing sulfonated lignin revealed significant reductions of the peak of the heat release rate (−51%) and of the total heat release (−23%) and a lower average mass loss rate together with a noticeable increase of the final residual mass (about 9 wt %). Conversely, the microcomposites containing kraft lignins showed opposite effect, since heat release rate (HRR) and total heat release (THR) values increased in the presence of kraft lignin.

Flame retardancy of polymers is a recurring obligation for many applications. The development trend of biobased materials is no exception to this rule, and solutions of flame retardants from agro-resources give an advantage. Lignin is produced as a waste by-product from some industries, and can be used in the intumescent formation development as a source of carbon combined with an acid source. In this study, the flame retardancy of polyamide 11 (PA) is carried out by extrusion with a kraft lignin (KL) and ammonium polyphosphate (AP). The study of the optimal ratio between the KL and the AP makes it possible to optimize the fire properties as well as to reduce the cost and facilitates the implementation of the blend by a melting process. The properties of thermal decomposition and the fire reaction have been studied by thermogravimetric analyzes, pyrolysis combustion flow calorimetry (PCFC) and vertical flame spread tests (UL94). KL permits a charring effect delaying thermal degradation and decreases by 66% the peak of heat release rate in comparison with raw PA. The fire reaction of the ternary blends is improved even if KL-AP association does not have a synergy effect. The 25/75 and 33/67 KL/AP ratios in PA give an intumescence behavior under flame exposure.

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