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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.

Biobased lignin represents one of the possible materials for next-generation flame retardant additives due to its sustainability, environmental benefits and comparable efficiency to other flame retardant (FR) additives. In this context, this study presents the development of FR polyamide 11 (PA11) multifilament yarns and fabric structures containing different industrial lignins (i.e., lignosulfonate lignin (LL), and Kraft lignin (KL)) and zinc phosphinate (ZnP). The combination of ZnP and lignin (KL or LL) at different weight ratios were used to prepare flame retarded PA11 blends by melt mixing using a twin-screw extruder. These blends were transformed into continuous multifilament yarns by the melt-spinning process even at a high concentration of additives as 20 wt%. The mechanical test results showed that the combination of KL and ZnP achieved higher strength and filaments showed regularity in structure as compared to the LL and ZnP filaments. Thermogravimetric (TG) analysis showed the incorporation of lignin induces the initial decomposition (T 5% ) at a lower temperature; at the same time, maximum decomposition (T max ) shifts to a higher temperature region and a higher amount of char residue is reported at the end of the test. Further, the TGA-FTIR study revealed that the ternary blends (i.e., the combination of LL or KL, ZnP, and PA11) released mainly the phosphinate compound, hydrocarbon species, and a small amount of phosphinic acid during the initial decomposition stage (T 5% ), while hydrocarbons, carbonyls, and phenolic compounds along with CO 2 are released during main decomposition stage (T max ). The analysis of decomposition products suggests the stronger bonds formation in the condensed phase and the obtainment of a stable char layer. Cone calorimetry exploited to study the fire behavior on sheet samples (polymer bulk) showed an improvement in flame retardant properties with increasing lignin content in blends and most enhanced results were found when 10 wt% of LL and ZnP were combined such as a reduction in heat release rate (HRR) up to 64% and total heat release (THR) up to 22%. Besides, tests carried out on knitted fabric structure showed less influence on HRR and THR but the noticeable effect on postponing the time to ignition (TTI) and reduction in the maximum average rate of heat emission (MARHE) value during combustion.

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.

In this study, two different types of industrial lignin (i.e., lignosulphonate lignin (LL) and kraft lignin (DL)) were exploited as charring agents with phosphorus-based flame retardants for polyamide 11 (PA11). The effect of lignins on the thermal stability and fire behavior of PA11 combined with phosphinate additives (namely, aluminum phosphinate (AlP) and zinc phosphinate (ZnP)) has been studied by thermogravimetric analysis (TGA), UL 94 vertical flame spread, and cone calorimetry tests. Various blends of flame retarded PA11 were prepared by melt process using a twin-screw extruder. Thermogravimetric analyses showed that the LL containing ternary blends are able to provide higher thermal stability, as well as a developed char residue. The decomposition of the phosphinates led to the formation of phosphate compounds in the condensed phase, which promotes the formation of a stable char. Flammability tests showed that LL/ZnP ternary blends were able to achieve self-extinction and V-1 classification; the other formulations showed a strong melt dripping and higher burning. In addition to this, cone calorimetry results showed that the most enhanced behavior was found when 10 wt % of LL and AlP were combined, which strongly reduced PHRR (-74%) and THR (-22%), due to the interaction between LL and AlP, which not only promotes char formation but also confers the stability to char in the condensed phase.

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.