Improving the Wet-Spinning and Drawing Processes of Poly(lactide)/Poly(ethylene furanoate) and Polylactide/Poly(dodecamethylene furanoate) Fiber Blends.

This work aims to produce poly(lactic acid) (PLA)/poly(alkylene furanoate)s (PAF)s fiber blends for textile applications and evaluates their microstructural, chemical, thermal, and mechanical properties. The work focuses on two PAFs with very different alkyl chain lengths, i.e., poly(ethylene 2,5-furandicarboxylate) (PEF) and poly(dodecamethylene 2,5-furandicarboxylate) (PDoF), which were blended in solution at various concentrations (in the range 2.5-10 wt %) with PLA, wet spun, and subsequently drawn. Light optical micrographs highlight that PLA/PEF blends present large and concentrate PEF domains, whereas PLA/PDoF blends show small and homogeneously distributed PDoF domains. The blends appear to be immiscible, which is confirmed also by scanning electron microscopy (SEM), Fourier-Transform Infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) highlights that the addition of the PAFs improves the thermal stability of the fibers. The drawing process, which was carried out at 80 °C with a heat setting step at 95 °C and at three draw ratios, improves the mechanical properties of the fibers upon the addition of the PAFs. The results obtained in this study are promising and may serve as a basis for future investigations on these novel bio-based fiber blends, which can contribute to increase the environmental sustainability of industrial textiles.

Statistical Modeling and Optimization of the Drawing Process of Bioderived Polylactide/Poly(dodecylene furanoate) Wet-Spun Fibers.

Drawing is a well-established method to improve the mechanical properties of wet-spun fibers, as it orients the polymer chains, increases the chain density, and homogenizes the microstructure. This work aims to investigate how drawing variables, such as the draw ratio, drawing speed, and temperature affect the elastic modulus (E) and the strain at break (εB) of biobased wet-spun fibers constituted by neat polylactic acid (PLA) and a PLA/poly(dodecamethylene 2,5-furandicarboxylate) (PDoF) (80/20 wt/wt) blend. Drawing experiments were conducted with a design of experiment (DOE) approach following a 24 full factorial design. The results of the quasi-static tensile tests on the drawn fibers, analyzed by the analysis of variance (ANOVA) and modeled through the response surface methodology (RSM), highlight that the presence of PDoF significantly lowers E, which instead is maximized if the temperature and draw ratio are both low. On the other hand, εB is enhanced when the drawing is performed at a high temperature. Finally, a genetic algorithm was implemented to find the optimal combination of drawing parameters that maximize both E and εB. The resulting Pareto curve highlights that the temperature influences the mechanical results only for neat PLA fibers, as the stiffness increases by drawing at lower temperatures, while optimal Pareto points for PLA/PDoF fibers are mainly determined by the draw ratio and the draw rate.

Thermal Mending of Electroactive Carbon/Epoxy Laminates Using a Porous Poly(ε-caprolactone) Electrospun Mesh.

For the first time, a porous mesh of poly(ε-caprolactone) (PCL) was electrospun directly onto carbon fiber (CF) plies and used to develop novel structural epoxy (EP) composites with electro-activated self-healing properties. Three samples, i.e., the neat EP/CF composite and two laminates containing a limited amount of PCL (i.e., 5 wt.% and 10 wt.%), were prepared and characterized from a microstructural and thermo-mechanical point of view. The introduction of the PCL mesh led to a reduction in the flexural stress at break (by 17%), of the interlaminar shear strength (by 15%), and of the interlaminar shear strength (by 39%). The interlaminar fracture toughness of the prepared laminates was evaluated under mode I, and broken samples were thermally mended at 80 °C (i.e., above the melting temperature of PCL) by resistive heating generated by a current flow within the samples through Joule's effect. It was demonstrated that, thanks to the presence of the electrospun PCL mesh, the laminate with a PCL of 10 wt.% showed healing efficiency values up to 31%.

Novel Poly(Caprolactone)/Epoxy Blends by Additive Manufacturing.

The aim of this work was the development of a thermoplastic/thermosetting combined system with a novel production technique. A poly(caprolactone) (PCL) structure has been designed and produced by fused filament fabrication, and impregnated with an epoxy matrix. The mechanical properties, fracture toughness, and thermal healing capacities of this blend (EP-PCL(3D)) were compared with those of a conventional melt mixed poly(caprolactone)/epoxy blend (EP-PCL). The fine dispersion of the PCL domains within the epoxy in the EP-PCL samples was responsible of a noticeable toughening effect, while in the EP-PCL(3D) structure the two phases showed an independent behavior, and fracture propagation in the epoxy was followed by the progressive yielding of the PCL domains. This peculiar behavior of EP-PCL(3D) system allowed the PCL phase to express its full potential as energy absorber under impact conditions. Optical microscope images on the fracture surfaces of the EP-PCL(3D) samples revealed that during fracture toughness tests the crack mainly propagated within the epoxy phase, while PCL contributed to energy absorption through plastic deformation. Due to the selected PCL concentration in the blends (35 vol %) and to the discrepancy between the mechanical properties of the constituents, the healing efficiency values of the two systems were rather limited.