Poly(l-lactic acid) (PLLA) based piezoelectric polymers are gradually becoming the substitute for the conventional piezoelectric ceramic and polymeric materials due to their low cost and biodegradable, non-toxic, piezoelectric and non-pyroelectric nature. To improve the piezoelectric properties of melt-spun poly(l-lactic acid) (PLLA)/BaTiO3, we optimized the post-processing conditions to increase the proportion of the β crystalline phase. The α → β phase transition behaviour was determined by two-dimensional wide-angle x-ray diffraction and differential scanning calorimetry. The piezoelectric properties of PLLA/BaTiO3 fibres were characterised in their yarn and textile form through a tapping method. From these results, we confirmed that the crystalline phase transition of PLLA/BaTiO3 fibres was significantly enhanced under the optimised post-processing conditions at a draw ratio of 3 and temperature of 120 °C during the melt-spinning process. The results indicated that PLLA/BaTiO3 fibres could be a one of the material for organic-based piezoelectric sensors for application in textile-based wearable piezoelectric devices.
The application of nanofiber (NF) and porous metal-organic framework (MOF) has increasingly attracted attention for the protection of public health. This composite platform provides the physical sieving of particulate matters (PMs) and capturing gases, serving as an outstanding filtering medium with lightweight and multifunctionality. Herein, process design and optimization are performed to produce a multifunctional membrane comprised NFs and MOF particles. Electrospinning/electrospray techniques are used to fabricate a hybrid membrane of poly(vinyl alcohol) NF and Fe-BTC as an adsorptive MOF on a macroporous nonwoven (NW). Three types of filters are prepared by varying the order of processing steps, that is, MOF/NF/NW, MOF+NF/NW, and NF/MOF/NW, to elucidate the effect of the fabrication process in the filtration of air pollutant. The optimal filtration performance is achieved in MOF+NF/NW system: the highest filtration efficiency (97%) and outstanding gas capturing efficiencies (≈60% and ≈35% decreases from initial NH 3 and H 2 S concentrations, respectively). However, when air permeability and filtration efficiency are considered, the most desirable configuration for personal protection equipment (PPE) is NF/MOF/NW system, which effectively enabled comfortable breathing without compromising the lightweight and multifunctional performance.
Super engineering plastics, such as polyetherimide (PEI), are widely used in various fields owing to their multifunctional properties. PEI is used in automobiles, electronics, and medicine owing to its high thermal resistance, excellent mechanical strength, flame retardancy, and chemical resistance. In this study, melt‐spun PEI filaments were thermally drawn and the effect of the drawing process conditions on their mechanical properties was investigated. To understand the mechanical properties of various forms, such as films, sheets, granules, tubes, and rods of PEI postprocessing, it is based on analyzing the behavior in one‐dimensional structures. The mechanical properties of the PEI filaments were dictated by the draw ratio, process temperature, and cooling temperature of the thermal drawing process. In addition, maintaining the drawing process temperature around the glass transition temperature (220°C) of PEI elongated the filament by up to 80%. Furthermore, the optimized cooling temperature was 150°C and draw ratio was 50%. In conclusion, PEI filaments with excellent mechanical properties were obtained by optimizing the draw ratio, process temperature, and cooling temperature of thermal drawing. Through the behavior of the molecular and crystal structures by thermal drawing of PEI filament, it is expected to be applied to two‐ or three‐dimensional structures.
Polytetrafluoroethylene (PTFE) has high thermal stability and chemical resistance, and hence is gaining great attention in the industrial field of high-performance filters, membranes, and medical applications. However, since PTFE possesses a narrow gap between melting (330°C) and decomposition temperatures (350°C), the melt-spinning process that is required to satisfy industrial needs for mass production has been limited. Here, perfluoro(propyl vinyl ether) (PPVE) was introduced to decrease the melting point of PTFE then fiber fabrication was performed with the melt-spinning process using a single-screw extruder, enabling the PTFE fiber to fabricate continuously. We selected an optimal melt-spinning condition and obtained PTFE fiber from the melt-processable PTFE/PPVE copolymer. The as-spun PTFE fiber showed low mechanical strength (0.90 g/denier or 89.1 MPa of tenacity). A post-thermal drawing process was performed to increase the mechanical strength of the PTFE as-spun. It demonstrated that the thermally drawn PTFE fiber showed higher mechanical strength (1.84 g/denier or 220.0 MPa of tenacity) due to the increased degree of crystallinity. Also, the other trial, thermal stabilization under N2, suggested as a future modification method to increase mechanical strength further, preventing thermal constriction of the PTFE fiber. The melt-spun and thermally drawn PTFE fibers were knitted and it was confirmed that the fiber has high chemical resistance and similar surface chemistry to conventional PTFE fibers. This study developed a method to enable a melt-processable PTFE fiber fabrication and opens up opportunities for mass production that is crucial in the industrial aspect.
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