Satoko Okubayashi

Effect of electron beam irradiation on the structure and properties of electrospun PLLA and PLLA/PDLA blend nanofibers.

Poly(L-lactide) (PLLA) and a PLLA/poly(D-lactide) (PDLA) blend (50/50 wt.%) were electrospun into nanofibers. Electron beam (e-beam) irradiation of the electrospun PLLA and blend nanofibers was used as a method to alter their structures and surface properties. The crystalline structures of the nanofibers before and after irradiation were investigated by differential scanning calorimetry. Tensile tests of the aligned nanofibers were also performed to determine the effects of irradiation on the mechanical properties of the nanofibers. The hydrophilicity of the nanofibers was determined by water contact angle measurements, while any degradation of the fibers caused by irradiation could be detected by intrinsic viscosity measurements. The e-beam irradiation method was able to improve the surface hydrophilicity of the PLLA and blend nanofibers, although bulk degradation was inevitable.

Irradiation of cellulosic pulps: understanding its impact on cellulose oxidation.

Different pulp samples were irradiated by three energy sources: plasma, electron beaming, and γ radiation. The effect of increased exposure to irradiation was studied by multidetector gel permeation chromatography with fluorescence labeling of carbonyl groups to quantify changes of the cellulose. Whereas plasma treatment had no effect, for gamma and electron beam the degradation primarily affects the high molar mass area. Kinetic calculations based on DPw were performed. They show close-to-linear relations with slopes in the same order of magnitude, suggesting that wood-derived pulps degrade slower than pulps from annual plants. The rise in carbonyl group content is linear with increasing dose. In particular, in pulps from annual plants, most detected carbonyl structures originate from the new reducing end groups. Therefore, oxidative modification of cellulose molecules by means of radiation appears to be viable for pulps produced from wood. Here the increase in oxidized functionalities is partially disconnected from chain scission.

Generation of PVP fibers by electrospinning in one-step process under high-pressure CO2

BackgroundElectrospinning is a process of electrostatic fiber formation using electrical forces to produce polymer fibers from polymer solution in nano/micrometer scale diameters. Various polymers have been successfully electrospun into ultrafine particles and fibers in recent years, mostly in solvent solution and some in melt form. In this work, electrospinning was conducted under high-pressure carbon dioxide (CO2) to reduce the viscosity of polymer solution. The experiments were conducted at 313 K and approximately 8.0 MPa. Polyvinylpyrrolidone in dichloromethane was used as a polymer solution with 4 wt.% of concentration. The applied voltage was 17 kV, and the distance of nozzle and collector was 8 cm. The morphology and structure of the fibers produced were observed by scanning electron microscopy.ResultsWhen the CO2 pressure was 5 MPa, the resultant fibers had an average diameter of 2.28 ± 0.38 to 4.93 ± 1.02 μm. The ribbon-like morphology was formed with increasing pressure of CO2 at 8 MPa with a tip 0.75-mm inside diameter.ConclusionsThe results show that the depressurization of CO2 at the end of experiment assists the removal process of the polymer solvent and produces the porous nature of fibers without collapsing or foaming. These behaviors hold the potential to considerably improve devolatilization electrospinning processes.

A Pilling Mechanism of Man-Made Cellulosic Fabrics—Effects of Fibrillation

The effects of washing and drying treatments on fibrillation, fuzz, and pill formation of lyocell knitted fabrics are investigated in this study. Pilling ratings of the fabrics after wash (W), dry (D), and wash/dry (WD) treatments are evaluated according to a pilling scale using a microscope. Water retention values and fiber-fiber friction are also measured after the treatments. Fuzz occurs on fabrics treated with D and WD treatments, indicating that fuzz is mainly generated during mechanical abrasion in dry conditions. But fibers fibrillate with W and WD treatments, suggesting that fibrillation is induced by mechanical abrasion in wet conditions. Pills form only on fabrics treated with WD in the experimental conditions used here. The water retention value decreases, fiber-fiber friction increases, and the degree of pilling increases with increases in the repetitions of WD. Considering these changes in fiber and textile properties during W, D, and WD treatments, a mechanism of pill formation is proposed, including the fibrillation process, and it is suggested that pills are significantly promoted by a combination of fuzz formed in the dry state with fibrillation occurring in wet state. Increasing fiber-fiber friction and decreasing water accessibility after certain numbers of WD treatments lowers the pilling tendency.

A pilling mechanism for cellulosic knit fabrics - effects of wet processing

Abstract The length of fuzz and pill formed on regenerated cellulosic knitt fabrics after washing and drying (WD) was determined by electrical resistivity measurements perpendicular to the plane of fabric. The fuzz length of Lyocell Knitted Fabric 1 after 25 times WD was 1.05 mm and was the longest among the three different lyocell fabrics. The visual pilling extent of the Lyocell 1 was also higher compared to the other lyocell fabrics. Fiber–fiber friction was measured as counts of twist to open the yarn until it starts to slip in dry (T rdry) and in wet (T rwet) conditions. The T rdry of Lyocell 1 was 30.5 counts and comparatively low. However, the T rwet of Lyocell 1 was remarkably high. The high T rwet of Lyocell 1 was related to a higher water retention value (0.943 g/g) which was centrifugally measured. The contraction force of the yarn bundle in water was additionally determined. The results of parameters indicating the fiber properties in dry and wet conditions suggested a mechanism of pill formation. The fuzz formation was promoted by lower fiber–fiber friction, which allows the ends of fibers to come out from the yarn during mechanical abrasion. As the fibers get softer and the fiber–fiber friction gets higher due to the swelling in water, the fibers easily tangle to develop pills.

Fabrication of micro-hollow fiber by electrospinning process in near-critical carbon dioxide

Electrospinning is a simple technique that has gained much attention because of its capability and feasibility in the fabrication of large quantities of fibers from polymer with diameters ranging in nano-microscale. These fibers provided high surface area to volume ratios, and it was of considerable interest for many applications, such as nanoparticle carriers in controlled release, scaffolds in tissue engineering, wound dressings, military wear with chemical and biological toxin-resistance, nanofibrous membranes or filters, and electronic sensors. Recently there has been a great deal of progress in the potential applications of hollow fibers in microfluids, photonics, and energy storage. In this work, electrospinning was conducted under high-pressure carbon dioxide (CO2) to reduce the viscosity of polymer solution. The experiments were conducted at 313 K and ∼8.0 MPa. Polymer solution containing 5 wt% polymers which prepared in dichloromethane (DCM) with polyvinylpyrrolidone (PVP) to poly-L-lactic acid (PLLA) ratio 80:20 was used as a feed solution. The applied voltage was 15 kV and the distance of nozzle and collector was 8 cm. The morphology and structure of the fibers produced were observed using scanning electron microscopy (SEM). Under pressurized CO2, PVP electrospun was produced without bead formation with diameter ranges of 608.50 - 7943.19 nm. These behaviors hold the potential to considerably improve devolatilization electrospinning processes.Electrospinning is a simple technique that has gained much attention because of its capability and feasibility in the fabrication of large quantities of fibers from polymer with diameters ranging in nano-microscale. These fibers provided high surface area to volume ratios, and it was of considerable interest for many applications, such as nanoparticle carriers in controlled release, scaffolds in tissue engineering, wound dressings, military wear with chemical and biological toxin-resistance, nanofibrous membranes or filters, and electronic sensors. Recently there has been a great deal of progress in the potential applications of hollow fibers in microfluids, photonics, and energy storage. In this work, electrospinning was conducted under high-pressure carbon dioxide (CO2) to reduce the viscosity of polymer solution. The experiments were conducted at 313 K and ∼8.0 MPa. Polymer solution containing 5 wt% polymers which prepared in dichloromethane (DCM) with polyvinylpyrrolidone (PVP) to poly-L-lactic acid (...

A simplified measurement of adhesion between p-aramid fiber and polypropylene

It is well known that p-aramid fiber is difficult to reinforce the polypropylene (PP) matrix with high adhesion. In addition, the conventional adhesion measurements were always extremely inconvenient. Therefore, it is necessary to simplify the adhesion measurement and also produce a p-aramid/PP composite with high adhesion. In this work, “Bundled filaments pull out (BFPO)” method as a simplified measurement was applied to measure the adhesion properties of p-aramid fiber/PP composite. The suitable processing parameters of the p-aramid fiber/PP composite preparation were also discussed from BFPO test results. Feasibility of this BFPO method was examined through comparing the tendency of adhesion between p-aramid fiber and PP by BFPO method and micro-droplet method. The resultant p-aramid fiber/PP composite prepared at 180°C with a 3 mm embedded length showed a high degree of PP impregnation. The adhesion tendency of p-aramid fiber/PP composites was mainly the same when comparing the results using BFPO method and micro-droplet method.