| Research Abstract |
We succeeded in producing microfibers, such as poly(ethylene terephthalate) (PET), nylon 6, isotactic polypropylene (i-PP), poly(L-lactic acid) (PLLA), and poly(glycolic acid) fibers, by a continuous thinning method using a carbon dioxide (CO_2) laser. A laser-thinning apparatus to continuously prepare the microfiber was developed in our laboratory and consists of fiber supplying and winding spools, a continuous wave CO_2 laser emitter, a supplying system of fibers, and a traverse. The laser-thinning apparatus could produce the microfiber in the range of 100 m・min^<-1> to 2,500 m・min^<-1>. The diameter of the laser-thinned microfiber decreased with increasing a winding speed, and its birefringence increased with increasing the winding one. When the nylon 6 microfiber obtained by irradiating the laser operated at a power density of 19.8 W・cm^<-2> to the undrawn nylon 6 fiber supplied at 0.32 m・min^<-1> was wound up at 848 m・min^<-1>, the obtained microfiber had a diameter of 3.2 μm and
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a birefringence of 47 x 10^<-3>. The draw ratio calculated from the supplying and the winding speeds was 2650 times. The SEM showed that the microfiber obtained by the laser-thinning apparatus had a smooth surface without a surface roughened by a laser-ablation and is uniform in diameter. The developed apparatus could more easily produce the microfiber when compared with the conventional technology such as a conjugate spinning, an islands-in-a-sea type fiber spinning, a melt blowing, and a flash spinning.
A zone-drawing and zone-annealing method was applied to the PET microfiber obtained by using the CO_2 laser-thinning in order to develop its mechanical properties. The microfiber used for the zone-drawing and the zone-annealing was prepared by winding at 1,386 m/min the microfiber that was obtained by irradiating the laser at 18.1 W/cm^2 and had a diameter of 2.8 μm and a birefringence of 0.097. The zone-drawing was carried out at a drawing temperature of 105 ℃ under an applied tension of 53 MPa, and the zone-annealing at 155 ℃ under 195 MPa. The zone-drawing and the zone-annealing were carried out at a treating speed of 0.21 m/min. The zone-annealed microfiber finally obtained had a diameter of 2 μm, a birefringence of 0.234, a tensile modulus of 17.9 GPa, and a tensile strength of 1.1 GPa.
The CO_2 laser-thinning method was applied to PET fiber to produce web formed by PET microfiber. The apparatus used for the preparation of microfiber web consists of fiber supplying spool, a continuous wave CO_2 laser emitter, air gun, and a net conveyor to collect the microfiber web. The diameter of microfiber web was depended on a supplying speed the air supply to the air gun, and laser power. Nonwoven fabrics were obtained by heating the collected microfiber web at 190 ℃ under constant length and obtained nonwovens were formed by continuous filament with a uniform diameter. Less
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