Young Sik Nam

Theoretical analysis of the melt spinning process of poly(trimethylene terephthalate) fibers

Profiles development of the melt spinning process of poly(trimethylene terephthalate) (PTT) was simulated by a numerical method. The spinning speed of 3 km/min to 5 km/min was analyzed and the characteristic of PTT spinning process was compared with that of poly(ethylene terephthalate) (PET). Velocity development of PTT was slower than that of PET. Although PTT’s spinning temperature was lower than PET’s, the PTT solidified slower because of a smaller super-cooling and the large specific heat capacity. The diameter profile of PTT decreases gradually in comparison with that of PET. PTT’s strain rate has a broader distribution than PET’s and its maximum ranged from 541 to 570 s−1 for PET and 136 to 149 s−1 for PTT. PTT’s tensile stress was smaller than PET’s.

Preparation and Dyeability of Thermally Resistant Aramid Nanofibers

Abstract: The dyeing of meta-aramids (m-aramids) has conventionally been difficult due to their rigid molecular anddense crystalline structure that results from hydrogen bonding, although various dyeing techniques have been applied inthe past to improve their dyeability. In this study, m-aramid nanofibers were fabricated by electrospinning with a15 wt% m-aramid/DMAc solution, followed by either water or thermal treatment. The thermal stability and crystallinestructure of the m-aramid nanofibers were investigated by thermogravimetry (TGA) and X-ray diffractometry (XRD),respectively. The effects of the water and thermal treatments on the dyeability of m-aramid nanofibers containing eitherpigment or dye were compared based on the K/S value and color difference. The results indicated that the use of dye ispreferable to the use of pigment to improve the color depth of m-aramid nanofibers.Keywords: m-aramid nanofibers, pigment, dye, K/S value, dyeability 1. 서론 1972년 미국의 DuPont사에 의해 최초로 개발된 아라미드(aramid) 섬유는 내열성, 난연성, 내약품성이 우수하여 소방복 등의 보호복 소재로 많이 사용되고 있다. 아라미드는선형사슬을 따라 주기적으로 존재하는 아미드기의 분자 간수소결합에 의한 견고한 분자구조와 고결정성에 기인한 치밀한 결정구조로 인하여 염료의 침투가 어렵기 때문에 염색하기가 곤란하다[1−3]. 이를 극복하기 위하여 안료를 고분자 용액 속에 혼입하는 원착법이나 다른 소재와의 혼방혹은 교직 등을 통해 염색성을 해결하고자 하는 시도가 있었고[4], 초임계 유체를 용매로 사용하여 아라미드 방적사를 염색하는 방법[5,6], 치밀한 결정구조를 느슨하게 하여다량의 용매로 팽윤시켜 염료를 분자들 사이에 염착시키는캐리어법, 초고온고압 염색법[7] 등이 행해지고 있다. 또한, 메타아라미드(meta-aramid) 섬유의 결정구조를 느슨하게 팽윤시켜서 양이온 염기성 염료의 침투를 도와주는 역할을 하는 팽윤제를 사용하여 염기성 염료로 염색하는 방법이진행되고있다[8,9]. 원착법은섬유제조시안료를고분자에 혼입해야 하므로 오염이 발생하였을 때 색상교체가어렵고 한 번에 단일 색상을 대량으로 생산해야 하며 내열성이 있는 안료의 선정이 필요하다는 문제점이 있고, 캐리어 염색법은 다량의 유기용제를 사용하여 섬유구조를 느슨하게 만들어야 하므로 섬유의 강도가 저하되는 문제점이발생하며, 초임계 염색법과 초고온고압 염색법은 특별한설비를 필요로 한다는 점, 팽윤제를 이용하는 염색법은 재현성 문제가 있다는 점[7] 등이 단점으로 지적되고 있다.최근, 나노섬유에 대한 관심과 활용도가 높아지면서 다양한 소재에 대한 나노섬유화가 이루어지고 있다. 나노섬유는 섬유 직경 대비 표면적의 비가 높아서 필터소재나 의료용 소재 등으로의 전개가 용이하고, 특히 전기방사를 통한 나노섬유화 방법은 간편한 공정으로 나노섬유 집합체를얻을 수 있기 때문에 최근 많이 사용되고 있는 방법이다.메타아라미드 소재는 내열성이 우수하기 때문에 나노섬유화할 경우 고온에서 사용되는 여러 가지 여과재 및 소방복등의 투습 방수 소재에 사용될 수 있으며 이 분야에서의활용도를 높이기 위하여 염색성 확보가 필요하다고 할 수있다.따라서 본 연구에서는 메타아라미드 고분자 용액에 안료

Studies on Molecular Structure Changes in Polyethylene/Polypropylene Sheath-Core Monofilament

Abstract: In this study, changes in the molecular structure of a sheath-core polyethylene (PE)/polypropylene (PP) bicompo-nent monofilament were investigated using different fractions of sheath or core components. The melt complex viscosity ofsheath PE showed a greater shear thinning behavior than core PP. For both as-spun and drawn filaments, the crystal structureof sheath PE developed better than that of core PP. In the as-spun monofilament, the core PP crystal structure did not developwell, while sheath PE showed a more developed crystal structure. Further, sonic velocity indicating the molecular orientationincreased upon drawing but was rarely dependent on the sheath PE fraction for both as-spun and drawn monofilaments. Keywords: sheath-core, PE, PP, bicomponent, monofilament 1. Introduction Monofilament is a single filament used for industrialprocesses that differ from those used for apparel, which aremulti-filaments [1−3]. Most monofilament contains circularcross-section, but shaped monofilament can also bemanufactured if required. Polyethylene (PE), polypropylene(PP), polyamide (Nylon) and poly(ethylene terephthalate)(PET) are common polymers used for generation ofmonofilament. Monofilament is usually manufactured via amelt spinning process; however, coagulation solution isgenerally used as quenching medium instead of air [3].Monofilament manufacturing equipment requires a longdistance from extrusion to take-up owing to the longdistance of the coagulation bath and drawing line. Monofilament can be used to make apparel, artificial hair,fishing lines and nets, cosmetic brushes, thermal bonds andsutures. Additionally, so called fancy yarn for apparel useand mesh fabrics for shoes, bags and furniture textiles aremade of monofilament. Mesh fabrics of monofilament havecoarser fabric density than normal woven fabrics because ofdifficulty in increasing picks in the weft and warp due totheir thicker diameters. Sheath-core monofilament can be spun by bicomponentspinning. If low melting polymer is used as the sheath, themonofilament will have thermal bonding properties. Unlikehomo monofilament, sheath/core monofilament imparts thermalbonding properties to fabrics during post processing and cantherefore provide dimensional stability. The use of thermalbonding sheath/core monofilament removes the need foradditional chemical adhesives during post processing andhence reduces production costs and is good for environmentalprotection. Moreover, thermoplastic monofilament is easy torecycle. There have been several reports [4−6] of sheath-core multifilaments; however, very few investigations ofsheath-core monofilament have been conducted to date.Therefore, in this study, changes in the molecular structureof sheath-core PE/PP monofilament containing differentamounts of sheath PE and core PP were investigated.

Characterization of Nanofibrous and Microfibrous Web Fabricated Using Polyurethane-Impregnated Poly(trimethylene terephthalate)

Abstract: Poly(trimethylene terephthalate) (PTT), a semi-crystalline polyester, has been used in many applicationsbecause of its good dyeability and good mechanical properties such as elasticity. Sorona (DuPont) and Corterra (ShellChemicals) are some trade names of PTT. We describe herein a PTT nanofibrous web fabricated by electrospinning,which is a simple technique for generating nanofibers from a polymer solution and a melt. PTT pellets were dissolvedin 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) followed by electrospinning to yield PTT nanofibers with an average diam-eter of 900±97 nm. Then, the PTT nanofibrous web was impregnated with a polyurethane (PU) solution. The resultingmaterial had better mechanical properties and also displayed a lower water contact angle than the PTT nanofibersbecause a relatively hydrophilic PU was coated onto the PTT nanofibrous web. Additionally, the pilling property of thePU-impregnated PTT nanofibrous web was enhanced by the induced welding among the PTT nanofibers because of PUimpregnation. The air permeability of the PTT nanofibrous web was evaluated both before and after PU-impregnation.The results indicated that the PU-impregnated PTT nanofibrous web could be used in various industrial applications.Keywords: poly(trimethylene terephthalate), polyurethane coating, electrospinning, nanofiber, microfiber

Effect on the Mechanical Properties and Water Vapor Permeability of Processing Parameters in the Electrospinning of Meta-aramid Nanofibers

Meta-aramid nanofibers were prepared by the electrospinning process. In this study, electrospun meta-aramid nanofiber webs were prepared with various velocity ratios of a collector drum, the fiber diameter and thickness of electrospun nanofiber webs, and then compared with values of tensile properties and breathable water-resistance. The meta-aramid nanofiber webs were analyzed by field-emission scanning electron microscopy, a tensile tester, water vapor permeability, an X-ray diffractometer and thermogravimetric analysis. The diameter of meta-aramid nanofibers ranging from 165 to 252 nm was obtained by electospinning. The tenacity, young`s modulus and crystallinity of meta-aramid webs were decreased by increasing the diameter of meta-aramid nanofibers, however, water vapor permeability increased. It was confirmed that the breathable water-resistance of meta-aramid nanofiber webs were similar to that of chemical treated PTFE film.

Study on Improving Strength of Industrial Polyester Fibers

Abstract: In this work, effects of total draw ratio change on the mechanical properties of polyester fibers were stud-ied. The process parameter was a total draw ratio and the draw ratios that were used ranged from 6.6 to 7.0. Tensileproperties are determined from the tensile tester, and crystallite parameters from the density measurement and X-raydiffraction were discussed with the different total draw ratios. The tenacity, youngs modulus and crystallinity wereincreased to 10.6 g/d, 123.2 g/d and 42.1%, respectively, with increase in the total draw ratio. The relations betweentotal draw ratio and mechanical properties of high tenacity polyester fiber were discussed. Keywords: polyester, draw ratio, high tenacity, crystallinity, X-ray diffraction 1. 서 론 대표적인 범용고분자로 3대 합성섬유인 나일론(nylon),폴리에스터(polyester), 아크릴(acryl)이 있으며, 이는 원유를 정제하여 얻어진 화학물질을 사용하여 합성된다. 폴리에스터는 나일론 보다 가격대비 성능이 우수하여 가장 널리 사용되는 합성섬유로서 밀도가 높고, 내열성, 강성, 전기적 성질 등이 뛰어나 합성섬유와 필름의 원료로 많이 사용된다[1].폴리에스터 섬유는 크게 의류용 섬유(apparel textile)와산업용 섬유(technical textile)로 구분되며, 의류용 폴리에스터는 면, 양모, 마, 레이온 등과 함께 혼방하여 사용되는방적사와 필라멘트로 사용되는 완전연신사(FOY)와 부분연신사(POY)가 대표적이다. 의류용 폴리에스터 필라멘트는강도 2.8~5.2 g/d, 신도 19~40%의 인장특성을 가지며, 텍스처링(texturing) 공정이후 크림프를 주어 사용된다[2,3].산업용 폴리에스터 섬유의 기본 요구조건은 최소강도7.0 g/d 이상이며, 외부 변형에 의한 형태안정성이 우수해야한다. 이러한요구조건으로 산업용 폴리에스터섬유는고강도, 고탄성 특성을 가지며 타이어코드, 안전벨트, 산업용 고무 보강재, 컨베이어 벨트, 텐트, 로프, 산업용 직물등 다양한 분야에 사용되고 있다.타이어코드용 폴리에스터 섬유는 고온에서의 반복신장,압축변형, 화학적 열화를 견딜 수 있는 극한 물성이 요구된다. 따라서 고강도, 고탄성, 치수안정성, 내피로성 등의성능을 갖는 분자 구조의 설계가 요구되고, 현재 래디얼 타이어에 적용되어 사용된다.안전벨트용 폴리에스터 섬유는 안전벨트 웨빙의 기본 요구조건인 인장강도 26.7 kN 이상, 신도 20% 이하, 우수한내마모 특성 등이 요구되고, 이는 폴리에스터 섬유를 고강도화, 고탄성화, 저수축화하여 적용되고 있다(KS R 4027).산업용 폴리에스터 섬유의 용융방사는 의류용 섬유와 큰차이가 없고, 제조방법에서는 공정상의 차이를 보인다. 용융방사공정은 방사단계와 연신단계로 구분할 수 있다. 첫번째 방사단계는 압출기(extruder) 내부에서 용융된 고분자를 스크류(screw)의 회전으로 이동하고, 용융된 고분자는스크류와 배럴(barrel) 사이에서 전단응력(shearing stress)을일으키며, 방사구금(spinneret)에서는 전단변형과 신장변형이 동시에 작용하여 방사구금을 통해 외부로 압출된다. 두