기체 역학이 poly(2-cyano-p-phenylene terphthalamide)/dimethyl acetamide/LiCl용액의 전기방사공정에서 섬유 morphology 미치는 영향

Abstract

N,N-dimethyl acetamide/lithium chloride 용매계에 녹인 poly(2-cyano-p-phenylene terephthlamide) (CY-PPTA) 방사용액의 유변학적 특성을 조사하였다. 또한, 이로부터 최적화된 농도에서 전기방사로 제조된 나노 섬유의 morphology에 기체 역학이 미치는 영향에 대해서도 고찰하였다. CY-PPTA용액은 전형적인 lyotropic liquid-crystalline 거동을 보였으며 전기방사에 적합한 포화농도(B-point)는 20 wt%로 나타났다. 노즐과 동축으로 흐르는 기체 유동을 접목하여 전기방사한 섬유의 평균 직경과 직경의 표준편차는 감소하였으며 기체의 압력이 0.2 에서 0.4 bar 로 증가함에 따라 차이는 더 뚜렷하게 나타났다. 기체의 유동 mode 가 CY-PPTA 전기방사 섬유의 morphology 에 미치는 영향을 확인하기 위해서 각각 7 과 10 cm 의 길이를 가지는 원통형과 내부의 단면적이 점차 증가하였다 다시 감소하는 유선형, 그리고 도입부에 3 cm의 기체 유동의 안정화 구간을 추가하여 개선된 유선형을 포함한 총 4가지 형태의 shroud 를 제작하였다. Shroud 를 이용함으로써 최소 300 nm 의 직경의 보다 균일하고 얇은 전기방사 섬유를 제조할 수 있었다. 원통형의 shroud 길이가 7 에서 10 cm로 증가함에 따라 섬유의 평균 직경과 그의 표준편차는 근소하게 감소하였다. 반면, 베르누이 정리를 만족하는 개선된 유선형의 shroud 를 이용한 전기방사 섬유는 원통형 ３６ shroud 를 이용한 전기방사 섬유에 비해 직경과 표준편차가 매우 크게 감소하였다. 그러나 도입부에 3 cm의 안정화 구간이 없는 유선형의 shroud는 내부 단면적의 급격한 증가로 발생하게 되는 불안정한 기체 유동으로 인해 오히려 원통형의 shroud 보다 직경과 표준편차가 큰 전기방사 섬유가 제조되었다.|The rheological properties of spinning dopes of poly(2-cyano-p-phenylene terephthalamide) (CY-PPTA) in N,N-dimethyl acetamide/lithium chloride were investigated to determine the optimized concentration. The effects of air-dynamics on the morphology of electrospun nanofiber were also examined. CY-PPTA solutions showed a typical lyotropic liquid-crystalline behavior with the saturated concentration (B-point) of 20 wt%. The average fiber diameters and standard deviation of electrospun fibers were decreased by the presence of air flow from the outer nozzle, which was more notable at 0.4 bar than 0.2 bar. To investigate the effects of air-dynamics, 4 types of shrouds were prepared, 7 and 10 cm cylinder, curved, and stabilized curved types. More uniform and thinner fibers iii down to the nano-scale of 300 nm were obtained than the simple air assistance without shrouds. The increase of shroud length from 7 to 10 cm in cylinder type shrouds slightly reduced average diameters and standard deviation. The use of shroud of stabilized curved type where an increase of cross-sectional area was present in the middle of shroud (3 cm from the nozzle exit) produced much thinner fibers than cylinder type shrouds, satisfying Bernoulli theorem. However, in the absence of 3 cm stabilization region before reaching curved region, the average fiber diameter and standard deviation were larger than those of cylinder type shrouds due to the turbulence of air flow caused by the abrupt increase of cross-sectional area.; The rheological properties of spinning dopes of poly(2-cyano-p-phenylene terephthalamide) (CY-PPTA) in N,N-dimethyl acetamide/lithium chloride were investigated to determine the optimized concentration. The effects of air-dynamics on the morphology of electrospun nanofiber were also examined. CY-PPTA solutions showed a typical lyotropic liquid-crystalline behavior with the saturated concentration (B-point) of 20 wt%. The average fiber diameters and standard deviation of electrospun fibers were decreased by the presence of air flow from the outer nozzle, which was more notable at 0.4 bar than 0.2 bar. To investigate the effects of air-dynamics, 4 types of shrouds were prepared, 7 and 10 cm cylinder, curved, and stabilized curved types. More uniform and thinner fibers iii down to the nano-scale of 300 nm were obtained than the simple air assistance without shrouds. The increase of shroud length from 7 to 10 cm in cylinder type shrouds slightly reduced average diameters and standard deviation. The use of shroud of stabilized curved type where an increase of cross-sectional area was present in the middle of shroud (3 cm from the nozzle exit) produced much thinner fibers than cylinder type shrouds, satisfying Bernoulli theorem. However, in the absence of 3 cm stabilization region before reaching curved region, the average fiber diameter and standard deviation were larger than those of cylinder type shrouds due to the turbulence of air flow caused by the abrupt increase of cross-sectional area.