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1 Vol. 31, No. 6, (2018) DOI: ISSN (Print), ISSN (Online) Paper Oxi-PAN 섬유를기반으로제조한탄소섬유의탄화조건에따른구조및물성의변화 최경훈 * 허소정 * 황상하 * 배수빈 ** 이형익 ** 채한기 * The Effect of Heat Treatment Condition on the Mechanical Properties of oxi-pan Based Carbon Fiber Kyeong Hun Choi*, So Jeong Heo*, Sang-Ha Hwang*, Soo Bin Bae**, Hyung Ik Lee**, Han Gi Chae* ABSTRACT: In this study, carbon fibers were fabricated via carbonization of oxidized polyacrylonitrile (oxi-pan) under different carbonization conditions. Carbonization of oxi-pan fiber was performed under four different temperature (1300, 1400, 1500, 1600 o C) with four different fiber tensions (14, 25, 35, 45 MPa). Effect of carbonization process on the structural development and mechanical properties of carbon fiber were characterized by single filament fiber tensile test and Raman spectroscopy. A clear correlation exists between the Raman spectrum and the tensile modulus of carbon fiber and effect of carbonization temperature on the tensile modulus showed increased tendency only at higher fiber tension ( 25 MPa) while tensile strength showed decreased or random tendency. Therefore, it may be concluded that the optimization of carbonization temperature of oxi-pan fiber also requires optimization of fiber tension. 초록 : 본연구에서는 oxi-pan 섬유를이용하여각각의온도와각온도에서의섬유에부가되는장력을조절하여탄소섬유를제조하고단섬유인장실험과라만분광분석을수행하여결과를바탕으로 oxi-pan 섬유의탄화조건에따른구조적변화와그에따른물성의변화를관찰하고자하였다. 라만분광분석을통해계산된 I D /I G 측정값들은탄소섬유의탄성율과동일한변화양상을보여주었으며특히탄화온도는일반적으로고온일수록흑연구조가발달하여섬유의탄성율이증가하는양상이나타난다고알려져있으나결과를통해분석한바에따르면일정한장력 ( 25 MPa) 이상에서만그러한결과가관찰되는것으로나타났다. 이와는대조적으로인장강도의경우라만분광분석결과와의연관성을찾을수없었으며또한부가되는장력에의해증가혹은감소하는상반된경향이다양하게나타나특정변수에따른영향을판단하기어려웠다. 따라서본연구의결과를통해특히고탄성율의탄소섬유의제조를위한 oxi-pan 섬유의탄화온도최적화를위해서는최적의섬유장력조건또한중요하게고려되어야함을알수있었다. Key Words: 탄소섬유 (Carbon fiber), 기계적물성 (Mechanical properties), 구조분석 (Structural analysis), 탄화온도 (Carbonization temperature) Received 20 August 2018, received in revised form 2 December 2018, accepted 7 December 2018 * School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Korea * School of Materials Science and Engineering, Ulsan National Institute of Science and Technology, Corresponding author ( hgchae@unist.ac.kr) ** Agency for Defense Development, Korea

2 386 Kyeong Hun Choi, So Jeong Heo, Sang-Ha Hwang, Soo Bin Bae, Hyung Ik Lee, Han Gi Chae 1. 서론 탄소섬유 (carbon fiber) 는극한조건의온도와압력에서구조적물성을유지할수있으며, 여러종류의모재 (matrix) 들, 즉고분자, 세라믹그리고금속과함께복합재를제조할수있다 [1,2]. 이렇게제조된탄소섬유강화복합재료 (carbon fiber reinforced composite material) 들은우수한열적, 기계적, 물리적특성으로인해수십년간우주항공분야를포함한다양한분야에서연구가이루어지고중요한역할을맡아왔다. 특히다양한탄소섬유의전구체 (precursor) 들중에서고성능탄소섬유를제조하는데적당한것으로알려진폴리아크릴로니트릴 (polyacrylonitrile, PAN) 섬유가주요하게다뤄졌다 [3-6]. PAN 섬유는일반적으로안정화 (stabilization 혹은 oxidation), 탄화 (carbonization) 그리고선택적으로흑연화 (graphitization) 공정의유무에따라최종적으로탄소섬유 (carbon fiber) 혹은흑연섬유 (graphite fiber) 로전환된다. 안정화단계에서 PAN 단일중합체혹은공중합체섬유는일정한장력을섬유에부가한상태에서산소분위기의 250 o C 내외의온도범위에노출되는데해당과정을통해 PAN 섬유의인접한분자간산화가교반응및 nitrile 반응기들의고리화반응을통해사다리형의 ladder polymer 를형성하여내열성과내화학특성이크게증가된비교적안정적인특성의섬유가형성된다 [7,8]. 해당섬유를일반적으로산화 PAN 섬유 (oxidized PAN fiber, oxi-pan) 이라지칭하며안정화섬유혹은내염섬유로도불린다. 특히우주항공분야에응용되는탄소-탄소복합재료는지금까지평직및주자직의직물을적층한형태의탄소섬유를많이활용해왔기때문에, 기계적및열적충격에의해발생하는층간분리현상이재료의기계적성질과삭마저항성을저하시키는주요원인으로지적되어왔다. 이러한단점을극복하기위해 3차원구조의프리폼 (preform) 을제조하여복합재료에적용하고자하는연구가활발히진행되고있다 [9]. 3차원탄소섬유프리폼을제조하는방법에는 3D weaving 이나 3D braiding 등의다양한방법들이있으나이러한방법들중니들펀칭 (needle punching) 은장비와구조및제조공정이간단하기때문에생산성과작업성및경제성이우수하다는장점을가지고있다. 이러한제조상의공정을효율화하기위해특히취성이높아공정중손상이우려되는완전히탄화가끝난탄소섬유보다는 oxidized-polyacrylonitrile (oxi-pan) 섬유로이루어진섬유를이용하여프리폼을형성하고이후탄화및밀도화하여탄소-탄소복합재를형성하는방법이고려되었다. 그러나해당방법은탄화중섬유의화학적변화과정과그에따른구조적변화및수치상의변화, 특히공정조건이최적화되어있지않다는점이문제로지적되어왔다 [10]. 일반적으로섬유의탄화공정에서가장중요한변수들은섬유에부가되는장력, 탄화온도, 승온조건그리고탄화시이용되는불활성기체의종류와그 유량이다. 이러한다양한요소들중가장중요한공정변수로생각되는섬유에부가되는장력과탄화온도의영향을조사하고최적화하고자그외의공정조건들은일정하게하고다양한장력 (14, 25, 35, 45 MPa) 과탄화온도 (1300, 1400, 1500, 1600 C) 에따라 Oxi-PAN섬유를탄화하여탄소섬유를제조하였으며, 공정조건들에따른탄화거동의변화와이에따른탄소섬유의구조및물성의상관관계를라만분광법과단섬유인장실험결과들을이용하여규명하고자하였다. 2. 실험방법 2.1 실험에사용한 oxi-pan 섬유 Oxi-PAN은국내탄소섬유업체 (( 주 ) 태광산업 ) 에서확보하였으며, Fig. 1에나타낸바와같이 tow형태로제공되었다. 섬유직경은 11.7 ± 0.9 μm, 인장강도 0.34 ± 0.02 GPa, 인장탄성율 10.4 ± 0.4 GPa 그리고파단신율 16.7 ± 1.4% 로측정되었고별도의물리적혹은화학적처리를거치지않고사용하였다. 2.2 탄화공정 Oxi-PAN 섬유의탄화과정은일반적으로최저 1000 o C 이상에서최대 1600 o C 정도의범위에서행해지는것으로알려져있다 [11,12]. 또한흑연결정구조의섬유방향으로의배향을최대화하여최대물성을발현할수있도록탄화공정중섬유에장력을가해주는것이일반적이다. 이에따라 Table Fig. 1. (a) Digital image of OxiPAN tow and (b) SEM image of its fractured surface. (c) Raman spectrum of oxipan shows I D /I G of 1.52 Table 1. Carbonization temperatures and fiber tensions applied for carbonization of OxiPAN Temp ( o C) Fiber tension (MPa) * Identification codes were given to each carbon fibers from CF to CF based on the carbonization temperature and applied fiber tension

3 The Effect of Heat Treatment Condition on the Mechanical Properties of oxi-pan Based Carbon Fiber 387 electron microscope FE-SEM) 을이용하여파단면분석을진행하였다. 3. 결과및고찰 Fig. 2. A digital image of graphite platform and clamp used for applying tension to oxipan fiber during the carbonization 1에나타낸바와같이본연구에서는 1300 o C, 1400 o C, 1500 o C 그리고 1600 o C에서탄화공정을진행하였으며, 섬유에부가되는장력은온도별로각각 14 MPa, 25 MPa, 35 MPa 그리고 45 MPa의 4 단계로조절하였다. Table 1에계획된조건에따라 iso-stress 조건하에서 oxi- PAN 섬유의탄화를진행하기위해 Fig. 2에나타낸바와같은흑연플랫폼및클램프를제조하여사용하였다. Fig. 2에서볼수있듯이장력은섬유 tow에서한가닥의단면적과부가해야하는장력을기준으로계산하여클램프의무게 를조절하였으며튜브형 furnace 를이용하여질소분위기하에서 3 o C/min 의승온속도로각각의최종온도를가하여탄화를진행하였다. 2.3 탄화조건에따른섬유의구조-물성분석각기다른조건에따라진행된탄화실험을통해얻어진섬유들의단섬유인장물성측정평가를 Textechno사의 Favimat+ 인장측정장비를이용하여수행하였다. 각시편은인장시험을 50회반복실험하여평균값을측정하였다. 라만분광분석에는 WITec 사의 alpha300r 공초점라만분광기를이용하였다. 1회측정시 5초의노출시간을적용하였으며동일지점에대하여 50회측정결과를누적하였다. 이러한실험은실험조건별로 10개의시편에대하여행해졌으며, 결과로부터얻어진스펙트럼에서 D Band에대한 G Band의 intensity 비율 (I D /I G ) 을구하였다. 최종적으로 FEI 사의 Nova Nano SEM 주사전자현미경 (field emission scanning 각조건별로얻어진섬유들의인장특성측정결과를장력조건에따라정리하여표로정리하고최대값이얻어진온도및장력조건들에서의물성변화를도표로정리하였다. Table 2에는 14 MPa의장력을가하여탄화한섬유의인장물성을탄화온도별로정리하였다. 탄화중의섬유절사현상이탄화온도 1600 o C에서일부발견되었으며해당온도에서인장강도가약 0.7 GPa로나타나모든섬유들중가장낮은값을확인하였다 o C 구간에서탄화된섬유들의인장강도는최소 1.1 GPa에서최대 1.2 GPa로나타났으나오차범위내에서의편차를보였고, 인장탄성율의경우최소 233 GPa에서최대 260 GPa로 1400 C에서가장높게나타나는것으로측정되었다. 파단신도의경우 1300 o C 에서 1400 o C까지는 0.53% 에서 0.57% 로약 7.5% 상승하여섬유인성이전반적으로상승하는경향을보였으나이후 1500 C 에서 1600 C에이르기까지 0.44%, 0.28% 로급격히감소하는경향을보였다. 또한전온도구간에서섬유의수축률은 4% 내외로비슷하게나타나는것을알수있다. 해당실험결과를통해 14 MPa의장력을가해준경우, 1400 o C가최적의탄화온도인것을확인하였다. Table 3에는 25 MPa의장력을가하여각온도별로탄화한섬유들의인장물성을정리하여나타내었다. 해당조건에서는 14 MPa의장력조건과는달리섬유가탄화시키고난후수축되는것이아닌오히려조건에따라 1.5% 에서 2.2% 까지연신이된것을알수있다. 또한 1500 o C 이상의온도에서는섬유다발중일부섬유들이절사되는현상이나타나며 1600 o C의경우탄화과정중섬유가모두끊어져해당조건이가공한계점이상임을확인하였다. 이러한현상의원인으로는일반적으로 PAN계고분자섬유들의탄화과정에서발생하는구조변화가질소와산소등의원소를제거하고그래핀구조를형성하는메커니즘으로이루어지며따라서부피의감소즉, 섬유의경우섬유방향으로의수축이일어나는것이필연적인데수축에대한한계수축력이상 Sample Table 2. Tensile properties of carbon fiber carbonized at various temperature with 14 MPa of fiber tension Shrinkage Tensile strength Young s modulus Elongation Diameter (μm) CF ± ± ± ± 0.5 CF ± ± ± ± 0.3 CF ± ± ± ± 0.2 CF ± ± ± ± 0.7

4 388 Kyeong Hun Choi, So Jeong Heo, Sang-Ha Hwang, Soo Bin Bae, Hyung Ik Lee, Han Gi Chae Sample Table 3. Tensile properties of carbon fiber carbonized at various temperature with 25 MPa of fiber tension Shrinkage Tensile strength Young s modulus Elongation Diameter (μm) CF % increased 1.2 ± ± ± ± 0.4 CF % increased 1.1 ± ± ± ± 0.4 CF CF % increased, partially broken 0.9 ± ± ± ± 0.4 Fibers broken 의응력이반대방향으로가해지거나그래핀구조가형성되는영역의 boundary 사이에서혹은승온과정에서그래핀구조형성온도에도달하기전에일정수준이상의변형이일어나그래핀형성과정에서의수축을상쇠시키는경우등이복합적으로작용하여이러한현상을발생시킨것으로가정할수있다 [13]. 이러한현상을고려하여 Table 3에서탄화온도의영향을확인해보면인장강도의경우 1300 o C 에서 1.2 GPa, 1400 C에서 1.1 GPa로오차범위내에서감소하지만인장탄성률의경우 1300 C에서 236 GPa, 1400 o C에서 248 GPa, 1500 C에서 254 GPa로탄화온도에대하여지속적으로증가하는것을볼수있다. 이러한인장강도와탄성율의탄화온도에따른증감추세의차이는 PAN계탄소섬유의온도에따른탄화거동에서일반적으로관찰되는것으로알려져있으며그원인은탄성율의경우탄화온도에따라증가하는그래핀결정구조의크기, 배향에따른영향이며특정온도를기점으로감소하는인장강도의경우가해진섬유장력에의해감소한분자의 mobility와이로인해형성된 pore 및 defect 구조의영향이라고알려져있다 [13]. 이러한영향으로 25 MPa의장력에서는최대인장강도를얻기위한탄화온도조건과최대탄성율을얻기위한탄화온도조건이큰차이를보임을확인하였다. Table 4에는 35 MPa과 45 MPa의장력조건에서제조된탄소섬유들의물성을정리하였다. 일부섬유에서 25 MPa 조 건과동일하게탄화공정이후섬유의연신이발생하였음을알수있으며연신율또한증가하였음을확인할수있다. 각각의장력조건에최대탄화가능온도는모두 1400 o C 가최대이며탄화온도에따라인장강도의감소와인장탄성율의증가가 25 MPa의장력조건과마찬가지로나타남을확인할수있다. 최대인장강도는 1300 C에서 1.3 GPa로 나타났으며최대탄성율은 1400 C에서 266 GPa로나타났다. 이러한현상은 45 MPa의장력조건에서도반복적으로나타나는데 1300 C 탄성율과인장강도또한오차범위에서거의동일한값을보이는것을확인할수있다. 위에서관찰한결과들을탄화조건에따라종합적으로정리하기위해 Fig. 3에탄화온도 1300 C와 1400 C에서장력에따른섬유들의인장강도와인장탄성율을정리하였다. Fig. 3. Tensile strength and modulus of fibers carbonized at (ab) 1300 o C and (c-d) 1400 o C with various fiber tension Table 4. Tensile properties of carbon fiber carbonized at various temperature with 35 and 45 MPa of fiber tensions Sample Shrinkage Tensile strength Young s modulus Elongation Diameter (μm) CF % increased 1.3 ± ± ± ± 0.7 CF % increased 1.1 ± ± ± ± 0.6 CF % increased 1.4 ± ± ± ± 0.4 CF % increased partially broken 0.9± ± ± ±0.5

5 The Effect of Heat Treatment Condition on the Mechanical Properties of oxi-pan Based Carbon Fiber 389 Fig. 3의 (a) 와 (b) 를보면 1300 o C의탄화온도에서섬유장력의증가에따라인장강도와인장탄성율이모두오차범위내에서증가함을볼수있다. Fig. 3의 (c) 와 (d) 에서나타낸 1400 o C의탄화온도에대해서는인장강도는오차범위내에서감소하는반면인장탄성율은 25 MPa에서감소하고나머지조건에서일정한수준을유지하며, 탄화온도증가에대하여서는인장강도는 14 MPa 조건을제외하면모두감소하는반면인장탄성률은모든조건에서온도증가에대하여증가함을확인할수있다. 탄화온도에따른인장강도의감소율은섬유장력조건에대하여점차적으로증가하는데 25 MPa에서 8.3%, 35 MPa에서 15.4% 감소하고 45 MPa에서 35.7% 의급격한감소세를보인다. 인장탄성율의증가율은이와는반대의경향을보이는데 14 MPa에서 11.6% 증가한반면이후로는섬유장력이증가함에따라 5.1%, 3.5% 로순차적으로증가율이감소하는경향을보이는것을확인할수있었다. 탄화실험과인장물성측정을통해가장안정적인탄화조건으로확인된 1300 C와 1400 C에서섬유장력에따라얻어진섬유들을라만분광법을이용하여구조분석을진행하였다. 측정된라만스펙트럼의결과를장력조건에따라표로정리하고섬유내의상대적인 Graphite 구조의형성비율을조사하고자 G-band에대한 D-band의비율 (I D /I G ) 을각스펙트럼으로부터계산하여표로정리하였다. 본연구에서각 peak의 fitting에사용된 peak은 1200 cm -1 부근의 D4 Band와 1350 cm -1 부근에서관찰되는 D Band, 1580 cm -1 부근의 G Band, 그리고비정질탄소로부터기인하는 1500 cm -1 부근의 peak이사용되였다 [13]. 해당 peak 구성요소를이용하여 fitting된라만스펙트럼의예시를 Fig. 4에나타내었다. 비록탄소섬유의라만스펙트럼은섬유내의 graphite 구조의상대적비율과구조적완결성분자단위의상대적인 defect의비율을반영하기때문에섬유의기계적인물성과완전한연관성을설명하기에는무리가있으나인장탄성율의경우 graphene 결정구조의크기와결정구조내의 defect Fig. 5. Raman spectra of fibers carbonized at (a) 1300 o C and (b) 1400 o C with various fiber tension Table 5. I D /I G of carbon fibers carbonized at 1300 o C and 1400 o C with various fiber tension Sample I D /I G Sample I D /I G CF CF CF CF CF CF CF CF 를반영하는것으로알려져있어 I D /I G 의변화를연관지어설명할수있는부분이있다고판단된다 [14]. 본연구에서얻어진결과또한탄성율과 I D /I G 의결과사이에연관성이있는것으로판단되는데 Fig. 5에나타낸장력에따른라만스펙트럼의변화를통해 CF 에서가장높은 I D /I G = 1.66이확인되었으며 Fig. 5에서는 CF 에서가장높은 I D /I G = 1.58이나타남이확인되었다. 해당섬유들은인장탄성율결과에서확인된바와같이동일한탄화온도의다른섬유들에비해상대적으로낮은탄성율을가지는것을확인할수있어낮은구조적완결성이섬유의탄성율에반영된것으로생각해볼수있다. 이에비해인장강도는실험결과를통해서라만스펙트럼의변화추세와의연관성을발견하기어려웠는데이는탄소섬유의인장강도에있어서는 1차적으로 void나 pore 등이큰영향을미치기때문인것으로생각된다. 일반적으로탄소섬유의인장탄성율의경우결정화도및결정의크기등과관련한해석이정설로받아들여지고있으나인장강도의경우에는영향을미치는구조적요소를복합적이라고보거나새로운요인을분석하는등현재까지도다양한연구가진행중이다 [15]. 4. 결론 Fig. 4. Raman spectrum of fiber carbonized at (a) 1300 o C and (b) 1400 o C with 14 MPa fiber tension. Five most representative peak components were used to analyze each spectrum Oxi-PAN 섬유를기반으로한탄소섬유제조공정의다양한공정요소들중가장중요한변수로생각되는섬유에부가되는장력과탄화온도의영향을조사하고최적화하고자다양한장력과탄화온도에따라섬유의탄화실험을진행하였다. 탄화온도를증가시킴에따라가공가능한최대부

6 390 Kyeong Hun Choi, So Jeong Heo, Sang-Ha Hwang, Soo Bin Bae, Hyung Ik Lee, Han Gi Chae Defense Acquisition Program Administration, DAPA) through Institute of Civil-Military Technology Coorperation. REFERENCES Fig. 6. Overall change in tensile properties caused by carbonization temperature and fiber tension 가장력은감소하여 1300 C와 1400 C에서최대 45 MPa, 1500 C에서최대 25 MPa, 1600 C에서최대 14 MPa까지로나타났다. 제조된섬유의인장실험은탄화공정이가장안정적인 1300 C와 1400 C를중심으로분석하였으며, 그결과를 Fig. 6에정리하여나타내었다 o C의탄화온도에서섬유장력의증가에따라인장강도와인장탄성율이부가된장력에대하여모두오차범위내에서증가함을볼수있었고 1400 o C의경우부가된장력에대해인장강도는오차범위내에서감소하는반면인장탄성율은 25 MPa에서감소하고나머지조건에서일정한수준을유지하는것으로나타났다. 탄화온도증가에대하여서는인장강도는 14 MPa 조건을제외하면모두감소하는반면인장탄성률은모든조건에서온도증가에대하여증가함을확인하여기존의발표된결과들과동일한경향을보였다 [16,17]. 탄화온도에따른인장강도의감소율은섬유장력조건에대하여점차적으로증가하여 45 MPa에서최대 35.7% 의급격한감소세를보였고인장탄성율의증가율은섬유장력이증가함에순차적으로감소하여 45 MPa에서 3.5% 의최저증가율을보이는것을확인할수있었다. 특히인장탄성율결과는라만스펙트럼분석을통해얻어진 I D /I G 결과와연관지어구조-물성의상관관계를생각해볼수있었으며, 이에비해인장강도는라만스펙트럼의변화추세와의연관성을발견하기어려웠는데이는일반적으로탄소섬유의인장강도에있어서는 1차적으로 void나 pore 등이큰영향을미치기때문인것으로생각되며또다른복합적요소가작용하기때문인것으로분석된다. ACKNOWLEDGEMENT This work was supported by the Korean Government (Ministry of Trade, Industry and Energy, MOTIE, and 1. Chung, D.D.L., and Chung, D., Caron Fiber Composites, Elsevier, USA, Chawla, K.K., Composite Materials, Chapter 8 Carbon Fiber Composite, Springer Science & Business Media, LLC, USA, Rahman, M.S.A., Ismail, A.F., and Mustafa, A., A Review of Heat Treatment on Polyacrylonitrile Fiber, Polymer Degradation and Stability, Vol. 92, No. 8, 2007, pp Fitzer, E., PAN-based Carbon Fibers Present State and Trend of the Technology from the Viewpoint of Possibilities and Limits to Influence and to Control the Fiber Properties by the Process Parameters, Carbon, Vol. 27, No. 5, 1989, pp Eddie, E., The Effect of Processing on the Structure and Properties of Carbon Fibers, Carbon, Vol. 36, No. 4, 1998, pp Wangxi, Z., Jie, L., and Gang, W., Evolution of Structure and Properties of PAN Precursors during their Conversion to Carbon Fibers, Carbon, Vol. 41, No. 14, 2003, pp Johnson, D.J., Structure-Property Relationships in Carbon Fibres, Journal of Physics D: Applied Physics, Vol. 20, No. 3, 1987, pp Lee, S.H., Kim, J.H., Ku, B.C., Kim, J.K., and Joh, H.I., Structural Evolution of Polyacrylonitrile Fibers in Stabilization and Carbonization Advances in Chemical Engineering and Science, Vol. 2, No. 2, 2012, pp Mouritz, A.P., Bannister, M.K., Falzon, P.J., and Leong, K.H., Review of Applications for Advanced Three-dimensional Fibre Textile Composites, Composite Part A: Applied Science and Manufacturing, Vol. 30, No. 12, 1999, pp Chen, T., Liao, J., Liu, G., Zhang, F., and Gong, Q., Effects of Needle-punched Felt Structure on the Mechanical Properties of Carbon/Carbon Composites, Carbon, Vol. 41, No. 5, 2003, pp Ko, T., Influence of Continuous Stabilization on the Physical Properties and Microstructure of PAN based Carbon Fibers, Journal of Applied Polymer Science, Vol. 42, No. 7, 1991, pp Nunna, S., Naebe, M., Hameed, N., Fox, B.L., Creighton, C. Evolution of Radial Heterogeneity in Polyacrylonitrile Fibres during Thermal Stabilization: Overview, Polymer Degradation and Stability, Vol. 136, 2017, pp Newcomb, B.A., Processing, Structure, and Properties of Carbon Fibers, Composites Part A: Applied Science and Manufacturing, Vol. 91, No. 1, 2016, pp Sadezky, A., Muckenhuber, H. Grothe, H., and Pöschl, U., Raman Microspectroscopy of Soot and Related Carbonaceous Materials: Spectral Analysis and Structural Information, Carbon, Vol. 43, No. 8, 2005, pp Huang, Y., and Young, R.J., Effect of Fibre Microstructure

7 The Effect of Heat Treatment Condition on the Mechanical Properties of oxi-pan Based Carbon Fiber 391 upon the Modulus of PAN- and Pitch-based Carbon Fibres, Carbon, Vol. 33, No. 2, 1995, pp Naito, K., Tanaka, Y., Yang, J.M., and Kagawa, Y., Tensile Properties of Ultrahigh Strength PAN-based, Ultrahigh Modulus Pitch-based and High Ductility Pitch-based Carbon Fibers, Carbon, Vol. 46, No. 2, 2008, pp Salim, N.V., Blight, S., Creighton, C., Nunna, S., Atkiss, S., and Razal, J.M., The Role of Tension and Temperature for Efficient Carbonization of Polyacrylonitrile Fibers: Toward Low Cost Carbon Fibers, Industrial & Engineering Chemistry Research, Vol. 57, No. 12, 2018, pp Jang, D., Joh, H.-I., Ku, B.-C., Kim, S.R., Bang, Y.H., and Lee, S., Effect of Heating Rate in Carbonization on Mechanical Properties of Polyacrylonitrile Based Carbon Fibers, Polymer (Korea), Vol. 41, 2017, pp

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