木材苯酚液化生成物碳素纖維化材料的制備及結構性能表征

1、木材苯酚液化生成物碳素纖維化材料的制備及結構性能表征（作者：馬曉軍，導師：趙廣杰教授）摘要 為了實現(xiàn)碳纖維原料資源的可持續(xù)利用，用木質生物資源替代化石資源，改良生物質碳纖維的工藝缺陷，本論文以速生人工林杉木木材為原料，通過一步法合成法將其苯酚液化產物制備成紡絲原液，熔融紡絲后直接炭化成功獲得通用級木材液化物碳纖維。同時利用掃描電子顯微鏡、紅外光譜、X射線衍射、拉曼光譜、元素分析等多種手段對碳纖維的形貌、結構進行了表征，并對木材液化物原絲及其碳纖維的炭化機理、力學性能、熱力學特性以及比表面積、孔隙分布等物理性能進行了系統(tǒng)研究。得到主結論如下：1. 以木材苯酚液化物為原料，加入六次甲基四胺后熔融紡

2、絲，將熔紡纖維置于甲醛和鹽酸溶液中固化處理后制成最大拉伸強度達365MPa的碳纖維原絲，并研究了紡絲液合成因素和拉絲工藝因素對木材液化物原絲性能的影響。結果表明，原絲的拉伸強度隨苯酚/木材比、合成溫度以及收絲輥的轉速的增加而增加；隨著合成劑用量的增加而逐漸減小；隨著紡絲液合成升溫時間、固化液中鹽酸濃度以及固化時間的增加而先增加后減小。2. 研究了木材苯酚液化物紡制碳纖維原絲的分子轉化過程和反應機理。液化物中加入的甲醛給與體（六次甲基四胺）與液化中未反應完全的游離苯酚進行加成反應形成新的羥甲基，同時羥甲基之間或羥甲基和苯環(huán)上活波H之間發(fā)生縮合反應，形成次甲基醚鍵和亞甲基鍵，分子內交聯(lián)程度較低，形

3、成具有可拉絲的線性結構的紡絲液；初始纖維經過酸性固化液處理后，纖維中芳環(huán)與固化液中的+CH2OH離子發(fā)生了交聯(lián)反應，苯環(huán)上的活波氫原子數(shù)量減少，同時次甲基醚鍵轉化為亞甲基鍵，以及酚羥基之間、酚羥基與固化液中生成的+CH2OH離子之間發(fā)生了脫水縮合反應，纖維的交聯(lián)度增大，初步形成網(wǎng)狀結構，原絲纖維的力學性能大幅度增加3. 對木材苯酚液化物、紡絲液、原絲的熱力學特性進行了綜合評價。150600是液化物、紡絲液、原絲的主要熱失重區(qū)間，其熱失重分別達到36.9%、41.3%、43.3%；600以后，原絲在此階段發(fā)生了明顯的二次熱解重組；三種材料的殘余重量的比率說明原絲和紡絲液比液化物的熱穩(wěn)定性好。木材

4、苯酚液化物原絲的DSC曲線上在0600之間存在兩個明顯的放熱峰，且隨著升溫速率的增加，原絲的放熱峰向高溫方向移動，放熱峰的峰形加寬變大；利用Kissinger和Crane公式，求得原絲的第一個放熱峰的表觀活化能為69.36 KJmol-1 ，反應級數(shù)為0.862；第二個放熱峰的表觀活化能59.02KJmol-1；反應級數(shù)為0.734。4. 研究了炭化因素對木材液化物碳纖維力學性能的影響。木材液化物碳纖維的力學性能隨炭化溫度和炭化時間的增加而顯著提高；隨著炭化升溫速率的增加而逐漸下降。同時，原料中木材/苯酚比越大，其碳纖維的拉伸強度和拉伸模量增幅比例越大，且直徑收縮越小。優(yōu)化炭化工藝后，木材液化

5、物碳纖維的拉伸強度、模量、炭化率可分別達到1.7GPa、159GPa和60%。5. 研究了木材液化物碳纖維的微晶結構及在炭化過程中的變化規(guī)律。炭化溫度400以上，原絲的X射線衍射（002）衍射峰隨著炭化溫度的提高而明顯增強；同時碳絲出現(xiàn)了較明顯的（100）衍射峰。木材液化物碳纖維的微結構d（002）、d（100）值隨炭化溫度的升高逐漸減小，La、Lc、Lc/d（002）值先減小后增大，表征材料石墨化程度的g值由小變大。另外，500以上得到的碳絲其拉曼光譜譜圖中都出現(xiàn)了具有類石墨炭材料典型馬鞍狀的表征無序結構的D峰和表征石墨微晶的G峰。隨著炭化溫度的提高，D峰衍射強度逐漸減小，G峰衍射強度逐漸增

6、大，材料的無序化度R值逐漸減小。6. 研究了炭化過程中木材液化物原絲的結構變化。在炭化處理過程中木材苯酚液化物纖維的紅外光譜其3444cm-1、29242852cm-1、1632 cm-1、1454cm-1、900650cm-1處的吸收峰都發(fā)生了明顯的減弱，說明隨炭化溫度的提高，纖維的結構發(fā)生了較大的改變；但1632 cm-1、1454cm-1處芳環(huán)骨架中碳碳雙鍵吸收峰的減弱速度較慢，并且在1000以下的炭化處理中沒有消失，表明1000以下木材苯酚液化物原絲炭化處理是一個難石墨化的過程；紅外光譜的變化顯示500和800附近成為其炭化處理的兩個關鍵溫度段；另外，23782311cm-1處出現(xiàn)與P

7、-H伸縮振動相關吸收峰成為木材苯酚液化物碳纖維具有較強熒光的佐證，其原因主要是木材液化時加入的磷酸催化劑所致。7. 研究了木材液化物原絲的炭化機理。1000以下木材苯酚液化物原絲的炭化過程較為復雜，可分為三個階段，第一階段為300以下，主要表現(xiàn)為分子內部分醚鍵斷裂和脫羥甲基，產物以CO、CO2、CH2O等低分子物質及游離苯酚為主；第二階段300600之間是炭化的關鍵區(qū)間，分子內的網(wǎng)狀交聯(lián)結構被破壞，分子結構體系發(fā)生重排，碳網(wǎng)結構初步形成，分解產物除了苯酚、甲苯酚、二甲苯酚等酚類物質和CO、CO2、CH4等低分子物質外，苯、甲苯以及部分大分子產物的含量也很高，其主要在500附近逸出；第三階段為7

8、00以上，碳網(wǎng)結構繼續(xù)成長，碳網(wǎng)聚合度進一步提高，分子結構在800附近出現(xiàn)二次調整，分解產物主要以CO2和甲苯為主。8. 研究了木材液化物碳纖維的比表面積和孔隙分布特征。木材液化碳纖維的比表面積、BET表面積、微孔面積、總孔容積、微孔容積隨著炭化溫度的提高呈增大趨勢，而孔隙半徑卻逐漸下降，其中600800是木材苯酚液化物碳纖維孔隙結構發(fā)生變化的關鍵溫度區(qū)間。隨著炭化溫度的提高，碳纖維的吸附等溫線從具有清晰平穩(wěn)部分的I-A型向I-B型過渡，吸附滯后回線從A類管狀毛細孔回線向B類狹縫狀毛細孔回線過渡。關鍵詞：碳纖維，木材液化物，微結構，力學性能，炭化機理Preparation and Charac

9、terization of Carbon Fibrous Material from Liquefied Wood in Phenol（Ma Xiaojun Directed by Prof. Zhang Guangjie）Abstract In order to release the shortage of fossil resource, realize the sustainable development of carbon fiber, change the process defects of tradition biomass-based carbon fiber and ef

10、ficiently improve the utilization of wood-based resource, carbon fibers (LWCFs) from the phenolated Chinese Fir (Cunninghamia Lanceolata) were prepared by direct carbonization, after the melt-spinning of spinning solution synthesized with one-step reaction. Morphologies, structures of LWCFs have bee

11、n characterized by scanning electron microscope (SEM), FT-IR spectrometer,X-ray diffraction (XRD), Raman spectroscopy, Elemental analysis, etc. The carbonization mechanisms, mechanical property, thermodynamic behavior and physical properties (including specific surface area and pore distribution) ha

12、ve been investigated.1. The phenolated wood was modified to spinning solution by adding hexamethylenetetramine, melt-spinning then cured in combined solution of hydrochloric acid and formadehyde to obtain carbon fiber precursors (LWCFPs) with tensile strength 356MPa. The effect factors of spinning s

13、olution and spinning process on mechanical properties of LWCFPs have been studied. The tensile strength of LWCFPs increased obviously with increasing the phenol/wood ratio, the synthesis temperature, and the spinning speed, but decreased with increasing synthetics agent content. In addition, the ten

14、sile strength of LWCFPs firstly increased and then decreased with increasing synthesis temperature rise time, concentration of HCl, and the curing time.2. The molecular transformation and reaction mechanism of LWCFPs have been studied. Firstly, formaldehyde (HCHO) from hexamethylenetetramine (HMTA)

15、combined with unreacted phenol during wood liquefaction to produce new hydroxymethyl. At the same time, hydroxymethyl or hydroxymethyl reacting with alive hydrogen of aromatic ring formed diphenyl ether linkage and carbonyl brigdes, so that spinning solution with the low degree of crosslinkage and l

16、inearity structure was prepared. Secondly, many aromatic ring of fiber reacted with +CH2OH in curing solution during curing reaction; the relative intensity of the out-of-plane CH deformation band decreased; the crosslinkage of fibers were improved; the precursors preliminary had net-crosslinking st

17、ructure and good mechanical properties.3. The thermodynamic properties of liquefied wood, spinning solution, and LWCFPs have been comprehensive evaluated. Temperature rang 150600 was the main weight loss stage for three materials, which were 36.9%, 41.3% and 43.3% respectively. Weight retention rati

18、o illustrated that thermal stability of LWCFPs and spinning solution was better than that of liquefied wood. There were two exothermic decomposition peaks on DSC curves of LWCFPs from 0 to 600. The location of these peaks move to high temperature with increasing heating rate and the shape of peaks b

19、ecame larger and wider. According to Kissinger and Crane formula, the activation energy of two peaks were 69.36kJmol-1 and 59.02kJmol-1; the reaction order were 0.862 and 0.734, respectively.4. The influence of carbonization condition on the mechanical properties of LWCFs has been investigated. The

20、mechanical properties of LWCFs increased obviously with increasing carbonization temperature and time, and decreased with increasing the heating rate. The trend of the breaking elongation was opposite to that of tensile strength and modulus. It was also found that, the higher the wood/phenol ratio,

21、the higher the increasing amplitude of mechanical properties, and the smaller the dimension shrinkage. LWCFs with tensile strength of 1.7GPa, modulus of 159GPa and yield of 60% were reached at optimal carbonization conditions.5. The Variation of microcrystalline structure of LWCFs during carbonizati

22、on has been studied. Above carbonization temperature 400, the (002) crystal plane diffraction peak of the precursors at were obviously heighten with the rise of carbonization temperature, and gradually approached to the (002) plane peak of graphitoidal. LWCFs showed obvious (100) crystal plane diffr

23、action peak, which illustrated that this material changed from non-crystal to crystal structure. With temperature rising，the value of d（002）and d（100） decreasd; Values of the crystallite sizes La and Lc, the Lc/d（002）rate reduced then increased. The g value corresponding to the change degree of grap

24、hitoidal structure increased. Above 500, the Raman spectra of carbon fibers appeared the known D band which is related to disorder carbon and G band which corresponds to graphite with varying characteristics that are similar to other graphitoidal material. With carbonization temperature rising, inte

25、nsity of the D band decreased and that of G band increased; the integrated intensity ratio R=ID /IG (R-value) which is the degree of disorder of material gradually decreased with increasing carbonization temperature.6. The structure changes of LWCFPs during carbonization have been investigated in de

26、tail. FTIR absorded band of LWCFPs were evidently weakened in 3444cm-1，29242852cm-1，1632 cm-1，1454cm-1，900650cm-1 during carbonization, which indicated that the structure of carbon fiber changed. The intensity of the carbon-carbon double bond at 1632 cm-1 and 1454cm-1, which is corresponding to the

27、characteristic vibrations of aromatic ring, decreased slowly, but both bands did not disappear under 1000. It indicated that carbonization process of LWCFPs was a typical non-graphitizing course. 500 and 800 are the critical temperature section during carbonization of LWCFPs. The infrared absorption

28、 band in 23782311cm-1 is believed to be P-H stretching vibration band, which is caused by phosphoric acid during wood liquefaction. 7. The carbonization mechanisms of LWCFPs have been studied. The complex carbonization of the precursors was divided into three phases. In the first stage, the carboniz

29、ation temperature was lower than 350, the cleavage of intramolecular ether linkage and the removal of end hydroxymethyl mainly occurred, and some molecules such as H2O, CO2 , CH2OH and free phenol were found. In the second stage, 300600 was the main rang of carbonization; the bond cleavage occurred at different positions of the most molecule chain; many substance were observed at around 500, s