【作者】 刘建军；

【导师】 王成国；

【作者基本信息】 山东大学 ， 材料学， 2007， 博士

【摘要】 本文采用自由基溶液聚合方式和湿法纺丝方法，研究了碳纤维用聚丙烯腈原丝的制备工艺，以及制备工艺与原丝各级结构之间的关系。首先，本文研究了丙烯腈（AN）与衣康酸（IA）、衣康酸铵（AIA）、衣康酸甲酯（MIA）等衣康酸系共聚单体的自由基溶液共聚合反应。三种反应体系的聚合速率都比均聚体系的聚合速率低，聚合速率快慢有以下规律：AN／MIA＜AN／AIA＜AN／IA＜AN。这是由于电子效应和体积效应引起的链自由基活性差异而造成的结果。利用经典Kelen-Tudos方法，测定了IA、AIA、MIA三种共聚单体在分别与AN进行的二元共聚反应中的竞聚率，发现三种共聚单体共聚活性较高，竞聚率均大于1。本文比较了溶液聚合、水相悬浮聚合和混合介质沉淀聚合三种聚合方式的特点。溶液聚合反应平稳，聚合物粘均分子量可达2.5×10⁵，分子量分布D可控制在2.4以下；水相悬浮聚合反应快速，分子量可高达6.6×10⁵，但分子量分布D在3.2左右；混合介质沉淀聚合反应较快，产物分子量较高，可达5.2×10⁵，分子量分布D为3.0左右。根据自由基聚合反应的基本原理，计算了聚丙烯腈理论平均分子量。在引发剂用量为单体重量的0.45％条件下，当采用DMSO溶液聚合且单体浓度分别为20％、30％（wt）时，聚合物理论数均分子量分别为5.39×10⁴、6.89×10⁴；当采用水相悬浮聚合时，产物理论数均分子量则为1.30×10⁵。采用Monte Carlo法模拟了IA、AIA、MIA分别与AN共聚所得三种共聚物的链结构和序列分布，模拟结果表明，为保持均匀的序列结构，第二单体的浓度不易太高，最好控制在2w％以下。研究了共聚物溶液的流变性，讨论了分子量、固含量、共聚单体含量、温度、外加添加剂对共聚物溶液粘度的影响。发现以MIA作为共聚单体和添加表面活性剂是降低PAN共聚物体系粘度的两种有效途径。本文进行了聚合物溶液改性研究，发现P（AN／IA）氨化改性后变为P（AN／AIA），聚合物亲水性大幅提高。本文从双扩散和微相分离的角度，对聚丙烯腈原丝初生纤维成形机理进行了初步探讨。小分子DMSO、H₂O的双扩散，导致原液细流内PAN固相与DMSO-H₂O液相的微相分离。其中，固相为连续相，液相散布在连续相中形成孔洞，微相分离是初生纤维组织结构形成的基础。在微相分离过程中，如果PAN聚合物的亲水性不够大，则在凝固区易形成大而疏的孔隙结构，大而疏的孔隙结构形成孤立的闭孔，不利于双扩散的继续进行，为了开辟新的双扩散通道，丝条会变形，因而得到截面形状非圆形的初生纤维。当扩散强度过高时，丝条凝固区甚至会崩裂，出现微裂纹，过大的孔隙和微裂纹将会遗传到原丝结构中，形成缺陷。提高聚合物的亲水性，可以改善初生纤维微相分离的孔隙结构，得到细而密、相互贯通的开孔结构，使双扩散平缓而顺利地进行，因而可得到截面形状为圆形的初生纤维。建立了原丝中残留DMSO的高压液相色谱检测方法。原丝中残留DMSO在水中的溶出率与水温和浸泡时间正相关。通过提高水洗温度、延长水洗时间，可使原丝中DMSO的残留量由93 mg/L下降到2 mg/L以下。本文从晶态结构、取向结构和孔隙结构的角度，对原丝的组织结构进行了分析。在多级牵伸过程中，PAN大分子整链或部分链段发生滑动，沿纤维轴向重排取向，重排取向过程中相邻的取向度高的分子链或链段形成束状结构，取向度低的分子链或链段则存在于束状结构之间，形成束状结构之间的联系结构。SEM和HRTEM测试显示，PAN原丝的取向结构表现为原纤和微原纤两级束状结构，原纤直径在50～200nm之间，微原纤直径在10nm左右，微原纤结构是原丝组织结构的基本单元。共聚单体IA、MIA能有效降低PAN原丝的结晶度和晶粒尺寸。PAN聚合物亲水性的改善有利于提高原丝的牵伸比和取向度。本文借助差示热分析（DTA）、差示热量扫描法（DSC）、热重分析（TG）等测试手段，研究了共聚单体对共聚物热性能的影响。试验结果表明，共聚单体MIA和IA均能使PAN放热峰向低温区移动，P（AN／MIA）、P（AN／IA）放热峰比均聚PAN放热峰向低温区分别移动了5.7℃、42.7℃，IA对PAN放热特性的改善比MIA更有效；氨改性没有改变P（AN／IA）原丝的热性能，P（AN／AIA）聚合物在纺丝过程中重新变成了P（AN／IA）。进行了热稳定化纤维的傅立叶红外光谱（FTIR）分析、氧元素分析和X-射线衍射（XRD）分析，标明了各温区发生的环化脱氢、脱氢环化以及氧化反应中氰基等官能团的变化，揭示了线形PAN大分子链转化为耐热梯形结构过程中的特征。更多还原

【Abstract】 In this paper, the preparation technology and structure at different levels of PAN-based carbon fiber precursor were investigated in detail. The preparation technology was composed of free-radical solution copolymerization, dope modification and wet-spinning.Firstly, the radical solution copolymerization of AN with comonomers IA, AIA, MIA was investigated, respectively. The reactivity rates of the three copolymerization systems were all slower than that of homo-polymerization of AN, AN/MIA<AN/AIA<AN/IA<AN accordingly. This was because of reaction activity difference result from electron-effect and bulk-effect. Values of monomer reactivity ratios in the three copolymerization systems were calculated by Kelen-Tudos method. The reactivity ratios of the three comonomers were all bigger than 1, showing the copolymerization activity of the three comonomers higher than AN.The characteristics of solution polymerization, aqueous suspension polymerization and mixed-medium precipitation polymerization were summarized. The reaction rate of solution polymerization was the smoothest of the three, with the viscosity molecular weight reaching 2.5 × 10⁵ at the high end and molecular weight distribution D at the range of 2.0-2.4. The reaction rate of aqueous suspension polymerization was the fastest of the three, with the viscosity molecular weight reaching 6.6 ×10⁵ at the high end and molecular weight distribution D at about 3.2. The viscosity molecular weight can reach 5.2 ×10⁵ at the high end and molecular weight distribution D was about 3.0.The theoretical molecular weight was calculated according to free-radical solution polymerization principle. When the monomer concentration was 20 30%（wt） respectively, the theoretical number-average molecular weight was 5.39 ×10⁴ 6.89 × 10⁴ accordingly. For the aqueous suspension polymerization products, the theoretical number-average molecular weight was 1.30×10⁵. The composition and sequence distribution of copolymers of AN with IA, MAA and AA as comonomers were simulated by Monte Carlo method.The rheological behavior of the polymer solution was studied. Effects of molecular weight, polymer concentration, comonomer concentration, temperature and additives on the viscosity of the solution were discussed. It was discovered that MIA as comonomer and surfactants as additives were both effective methods to reduce the viscosity of the solution.The polymer solution modification was carried out in this paper. When P（AN/IA）changed to P（AN/AIA） after amino-modification, the hydrophilic property of the polymer was improved dramaticly.From the view of mutual-diffusion and micro-phase separation, the protofiber coagulation was analyzed. The mutual-diffusion of the solvent DMSO and coagulate H₂O made the polymer micro-phase and the DMSO-H2O micro-phase separated from the dope, with the polymer as continuous phase, and liquid phase dispersing as micro-void.In the progress of micro-phase separation, if the hydrophilic property of the polymer was not high enough, big and loose voids were formed in the coagulation zoo. The big and loose voids were not interconnected and interfered the diffusion of DMSO and H₂O. The protofiber deformed for open new diffusion paths and the transverse section of the protofiber was no longer round. If the hydrophilic property of the polymer was high enough, small and interconnected voids were formed and the diffusion would progress smoothly, with protofiber transverse section round.A method was established for the determination of DMSO in the precursor fibers by high performance liquid chromatography （HPLC）. By means of spinning processes improving, the residual of DMSO in PAN precursor fibers was reduced from 93 mg/L to 2 mg/L.The texture of precursor fibers was studied from the view of crystal structure, orientation structure and void structure. In the multi-level drawing process, the PAN chains or part of chain segments slide relatively and rearranged and oriented along the fiber axis. In the rearrangement and orientation process, chains or part of chain segments with high degree of orientation formed bundle-shaped structure, with chains or part of chain segments with low degree of orientation forming the connection structures among the bundle-shaped structures. SEM and HRTEM tests showed that the bundle structure had two levels: fibrils and micro-fibrils. The diameter of fibrils was at the range of 50-200nm, while the diameter of micro-fibrils was about 10nm. Micro-fibrils were the base structure of PAN precursor fibers. Comonomer IA or MIA could effectively decrease the crystal degree and crystal size. The increase of hydrophilicity of PAN made the polymer sustainable to high drawing-ratio and high degree of orientation.The effect of comonomers on the thermal properties of PAN fibers was studied by differential thermal analysis （DTA）, differential scanning calorimetry （DSC） and thermal gravimetric analysis （TG）. It was discovered that comonomers IA or MIA could make the exothermal peak shift to low temperature zone, with the exothermal peak of P（AN/MIA） and P（AN/IA） 5.7°C and 42.7°C lower than that of homo-PAN, respectively. Amino-modification didn’t change the thermal properties of the precursor fibers because P（AN/MIA） changed back to P（AN/IA） in the spinning process.In the last part of the paper, fiber samples from every important thermal stabilization steps were studied by infrared spectroscopy （IR）, oxygen element analysis and X-ray diffraction （XRD）. The changes of -CN and other key functional groups during the reactions of thermal stabilization were tracked. Several characteristics of the reaction were summarized.更多还原