【作者】 赵亚奇；

【导师】 王成国；

【作者基本信息】 山东大学 ， 材料学， 2010， 博士

【摘要】 碳纤维前驱体聚丙烯腈(PAN)是由丙烯腈(AN)和少量共聚单体聚合而成的,最常用的共聚单体是衣康酸(IA)。采用高分子量PAN共聚物进行纺丝是制备高性能PAN原丝的有效途径。与传统的均相溶液聚合体系相比,水相沉淀聚合体系由于采用链转移系数为0的水(H20)作为反应介质,可以避免AN自由基向溶剂的链转移反应,有利于提高PAN聚合物的分子量和聚合反应的转化率,并减少大分子链的支化。本文主要针对水相沉淀聚合工艺制备碳纤维用高分子量PAN开展基础性科学研究。借助乌氏粘度计(UVM)、差示扫描量热(DSC)分析、热重分析(TGA)、元素分析(EA)、傅里叶变换红外光谱(FTIR)、激光Raman光谱(LRS)、广角X射线衍射(WAXRD)、核磁共振(NMR)和旋转粘度计等多种测试方法,研究了各聚合反应因素对AN/IA水相沉淀共聚合反应的影响,探讨了聚合工艺参数与聚合物结构和性能之间的相互关系,获得了可应用于碳纤维工业化生产的有价值的理论成果。与大多数采用含碱金属离子的复合引发体系不同,以不含碱金属离子的单一水溶性铵盐——过硫酸铵[(NH4)2S2O8:APS]为引发剂,采用水相沉淀聚合工艺,研究了AN与IA的共聚合反应。结果表明：采用水相沉淀聚合工艺可以制备出IA单体链节含量合适,聚合物分子量和聚合反应转化率均较高的PAN共聚物。在聚合反应开始阶段,AN／IA的水相沉淀聚合体系中存在两相——单体相和水溶液相；反应过程中,水溶液相中的引发剂APS受热分解产生硫酸根离子自由基(SO4-),引发AN与IA发生自由基共聚合反应。当白色PAN聚合物沉淀产生时,聚合物颗粒相随之产生。随着AN单体的消耗,单体相中的AN向水相中扩散,并且被吸附在聚合物颗粒相上,使聚合反应在水溶液相和聚合物颗粒相同时发生。随着聚合体系中引发剂用量、总单体浓度、反应温度的提高,聚合反应转化率均升高,聚合物平均分子量下降；随着反应时间延长,聚合反应转化率和聚合物平均分子量均升高。AN／IA的共聚合反应及PAN聚合物的结构和性能都受到IA单体的影响。由于单体活性的差异,原料组成与聚合物的组成并不一致。随着喂料时IA加入量的提高,聚合反应转化率和聚合物分子量呈现先升高后下降的趋势。在IA用量为2wt%时,转化率和分子量达到最大值。聚合物中的氧(O)元素含量随IA用量的提高而增加,表明IA单体链节在聚合物中的含量增加,而碳(C)、氮(N)、氢(H)元素的含量降低。FTIR谱图中代表IA单体链节的1737cm-1附近的羰基(C=O)伸缩振动峰强度增强。共聚单体IA的引入,降低了PAN聚合物的结晶度,使其晶粒尺寸下降。采用分子量调节剂对AN／IA水相沉淀共聚合反应的转化率和聚合物的平均分子量进行控制。随着分子量调节剂异丙醇(IPA)和正十二硫醇(n-DDM)用量的增加,聚合反应转化率和分子量下降,但是聚合物中C、N、H、O元素含量变化不大。分子量调节剂IPA的引入使PAN聚合物的结晶度提高,晶粒尺寸增大,但对化学结构影响不大。IA单体和IPA的引入对PAN聚合物的三单元立构规整度影响不大。在总单体浓度Ct=22wt%,引发剂浓度[APS]=0.8wt%,反应温度T=60℃,单体转化率约6.2%的条件下,采用Kelen-Tudos(K-T)法和Fineman-Ross(F-R)法,计算单体竞聚率分别为：r1(AN)=0.64, r2(IA)=1.37; r1(AN)=0.61, r2(IA)=1.47。从竞聚率的大小可以看出,IA单体的反应活性大于AN。随聚合反应转化率和反应温度的提高,AN的单体竞聚率增大,IA的单体竞聚率降低。建立了AN／IA共聚合反应的动力学方程为,该聚合体系的反应活化能为E=180.8kJ/mol。应用上述结构和性能分析手段,对水相沉淀聚合工艺制备的PAN聚合物的热性能相关性进行了研究。结果表明：IA单体的引入有效改善了PAN聚合物的热性能,能在较低温度下通过离子基机理引发环化反应。不论是在惰性气氛下,还是在空气气氛下,PAN均聚物和共聚物的DSC放热曲线呈现出多峰现象。而当有氧存在时,多峰现象尤为明显。随平均分子量的降低,PAN共聚物的DSC放热峰特征温度变化不大,放热峰形表现为双峰或三峰。PAN聚合物DSC放热曲线的多峰现象是加热过程中聚合物大分子链发生多种热反应的表现。对PAN聚合物在空气气氛中热处理后的结构和性能变化进行表征,结果表明：随着热处理温度的提高,PAN聚合物的颜色从淡黄色逐渐向黑色转变,聚合物中O元素含量逐渐增加,C、N、H元素的含量下降；PAN聚合物的结晶度和晶粒尺寸呈现先增大后减小的趋势,且在预氧化后期代表非晶区的2θ≈25.5°附近的衍射峰逐渐出现并增强；FTIR谱图中,2940cm-1和1455cm-1附近代表亚甲基(CH2)的伸缩振动和弯曲振动、2244cm-1附近代表氰基(C≡N)伸缩振动峰逐渐减弱并消失,1600cm-1附近代表梯形结构的双键基团(C=C和C=N)的伸缩振动峰逐渐出现并增强,1737cm-1附近代表C=O伸缩振动和1180cm-1附近代表C-O单键伸缩振动的两个含氧官能团的红外吸收峰始终存在。对不同溶剂类型(二甲基亚砜：DMSO;二甲基甲酰胺：DMF；二甲基乙酰胺：DMAc)配制的PAN共聚物浓溶液和PAN聚合物/DMSO的稀溶液体系进行流变学性能研究。在DMSO稀溶液体系中,PAN均聚物的Huggins曲线在测试浓度区域保持着较好的线性关系。PAN共聚物由于羧基含量的不同,具有或强或弱的聚电解质效应,其Huggins曲线在高浓度区域保持线性关系,而在低浓度区域表现出不同程度的偏离。研究了不同PAN共聚物浓溶液的表观粘度变化规律,结果表明：PAN纺丝溶液是剪切变稀流体,其表观粘度随分子量和原液固含量的提高均增大。对于不同溶剂类型配制的PAN纺丝原液来说,其表观粘度的变化趋势为：PAN/DMSO>PAN/DMAc>PAN/DMF。PAN纺丝溶液表现出较大的温度敏感性,其表观粘度随测试温度的升高而降低。对不同PAN原丝的结构和性能进行研究表明,提高PAN原丝的平均分子量和结晶度,有利于提高原丝的拉伸强度。研究发现采用水相沉淀聚合工艺制备的PAN共聚物,通过干喷湿纺工艺可以纺制出高性能的PAN原丝。干喷湿纺工艺纺制的PAN原丝具有不同于相应PAN共聚物的DSC放热曲线和WAXRD曲线。结合实验室多次实验,确定了粘均分子量(My)在20～25万的PAN共聚物有利于制备高性能的PAN原丝。以Mv=24万的PAN共聚物为溶质配制合适浓度的PAN/DMSO纺丝原液,采用干喷湿纺工艺可以获得纤度为1.07dtex,拉伸强度为7.54cN/dtex的PAN原丝。更多还原

【Abstract】 Polyacrylonitrile (PAN) precursors used to produce carbon fibers are polymerized by acrylonitrile and a small quantity of comonomers. Itaconic acid (IA) is the most frequently employed. The effective approach to manufacture high performance carbon fibers is adopting high molecular weight PAN copolymers as solute to prepare spinning dope. Compared to the conventional homogenous solution radical polymerization, it is propitious to utilize aqueous deposited polymerization to synthesize high molecular weight PAN polymers. And the polymerizations have higher conversions. In this polymerization system, water (H2O) is used as reaction medium, whose chain transfer constant is 0. And chain transfer reactions to AN radicals can be avoided. Chain branching also reduces. The main objective of this paper was specific to preparation of high molecular weight PAN used to manufacture carbon fibers by aqueous deposited polymerization technology. Effects of various polymerization factors on aqueous deposited copolymerization of AN and IA were investigated through Ubbelohde viscometer (UVM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), element analysis (EA), wide angle X-ray diffraction (WAXRD), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) and rotational viscometer. Structures and properties of the obtained PAN polymers were studied, whose relationships with the parameters of polymerization technology were also discussed. And valuable theoretical achievements applied to industrialized production stage of carbon fibers were acquired.As a single water-soluble ammonium salt, ammonium persulphate [(NH4)2S2O8: APS], was adopted as initiator to polymerize AN and IA. This was not identical with many researches, which employed complex initiation systems containing alkali metal ions. It is indicated that high molecular weight PAN copolymers with proper IA contents can be synthesized by this method. At the beginning, the polymerization system was separated into two phases, monomer phase and water solution phase. During the polymerization process, APS was decomposed into sulfate ion radicals (SO4(?)) under heating to initiate radical copolymerization of AN and IA. When the white PAN polymer precipitate emerged, polymer particle phase appeared. With the consumption of AN in the polymerization system, AN was transported from monomer phase to water solution phase. And then AN was absorbed to polymer particle phase. The polymerizations occurred in both water solution phase and polymer particle phase. With the increase of initiator concentration, total monomer concentration and polymerization temperature, molecular weights of PAN polymers all decreased, while polymerization conversions increased. With the extension of polymerization time, both molecular weights and polymerization conversions heightened.Structures and properties of PAN copolymers were affected by copolymerization of AN and IA. Because of different reactivity of monomers, the copolymer composition was not the same as the monomer ratio in the feed. With the increase of IA content in the feed, polymerization conversions and molecular weights firstly increased and then decreased. While the oxygen (O) content in the polymer increased. And the carbon (C), nitrogen (N) and hydrogen (H) contents in the polymer decreased. Stretching vibration of carboxyl group (C=O) around 1737cm-1 in FTIR assigned to IA chain segments increased. When the required IA amount in the feed was 2wt%, the polymerization conversion and molecular weight got the maximum values. Crystallinity and grain size decreased with the introduction of IA in the feed.Polymerization conversions and molecular weights of AN/IA copolymers could be controlled by using molecular weight regulators during aqueous deposited copolymerizations of AN and IA. With the increase of isopropanol (IPA) and n-dodecyl mercaptan (n-DDM) in the feed, polymerization conversions and molecular weights of PAN copolymers increased. But there were few changes of C, N, H and O contents in PAN copolymers. Crystallinity and grain size increased with the introduction of IPA in the feed. While chemical structures had few changes. Moreover, triad stereoregularity was not basically affected by IA and IPA.When the total monomer concentration C1 was 22wt%, the initiator concentration [APS] was 0.8wt%, the polymerization temperature T was 60℃, and the polymerization conversion was about 6.2%, values of monomer reactivity ratios were calculated by Kelen-Tudos (K-T) method and Fineman-Ross (F-R) method. Corresponding to the former method, the r1(AN) value was 0.64 and r2(IA) was 1.37. And the latter r1(AN) value was 0.61 and r2(IA) was 1.47. Evidently, the reactivity of IA is higher than AN. With the increase of polymerization conversion and temperature, monomer reactivity ratio of AN increased. Whereas monomer reactivity ratio of IA decreased. Kinetics equation of the copolymerization system was obtained, i.e. Rp[APS]0.538[M]1.696. And the activation energy was also figured out, i.e. E=180.8kJ/mol.Thermal properties of PAN polymers synthesized by aqueous deposited polymerization were characterized by the measuring methods above. It is shown that thermal properties of PAN polymers were improved with the introduction of IA comonomer. Cyclization reactions could be initiated through ionic mechanism under low temperature. DSC curves of PAN homopolymer and copolymers exhibited multiple peaks under inert atmosphere or air atmosphere. When there was oxygen in heating atmosphere, multiple peaks became more evident. With the increase of molecular weight of PAN copolymers, characteristic temperatures of DSC exothermic peaks had few changes. And the exothermic peaks represented doublets or triplets. The multiple peaks in DSC curves of PAN polymers were attributed to many exothermic reactions in macromolecular chains during heating process. Structure and property changes of PAN polymers heat-treated under air atmosphere were investigated. It is indicated that colours of heat-treated PAN polymers became from faint yellow to black gradually with the increase of the heat treatment temperature. And O contents in the polymers increased. Contents of C, N and H elements decreased. Crystallinity and grain sizes of heat-treated PAN polymers firstly increased and then decreased. At the later period of pre-oxidation reactions, diffraction peaks around 2θ≈25.5°corresponding to amorphous areas in the heat-treated PAN polymers appeared and then increased by degrees. In FTIR spectra, stretching vibrations and bending vibrations of methylene group (CH2) around 2940cm-1 and 1455cm-1, and stretching vibrations of nitrile group (C=N) around 2244cm-1 decreased by degrees and then disappeared. Stretching vibrations of double bond group (including C=C and C=N) around 1600cm-1 representing the ladder structure appeared and then became stronger by degrees. Whereas FTIR absorption peaks of the two oxygen-containing functional groups, including stretching vibrations of C=O around 1737cm-1 and C-O single bond around 1180cm-1, maintained in the PAN polymers and heat-treated PAN polymers all the time.Rheological properties of different PAN solutions were discussed. The solvents used in concentrated solutions of PAN copolymers were dimethylsulphoxide (DMSO), dimethyl formamide (DMF) and dimethylacetamide (DMAc). Only DMSO was utilized in dilute solutions of PAN polymers. In the dilute solution system of PAN homopolymer, its Huggins curve owned better linear relation under the testing concentration region. Because of different polyelectrolyte effects in dilute solutions of PAN copolymers, their Huggins curves only had linear relation under the high concentration region. Different degrees of deviations were shown under the low concentration region. Apparent viscosities of different PAN concentrated solutions were studied. It is shown that PAN spinning solution is a shear-thinning fluid. Their apparent viscosities became larger with the increase of molecular weight and solid content. As for PAN spinning solutions prepared by different solvents, the apparent viscosity values changed in sequence as follows, i.e. PAN/DMSO>PAN/DMAc> PAN/DMF. PAN spinning solutions were temperature-sensitive. The apparent viscosities decreased with the increase of testing temperature.Structures and properties of different PAN fibers were discussed. It is convenient to enhance tensile strength of PAN fibers by increasing average molecular weights and crystallinity of PAN fibers. It is found that AN/IA copolymers synthesized by aqueous deposited polymerization could be used to prepare high performance PAN fibers by dry-jet wet spinning technology. Furthermore, the PAN fiber had different DSC curve and WAXRD curve from the corresponding PAN copolymer. Combining several laboratory experiments, PAN copolymers with viscosity average molecular weight (Mv) ranging from 20×10 to 25×10 were preferable to manufacture high performance PAN fibers. And the final PAN fiber, whose fiber fineness was 1.07dtex and tensile strength was up to 7.54cN/dtex, had been produced by dry-jet wet spinning technology using the PAN copolymer with Mv equaling to 24×104.更多还原