用在位X-射线衍射技术对PAN纤维的动态热解特征和环化动力学的研究

本文用在位Ｘ－射线衍射技术研究了ＰＡＮ（聚丙烯腈）纤维的预氧化过程。由广角测得不同温度下试样随热解时间而变化的一系列的解析谱图中计算出样品的结晶度、微晶尺寸、晶面间距和芳构化指数,并对这些参数随实验条件变化的瞬间情况给予了解释。同时,还描述了ＰＡＮ纤维在预氧化过程中的环化动力学行为。求解了各温度下的环化反应速率和活化参数。     

聚丙烯腈基碳纤维预氧化过程组成结构的演变

采用扫描电子显微镜、X射线衍射结构分析、裂解色谱-质谱、红外光谱等手段,探索了聚丙烯腈(PAN)基碳纤维预氧化过程中组成及结构演变的规律.预氧化初期,PAN丝束结构消失,呈半融状.共聚体首先参加反应,酯类等消失,分子发生环状交联,环化指数缓慢增加.预氧化初期与中期为环化反应最激烈阶段,易使结构固定化,形成结构性缺陷,应加强前期牵伸.预氧化中期重排形成新的片块堆垛束状结构,并逐步向片状扇形发散结构转变,框架结构在预氧化后期趋于稳定.此阶段,由于羧酯共聚体的诱发逐步形成非常稳定的环状结构,单体、二聚体、三聚体明显减少.预氧化后期只剩下含?/FONT>CN基的碎片,最后?/FONT>CN碎片亦消失,环化指数随预氧化过程升高, 结构形貌不再发生大的变化.     

聚丙烯腈基碳纤维预氧化过程

采用扫描电子显微镜、X射线衍射结构分析、裂解色谱-质谱、红外光谱等手段,探索了聚丙烯腈(PAN)基碳纤维预氧化过程中组成及结构演变的规律.预氧化初期,PAN丝束结构消失,呈半融状.共聚体首先参加反应,酯类等消失,分子发生环状交联,环化指数缓慢增加.预氧化初期与中期为环化反应最激烈阶段,易使结构固定化,形成结构性缺陷,应加强前期牵伸.预氧化中期重排形成新的片块堆垛束状结构,并逐步向片状扇形发散结构转变,框架结构在预氧化后期趋于稳定.此阶段,由于羧酯共聚体的诱发逐步形成非常稳定的环状结构,单体、二聚体、三聚体明显减少.预氧化后期只剩下含-CN基的碎片,最后-CN碎片亦消失,环化指数随预氧化过程升高,结构形貌不再发生大的变化.     

超高相对分子质量聚丙烯腈基多孔中空氧化纤维的制备工艺研究

以超高相对分子质量聚丙烯腈基多孔中空纤维为原丝制备了多孔中空氧化纤维 ,研究了其制备工艺 .详细考察了氧化工艺条件 (温度、时间 )对多孔中空氧化纤维环化程度的影响 ,发现环化程度随氧化温度升高和氧化时间延长而提高 ;与以普通分子质量聚丙烯腈基实心纤维为原丝相比 ,氧化温度应较低 (<2 4 0℃ )、氧化时间应较短 (<2h) .     

STXM研究氧元素在PAN预氧化纤维截面上的分布

采用扫描透射X射线显微镜( STXM),对聚丙烯腈(PAN)预氧化纤维截面进行具有30 nm空间分辨率的元素分布研究,结合将两幅吸收图上对应像素点的光密度相比求解元素分布的双能衬度分析法,获得氧元素在PAN预氧化纤维截面上的分布信息.STXM实验结果表明,氧元素在PAN原丝截面上分布是均匀的;经过预氧化后,PAN纤维皮...     

分子筛型PAN-ACF制备及表面结构的XPS研究

以聚丙烯腈基活性炭纤维（PAN ACF）为原料,首次采用液相浸渍结合空气氧化的方 法,在较为温和的条件下改变原料的表面结构和孔隙结构,制备出具有分离N2/O2性能的分子 筛型PAN ACF.采用TGA DTA、电子天平及XPS技术分析表征了分子筛型PAN ACF的吸附性能 和表面结构.结果表明:浸渍煤焦油后的PAN ACF在100～400 ℃之间失重缓慢,是煤焦油中苯 环及杂环类化合物与纤维表面氧化接枝的过程;经350 ℃浸渍空气氧化ACF对N2/O2吸附量及 选择性均得到了显著提高,选择系数达到5.6;浸渍煤焦油的PAN ACF表面具有一定量的羟基 、醚基、羰基和羧基等含氧官能团,氧化过程中各类官能团含量发生改变,类石墨碳含量随浸 渍浓度增加而增大;浸渍氧化再炭化的结果使PAN ACF对N2/O2吸附选择性得到明显提高.     

预氧化过程中张力对聚丙烯腈预氧化纤维微缺陷结构的影响

本文报道用同步辐射二维小角X射线散射(2D\|SAXS)研究预氧化过程中张力对PAN纤维缺陷的影响.     

改性PAN纤维与Fe3+的配位反应及配合物的催化性能

采用盐酸羟胺和水合肼的混合物分别对PAN纤维进行改性制备了偕胺肟改性PAN纤维(AO-PAN)和混合改性PAN纤维(M-PAN), 并分别与Fe³⁺进行配位反应生成两种改性PAN纤维铁配合物(Fe-AO-PAN和Fe-M-PAN). 研究了配位反应的动力学特性及温度和Fe³⁺初始浓度的影响, 并采用DRS和ESR技术比较了两种不同改性PAN纤维铁配合物对偶氮染料活性红195氧化降解反应的催化性能. 结果表明, 在所设定的温度和浓度范围内, 两种改性PAN纤维与Fe³⁺之间的配位反应平衡符合Langmuir 和Freundlich 吸附等温模型以及Lagergren准二级动力学方程, 并且AO-PAN比M-PAN更容易与Fe³⁺发生配位反应. 在相同条件下AO-PAN与Fe³⁺反应的配合量和反应速率常数均比M-PAN与Fe³⁺反应的高. 两种配合物对染料的氧化降解反应具有催化作用, 暗态条件下Fe-M-PAN比Fe-AO-PAN表现出更高的催化活性, 而光辐射条件下Fe-AO-PAN的催化活性显著增强.     

PAN预氧丝环化程度的定量表征

应用恒温定长方法制备聚丙烯腈(PAN)预氧丝, 并测量该预氧丝长周期多层结构的小角X射线衍射谱. 解析图谱发现, 经不同预氧化时间所得预氧丝的长周期L均为11.7 nm; 当预氧时间从20 min增加到210 min, 预氧丝中环化结构相的体积分数X0/L从7.9％增加到86.5％. 而应用广角X射线衍射法测得同批的预氧丝试样环化指数AI值则小很多. 因此, 用X0/L定量表征预氧丝环化程度更为严格准确.     

不同直径改性PAN纳米纤维膜与Fe3+的配位反应及其配合物对有机染料降解的催化性能

使用静电纺丝技术和偕胺肟反应制备了三种不同直径的改性聚丙烯腈(PAN)纳米纤维膜,然后将它们作为配体分别与Fe3+进行配位反应制备改性PAN纳米纤维膜铁配合物,重点研究了三种改性PAN纳米纤维膜与Fe3+配位反应的动力学特性及其温度和Fe3+初始浓度的影响.最后将其作为非均相Fenton反应催化剂应用于染料降解反应中,考察了改性PAN纳米纤维膜直径对其催化活性的影响.结果表明,在所涉及的温度和浓度范围内,改性PAN纳米纤维膜与Fe3+之间配位反应不仅符合Langmuir和Freundlich吸附等温式,而且可理想地使用Lagergren准二级动力学方程进行描述,反应速率常数随着Fe3+初始浓度的增加而逐渐降低.在相同反应条件下,较小直径的纤维膜更容易与Fe3+发生配位反应,且反应速率常数和Fe3+配合量均随着纤维直径的降低而增大.不同直径改性PAN纳米纤维膜铁配合物在暗态条件下对染料的氧化降解反应表现出很好的催化活性,且在辐射光下其催化活性得到加强.改性PAN纳米纤维膜铁配合物的催化作用受到纤维直径的显著影响,由中等直径纳米纤维构成的配合物表现出最高的催化活性.     

用SbCl_3使聚丙烯腈纤维稳定化的研究

<正> 众所皆知,梯型高分子是相当耐热的,其中一大部分是耐燃的梯型高分子。制造梯型高分子的方法很多,它可以通过小分子的有机化合物,经缩合或用大分子中的功能基反应得到梯型高分子。聚丙烯腈(PAN)中有大量的腈基,通过聚合而得到含聚氢化吡啶并经得起950℃的耐热梯型高分子。     

Kinetics of cyclization reaction in poly(acrylonitrile/methyl acrylate/dimethyl itaconate) copolymer determined by a thermal analysis

The PAN/MA/DMI (poly(acrylonitrile/methyl acrylate/dimethyl itaconate)) copolymer was synthesized for being used as a carbon fiber precursor. Its high melt-spinnability at 175–210 °C has been demonstrated elsewhere but the cyclization kinetics was thoroughly investigated by DSC analysis herein. The isothermal analysis based on the Kamal equation demonstrates that at a given temperature, the cyclization rate constant k of PAN/MA/DMI system is five to seven times that of a regular PAN/MA system. The activation energy E_a of the PAN/MA/DMI system, owing to the acid-catalysis by the DMI compound, is approximately 30 kJ/mol lower than that of a regular PAN/MA system. An isothermal Avrami analysis confirmed the above finding. Furthermore, based on the obtained nucleation index n, DMI may induce intermolecular cyclization which can rapidly stabilize the fiber shape of PAN/MA/DMI precursor. A nonisothermal analysis, obtained from the Ozawa's method, revealed the same tendency as did the isothermal results, but the difference between the average activation energies E_a obtained with and without DMI was reduced from 30 to 25 kJ/mol. Finally, a cyclization mechanism that involves the formation of a cyclic anhydride was proposed.     

Thermal behavior of polyacrylonitrile polymers synthesized under different conditions and comonomer compositions

Polyacrylonitrile (PAN) polymers are used as precursors for carbon fiber production. This process requires an oxidative stabilization step, which can be studied by differential scanning calorimetry (DSC). In this sense, thermal behavior of PAN based terpolymers by different polymerization processes, compositions and itaconic acid concentrations in the reaction media were investigated. The obtained results showed that the addition of itaconic acid and methyl acrylate as comonomers resulted a lower heat flow during the process comparing to the PAN homopolymer. It suggested that these comonomers aid the oxidative stabilization stage for all studied process. The redox system polymerization at 40°C resulted in a lower heat flow. Itaconic acid decreases slightly initial and peak temperatures of the terpolymer and heat flow until concentration of 3y. The cyclization temperature decreases when MAis incorporated into the terpolymer compared to the MMA terpolymer and increases when MAA is the acidic monomer. Among terpolymers the AN/MA/AA polymer showed the best thermal behavior for carbon fiber producing.     

Investigation into the gelation and crystallization of polyacrylonitrile

Polyacrylonitrile (PAN) is soluble in dimethyl sulfoxide (DMSO) and the resulting solution can gel by various mechanisms. The effects of temperature and water on the thermoreversible gelation of PAN have attracted much attention because of their importance in the fiber formation and film casting. Rheological tests were employed in this study to examine the gelation behavior and determine the gel point temperature of PAN-DMSO solution. Calorimetric studies of PAN-DMSO gels were conducted through Differential Scanning Calorimetry and no crystallization was discovered in these gels prepared at low temperature. X-ray diffraction of different PAN gels indicated that in the absence of water, gels resulted from PAN-DMSO solution by decreasing temperature were not crystallizable. In contrast, water-induced gelation led to crystallization of PAN gel. The water content in the formed gel is responsible for its crystallinity and average crystallite size.     

Evolution of the composition and structure of PAN carbon fiber during preoxidation

Using scanning electronic microscope, X-ray diffraction analysis, PYR-GCMS and IR etc., we studied the evolving process of the composition and structure of PAN carbon fiber during preoxidation. In the initial stage of preoxidation, PAN filament tows disappear and become semi-thaw. At first, reactions happen between the copolymers and esters disappear. The molecules annularly crosslink and the index of cyclation slowly increases. It is easy to fix the structure and form defects during the initial and the medium stages, which are most reactive. More traction is advised in these stages to minimize the structural deficiencies. In the medium stage of preoxidation, the fiber was reshaped into new sheet stacks and gradually changed to sheet sectors, and this structure tends to be stable in the final stage. Induced by acid and ester copolymer, PAN fiber forms a very stable cycle structure in the final stage. Besides, monomer, dimmer and trimer obviously decrease. In the final stage of the preoxidation, there exi     

CuS表面改性聚丙烯腈纤维的结构及导电机理的研究

研究了用一步反应法制备的CuS表面改性的聚丙烯腈导电纤维的微观结构、导电性和温度的变化规律及其导电机理,观察了CuS在纤维表面上的结晶态及晶型变化现象,证实了该导电纤维的以电子导电为主的导电机理。     

Preparation of Photocatalyst-supported Polyacrylonitrile Micro/Nano Composite Fiber Material and Its Photocatalytic Activity

Acomposite photocatalyst, with branch-like BiOI/Bi₂WO₆ he-terojunction deposited on the polyacrylonitrile micro/nano composite fiber(PAN MNCF), was prepared via two step hydrothermal method. The products are characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), photoluminescence(PL) spectra, UV-Vis diffuse reflection spectroscopy(UV-Vis DRS) and time-resolved fluorescence spectra. The PAN/BiOI/Bi₂WO₆ micro/nano composite fiber(PAN/BiOI/Bi₂WO₆ MNCF) showed better visible-light photocatalytic performance than PAN MNCF or BiOI/Bi₂WO₆ powder, probably ascribed to the collective effect between PAN MNCF and BiOI/Bi₂WO₆ heterojunction. Significantly, the PAN/BiOI/Bi₂WO₆ MNCF could be easily recycled through filtration method, thus avoiding the secondary pollution.