高性能聚丙烯腈碳纤维中纳米级微孔分析表征研究

高性能碳纤维由于其优异的性能,在各行各业中具有广泛应用。为深入研究碳纤维内结构与其性能之间的相关性,本文应用小角X射线散射研究了一系列典型的聚丙烯腈碳纤维样品,分析了样品内微孔的尺寸及取向,讨论了强度和模量与微孔的相关性,研究结果表明:高性能碳纤维的力学强度和模量与碳纤维内微孔缺陷的长度和长径比有关,控制碳纤维内微孔缺陷的长度有望实现高强碳纤维的制备,控制牵伸倍率从而控制碳纤维内微孔的长径比有望实现高模碳纤维的制备。     

液态丙烯腈低聚物修复聚丙烯腈基碳纤维微孔缺陷

提出一种全新的缺陷修复的方法,即将聚丙烯腈基(PAN)碳纤维T300在液态丙烯腈低聚物(LAN)中浸渍后,再进行预氧化和碳化热处理,可以将T300的拉伸强度提高25%.应用二维小角X射线散射(SAXS)法可以计算出LAN修复缺陷前后T300微孔缺陷的长度(L)、横截面尺寸(lp)、取向角(Beq)、相对体积(Vrel)的变化,结果表明碳纤维的拉伸性能越好,微孔的长度、取向角、相对体积含量越小.T300拉伸性能的提高是由于缺陷修复的结果.应用BET比表面积法、扫描电子显微镜(SEM)表征LAN修复缺陷前后T300的比表面积以及表面形貌的变化,结果表明,T300在LAN中浸渍并经过预氧化和碳化热处理,比表面积变小,表面缺陷明显减少.进一步验证LAN对碳纤维中的微孔缺陷具有修复作用.应用X射线光电子能谱(XPS)法表征LAN修复前后T300表面化学成分的变化,结果表明,LAN修复后含氧官能团(C―OH,C=O,HO―C=O)显著增加,有利于增强碳纤维与树脂基体之间的相互作用,从而提高碳纤维的力学性能.     

聚丙烯腈基碳纤维中微孔洞的一维多取向小角X射线散射研究

应用一维多取向小角X射线散射(SAXS)方法研究了聚丙烯腈(PAN)基碳纤维中微孔洞的形态.结果表明,这些微孔洞沿纤维轴方向呈针状,并与纤维轴呈Φ=14°角的取向排列;微孔洞投影在碳纤维横截面上的平均半径R=1.14nm,投影在碳纤维轴向上的平均长度L=17.97nm.建立的一维多取向SAXS方法可以得到若干二维SAXS方法才能得到的微孔洞形态及分布信息等参数(如Φ和L),且在各种纤维的微孔洞或微纤维的表征方面具有一定的普适性.     

小角X射线散射在高分子研究中的应用

本文综述了小角X射线散射理论,并介绍了小角散射在高分子溶液、结晶聚合物、嵌段共聚物和离聚物等研究中的应用.     

高效液相色谱法测定聚丙烯腈基碳纤维原丝中的二甲基亚砜残留

建立了聚丙烯腈（PAN）基碳纤维原丝中二甲基亚砜（DMSO）残留量的高效液相色谱（HPLC）检测方法。采用的色谱柱为Phenomenex C18柱（150 mm×4.6 mm,5 μm）,流动相为甲醇-三氟乙酸-水（体积比为29∶1∶70）混合溶液,流速为1.0 mL/min,进样量为10 μL,检测波长为205 nm,柱温为常温。研究结果表明,在DMSO的质量浓度为1.00~100.00 mg/L范围内,峰面积与质量浓度的线性关系良好,相关系数r=0.9989,最低检出限为0.3 mg/L,平均回收率为98.4%,相对标准偏差（RSD）为2.6%。该方法简便、快速、准确。另外,利用建立的HPLC方法,对原丝中残留的DMSO在水中的溶出规律也进行了研究。     

应用弦长度分布函数研究中孔分子筛的精细结构

弦长度分布(chord length distribution, 简称CLD)可以用来描述几何对象(球形颗粒、柱状孔、薄片等)的大小、形状和空间排布等特点. 原理上, 弦长度分布正比于由小角散射所得的相关函数的二次微分, 因此可以由相对散射强度进行计算. 在结构研究中, 将实验所得弦长度分布与理论计算某种确定几何体所得高度准确的弦长度分布进行比较, 可以获知对象的特征几何结构. 本文以中孔氧化硅分子筛为研究对象, 介绍了弦长度分布的计算方法, 以此精确计算了中孔分子筛的孔径分布, 得到了分子筛表面有机官能化对孔径的影响规律.     

NiSO_4改性对聚丙烯腈原丝及其碳纤维结构与性能的影响

碳纤维具有高比强度、高比模量、导电、耐热、自润滑等优异的综合性能,在纤维增强复合材料中得到了广泛的应用.可制备碳纤维的前驱体有人造丝、沥青、聚丙烯腈纤维、木质素、聚乙烯纤维、聚苯并噻唑(PBO)纤维等.但大多数高强碳纤维目前仍然是由聚丙烯腈纤维制备的,同时,许多工作都集中在更进一步提高碳纤维的机械性能.特别是在我国, 碳纤维质量与某些发达国家相比,还有较大的差距,急需解决的问题就是如何尽快研制出高力学性能的碳纤维.采用氨基硅氧烷、脂肪族羧酸[1]、CuCl[2]、KMnO 4[3]、CoCl2[4]等有机或无机化学试剂对聚丙烯腈原丝进行化学处理, 以改进最终碳纤维的结构与性能是一种有效的方法.国内在这方面的研究还很少.文献[1 ～4]中所采用的方法都是利用商业聚丙烯腈原丝在碳化前进行洗油、浸渍、洗涤烘干处理 ,增加了碳纤维制备的工序,同时,原丝损伤较大,在连续生产中难以适用.我们在原丝连续制备的同时采用NiSO4溶液浸渍处理聚丙烯腈纤维,本文主要研究了采用NiSO4浸渍改性后聚丙烯腈原丝及其碳纤维的结构与性能.研究表明,采用NiSO4在线浸渍改性聚丙烯腈原丝,生产工艺简单,且能有效地改进最终碳纤维的结构与性能.     

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.     

聚乙烯片晶辐照破坏的X射线散射研究

聚乙烯片晶辐照破坏的Ｘ射线散射研究王国英，姜炳政（中国科学院长春应用化学研究所长春１３００２２）关键词辐照聚乙烯，广角Ｘ射线衍射，小角Ｘ射线散射有关聚乙烯辐照破坏和交联问题，Ｈｏｓｅｍａｎ等［１］从Ｘ射线衍射的研究指出，辐照交联和破坏在晶区内部发生；...     

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.     

Properties,Morphology and Structure of BPDA/PPD/TFMB Polyimide Fibers

The mechanical properties of fibers were notably improved by incorporating 2,2′-bis(trifluoromethyl)- benzidine(TFMB) into 3,3′,4,4′-biphenyltetracarboxylic dianhydride(s-BPDA) and p-phenylenediamine(PPD) backbone. The best strength and modulus of BPDA/PPD/TFMB polyimide(PI) fiber(diamine molar ratio of PPD/TFMB= 90/10) were 1.60 and 90 GPa, respectively, which was over two times that of BPDA/PPD PI fiber. SEM image showed that the cross-section of fibers at each stage was round and voids free. Besides, the “skin-core” and microfibrillar structure were not observed. The thermal properties of PI fibers were also investigated. The results showed that the fibers owned excellent thermal stability, moreover, the structural homogeneity of fibers were significantly improved by heat-drawn stage. The T_g values were found to be around 300℃ by dynamic mechanical analysis(DMA). Wide angle X-ray diffraction(WAXD) and small angle X-ray scattering(SAXS) experiments indicated that the order degree of longitudinal and lateral stacks, the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.     

The exponential distribution in small angle X-ray scattering. Theory and practice

Summary From all the theoretical small-angle X-ray scattering (SAXS) curves of compact (non-particulate) systems elaborated systematically by Porod [2], we give a theoretical analysis of only one scattering curve, the corresponding correlation function of which is an exponential distribution. To obtain a correct as well as an easier determination of the zero-intensityI ₀ and the correlation lengthl _c than with the procedure usual up to now (analysis of the plotI(s)^–1/n vs.s ² withn=2 or 3/2) the classical SAXS-parameters of particle scattering will be involved in the evaluation. In this way the results get also a more useful conception for a practical application.Von den systematisch besprochenen Röntgenkleinwinkelstreukurven der dichtgepackten Systeme von Porod [2] wird nur eine Streukurve, deren Korrelationsfunktion eine exponentielle Verteilung aufweist, theoretisch analysiert und mit den klassischen Auswertungsmethoden der Partikelstreuung in Verbindung gesetzt. Dadurch werden die die Streukurve bestimmenden Parameterl _c (Kohärenzlänge) und die NullintensitätI ₀ besser erfaßt als mit der in der Literatur bisher veröffentlichten Methode (AuftragungI(s)^–1/n gegens ², mitn=2 oder 3/2). Damit erhalten außerdem die Meßergebnisse eine anschaulichere Auslegung.Dedicated to Prof. Dr. Dr. h.c. mult. Otto Kratky on the occasion of his 90th birthday     

Relationships between nanostructure and thermomechanical properties in poly(vinyl alcohol)/montmorillonite nanocomposite with an entrapped polyelectrolyte

Poly(vinyl alcohol)/montmorillonite (PVA/MOM) hydrogels containing coacervated microparticles of sulfonated polyester (PES) were prepared by direct mixture of the components in water. The system was characterized by using differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and dynamical mechanical analysis (DMA). The influence of PES and MOM on the microstructure of the nanocomposite hydrogels was established. The presence of PES causes a significant change on the crystallinity of PVA. Furthermore, the presence of MOM leads to a hierarchical nanostructure that also contributes to change the crystallinity of PVA. The results of structural investigation are correlated with the mechanical properties of the composites obtained by DMA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2618–2629, 2008     

Structural Characterization of Biomaterials by Means of Small Angle X-rays and Neutron Scattering (SAXS and SANS), and Light Scattering Experiments

Scattering techniques represent non-invasive experimental approaches and powerful tools for the investigation of structure and conformation of biomaterial systems in a wide range of distances, ranging from the nanometric to micrometric scale. More specifically, small-angle X-rays and neutron scattering and light scattering techniques represent well-established experimental techniques for the investigation of the structural properties of biomaterials and, through the use of suitable models, they allow to study and mimic various biological systems under physiologically relevant conditions. They provide the ensemble averaged (and then statistically relevant) information under in situ and operando conditions, and represent useful tools complementary to the various traditional imaging techniques that, on the contrary, reveal more local structural information. Together with the classical structure characterization approaches, we introduce the basic concepts that make it possible to examine inter-particles interactions, and to study the growth processes and conformational changes in nanostructures, which have become increasingly relevant for an accurate understanding and prediction of various mechanisms in the fields of biotechnology and nanotechnology. The upgrade of the various scattering techniques, such as the contrast variation or time resolved experiments, offers unique opportunities to study the nano- and mesoscopic structure and their evolution with time in a way not accessible by other techniques. For this reason, highly performant instruments are installed at most of the facility research centers worldwide. These new insights allow to largely ameliorate the control of (chemico-physical and biologic) processes of complex (bio-)materials at the molecular length scales, and open a full potential for the development and engineering of a variety of nano-scale biomaterials for advanced applications.     

PAN基活性炭纤维的氮吸附研究

用相同原料不同活化方法制备聚丙烯腈基活性炭纤维,并对其进行了氮吸附研究.结 果表明,由不同活化方法所制备的活性炭纤维的孔结构存在较大差异,并对随着活化程度的 改变其孔结构的发展进行了研究.结果表明,通过简单的改变活化方法即可以制得不同孔隙占 主导地位的炭质吸附剂;也揭示出,不同的活化方法其活化机理有所差别.     

Pore Development during the Carbonization Process of Lignin Microparticles Investigated by Small Angle X-ray Scattering

Application of low-cost carbon black from lignin highly depends on the materials properties, which might by determined by raw material and processing conditions. Four different technical lignins were subjected to thermostabilization followed by stepwise heat treatment up to a temperature of 2000 °C in order to obtain micro-sized carbon particles. The development of the pore structure, graphitization and inner surfaces were investigated by X-ray scattering complemented by scanning electron microscopy and FTIR spectroscopy. Lignosulfonate-based carbons exhibit a complex pore structure with nanopores and mesopores that evolve by heat treatment. Organosolv, kraft and soda lignin-based samples exhibit distinct pores growing steadily with heat treatment temperature. All carbons exhibit increasing pore size of about 0.5–2 nm and increasing inner surface, with a strong increase between 1200 °C and 1600 °C. The chemistry and bonding nature shifts from basic organic material towards pure graphite. The crystallite size was found to increase with the increasing degree of graphitization. Heat treatment of just 1600 °C might be sufficient for many applications, allowing to reduce production energy while maintaining materials properties.     

BPDA/PPD/OTOL聚酰亚胺纤维的力学性能、形貌和结构

在3,3’,4,4’-联苯四酸二酐(BPDA)和对苯二胺(PPD)体系中引入3,3’-二甲基联苯胺(OTOL),显著改善了纤维的力学性能。当n(PPD)∶n(OTOL)=70∶30时,纤维的拉伸强度可达到改性前的2倍,其拉伸强度和拉伸模量分别为1.50和80 GPa。SEM照片显示了纤维的断面为圆形且没有孔穴,也没有明显的"皮芯"结构和原纤结构。WAXD和SAXS分析表明,纤维的轴向堆积和分子链取向在热牵伸过程中得到改善。