不同热处理条件下聚丙烯腈的结构演变

采用傅里叶变换红外光谱(FTIR)和广角X射线衍射(WAXD)研究了处理温度、处理时间、气体氛围对聚丙烯腈(PAN)均聚物及其共聚物P[丙烯腈(AN)/甲基丙烯酸甲酯(MMA)/衣康酸(IA)]热处理过程中结构演变的影响。FTIR结果表明,在氮气中,环化反应可以大量出现,但脱氢反应较少;而在空气氛围中,环化反应和脱氢反应都可以大量发生。氧气对PAN均聚物的环化反应有抑制作用,而对P(AN/MMA/IA)的环化反应有促进作用。WAXD结果表明,PAN均聚物的预氧化反应首先发生在非晶区,而后发生在晶区。在240℃时,t=1 h,环化反应主要发生在非晶区;t≥1.5 h,主要发生在晶区。     

PAN预氧化纤维结构与热处理温度的关系

在空气气氛中不同温度下对聚丙烯腈(PAN)原丝热处理8 h,制得PAN预氧化纤维。借助差示扫描量热分析、红外吸收光谱、X射线衍射、固体核磁等测试手段,表征了不同温度处理的PAN纤维的预氧化程度,研究了PAN预氧化纤维的结构特点。结果表明:不同温度下PAN纤维的预氧化程度不同,随着温度的提高而提高;PAN纤维预氧化程度不同,缘于不同温度下预氧化反应差异造成的预氧化结构的不同;预氧化温度越高,未环化的C≡N结构中共轭的C≡N结构相对含量越多,不利于进一步环化;环化反应在190~220℃较剧烈,在220℃以后反应趋于缓和;脱氢反应在190~210℃比较缓慢,在温度高于220℃开始剧烈进行;190℃以上发生氧化反应。     

PAN膜在低温热氧化过程的结构变化研究

采用溶剂挥发法制备得到聚丙烯腈(PAN)膜,通过傅里叶变换红外光谱(FTIR)、元素分析、差示扫描量热(DSC)法研究PAN膜在120~180℃低温热氧化过程的结构和热稳定性的变化。结果表明,PAN膜在低温热氧化过程主要发生环化和氧化反应。在120℃和140℃温度下,氧化反应先于环化反应发生,环化反应程度较小;在160℃和180℃温度下,环化反应显著加剧,环化反应占主导。形成的环化和氧化结构提高了膜的热稳定性。     

预氧化过程中聚丙烯腈纤维结构与性能的变化

综述了聚丙烯腈(PAN)纤维在预氧化过程中的反应机制,分析了预氧化过程中纤维颜色、元素含量、纤维结构、力学性能的变化以及金属离子对于预氧化的影响。结果表明:PAN原丝在预氧化过程中发生的环化、氧化、脱氢反应,在很大程度上受到预氧化温度、预氧化时间和施加在纤维上的张力的影响。     

丙烯腈—衣康酸共聚物的热性能——共聚纤维的氧化与温度和时间的关系

<正> 聚丙烯腈(PAN)纤维是制取高强度、高模量碳纤维的基本原料之一。用丙烯腈共聚物制取原丝,除可以改善纺丝性能以外,还能够改善预氧化条件。纤维在100～300℃加热过程中链状分子内部发生氰基重排的环化反应,形成稳定的梯形结构。在氧化性气氛中或使用能促进环化的共聚单体能够加快这一环化过程。纤维在热处理过程中,温度是一     

增塑熔纺聚丙烯腈纤维的预氧化过程

以增塑熔纺聚丙烯腈(PAN)纤维为研究对象,借助于傅里叶变换红外光谱对其结构以及预氧化过程中官能团的变化进行了分析研究,并进一步研究了预氧化温度和时间对反应程度的影响。研究结果表明:熔纺PAN纤维在纺丝过程中已发生了部分环化,其环化度为0.18;反应程度随着预氧化温度的升高逐渐增大,但在230℃之后变化不明显;预氧化时间对预氧丝的反应程度具有类似的影响,在预氧化20 min时反应程度迅速增大,但进一步延长预氧化时间,预氧丝的反应程度增幅较小。     

基于低环化反应活化能的PAN纤维快速预氧化研究

本文研究了PAN纤维环化反应活化能与其耐热性的关联性,进而开展了快速预氧化的研究。研究结果表明:通过聚合第二单体对聚合物结构的改性,可以实现对纤维环化反应活化能的有效调控,环化反应活化能越低,PAN纤维的耐热性就越高,在预氧化过程中能够承受较高的预氧化温度; PAN纤维的环化反应和氧化反应具有不同步性,且在230℃之前二者均没有显著发生。基于此,本文通过对PAN纤维的低环化反应活化能和高预氧化温度的综合控制,预氧化时间大幅缩短至35 min以内,所制备的碳纤维(T700级)的拉伸强度为5 411 MPa,CV值为3. 9%。     

PAN 基碳纤维预氧结构形成过程中的纤维尺寸效应

对预氧纤维进行预处理以达到脱除纤维中未环化分子的目的,借助X射线衍射（ XRD ）,拉曼光谱（ Ra-man）,红外吸收光谱（ FTIR）分析、差示扫描量热（ DSC）分析对两种不同纤度预处理前后的聚丙烯腈（ PAN）氧化丝进行了研究,并初步讨论了PAN纤维尺寸效应对预氧结构的影响机理。研究结果表明：同等条件下低纤度PAN纤维得到的预氧纤维环化程度较高,皮芯结构不明显,并且低纤度预氧纤维的环化结构中SP2杂化碳含量较高,且SP2杂化碳中芳香碳含量较高。     

张力拉伸对PAN纤维热稳定化反应进程的影响

在不同拉伸条件下,对聚丙烯腈(PAN)纤维进行热处理。借助傅里叶变换红外光谱、X射线衍射等表征手段,研究了PAN纤维热稳定化过程中,拉伸张力对纤维分子链聚集态结构及化学反应的影响。结果表明:PAN纤维热处理过程中,施加张力会在一定程度上影响纤维的环化反应。当热处理温度较低(180℃)时,施加张力可抑制环化反应的发生;热处理温度较高(大于200℃)时,拉伸张力有利于环化反应的发生。热处理过程中,施加张力,对PAN纤维结晶度影响较小,晶区取向和全取向度增加,晶粒尺寸增大。这是由于拉伸与温度双重作用影响了纤维的聚集态结构,导致参与环化反应的分子数量发生变化。     

磷酸二氢铵对聚丙烯腈纤维预氧化程度及热稳定性的影响

聚丙烯腈(PAN)纤维的预氧化过程是PAN基炭纤维生产中最耗能耗时的阶段。为了加快PAN纤维的预氧化过程,提高PAN纤维的预氧化程度,采用非金属化合物磷酸二氢铵(NH_4H_2PO_4)对PAN纤维进行改性,探讨了磷酸二氢铵对PAN纤维化学结构和热性能的影响。通过傅里叶红外光谱(FT-IR)和X射线衍射(XRD)分析得到,PAN纤维的预氧化程度随着预氧化温度和试验设定的NH_4H_2PO_4浓度范围内升高而升高。与未改性PAN纤维相比,相同温度下,改性PAN纤维环化度更高,在180℃和200℃低温条件下更为明显,240℃及260℃的促进效果一般,另外改性PAN纤维在240℃可提前完成环化反应。热重(TGA)结果表明,NH4H2PO4受热分解产生的磷酸与羟基反应导致分子链交联,能降低预氧化过程中的热失重,提高热稳定性。     

Structure evolution mechanism of polyacrylonitrile films incorporated with graphene oxide during oxidative stabilization

Oxidative stabilization is a key process for polyacrylonitrile (PAN)-based carbon materials. During this process, oxygen has a significant influence on the formation of cyclization structure and crosslinking structure of PAN matrix. Here, graphene oxide (GO) was used as filler in PAN matrix, the structure evolution of GO/PAN composite was studied during oxidative stabilization. Solubility measurement revealed that the crosslinking degree increased, while the cyclization degree of stabilized films decreased after GO incorporation. The effect of GO on the structure of PAN film was characterized by XRD, DSC, DMA, FTIR, and XPS. These results verified that GO could initiate the cyclization reaction of PAN at a lower temperature. The carboxylic groups on GO sheets might take part in the cyclization reactions during the heat treatment. Moreover, the oxygen-containing molecules released from GO decomposition during the heat treatment were beneficial to the formation of crosslinking structure. The possible mechanism of the structure evaluation was proposed in this article. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47701.     

硼酸改性PAN热稳定化行为的研究

将硼酸直接加入聚丙烯腈(PAN)聚合液中,制成硼酸改性PAN膜,采用差示扫描量热(DSC)法、傅里叶变换红外光谱(FTIR)、元素分析等手段分析了硼酸对PAN热稳定化过程的影响。结果表明:硼酸改性提高了PAN的热稳定化反应活化能,并使放热峰值温度提高,当硼酸质量分数为2%时,活化能达271.27kJ/mol;硼酸含量越高,对环化反应的抑制作用越强,相对环化率越低;经过相同时间预氧化,改性PAN氧含量相对较低,硼酸改性阻碍了致密氧化层的快速形成,有利于减轻皮芯结构。     

Studies of reaction mechanisms during stabilization of electrospun polyacrylonitrile carbon nanofibers

Various reaction mechanisms such as cyclization, oxidation, dehydrogenation, and crosslinking are studied during stabilization of electrospun polyacrylonitrile nanofibers using different in situ techniques such as differential scanning calorimetry (DSC), shrinkage measurement, and dynamic mechanical analysis (DMA). DSC results show that oxidation preferentially occurs in cyclized structure. It is also found that the cyclization reaction has the highest activation energy followed by oxidation/dehydrogenation and crosslinking reactions. In situ shrinkage measurement and DMA data are used to study the extent of cyclization and cross‐linking reactions, respectively, in air. Comparing the in situ shrinkage measurement with DSC data, it is found that cyclization reaction in air progresses in two different mechanisms such as radical cyclization, which depends only on the temperature and ionic cyclization, which is limited by the rate of oxygen diffusion. It is found that complete cyclization time occurs at about 189 min for isothermal heat treatment at 260°C with 5°C/min ramp, while cross‐linking reaction becomes dominant at 132 min. POLYM. ENG. SCI., 58:1315–1321, 2018. © 2017 Society of Plastics Engineers     

Ferric Chloride Assisted Thermal Stabilization of Polyacrylonitrile Precursor Fibers Prior to Carbonization

The effect of ferric (Fe³⁺) ion incorporation on the thermal stabilization of polyacrylonitrile (PAN) fibers was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction analysis and infrared spectroscopy methods. The results obtained from the DSC and TGA measurements indicated that there was an improvement in thermal stability when Fe³⁺ ions were incorporated into the polymer structure. TGA thermograms showed a relative improvement in thermal stability as indicated by increasing carbon yield with progressing time. The degree of lateral order and apparent crystallite size estimated by X-ray diffraction decreased with increasing stabilization time. Incorporation of Fe³⁺ induced distinct changes in the infrared spectra of the thermally stabilized PAN fibers. The spectral changes appeared to be due to the formation of coordination bonds between the nitrogen atom of the nitrile group and Fe³⁺. The formation of ferric ion-nitrile coordination bonds accelerated thermal stabilization by catalyzing the occurrence of dehydrogenation, cyclization and oxidation reactions.     

The Role of Different Factors in Creation of the Structure of Stabilized Acrylic Fibres

Chemical aspects of transformations of PAN fibres in the stage of thermooxidative stabilization are examined with methods of thermal analysis. The regions of cyclization and oxidation reactions are determined for three PAN copolymers of different composition. It is shown that the cyclization and oxidation reactions appearing on the DSC curves in the form of unseparated exothermic peaks can be separated by selecting the conditions of preliminary heat treatment of the fibres. It was found that preliminary heating of PAN fibres to a certain temperature causes the formation of a structure that does not undergo oxidation on repeated heating. An explanation of this phenomenon is proposed. Loading within certain limits does not affect the course of structural transformations of the fibres during thermooxidative stabilization.     

Fe~(3+)对聚丙烯腈纤维预氧化反应的影响

在空气气氛中对含有Fe3+的聚丙烯腈(PAN)纤维进行预氧化处理,研究了Fe3+对PAN纤维氰基环构化和纤维结构的影响及其影响机理。结果表明:在相同的预氧化条件下,含有Fe3+的PAN纤维的预氧化程度较低,添加Fe3+后,减缓了PAN纤维预氧化进程;含有Fe的PAN预氧化纤维的体密度较低,氮气气氛下,热失重增加;在PAN纤维预氧化时,纤维表面的Fe元素大部分以Fe3O4的形式包覆在纤维表面,阻碍氧的扩散,延缓PAN纤维预氧化进程。     

Mechanism and kinetics of oxidation during the thermal stabilization of polyacrylonitrile fibers

The thermal behavior and structural evolution during the thermal stabilization of polyacrylonitrile (PAN) fibers in N₂ and air were investigated using differential scanning calorimetry and solid‐state ¹³C nuclear magnetic resonance. It was found that an oxidation reaction, that generated carbonyl (C?O) groups could occur at 160°C which has not been reported in the literature. It is proposed that the cyclized structures in the PAN macromolecule chains are a prerequisite for the oxidation. Further investigations indicate that with more cyclized structures in the PAN macromolecule chains, the oxidation proceeds more readily, which is consistent with the proposed mechanism. The kinetic parameters for the oxidation and cyclization reactions were estimated using the Kissinger method. The activation energies for the reactions of oxidation and cyclization for PAN fibers are about 96.4 kJ/mol and 190.0 kJ/mol, respectively, which implies that the cyclization is the rate determining step during the thermal stabilization of PAN fibers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013