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。     

光密度法研究聚丙烯腈纤维的热稳定化过程

采用梯度升温曲线,在170～310℃内,每间隔10 min升高10℃对聚丙烯腈(PAN)纤维进行热处理,使用光密度法研究了PAN纤维的热稳定化。结果表明:PAN纤维在热稳定化过程中光密度发生了变化,热稳定化过程中纤维表面会发生反应生成致密的氧化层,导致皮芯结构的形成。光密度法是系统研究PAN纤维热稳定化程度与氧化均匀性的理想方法,具有良好的准确性灵敏性;引入了光密度标准差有效评估PAN纤维皮芯结构程度。     

丙烯腈系纤维

20043131 在产生稳定的聚丙烯腈纤维时不同因素所起的作用Kalashnik A.T.…;Fibre Chemistry,2002,34(1),p. 10(英) 用热分析方法在聚丙烯腈热氧化阶段检查其化学转变。对不同化合物的3PAN(聚丙烯腈)共聚物, 测定环化和氧化反应的区域。结果显示,环化和氧化反应以不分开的放热峰形式出现在DSC曲线上,     

热稳定化过程中聚丙烯腈-氧化石墨烯纤维的结构变化

采用原位聚合法制备了聚丙烯腈(PAN)-氧化石墨烯(GO)纳米复合物,并采用静电纺丝法制备了PAN及PAN-GO纳米复合物的电纺纤维。采用扫描电镜、傅里叶变换红外光谱、X射线衍射等研究了电纺纤维在恒温热稳定化过程中表面形貌、微晶结构、化学结构的变化,结果表明:恒温热处理后,纤维表面均较为光滑,GO的引入不仅能够加快热稳定化过程中环化反应的速度,而且能显著提高环化程度。     

氧对PAN分子侧氰基反应进程的影响

采用固体13C-CP／MAS,FT-IR和DSC方法分析自制二元共聚PAN纤维在不同气氛下的热稳定化 行为,研究氧对PAN分子侧氰基反应的影响。结果表明:在无氧气氛下处理时,PAN分子先发生环化反应; 而在有氧气氛下,先发生脱氢反应,再发生环化、氧化反应,氧化反应中氧与PAN分子链结合生成C=O, HC-OH等官能团,氧可以促进环化、脱氢反应的发生,PAN链状分子结构逐渐演变为耐热的含氧梯型聚合 物结构。     

聚丙烯腈纤维烯胺结构的形成及其氧化特性的研究

将聚丙烯腈(PAN)纤维在惰性气氛下进行热处理,通过傅里叶红外光谱(FT-IR)、1 3C固体核磁共振(13C-NMR)、差示扫描量热(DSC)等方法研究了PAN纤维中烯胺结构的形成及其氧化特性。结果表明:惰性气氛下PAN纤维在热处理过程中氰基发生键断裂形成亚胺结构,并在温度达到190℃时开始向烯胺结构转变;随着热稳定化过程的进行,亚胺结构增加到一定程度后呈现下降趋势,而烯胺结构不断增加;热处理温度越高,亚胺结构向烯胺结构转变的越多且速率越快;将在惰性气氛下经不同温度热处理得到的PAN纤维进行空气气氛下的DSC分析,发现氧化反应的放热量与烯胺结构含量存在较好的线性关系,表明烯胺结构比其他特征结构更容易发生氧化反应。     

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。     

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。     

偶氮引发剂对PAN及其原丝结构和热稳定化行为的影响

以丙烯腈和衣康酸为单体,以二甲基亚砜(DMSO)为溶剂,分别以含脒基的偶氮二异丁脒盐酸盐(AIBA)、偶氮二异丁腈(AIBN)为引发剂,采用溶液聚合法,制备了具有不同端基结构的丙烯腈与衣康酸共聚物PAN-AIBA和PAN-AIBN;经湿法纺丝得到聚丙烯腈(PAN)原丝,研究了AIBA,AIBN引发剂的分子结构对PAN相对分子质量、原丝结构、热行为的影响。结果表明:采用溶液聚合的方法,以AIBA为引发剂可制得适于湿法纺丝的PAN-AIBA,其环化反应的起始温度较PAN-AIBN的提前了20℃,放热峰较宽;与PAN-AIBN相比,PAN-AIBA原丝的晶粒尺寸更大、结晶度较高;在低温热稳定化条件下,PAN-AIBA原丝表现出优于PAN-AIBN的较高热环化效率,而在高温热处理时,二者热环化效率相近;通过利用AIBA引发剂在PAN大分子结构中引入脒基,有望改善PAN原丝的低温热稳定化行为。     

酯类共聚单体对PAN结构及热稳定化行为的影响

采用K2S2O8-NaHSO3氧化还原引发剂和水相沉淀聚合法制备了丙烯腈均聚物(PAN)、丙烯腈-醋酸乙烯酯共聚物(P(AN-VAc))、丙烯腈-丙烯酸甲酯共聚物(P(AN-MA));采用红外光谱、核磁共振、差示扫描量热/热重同步分析仪、X射线衍射仪等手段对聚合物的结构及热稳定化行为进行了研究。结果表明:引入VAc,MA酯类共聚单体对PAN聚合物的立构规整性几乎没有影响,3种聚合物的等规、无规、间规比例均约为1∶2∶1,平均序列长度约为2,呈现典型的无规聚合物结构特征;在空气气氛热稳定化过程中,VAc,MA酯类共聚单体不能以离子形式在低温下引发环化反应,但是都可以起到缓和放热和减少失重的作用,从而提高热稳定化过程的可控性;在相同条件下进行热稳定化处理,P(AN-MA)具有较高的相对环化率和芳构化指数,表明MA更有利于提高热稳定化程度。     

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.     

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.     

Structure and thermo-chemical properties of continuous bundles of aligned and stretched electrospun polyacrylonitrile precursor nanofibers collected in a flowing water bath

Continuous bundles of aligned and stretched electrospun polyacrylonitrile (PAN) precursor nanofibers were prepared in an attempt to develop carbon nanofibers with superior strength. The bundles were prepared through collection of electrospun nanofibers with a flowing water bath followed by stretching in water at 97 °C. Their morphologies, structures, and thermo-chemical properties were characterized by SEM, XRD, and DSC. The shrinkages in boiling water and the amounts of residual solvent were also measured. The results indicated that, the nanofibers in the bundles were uniform with smooth surfaces and small variations in diameters; after stretching the bundles by 4 times, the average fiber diameter was reduced to 56%, while the crystallinity of PAN was improved by 72%. The post-spinning stretching process facilitated the stabilization of PAN, as evidenced by the shift of the cyclization reaction to a lower temperature with smaller activation energy and larger enthalpy change. In comparison with the commonly adopted nanofiber collection method of a rotating drum, the flowing water bath method results in higher degree of uni-axial alignment and more desired structures of nanofibers.     

硼酸改性对聚丙烯腈纤维预氧化的影响

通过在线监测聚丙烯腈(PAN)纤维的热收缩应变和应力,研究了硼酸改性对PAN纤维预氧化的影响。试验结果表明:随着硼酸溶液浓度的增加,PAN纤维化学反应的起始和结束温度向高温方向移动,化学收缩量降低,预氧化纤维体密度逐渐降低,硼酸对PAN纤维化学反应有抑制作用;硼酸对分子内环化和分子间交联反应的抑制可有助于预氧化纤维均质化程度的提高,并可防止PAN纤维表面在较高温度下被过度氧化。     

不同共聚单体与丙烯腈的共聚合及其表征

采用四种共聚单体衣康酸(IA)、丙烯酸甲酯(MA)、丙烯酰胺(AM)、甲基丙烯酸甲酯(MMA)分别与丙烯腈(AN)进行自由基溶液共聚合,讨论了不同共聚单体对聚合反应动力学及所得纺丝原液的粘度的影响,对聚合物的热性能进行了DSC分析,考察了不同共聚单体对聚丙烯腈原丝热性能的影响。结果表明:AN/IA体系随IA含量的增加其反应速率明显下降;与其它单体相比AM更可能有效地降低聚丙烯腈原丝的预氧化温度,缓和放热,而衣康酸次之。同时,IA含量过大,会导致原丝预氧化时的降解。     

The effect of modification on structure and dynamic mechanical behavior during the processing of acrylic fiber to stabilized fiber

Polyacrylonitrile (PAN) fibers pretreated with potassium permanganate have reduced the time required for stabilization, and also improved mechanical properties of the resultant carbon fibers. In this study, the effect of modification on the stabilization process and the dynamic mechanical properties of PAN fibers have been examined. The beta peak appeared at about 125°C on the loss tangent curves caused by molecular motion in the PAN fiber. Appearing at about 254°C, the alpha peak is attributed to chemical reactions and molecular motion in the formation of the crystalline phase of stabilized fibers. The alpha peak of the modified PAN fiber had lower absorption and had a smaller peak in the temperature range of 212–239°C. This indicated that potassium permanganate acts as a catalyst to lower the reaction temperature by about 20°C of the initial cyclization reaction. The dynamic storage modulus analysis indicated that modified PAN fibers have a lower initial transition temperature and that formation of the ladder polymer is gradual and steady.     

Structural changes and molecular motion of polyacrylonitrile fibers during pyrolysis

The stabilization process of polyacrylonitrile (PAN) fiber is necessary to develop high-performance carbon fiber. This work is concerned with studies of the activation energy of PAN fibers during the stabilization process. A wide-angle X-ray diffractometer combined with a fiber specimen holder for heating was used to measure the activation energy of crystal transition E_c. E_c is almost the same as the activation energy of the cyclization reaction E which is measured by a differential thermal analysis (DTA). The variation of crystal size in PAN fiber and a model of the ladder polymer in stabilized fiber transformed from acrylontrile (AN) units of PAN fiber are discussed also. The crystal size of PAN fiber increases when the thermal treatment temperature is raised. When exposed to temperatures above the crystal degradation temperature T_d, the molecular rods of PAN fiber are destroyed completely, and ladder polymer is formed in the ordered phase of the original PAN fiber. The transformation of ladder polymer is initiated in the disordered phase, and then at the boundaries of the ordered phase.