PAN纤维热稳定化过程中环化反应对氧化反应的影响

在惰性气氛中制备了不同环化程度的聚丙烯腈(PAN)热稳定化纤维,并将其在含氧气氛中进一步氧化处理,通过差示扫描量热仪(DSC)、傅立叶变换红外(FT-IR)和元素分析(EA)等方法研究了PAN纤维热稳定化过程中环化反应对氧化反应的影响。结果表明,与环化反应相比,氧化反应可在更低的温度下进行;对于环化程度越高的PAN热稳定化纤维,在含氧气氛中经相同条件热处理后氧含量越高,即氧化反应程度越高,故环化反应对氧化反应具有促进作用。     

晶态结构对聚丙烯腈(PAN)原丝预氧化反应的影响EI北大核心CSCD

对不同晶态结构特点的聚丙烯腈(PAN)原丝进行预氧化处理,采用X射线衍射(XRD)、红外光谱法表征PAN纤维的晶态结构(物理)和化学结构变化。结果表明,PAN原丝的晶态结构影响预氧化反应及反应程度,结晶度小的PAN原丝由于其有序性差,易于向预氧纤维芳构化结构转化,而结构疏松,有利于氧的扩散,促进环化反应和初期氧化反应,PAN纤维芳构化指数和相对环化率都较高,预氧化反应程度较高;原丝结晶度的差异对纤维晶粒尺寸的变化起决定性作用,结晶度大的PAN原丝到预氧化后期仍保持较大的晶粒尺寸。     

晶态结构对聚丙烯腈(PAN)原丝预氧化反应的影响

对不同晶态结构特点的聚丙烯腈(PAN)原丝进行预氧化处理,采用X射线衍射(XRD)、红外光谱法表征PAN纤维的晶态结构(物理)和化学结构变化。结果表明,PAN原丝的晶态结构影响预氧化反应及反应程度,结晶度小的PAN原丝由于其有序性差,易于向预氧纤维芳构化结构转化,而结构疏松,有利于氧的扩散,促进环化反应和初期氧化反应,PAN纤维芳构化指数和相对环化率都较高,预氧化反应程度较高;原丝结晶度的差异对纤维晶粒尺寸的变化起决定性作用,结晶度大的PAN原丝到预氧化后期仍保持较大的晶粒尺寸。     

氧对聚丙烯腈预氧化环化的促进机理EI北大核心CSCD

通过比较聚丙烯腈(PAN)纤维在空气条件下的热重分析(TG)及不同含氧量气氛中的差示扫描量热分析(DSC)结果,发现氧对PAN纤维有增重及对预氧化环化有促进作用。氧化增重是气氛中的氧对PAN分子链氧化的结果,氧化对PAN分子链螺旋结构的解旋有利于PAN预氧化环化。借助于纤维电子强力仪、显微镜等技术,测定了样品PAN的初始模量、断裂强度及断裂模量。统计结果表明,氧通过参加PAN分子链上的反应,促使PAN分子链的螺旋结构解旋,形成了非螺旋结构,有利于分子内的环化反应,提高了预氧化环化的速度及质量。     

氧对聚丙烯腈预氧化环化的促进机理

通过比较聚丙烯腈(PAN)纤维在空气条件下的热重分析(TG)及不同含氧量气氛中的差示扫描量热分析(DSC)结果,发现氧对PAN纤维有增重及对预氧化环化有促进作用。氧化增重是气氛中的氧对PAN分子链氧化的结果,氧化对PAN分子链螺旋结构的解旋有利于PAN预氧化环化。借助于纤维电子强力仪、显微镜等技术,测定了样品PAN的初始模量、断裂强度及断裂模量。统计结果表明,氧通过参加PAN分子链上的反应,促使PAN分子链的螺旋结构解旋,形成了非螺旋结构,有利于分子内的环化反应,提高了预氧化环化的速度及质量。     

PAN纤维预氧化过程的结构变化及热行为

采用X射线衍射(XRD)、透射电子显微镜(TEM)和差示扫描量热分析(DSC)研究了PAN纤维在预氧化过程的结构和热性能变化。结果表明:随着预氧化温度的升高,纤维的微晶尺寸增大,到220~230℃时达到最大,此后逐渐减小,原准晶结构逐渐被破坏。纤维的芳构化指数随预氧化温度的升高不断增大,PAN链状分子在逐渐演变成梯形环状分子结构,230℃和275℃是PAN原丝热稳定化的转折点。随着预氧化温度的升高,洋葱球非晶组织发生了结构演变。非晶化转变是从晶区边界开始,由外部向芯部逐步进行。纤维的环化度随着预氧化温度的升高表现为增大。在较低温度增加较快,随后增加变缓。230℃后,环化反应加剧,环化度迅速提高。     

PAN纤维在惰性气氛中的热行为研究

聚丙烯腈(PAN)纤维在惰性气氛中的热行为主要包括3个反应:热致收缩反应、环化反应和热解反应。通过差示扫描量热仪和热重分析仪研究了PAN纤维在惰性气氛中的热行为。结果表明,热致收缩和热解反应并无明显的吸放热现象,而环化反应放热剧烈且短促。环化反应过程中存在明显的传热过程,环化反应速率达到最大值时,温度随着升温速率的提高而上升。热解反应使得可发生环化反应的原料总量下降,且随着升温速率的提高,反应放热量下降。分别采用Ozawa法与Kissinger法计算了环化反应的表观活化能,并建立了修正后的动力学模型。该模型可以有效地描述不同升温速率条件下的反应过程。     

硼酸改性对预氧化过程中PAN纤维结构变化的影响

预氧化前对聚丙烯腈(PAN)纤维进行硼酸溶液浸渍改性,通过红外吸收光谱和固体核磁研究硼酸改性对PAN纤维预氧化结构变化的影响。结果表明:硼酸对PAN纤维预氧化环化反应有一定的抑制作用,随着硼酸溶液浓度增加,硼酸对PAN纤维环化反应的抑制程度增加。硼酸对环化反应的抑制可防止纤维外层致密层的形成,有利于均质化程度的提高,并可防止PAN纤维表面被过度氧化。     

聚丙烯腈原丝的预氧化过程研究

采用密度分析、红外吸收光谱(FT-IR)分析仪、广角X射线衍射(WXRD)仪、差示扫描量热(DSC)分析仪和扫描电子显微镜( SEM)等手段,系统地研究了聚丙烯腈(PAN)原丝预氧化过程中的结构变化.结果表明,在预氧化过程中,PAN原丝的密度和相对环化率均增加,结晶尺寸先变大后变小,结晶度降低,说明环化反应先主要在非晶...     

石墨烯改性聚丙烯腈基纳米炭纤维的制备及其性能

以氧化石墨为前驱体,采用真空热膨胀还原法获得了功能化的石墨烯材料。以石墨烯为纳米填料,采用静电纺丝法制备了一系列石墨烯改性聚丙烯腈(PAN)纳米复合纤维,经进一步预氧化和炭化得到纳米炭纤维。使用扫描电镜(SEM)、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、元素分析(EA)、热重(TGA)和差示扫描量热仪(DSC)研究了石墨烯对纳米炭纤维的宏观性能与微观结构的影响。结果表明,加入石墨烯后,PAN纳米纤维中分子取向变大,结晶度下降。对氧化、环化和脱氢反应可产生一定的抑制作用,导致预氧化反应程度下降。同时,石墨烯可作为炭化阶段微晶生长的晶核,有利于碳网平面的快速生长。     

静电纺丝法制备聚丙烯腈基纳米炭纤维及其表面结构表征

通过稳定化、炭化静电纺制的聚丙烯腈(PAN)前驱体纤维制备了直径为100nm～300nm的纳米炭纤维.用扫描电镜(SEM)、场发射扫描电镜(FESEM)、扫描隧道显微镜(STM)及扫描量热分析法(DSC)研究了纳米炭纤维及其前驱体纤维的形貌及结构.结果表明:纳米炭纤维及其前驱体纤维的直径表现为对数正态分布.静电纺制纤维的环化放热峰移向低温,表明静电纺制纤维可在较低的温度下引发环化.由于静电纺制纤维的粗糙表面及在热处理过程中的收缩行为,在纳米炭纤维表面形成了长度为10nm宽度为5nm的凹坑.     

Preparation and characterization of silica nanoparticulate-polyacrylonitrile composite and porous nanofibers

In this study, polyacrylonitrile (PAN) composite nanofibers containing different amounts of silica nanoparticulates have been obtained via electrospinning. The surface morphology, thermal properties and crystal structure of PAN/silica nanofibers are characterized using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, wide-angle x-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results indicate that the addition of silica nanoparticulates affects the structure and properties of the nanofibers. In addition to PAN/silica composite nanofibers, porous PAN nanofibers have been prepared by selective removal of the silica component from PAN/silica composite nanofibers using hydrofluoric (HF) acid. ATR-FTIR and thermal gravimetric analysis (TGA) experiments validate the removal of silica nanoparticulates by HF acid, whereas SEM and TEM results reveal that the porous nanofibers obtained from composite fibers with higher silica contents exhibited more nonuniform surface morphology. The Brunauer-Emmett-Teller (BET) surface area of porous PAN nanofibers made from PAN/silica (5?wt%) composite precursors is higher than that of pure nonporous PAN nanofibers.     

Mechanical properties of polymer matrix composites at 77 K and at room temperature after irradiation with 60Co γ-rays

Ten different polymer matrix composites were irradiated with ⁶⁰Co γ-rays at room temperature, and were examined with regard to the mechanical properties at 77 K and at room temperature. The radiation-induced degradation of these composites is observed much more significantly in the ultimate strength and in the shear modulus than in the Young's modulus. The radiation resistance of these composites depends primarily on the radiation resistance of matrix resins, which increases in the order diglycidyl ether of bisphenol A < tetraglycidyl| diaminodiphenyl methane < Kerimid 601. Comparison of the mechanical properties tested at 77 K and at room temperature demonstrates that the extent of radiation-induced decrease in the composite strength is appreciably greater in the 77 K test than in the room temperature test. Interpretation of these results is based on the competition between the two opposing effects due to the hardness and brittleness of matrix resins.     

聚丙烯腈基静电纺纳米碳纤维的制备及拉伸强度测定

采用DMSO/H2O混合溶剂法制备两种不同分子量聚丙烯腈(PAN),将PAN配成纺丝液高压静电纺丝制备纳米纤维毡,然后预氧化和碳化;通过热重、红外光谱、电镜等分析手段对纤维毡、预氧化纤维毡和碳纤维毡进行表征,研究热处理过程中的PAN纳米纤维毡的失重情况、结构变化;采用电子万能试验机对不同纳米纤维束拉伸强度进行测量和分析,相关数据可为静电纺纳米碳纤维毡的制备应用提供方向参考和数据支持。     

湿法纺丝Amid-CNT/PAN复合纤维的结构与性能

通过溶液聚合得到胺化碳纳米管（Ami-CNT）/聚丙烯腈（PAN）复合溶液, 采用湿法纺丝技术制备了Amid-CNT/PAN复合纤维。利用红外光谱、 拉曼光谱、 差示扫描量热仪、 热失重仪和扫描电镜等方法分析Amid-CNT对PAN纤维结构的影响。结果表明: Amid-CNT与PAN大分子之间有很强的化学作用力; Amid-CNT在复合纤维中具有很高程度的取向, 使PAN纤维中氰基的取向从1.61提高到了2.30; 复合纤维在空气中的起始放热温度相对PAN纤维从212.30℃提前到206.01℃, 反应放热量从3054J/g降低到2346J/g; 复合纤维比PAN纤维的起始失重温度提前了3.7℃, 在700℃时的剩余质量提高了13.5%; 复合纤维的断面比PAN纤维具有更多的絮状结构。      

Characterization of polyacrylonitrile based carbon nanofiber mats via electron beam processing

The aim of this study was to evaluate the ability of electron beam irradiation to drive stabilization reactions within PAN nanofiber mats to obtain carbon nanofiber mats. PAN nanofiber mats with fiber diameters of 300-400 nm were prepared via an electrospinning method. Electrospun PAN nanofiber mats were stabilized by electron beam irradiation with various doses up to 5,000 kGy. Using the irradiation-stabilized PAN nanofiber mats, carbon nanofibers were obtained by pyrolysis in a tube furnace for 1 h at 1,000 degrees C under an N2 atmosphere. FT-IR analysis indicated that the transformation of C[triple bond]N groups to C==N groups was accelerated by electron beam stabilization. The thermal behavior of the PAN nanofiber mats was studied using DSC and TGA. DSC thermograms showed that the peak temperatures of the exothermic reactions were found to decrease with increasing electron beam irradiation doses. Irradiation-stabilized PAN nanofiber mats were not observed to dramatically decrease in weight between 290 degrees C and 320 degrees C, an observation presumed to be related to cyclization. The char yields of PAN were found to increase with increasing irradiation doses.     

The effect of embedded carbon nanotubes on the morphological evolution during the carbonization of poly(acrylonitrile) nanofibers

Hybrid nanofibers with different concentrations of multi-walled carbon nanotubes (MWCNTs) in polyacrylonitrile (PAN) were fabricated using the electrospinning technique and subsequently carbonized. The morphology of the fabricated carbon nanofibers (CNFs) at different stages of the carbonization process was characterized by transmission electron microscopy and Raman spectroscopy. The polycrystalline nature of the CNFs was shown, with increasing content of ordered crystalline regions having enhanced orientation with increasing content of MWCNTs. The results indicate that embedded MWCNTs in the PAN nanofibers nucleate the growth of carbon crystals during PAN carbonization.     

Fabrication of alumina nanofibers by precipitation reaction combined with heterogeneous azeotropic distillation process

γ-Alumina nanofibers have been prepared from a precipitation reaction between aluminum ammonium sulfate and Baker's salt solutions followed by a heterogeneous azeotropic distillation process with N-butanol and calcination at 1173 K. Experimental results indicate that the terminal pH value of the reaction mixture should be kept at 7.00-8.00 in order to obtain γ-Al₂O₃ nanofibers. The resulting spherical aluminum hydrate precipitates are evolved into two-dimensional crystallized pseudoboehmite lamellae after the heterogeneous azeotropic distillation and then transformed into γ-Al₂O₃ nanofibers with ca. 3-5 nm thick and 50-150 nm long after further calcination at 1173 K. The formation of γ-Al₂O₃ nanofibers can attribute to the preferential growth along the longitudinal axis due to the inherent instability of the planar structure of the pseudoboehmite during the calcination process.     

Microstructure and oxidation resistance of porous NbAl3 intermetallic prepared by thermal explosion reaction

Porous Nb–Al intermetallic was prepared by thermal explosion (TE) of combustion synthesis (CS). The temperature profile, phase composition, open porosity and oxidation resistance of Nb–Al compact were investigated. The results showed that the significant exothermic reaction occurred, which means that an obvious TE appeared during heating. The volume expansion of 190% was observed, and the prepared sample exhibited interconnected pores with an open porosity of 65.7%. The porous NbAl₃ intermetallic showed ‘pest’ oxidation in the temperature range of 500–600°C, and followed the parabolic oxidation law at 400°C. Moreover, due to the highly porous structure, this material had great potential for application to separation and heat insulation at a temperature range of room temperature to 400°C.