Effects Of The Different Functional Groups Of Carbon Nanotube On The Structure For Acrylonitrile Polymer

Carbon nanotubes (CNT) are the nano-tube materials with the remarkable mechanical properties, electrical properties and magnetic properties owing to the unique structure. So the CNT in the composite was focused by many researchers. Acrylonitrile polymer (PAN) is the main precursor for manufacturing the high strength carbon fiber. The addition of CNT into the PAN polymer would obtain the excellent properties for the carbon fiber. In this paper the CNT was modified by different methods, and then was added into the PAN matrix. According to the formation and evolving of the PAN molecular structure, the CNT with different function groups on the chemical structure of acrylonitrile polymer, the aggregation structure of acrylonitrile polymer during spinning, the heat chemical reaction for the acrylonitrile polymer were studied, respectively. Through the systemic experiment and theoretical analysis, the academic contents were enriched by the CNT/acrylonitrile polymer, which laid a solid foundation for the continuous scientific and technological research. The purified CNT was modified by hydrogen peroxide and triethylenetetramine to obtain the carboxylic acid and hydroxyl group on the surface of CNT (Acid-CNT) and the amide-groups on the surface of CNT (Amid-CNT), respectively. The modified CNT were characterized by Fourier transform infrared spectrum (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrum and Transmission electron microscopy (TEM). The results showed that the metal catalyst and amorphous carbon in the pristine CNT disappeared after purification. The results from the FTIR spectrum showed that the surface of CNT contained the carboxylic acid and hydroxyl groups after modification by hydrogen peroxide. The content of oxygen element on the surface of CNT was increased through XPS analysis. After modification by thionyl chloride and triethylenetetramine for the Acid-CNT, the amide-groups were grafted onto the surface of CNT. The surface of Amid-CNT have new element-nitrogen element by XPS analysis.The different function CNT/acrylonitrile (co-)polymer composite were synthesized by aqueous deposition in situ polymerization. The composite spinning solutions were prepared by radical solution polymerization, and the different drafting composite fibers were obtained by wet spinning method. The Effects of functional CNT on the chemical structure for the acrylonitrile (co-)polymer were studied. The results from the FTIR spectrum showed that the hydrolysis of nitrile groups for the PAN homopolymer was affected by the different functional groups on the surface of CNT. The Acid-CNT/PAN composite have more nitrile groups than PAN homopolymer, and the Amid-CNT/PAN composite have more ester groups. For the acrylonitrile copolymer (PANIA), the hydroxyl groups on the surface of Acid-CNT had reacted with the carboxylic acid groups on the molecular chain of PANIA polymer and formed the ester groups, which made the Acid-CNT/PANIA composite having lower relative content of carboxylic acid groups than the PANIA polymer. The amide-groups on the surface of Amid-CNT had reacted with the carboxylic acid groups on the molecular chain of PANIA polymer, which made the Amid-CNT/PANIA composite having lower relative content of carboxylic acid groups than the PANIA polymer. After in situ polymerization, the CNT could be homogeneously dispersed into composite by Scanning electron microscopy (SEM) analysis. The interfacial interaction between the Amid-CNT and acrylonitrile (co-)polymer composite was stronger than that of the Acid-CNT/acrylonitrile (co-)polymer composite by Raman spectrum analysis.The effects of functional CNT on the aggregation structure were studied. For the PAN homopolymer, the addition of CNT decreased the degree of crystallization, and improved the size of crystalline for the composite. For the PANIA polymer, the addition of CNT increased the degree of crystallization and the size of crystalline for the composite, respectively. The CNT/PANIA composite fiber had lower degree of crystallization than the PANIA fiber during spinning. However, the composite nascent fiber had higher size of crystalline than the PANIA nascent fiber. For the first-drafting fiber and precursor fiber, the composite had lower size of crystalline than the PANIA fiber. The Amid-CNT has bigger influence compared with the Acid-CNT on the size of crystalline during spinning. The degree of orientation for CNT in the composite fiber increased with the drafting, which made the composite having lower crystal region orientation than the PANIA fiber. But the composite had higher nitrile group orientation than the PANIA fiber. The Amid-CNT/PANIA composite precursor fiber had helical conformation, and the PANIA precursor fiber only had zigzag conformation by meridional scan analysis.The acrylonitrile (co-)polymer took place complex reactions during the processing of heat treatment. The effects of different function CNT on those evolving were characterized by FTIR spectrum, DSC and SEM images. The Amid-CNT/PAN composite had lower initiation temperature and cyclization temperature than PAN homopolymer in air atmosphere. The Acid-CNT/PANIA composite had lower evolved heat than the PANIA polymer, but the Amid-CNT/PANIA composite had higher evolved heat than the PANIA polymer in air atmosphere. Moreover, the addition of CNT decreased the glass transition temperature of acrylonitrile (co-)polymer. During the spinning, the Amid-CNT/PANIA composite fiber had lower initiation temperature, cyclization temperature and evolved heat compared with PANIA fiber in air atmosphere. After the same heat treatment in air atmosphere, the Amid-CNT/PANIA composite fiber had higher relative cyclization ratio and density compared with PANIA fiber. For the exothermic effect of the heated fiber, the Acid-CNT/PANIA composite fiber had higher evolved heat than the PANIA fiber, and the Amid-CNT/PANIA composite fiber had lower evolved heat. The break sections of composite fiber with heat treatment became irregular compared with the heated PANIA fiber by SEM image analysis.The effects of the different function CNT on the kinetics for the PANIA fiber during heat chemical reaction were studied by non-isothermal DSC methods. The results showed that addition of CNT improved the activation energy of the cyclization reaction compared with PANIA fiber in nitrogen atmosphere. The activation energy of the Acid-CNT/PANIA composite fiber, Amid-CNT/PANIA composite fiber and PANIA fiber is 177.62KJ/mol, 158.30KJ/mol and 156.45KJ/mol, respectively. In air atmosphere, the activation energy of cyclization reaction for the PANIA fiber, Acid-CNT/PANIA composite fiber and Amid-CNT/PANIA composite fiber is 211.18KJ/mol,200.39KJ/mol and 149.76KJ/mol, respectively. The activation energy of oxygen reaction for the PANIA fiber, Acid-CNT/PANIA composite fiber and Amid-CNT/PANIA composite fiber is 136.74KJ/mol,140.63KJ/mol and 143.58KJ/mol, respectively. The addition of CNT did not greatly influence the order reaction for the PANIA fiber during heat treatment, which was close to the first order reaction.