New organic precursors for carbon material : precursor development and carbonization process

• Main Author: Tay, Yu Shan
• Other Authors: Hu Xiao
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Materials::Material testing and characterization
• Online Access: https://hdl.handle.net/10356/153306
• Institution: Nanyang Technological University

Carbon materials possess properties such as being light weight, having high strength, thermal and electrical conductivity etc. which made them highly sought after for many applications. Polyacrylonitrile (PAN) is one of the few organic precursors with a relatively high char yield and an organised structure after carbonization. Phthalonitrile-based carbon materials are usually high temperature resistant with intrinsic porosity. As research progresses, many more carbon precursors have been discovered. However, each carbon precursor has its own advantages and disadvantages. For example, PAN can retain structure after carbonization with proper oxidative stabilization step but has a low char yield compared to resorcinol-based phthalonitrile (rPN). On the other hand, rPN has a high char yield but tedious curing procedure and its physical structure is not maintained after carbonization as it melts during curing. It would be ideal to combine the advantages of two good carbon precursors and at the same time solve the problems arising from using individual precursors alone, in order to produce better carbon materials. This study belongs to ongoing research efforts to develop new precursors for carbon materials with enhanced properties. This research work presents a new approach to produce carbon materials by blending of PAN and resorcinol-based phthalonitrile prepolymer (pPN), which offers a much simpler route compared with those of the more complex, currently reported studies that focus on chemical-physical modifications of the precursor and on modified stabilization/carbonization mechanisms. The proposed blends followed the main prerequisites for high char yield in carbonization and graphitization of organic compounds, namely, a precursor of high carbon yield, where the initial carbon proportion is higher than around 50% and the compound exhibits high thermal stability up to 1000 °C, which prevents thermal degradation during the pyrolytic process. The results, supported by the elaborate discussion of the intermolecular interaction between PAN and pPN prepolymer, demonstrated a major synergistic increase in the pyrolytic char yield and a significant reduction of the stabilization temperature. This synergistic enhancement of the carbon material obtained is not achievable by individual precursor system consisting of fillers or comonomers alone. Moreover, PAN/pPN-based carbon materials demonstrated structural versatility as it can exist in multi-form carbon, and this can be beneficial for meeting various application requirements. A new methodology to alter the physicochemical properties of derived carbon from the same organic precursor was developed which points to a simpler route compared to the currently reported heteroatom doping methods. Neat PAN and optimized PAN/pPN blend were two precursor systems used for this investigation. With the fundamental understanding of PAN thermal oxidative stabilization (TOS) and carbonization steps, this work investigated the different TOS and carbonization pathway leading to a different derived carbon. The results, supported by elaborate discussion of the gelation mechanism of PAN and pPN, demonstrated a major enhancement in the derived carbon making it suitable for potential applications such as adsorbent and catalysis. This research work demonstrated the use of a simpler method to synthesis new organic precursor by addition of pPN in small amounts to PAN. The synergistic enhancement was unique to the new system due to the chemical interaction of same functional groups on PAN and pPN. This new precursor system expanded the application possibilities of the derived carbon due to improved mechanical integrity that allowed it to exist in multi-form. With the ongoing efforts to decipher the TOS and carbonization mechanism of PAN, this work provides an insight on the factors affecting TOS and carbonization pathway leading to different properties of the derived carbon.