Study On Modification Of Coal To The Effect Of Properties Of Coal-based Polyaniline Composites

The structure and properties of coal are the key factors that control the conductivity of coal-based polyaniline composites. In this work, the effect of swell pretreatment and oxidation modification of coal on the structure of coal and the conductivity of coal-based polyaniline were studied. The effects of swelling time, temperature, types of solvent, and the ratio of coal vs solvent on the swelling properties of shenfu coal (SFC) were explored. The results show that the maximum degree of equilibrium swelling of SFC was obtained under the conditions of 80℃, 2 hours and 0.05 g/ml of coal vs solvent. The study of swelling dynamics indicates that the swelling process of SFC in aniline can be illustrated by Caseâ…¡diffusion. The structure of the swelled SFC was analyzed by means of FTIR, TG and SEM analysis. The results show that the network structure of SFC macromolecular was destroyed to a certain extent due to its swelling in aniline at 80℃. The SFC was swelled by aniline for 2 hours at a given temperature, and then was filtrated and dried, finally the swelled coal (STSFC) was obtained. STSFC-PANI was prepared by means of swelling-in-situ-oxidation-polymerization at room temperature from STSFC and aniline. The effects of the swelling temperature and hydrochloric acid doping on the conductivity and thermal stability of STSFC-PANI were investigated. At the swelling temperature of 80℃, DSTSFC-PANI(STSFC-PANI doped by hydrochloric acid) had higher conductivity and thermal stability. The conductivity order of the coal-based polyaniline are in the sequence of DSTSFC-PANI> DSFC-PANI >SFC-PANI> STSFC-PANI (SFC-PANI and DSFC-PANI were prepared by swelling-in-situ-oxidation-polymerization at room temperature from SFC and aniline, but the former is doped only by acid group in SFC, the late is further doped by HCl). The results show that the hydrochloric acid doping is able to promote the conductivity of STSFC-PANI, but the swelling pretreatment decreases the conductivity of SFC-PANI. To investigate the effect of the soluble matter in the SFC that can be dissolved in aniline on the properties of the coal-based polyaniline composites, the SFC was swelled in aniline for 2 hours at the same temperature as mentioned above, and then the mixture of SFC and aniline were cooled up to room temperature, the SFC in this mixture is named as HSSFC. HSSFC-PANI was prepared by the same method as mentioned above from this mixture. The results show that the conductivity of HSSFC-PANI was close to that of STSFC-PANI, but lower than that of SFC-PANI and DSTSFC-PANI. It was clear that the conductivity of HSSFC-PANI was slightly affected by the aniline soluble matter of SFC. Therefore, the decrease of the conductivity of the coal-based polyanilne composites is mainly attributed to influence of swelling of SFC at higher temperatue. TG analysis indicated that the different type of the coal-based polyanilne composites were different thermal stability, the order of their thermal stabilities are in the sequence of SFC-PANI>DSTSFC-PANI>HSSFC-PANI> STSFC-PANI. Therefore, the destroying of the network structure of SFC macromolecular because of higher temperature swell is the main reason for the decrease of the conductivity of the coal-based polyaniline composites. Furthermore, In order to understand the effect of macromolecular network structure of SFC on the conductivity of coal-based polyaniline, oxidation pretreatment of the SFC were performed by HNO₃ and H₂O₂ (the products were named HNO₃-SFC, H₂O₂-SFC respectively). In the oxidation process, macromolecular structure and pore structure of SFC were destroyed to a certain extent; the main products of HNO3-SFC were non-water-soluble macromolecular acids; and that of H₂O₂-SFC were water-soluble small molecular acids; the functional groups content in HNO₃-SFC were higher than that in H₂O₂-SFC. The oxidized-coal-based polyaniline (OCPANI) and aniline-extractives based polyaniline (CEX-PANI) were prepared by using the same polymerization method mentioned above. The conductivity of HNO3-OCPANI was higher than that of H2O2-OCPANI, but lower than that of SFC-PANI. The conductivity of H₂O₂-OCEX-PANI is close to that of HNO3-OCEX-PANI, but they are both lower than that of SFC-PANI. Thus the results further show that the macromolecular network structure is important to the conductivity of coal-based polyaniline, the functional group in the SFC only plays a doping role. The solubility order of the CEX-PANI in THF are in the sequence of H₂O₂-OCEX-PANI> HNO₃-OCEX-PANI> SFCEX-PANI, however, the forming film ability of SFCEX-PANI is better than that ofH₂O₂-OCEX-PANI and HNO3-OCEX-PANI. In a brief, there are the three steps during the aniline polymerization process in coal: the absorption of aniline monomer in the pore channels, swelling in the macromolecular network and the oxidation-polymerization in limited space. The acid groups, network structure, and the pore structure in coal macromolecule are benefit to the self-assembly polymerization of aniline monomer in coal. Meanwhile, the macromolecular acids in coal play a self-doping role in coal based polyaniline...