Synthesis Of Lignin Modified Phenolic Resin And Effect On Structure And Properties Of Magnesia Carbon Materials

As an important binder for carbon-containing refractories, Phenolic resin (PF)plays a primordial role in the bonding strength of these refractories because of thenetwork structure by cross linked of its molecules. However, with the widespread use ofthe unburned process, the demand to the cold bonding strength of carbon-containingrefractories is growing. In order to meet the production needs, finding a new resinwhich has higher crosslinking density to further improve the cold bonding strength ofcarbon-containing refractories is necessary. Hence, in this paper, the lignin modifiedphenol-formaldehyde resin was synthetized by using lignin as a partial replacement ofphenol. One hand, these modified resin can form three-dimensional interpenetratingnetwork after cured, which can increase the crosslinking density. On the other hand, thecost and the content of free phenol will be decreased due to the replacement of phenolby lignin. In addition, the transition metal catalyst precursor was added in the LPFduring the the synthesis process with in-situ composite, preparing lignin modifiedphenol-formaldehyde resin composited with nickel nitrate, to increase the dispersity ofcatalyst and improve the mcrostructure of pyrolytic carbon from isotropic glassy carbonto one-dimensional carbon nanostructure by meas of catalysis of Ni. Then the modifiedresin and traditional phenol-formaldehyde resin (PF) were used in magnesia carbonbrick. The effect of modified resin on the structure and properties of magnesia carbonbrick was studied. In the contrast, the physical properties of magnesia carbon brickbonded by PF were obtained. Specific studies and results as follows:(1) The lignin modified phenol-formaldehyde resin (LPF) was synthetized by usingcalcium lignosulfonate as a partial replacement of phenol. Properties and structure wasinvestigated by Fourier transform infrared spectrometer (FTIR), high-resolutiontransmission electron microscope (HRTEM) and TG-DSC. In addition, the differentprocess conditions of LPF such as substitution of lignin, catalyzer addition and reactiontime were investigated, their effect on performances of LPF was researched. Resultsshowed: LPF possess three-dimensional structure and has good water solubility.Properties such as viscosity, solid content and char yield of LPF were different whensubstitution of lignin, catalyzer addition and reaction time were changed.(2) The magnesia carbon brick was prepared by using the LPF synthetized with different process conditions as a binder. Physical properties and microstructure ofmagnesia carbon brick were tested. In order to obtain optimal process condition, theinfluence of LPF on the structure and properties of magnesia carbon brick was studied.Results showed: When catalyzer addition is1%, substitution of lignin is30%andreaction time is2h, the magnesia carbon brick bonded by LPF achieves the bestproperties, with heat treatment at200℃and1200℃, the cold modulus of rupture andcold crushing strength were17.78MPa,72.3MPa and5.00MPa,37.3MPa, respectively,the hot modulus of rupture of magnesia carbon brick at1400℃was7.32MPa. Inaddition, as the test temperatures used were to1200℃, SiC whiskers were grown viaconventional V-L-S mechanism because the inorganic salts in LPF can formmicro molten-salt reaction pools at high temperature.(3) Due to the good water solubility of LPF, the lignin modified phenol-formaldehyde resin composited with nickel nitrate (NLPF) was synthetized by addingnickelousnitrate (NNH) as catalyst precursor during the synthesis process of LPF. Thedispersity of catalyst (Ni) and the structure of pyrolytic carbon derived from NLPF wereinvestigated by scanning electron microscope (SEM), high-resolution transmissionelectron microscope (HRTEM), X-ray diffraction (XRD) and Raman spectrometer.Results showed: Catalyst (Ni) was dispersed homogeneously in the system of NLPF.The in situ forming transition metal Ni catalyzed the product of linear carbon nanotubeswith a high degree of crystallization and the graphitization extent of pyrolytic carbonwas improved. Increasing the addition of NNH and carbonization temperature, theproduction of carbon nanotubes and graphitization extent of pyrolytic carbon wereinproved. What’s more, the magnesia carbon brick was prepared by using the NLPF asa binder. Physical properties and microstructure of magnesia carbon brick were tested.Effects of LPF synthetized with different addition of NNH on the structure andproperties of magnesia carbon brick were researched. Results showed that when theaddition of NNH was1.5wt%, the magnesia carbon brick samples achieved the bestphysical properties.