Porous Polvacrvlonitrile Materials Via Themallv Induced Phase Separation And Their Potential Applications

Porous polyacrylonitrile (PAN) materials possess excellent resistance to inert solvents and bacterial corrosion, heat and physicochemical stability, so they have been widely used in water treatment, pervaporation, enzyme-immobilization, biological medicine, and carbon materials. However, they are almost made by immersion precipitation phase inversion method, which has limited the further development of PAN. Thermally induced phase separation (TIPS), as another popular way for porous materials, has attracted much attention due to its definite mechanism and ease to control. In this thesis, we selected crystallizable diluent systems for PAN, investigated the specific phase separation mechanism for each PAN/diluent system, and prepared several kinds of porous PAN materials, which were pyrolyzed for porous carbon. This work is expected to expand new applications not only for PAN, but also for TIPS method. Our specific studies are concentrated as follows:The interactions between PAN and six solvents (dimethyl sulfone (DMSO2), dimethly sulfoxide, ethylene carbonate, propylene carbonate, N,N-dimethyl formamide, N,N-dimethyl acetamide) were discussed by computational calculation based on density functional theories. Moreover, the molecular change and dissolving process of PAN in the solvents were analyzed by concentration-or temperature-dependent FTIR and two-dimensional infrared correlation analysis. The results show that PAN-DMSO2has the strongest dipole-dipole interaction. Moreover, PAN/DMSO2system becomes homogeneous solution at elevated temperature, and undergoes phase separation upon cooling. It means that DMSO2could be an appropriate crystallizable diluent for PAN.We characterized the crystallization behavior and determined the phase diagram of PAN/DMS02system by using DSC, POM, WAXD, and SXAS methods. The binary system undergoes solid-solid thermally induced phase separation, and PAN foams with honecomb-or channel-like pores can be modulated by varying the polymer composition. It is confirmed that these pores are shaped by DMSO2crystals in the mixtures. On the other hand, giant spherulites came out in PAN/DMS02mixtures, whose morphology, structure and formation mechanism were detailedly discussed. Results indicate that the giant spherulites can be contributed to both the DMSO2crystallization and the dipole-dipole interaction between PAN and DMS02.Combining optical microscope equipped by hot stage and DSC method, we traced the liquid-liquid phase separation process, studied the droplet growth kinetics, and determined the phase diagrams of PAN/DMS02/additive (glycerol or polyethylene glycol (PEG)) ternary systems. A powder premixing process and one-step molding route were introduced to prepare PAN membranes. The PAN membranes show various structure, uniform pores, high porosity, and excellent mechanical properties. Besides, it exhibits that polymer concentration, additive content, PEG molecular weight, and cooling rate exert influences on the phase separation temperature, the droplet growth rate, pore structure, permeability, and mechanical properties.To obtain the optimum condition for pyrolysis, PAN membranes were oxidized and carbonized at different conditions, and then their chemical structure, pore morphology, and weight loss were studied by FTIR, SEM, and weighing, respectively. The resultant carbon membranes possess concentrated cellular pores and large specific surface area. Furthermore, they present selective adsorption to methyl orange and good reusability.