The title of my PhD thesis is: “Synthesis and evaluation of the structure and gas separation properties of the bulky groups contained polyurethane membranes and the effect of modified silica nano-particles on it”.
Global warming and increased carbon dioxide concentration in atmosphere as a result of use of fossil fuels is one of the most significant dilemmas in environmental aspects, these days . Hence, reduction of emitting greenhouse gases to the atmosphere is an important challenge in industries and therefore, high efficient approaches include absorption, adsorption and cryogenic separations have been developed for CO2 capture and storage. In recent years, polymeric gas separation membranes are getting more importance since they are energy-efficient and have low capital costs and appropriate performance in gas separation.
Rubbery polymers have been known as outstanding materials for CO2 gas separation, owing to the high solubility of polar gases. Among them Polyurethanes (PU) are the good candidates to polar gas removal due to the possibility of tailoring their transport properties by varying the polymer microstructure.
Polyurethane elastomers are usually composed of a polyether or polyester soft segment and a hard segment. The hard segment itself consists of Isocyanates and chain extenders. The long-chain polyols, which are flexible and are usually tangled (soft segments), alternate along the polymer chain with oligomeric rigid urethane or urea units (hard segments). Diamines and Diols can be used as chain extenders in polyurethane preparation. The first leads to Urea production and the last produces Urethane groups in the PU structure. The hard segments are responsible for tensile strength, tear resistance, hardness and permanent elongation, while the soft segments determine the elastic expansion. The low miscibility of the hard and soft segments leads to microphase separated structure. The amount of phase separation of PU is determinative for its capability in gas permeation. More phase separation is in favor of gas permeation. Since the hard segment is impermeable, the main goal of this thesis is changing the chemical structure of hard segment to increase its contribution to gas transport and using absorbent nano-particles to increase in CO2 permeability, CO2/N2 and CO2/CH4 gas selectivities. For this purpose different bulky chain extenders based on Cyanuric Chloride are synthesized and used in PU preparation to increase in free volume of hard segments and prevention of chain compaction. Also surface special modified silica nano-particles are used to prepare mixed matrix membrane. The relationship between structure and gas permeation behavior of prepared PU membranes are studied.