Abstract
The non-porous rubbery polyurethane membranes (PUMs) have been successfully prepared from different molecular weights of polycaprolactone (PCL), 4,4,-dicyclohexylmethane (H12MDI diisocyanates) and 1,4-Butane diol (BDO), which are used in synthesis of soft and rigid segment, in gas separation. All structure of membranes were confirmed by FTIR technique that exhibits high molecular weight content of PCL conveniences the strong peak at 1710 cm(-1) corresponds to hydrogen bonding in urethane groups that controls the packing, morphology and crystallization in polyurethane membranes. Differential scanning calorimeter (DSC) measurement provided a lower T-g at 50 degrees C and T-max at 550 degrees C in the heating scanning curve of PCL 750-2000, which indicated that lower energy is required to overcome the chain-chain interaction. The polyester groups in PCL structure created hydrogen bonding which increased hydrophilicity, chain mobility, flexibility and transport of gases. Atomic force microscopy confirmed the non-porous, wettability and increase roughness on membrane surface as high molecular weight of polyol increases the gas solubility and diffusivity. Excellent values of tensile strength (13.25 Mpa), elongation at break hardness (361%) and hardness (86A) were observed for higher molecular weight (2000) PUM by universal testing machine. The lower molecular PUM-1 (750 Mw) content has 46% lower CO2, CH4, N-2 and O-2 permeability of pure gases as compared to high PUM-4 and PUM-5 having 1600, 2000 of PCL content in polyurethane. Permeability property of gases is associated with free volume and flexibility of polymer backbone segments within the membrane, which is dominated by the chain mobility of polymeric substance. The high permeation flux and selectivity were achieved by increasing feed temperature, pressure and transient gaps. The CO2/N-2 selectivity increased as compared to CO2/CH4 due to chain packing density, lower free volume and saturation of carrier efficiency.