Preparation And Characterization Of SMPU/PNIPAM Semi-IPN Temperature Sensitive Membrane

Both water repellency and water vapor permeability are the important characteristic of modern fabrics, with the development of textile material science in theory and practice, our understanding and demand of waterproof and breathable textile has been transformed from static waterproof and breathable concept to dynamic and smart, and textiles with temperature-sensitive breathability are required. The temperature-sensitive membranes rely on the temperature sensitive material. In order to overcome the weakness of single temperature-sensitive material, the semi-interpenetrating polymer network (semi-IPN) of shape memory polyurethane (SMPU) and poly (N-isopropylacrylamide) (PNIPAM) were synthesized with the strategy of in situ crosslinking polymerization. Following that, microporous membranes were fabricated from the semi-IPN material by immersion precipitation phase inversion method. The relationship between structure and properties of the SMPU/PNIPAM semi-IPN membranes was studied and the mechanism of water vapor transmission was discussed.The paper can be divided into two parts. In the first part, shape memory polyurethanes were synthesized by a two-step method with poly (ε-caprolactone) as the soft segment, 4,4'-methylenebis (phenyl isocyanate) as the hard segment and 1,4-butanediol as the chain extender. Semi-IPNs were synthesized by SMPU and PNIPAM with the strategy of in situ polymerization. The molecular structure of the semi-IPN were characterized by FTIR and DSC. The result proved the intensive molecular interactions between SMPU and PNIPAM chains, which modifies the phase transition behaviors of SMPU.In the second part, the semi-IPNs were fabricated into microporous membranes with the strategy of immersion precipitation phase inversion. And the influence of preparation parameters on the morphology of membrane was investigated. The increase of PNIPAM content in the semi-IPNs facilitates the formation of large pores and increases the porosity. In contrast, the increase of coagulation bath temperature and concentration of DMF in the coagulation solution inhibit the formation of large pores. More sponge-like pores were formed, leading to a lower porosity.The water vapor permeability of the membranes shows significant temperature sensitivity. The mechanism of the temperature-sensitive water vapor transmission is as follow. The semi-IPNs inherit the temperature sensitivity of PNIPAM on water adsorption., and swell or deswell dramatically with the decrease or increase of environmental temperature. When the temperature drops, the semi-IPNs swell and the membrane pores are therefore clogged, inhibiting the transmission of water vapor molecules through the membrane pores. On the other hand, the increase of temperature leads to the shrinking of the semi-IPNs and the blocked pore structure are restored. The water vapor permeability of the membranes is thus greatly enhanced with the increase of temperature. According to the above mechanism, the temperature-sensitivity of the membranes can be improved with the increase of PNIPAM content. However, considering the mechanical stability, the composition of the semi-IPN should be optimized to achieve membranes with better performance.