PERMEATION AND SORPTION OF CO2 THROUGH AMINE-CONTAINED POLYURETHANE AND POLY(UREA-URETHANE) MEMBRANES

As an absorbent of CO2, tetraethylenepentamine (TEPA) and/or N-methyld iethanolamine (MDEA) was introduced into the hard segment as chain ext enders of the series methane polymer (PU), urea-urethane polymer (PUU) , and segmented urethane/urea-urethane copolymer (SPU) based on 4,4'-d iphenylmethane diisocyanate (MDI) and either poly(ethylene glycol (PEG )-400 or -600. The obtained polymers thus contained a nearly equal wei ght composition of both soft and hard segments and were prepared as po lymer membranes for permeation and sorption of CO2. The properties of the polymer membranes were characterized using a Fourier transform IR spectrophotometer, thermal gravimetric analysis, and rheometric measur ement. The permeation and sorption isotherms as a function of temperat ure and pressure as well as the activation energy of permeability and diffusivity and the enthalpy change of the solution were measured. The test temperatures were carried out above and below the T-gs of soft-s egment domains or the T-gh of hard-segment domains. The steady-state p ermeability (P) and diffusion coefficients (D) obtained ranged from 1. 01 to 12.9 barrer and 1.04 to 4.04 cm(2)/s, respectively, and the solu bility coefficients (S), from 0.529 to 3.43 cm(3)(STP)/cm(3) polymer-a tm at 10 atm and 35 degrees C. The TEPA-containing polymer membranes s howed a smaller P and D but a larger S than did MDEA-containing ones. The membranes comprising PEG-600 exhibit the values of P, D, and S at about 11.5-, 2.5-, and 4.5-fold the PEG-400 ones, respectively. For SP U membranes, above T-gs or T-gh, the pressure dependencies of P follow ed the modified free-volume model. On the other hand, below T-gs, they exhibited a minimum permeability at a certain pressure caused by the plasticization action of sorbed CO2. The sorption isotherms of CO2 ind icated that the membranes comprising PEG-400 can be described by a dua l-mode sorption model below T-gs. Also, the SPU polymer membranes obie d the Henry's law above T-gs as well as T-gh. The characteristic const ants of the sorption model were also determined and are discussed. (C) 1996 John Wiley & Sons, Inc.