Measurement On Diffusion Coefficient Of DMF(DMAc)-Segmented PolyUrethane-Urea System

Diffusion behavior of solvent in a polymer matrix is very important for industrial technology and theoretic analysis. As solvent diffusion coefficient is an essential parameter to describe the procedure of getting rid of solvent from matrix material, mutual diffusion coefficients for solvent-polymer systems are needed to analyze drying process of polymer, especially for dry spinning process of polymer fiber.In the present work, it was proposed to obtain the temperature dependent diffusion coefficients for solvent-polymer system which included two organic solvents (Dimethylformamide, DMF & Dimethylacetamide, DMAc) and segmented polyurethane-urea solid film (SPUU). The diffusion coefficients are indispensable for engineering design of dry spinning for polyurethane-urea fiber.The calculation theory about diffusion coefficients reported in the previous papers was adopted to deduce the equations to determine thetemperature dependent diffusion coefficients from sorption experimented data. And adsorption experiments were conducted for the binary component system of solvent and film with a quartz-spring micro-balance apparatus in the range of 120℃~160℃. The equilibrium sorption weights and equilibrium time could be obtained experimentally at different temperature.The results revealed that the equilibrium sorption weight of SPUU to both solvents, DMF and DMAc, increased, and the equilibrium time decreased with elevation of temperature. That the solvent vapor pressure enhanced, solvent molecular activity was added, and the free volume of polyurethane-urea augmented with increment of temperature could be responsible for these mentioned experimental results. At the same time, the equilibrium sorption weight of DMAc was greater than that of DMF, and this difference was more obvious under higher temperature. This diversity may be attributed to the different boiling point of DMAc and DMF. The boiling point of DMAc was higher than that of DMF, thus DMAc is easier to condense in the film, that is to say, it is difficult to diffuse along the opposite direction. As well, this might be why DMAc needed longer time to reach equilibrium under lower temperature and shorter time to reach equilibrium under higher temperature.The value of diffusion coefficients calculated for both DMF and DMAc showed the increased trend with ascended temperature. It wasalso noticed that under higher temperature, diffusion coefficient of DMAc was a little more than that of DMF, under lower temperature, it was a little less. The relationship between temperature and diffusion coefficients of both systems was expressed by Arrhenius equation, they could be used to evaluate diffusion coefficient in wider temperature range.Moreover, for solvent DMF, the dependence of diffusion coefficient to temperature obtained in present work was compared with the results reported by Y. Ohzawa et al. which was deduced from moire pattern. Although the dependence of diffusion coefficients to temperature was similar for both results, the resultant values shown in this paper were some lower. That the polymer SPUU used in experiments was different may result in this dissimilarity. SPUU solutions (in DMF) was used by Y.Ohzawa et al, and SPUU solid film was employed in our work.Furthermore, desorption experiments of DMF from SPUU dope (SPUU dissolved in DMF) were also carried out, it was found that, with temperature rise, desorption rate of DMF from dope became faster, time reached desorption-sorption equilibrium shortened, as well.