32. Cai, Wensheng; Gupta, Ram B.  Poly(N-ethylacrylamide) hydrogels for lignin separation.    Ind. Eng. Chem. Res.  (2001), 40(15), 3406-3412.


Poly(N-ethylacrylamide) (I) hydrogel and N-ethylacrylamide (II) bulk hydrogel with microstructure were prepd.  The lower crit. soln. temp. (LCST) of I was detd. to be 73 by DSC, and the microstructures of the hydrogels were characterized by SEM.  When the microgel particles were incorporated into the matrix of II hydrogel, the formed bulk hydrogels had a faster swelling rate and a higher swelling ratio, as compared to those of the conventional I hydrogels.  The swelling diffusion mechanism in I hydrogel changed from Fickian to non-Fickian when the crosslinker content was increased to 8 wt.%.  Both II and conventional I can be used to sep. lignin (III) at a high temp. (.apprx.55, typical in a pulp mill).  Because of the microgel particles, the II has a higher swelling ratio in III soln., whereas the large surface area of the microgel also increases the adsorption of III on the hydrogel, thus decreasing the sepn. efficiency.  The effects of III concn., sepn. temp., and salt on the sepn. efficiency are also studied.


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