Poly(N-ethylacrylamide) hydrogels for lignin separation

Poly(N-ethylacrylamide) hydrogel (PEAM) and N-ethylacrylamide bulk hydrogel with microstructure (EAM-BHM) are prepared. The lower critical solution te mperature (LCST) of PEAM is determined to be 73 degreesC by DSC, and the mi crostructures of the hydrogels are characterized by SEM. When the microgel particles are incorporated into the matrix of EAM hydrogel, the formed bulk hydrogels have a faster swelling rate and a higher swelling ratio compared to those of the conventional PEAM hydrogels. The swelling diffusion mechan ism in PEAM hydrogel changes from Fickian to non-Fickian when the cross-lin ker content is increased to 8 wt %. Both EAM-BHMs and conventional PEAM can be used to separate lignin at a high temperature (similar to 55 degreesC, typical in a pulp mill). Due to the microgel particles, the EAM-BHMs have a higher swelling ratio in lignin solution while the large surface area of t he microgel also increases the adsorption of lignin on the hydrogel, thus d ecreasing the separation efficiency. The effects of lignin concentration, s eparation temperature, and salt on the separation efficiency are also studi ed.