Isolation of Highly Purified Cellulose from Wheat Straw and Its Application
|School||University of Science and Technology of China|
|Course||Renewable and clean energy|
|Keywords||wheat straw cellulose separation dissolving super absorbent polymer homogeneous reaction acrylamide graft-copolymerization|
As an alternative resource, biomass has attracted much attention recently for its potential application in both regenerated energy and chemicals. Cellulose is the major component of biomass and the most affluent biopolymer in the world, and it is also a potential feedstock for preparing different kinds of novel polymers and materials. Currently biomass such as wheat straw is a resource of cellulose and the separation of cellulose from it is still a big challenge. In this study, a green chemical method of isolating cellulose from wheat straw was developed. The whole separation process was carried out in aqueous phase under atmospheric pressure, which opened up a way for the green production of cellulose. The dewaxed wheat straw was pretreated with hydrochloric acid aqueous solution at first followed by delignification using poly(ethyleneglycol) (PEG)/salt aqueous biphasic system (ABS). By varying the reaction parameters, the optimal reaction condition was found. The results of the kappa number analysis and the neutral sugar composition analysis revealed that 94.33-79.8% of the lignin in wheat straw was removed, and the remaining hemicelluloses in separated cellulose samples was 1.2-3.2%, indicating the obtained cellulose owns high purity. Moreover, all the cellulose samples can be well dissolved in NaOH/urea aqueous solution, the green solvents for cellulose. The effectiveness of the isolation process and the dissolving of cellulose were proved by FT-IR, XRD and SEM, etc. The yield of the seperated cellulose after two-stage treatment was 48.9-55.5%, which did not meet the requirement of industrialization. A way to increase the cellulose yield was developed by analyzing the mass and the components of the residue after being treated by hydrochloric acid aqueous solution and the yield could be improved to 67.9%, making a step toward industrialization. Based on the work above, acrylamide was added into the cellulose aqueous solution in NaOH/urea solvent to prepare super absorbent polymer by graft-copolymerization in homogeneous condition, which overcame the difficulty of low accessibility of cellulose in traditional derivatization reaction in heterogeneous condition and broadened the ideas of utilizing cellulose in homogeneous condition. The water absorbency of the synthesized absorbent polymer can reach up to 1326, truly realizing the green conversion from biomass wheat straw to functional cellulose material.