Preparation and characterization of physical gels and beads from chitin solutions

A detailed account of physical bulk gel and bead formation from various chitin solutions and nonsolvents is given. Instant gel formation occurs upon contact of chitin solutions in dimethylacetamide (DMAc)/lithium chloride (LiCl) or N-methyl-pyrrolidinone (NMP)/LiCl solvents and nonsolvents such as water, ethanol, or acetone. Ethanol was found to be the optimal nonsolvent for homogeneous spherical bead formation from chitin solutions. Similarly, DMAc-based chitin solutions proved to yield higher quality beads compared to NMP-based solutions. The differences in bead morphology, crystallinity, and thermal degradation are explained in light of the attainment of a balance between attractive hydrogen bonding in the chitin gel network and segment–nonsolvent interactions. The dependence of swelling of chitin gels on pH indicated a maximum of swelling ratio value of 4.3 at pH 11 in aqueous solutions while the equilibrium swelling ratio value of chitin beads formed with ethanol reached a maximum of 2.4. Bulk gels formed under favorable conditions were demonstrated to be recyclable after solvent separation and drying.