Spherical cellulose gel particles with donut-shaped interior structures

Partially carboxylated cellulose wood fibers (CMF) with highly swollen balloon-like structures were ultrasonicated to produce spherical cellulose gel particles with donut-shaped interior structure. The formation of these particles is most likely due to the characteristic microfibril arrangements in swollen CMF consisting of alternating regions of “balloons” and “collars”, which have different structural rigidity. Upon applying an intense mechanical energy, the more physically strained parts break up prior to the flexible areas. Hence the helically extended S1 microfibrils and the axially compressed S3 layers are damaged first, while partially or fully carboxymethylated flexible cellulose chains in the S2 layers are rearranging themselves around the tightly wound collars. The interior donut structure likely originates from the collars, which do not collapse upon drying. The carboxymethylated spherical cellulose gel particles have a wide size distributions ranging from 15 to 200 μm in diameter with excellent rewettability and pH sensitivity in water.