Structure of swollen carboxylated cellulose fibers

Structural changes in cellulose fibers were elucidated for carboxymethylated fibers and fibers that are oxidized by periodate and chlorite. Non-fibrillated and partially fibrillated softwood, kraft fibers (SKF, m-SKF) were carboxymethylated to investigate the contribution of the S1 layer to the swollen fiber structures. Carboxymethylated non-fibrillated fibers (CMF) form balloon-like structures as they swell heterogeneously. When partially fibrillated SKF is carboxymethylated (m-CMF), the fibers do not exhibit this ballooning phenomenon due to the degradation of the S1 layer. Carboxymethylation disrupts the native cellulose crystalline structure without breaking the fibers apart. Periodate–chlorite oxidized fibers, on the other hand, swell homogeneously without disrupting the native cellulose I crystalline form. Periodate–chlorite oxidation damages all three secondary layers to the extent that any microfibril confinement caused by the swelling is removed. Each chemistry and mechanical treatment affects the cellulose fibers differently to yield various swollen structures.