Due to the delignification procedur

Due to the delignification procedure, we expect the CNF to consist primarily of two classes ofcarbohydrate polymers in the form of cellulose fibrils and hemicelluloses. The chemical composition is reported in Table S1 in terms of cellulose and hemicellulose content. Peracetic acid-(PAA) treated CNF has a cellulose content of 76-77% with 23-24% hemicellulose. Chlorite treated CNF has 82-84% cellulose and 16-18% hemicellulose The reason for these differences is the higher selectivity of the PAA method and the mild conditions under which lignin was removed. The high hemicellulose content in the present CNFs, in combination with the small CNF diameter, makes it possible to propose a physical model structure for the holocellulose CNF. The core is a wood cellulose microfibril (botany term), and the microfibril is coated with a layer of native hemicelluloses so that we have a core-shell CNF. In fact, the core-shell CNF is likely to reflect an original ultrastructure of the wood cellulose microfibrils. For aspen, this layer is dominated by xylan, whereas the spruce CNFs contain a xylan-mannan polymer coating mixture. Let us assume that the CNF has quadratic cross-section with an edge length of 4 nm,and a 20% hemicellulose “shell” coating over a cellulose core (Figure 2b). With an assumption of similar densities, then the cellulose edge length is roughly 3.6 nm and the coating thickness about 0.2 nm. This corresponds to a few layers of hemicellulose in adsorbed “flat” conformation and provides a hypothetical physical model as a starting point for interpretations.