Nanocrystals of cellulose allomorphs have different adsorption of cellulase and subsequent degradation

Suspensions of cellulose nanocrystals (CNCs) having different allomorphs were prepared from pulp and microcrystalline cellulose. Comparison found varying particle features. In situ observation of cellulose enzymes interacting with CNC I, II and III by atomic force microscopy (AFM) and transmission electron microscopy (TEM) found diverse adsorption of the enzymes on the CNC. Greater degradation to glucose was revealed for short rod-like CNC II and thin needle-like CNC III than CNC I, which were mainly due to their greater d-spacings for the (110) (CNC II) and (1–10) (CNC III) planes compared to the (200) spacing for CNC I. According to the model crystal structures, the surface areas for those planes where the enzymes would adsorb were also lager for CNC II and III. However, CNC III had significantly enhanced adsorption capability compared to the low affinity of CNC II. Enzymes tended to gather near hydrophobic surfaces that correspond to planes with small crystallite sizes on CNC III, and the enzymes caused breaks of nanocrystals during the degradation. Understanding the interactions between CNC allomorphs and cellulase would provide deep insights into biodegradation of crystalline cellulose as well as extensive application of CNCs.