Mapping humidity-dependent mechanical properties of a single cellulose fibre

Modelling of single cellulose fibres is usually performed by assuming homogenous properties, such as strength and Young’s modulus, for the whole fibre. Additionally, the inhomogeneity in size and swelling behaviour along the fibre is often disregarded. For better numerical models, a more detailed characterisation of the fibre is required. Herein, we report a method based on atomic force microscopy to map these properties along the fibre. A fibre was mechanically characterised by static colloidal probe AFM measurements along the longitudinal direction of the fibre. Thus, the contact stress and strain at each loading point could be extracted. Stress–strain curves were be obtained along the fibre. Additionally, mechanical properties such as adhesion or dissipation were mapped. Local variations of the effective fibre radius were recorded via confocal laser scanning microscopy. Scanning electron microscopy measurements revealed the local macroscopic fibril orientation and provided an overview of the fibre topography. By combining these data, regions along the fibre with higher adhesion, dissipation, bending ability and strain or differences in the contact stress when increasing the relative humidity could be identified. This combined approach allows for one to obtain a detailed picture of the mechanical properties of single fibres. Graphic abstract