Nanoindentation of bleached and refined pulp fibres

In this study, an attempt has been made to determine the mechanical properties of the wood pulp cell wall after pulping, bleaching and refining by means of nanoindentation in comparison with flax and lyocell fibres. Based on the indents performed on single fibre cell wall cross-sections, it has been found that bleaching and refining processes are causing reduction in indentation modulus and hardness values. It is assumed that the reduction is attributed to the change in lignin content as well as microfibril angle. Surprisingly, refined pulp fibres and lyocell have the same hardness and indentation modulus, which conforms that no residual lignin is present in the refined pulp. The bast fibre, flax, extracted without Kraft cooking revealed higher indentation modulus (23 GPa) and hardness (0.50 GPa) compared to wood pulp fibres.