Effect of processing on fracture of binderfree all-cellulose composites

Binderfree all-cellulose composites were prepared by a mechanical refinement process that allows the formation of intramolecular hydrogen bonds between the cellulose molecules during the drying process. The extent of this hydrogen bond network strongly depends on the duration of the refinement process. The fracture properties are studied at five different refining times. Due to the non-linear mechanical response of the binderfree all-cellulose composites, a method is first developed to obtain the fracture properties (fracture resistance and mode I cohesive law). The method uses a Double Cantilever Beam (DCB) sandwich specimen loaded with pure bending moments and it is based on the J integral. It is found that an increase of the refining times results a) in an increase of the crack initiation fracture energy and in a decrease of the steady-state fracture energy, and b) in an increase of the mode I peak cohesive traction.