The effect of fibre volume fraction and mercerization on the properties of all-cellulose composites

Abstract

All-cellulose composites with 85–95% fibre volume fraction were successfully prepared by using solutions of 1–7% (wt/v) cellulose concentrations (dissolved ligno-cellulosic ramie fibres in LiCl/DMAc) for impregnation of aligned ramie fibres. The effect of mercerization or alkali treatment to the properties of the prepared composites was also investigated. The structure, morphology, and mechanical properties of the composites were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and tensile testing. After mercerization, tensile strength of the prepared composites was improved by 15–95%. The optimal all-cellulose composite, was based on a cellulose matrix obtained from a 4% cellulose concentration in solution, which led to a fibre volume fraction of 85%, resulting in an optimal combination of a sufficient amount of matrix phase with good fibre wet-out due to a low matrix viscosity and a high tensile strength due to a high fibre volume fraction. Alkali treatment successfully further improved the tensile strength of these composites from 440 MPa for un-mercerized composites to 540 MPa for mercerized composites, which are values that compare very favourable to more traditional random and unidirectional natural fibre based composites. Raman spectroscopy indicated that orientation of the aligned ramie fibres in the mercerized composites is well-maintained. X-ray diffraction confirms that native cellulose I, which is the major polymorphic modification of cellulose in these composites, is rearranged to cellulose II crystal packing after mercerization.