Mechanical and dynamic mechanical properties of sheets made from micro-fibrillated cellulose and cationic polyacrylamide

Abstract

A diluted micro-fibrillated cellulose (MFC) dispersion with cationic polyacrylamide (C-PAM) aq. solution was casted and dried as a plausible model material of fiber-to-fiber bonds in paper containing C-PAM. Mechanical and dynamic mechanical properties of the MFC/C-PAM mixture sheets (MFC/C-PAM sheets) obtained were studied, comparing with those of papers containing C-PAM. The high density and Young's modulus of the MFC/C-PAM sheet, which was twice those of the paper without C-PAM, suggested higher consolidation and fully developed fibril-fibril bonds due to the quite small dimensions of MFC. A significant decrease in scattering coefficient of the MFC/C-PAM sheets accompanied by an increase of C-PAM content suggested that almost all of the C-PAM in the MFC/C-PAM sheets could locate surrounding fibril-fibril bonds. Tensile strength of MFC/C-PAM sheet was far larger than that of the paper without C-PAM. However, the strength increment of the MFC/C-PAM sheets with increasing C-PAM content was smaller than that expected from the difference of Young's modulus between MFC/C-PAM sheets and the papers containing C-PAM, partly because C-PAM itself is brittle. The dynamic mechanical properties of the MFC/C-PAM sheets were, on the whole, similar to those of the paper containing C-PAM, suggesting that the role of C-PAM on the mechanical property (or bonding) was minimal and the most of it was derived from fibril-fibril (hydrogen) bonding in the MFC/C-PAM sheets. Measurement of (dynamic) mechanical properties of the sheets consisted of MFC and various water soluble polymers could be used to evaluate the effects of the polymers on mechanical properties of papers when the polymers were used as dry strength agents.