The effect of microfibrillated cellulose addition on drying shrinkage and dimensional stability of wood-free paper

Microfibrillated cellulose (MFC) is known to enhance strength properties of paper. Improved strength usually means increased bonding which is strongly connected to dimensional instability of paper. The main objective of this work was to evaluate the dimensional stability of wood-free paper containing different amounts of varying grades of MFC and the effect MFC has with starch. Another important area was to develop a preparation method to produce sheets containing MFC. These sheets were dried using diverse methods to examine how drying strains induced by restraint drying affected hygroexpansion. The obtained results were compared to the results of the sheets containing kraft fines, and in specific test points cationic starch was used together with MFC. Tensile strength was also measured to study the type of bonding. Allowed shrinkage during drying had a significant effect on hygroexpansion. MFC decreased the dimensional stability of the freely dried sheets, but that of the restraint dried ones remained almost constant. As the amounts of MFC increased, the effects on dimensional stability became more severe. However, the fineness of MFC did not play an important role in dimensional stability. Both hygroexpansion and drying shrinkage were decreased with a cationic starch addition. The prevention of drying shrinkage produced sheets with similar hygroexpansion despite the type and amount of additives. For the restraint dried sheets, the tensile strength improved up till 7% addition. The combination of MFC and starch produced a sheet with improved dimensional stability and strength properties.