Fractionation of microfibrillated cellulose and its effects on tensile index and elongation of paper

In this work we examine the fractionation of microfibrillated cellulose (MFC) and its effect on the physical properties of paper. In the first part of this work, we evaluate the fractionation of commercially available MFC using multiple stages of traditional fractionation unit operations, namely a hydrocyclone, a pressure screen, and a novel technique based upon the control of the threshold for motion in a weak gel. The results indicate that a smaller fibre length average fraction could be obtained using the gel separation technique than using multiple stages of separation in both the hydrocyclone and the pressure screen. With the gel technique we were able to reduce the average fibre length of the MFC from 221 μm to 100 μm. In the second part of the work, composite paper samples were formed by addition of fractionated and non-fractionated MFC to chemical wood fibres and the strength of the resulting composites were studied. The results showed 25% improvement in tensile index by addition of MFC and an additional 10% improvement in tensile strength by addition of fractionated MFC using the gel technique.