Combined Effect of the Morphology and Rate of Addition of Fine Cellulosic Materials Produced from Chemical Pulp on Paper Properties

Recently fine cellulosic materials such as microfibrillated celluloses (MFCs) have become an interesting additive in papermaking, improving paper mechanical properties thanks to their intrinsic high mechanical strength along with high potential to interact with cellulosic fibres.
In this study, we produced and compared: (i) a mixture of primary and secondary fines isolated from the pulp by means of a purpose-built laboratory pressure screen and (ii) MFC-like materials obtained by refining and subsequent steps of high-pressure homogenization. Morphological properties were determined using flow cell based and microscopic techniques, showing a wide size distribution of the fibrillated materials produced. The thus obtained materials were applied in handsheet forming in blends of different proportions to evaluate their influence on paper properties. Already at low concentration all tested products lead to a substantial decrease in air permeability and to improved mechanical properties, independent of the type and morphological character of the added fine cellulosic material. At higher addition rates, only highly fibrillated materials allowed a further considerable increase in tensile strength, which could be explained by the creation of a secondary network structure of highly fibrillated materials improving the load-bearing capacity of the whole paper structure.