Potential of fibrillated cellulose in papermaking: Looking for optimal conditions to maximize paper performances

In papermaking, the use of nano/micro fibrillated celluloses (NFC, MFC) can bring a wide range of remarkable properties to the material1,2. Because of their highly fibrillated structure, the addition of such products increases specific surface area and improves the overall tensile strength, rigidity and Z-strength of paper by promoting the formation of fibre-fibre bonds. Such results are encouraging and suggest that the addition of fibrillated cellulose could replace beating since it brings similar mechanical properties without damaging fibres´ structure, improving products lifetime and reducing energy costs3. Moreover, fibrillated celluloses also feature good barriers properties while being biocompatible, biodegradable and non-toxic and can be easily chemically modified to bring functional properties.

For these reasons, the potential of NFC/MFC for paper applications received a lot of attention in the past decade. A positive correlation between the fibrillation rate of the material added to the pulp and paper mechanical performances have been reported by many authors4. Nonetheless, if the high fibrillation of NFC/MFC improve mechanical properties, it also entails the plugging of the inter-fibre pores, which reduces sheets permeability5. The resulting decreasing of drainage rate constitutes a major limiting factor for industrial uses. A threshold then need to be found to maximize the effect on paper strength without damaging drainage rate. The numerous studies addressing this topic report contrasting results depending on the nature and the quantity of fibrillated cellulose added to the pulp. Indeed, different parameters come into play here: (i) the fibrillation rate of the cellulose, (ii) the pre-treatment of NFC/MFC and (ii) the amount of material mixed to the pulp. This work aims to better understand the combined effect of these parameters on paper´s structure to identify the optimal conditions leading to the highest performances.
For this purpose, different types of fibrillated material originating from the same softwood bleached kraft pulp are produced: (a) primary fines separated from the pulp with a lab scale pressure screen6; (b) secondary fines separated from refined pulp produced with an industrial single disk refiner; and (c) different NFC/MFC materials produced with a homogenizer using varying high pressure steps. These samples of different degrees of fibrillation are morphologically characterised using methods developed for this purpose7. For a subsample, fluorescent markers are used to localize the added fibrillated cellulose in the sheets. Subsequently, the different materials are mixed to the pulp in different proportions. After testing pulp properties, handsheets of 60 g/m² are prepared on a Rapid – Köthen sheet former (ISO 5269-2:2004) using white water recirculation8. After successful preparation, the properties of the sheets are analysed, using standard paper testing and state of the art methodologies such as CLSM, SEM, and atomic force microscopy.

The comparison between pulp composition, distribution of the fibrillated cellulose within the fibres and sheet properties is expected to give interesting clues to better understand the interactions between fibres and fibrillated cellulose and their effect on pulp properties and paper strength. This presentation will focus on the general design of the experiments which are targeted to evaluate the potential of using such materials in the papermaking production lines.