Towards optimised size distribution in commercial microfibrillated cellulose: a fractionation approach

Today, strong research efforts are focused on finding sustainable materials as alternatives to non-biodegradable petroleum-based materials. One material that has been identified as a strong candidate is cellulose, especially when the macroscopic fibres have been broken down into their constituent fibrous parts, commonly referred to as cellulose microfibrils or nanofibrils. It has been suggested that this type of material can be used for example in barrier films, coatings, paper strengthening agents and dispersion agents (Eichhorn et al. 2010 ; Klemm et al. 2011 ; Moon et al. 2011 ; Lavoine et al. 2012 ). The microfibrillation of cellulose fibres stems from the early 1980s (Turbak et al. 1983 ) but, due to the energy-demanding process of homogenisation or fluidisation, it was not until the early 2000s when energy-reducing pre-treatments, such as enzymatic hydrolysis (Pääkkö et al. 2007 ; Henriksson et al. 2008 ), or oxidative treatments to introduce charges (Saito et al. 2006 ; Wågberg et al. 2008 ), were developed that the research and development really gained momentum (Eichhorn et al. 2010 ; Klemm et al. 2011 ; Moon et al. 2011 ; Lavoine et al. 2012 ). The development has also been further accelerated by the increasing demand for producing high-value-added products from forest raw materials. However, due to the heterogeneous chemical and structural nature of wood and consequently of the pulp produced from it, this type of process naturally produces a chemically and structurally heterogeneous material. This heterogeneity is often decreased by further ultrasonication to break down aggregates remaining after homogenisation and/or ultracentrifugation to exclude particles that do not fulfil some defined size quality criterion (Saito et al. 2006 ; Ahola et al. 2008 ; Wågberg et al. 2008 ; Aulin and Lindström 2011 ). This is however hardly a feasible alternative for large-scale production and it is therefore crucial to characterise the material produced and to facilitate its proper use in suitable products. To make things even more complex, microfibrillated cellulose (MFC) can be produced from basically any cellulose fibre raw material, and this affects the properties of the MFC produced even if the process itself is standardised.