EU nano or not nano: An unbiased approach to classifying FiberLean microfibrillated cellulose

FiberLean microfibrillated cellulose (MFC) was assessed against the recent definition of a nanomaterial published by the European Union. FiberLean MFC is made by mechanical grinding with the aim of fibrillating traditional wood pulp fibres to generate a highly networked high surface area structure capable of reinforcing a matrix as a filler or modifying the rheology of liquids and gels. The networked structure is complex; consisting of a broad range of fibre sizes which are challenging for any one characterisation technique to accurately represent. Scanning electron microscopy allows investigators to identify the boundaries of discrete complex fibre structures; the challenge is to represent the whole fibre size range. In this study a method is presented for the unbiased quantification of fibre width size distribution from systematic uniform random sampled high-resolution areas (164 µm \(\times\) $\times$ 164 µm) using automated scanning electron microscope software. From such images the boundaries of both large- and small-scale fibres could be identified and measured, thus represent the complete size range. The resulting size distribution of FiberLean MFC generated using this method does not meet the criteria specified in the EU definition of a nanomaterial.