New approach to classification of cellulose fibrils and suitable methods for their characterization

Nowadays the manufacturing of cellulose micro- and nanofibrils has been significantly developed and products with tailored properties can now be introduced. Different fibrillation methods and chemical treatments generate cellulose fibrils with varied dimensions, branching degree and chemical properties. It would be beneficial to classify the different kind of cellulose fibrils according to their properties with consensual agreement. We present here a classification based on the morphological and chemical properties of cellulose fibrils. We discuss the applicability of classification and different characterization methods for certain grades (from nanowhiskers and nanofibres to nano fibrillated materials with branched or ribbon-like structures) and for different applications. Characterization of cellulose fibrils is challenging not only because of the wide size distribution and high aspect ratio but also due to the wide variety of morphological properties and the complex structure of single fibrils. This paper introduces a set of simple methods which gives the basic characteristics of nanocelluloses. Five commercially available cellulose nano/microfibrils and three self-made samples produced by and birch pulp ground to various levels using supermasscolloider equipment were analysed in detail. Different rheo- and viscometers were tested and a viscosity measurement sensitive towards high aspect ratio fibrils is introduced. The transmittance measurement gives an estimation of the amount of large particles and the optical microscopy effectively detects the amount of unfibrillated material. SEM measurements can be used to analyze the fine structure nanofibers. The aspect ratio, degree of fibrillation, fibril size and the amount of unfibrillated material can be evaluated with a combination of these indirect measurements, which provide a basic set for quality assurance.