H. Kangas, J. Pere, P. Qvintus
VTT Technical Research Centre of Finland Ltd.,
Keywords: cellulose nanofibrils, CNF, enzyme, high consistency, cost efficiency, applications
Summary:Cellulose nanofibrils (CNF) are promising bio-based materials for numerous applications, either as replacement of oil-based materials in existing products, potentially with added functionality, or in generating completely new materials and products. The production of material consisting of thin cellulose fibrils with unique properties was invented already in the 1980’s. However, back then the high energy consumption needed for production proved to be an obstacle for industrial production. Extensive research since then has resulted in more feasible production concepts and led to pilot, pre-commercial and even commercial plants all over the world. Despite the rapid development, some challenges still remain with the traditional production of CNFs by mechanical treatments alone or in combination with enzymatic or chemical pre-treatments. Usually the production costs are still high, and the resulting material is at low consistency. The high water content generates problems, such as difficulties in dewatering and drying, problems in post-treatment and restricted applicability for certain applications, such as composites. In addition, long-distance transportation is not feasible leading to limited availability of the material. In the high-consistency enzymatic fibrillation (HefCel) technology, recently developed at VTT, cellulose fibrils are produced at high consistency (20-40%). The raw material is gently agitated at high consistency (20-40%) in the presence of cellulase enzyme cocktail, resulting in fibrillation due to the high fibre-fibre friction in low water content and resulting in paste-like material in appearance. The degree of fibrillation can be adjusted by the enzyme dosage and the treatment time. In addition, the fibrillated cellulose material can be further modified after treatment at high consistency. The method is applicaple to diverse feed stocks; wood and non-wood pulps, recycled fibres, textile waste, agro-based residues etc. The HefCel fibrillated material could be used instead of the traditional cellulose nanomaterials in applications where cheaper, rather homogenous, but highly fibrillated material is needed. Examples of potential applications include reinforcement of paper and packaging materials, ductile films with good barrier properties, air filters, novel cellulose structures e.g. by 3D printing, such as scaffolds for regenerative medicine, machineable hard objects for replacement of plastics, electronic components (e.g. bio-based batteries) and biocomposites (e.g. reinforcement of PLA and PHB). The benefits of the HefCel technology compared to the traditional CNF production include simple and economic process, the high material consistency enabling off-site production and long-distance transportation, easy-to-handle material and enhanced water removal and drying. The process has been shown to result in significant reductions in the energy needed for fibrillation and the chemical costs are also reasonable. In addition, there is a potential revenue from a valuable by-product of the process, cellobiose. With the HefCel technology, problems related to the low consistency of cellulose nanofibrils are solved and thus, the use of CNFS in commercial applications in various industrial branches can be envisaged.