Invited Perspective: Current and Potential Use of Highly Fibrillated Cellulose in the Paper and Board Industry

Abstract

The use of microfibrillated cellulose (MFC) in the paper industry has become established following many years of development by both academic and industrial researchers. Commercial installations typically use mechanical disintegration techniques such as refiners and grinders to convert aqueous suspensions of pulp fibres into a material consisting of fibrils and fibre fragments with diameters ranging from the nanometre to the micron scale. MFC suspensions of a few percent solids content show very high viscosity at low shear rates, but also very significant shear thinning behaviour, rapid viscosity recovery after shear and high filtration resistance. MFC added to paper furnishes at up to 5% by weight functions as a strength additive, enabling increases in mineral filler content, improvements in paper properties, reductions in weight and cost savings across a wide range of paper and board grades. As a complementary technology to pulp refining, addition of MFC offers process flexibility as well as improved wet web strength and runnability, reduced air permeability and increased z-direction strength. Although the fine fibrils of MFC do not dewater easily on their own, when added at low levels to paper their effect on machine drainage can be managed without loss of paper machine speed. In recent years, MFC has attracted much interest as a coating material. Layers or films of pure MFC show near-zero air permeability, high resistance to oil and grease and an effective barrier to organic vapours and oxygen. Mixtures of mineral particles and as little as 15% MFC provide an effective surface for water-intensive printing techniques such as flexography and inkjet. Application of MFC suspensions after the wet line of a papermachine has been demonstrated as a practical solution to obtain coatings, exploiting the rheological behaviour of the MFC to achieve excellent holdout onto a poorly-consolidated sheet, and using the vacuum and press sections of the machine to remove excess water. Further development and commercialisation of this technology, together with low cost MFC production and improved product characterisation, should ensure the continued growth of its use in the paper and board industry.