Rheology of cellulose nanofibers in paper making: An overview

Today, the use of cellulosic nanofibers is widely researched for the production of various products, such as paper and paperboard. Cellulose nanofibers are made from pulp produced from various lignocellulosic sources in various methods. The quality of these materials can be evaluated in different ways. Meanwhile, the rheology indices of cellulosic nanofibers are one of the simplest and least costly methods to evaluate the quality of this material. In this paper, specifically, the relationship between indices of rheology of cellulosic nanofibers and their ability to improve paper and board strengths for papermaking are introduced.

In this article, materials were categorized in terms of rheology sciences and cellulose nanofibers were specified among them. Then, important indices of rheology of cellulose nanofibers such as yield point, damping coefficient, storage modulus, loss modulus, and yield strain were introduced by presenting some of the results of measuring the rheological indices of cellulosic nanofibers. In the following, the relationship between rheological indices and strengthening ability of cellulose nanofibers to improve tensile and burst strengths of paper and paperboard production were investigated.

The more storage modulus, as the most sensitive parameter in viscoelastic measurements compared to the loss modulus, the more viscoelastic ability and more elastic tendency. For cellulose nanofibers, if the ratio of the storage modulus is about 4 times greater than the loss modulus in the same concentrations, this indicates that the material is viscoelastic with considerable elasticity. If the amount of damping coefficient for cellulose nanoparticle gel is less than 0.3, this indicates that these gels are highly elastic with components in the nanometer scale and these characteristics indicate the presence of tangled cellulose nanofiber network and as a result, more strengthening feature is available for a variety of applications as strengthening paper and paperboard products. The critical strain on the behavior of the cellulosic nanofiber’s rheology appears almost independent of its dry matter content which implies the sustainability of the viscoelastic properties of these gels. The thick and dilute produced nanofiber gels have an exponential, with power 3, relationship with dry content (n ∝ G∅). The exponential, with power 3, relationship between the modulus and dry matter percentage is one of the criteria for the achievement of a gel of nanoscale cellulosic fibres.

In general, cellulose nanofibers gel is considered as a viscoelastic and thixotropic fluid and when used in paper and paperboard productions, the higher elastomeric index of it creates more strength properties of products. Therefore, in order to predict the achievement of nanosized fibres gel during production, a cheaper evaluation of the cellulosic rheology indices could be used instead of expensive images and even with the comparison of two types of cellulosic nanofibers, their rheological properties predict their performance for reinforcing paper and paperboard.