Synthesis of cellulose filament for recycled fiber reinforcement

Abstract

The objective of this master’ thesis was to develop techniques for recycled fiber pre-treatments in order to produce both continuous cellulosic filaments as well as other nanocellulose structures. This exploratory work, therefore, investigated the properties of these materials in applications such as technical filaments and strength enhancers for use in papermaking, respectively.

Recycled fibers obtained from old cardboard was chemically pre-treated by either TEMPO oxidation or carboxymethylation and subsequently disintegrated into cellulose nanofibrils by using both homogenization and microfluidization. The surface hydroxyl groups (-OH) of the recycled, cellulosic fibers were successfully converted to carboxylic (-COOH) groups to different extent. The presence of carboxylic functional groups was confirmed by FTIR and conductometric titration. Homogenization and microfluidization were used in order to deconstruct the pretreated cellulosic fibers into small fibrils. The carboxymethylated fibers required higher mechanical energy than the TEMPO-oxidized ones. This was explained by the lower carboxylic group content introduced onto the fiber surface in the former system. The cellulose nanofibrils were examined via Scanning Electron Microscopy (SEM) and their size was assessed by the Atomic Force Microscopy (AFM). The nanofibrils were found to be 10-50 nm in width and several microns in length. From these efforts, it was concluded that nanofibrils can be obtained relatively easily from recycled fibers.

Two potential applications of the isolated cellulosic nanofibrils were addressed in this thesis. First, the production of continuous filaments by wet spinning and, secondly, the development of fibrils for deployment as additives for enhancing the mechanical strength of paper by addi-tion in the wet-end. The filaments produced from cellulosic nanofibrils from recycled cardboard displayed slightly lower tensile strength compared to those from cellulose nanofibrils obtained from bleached virgin fibers. The addition 0f a co-adjuvant to the fibril hydrogel dope, namely, poly vinylalcohol, improved the dry and wet tensile strength properties of the filaments. More remarkably, however, was our finding in relation to paper strength enhance-ment: a significant improvement in mechanical strength (tensile strength, stiffness, and TEA) was observed upon addition of the nanofibrils to fibrt disperions followed by drainage and drying. In addition, lower paper surface porosity was measured. Provided the negative effects realized in dewatering are minimized, the results indicate a new potentially promising use for recycled fibers.