Cellulose Nanofibril (CNF) Films and Xylan from Hot Water Extracted Birch Kraft Pulps

Marc Borrega,Hannes Orelma

doi:10.3390/app9163436

Marc Borrega, Hannes Orelma

Open Access

https://doi.org/10.3390/app9163436

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Abstract

The effects of xylan extraction from birch kraft pulp on the manufacture and properties of cellulose nanofibril (CNF) films were here investigated. Hot water extractions of bleached and unbleached kraft pulps were performed in a flow-through system to remove and recover the xylan. After the extraction, the pulps were oxidized with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and fibrillated in a high-pressure microfluidizer. Compared to CNF from bleached kraft pulp, the CNF dispersions obtained from water-extracted pulps were less viscous and generally contained a higher amount of microfiber fragments, although smaller in size. In all cases, however, smooth and highly transparent films were produced from the CNF dispersions after the addition of sorbitol as plasticizer. The CNF films made from water-extracted pulps showed a lower tensile strength and ductility, probably due to their lower xylan content, but the stiffness was only reduced by the presence of lignin. Interestingly, the CNF films from water-extracted bleached pulps were less hydrophilic, and their water vapour permeability was reduced up to 25%. Therefore, hot water extraction of bleached birch kraft pulp could be used to produce CNF films with improved barrier properties for food packaging, while obtaining a high-purity xylan stream for other high-value applications.

Highlights

Cellulose nanomaterials, which include cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), are a relatively new family of cellulosic materials with at least one dimension in the nanometre scale [1]
Bleached and unbleached birch kraft pulps were extracted with water at 240 ◦ C in a flow-through reactor to partially remove the xylan prior to fibrillation and preparation of CNF films
The xylan content was reduced by 70% after 10 min of extraction time, and the lignin content remained the same (~3% on pulp) even if about 25% of the lignin in the original unbleached pulp was removed

Summary

Introduction

Cellulose nanomaterials, which include cellulose nanofibrils (CNF), cellulose nanocrystals (CNC), and bacterial cellulose (BC), are a relatively new family of cellulosic materials with at least one dimension in the nanometre scale [1]. Both CNF and CNC are obtained from wood and plants, but CNF are prepared by mechanical fibrillation of chemical pulps (often after a suitable pre-treatment), and CNC are prepared by acid hydrolysis of highly purified cellulosic substrates (i.e., cotton, microcrystalline cellulose, filter paper). Since cellulose-based films are rather brittle, the addition of plasticizers is often required to reach the desired workability and performance

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