Preserving Cellulose Structure: Delignified Wood Fibers for Paper Structures of High Strength and Transparency

Abstract

To expand the use of renewable materials, paper products with superior mechanical and optical properties are needed. Although beating, bleaching, and additives are known to improve industrially produced Kraft pulp papers, properties are limited by the quality of the fibers. While the use of nanocellulose has been shown to significantly increase paper properties, the current cost associated with their production has limited their industrial relevance. Here, using a simple mild peracetic acid (PAA) delignification process on spruce, we produce hemicellulose-rich holocellulose fibers (28.8 wt %) with high intrinsic strength (1200 MPa for fibers with microfibrillar angle smaller than 10°). We show that PAA treatment causes less cellulose/hemicellulose degradation and better preserves cellulose nanostructure in comparison to conventional Kraft pulping. High-density holocellulose papers with superior mechanical properties (Young's modulus of 18 GPa and ultimate strength of 195 MPa) are manufactured using a water-based hot-pressing process, without the use of beating or additives. We propose that the preserved hemicelluloses act as "glue" in the interfiber region, improving both mechanical and optical properties of papers. Holocellulose fibers may be affordable and applicable candidates for making special paper/composites where high mechanical performance and/or optical transmittance are of interest.

Lytic polysaccharide monooxygenase (LPMO) mediated production of ultra-fine cellulose nanofibres from delignified softwood fibres

“…19 The ζ-potential of the control holocellulose fibres (−25.4 ± 1.5 mV) corresponded well to previous results obtained with the same type of fibres. 27 Conductometric titration on the fibres also revealed that the LPMOs increased the carboxyl content by 27% and 88% compared to the control. The obtained carboxyl contents were 0.38 and 0.53 mmol g −1 for NcLPMO9E and NcLPMO9F, respectively (Fig.…”

“…The holocellulose fibres were prepared according to a previously reported method. 27 Briefly, softwood spruce sticks were first soaked in water under vacuum, and subsequently treated with 4% (w/w) peracetic acid (PAA) for 45 min at 85°C. The PAA solution was prepared by diluting 38-40% (w/w) PAA solution (Sigma-Aldrich), followed by adjusting the pH to 4.6 using NaOH before the reaction.…”

“…Treatment with PAA selectively removes lignin while preserving the native wood fibre structure without the defects typically present in commercial wood pulp fibres, and the process is environmentally sustainable. 27 The LPMOs were removed after the enzymatic reaction, and the fibres were subjected to mild and short mechanical homogenisation. The structure and morphology of the resulting nanofibres after the reaction with a CBM-containing LPMO and a non-modular LPMO were characterised and compared.…”

Microfibrillated lignocellulose (MFLC) and nanopaper films from unbleached kraft softwood pulp

“…The Klason lignin content was measured according to the standard TAPPI T222 om-02, and sugar analysis was carried out after acid hydrolysis, using a highperformance anion-exchange chromatography Dionex ICS-3000 (Thermo Fisher Scientific Inc., USA) with references of rhamnose, arabinose, galactose, glucose, xylose, and mannose (Herrera et al 2018). The hemicellulose and cellulose contents were calculated based on glucomannan and xylan as the principal hemicelluloses in spruce (Yang et al 2018). Xylan content was calculated based on xylose and arabinose, glucomannan content was calculated based on galactose, glucose, and mannose contents using a 1:3 ratio of glucose: mannose (Sjöström 1993;Walker 2006;Yang et al 2018), and cellulose content was then calculated based on the remaining glucose content.…”

“…The hemicellulose and cellulose contents were calculated based on glucomannan and xylan as the principal hemicelluloses in spruce (Yang et al 2018). Xylan content was calculated based on xylose and arabinose, glucomannan content was calculated based on galactose, glucose, and mannose contents using a 1:3 ratio of glucose: mannose (Sjöström 1993;Walker 2006;Yang et al 2018), and cellulose content was then calculated based on the remaining glucose content.…”