Toughening mechanisms in cellulose nanopaper: the contribution of amorphous regions

Rui Mao,Nan Meng,Wei Tu,Ton Peijs

doi:10.1007/s10570-017-1453-0

Rui Mao, Nan Meng + Show 2 more

https://doi.org/10.1007/s10570-017-1453-0

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Abstract

Cellulose nanopaper is a strong and tough fibrous network composed of hydrogen bonded cellulose nanofibres. Upon loading, cellulose nanopaper exhibits a long inelastic portion of the stress–strain curve which imparts high toughness into the material. Toughening mechanisms in cellulose nanopaper have been studied in the past but mechanisms proposed were often rather speculative. In this paper, we aim to study potential toughening mechanisms in a systematic manner at multiple hierarchical levels in cellulose nanopaper. It was proposed that the toughness of cellulose nanopaper is not, as is often assumed, entirely caused by large scale inter-fibre slippage and reorientation of cellulose nanofibres. Here it is suggested that dominant toughening mechanism in cellulose nanopaper is associated with segmental motion of molecules facilitated by the breakage of hydrogen bonds within amorphous regions .

Highlights

Cellulose widely exists in plant cell walls in the form of microfibrils (Barnett and Bonham 2004; Keckes et al 2003)
Some nanofibres are less loaded than others with strain values at every position in the nanopaper exceeding the value at the transition from elastic to inelastic region, indicating that inelasticity occurs throughout the whole cellulose nanopaper
Cellulose nanopaper is a strong and tough fibrous network composed of hydrogen bonded cellulose nanofibres

Summary

Introduction

Cellulose widely exists in plant cell walls in the form of microfibrils (Barnett and Bonham 2004; Keckes et al 2003). Cellulose nanofibres can be extracted in the form of individual microfibrils and/or their aggregations by deconstructing the cell wall structure (Eichhorn et al 2010). The amorphous cellulose is present at the surface of the crystallites. Cellulose crystals prepared via acid hydrolysis displayed a crystallinity index of about 80% (Kargarzadeh et al 2012), which suggests a contribution of cellulose chains within the crystallite surface to the amorphous phase of the nanofibres. Cellulose nanopaper is a fibrous network composed of cellulose nanofibres connected together by van der Waals forces and hydrogen bonding. Typical stress–strain curves of cellulose nanopaper show an elastic region followed by a long inelastic region where the toughness primarily originates from. The exploration of toughening mechanisms in cellulose nanopaper should focus on mechanisms of inelasticity in such nanopapers

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