Moisture uptake in nanocellulose: the effects of relative humidity, temperature and degree of crystallinity

Mohit Garg,Mathieu Linares,Varvara Apostolopoulou-Kalkavoura,Tahani Kaldéus,Igor Zozoulenko,Lennart Bergström,Eva Malmström

doi:10.1007/s10570-021-04099-9

Abstract

Foams made from cellulose nanomaterials are highly porous and possess excellent mechanical and thermal insulation properties. However, the moisture uptake and hygroscopic properties of these materials need to be better understood for their use in biomedical and bioelectronics applications, in humidity sensing and thermal insulation. In this work, we present a combination of hybrid Grand Canonical Monte Carlo and Molecular Dynamics simulations and experimental measurements to investigate the moisture uptake within nanocellulose foams. To explore the effect of surface modification on moisture uptake we used two types of celluloses, namely TEMPO-oxidized cellulose nanofibrils and carboxymethylated cellulose nanofibrils. We find that the moisture uptake in both the cellulose nanomaterials increases with increasing relative humidity (RH) and decreases with increasing temperature, which is explained using the basic thermodynamic principles. The measured and calculated moisture uptake in amorphous cellulose (for a given RH or temperature) is higher as compared to crystalline cellulose with TEMPO- and CM-modified surfaces. The high water uptake of amorphous cellulose films is related to the formation of water-filled pores with increasing RH. The microscopic insight of water uptake in nanocellulose provided in this study can assist the design and fabrication of high-performance cellulose materials with improved properties for thermal insulation in humid climates or packaging of water sensitive goods.Graphic abstract

Highlights

Cellulose is one of the most abundant biopolymers on Earth
We find that the moisture uptake in both the cellulose nanomaterials increases with increasing relative humidity (RH) and decreases with increasing temperature, which is explained using the basic thermodynamic principles
Three different types of cellulose nanomaterials (CNMs) foams were produced by ice-templating of 0.5 wt% TEMPO-oxidized cellulose nanofibers (TCNFs), TEMPO-oxidized cellulose nanocrystal (CNC) (TCNCs) and carboxymethylated cellulose nanofibers (CMCNFs) aqueous suspensions in a mold equipped with a copper bottom and teflon walls to allow unidirectional freezing

Summary

Introduction

Cellulose is one of the most abundant biopolymers on Earth. It can be found in wood, algae, tunicates, and cotton usually combined with other components such as hemicellulose and lignin (Cosgrove 2005). Cellulose is a light-weight and versatile material that exhibits a structural hierarchy from the angstrom- to the micrometer scale, and cellulose nanomaterials (CNMs) display a high surface area and tunable surface chemistry making them versatile materials for a variety of applications (Klemm et al 2011; Moon et al 2011; Thomas et al 2018). CNMs in the form of cellulose nanocrystals (CNCs) or cellulose nanofibrils (CNFs) can be produced by acid hydrolysis or mechanical and chemical defibrillation, respectively.

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