Abstract
Cellulose nanocrystals (CNCs) exhibit outstanding gas barrier properties, which supports their use as a biobased and biodegradable barrier coating on flexible food packaging materials. As highly hydrophilic biopolymers, however, CNCs have a strong sensitivity to water that can be detrimental to applications with fresh foods and in moist conditions due to the loss of barrier properties. In this work, the oxygen and water vapor permeability of polyethylene terephthalate (PET) films coated with CNCs obtained from cotton linters were measured at varying levels of relative humidity, both in adsorption and desorption, and from these data, the diffusion and solubility coefficients were estimated. Therefore, the characterization of CNCs was aimed at understanding the fundamentals of the water-CNCs interaction and proposing counteractions. The CNCs’ moisture absorption and desorption isotherms at 25 °C were collected in the range of relative humidity 0–97% using different techniques and analyzed through GAB (Guggenheim-Anderson-de Boer) and Oswin models. The effects of moisture on the water status, following the freezable water index, and on the crystal structure of CNCs were investigated by Differential Scanning Calorimetry and by X-ray Powder Diffraction, respectively. These findings point to the opportunity of coupling CNCs with hydrophobic layers in order to boost their capabilities as barrier packaging materials.
Highlights
In any cellulosic material, the water content and interactions with the material’s components have a great influence on its final properties
The way in which water molecules interact with cellulose and their distribution within the often complex and heterogeneous system of cellulosic materials are critical to their applications
Cellulose nanocrystals were obtained from cotton linters by the hydrolyzing-oxidative method, already used in previous works [19,31], with a yield of about 50%; the morphological and main chemical characteristics of the CNCs were identical to the ones already described and are recalled in
Summary
The water content and interactions with the material’s components have a great influence on its final properties. A great deal of scientific literature on this topic focuses on water sorption isotherms and other means of studying the interaction of water with cellulose, hemicellulose and lignin components, which are key components of materials in a wide range of applications [2,3,4,5,6]. Through FTIR spectroscopy studies, led to the idea that water molecules are adsorbed to specific sites, both as layered adsorption or as cluster formation. Even at relative humidity( RH) values below 100%, it was possible to establish the number (1.0–1.3) of water molecules that adsorb to a single hydroxyl group [8,9,10]. Studies of the diffusion of water molecules in cellulosic materials led to the conclusion that cellulose wetting can be related to acid-base interactions, weak hydrogen bonding and van der
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