Abstract
The use of nanomaterials and polymers from renewable resources is important in the search for sustainable alternatives to plastic-based packaging materials and films. In this work, self-supporting thin films prepared from derivatized and non-derivatized nanocellulose and cellulose derivatives were studied. The effect of drying temperature on the film-forming behavior of compositions comprising hydrophobically modified ethyl(hydroxyethyl)cellulose (EHEC), native microfibrillated cellulose (MFC) and nanocellulose made from methyl cellulose was determined. The interaction between the components was assessed from viscosity measurements made at different temperatures, the result being linked to a thermal-dependent association during liquid evaporation, and the subsequent barrier and film-forming properties. The effect of temperature on suspensions was clearly different between the materials, confirming that there were differences in interaction and association between EHEC–MFC and methyl nanocellulose–MFC compositions. The amphiphilic EHEC affected both the suspension homogeneity and the film properties. Air bubbles were formed under certain conditions and composition particularly in MFC films, dependent on the drying procedure. The presence of air bubbles did not affect the oxygen transmission rate or the oil and grease resistance. An increasing amount of MFC improved the oxygen barrier properties of the films.
Highlights
Fossil-based polymers are used in packaging applications because of their high barrier properties and low manufacturing costs, but environmental concerns have increased the need to develop renewable materials for barrier applications (Lavoine et al 2012) and interest in the utilization of cellulosic materials for barrier applications has grown considerably.The barrier properties of microfibrillated cellulose (MFC) have been studied widely
The oxygen transmission rate (OTR) of MFC films is low under dry conditions due to the dense network, but it increases with increasing relative humidity (Aulin et al 2010; Osterberg et al 2013; Herrera et al 2017), because the increase in relative humidity weakens the hydrogen bonds and the structure of the cellulose network is loosened
Viscosity measurements showed that there was an interaction between the components in the EHEC– MFC and methyl nanocellulose–MFC compositions, indicated by changes in initial viscosity and in gelation temperature
Summary
Fossil-based polymers are used in packaging applications because of their high barrier properties and low manufacturing costs, but environmental concerns have increased the need to develop renewable materials for barrier applications (Lavoine et al 2012) and interest in the utilization of cellulosic materials for barrier applications has grown considerably.The barrier properties of microfibrillated cellulose (MFC) have been studied widely. The dense network and the crystalline regions of MFC hinder other molecules such as oxygen from penetrating through the film (Syverud and Stenius 2009; Lavoine et al 2012; Osterberg et al 2013). The oxygen transmission rate (OTR) of MFC films is low under dry conditions due to the dense network, but it increases with increasing relative humidity (Aulin et al 2010; Osterberg et al 2013; Herrera et al 2017), because the increase in relative humidity weakens the hydrogen bonds and the structure of the cellulose network is loosened. The crystalline regions are impermeable to water and a lower OTR can be achieved with nanocellulose films at high relative humidities (Herrera et al 2017; Solala et al 2018). The water vapor transmission rate (WVTR) and water sorption of MFC are high due to the amorphous regions of the cellulose and they increase with increasing relative humidity (Aulin et al 2010; Tammelin et al 2015), so that MFC is a poor or only moderate water vapor barrier
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