Abstract
Plant-based polysaccharides (cellulose and hemicellulose) are a very interesting option for the preparation of sustainable composite materials to replace fossil plastics, but the optimum bonding mechanism between the hard and soft components is still not well known. In this work, composite films made of cellulose nanofibrils (CNF) and various modified and unmodified polysaccharides (galactoglucomannan, GGM; hydrolyzed and oxidized guar gum, GGhydHox; and guar gum grafted with polyethylene glycol, GG-g-PEG) were characterized from the nano- to macroscopic level to better understand how the interactions between the composite components at nano/microscale affect macroscopic mechanical properties, like toughness and strength. All the polysaccharides studied adsorbed well on CNF, although with different adsorption rates, as measured by quartz crystal microbalance with dissipation monitoring (QCM-D). Direct surface and friction force experiments using the colloidal probe technique revealed that the adsorbed polysaccharides provided repulsive forces–well described by a polyelectrolyte brush model – and a moderate reduction in friction between cellulose surfaces, which may prevent CNF aggregates during composite formation and, consequently, enhance the strength of dry films. High affinity for cellulose and moderate hydration were found to be important requirements for polysaccharides to improve the mechanical properties of CNF-based composites in wet conditions. The results of this work provide fundamental information on hemicellulose-cellulose interactions and can support the development of polysaccharide-based materials for different packaging and medical applications.
Highlights
The increasing urge to replace petrol-based materials has aroused interest in biodegradable, environmentally friendly, and sustainable novel materials
They speculated that the reason for this is the b-configuration of the C-4 in Gal that might sterically hinder the formation of the oxidation intermediates
Even if GGM contains more accessible (1 ! 6)-bonded Gal side-groups, and even if some of the oxidations were performed at room temperature, no significant degradation could be observed during the oxidations (Figure 2)
Summary
The increasing urge to replace petrol-based materials has aroused interest in biodegradable, environmentally friendly, and sustainable novel materials. Cellulose nanofibrils (CNF) with diameters at the nanoscale received much attention due to their outstanding chemical and mechanical properties (Chen et al 2010; Lee et al 2012a; Klemm et al 2011) They were utilized for a wide range of applications (Klemm et al 2011), such as membranes (Mautner et al 2014, 2015), flame-retardant and fireprotection applications (Carosio et al 2015, 2016; Liu and Berglund 2013) and in particular for the production of composites (Blaker et al 2011; Lee et al 2009, 2012b c, 2014b; Nogi and Yano 2008; Lee and Bismarck 2012; Eichhorn et al 2010; Pommet et al 2008; Wan et al 2006). One approach to utilize the potential of CNF was to directly reinforce a soft matrix with small amounts of CNF, which resulted in improved strength of the composites provided that the affinity between matrix and cellulose fibrils was high enough. Native cellulose has a high molecular weight of about 1.5 million mol/g (Kraemer 1938, Gralén, Svedberg 1943)
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