Influence of Low-Molar-Mass Xyloglucans on the Rheological Behavior of Concentrated Cellulose Nanocrystal Suspensions

Hydrogels were prepared at high solid contents (70-100 g/L) with cellulose nanocrystals (CNC) and very short xyloglucans (XGs). At 70 g/L, CNCs form cholesteric liquid crystals regularly spaced by a distance of 30 nm. This structure was preserved after adsorption of XG with a molar mass (M_w) of 20,000 g/mol (XG20) but was lost at 40,000 g/mol (XG40). Rheological measurements discriminated domains where an increasing M_w from XG20 to XG40 gave rise to drastic changes in storage moduli (on 3 orders of magnitude). At 40,000 g/mol, transient systems were obtained and a re-entrant glass-gel-glass transition was observed with increasing XG concentrations. This was interpreted in terms of the length and stiffness of the chain in relation to the inter-CNC distance. Liquid-to-glass-to-gel transitions were attributed to an XG adsorption type according to train or trail conformations or interconnected structures. Such tunable properties may further have implications on the in vivo role of XG during cell wall extension.