Rheology of fibrillated cellulose suspensions after surface modification by organic nanoparticle deposits

The role of surface modification on rheological properties of fibrillated cellulose suspensions has been evaluated under creep, oscillatory, and rotational testing conditions. Two types of fibrillated cellulose were produced by mechanical homogenization, followed by the deposition of poly(styrene-co-maleimide) or SMI nanoparticles containing encapsulated palm oil on the fibril surfaces. During static creep testing, the modified fibrils changed into fully viscous properties, while native fibrils showed viscoelastic behavior at low stresses. A lower viscosity and reduction in hysteresis effects were experienced during steady-state rotational flow testing, together with a reduction in yield stress after modification. A study of viscoelastic properties by oscillatory testing illustrated that the cross-over point between storage and loss moduli was shifted towards lower strains by surface modification as an indication for the enhancement of liquid-like properties observed for SMI/oil nanoparticle dispersions, while the transition point was hardly affected by fibrillation. The variations in rheological properties were overruled by surface modification and reduction in hydrogen bonding interactions of modified fibrillated cellulose, whereas rheological properties of a physical mixture of native fibrillated cellulose suspension and nanoparticle dispersion remained dominated by the fibrillated cellulose.