Biomacromolecules, Vol.20, No.12, 4457-4465, 2019
Physical Modification of Cellulose Nanocrystals with a Synthesized Triblock Copolymer and Rheological Thickening in Silicone Oil/Grease
This study investigates the rheological thickening effect of surface-modified cellulose nanocrystals (mCNCs) with a triblock copolymer on silicone oil. An amphipathic copolymer comprising hydrophilic methoxypolyethylene glycols and hydrophobic polydimethylsiloxane segments is synthesized and introduced in silicone oil by physical adsorption of rodlike cellulose nanocrystals (CNCs). The surface-modified copolymer acts as a "bridge" to enhance the compatibility between CNCs and base oil, which produces the hybrid oils/greases containing homogeneously dispersed mCNCs at varied loading levels of 5-20 wt %. The presence of this rigid additive remarkably increases the viscosity of silicone oil, accompanied with the transition from flowable to nonflowable behavior with a gradual increase of mCNC loading levels. Furthermore, the change of storage and loss modulus of the fabricated hybrid oils/greases indicates the formation of a three-dimensional network by the chain entanglement and interactions between the copolymer and silicone oil (at a critical loading level of 15 wt % mCNC), which promotes the rigid CNCs to act as the physical cross-linking point for the significant transition from liquid to quasi-solid state.