Relatively Independent Motion of a Continuous Nanocellulose Network in a Polymer Matrix

Nanocellulose has been studied extensively in polymer composites as it can be employed as biobased reinforcement for synthetic polymers. However, the challenge to optimize the reinforcing component to consume applied energy as much as possible remains. This is related to the reacting force in the test sample and its extensibility. Prolonging the fracture strain of the material is one of the most effective strategies for such a purpose. The investigation on nanocellulose movement in a polymer matrix could shed light on the nanocellulose reinforcing mechanism's fundamental understanding. In this work, a continuous nanocellulose network was used to prepare nanocellulose/polymer composites. Different from using noncontinuous nanofillers, e.g., cellulose nanofibers and nanocrystal, the regenerated cellulose gel network used in this work could move together with the polymer under an axial signal force, serving as an excellent model advantageous in investigating the movement of nanocellulose in the polymer matrix. The deformation of the nanocellulose in the matrix was able to be evaluated by tracking the fracture strain of the materials. A series of chemical cross-linked nanoporous cellulose hydrogels (CCNCGs) were prepared, and their fracture strain increased first and then decreased as the molar ratio of epichlorohydrin (ECH) to the anhydroglucose unit (AGU) of cellulose increased. Two polymer matrices, polycaprolactone (PCL) and polyurethane (PU), were selected to be polymerized in CCNCGs in situ. The fracture strain of CCNCG/PCL and CCNCG/PU nanocomposites in the tensile test showed the same tendency as neat CCNCGs in the hydrated state, regardless of the surrounding environment. The relatively independent motion of the nanocellulose network in the polymer matrix was clearly demonstrated. Possible mechanisms of the nanocellulose's independent motion in the polymer matrix were discussed, implying the potential of independent deformation of the continuous nanocellulose network in the polymer matrix.