Hybrid nanopaper of cellulose nanofibrils and PET microfibers with high tear and crumpling resistance

Cellulose nanofibrils (CNF), once filtered and dried, have the particularity to form a highly cohesive network, nanopaper. One of the drawbacks of all CNF nanopapers is their relative brittleness and low tear resistance, measured as the force needed for crack propagation after introducing a notch. In this work, hybrid nanopapers with drastically improved tear and crumpling resistance were produced by introducing polyethylene terephthalate (PET) microfibers into the CNF suspension prior to sheet fabrication. The PET microfibers were well dispersed in the CNF suspension and subsequently evenly distributed in the formed sheets. Incorporation of 10wt% PET fibers increased the dry tear resistance with notch by a factor of 10 while still maintaining most of the mechanical properties. This effect is attributed to the loosely bound PET fibers which limit the crack propagation by dissipating the energy. It was also possible to improve the wet tear resistance by a factor of 4. Furthermore, incorporation of PET fibers allowed for crumpling of nanopaper that previously was so brittle it shattered from the deformation. Finally, incorporation of PET fibers also improved the crumpling resistance of wet samples. The improved wet properties, together with a higher and tunable porosity, open up the possibility to use these hybrid nanopaper sheets in filtration applications. [GRAPHICS]