Cellulose-Nanofiber-Reinforced Rubber Composites with Resorcinol Resin Prepared by Elastic Kneading

A resorcinol resin/water dispersion and a rubber latex are added to 1% 2,2,6,6,-tetramethylpyperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) dispersed in water, followed by oven drying at 40 degrees C for 20 h to prepare a dried TEMPO-CNF/resorcinol resin/latex rubber (DTRL) mixture with a weight ratio of 1/0.5/3. DTRL is then added to a nitrile-butadiene rubber (NBR) or a carboxy group-containing NBR (X-NBR) sheet, and the mixture is kneaded by a two-roll mill at 20-30 degrees C with high shear forces. The tensile strength and Young's modulus of the crosslinked DTRL/rubber composite sheets remarkably increased from 10 and 12 MPa, respectively, for the reference sheet to 24 and 82 MPa, respectively, for the DTRL/rubber composite sheets containing approximate to 10 vol% TEMPO-CNFs. Scanning electron microscopy revealed that no TEMPO-CNF agglomerates are present in the DTRL/rubber composite sheets. The tensile properties of the composite sheets are the best when a X-NBR sheet and NBR latex are used as the matrix rubber and latex in DTRL preparation, respectively. When water-extracted DTRL (WDTRL, mass recovery ratio approximate to 94%) is used in place of DTRL, the WDTRL/rubber composite sheets show sufficient water resistance, while the tensile properties are almost the same as those of the DTRL/rubber composite sheets.