Counterion design of TEMPO-nanocellulose used as-filler to improve properties of hydrogenated acrylonitrile-butadiene matrix

A nanocellulose containing carboxylate groups was prepared from cellulose by catalytic oxidation with the 2,2,6,6-tetramethylpiperidine-l-oxyl radical (TEMPO). The aqueous TEMPO-oxidized cellulose nanofibrils (TOCNs) with lithium (Li+), sodium (Na+) or tetraalkylammonium (+NR4) counterions (TOCN-X) were mixed with aqueous hydrogenated acrylonitrile-butadiene rubber (H-NBR) latex, and TOCN-X/H-NBR composite films were prepared by casting and drying. All of the composite films are transparent and flexible. The TOCN-Na/HNBR (TOCN/H-NBR = 5/100, w/w) composite film has a high Young's modulus of similar to 63 MPa, a high storage elastic modulus of 112 MPa at 25 degrees C, and a low coefficient of thermal expansion (CTE) of 122 ppm/K, whereas the neat H-NBR film has the values o 5.3 MPa, 2 MPa, and 2660 ppm/K, respectively. Microscopy images show that the hydrophilic TOCN-Na elements form grid-like network structures surrounding the hydrophobic H-NBR latex particles. Thus, the hydrophilic TOCN-Na elements cannot penetrate into hydrophobic H-NBR molecules, and the TOCN-Na elements are not homogeneously distributed in the TOCN/H-NBR composite films prepared under the conditions used in this study. Nevertheless, clear improvement of thermal and mechanical properties is achieved for the TOCN/H-NBR composite films at TOCN/H-NBR weight ratios of 1-5/100. TOCN-Li/H-NBR film has the highest Young's modulus, while the hydrophobic TOCN-NR4/H-NBR films have low CTE values < 100 ppm/K.