Color improvment of C 9 hydrocarbon resin by hydrogenation over 2% Pd/γ‐alumina catalyst: Effect of degree of aromatic rings hydrogenation

Color improvement of commercial C 9 hydrocarbon resin (c‐C 9 HR) and prepared C 9 hydrocarbon resin (p‐C 9 HR) has been investigated under various hydrogenation conditions over 2% Pd/γ‐alumina catalysts. The degrees of aromatic rings hydrogenation (DHs) and molecular structure of resin were determined from nuclear magnetic resonance of 1 H and 13 C ( 1 H‐NMR and 13 C‐NMR) and Fourier transform infrared spectroscopy (FTIR) analyses. The starting c‐C 9 HR presented in yellow color (Gardner color No. 8.4). Under the hydrogenation conditions used (H 2 pressure 70 bar, 250°C, and 8 h), the ethylenic proton in c‐C 9 HR was completely removed, but the aromatic rings content remained unaltered and very little change in resin color was observed (Gardner color No.8.1). On the other hand, the starting p‐C 9 HR contained only unsaturated aromatic proton with Gardner color No.17.1. Under similar conditions, aromatic rings in p‐C 9 HR were converted to alicyclic rings, and its color was reduced to Gardner color No.5.7. By varying the DH of aromatics in p‐C 9 HR, two‐step decolorization was observed in which at lower DH (≤10%) the color decreased sharply from 17.1 to 9.3, while further color reduction to 5.7 was obtained when the DH was increased to 94%. It is suggested that both color body and aromatic rings were the main sources contributing to C 9 HR color. Nevertheless, color stability of the resin during heat treatment was significantly improved by hydrogenation especially at DH ≥ 50%. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010