Abstract
High-pressure differential scanning calorimetry (HPDSC) was used to determine the oxidative stability of various rosins and rosin products. Gum rosin was considerably more stable to oxidation than were wood rosin and tall oil rosin, suggesting the presence of more natural antioxidant in gum rosin. Hydrogenation, polymerization and disproportionation of rosin all resulted in increased oxidative stability, presumably due to the decrease in conjugated double-bond structures typical of abietic acid-type molecules. Esterification of rosin with glycerol or with pentaerythritol also increased oxidative stability. HPDSC exotherms were also determined for six purified rosin acid structures including abietic, neoabietic, palustric, levopimaric, isopimaric and dehydroabietic acid. Dehydroabietic acid was far more stable to oxidation than the others. In general, the HPDSC results fit the picture that an allylic H atom is oxidized much faster than a nonallylic H atom, and that two conjugated double bonds result in extreme activation.
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