A sustainable approach to produce light-colored rosin and rosin esters during processing using natural antioxidants

Rosin is a biobased product from pine trees used as raw material in several industries. However, rosin is prone to oxidation during thermal treatments, causing material degradation and particularly darkening. Synthetic antioxidants are used to produce light-colored rosin or rosin esters. Nevertheless, concerns about their use have prompted searches for natural alternatives. This study aims to replace synthetic antioxidants with natural alternatives for rosin processing. A preliminary screening of eight natural antioxidants allowed to show that by using α-tocopherol or thymol, rosin samples with Garnder color very similar to those obtained using the synthetic antioxidant Lowinox TBM-6 can be obtained. Further analysis was carried out by combining them with iodine, with inert atmosphere or both. Results showed that similar values of Gardner color, acid number, and softening point can be obtained using Lowinox TBM-6 and natural antioxidants and, when combining α-tocopherol or thymol with inert atmosphere and iodine, the resulting rosins or rosin esters have better Gardner color than by using Lowinox TBM-6. Moreover, gas chromatography coupled with mass spectrometry (GC-MS) and Fourier transform infrared coupled with attenuated total reflection spectroscopy (FTIR-ATR) analysis showed that rosins and rosin esters with similar chemical compositions can be obtained using synthetic and natural antioxidants confirming the enormous potential of the natural alternatives for the oxidative stability of rosin and rosin esters. Finally, the detailed GC-MS analysis of rosin samples enables understanding the essential role of iodine combined with the antioxidants to prevent rosin darkening. • A process to prevent rosin oxidation during thermal treatment with natural antioxidants. • A process to prevent rosin oxidation during esterification with natural antioxidants. • Tocopherol or thymol combined with iodine and nitrogen allow improved processed rosin. • The proposed solution is a good alternative to synthetic antioxidant Lowinox TBM-6.