Suberinic Acid Isolation from Birch Outer Bark and their Characterization

Abstract

Global sustainability challenges prompt the world to modify their strategies and shift from a fossil-fuel-based economy to a bio-resources-based one and to the production of renewable biomass-based chemicals. Different processes exist that allow the transformation of raw biomass into desirable bio-based products and/or energy. Depolymerized suberinic acids (SA) can be considered as an alternative resource to different feedstocks for value-added product obtaining, for example to develop bio-polyols that can be further used in polymeric material production. Birch outer bark was used as a raw material for obtaining SA and was extracted with ethanol to remove extractives. Further extracted birch outer bark was depolymerized with potassium hydroxide ethanol/methanol/n-butanol/2-propanol solutions. Obtained SA suspension was dried by performing lyophilization or by drying at 100 °C. As a result, we obtained 8 SA samples, which were characterized using chemical (total phenolics content, solubility in DMSO, acid number, hydroxyl number, and saponification number) and instrumental analytical methods (GC-MS, SEC-RID, FTIR). The most suitable SA for obtaining value-added product, such as bio-polyol, were obtained by using ethanol as a solvent for depolymerization process. The corresponding SA had the best results in terms of dry matter content, yield, solubility in DMSO, epoxy groups, acid number and ash content. After GC-MS results it was concluded that the amount of diacids, hydroxyacids and extractives are dependent of the used alkanol for SA depolymerization as well as the drying method.