Phenolic acids such as 4-hydroxybenzoic acid (4-HB) or 3,4-dihydroxybenzoic acid (3,4-DHB) can be obtained from biomass or by a chem-biotech approach from various substrates, including plastic waste . They have been known to have antioxidant activities . Nevertheless, molecules bearing a phenol in the meta position to the acid or ester group, appear to have weaker antioxidant activity than those in the ortho or para positions . Also, the introduction of electrondonating or electron-accepting groups at different positions on the aromatic ring, close to the phenol groups, can enhance the molecule's antioxidant potential . These are often o-methoxy or o-hydroxyl groups and alkyl esters .