Attempt to approach the role of phenolic phenylpropenol structures in the photoyellowing of softwood mechanical pulps

Abstract

Three biphenyl (I, II, III) compounds and a benzylarylether (IV) compound were synthesized to detect and quantify the presence of phenolic phenylpropenols in unbleached, peroxide-bleached, or sodium borohydride-reduced mechanical softwood pulps. The methodology used is based on a gas chromatography – mass spectrometry search of the prepared compounds in the residue obtained after ethylation, thioacidolysis, and desulfurization of the pulps. Detection of biphenyl I ([Formula: see text]4 × 10–6 mol g–1) in unbleached and NaBH4-reduced pulps is indicative of the presence of phenolic coniferaldehyde units in these pulps. Traces of biphenyl II, found in the peroxide-bleached pulp, probably came from ferulic acid units formed by oxidation of coniferaldehyde by H2O2. No biphenyl ether III or benzylaryl ether IV were detected in the three pulps. This result indicates that phenolic phenylpropenol units are not present in softwood mechanical pulps and do not contribute to the fast part of their photoyellowing.Key words: mechanical pulp, photoyellowing, phenol, coniferyl alcohol, biphenyl.