Structural modification of Kraft lignin after acid treatment: characterisation of the apolar extracts and influence on the antioxidant properties in polypropylene

Kraft lignin and vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol, used as model compound) were treated under acidic conditions (sulphuric and hydrochloric acid). Hydroxyl content and molar masses of dichloromethane extracted fractions were determined. The acidic treatment decreased the aliphatic hydroxyl content and so lowered the polarity of the lignin molecules without derivatization. Antioxidant properties in polypropylene of the treated fractions were increased compared to that of untreated ones.