Kinetic study of the thermal decomposition of poly(vinyl alcohol)/kraft lignin derivative blends

A kraft lignin derivative (KLD) obtained by reaction with p-aminobenzoic acid/phthalic anhydride, was blended with poly(vinyl alcohol) (PVA) by solution casting from DMSO. PVA and PVA/KLD films were exposed to ultraviolet radiation (Hg lamp, 96 h) and analyzed by thermogravimetry (TG) in inert and oxidative atmosphere. Typical multi-step decomposition profiles were obtained. The apparent activation energy (Ea) of the thermal degradation of the samples was computed by the Vyazovkin method. The KLD degradation presented only small intervals of decomposition degree with constant Ea values. PVA and blends showed intervals of up to 50% in decomposition degree with nearly constant Ea, and smaller intervals in which Ea varies drastically. The influences of samples irradiation and of surrounding gas in TG analysis on Ea are also shown.