The effects of oxidant dosage

oxidation temperature and time on the degradation of soda lignin by hydrogen peroxide with and without the presence of microwave irradiation were investigated.It is found that the oxidative degradation of lignin includes the cleavage of ether bond in

β-O-

4 structure

the partial destruction of aromatic ring

and the re-condensation of the degraded lignin.Compared to the conventionally heated oxidation of lignin

the microwave irradiation efficiently facilitates the degradation of the lignin with high molecular weight and the re-condensation of that with low molecular weight at a low oxidant dosage

low oxidation temperature

or a short oxidation time

which leads to the formation of the degraded lignin with narrower molecular weight distribution and lower molecular weight.Additionally

the lignin degraded in the presence of microwave irradiation has the characteristics of higher content of phenolic hydroxyl group

lower content of methoxyl group

and lower degree of condensation

which enhances the reactivity of lignin.Therefore

the oxidative degradation of lignin assisted by microwave irradiation may be a new pretreatment approach for efficiently utilizing the soda lignin.