The Change of Lignin Structure of the Triploid of Polulus Tomentosa during Kraft Pulping

The Chinese northern fast-growing hardwood-Triploid of Polulus Tomentosa was used as the raw material in this study.Conventional kraft pulping was carried out.The two-stage method was used to prepare the lignin from raw material and the lignin from the pulp.The acid-precipitating method was used to separate the dissolved lignin from the black liquor and the crude lignin was further purified by mild-acidic hydrolysis.The lignin samples were studied with GPC, and the changes of molecular weight during KP were investigated and compared.The lignin()~(31)P-NMR spectra of different lignin samples were obtained and the functional groups of the lignin were quantitatively analyzed and compared in order to discover the change of lignin structures during kraft pulping.