Extraction and examination of residual lignin from sulphate pulp

The goal of the research work is extraction and investigation of residual lignin from sulfate pulp. The subject of the research is hardwood sulfate pulp produced by OJSC “Mondi Syktyvkar” – the largest paper producer in Russia. Three different pulp samples were investigated: • Pulp sample 1 – unbleached sulphate pulp after cooking: • Pulp sample 2 – sulphate pulp after the first bleaching stage (hydrogen peroxide in acid medium as a bleaching agent): • Pulp sample 3 – sulphate pulp after the second bleaching stage (hydrogen peroxide in alkali medium as a bleaching agent). Sample 1 came directly from “Mondi Syktyvkar”, samples 2 and 3 were produced in the laboratory of Chemical Department, Syktyvkar Forest Institute. The pulp samples were further analyzed by different methods: extractive substances content were determined, aldehyde groups content was found by a photocolorimetric method, Kappa number was determined by permanganate index, and finally electron microscopy of the three samples was done. Further, residual lignin extraction from sulphate pulp was conducted, and the lignin samples obtained were conducted by ÑÍ3ÑÎÎÍ-Í2Î – ZnCl2 blend. Extracted residual lignin was estimated by Komarov’s method, the amount of carboxyl groups in lignin was determined by potentiometry method, lignin molecular weight was calculated by cryoscopy method. Finally, infrared and nuclear magnetic resonance spectroscopy methods were used to analyze extracted lignin spectrum. During the bleaching process, the lignin content of the pulp decreased from 16 to 9 Kappa units. Also, a reduction in the amount of aldehyde group was observed after the second bleaching stage compared to the first stage. Komarov’s method showed that residual lignin content decreased from 6 to 4 % for unbleached and bleached pulp (after I bleaching stage) respectively. The molecular weight of residual lignin, extracted from unbleached sulphate pulp, is higher than the one from bleached pulp. Spectroscopy methods showed that the residual lignin is composed of guaiacyl and syringal structures, typical for hardwood pulp lignin.Validerat; 20101217 (root