Study on sulfomethylation of kraft lignin for use as a superplasticizer

리그닌;sulfomethylation;전하밀도;시멘트 유동성;리그닌 개질;음전하;634.9

농업생명과학대학 산림과학부 ;

University:서울대학교 대학원

关键词: 리그닌;    sulfomethylation;    전하밀도;    시멘트 유동성;    리그닌 개질;    음전하;    634.9;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/141796/1/000000150724.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

The large amount of kraft lignin has been produced from kraft pulping and incinerated to be converted to energy. However, kraft lignin has a possibility to be used as more value-added material via chemical modification. Lignosulfonate produced by sulfite pulping is used as a superplasticizer, but the production of lignosulfonate has been dwindled because sulfite pulping has been substituted to kraft pulping. Therefore, there are a lot of efforts to substitute lignosulfonate to kraft lignin via a variety of chemical modification. In this study, sulfomethylation of kraft lignin was conducted by using formaldehyde and sodium sulfite in sodium hydroxide solvent with various reaction conditions. And then, final pH was adjusted with sulfuric acid (1 M) followed by centrifugation (12000 rpm, 15 min) to separate liquid and solid phases. Dried-solid sample was obtained by freeze-drying. Sulfomethylation of kraft lignin was conducted at final pH (7, 5 and 2), reaction temperature (80, 100 and 120℃), reaction time (1, 3, 5, 8 and 11 h), the dosage molar ratio of reagents (formaldehyde and sodium sulfite) to lignin (0.225, 0.45, 0.9 and 1.2:1). A particle charge detector (PCD) was utilized to measure charge density of the sulfomethylated kraft lignin by using a titrant (polydiallyldimethylammonium, PolyDADMAC). By fourier-transform infrared (FT-IR) spectroscopy analysis, the changed functional group on lignin could be examined, and the different ratio of guaiacyl and syringyl group could be investigated by phosphorus-31 nuclear magnetic resonance (31P-NMR). Furthermore, elementary analysis was utilized to compare the content of sulfonate. Through these analyses, the characteristics of sulfomethylated lignin under different reaction conditions were compared. As a result of this study, the reaction condition for the highest charge density was determined as pH 5 for final pH, 100℃ for reaction temperature, 5 h for reaction time and 0.9:1 for the dosage molar ratio of reagents to lignin. On the other hand, the maximum fluidity of cement was obtained at pH 5 for final pH, 100℃ for reaction temperature, 3 h for reaction time and 0.45:1 for the dosage molar ratio of reagents to lignin. It was anticipated that more charge density made workability of cement increase, but the tendency between charge density and fluidity of cement was not corresponded.Moreover, there was not proportional tendency among the content of sulfur, charge density and fluidity of cement. According to similar studies, polycarboxylate which had high molecular weight, low charge density and longer chain structure was compared to sulfonated naphthalene formaldehyde condensate (SNFC), which had low molecular weight and high charge density. As a result, cement fluidity was better in case of polycarboxylate. Moreover, the separation of lignosulfonate with different molecular weight was carried out, and viscosity of cement paste was not proportional to molecular weight. Considering charge density and molecular weight were not in proportional relation with fluidity of cement, longer chain structure may have been regarded as the key factor for high fluidity of cement. To investigate the influence of constituent unit of lignin in sulfomethylation, softwood kraft lignin (SKL) was sulfomethylated in same reaction condition and compared to hardwood kraft lignin (HKL). SKL which had more guaiacyl group indicated higher charge density and fluidity of cement than HKL.