Soda lignin from rice straw was sulfomethylated, and the dispersion ability of sulfomethylated lignin was compared with that of commercial softwood lignosulfonate. The results are summarized as follows :
(1) Black liquor from soda cooking of rice straw was adjusted to pH 8.2 with aq. sulfurous acid. Same mole of formaldehyde as sodium sulfite formed in black liquor was added, and then dissolved lignin was directly sulfomethylated (SML I). Sulfomethylated black liquor was separated by gel filtration method (SML II : 0.18 S/C6-C3).
(2) SML I shows the similar standard dispersion number (SDN), regardless of max. temperature of soda cooking and reaction time of sulfomethylation.
SDN of sulfomethylated liquor including SWL I, however, is inferior to that of lignosulfonate. This may be due to the low content of sulfonic acid group and low purity of SML I. In order to utilize straw soda lignin as dispersant, it is necessary to isolate soda lignin from black liquor and to sulfomethylate the isolated soda lignin.
(3) The setting time of mortar with SML II show the relatively similar results to that of commercial lignosulfonate. SML I, however, requires a long period of the setting time. The utilization of SML I as the dispersant is impractical in mortar manufacture.
(4) The dispersion effect with SML II was compared by the use of various types of additives. Among seventeen additives tested here, citric acid, gluconic acid, glucuronic acid and K, H-glucarate show the excellent SDN. Very high SDN shown by K, H-glucarate is worth noting.
