Chemical Intermediary
Soluble sodium dithiocarbonate ester solutions formed by reacting alkali cellulose with carbon disulfide constitute the spinning dope for traditional rayon filament and staple production. Within wet-spinning facilities, xanthate viscose represents the intermediate chemical state that permits solid timber pulp to dissolve into a viscous alkaline fluid before extrusion into acidic regeneration baths. The boundary of this term encompasses only the soluble dithiocarbonate derivative, concluding once acid neutralization strips carbon disulfide to regenerate insoluble pure cellulose.
Dithiocarbonate Reaction
Manufacturing begins by treating dissolving wood pulp with concentrated sodium hydroxide to produce reactive alkali cellulose, followed by aging to control the degree of polymer chain polymerization. Gaseous carbon disulfide is introduced into vacuum churns containing alkali cellulose, converting hydroxyl groups at the C-6 and C-2 positions of the anhydroglucose units into sodium cellulose xanthate. This orange-yellow crumb dissolves readily in dilute aqueous sodium hydroxide, yielding an amber, high-viscosity colloidal solution suitable for filtration, de-aeration and spinneret extrusion.
Ripening State
Chemical aging, known in processing plants as ripening, allows controlled spontaneous hydrolysis and redistribution of xanthate groups along the cellulose chains. The esterification index, or gamma value, drops predictably during ripening, decreasing the solubility of the dope until it reaches optimal coagulability for wet spinning. If extruded too early, the dope dissolves into the spin bath without forming continuous filaments; if aged excessively, premature gelation plugs spinneret orifices and halts spinning lines.
Coagulation Mechanics
Metering pumps deliver the ripe dope through submerged precious-metal spinneret jets into an aqueous bath of sulfuric acid, zinc sulfate and sodium sulfate. Acid contact decomposes xanthate viscose instantly, neutralizing the alkali and evolving gaseous carbon disulfide and hydrogen sulfide while precipitating solid cellulose filaments. Mill safety protocols mandate heavy-duty exhaust ventilation and sulfur recovery scrubbers to capture volatile emissions during regeneration.
