Dissolution mechanism of sodium alginate and properties of its regenerated fiber under low temperature.

Sodium alginate (SA) solution with high quality fraction was prepared by NaOH/urea, NaOH/thiourea/urea, NaOH/thiourea and LiOH/urea at low temperature. The results showed that we got 5.5 wt% SA solution by using 5.5 wt% LiOH/20 wt% urea. The viscosity of the solution was 62.44 Pa·s, which had declined by 64% compared to that of 5 wt% SA solution (176.12 Pa·s). The difference from the traditional low temperature dissolution principle is that the urea is mainly wrapped on the SA surface by the interaction between the OH- in LiOH through the ether bond (O) and the π bond in the SA instead of the -OH in the SA. Only the crystallization peak of urea appeared in the XRD spectrum. It indicated that urea was successfully wrapped on the surface of SA to form urea-LiOH-SA inclusion complex. The 23Na NMR showed that the interaction between Na+ and other ions or molecules around it increased at low temperature. Breaking strength of regenerated CA was 2.44 cN/dtex, which rose by about 21.39% compared to that of CA fiber (2.01 cN/dtex). The "groove" on the surface of regenerated fiber is denser and the section is more loosely compared with those of CA fiber.