Faxue Li

Structure and properties of novel regenerated cellulose fibers prepared in NaOH complex solution

Novel spinning solution, prepared by dissolving hydroxyethyl cellulose (HEC) owning a low molar substitution (MS) into NaOH/urea/thiouea aqueous solution with a specific weight ratio of 8:8:6.5, was employed to fabricate a new type of regenerated fibers by wet-spun method. The structure and properties of the resultant HEC fibers were characterized by (13)C NMR, FTIR, synchrotron WAXS, SEM, and tensile tester. The results showed that HEC fibers exhibited structure identical with HEC because of the physical dissolution and coagulation processes, but quite different from native cellulose due to partial breakage of hydrogen bonds and crystal transformation from cellulose I to cellulose II during cellulose modification. The resultant HEC fibers with relatively dense and homogenous structure displayed good moisture related properties and stayed stable in alkali solution with low concentration. Moreover, the novel fibers owned good dry mechanical properties in spit of their slightly poor wet mechanical properties comparable to viscose rayon, showing great potential in substituting the traditional viscose fibers.

Mechanical Properties and Crystal Structure Transition of Biodegradable Poly(butylene succinate-co-terephthalate) (PBST) Fibers

Mechanical properties of biodegradable poly(butylene succinate-co-terephthalate) (PBST) fibers with 70 mol% butylene terephthalate (BT) were intensively investigated. Chemical structure composed of hard BT units and soft butylene succinate (BS) units made contributions to the higher elongation at break and lower initial modulus of PBST fibers than poly(butylene terephthalate) (PBT) fibers. Moreover, PBST fibers had better elastic properties than PBT fibers by exploring their elastic recovery. The stretch elastic recovery mechanism of PBST fibers was clarified from the point of crystal structure transition. According to the preliminary studies by wide angle X-ray diffraction (WAXD) measurements, two polymorphs (α form and β form) were confirmed when PBST fibers were applied to different deformations. With the help of intensive study by small angle X-ray scattering (SAXS) measurements, the crystal structure transition of PBST fibers was further verified.

Preparation and Properties of Fibers Produced from a Cellulose/Complex PA Solvent System Precipitating in Diverse Coagulants

Ethanol, as the first coagulation bath, and several common organic solvents, as well as aqueous solutions of NH4Cl, NaHCO3 and NaOH were explored and demonstrated to be adopted as the second coagulation bath for cellulose/phosphoric acid/tetraphosphoric acid (cellulose/complex PA solvent) solution to produce novel cellulose fibers by two-stage dry-wet spinning in a laboratory scale, and effect of coagulants, cellulose concentration, solvent concentration (P2O5 concentration) and coagulation temperature on crystal structure and properties of corresponding fibers were investigated. Surface morphology of regenerated fibers as-spun from different coagulants was observed by scanning electronic microscope (SEM), indicating that methanol and 8 wt% NaOH aqueous solution all rendered cellulose fibers relatively dense and smooth surface. X-ray diffraction (XRD) analysis showed that cellulose fiber precipitated from 8 wt% NaOH aqueous solution had pronounced characteristic peak of cellulose II than those of fibers precipitated from other coagulants, and highest crystallinity and orientation. Meanwhile, those two coagulants referred above also gave cellulose fibers relatively higher tensile strength under the same prerequisite. TGA curves exhibited that fibers were thermally stable produced from two salt aqueous solutions (8 wt% NH4Cl and NaHCO3) since they had the relatively higher onset decomposition temperatures. By evaluating the effect of cellulose concentration, P2O5 concentration and coagulation temperature on the structure and properties of asprepared fibers, it was preferable to produce cellulose fiber from a solution at 20 wt% cellulose concentration, 73 % P2O5 concentration, and coagulating in methanol at coagulation temperature of 60 °C at the second-stage.

Coagulation studies of cellulose/NaOH/thiourea/urea/H2O fiber spinning system

Abstract The coagulation properties of cellulose from cellulose//NaOH/thiourea/ urea/H2O solutions were investigated with the goal of determining the optimal coagulation conditions for the spinning of cellulose fibers. The present study was concentrated on the effect of the coagulation variables upon the coagulation process. It was observed that at the start of the process, the thickness of the solidified layer ε was proportional to the square root of time. Model experiments were performed on gelled solutions of cellulose/NaOH/thiourea/urea/H2O in a coagulation bath to determine the coagulation rate,e / t , and mass transfer rate difference between the solvent and the coagulant, Dk . The influence of coagulant compositions, coagulation time and temperature, and cellulose concentrations on coagulation rate and mass transfer rate difference performed on cellulose samples had been demonstrated by microscopic observations, which was important for understanding and controlling the process of cellulose shaping from NaOH/thiourea/urea/H2O solutions. The data were analyzed by means of the diffusion model based on Ficks law, thereby depicting the mechanism of the coagulation process, which could be described as a two-phase separation, namely a cellulose-rich phase in the coagulated layer and a cellulose-poor phase in uncoagulated layer.