Plasticization And Melt Spining Of Cellulose Diacetate With Imidazole Ionic Liquid As Plasticizing Agent

Regenerated cellulose fiber has become more and more important for both its raw material and products are environmental friendly and compatible with sustained development in the situation of exhaustible petroleum resources and the increasingly pollution of the petroleum-based textile wastes. Being the second largest variety of the regenerated cellulose fiber, only next to viscose fiber, cellulose acetate(CA) fiber has unique properties combining the characteristics of synthetic fibres and cellulose fibres. Cellulose diacetate(CDA) textile filaments with higher cost performance than viscose fibers possess not only a softness and suppleness with a silk-like handle, a pleasant feel against the skin, which other synthetic fibers cannot acquire, but also excellent draping qualities, natural crease resistance, low moisture absorption. CDA fiber is commercially manufactured by means of dry spinning with large quantities of acetone as solvent, which causes potential damage to the environment for the high volatility and flammability of acetone and lacks efficiency for its long processing flow. Moreover, the acetate via dry spinning shows a relatively low tensile strength with a range of 1.06-1.23 cN/dtex, which limited its application in textile field. Realization of melt spinning of CDA fiber would be surely a great progress in the production of regenerated cellulose fiber.This study aims to manufacture CDA fiber by melt spinning of plasticized cellulose diacetate based on the synergistic effect of intermolecular and intramolecular hydrogen bonds dissociation, combining the effect of acetylation in CDA and dissociation of hydrogen bonds by ionic liquids(ILs), so not only to provide a new method of formation for cellulose fiber, but also solve problems like lacks of efficiency and product performance as well as environmental problems caused by nowadays formation technology of cellulose fiber.The interaction between ILs and CDA was firstly studied. The solubility of CDA in various ILs was investigated, the rheological behavior of CDA/ILs solution was discussed, laser light scattering(LLS) was used to investigate the aggregation behaviors of CDA in ILs. Results showed that the dissolving capacity of used ILs for CDA in this study followed the order: 1-ethyl-3-methylimidazo liumphosphite([EMIM][P(OCH3)OHO])>1-butyl-3-methylimidazolium terafluoroborate(BMIMBF4)>1-butyl-3-methylimidazolium trifluoromethanesulfonate(BMIMOTF) > 1-butyl-3-methylimidazolium chloride(BMIMCl)>1-butyl-3-methylimidazolium hexafluorophosphate(BMIMPF6)>1-butyl-3-methylimidazolium formate(BMIMCOOH). Both CDA/BMIMBF4 solution and CDA/BMIMOTF exhibited the typical shear-thinning behavior and did not obey Cox-Merz rule, and viscous flow activation energy increased with the increase of CDA content. CDA was dissolved in BMIMBF4 and BMIMOTF in the form of single molecule chain in dilute solution and the aggregation was weak, the interaction between CDA and BMIMBF4 was stronger than that between CDA and BMIMOTF. Infrared analysis confirmed the interaction between acetyl groups of CDA and H in the imidazole ring of ILs in the solution.Then three types of ILs were selected as plasticizer of CDA, and the plasticization effect of ILs was investigated. Results showed that ILs as plasticizer can be effective in broadening the processing temperature by reducing Tg and Tf of plasticized CDA, resulting in improving the processability of CDA. Among three ILs, BMIMBF4 was considered to be the most effective plasticizer. The thermal stability of CDA was reduced by ILs. Then the structure of CDA plasticized by BMIMBF4 was further investigated. BMIMBF4 has good compatibility with CDA at certain content, and the crystallization of CDA could be decreased by BMIMBF4 in a certain extent. The interaction between acetyl groups of CDA and H in the imidazole ring of ILs in the plasticized CDA was also existed.The rheological properties of CDA plasticized by BMIMBF4 were investigated by rotary rheometer. BMIMBF4 content of plasticized CDA and the melt temperature should be paid much attention to because there would be a structure transformation when the BMIMBF4 content exceeded 25 wt% or the temperature was higher than 230 ℃. Time sweep results showed that complex viscosities, storage modulus and loss modulus increased firstly and then decreased with the time prolonging when temperature went from 210 ℃ to 240 ℃. CDA plasticized by BMIMBF4 exhibited typical shear-thinning behavior, its non-Newtonian index increased with the increase of BMIMBF4 content and decreased with the increase of temperature, and viscous flow activation energy decreased with the increase of shear rate. Structural viscosity index of plasticized CDA decreased with the increase of the BMIMBF4 content. However when the BMIMBF4 content increased from 25 wt % to 35 wt %, there were limit to structural viscosity index reduction. For CDA plasticized by 25 wt % BMIMBF4, its structural viscosity index went up after a decline with the temperature increase from 210 ℃ to 240 ℃, and reached a minimum at 230 ℃, which inferred that CDA/BMIMBF4 melt exhibits best flowability and spinnability at 230 ℃.In the end, the influence of melt technological conditions on molecular weight of CDA was studied, and the plasticized CDA by 25 wt% BMIMBF4 were successfully melting spun to fiber without other additives. The melt-spun fiber was characterized by DMA、TG、SEM、WAXD and FTIR. The mechanical properties were also tested. Results showed that the molecular weight decreased sharply when the extrusion temperature was too high or the residence time was too long, the chemistry structure of melt-spun CDA was not influenced by melt spinning and in agreement with that of commercial CDA fiber, hydrogen bond structure in CDA was partly recovered when BMIMBF4 was removed. The melt-spun fiber had a higher tensile strength of 1.78 cN/dtex, a greater crystallinity of 34 % and better thermal stability compared to commercial CDA fiber. The mechanical properties and crystallinity increased, but the elongation declined with the increasing of melt spinning speed.