Study On Structure And Properties Of Diacetate Filaments And Its Spun-like Processing By Air Texturing

As one of the most important cellulosic fiber, diacetate filament has been available commercially in 1920's. During a quite long period, diacetate filament has been mostly used to produce linings for top grade garments. By the end of 20 century, its application scope changed markedly and began to involve three sections including fabrics, linings and adornments. However, its manufacturing technology is still monopolized by a few multinational companies currently. In our country, there is little literature pertaining to original studies such as spinning and product development for diacetate filament.In light of developing diacetate filament targeted to produce textiles, samples of diacetate filament were made under different spinning conditions by the laboratory spinning machine for diacetate tow used in tobacco, and effect of spinning parameters on mechanical properties was discussed in this paper. When other parameters are kept constant, higher concentration of spinning dope results in higher fiber tenacity; under same dope concentration, fiber tenacity tends to increase with increase in residual solvent content; when hot air temperature is increased, the mass specific resistance is reduced; when dope concentration is decreased, the mass specific resistance is increased. Such structure properties as thermal property, crystallinity, orientation and morphology of diacetate fiber were tested by various methods including TG, DSC, X-ray diffraction and SEM. It was found that diacetate fiber would decompose in temperature of 220～260°C, and there are two characteristic melt peaks on DSC spectrum; its degree of crystallization and orientation are relatively low, as a result, diacetate fiber is poor in tenacity and wear resistance; fiber's cross section presents a shape of irregular tooth-like square and there are grooves on the longitudinal surface. Aiming at the disadvantage of its low tenacity, diacetate filament was heat treated under dry or wet heat environment respectively. Effects of temperature, time and tension on tensile property of diacetate fiber were discussed. The results show that the tensile property of diacetate fiber changes little after dry heat treatments without tension, but changes significantly after dry heat treatments with tension, and in the case of being treated by both dry heat treatment with tension and wet heat treatment without tension, diacetate fiber exhibits greater modification on tensile property.Secondly, air texturing was applied to process diacetate filament, and propertiesof yarn and fabric were examined in this paper. It was observed that higher airpressure is not practical during the air texturing of diacetate filament, or else, thetexturing process can not be carried out smoothly. The tenacity and breakingelongation of air textured diacetate yarns are quite lower. Diacetate fabric is poor intensile strength, tear strength and wear resistance, but good in anti-pilling tendency,subdued in luster and soft in handle. Herein, according to the design concept oflearning from others' strong points to offset one's weakness, synthetic filamentsincluding polyester and polyamide were chosen to blend with diacetate filament toproduce core-and-effect air textured yarns. Effects of core yarn on properties ofblended yarns and morphological structure of air textured diacetate/polyester yarnwere mainly analyzed. The results show that the introducing of synthetic filamentsmakes it possible to apply higher air pressure during the air texturing of diacetatefilament, which leads to a better texturing effect, and the process is very stable. It wasbelieved that the tensile property and shrinkage in boiling water of core-and-effectblended yarns are mostly depended on core yams. The three-dimensional videomicrographs revealed that there are some free diacetate fiber ends on surface ofblended air textured yarns by diacetate and synthetic filaments, which indicates that aspun-like effect of diacetate filament occurred when loops and arcs are formed onyarn surface. At lower overfeeds of effect yarn, loop/hair number is reduced withincrease in loop/hair height, the distribution of loop/hair number along height almostfollows an exponential curve, and loops or hairs are mostly located in height of0.5mm. With increase in overfeed of effect yarn, the distribution of loop/hair numberalong height gradually exhibits a quadratic curve, and loops or hairs shift to positionwith height of 0.5～1.5mm.Concerning the study on spun-like processing by air texturing for diacetate filament, influences of processing parameters and Texspun device on spun-like extent were discussed, the spun-like effects of different effect yarns during air texturing were also compared, and then an orthogonal experiment was used to optimize spun-like effect as well as yarn property. The influence of overfeed of effect yarn on hair number shows no obvious trend. With increase in overfeed of core yarn, hair number is slightly reduced. With increase in air pressure, hair number is increased in a way. At higher texturing speed, hair number tends to decrease. When winding underfeed is increased, hair number changes little, and the wetting of effect yarn results in a highest value of hair number. As a whole, the spun-like effect of diacetate filament during air texturing is insufficient under the single air texturing process, that is, the increase in number of free diacetate fiber ends on blended yarn surface is less. After treatment of Texspun, both hair number and loop number are increased, and the increase in hair number is higher than that in loop number, while yarn tenacity and stability are not affected. For different effect yarns, the increase in hair number or loop number differs from each other. When polyester or polyamide filaments are used as effect yarn, the increase in hair number or loop number is less. When effect yarn is diacetate filament, the increase in hair number or loop number is much larger, and its normal or Texspun yarn possesses the highest value of hair number. Orthogonal experiment shows that the first factor affecting hair number is texturing speed and the second one is air pressure, the overfeed of core yarn is the leading factor affecting yarn tenacity and instability, and the overfeed of effect yarn is the dominating factor for yarn core bulkiness.The spun-like shape of diacetate filament formed during air texturing was compared with rupture features of diacetate fiber reported in previous literatures as well as its tensile breaks under various extension rates, and then, the mechanism of air texturing spun-like effect of diacetate filament was briefly described, finally, influence of spun-like effect of diacetate filament on yarn surface property was investigated. It was believed that the fact that part of diacetate filaments break and form free fiber ends on yarn surface during air texturing is mainly caused by tensile action under normal extension rate, and therefore the low tenacity of diacetate fiber contributes most to its air texturing spun-like effect. With enhancing of spun-like effect, yarn frictional coefficient, mass non-uniformity, and compressional resilience tend to reduce, while appearance unevenness is increased and the wicking behavior does not show clear trend.