Sıbel Sardag, Ozcan Ozdemır, The Effects of Heat-Setting *Ismaıl Kara on the Properties of Polyester/Viscose Department of Textile Engineering, Uludag University, Blended Yarns Görükle, Bursa 16059, Turkey E-mail: [email protected] Abstract 30 tex and 20 tex yarn bobbins consisting of 67% PES - 33% viscose were subjected to heat- *Can Textile, setting at 90 °C & 110 °C, and under a pressure of 630 mmHg in order to investigate the Corlu, Tekirdag, Turkey effects of heat-setting conditions on the properties of twisted yarns. Both heat-set and unset yarns were dyed. The tensile strength properties (tenacity and elongation at break) of each yarns were measured before heat-setting, after heat-setting and after dyeing. The inner, middle and outer sections of the yarn bobbins were measured with a spectrophotometer to find differences in color. As a result, heat-setting and dyeing processes were found to be effective in the tenacity and elasticity of yarns. Key words: heat setting, twist setting, twisting, temperature, polyester (PES), viscose, tenacity, work of rupture. ventional systems and operate under ral qualities, brightness and comfortable vacuum with saturated steam are used wearing property of viskose fiber. In ad- in conditioning and heat-setting. With dition, viscose fiber has a high elasticity the aid of steaming in these systems, when compared with cotton fibres. When yarns are conditioned or heat-set with used together with PES fibers, viscose saturated steam under vacuum [3]. fiber gives a more hormonious blend as regards elongation at break [8]. The Heat-setting process, a treatment n Introduction with steam under vacuum, improves Since the tenacity of the wet cotton yarn efficiency and quality in weaving and is higher than that of dry ones, cotton Moisture in the atmosphere has a great knitting plants by reducing yarn ten- yarns have a higher tenacity under high impact on the physical properties of tex- sion, softening yarns, moisturising them moisture [9]. Studies concerning heat- tile yarns and fibres. Relative humidity homogenously, eliminating electrostatic setting are limited in literature and nearly and temperature decides the amount of effects and reducing fly and dust [4]. all of these studies are related to cotton moisture in textile materials. Exposing because of its positive reactions against yarn to high moisture during produc- Unset yarns squeeze bobbins during moisture. For this reason, the current tion generally yields negative results, as dyeing with a pressure from the out- study which has been performed on the well as being undesirable for technical side section towards the inside section, heat-setting of yarns consisting of PES/ processing. On the other hand, a high as a consequence of which bobbins get viscose is expected to make a contribu- degree of moisture adequatelly exposed deformed. The higher the temperature tion to textile literature. to yarn improves its physical proper- of heat setting is the less the bobbins get ties and enables the standard humidty deformed [5]. Improper heat setting is of yarn to be reached. Yarns with lower considered to be a factor which increases n Experimantal moisture content than the standard value skewness in weaving, a situation in In this study, 30 tex and 20 tex carded result in monetary loss in sale. Therefore, which warp and weft yarns cannot be tied yarns consisting of 67% PES and 33% conditioning and heat-set is to provide together with a right angle, although they viscose were used - the linear density and an economical device for supplying the are straight [6], and it increases diagonal staple length of PES fibres were 1,6 dtex necessary moisture in a short time [1]. run in knitwear [7]. and 38 mm respectively, and the linear density and staple length of viscose fibres Each step in the manufacturing proc- Since saturated steam used in heat-set- were 1.7 dtex and 39 mm, respectively. ess, such as twisting, spinning, weaving, ting provides man- made fiber with good Yarns were wound onto bobbins with knitting etc., causes tension in fiber and thermal conductivity, steaming processes a Schlafhorst Autoconer 238 machine. yarns. Yarns tend to snarl in order to re- under vacuum make it possible for bob- These yarns were subjected to heat-set- lax themselves and get rid of this tension. bins to shrink homogenously in every ting under 630 mmHg pressure and at Tension and snarling are likely to lead to section. The yarns of such a bobbin are temperatures of 90 °C and 110 °C with problems in the following manufactur- dyed homogenously without causing a machine working in compliance with ing processes [2]. The purposes of con- stripe effects or colour differences be- the direct vacuum steaming system of ditioning and heat-setting (twist-setting) tween the inner and outer sections of the the Welker Company. The cycles below are to relax yarns, to prevent them from bobbin [5]. were followed: snarling, to enable them to be worked n Pre-heating : 45 °C efficiently in the following processes and The blend consisting of PES and viscose n Vacuum : 630 mmHg to fix yarn-twisting. Today, besides con- is used widely in the textile industry. n Heating : 90 °C (10 min), ventional system, other systems which This type of blend benefits from the high 110 °C (20 min) can eliminate the downsides of the con- strength of PET fiber and from the natu- n Vacuum balance : 500 mmHg 50 FIBRES & TEXTILES in Eastern Europe October / December 2007, Vol. 15, No. 4 (63) FIBRES & TEXTILES in Eastern Europe October / December 2007, Vol. 15, No. 4 (63) 51 Yarn bobbins were dyed in a Mini-HT As can be seen in Figure 1, the heat-set laboratory-type bobbin dyeing machine process brought about a considerable produced by Dilmenler Machinary In- improvement in the tenacity of yarn. The dustry. The dyeing process was carried rate of increase varied between 15% and out according to the conventional two- 19.9%, depending on the yarn count and step dyeing method. PES fibres were first temperature of the process (Table 1). The dyed with disperse dyes at 130 °C, and tenacity of yarns, subjected to heat-set they were then subjected to reductive showed a decrease of 4.4 – 11.3% after clearing at 75 °C. In the second step, vis- the dyeing process; however, their yarn cose fibres in the blend were dyed with tenacity was still higher than the tenacity reactive dyes at 80 °C, and then after- of unset yarns. Fıgure 1. The effect of the heat-setting process on tenacity of yarn. treatments (washings) for reactive dye- ing were performed. Finally, the bobbins In textile material science, a classic and were dried on a radio frequency drier. fundamental problem is the connec- tion between the tensile properties of Yarn count, twist and tenacity measure- fibers and yarns. A yarn is a complex ments of the yarns were taken before system made by a fibrous structure, i.e., and after heat-setting and after dyeing. a bundle consisting of a given number of Before the measurements were taken, all single fibers; this bundle, after twisting, the yarns were kept under standard con- becomes a yarn. [11] The improvments ditions. (at 20 °C ± 2 °C and 65% ± 2% observed in the tenacity of PES/viscose relative humidity) Yarn count measure- yarns after heat-setting can be an attrib- uted to the effects of this thermal process ments were carried out in compliance Fıgure 2. The effect of the heat-setting with ISO 2060. Yarn twist measurements on PES fibers, which constituted 67% of the blend. The physical and chemical process on elongation at breake of yarn. were taken in accordance with ISO 2061 properties of fibers such as dye absorp- on a James H.Heal twisting meter. Te- tion, strength etc. are close related to the The heat-setting processes increased nacity measurement of all the yarns was structure of non-crystalline sections. Due the values of yarn elongation within the performed in accordance with ISO 2062 to the temperature of the heat-setting range of 5.4% and 8.7%. Since cellulose on Uster Tensorapid 3. applied, the rate of crystalline sections, macromoleculles, which form regener- the average distance between crystalline ated cellulose fibres, are short, the att- A spectrophotometer was used to find centers and the number of bonds between raction between these macromollekules out whether inner, middle and outer macromolecules in fibres increased, as a was not very strong. Therefore, when a sections of the bobbins had any differ- consequence of which the degree of ori- force parallel to the fiber axis was app- ences in colour. Measurement was made entation in fibres increased, causing an lied to the regenerated cellulose fibers, with an observational angle of 10° and improvement in the yarn tenacity [12]. bonds between the macromollecules with D65 illuminant, using the CMC 2:1 weakened, causing the fibers to break. equation [10]. To investigate the effects The slight decrease in the yarn tenacity Breakages of wet regenerated fibres took of heat-setting and dyeing properties on after the dyeing process was something place more easily because of the swell- the yarn tenacity and elongation at break, expected. This fall arose from the fact ing and sliding effects of water [12, 13]. t tests were performed at 5% (0.05) and that especially viscose fibers and partly Consequently, the elongation values of 10% (0.1) level of significance . PES fibres get slightly damaged dur- the wet regenerated cellulose fibers were ing reductive washing with NaOH. The noticeably higher than those of dry ones. n Results and discussion t-tests we performed show that heat- sett- Generally, the tenacity values decreased, ing and dyeing process affect the tenacity but elongation values (%) increased, The effects of heat-setting at 90 °C and of yarns.