Indian Journal of Fibre & Textile Research Vol. 21, March 1996, pp. 79~89 Recent advances in the development of silk-like polyester fabrics Pushpa Bajaj Department of Textile Technology, Indian In stitute of Technology, New Delhi 110016, India Silk-like polyester fibres have been one of the most important targets for the textile industry in the present era. Key technologies starting from fibre engineering to finishing process have been illustrated for producing silky polyester fabrics with bulky hand touch and superior drape. Effects of polymer additives, delustrants, surfacta nts, etc. on alkaline hydrolysis of polyester fabrics for improving silk-like characteristics have a lso been highlighted. Keywords: Alkaline hydrolys is, Bicomponent fibres, Micro-crator polyester, Microfibrcs. Shingosen, Silk-like polyester. Spinning techno fogies I Introduction by simulating the characteristic features of silk fibre , Polyester fibre has conquered the leading position VIZ. among the three major synthetics because of its • The design of cross-sectional shape, excellent properties such as high strength, abrasion • Enhancement of drape characteristics through resistance, wash and wear, and wrinkle-free weight reduction of conventional polyes ter characteristics. However, polyester does have some fibres or by the development offine denier fibres. deficiencies, i.e. it is hydrophobic and oleophilic. Due and to this, 1t is easily soiled and accumulates the static • Creation of moderate bulk and soft handle. charge. Oily stains are also difficult to remove. History of the progress made in silk-like polyester Polyester fabrics are, therefore, not as comfortable as fibres is given in Table I and the technologies natural fibre fabrics. developed for the production of Shin-Go sen (Shin = On the basis of consumers' comments, Latta I has new & Gosen = synthetic fibre) in Japan are . also mentioned the following limitations of illustrated in Fig.l . synthetics: In this review, the va rious processes developed for • Unnatural hand and unfamiliar skin cqntact sensations, Table I- Histpry of the progress of silk-like polyester fibres9 • Unpleasant thermal sensations, • Lack of moisture absorbancy, Generation Properties Idea of technology • Clamminess of fabric in contact with skin, and Copy of natural Lustre Brightness • Static related problems. silk Drape Shape of cross-section ( 1964-) Rustle of clothes (trilobal, triangle) To overcome some of these problems, blending Copy of silk Fullness and softness Shrinkage-mix fibres touch Drape Structure of crimps with natural fibres, particularly cotton, gained a big (1975-) Delicacy market. An extensive work related primarily to Persuit for the Silky-spun like Air texturing polyester fabrics comfort has been published in aesthetic Naturality False twisting 2 excellent reviews - 6 in the recent past. From the properties Dry touch Thick and thin ya rns wearer trials using knit fabrics it was reported that the (1979-) comfort of polyester was substantially improved by Persuit for Lustre Tri-petal like cross- cross-section variations, pressure jet treatments and micro shape of Fullness and softness section certain engineering modifications of the ·polyester. cross-section Drape Microfibres Rustle of clothes Cross-sectional shape The Japanese industry has also made great strides (1983-) Naturality in improving the comfort and aesthetic properties of 'lk I'k I "Sh' " h b Aim for high Very nice tailored Development of po Iyester. SI - I e po yester mgosen as een sense and quality fini sh characteristics new polymer developed by different technologies? Various (1988-) Liveliness approaches have been tried to develop silky polyester 80 INDIAN J. FIBRE TEXT. RES., MARCH 1996 Shrinkag~-mix filam~nt ----i High shrinkage yarn t---{ Di fference in '"r---Fullness and High spQed spinning yarn fibre length softn~ss . Spontaneous extension Polymer modification ------I Polymer with partic~s )----.Lu~e Brightness from catalyst residue Polym~r with added particles r:s-ur--:f:-a-ce-ro-u-g-:-hn-e-s.... s\.--L- Dee p co 10 ur Vi vid colour Dry hand Special spinning -------1 Non-circul~r cross­ I'---{ Shape of (ross - 'ff--- Soft hand section section Conjugated yarn Rustle of (Iothes Denier mix He<lvy denier I-----{ Difference of 'c---\-- Spread anti-drap! Fine dQnier denier Texturing ----------1 False twisting 1----;rr;(o~m;;;m;;ii~ng~l;in;;;g-:-· -~~r\--~ Naturality Air tuturing dagree Afttr treatment -------1 Twisting l---'~S;;tr~u::-ct:t u:r:e--:o f;-""""":----+-~S t iff ness After finish (austic reduction fabrics Springy properties Fabric density Drape Fig. I- Fabric properties of Shingosen and key technologies SI LOOK ROYAL 51 L~ SILK been developed with triangular or trilobal I fI cross-sections. This resulted in lustrous polyester fibres. The appearance also changed from that of I 1 1\ ..... 1...- \ I / plastic to a silk equi valent. I" / '" -- I \../ PET fibres with a tripetal cross-section have also \V been developed to provide silky look. There is a " groove at the tip of each lobe oftrilobal cross-section. 1/ This unique cross-section is believed to bring the o 10 20 30 0 10 20 30 0 10 20 30 rustling sound to polyester fabrics when friction Tim~Jms occurs among them. The wave of rustling sound of three typical fabrics has been compared (Fig.2) . fr----- 'Sillook Royal' has, therefore, not only the lustre of o natural silk, but also a rustling sound similar to that of A-Sompl, 'tobric I the natural sil k. B- '" ie rophont c- W,ight , SOOt 14 em I Polyester fibres with petal-like cross-sections ha ve 0-"'0_ '1Oem Imin I been produced by conjugate spinning technologylo. Fig. 2- Wave of rustli ng sound of three typical fabrics In this process, small amounts of easily hydrolysable components are located at the tips of each lobe. During saponification or caustic treatment, this the production of silk-like polyester have been component gets dissolved and grooves a re formed. highlighted. Special emphasis has been made on the The width and depth of each groove can be controlled saponification or caustic reduction treatments for at the submicron level. producing si lk-like polyester fabrics. 3 Differential Shrinkage Polyester Yarn 7 2 Cross-sectional Shape - <) One of the technologies to bring out silk-like bulk The shape of a silk fibre after removing sericine and handle in PET is to use differential shrinkage during scouring is triangular. For imitating the polyester component yarn. Two methods have been triangular shape of silk fibres, polyester fibres have tried to produce different shrinkage levels in mixed BAJAJ: SILK-LIKE POLYESTER FABRICS 81 yarns. One is a parallel sort of mixture, just like the heat treatment. In the parallel structure, higher Quiana (nylon ya rn produced by Du Pont) and the shrinkage components form a core, and lower other is a se rial kind (Fig. 3). shrinkage components form waves or loops around The parallel structure is made by mixing fibres of the core. On the other hand, in the serial type different shrinkage levels either by using different structure, higher and lower shrinkage parts are polymer fibres or by mixing fibres of polyester drawn di stributed randomy in the yarn and there is no core at different temperatures. The serial type is produced (Fig.3). The resulting fabric from serial type by random heat setting along individual fibres during arrangement of different shrinkage level fibres fibre processing 1 I . The fibres shrink randomly with showed a more natural silk look than the parallel type. Uchida 12 has also demonstrated the role of TYPE PARALLEL SERIAL shrinkage in producing Shingosen. Fukuhara 7 from Mi Xlld Yarn of Rnndom Hrat- set Toray Industries has shown that for the production pf I'ETHOO D~rmt Shrinkage AmollJ Individual Fibre Lt'it I Shingosen, initially dry heat shrink process was tried and later the wet-heat shrink process. But, a double .. _............... ........ .- ................... ...... shr'unk fabric appears to be closest to silky textiles (Fig. 4). It has comparatively hi'gher bulkiness and is YARN I--------:--+------:::---~ .~. '"'-./ .... ..../V..... more airy and soft. Sillook Sildew, produced recently, ~ ....... "'-.".... ""'" is a double shrunk fabric with large waves or loops on ~ --v-..... J"'v... _. the surface of the fabric. For making double shrinkage fibres, the researchers have to first design the polymers by selecting a suitable comonomer and its content for accomplishing the desired shrinkage level. Degree of polymerization (DP) should also be controlled as a polymer with higher DP is likely to provide higher shrinkage. Parallel yarn str ucture After screening the polymer with a desired composition and DP, the fibres can be made from two , or more polymer components by the same spinneret from different nozzles. This kind of conjugate spinning provides fibres with in situ differential shrinkage. So, additional step for mixing fibres as Strial yarn structure discussed earlier is not required and the resulting mixture directly produced from spinning line is Fig. 3- Two kinds of shrinkage. Parallel and seri al yarn structures uniform. 4 Topical Finishes Finishes also modify the tactile, static and moisture Double shrin k type related properties of polyester fabrics. The ~I enhancement of polyester properties by treatment with aqueous sodium hydroxide was recognized soon 13 after the invention of polyester . Treatment of untextured yarn fabric with alkali produces softer ----, .......... '----- tactility with a less synthetic hand. A calendar, heat-set' and caustic soda saponified fabric was patented a few.years later as the treatment was said to ~ I~~ ____ ~D_r_y_-_he_a_t_s_h_ri~nk~tY_p_e__ ~_~ produce high fabric lusture without paper-like , l4 handle . Grey 1st 2nd Final Polyester undergoes nucleophilic substitution and fabric hQat-set ntat-set heat-~t scouring caustic dyeing is hydrolyzed by aqueous sodium hydroxide. The reduction hydroxyl ions attack the electron-deficient carbonyl Fig, 4 Shrinkage d'iagram of polyest .r fab ri c after caustic carbons of the polyester to form an intermediate treatment anion, 82 rNDiAN 1.