Slot 1.25 Dense Irregular CT Elastic Fibers Collagen Fibers.
5__New Developments in Elastic Fibers by JINLIAN
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New Developments in Elastic FibersJinlian Hu a; Jing Lu a; Yong Zhu a
a The Hong Kong Polytechnic University, Hung Hum, Kowloon
Online Publication Date: 01 April 2008
To cite this Article Hu, Jinlian, Lu, Jing and Zhu, Yong(2008)'New Developments in Elastic Fibers',Polymer Reviews,48:2,275 — 301
To link to this Article: DOI: 10.1080/15583720802020186
URL: http://dx.doi.org/10.1080/15583720802020186
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New Developments in Elastic Fibers
JINLIAN HU, JING LU, AND YONG ZHU
The Hong Kong Polytechnic University, Hung Hum, Kowloon
This paper reviews the developments of essential elastic fibers. The elastic fibersinclude extensible polymer fibers with low or high elasticity and reversibility whichconsists of the polyurethane elastic fiber, polyester-ether elastic fiber, polyesterelastic fiber, olefin based elastic fiber like XLA, hard elastic fiber, bio-componentfiber, and the shape memory fibers. The emphasis of the review is on the developmentand research process of polymer synthesis, production, characteristics, microstructure,and end-use in industry. It also draws some conclusions about the current problemsand future directions.
Keywords elastic fibers, polyurethane fiber, polyester-ether fiber, polyester fiber,olefin based fiber, hard elastic fiber, bio-component fiber, shape memory polymer fiber
Introduction
Elastic fibers is a class of fiber with elasticity and reversibility, which can be obtained by
spinning polymers of specific molecular structure or modified polymers. On the elastic
elongation basis, elastic fibers can be classified by high elastic fiber (elongation of
400–800%), medium elastic fiber (150–390%), low elastic fiber (20–150%), and
micro-elastic fibers with elastic elongation below 20%.1 According to the polymer
material, elastic fibers consist of polyurethane elastic fiber, polyester-ether elastic fiber,
polyester elastic fibers, olefin based elastic fiber like XLA, and others such as hard
elastic fibers and shape memory fibers.
The traditional elastic fibers such as spandex or lycra have been commercialized for
many years. The new products development focuses on the functional fibers. The polyester
elastic fibers of PBT and PTT were discovered in 1940s. However, it was not until the
1990s that petroleum companies developed shorter and more economic process routes
to produce these new polymers. The polyester-ether elastic fibers are promising fibers
with wide range uses and lower cost than polyurethane elastic fibers. By controlling the
molecular structure, different functional polyester-ether fibers will be developed. The
development of hard elastic fiber will emphasize medical applications. The polyolefin
fibers XLA offers performance advantages compared to existing elastic fibers. The
shape memory fiber is a kind of polyurethane based and temperature stimulus fibers
which makes the textiles with different style and applications.
Received 23 May 2007; Accepted 23 February 2008.Address correspondence to Jinlian Hu, The Hong Kong Polytechnic University, Hung Hum,
Kowloon. E-mail: [email protected]
Polymer Reviews, 48:275–301, 2008
Copyright # Taylor & Francis Group, LLC
ISSN 1558-3724 print/1558-3716 online
DOI: 10.1080/15583720802020186
275
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1. Polyurethane Elastic Fiber
1.1 Introduction
Synthetic elastic fibers are generally referred to as elastane or spandex fibers in Europe and
the United States, respectively. By definition, these fibers have an elongation to break
more than 200%, usually 400–800%, and on release of the deforming stress, return
quickly and almost completely to their original length.1,2 A major advantage of spandex
fibers over rubber yarns is that they are easily spinnable into thin fibers making them
suitable for textile applications.
Spandex fiber, one of the most important thermo-plastic elastomeric fibers being
commercially produced worldwide, is made with long chain synthetic polymers
comprised of mostly segmented polyurethanes. Chemically, it is made up of a long-
chain polyglycol combined with a short diisocyanate, and contains at least 85% poly-
urethane.2 It is an elastomer, which means it can be stretched to a certain degree and it
recoils when released. These fibers are superior to rubber because they are stronger,
lighter, and more versatile. In fact, spandex fibers can be stretched to almost 500% of
their length.
The basis for the synthesis of polyurethane elastomeric fibers in commercial pro-
duction at present was the diisocyanate polyaddition process discovered in 1937 by
Bayer, H. Rink, and co-workers.3 H. Rinke first studied the addition reactions of diisocya-
nates and glycols and he succeeded in spinning fibers from the high molecular weight
polyurethane resulting from the reaction of butylene glycol and hexamethylene diisocya-
nate. In 1939, P. Schlack reacted linear polyesters with equivalent amounts of diisocya-
nates, obtaining high molecular combinations having high elongation and elastic
properties. The diisocyanate polyaddition process has been used since 1941 to synthesize
designated, high value elastomers having higher tenacities and better end-use properties
than the previously-known diene polymers.
Reaction spinning was first investigated by H.A. Pohl in 19424 and was later applied
to both linear and cross-linked polyurethane. E. Windemuth in 1949 developed a chemical
spinning process in which the chemical synthesis of high molecular weight polyurethane
occurred simultaneously with extrusion and fiber formation. W. Brenschede succeeded in
solution-spinning polyurethane elastomers in 1951. Based on earlier work by M.D.
Snyder, J.C. Shivers achieved the first large-scale technical production of elastane fibers
by the dry spinning route. The final development of the fibers was worked out indepen-
dently by scientists at Du Pont and the U.S. Rubber Company. Du Pont used the brand
name Lycra and began full-scale manufacture in 1962. They are currently the world
leader in the production of spandex fibers. All large producers attempted to find a melt-
spinning route for elastane yarns. In 1967 Nisshinbo Industries introduced a melt-spun
elastane into the Japanese market. This was followed by Kanebo Ltd. in 1977 and
Kuraray Co. Ltd. in 1991. A single stage synthesis was next sought, in which the poly-
urethane raw materials are obtained in the form of granulate, and are subsequently melt
spun as reacted polyurethane. A two-stage reaction process is both more modern and
provides filaments of improved properties. Despite these developments, dry spinning
remains the most widely used production process. Table 1 shows the main manufacturers
and branding of spandex in the world.3–5
J.C. Shivers described the segmented polyurethane including “hard” and “soft”
segments. Lyssy gave a schematic structure of polyurethane elastomer, consisting of
“soft” and “hard” segments, illustrated in Fig. 1.
J. Hu et al.276
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Table 1Major products and manufacturers of spandex (reprinted from Ref. 3 with permission from
Deutscher Fachverlag GmbH)
Country Company Trademark Plant location
USA Invista Inc. Lycra Waynesbore; VA
Dorlastan fibers LLC Dorlastan Bushy Pak, SC
Radici Spandex Corp. Cleerspan,
Glospan
Gastonia, NC; Tuscaloosa,
AL
Canada Invista (Canada) Co. Lycra Maitland
Mexico Fielmex Sade CV Lycra Mexico
Nylon de Mexico SA Licra Monterrey, Nuevo Leon
Brazil Invista Ltda. Lycra Paulinia
Santista Textil Jau, Sao Paulo
Argentina Invista Mercedes
Venezuela Gomelast, C.A. Spandaven Caracas
India Petrofils Co-Operative Naldhari, Gujarat
Israel Israel Spandex Co. Ltd Filabell
Spandex
Gamat Gan
Japan Asahi Kaser Fibers Corp. Roica Moriyama
Fujibo Kozakai Co. Ltd. Fujibo
Spandex
Kozakai
Invista –Toray Co. Ltd. Lycra Shiga
Kanebo Gosen Ltd. Kanebo
Loobell
Hofu
Nisshinbo Industries Inc. Mobilon Tokushima
Teijin Rexe Chuo -ku
Toyobo Co. Espa Tsuruga
Unitika
South Korea Huvis Corp. Nexpan Suwon
Hyosung T&C Co. Creora Anyang, Kumi
Kohap Ltd. Kopadex Euiwang, Ulsan
Tae Kwang Industrial Co. Acelan Busan, Ulsan
Tongkook Synthetic Fibers Texlon Kumi
Singapore Invista Singapore Fibres Lycra Singapore
P.R. China Anshan Synth. Group Anshan
Bailu Chemical Fiber Xinxiang
Baoding Swan Spandex
Corp.
Baoding
Fibre Co. Ltd. Choucun, Shandong
Fujian Changle Urethane
Fibre Co. Ltd.
Changle, Fujian
Haishan Spandex Industry
Hangzhou Asahikaser
Spandex Co.
Roica Hangzhou
Invista (china) Co. Ltd. Lycra Qingpu, Shanghai, Foshan
(continued )
New Developments in Elastic Fibers 277
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H. Herlinger, P. Hirt, and H. Hierlemann investigated the mechanical properties of
wet spun polyurethane elastic fibers by employing liquid crystal chain extenders. This
method made the intermolecular covalent bonds stronger and improved the properties
slightly relative to other wet spun elastic fibers. In order to improve the properties
further, F. Hermanutz and P. Hirt synthesized unsaturated elastomers incorporating
chain extenders and double bonds. These were wet spun into fibers, which were cross-
linked by electron or UV irradiation. The tenacity, elongation at break, and residual
elongation were improved relative to conventional elastane fibers. The methods of
liquid crystal chain extenders and crosslinking by irradiation has only been applied in
pilot studies. The melt spinning process is becoming important. The elastane polymer
Table 1
Continued
Country Company Trademark Plant location
Jiangsu Haimen Urethane
fibre Co. Ltd.
Nantong, Jiansu
LDZ Spandex Ltd. Lianyungang, Jiangsu
Shandong Zibo Urethane
Elastic
Zibo, Shandong
Shaoxing Longshan Span-
dex Co.
n.a.
Shuanghang Group Shuka Jiangyin, Jiangsu
Tongkook Zhuhai
Yantai Spandex New Star Yantai, Shandong
Zhejiang Shei Yung Hsin
Spandex
Haining, Zhejiang
Taiwan Acelon chemical Fang Yuan, Hsiang
Far Eastern Textiles Ltd.
FCFC
Formosa Asahi Spandex
Co.
Roica Chang Hua
Hualon Corp. Huastane
Shingkong Synthetic
Fibers
Tao Yuen
Shei Heng Hsin Sheiflex
Industry Co.
Sheiflex I-Lan Hsien
Tong Hwa Synthetic Fiber Spandex Chu Pei
Tuntex Distinct Hsin Su
Thailand Thai Asahi Kasei Spandex Roica Bangkok
Germany Dorlastan fibers GmbH Dorlastan Dormagen
Netherlands Invista (Netherlands) NV Lycra Dordrecht
Great
Britain
Invista (UK) Ltd. Lycra Maydown
Italy Fillatice SpA Linel Capriate, Cessalto
Russia State Enterprise Volzhsky
Poland Chemitex Elaston Jelenia Gora
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used in melt spinning has to be chemically cross-linked using an excess of isocyanate or
polyfunctional isocyanates.
1.2 Production
Polymer Reactions. Two types of prepolymers are reacted to produce the spandex fiber
polymer back-bone. One is a flexible macroglycol while the other is a stiff diisocyanate.
The macro-glycol can be polyester, polyether, polycarbonate, polycaprolactone, or some
combination of these. These are long chain polymers, which have hydroxyl groups (-OH)
on both ends. The important feature of these molecules is that they are long and flexible.
This part of the spandex fiber is responsible for its stretching characteristic. The other
prepolymer used to produce spandex is a polymeric diisocyanate. This is a shorter
chain polymer, which has an isocyanate (-NCO) group on both ends. The principal
characteristic of this molecule is its rigidity. In the fiber, this molecule provides strength.
Spandex fibers are vulnerable to damage from a variety of sources including heat,
light, atmospheric contaminants, and chlorine. For this reason, stabilizers are added to
protect the fibers. Antioxidants are one type of stabilizer.
Various antioxidants are added to the fibers, including monomeric and polymeric
hindered phenols. To protect against light degradation, ultraviolet (UV) screeners such as
hydroxybenzotriazoles are added. Another type of stabilizer compounds which inhibit
fiber discoloration caused by atmospheric pollutants is added. These are typically
compounds with tertiary amine functionality, which can interact with the oxides of
nitrogen in air pollution. Since spandex is often used for swimwear, anti-mildew additives
must also be added. All of the stabilizers that are added to the spandex fibers are designed
to be resistant to solvent exposure since this could have a damaging effect on the fiber.
Figure 1. Microstructure of spandex (reprinted from Ref. 2 with permission from Deutscher
Fachverlag GmbH).
New Developments in Elastic Fibers 279
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Spinning the Fibers. Spandex fibers are produced in four different ways including melt
extrusion, reaction spinning, solution dry spinning, and solution wet spinning. Each of
these methods involves the initial step of reacting monomers to produce a prepolymer.
Then the prepolymer is reacted further, in various ways, and drawn out to produce a
long fiber. Solution dry spinning is used to produce over 90% of the world’s spandex
fibres.2
Dry Spinning. The high viscosity elastomer solution, consisting of 20–25% polymer
solution in dimethyl formamide or dimethyl acetamide, is extruded through a plurality
of spinneret capillary holes vertically down a heated spinning chimney through which
heated air flows. Here the filaments are solidified by evaporation of the solvent. The
spinning conditions, especially the take-up speed, the spinning temperature, and the
false twist insertion, have a significant effect on the mechanical properties of elastane
filament yarns.
Wet Spinning. The elastane solution is spun into an aqueous bath, where the solvent
diffuses out and elastic filaments are formed by coagulation. After passing through
washing baths, the filaments are taken up at speeds of up to 100m/min, thereby causing
the filament to fuse together. The desired yarn properties are achieved by applying a
thermal post-treatment in hot water or hot air, after which the yarns are taken up on
winders.
Reactive Spinning. This process simultaneously combines the NCO prepolymer chain
extension and filament formation in a spinning bath. A fluid NCO prepolymer is
extruded through a plurality of spinneret capillary holes into a bath containing
diamines. Because of the intensity with which some diisocyanates react with diamines,
a relatively stable skin of cross-linked polyurea forms on the filament surface. This skin
enables the yarn to be taken up. Finally, the hardening of the filament core takes place
in hot water, in diamine/alcohol or other solutions. The prepolymer structure is trans-
formed into a covalently cross-linked, segmented elastane filament yarn, which is
insoluble in a solvent.
Melt Spinning. It is possible to melt spin elastanes from the so-called thermoplastic poly-
urethanes; these use diols as chain extenders. The melt is extruded through one or more
spinneret holes, and the filaments formed are cooled by quench air.6 This process
permits the production of monofilament or multifilament yarns. The required yarn proper-
ties are achieved by a thermal after-treatment.
As the fibers exit the spinnerette, a specific amount of the solid strands are bundled
together to produce the desired thickness. This is done with a compressed air device
that twists the fibers together. In reality, each fiber of spandex is made up of many
smaller individual fibers that adhere to one another due to the natural stickiness of their
surface.
The fibers are then treated with a finishing agent. This may be magnesium stearate or
another polymer such as poly (dimethylsiloxane).7 These finishing materials prevent the
fibers from sticking together and aid in textile manufacture. After this treatment, the
fibers are transferred through a series of rollers onto a spool. When the spools are filled
with fiber, they are put into final packaging and shipped to textile manufacturers and
other customers. Here, the fibers may be woven with other fibers such as cotton or
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nylon to produce the fabric that is used in clothing manufacture. This fabric can also be
dyed to produce a desired color.
1.3 Microstructure and Properties of Spandex
Microstructure. The unique elastic property of the spandex fibers is a direct result of the
material’s chemical composition. The fibers are composed of two types of segments: long,
amorphous segments and short, rigid segments of which glass transition temperatures (Tg)
are below and above the room temperature, respectively.
In their natural state, the amorphous segments have a random molecular structure.
They intermingle and make the fibers soft. Some of the rigid portions of the polymers
bond with each other and give the fiber structure. When a force is applied to stretch the
fibers, the intermolecular bonds between the rigid sections are broken, and the
amorphous segments straighten out. This makes the amorphous segments longer,
thereby increasing the length of the fiber. When the fiber is stretched to its maximum
length, the rigid segments again bond with each other. The amorphous segments remain
in an elongated state. This makes the fiber stiffer and stronger. After the force is
removed, the amorphous segments recoil and the fiber returns to its relaxed state.2,8,9
Due to the thermodynamic incompatibility between the two segments, polyurethanes
undergo micro phase separation resulting in the phase-separated heterogeneous structure
consisting of hard and soft domains and inter-phases between them. Upon phase separ-
ation, the hard segments tend to form the hydrogen bonding between them, which
increases the mechanical and thermal stability of the hard domains that act as physical
cross-linking sites due to their high Tg, whereas the soft segments form random coil con-
formations to impart the elastic property to the fiber. The various physical properties of the
spandex fibers such as strength, modulus, mechanical and thermal stability, elasticity, and
elastic recovery are closely correlated with the domain structure and interaction between
the segments inside the domains (Figure 1).
X-ray fiber diagrams of unstretched filaments show a broad, unoriented, amorphous
halo, indicating that the soft segment matrix is amorphous and unoriented.8 In the
stretched state (.200%), it is possible to differentiate between polyester and polyether
elastanes. In polyester elastanes, stretching causes the amorphous halo to become
oriented along the equator without any signs of crystallinity. Stretched polyether
elastane shows two oriented crystal reflections along the equator. The soft segment
matrix has been three dimensionally crystallized by the stretching (Figure 1).
Characteristics. Spandex has better physical properties than rubber fiber in tenacity,
modulus, anti-aging, minimum linear density and dyeability. Table 2 shows the perform-
ance comparison.
The longitudinal surface is smooth. The cross-sectional views are variable. Dry spun
elastane yarns show round, oval, or dumbbell shaped filament cross-sections, while wet
spun elastanes have mainly strongly lobed, irregular filament profiles. In some elastane
yarns the filament fusion can be so strong that they merge into one another. This is
particularly so in the case of wet spun yarns, where higher decitex yarns show filament
tale geometry. Melt spun elastanes are produced as mono-or multifilaments of predomi-
nantly round cross-section.
The thermal behavior of elastanes at low temperatures is governed by the soft
segments. At high temperatures, the thermal behavior depends on the hard segment
matrix, the molecular weight, and the type of chain extension and the orientation of the
New Developments in Elastic Fibers 281
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hard segment. At temperatures above 1708C, there is a noticeable thermal degradation of
the fiber, which manifests itself as yellowing and as a deterioration of the elastic proper-
ties.9–11
Elastane fibers are soluble in highly polar solvents, such as DMF and dimethylaceta-
mide. While elastanes containing polyether soft segment are less subject to hydrolysis,
polyester elastanes are more resistant to oxidation. Under “mild” conditions, elastane is
resistant to acids, alkalis, oxidizing agents and reducing agents. Treatment with highly
concentrated acids and caustics for an extended times; however, this results in a loss of
elastic properties, and the loss increases with increasing temperature.10 Elastane is insen-
sitive to hydrolytic effects during normal washing and handling, and is unaffected by the
use of normal solvents. Elastane fibers have good resistance to oxygen and ozone.
Nitrogen oxides cause a color change to yellow or yellow brown, the intensity
depending on the concentration, ambient temperature and relative humidity. Elastane
are more resistant to ageing and abrasion than rubber yarns. Long exposure, particularly
to UV radiation leads to a change in color of the fiber and to photochemical degradation.
Polyester urethane has higher resistance to photo-oxidation than polyether urethane.11
1.4 New Products of Spandex
Highly Hydroscopic and Moisture Liberating Spandex. Asahi Kasei was first to develop
the high hydroscopic and moisture liberating spandex (Roica BZ).11–15 This fiber has high
hydroscopic property like cotton, but also has quick moisture liberation property. It can
absorb water in a high humidity environment and release it under low humidity
environment.
Highly Soft Spandex. Spandex has a high elongation. If tensile modulus is high, the con-
strictive force is big. So it is uncomfortable when wearing especially for children and
elders. Grafting alkyl side chain on polyether dihydric alcohol of the soft segment is a
general method to reduce tensile modulus of the fiber. But it is difficult to do in
industry. Asahi Kasei invented a catalyst making this process possible. This high soft
spandex named Rioca HS17 has come into the market. Invista has developed a similar
product naming it Lycra soft.
Easy Setting Spandex. Spandex woven under tensile state resists shrinkage deformation.
It is necessary to release the deformation under certain thermal condition. Thermal setting
Table 2Performance compare of rubber fiber and spandex
Performance Rubber fiber Spandex
Tenacity (cN/tex) 3 9–13
Elongation (%) 600–700 500–600
Elastic modulus (cN/tex) 0.2 0.5
Anti-aging Bad Good
Lag elongation (%) 3 20
Dyeability No Yes
Minimum linear density (dtex) 100 11
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of spandex with polyester soft segment is good because of the good thermal plastic
property but that of spandex with polyether soft segment is poor. However, thermal
stability of polyester spandex is poor, so it cannot be interwoven with polyester fiber.16
Asahi Kasei has developed a low temperature setting spandex named Roica BX,
which not only have good setting effort but can interweave with polyester fiber and set
under high temperature. Other high setting spandex includes T560, T562 B of Invista
and Espa M of Toyobo and Mobilon P of Nisshinbo.
Other Functional Spandex. Some new products of specific functions were developed such
as the chemical or chlorine resistant spandex, anti-bacterial spandex, high tenacity
spandex, easy dyeing spandex.
The primary use for spandex fibers is in fabric. They are useful for a number of
reasons. First, they can be stretched repeatedly, and will return almost exactly back to
original size and shape. Secondly, they are lightweight, soft, and smooth. They are also
resilient, since they are resistant to abrasion and the deleterious effects of body oils, per-
spiration, and detergents. They are compatible with other materials, and can be spun with
other types of fibers to produce unique fabrics, which have characteristics of both fibers.
Spandex is used in a variety of different clothing types.11 Since it is lightweight and
does not restrict movement, it is most often used in athletic wear. This includes such
garments as swimsuits, bicycle pants, and exercise wear. The form-fitting properties of
spandex make it a good for use in under-garments. Hence, it is used in waist bands,
support hose, bras, and briefs.
2. Polyester Elastic Fiber
Recently polyester based elastic fiber has been developed rapidly. The main class
includes PBT poly(butylene terephthalate) fiber and PTT (polytrimethylene terephthalate)
fiber. PBT18 was included in the polyester patent issued by Whinfield and Dickson, two
scientists of the Calico Printers Association. Production of PBT fiber for textile use first
started between the end of the 70s and the mid 80s in Japan and in the USA. In Japan
producers were Toray (Sumola), Teijin (Finecell), Kuraray (Artlon), Unitika
(Wonderon), Kanebo. In the USA, the company was Celanese. PTT fiber19 was first
patented in 1941 but it was not until the 1990s, when Shell Chemicals developed a low
cost production method.
Poly(butylene terephthalate) was carefully studied in the mid of 1970s when two
distinct a and b crystalline phases were identified. About ten year later Lu and
Spruiell21 followed the work of Boye and Overton21a and Jakeways et al.22 to show that
the b form can be obtained in the unstrained state and indicated drawing conditions
which favor the production of this crystalline phase. High-resolution, solid-state 13C
NMR studies of the a and b polymorphs have revealed several important features concern-
ing the conformations and motions of PBT chains in both crystalline phases.22 It appears
the glycol residues are in the nearly extended trans conformations in both crystalline
forms, while different orientations of the ester groups and phenyl rings probably
account for the 10% difference in the fiber repeats of a and b structures. In both
crystals the methylene carbons are sampling rapid motions, which are significantly
faster than the motions experienced by the carbons of the terephthaloyl residues.
Recently, Tonelli21c proved by 13C NMR studies that in the a polymorphs, the ester
groups are rotated �408 out of the phenyl planes to which they are attached.
New Developments in Elastic Fibers 283
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PTT is a semicrystalline polymer synthesized by the condensation of 1,3-propanediol
(PDO) with either terephthalic acid or dimethyl terephthalate, followed by polymerization.
Studies of PTT had never gone beyond academic interest until recent years because one of
its raw materials, PDO, was very expensive and available only in small volume. PTT
received less attention when compared with PET and PBT. However, recent break-
throughs in PDO synthesis made PTT available in industrial quantities, thus offering
new opportunities in carpet, textile, film, packing, and engineering thermoplastics
markets.23,24 Numerous studies on the crystal structure and mechanical properties of
PTT have been reported.25–31 Analysis of the crystalline structure of PTT shows that
the aliphatic part of PTT takes a highly coiled structure of gauche-gauche conformation.
PTT has a triclinic crystalline structure, each cell of which contains two chemical repeat
units.
Thermal behavior and crystallization kinetics of PTT have also been extensively inves-
tigated.32,33 In general, the glass-transition temperature is in the range of 42–758C,depending on the thermal history; the melting temperature is about 2288C, which is
almost equal to that of PBT (about 2258C) and is much lower than that of PET (about
2658C). The well-known Avrami equation and secondary nucleation theory could well
describe the crystallization kinetics of the polymers. Pyda et al.32 investigated the heat
capacity of PTT and estimated the heat of fusion for a 100% crystalline PTT to be 30 kJ/mol.
Chung33 studied the bulk isothermal crystallization kinetics and compared the
crystallization rate of PTT with that of PBT and PET, using DSC. Based on the
analysis of crystal growth rate, the Avrami rate constant K and crystallization half-time
were determined. It was found that PTT’s crystallization rate is between that of PBT
and PET when compared at the same undercooling degree, contrary to the widely
believed concept that aromatic polyesters with odd numbers of methylene units are
more difficult to crystallize than the even-numbered polyesters. PTT does not follow
the odd–even effect. Among the three polyesters, PBT has the highest crystallization
rate, about an order of magnitude faster than PTT, which in turn is an order of
magnitude faster than that of PET. The crystallization rate for a semicrystalline
polymer is important in practical applications. The key advantage is that it combines
the desirable physical properties of PET (strength, stiffness, toughness, and heat
resistance), while retaining basic polyester benefits of dimensional stability, electrical
insulation, and chemical resistance.
2.1 PBT and PTT Elastic Fiber
Polymer Production. The polymer production is similar to the PET synthesis and involves
direct esterification and ester interchange polymerization (Figure 2).
Figure 2. Molecular formula of PET, PBT, and PTT.
J. Hu et al.284
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In fact, PBT is polyester in which, during the condensation reaction of the dihydric
alcohol with terephthalic acid, ethylene glycol is replaced by butanediol with four
methylene groups.
For PTT, Shell chemicals developed the low cost method of producing the high
quality PDO, the starting raw material of the PTT. There are two routes to synthesize
PTT namely, the transesterification of dimethyl terephthalate (DMT) with PDO and ester-
ification route with TPA (terephthalic acid) and PDO. In the first stage of polymer
synthesis, TPA or DMT is mixed with PDO to produce oligomers having 1-6 repeat
units with the help of a catalyst. In the second stage this oligomer is polycondensed to
a polymer with 60–100 repeat units. The catalyst used in the first step also accelerates
the polycondesation reaction (Table 3). Generally, this objective can be fulfilled by two
methods. The first is the use of a lower process temperature, which reduces the processing
time in the melt phase to a minimum and keeps oxygen out completely. The second way
might be selecting a sufficient amount of a catalyst and adding stabilizers like phosphorus
compounds or sterically hindered phenols.37–39
Fiber Spinning. PTT and PBT are melt spun and like PET are sensitive to hydrolytic
degradation. This means that a drying process is necessary before extrusion. The tempera-
ture must be below 1508C, otherwise oxidative degradation will occur. When considering
the use of the spinning and winding process from PET to PTT, one has to take three prop-
erties into account:20,33,34,36,40
. Melt temperature
. Glass transition temperature
. Intrinsic elasticity
The lower melt temperature means that there is a shorter length of time until the spun
filament in the yarn line is cooled down and the quench air adjustment and the cooling
Table 3
Physical properties of polyester spandex and polyether spandex
Performance Polyether type Polyester type
Tenacity (cN/tex) 6.18 � 7.94 4.85 � 5.47
Elongation (%) 480 � 550 650 � 700
Recovery elongation (%) 95 (elongation 500%) 98 (elongation 600%)
Elastic modulus (cN/tex) 1.1 —
Tg(8C) 270 � 508C 25 � 458CSpecific weight 1.21 1.20
Moisture regain 1.3 0.3
Heat resistance Yellowing at 1508C,stickiness at 1758C
Thermal plasticity
improving at 1508C;tenacity loss at 1908C
Acid and alkali resistance Acid resistance, yellowing
in H2SO4 and HCl
Dilute acid resistant, hot
alkali labile
Atmospheric resistance Tenacity loss after long
exposure to sunlight
Tenacity loss and color
change after long
exposure to sunlight
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length dimensions are different from the PET spinning process. Another important differ-
ence with PET is the lower glass transition temperature, which affects much faster cold
crystallization. This has a significant impact on the development of the fiber morphology
during solidification and cooling down. The spinning conditions are more comparable to
PA6 than to those of PET.
Characteristics and Microstructure. The diacid group affects the mechanical property
of polyester and its processability depends on the type of the diol group. In particular,
poly(trimethylene terephthalate) (PTT) is a highly crystalline polymer. Its melting temp-
erature is lower than that of PET by 20–308C. Therefore, the processability of PTT is
superior to that of PET. The highly flexible PTT fibers are obtained as a result of its
low initial modulus.
The elasticity and dyeability of PTT are better than those of PET or poly(butylene ter-
ephthalate) (PBT). It is well known that the number of methylene unit influences the
physical properties of many polycondensation polymers such as polyamides and poly-
esters, which is called the odd-even effect.
PET molecules are fully extended with two carboxyl groups of each terephthaloyl
group in opposite directions, and all open chained bonds are trans with successive
phenylene groups at the same inclination along the chain. PTT has a conformation with
bonds of the -OO(CH2)3OO- unit having the sequence of trans–gauche–gauche–trans,
leading to a concentration of the repeating unit. The opposite inclinations of successive
phenylene groups along the chain force the molecular chains to take on an extended
zigzag shape. Because of the molecular characteristic differences, the theoretical
maximum elongations (c-axis that is parallel to the fiber axis) of PET and PBT reach
about 98 and 86%, respectively, whereas that of PTT is only 76%.
On the contrary, PTT has a helical structure of an angle of 608 (gauche) for its odd-numbered carbons, resulting in the 75% gain of fully extended chain length. For this
reason, to enhance the physical properties of PTT fibrous materials, the PTT chain
should be extended with the change in distortion angles in crystalline as the spring
extension.36,38
Table 4 gives a rough comparison between PTT, PBT, PET, nylon, and spandex.37
. PTT have slightly more power stretch and recovery than PBT and more than PA6/66 and PET
. PBT remove extra pressure and give more comfort than spandex
. PTT have the best soft hand of all, as PBT will be close to PET
. Both are easily dyed at 1008C and can be mixed with other fiber and offer stain
resistance, chlorine resistance, and a good resilience.
The outstanding features of PTT fibers can be summarized as:35–40
. Very good elongation and recovery under low load creating a wearing comfort. The
fiber recovers 100% from 120% strain. For textured yarns, the fiber offers up to
145% stretch with 100% recovery.. Dyeable at low temperature: PTT can be dyed at 1008C with the same or slightly
deeper shades than PET at 1308C. Disperse dyed PTT shows excellent colorfast-
ness to laundering, crocking test, and UV light and ozone.. Soft handle, good dry-ability, and stylish drape (low Young’s Modulus).. Better abrasion resistance and dimensional stability.
J. Hu et al.286
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. Able to retain heat set pleats and creases. The fiber heat sets at lower temperatures
than PET.
The performance of the PBT fibers can be summarized as follows:37,40
. High extensibility even under low loads and quick recovery from deformation once
the strain has been relieved (in practice, an elasticity in between the height of
spandex yarns and the lower level of nylon textured yarns). Processability, in texturing, under gentler operating conditions than in the case of
PET. Dyeability at the boil. Good color fastness, dimensional stability also in the wet state, and fastness to
chlorine.
Applications. The applications of PTT in the textile industry include filament yarns, staple
fibers and BCF yarns for carpets. In blends with other synthetic fibers such as Lycra or
natural fibers such as cotton, PTT enables a variety of end products that have a soft
feel, good drape, and stretch and recovery qualities.37–40
. Sewing thread: one of the most recent application fields is sewing thread which will
endow clothing products with added value by appropriate extensibility, recovery
and dimensional stability.. Sportswear and leisurewear: the extraordinary properties of PTT are very much
useful for sports and leisurewear plus elastic interlinings and shirting fabrics. Spunbonded fabrics
Table 4Fiber properties comparison chart37
Property PTT PBT PET PA6/66 Spandex
Melting temperature (8C) 228 221 260 223 230–290
Glass transition (Tg) 45–65 20–40 70–80 80–90 270–50/25–45Density (gcm23) 1.33 1.35 1.38 1.14 1.21
Initial modulus (cN/dtex) 2.6 2.4 9.15 2.1 0.11–0.45
Elastic elongation (%) 28–33 24–29 20–27 27–32 400–800
Softness þ2 þ1 21 þ1 22
Recovery 1 1 21 — þ2
Bulk þ2 þ2 21 þ2 22
Heat-set capability — 22 — þ2 21
Abrasion þ1 þ1 þ1 þ2 22
Chlorine resistance þ2 þ2 21 21 22
Dyeability þ2 þ2 22 þ1 22
Stain resistance þ2 þ2 þ1 21 22
Light fastness — — þ1 21 22
Wash fastness þ2 þ2 þ2 21 22
Color intensity — — 21 þ1 22
Static resistance þ2 þ2 þ2 21 22
Cost — — þ2 — 22
þ2 ¼ best, — ¼ average, 22 ¼ worst.
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. Carpets: wear performance is equal to or better than nylon without the staining or
cleaning problem.. Upholstery: good stretch recovery, dye and print capability, stain resistance, and
resiliency.. Apparel: softness, stretch and brilliant lasting colors in both knit and woven fabrics,
in hosiery and intimate apparel, linings, denim, swimwear etc.
For PBT fiber, in addition to traditional end-use, such as stretch jeans, bathing suits,
sportswear and hosiery, a particularly promising application trend is that of
apparel stretch yarns, produced by twisting a textured PBT yarn with a natural staple
fiber yarn.40
2.2 Bicomponent Self-crimp Elastic Fiber
Self-crimp fibers behave like natural wool with a textured appearance. The crimps
are formed from a composite of two parallel but attached fibers with differing shrinkage
or expansion properties. Since the crimp is naturally formed, the false twist or air-
texturing involved in typical fiber processing for synthetic fibers becomes unnecessary
and can be eliminated. Another important characteristic of the self-crimp yarn is that
the crimp is not imposed on the fiber from the outside, but rather results from the
rearrangement of the internal molecular structure of the fiber material. Usually, the
crimp generated by either false twist or air-texturing is imposed on the fiber via mechan-
ical deformation of the fiber as a 2D zig-zag crimp. In some applications the crimped fiber
must be extremely resilient, for example, in fiber filling for pillows, furniture, and so on. In
such cases a mechanical 2D crimp is insufficient, and instead, a latent helical “self
crimping” of the fiber is necessary. A combination of various polyester materials can be
used, for example, PET (polyethylene terephthalate), CD (Cation Dyeable PET), PTT
(polytrimethylene terephthalate), and PBT (poly(butylene terephthalate)).
The basic driver of self-crimping is a shrinkage differential within the fiber. Early
theories to study the crimp mechanism were based on mechanical models of bimetallic
strips. During the early 1980s, Denton41 developed an advanced equation that used a geo-
metrical and mechanical approach to describe this effect. The equation has been proven
practical when applied to most fibers with regular cross-sections.
Denton41 reached three important conclusions based on his equation:
1. Fibers with a single interface exhibit the best crimp potential;
2. The crimp potential is maximized in a skein with a straight interface passing through
the center of the cross-sectional area of a conjugated fiber; and
3. The crimp potential is zero for any cross-section with a center of symmetry (such as
centric core/sheath).
To obtain sufficient crimp the differential shrinkage must exceed a certain value. The
differential shrinkage can be obtained in different ways and thermal shrinkage without.
A theoretical model proposed by Denton41 proved to be very useful for predicting
crimp potential. Maintaining identical or very similar melt viscosities of the two com-
ponents was demonstrated to be very critical for obtaining a straight interface and elimi-
nating the dog-legging problem during melt spinning. Regarding the thermal treatment
following melt spinning, a temperature range of 20 � 308 higher than the Tg of the
harder side in the fiber is the optimum condition. The crimp tests illustrate that the triangu-
lar shapes are found to be superior to the round cross section.
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Spinning of conjugated fiber has some technical difficulties:40
. The melt instability between the two ingredients;
. The need to instantly adjust the throughput ratio;
. The complex design of the conjugated spinnerets.
Du Pont de Nemours (Wilmington, DE) started to study the first self-crimp yarn (PP) in the
early 1960s. Recently, the newly commercialized self-crimp products of DuPont,
polyester T-400 and nylon T-800, have become very popular in the market. Unitica
(Hyogo, Japan) also commercialized the self-crimp yarns, Z-10 and S-10. Furthermore,
a nylon/polyurethane bicomponent filament, Sideria, developed by Kanebo (Japan), can
adapt heat treatment to self-crimp itself to an appropriate degree.
Some research shows that the crimp of triangular shapes is superior to the round cross
section. The optimum volume ratio for making a self-crimp bicomponent skein is 50/50.Finally, the study found that the combination of PET/PTT outperformed that of PET/PBTand PET/CD in terms of crimp potential, crimp stability, and elastic recovery. This
phenomenon is primarily attributed to the markedly different thermal shrinkages of PET
and PTT (Figure 3).
3. Polyether-ester Elastic Fiber
Polyether ester fiber was developed early as a thermoplastic elastomer in the 1970s and
industrialized in plastics trade. Recently some research center and factories have done
some research about the polyether ester, but don’t produce volume.43
Fiber of polyether-ester was obtained by melt spinning from the polyester and
polyether block copolymer.44 It was a medium elastic fiber with breaking elongation of
600% and the elastic recovery is above 85% at the elongation of 100%. It has good dye-
ability and anti-chemical properties.
There are many similar properties of polyether ester fiber and spandex. In chemical
structure, both fibers have long chain polyether and the elasticity root from the entropy
change. The advantages of polyether-ester fiber are the cheap raw materials and
nontoxic and spinning on PET conventional machines. So the polyether-ester fiber may
replace spandex in some applications.
There are no chemical crosslinking points and hydrogen bonds between the long
molecular chains.45 The intermolecular linking of the crystallites offers the elasticity.
Figure 3. Cross section of bicomponent self crimp fibers a) PTT/PBT bicomponent fiber, b) T400
fiber (reprinted from Refs. 40,42 with permission from John Wiley & Sons Inc.).
New Developments in Elastic Fibers 289
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For common polyether-ester, the crosslinking between molecules is weak. In order to
enhance the elasticity, appropriate tie points will be formed, which do not only relate to
the chemical structure but also the spinning and post treatments.
Polyether-ester also includes the hard segments of crystalline regions and soft segment
of amorphous regions.46,47 An elastomer can be described as a continuous amorphous
phase dotted with microcrystalline structure. When stretched, stress is applied to the crys-
talline phase through joint and microcrystalline phase orients, then finally the stress is
applied to the net structure of the polymer. So the soft segment deforms. When
unloaded, the soft segment will release energy and recover to the original state (Table 5).
Polyether-ester elastomer is a linear block copolymer. The typical chemical structure
is shown in Fig. 4. The most suitable materials are terephthalic acid, 1,4 butylene glycol,
ethylene glycol and polydihydric alcohol ether.
The polymerization process includes the esterification, prepolymerization, and post
polymerization as for the conventional polyester polymerization method.
Du Pon’s patent adopted branched dicarboxylic acid and dihydric alcohol as
amorphous soft segments to avoid the frozen crystallization during drawing. This
method improved the tear strength and flexibility properties.43
In order to improve the elasticity stability, a Japanese patent48 reported a method to
add an unsaturated compound of high temperature stability to the copolymer.
Improving the phase separation is another method to increase the stability. A patent49
reported that adding some crystalline nucleation agents such as calcium stearate or
magnesium stearate can accelerate phase separation and microcrystalline formation and
improve the elasticity finally.
Table 5Characteristics of polyether-ester
General tenacity Medium tenacity High tenacity
Tenacity (cN/dtex) 0.45–0.89 2.67–3.56 7.12–8.01
Elongation (%) 300–800 800–1000 7.0–10.0
Recovery elongation
(elongation of 50%)
80–90 95–97 —
Density (g . cm23) 1.0–1.3
Melting point (8C) 200–220 200–220 .230
Figure 4. Polyether-ester molecular formula.42,44
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Polyether-ester fiber can be gained by melt spinning as polyester does. The chips of
polyether ester dry in vacuum tumble dryer for half an hour at 1208C at 40Pa. The spinning
temperature is controlled 208C higher than the melting point.
4. Hard Elastic Fiber
Hard elastic material is characterized by its special morphology and mechanical proper-
ties. These materials are usually prepared from the melt in the form of extruded films
and fibers under specific condition of crystallization. For common elastic materials,
while under tension, the molecule of the high elastic state polymer material is
extended; when unloaded, the molecule tries to come back the coiled shape. From the
point of view of thermodynamics, this elasticity root is the change of entropy, so it is
called entropy elasticity. According to this mechanism, the polymers with high crystalli-
nity do not have high elasticity. But PP, PE, etc fibers present high elongation like rubber
and have good reversion under specific melt spinning condition. Because of the higher
modulus than rubbers, so they were called the hard elastic fibers.49,50
The essential morphological feature of the elastic materials, as revealed by X-ray dif-
fraction and electron microscopy,51 is the presence of stacked crystalline lamellae. Their
lamellar surfaces are aligned normal to the extrusion direction of the fibers. The general-
ized properties of these row structure materials include high elastic recovery from very
high strains such as 50–95% recovery from 100% extension, a reversible reduction of
density with an enormous increase of pore volume upon stretching, and high deformability
with good recovery at liquid nitrogen temperature. Polymers that can be used for the
formation of such elastic materials include semicrystalline polymers as polyoxymethylene
(POM), poly (propylene) (PP), poly-(4-methyl-1-pentene) (PMP) (TPX), polyethylene
(PE), etc.52,53
The mechanism of elasticity is based on splaying apart of their lamellae, and their
reversible bending and torsional deformation during macroscopic deformation of the
materials. Additional work on PP hard elastic fibers showed that the fiber exhibited a
porosity of a peculiar nature when it was stretched significantly. The formation of
microvoid is due to the stacked lamellar crystal structure normal to the fiber axis within
the material. When the fiber is stretched, the crystal lamellae are separated with a large
amount of voids that are interconnected. That is why hard elastic polymers can be
prepared into hollow fiber membranes through melting spinning-stretching (MS)
process. Hollow fiber membranes such as i-PP, PE made by the MS process have been
commercialized and widely applied in water treatments.
The deformation mechanism of hard elastic fibers results in special elastic properties.
At least four basic structural models have been proposed to explain their elastic properties.
These consist of
a. a leaf-spring model involving the elastic bending of lamellae;
b. reversible shear of lamellae between fixed tie points;
c. a general model based on a change in entropy in the intermolecular layer and an
increase in surface energy during extension of a hard elastic fiber, and
d. a combined structural model that attributes the stress for extension to the pulling of
fibrils from lamellae and the retractive force resulting in the particular elastic proper-
ties to surface energy and entropy effects in the fibrils. These four models indicate
different mechanical properties and structures in the strained state.
New Developments in Elastic Fibers 291
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The model in Fig. 5 shows the deformation process. From 5 to 40% extension, the oriented
crystal lamellae separate gradually and undergo an elastic process, the amorphous region
undergoes crystal rotation and plastic deformation processes. Further increase of stress
leads to increasing competition from elastic and plastic deformation processes and these
results correspond to the second yield point in the stress-strain curve. Above 40%
extension, the plastic deformation process becomes increasingly dominant. The whole
process can be divided into three parts: crystal rotation, lamellar separation, and plastic
deformation.
The hard elastic fibers can be interwoven with other common fiber to produce elastic
fabric such as sock, kneecap, and swimwear. It can replace spandex partly; can be used to
produce carpet, which have good recovery property; and produce elastic threads, elastic
safe nets, and fishnets.
5. XLA Fibers
XLATM is olefin-based stretch fiber that is naturally resistant to harsh chemicals, high heat,
and UV light. Incorporating XLA fiber into fabrics offers unmatched opportunities for
developing easy-to-handle, durable garments with improved shape retention. In USA
Lastol fiber is the new generic name for this polyolefin based elastic fiber.55–58
5.1 Microstructure
The special microstructure of XLA combines long, flexible chains with crystallites and
covalent bonds or cross-links, forming an intricate network (Fig. 6). Using Dow proprie-
tary technology, the length of the chains and number of crystallites are specifically con-
trolled to give XLA fiber a unique elastic profile. High stretch is achieved with low
Figure 5. Deformation models of hard elastic PVDF fibers (reprinted from Ref. 54 with permission
from John Wiley & Sons Inc.).
J. Hu et al.292
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levels of force, allowing garments to stretch and flex effortlessly and still return to their
original shape.
5.2 Characteristics
5.2.1 Heat Resistance. The cross-links formed in the fiber’s molecular structure are the
key to superior heat resistance. As the temperature increases, crystallites will gradually
disappear and cross-links take over, keeping the network intact. After cooling to room
temperature, crystallites will reform. This makes XLA very different from conventional
melt-spun fibers, which rely on crystallites for both recovery and heat resistance.
Figure 7 shows fibers at room temperature and after three minutes at 2208C. When the
slide cover was slightly pressed, the degraded spandex fiber came apart, while the XLA
fiber maintained its integrity.
Because XLA fiber can survive intense heat, it enables a greater range of processing
for stretch fabrics and garments. High temperature thermosol dyeing, high pressure and
high temperature jet dyeing of polyester (1308C), and high temperature or extended
Figure 7. Hot- stage photomicrographs of 40-denier XLA fiber and spandex (reprinted from Ref. 60
with permission from the Dow Chemical Co.).
Figure 6. Microstructure of XLA fibers (reprinted from Ref. 59 with permission from the Dow
Chemical Co.).
New Developments in Elastic Fibers 293
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time-curing processes for functional finishes are now possible. Stretch fabrics enhanced
with XLA can also withstand high temperature steam press (Hoffman Press), tumble
drying, and medium or high ironing temperatures.
5.2.2 Chemical and UV Resistance. XLA fiber technology is based on olefin chemistry
and just like other olefin-based plastics, which can be used to make bottles for bleach and
cleaners. The fibers are inherently resistant to chemical degradation. Fiber test exposures
were carried out in conditions closely simulating or even more severe than industrial
processes such as no-iron finishing, mercerizing, and industrial laundering. Under the
stress of these harsh conditions, the fiber strength did not noticeably change. Because
olefins have an affinity to hydrocarbon solvents and mineral oils, XLA fiber should not
be exposed to these classes of chemicals for extended periods of time.
Just as it wards off the effects of chemicals, XLA resists degradation caused by UV
light. The chemical and UV light resistance of XLA fiber technology enable valuable pro-
cessing advantages and offer excellent durability.
Resistance to chemicals allows for optimum processing conditions and enables the
application of a wide variety of functional finishes.
Chemical resistance enables aggressive garment processing like denim washes, no-
iron garment dipping, and refurbishment via commercial laundering and dry-cleaning
even industrial laundering and the high-heat tunnel drying of uniforms.
UV/Xenon resistance makes the fibers to deliver stretch in end-use applications
demanding top-notch performance such as active wear, industrial, and automotive.60
The unique fiber technology of XLA combines that soft feeling, smooth performance
and fluid motion into familiar base fabrics like cotton, wool, and linen, so fabrics stay
fresh, flexible, and durable for the future’s endless, exciting opportunities.
5.2.3 Application. XLA elastic fiber is being used in a number of different fabrics and
concept garments suitable:59–62
. Wool: suits, suit separates tailored sportswear, formal wear, and career wear made
from pure worsted wool and worsted wool blends can be enhanced with XLA
elastic fiber. These stretch wools and wool blends offer improved recovery over
natural stretch and improved drape and hand over spandex yarn alternatives.. Swimwear: for performance swimwear, XLA elastic fiber offers stretch that stays—
continuous exposure to chlorine and UV light will not compromise the lasting
stretch performance of XLA.. Intimates: XLA elastic fiber for intimates can offer a new standard in fit, color
matching, comfort, and drape.. No-wrinkle stretch cotton: ‘easy care’ can be achieved through performance and
functional finishes such as stain and wrinkle resistance and ‘permanent crease’–
without loss of elasticity.
6. Shape Memory Fibers
6.1 One Way Shape Memory Fiber
Presently, the study about shape memory polymer (SMPU) materials has been widely
conducted since it was introduced in 1984 in Japan.63 Based on the research result, the
mechanism of the thermally induced shape-memory effect of these materials has been
J. Hu et al.294
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established on the base of the formation of phase segregated morphology. In shape memory
polymer such as shape memory polyurethane, in one of the phases, there is a transition temp-
erature (Ttrans) in usage temperature range such as melting point or glass transition temperature
of soft segments domain. The obvious characteristic of shape memory polymer is the elastic
modulus, which can be changed at least two orders of magnitude times at the temperature
between lower and higher than the transition temperature (Ttrans). In addition, the formation
of stable hard segment domains acting as physical crosslink above the permanent transition
point (Tperm) is responsible for memorizing the permanent shape. Tperm may be melting temp-
erature of hard segment (Tmh) or glass transition temperature of hard segment (Tgh) according
to different molecular structure, such as hard segment content and the molecular regularity of
the hard segment. Above this temperature, the polymer melting occurs and will not be
different from the conventional elastomer. The transition temperature Ttrans is either a
melting temperature(Tms)64 or a glass transition temperature(Tgs).
65,66 In the case of Tms, a rela-
tively sharp transition can be observed in most cases while Tgs (glass transitions temperature of
soft segment) always is located in a broad temperature range. Mixed glass transitions temp-
erature Tg mix between the glass transition of the hard segment and the soft segment may
occur in the cases where there is no sufficient phase separation between the hard segment
and soft segment. Mixed glass transition temperature can also act as switching transitions
for the thermally induced shape-memory effect.67,68
As for the application of shape memory polymer used in fiber spinning to impart the
smart function into fabric, there are only few literatures references about the study of
shape memory polyurethane fiber. Nevertheless, the sparse application and production of
these kinds of functional fibers has aroused much attention. In the patent, Hayashi et al.67
reported that a woven fabric of shape memory polymer which is formed by weaving yarns
of shape memory polymer fibers along or by weaving said yarns or ordinary natural or
synthetic fibers wherein the shape memory polymer fibers are made of a polyurethane
elastomer having a shapedmemory property. Chun et al.69,70 studied the shape memory poly-
urethane composed of PTMG, BDO, MDI, with the switching temperature range
from 2 158C to 1.58C. The shape memory fiber made of their shape memory polyurethane
can be prepared with electrospinning with the use of the mixed solvent of DMF (N,N-
dimethylformamide) and THF (tetrahydrofuran)71 (Figure 8). The electrospun polyurethane
nonwovens with hard segment concentration of 40 and 50 wt% were found to have a
shape recovery of more than 80%. Hu et al.72,73 have studied the shape memory effect of
shape memory polyurethane fiber composed of PBA (poly (butylene adipate)) or PEA
(poly (ethylene adipate)), MDI (4,40-methylene-bis-phenyl isocyanate), BDO (1,4-butane-
diol) with the transition temperature at around room temperature (29 � 648C). Moreover,
with the usage of various processing technology, the shape memory polymer has been suc-
cessfully engineered into the series of fibers and yarns with tailor-made shape memory
function, applicable tenacity (6 � 14cN/tex) and maximum strain (35 � 204%). The
shape memory function of the fibers can be demonstrated by the applicable fixing ability
(70 � 100%) for stretching at room temperature and the admirable recovery ability after
heating the stretched fiber beyond the transition temperature.
6.2 Comparison between Shape Memory Fiber and Traditional Elastic Fiber
In the study of shape memory polyurethane fiber, not only the shape memory function was
worthy of being investigated systematically, but the comparison between shape memory
fiber and traditional man made fiber need to be made as well, so as to obtain an overall
understanding for such kinds of functional fibers.
New Developments in Elastic Fibers 295
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It is easy to notice that the man made filaments approximately might be attributed
to two features: one is of high tensile strength (tenacity: 5 � 7 g/den for Nylon 6)
and modulus, but low elongation at break (25 � 40% for Nylon 6) and high elastic
recovery with only minor deformation such as Nylon 673; the other one is of a
very low initial modulus, very high elongation ratio at break (500 � 600%) and
nearly complete instant elastic recovery after stretching (90 � 100%) such as
Lycra.74 In the study for shape memory polyurethane filament, the heating responsive
shape memory effect was expected to be introduced into the multi-filaments, namely
to cause the deformation to be recovered with stimulus of heating above the transition
temperature. The glassy or crystallizable soft segment at the temperature below tran-
sition temperature (Tg or Tm) can impart the fiber with relative high initial modulus,
applicable elongation ratio and strength at break, in which the last factor is usually
considered mostly for kitting process.71–73 As shown in Figure 8, the stress-strain
Figure 8. Stress-strain behaviour of various man-made fibers (reprinted from Ref. 72 with per-
mission from JohnWiley & Sons Inc.). (a) is the whole X scale from 10% to 700%. (b) is the enlarge-
ment X scale from 10% to 150%.
J. Hu et al.296
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curve of SMPU fibres (PU56-90, PU56-120, PU66-90, PU66-120) is located between
the high modulus fiber such as nylon and the high elasticity fibre such as Lycra; for
stress-strain behavior, the influence of thermal setting is found to be greater than the
hard segment content in the range of hard segments content used in this study; the
thermal setting with higher temperature will give rise to the lower modulus and
tenacity and the higher maximum elongation ratio in these two series of shape
memory polyurethane fibers. Furthermore, the yield points of shape memory poly-
urethane fiber can be observed at the strain at around 5% and the higher the hard
segment content in SMPU fibre, the higher the yield strength will be.
Using dynamic mechanical analysis (DMA), the elastic modulus (E0) in the normal
using temperature range about a variety of man-made fibers was demonstrated in Fig. 9.
The resultant data show that the main difference between SMPU fiber and conventional
man-made fibers is the variation of E0 in normal using temperature range. For SMPU
fibers such as PU56–120 and PU66–120, the variation of E0 is very significant.
Namely, when the temperature was increased above the transition temperature, the E0
will sharply decrease and the rubbery state platform will appear and be extended to
above 1808C. However, for other types of man-made fibers such as polyester and
Lycra, though in the entire heating scan range, there are some transition areas of E0,
such as 2408C for Lycra,74 100 � 1058C for polyester fibers and yarns,75 the elastic
modulus is almost the constant and change little with the increase of temperature in
room temperature range. Therefore, this point imparts the heating responsive shape
memory properties to the SMPU fibre in normal using temperature.
For common elastic fibers, might be the elasticity should be defined as the instant
recoverability of the length on release of the deforming stress. The recoverability in
shape memory fibers should be the recovery ability of deformed fibers with external
stimulus such as heat or chemicals. In this case, the external stimulus is a must.
Figure 9. Comparison of elastic modulus between SMPU fibre and various man-made fibers.
New Developments in Elastic Fibers 297
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6.3 Two Way Shape Memory Fiber
So far, most of the research on shape memory polymer was focused on shape memory
effect based on the programming comprising deforming with external force and automati-
cally recovering from deformed status with the external stimulus, which were usually
called “one-way” shape memory effect in the study of shape memory materials.75–77
Recently, Terentjev et al. developed new thermoplastic liquid-crystalline elastomers
synthesized by using the telechelic principle of microphase separation in triblock copoly-
mers, in which the large central block is made of a main-chain nematic polymer renowned
for its large spontaneous elongation along the nematic director and the crosslinking is
established by small terminal blocks formed of terphenyl moieties.78 The thin well-
aligned fiber, spun from the melt under heating condition at the temperature above the
nematic-isotropic transition, shows significant two-way shape memory effect, which is
characterized by the thermal actuator behavior—reversible contraction of heating and
elongation on cooling caused by the nematic director. In the spinning process, the
nematic ordering and the telechelic crosslinking were formed simultaneously. The
amplitude of actuation strain within the studied temperature range (408C � 1108C)even can reach 500%. The transition point located at around 1008C depends on the
nematic-isotropic transitions temperature. Presently, although the transition point is
quite high for ordinary apparel application, this two way shape memory fiber can help
inspire some novel practice of shape memory fiber in smart and functional textile design.
Conclusions
The new developments of spandex focus on the functional fibers such as highly hydro-
scopic and moisture liberating spandex, highly soft spandex, heat setting spandex, chemi-
cally or chlorine resistant spandex, anti-bacterial spandex, high tenacity spandex, easy
dyeing spandex.
The polyester-ether elastic fibers are promising fibers with a wide range of uses and
lower cost than polyurethane elastic fiber. By controlling their molecular structure,
different functional polyester-ether fibers will be developed.
The developments of hard elastic fiber will emphasize on the production of hollow
fiber and filter materials in medical application.
The polyolefin fibers XLA overcomes limitations of traditional polyolefin and offers
performance advantages compared to existing elastic fibers. It offers processing benefits to
textiles mills, and enhances durability of stretch garments.
The shape memory fibers make the textiles with different style and applications. The
future aim is to investigate two-way multi-stimulus, multi-function bionic shape memory
polymer, which can be activated by thermal, humidity, chemical, magnetism, and electri-
city or optical stimulus and has anti-bacterial, antistatic, anti-mildew, or ultraviolet
resistant functions and to establish a systematic, comprehensive, and an integrated
theory of the shape memory polymer and apply the shape memory polymer in textiles.
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