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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

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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


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


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

J. Hu et al.278


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).



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

J. Hu et al.280


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



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

J. Hu et al.282


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.



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


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



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


. 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.



. 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.

J. Hu et al.288


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.).



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

J. Hu et al.290


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.



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


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.).



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


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.



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


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.



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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