New fibres for the textile industry of the 21st century: characteristics and final applications

Technical paper by Antonio Piccolini, Rovetex. The original paper is available as a PDF.

Introduction

Innovation is today the main commitment for the future of the textile industry. New products are constantly being sought, and new generation fibres are a class of products of remarkable importance in the development of innovative textiles.

Most of the new fibres introduced to the market in the past decade are an evolution or modification of existing polymers and fibres. Others are completely new: for instance PLA fibre and PTT fibre in the family of synthetic fibres, and soy fibre and bamboo fibre in the family of artificial fibres.

Developing and manufacturing these products, both in fibre production and throughout the textile process, is more complex and expensive than processing conventional fibres, but they deliver high added value in the final application.

This paper explains the main differences between the families of new fibres introduced to the market in recent years and their main textile applications, covering:

• the chemical and physical intrinsic characteristics of the new fibres;
• basic concepts of how these products have to be processed in spinning, weaving and finishing;
• the requirements of the final applications, with examples in standard textile products and industrial end uses.

Fibrous materials and textile fibres

Definitions

• Fibre: a fine thread, or thread-like cell, of a natural or artificial substance.
• Textile fibre: any fibrous material that can be used to manufacture textile products.

Textile fibres come in two forms:

• Staple fibre: short fibre which, to become a textile product, has to be either spun and twisted into a yarn, or bonded into a nonwoven.
• Continuous filament: long filaments that are already a textile product.

Man-made fibres from natural polymers: artificial fibres

Cellulose fibres

Rayon (100% regenerated cellulose)

• 1892: nitrocellulose process, Hilaire de Chardonnet. Abandoned as too expensive and dangerous.
• 1925: viscose process. Courtaulds (UK) starts selling the first viscose staple fibre, “Fibro”.

Cuprammonium rayon (100% regenerated cellulose)

• 1892: first industrial developments in Germany, with poor commercial results.
• 1920 to 1930: J. P. Bemberg improves the industrial process and starts selling filament yarns.

Acetate rayon (cellulose diacetate and triacetate)

• 1921: Celanese develops the industrial process and starts selling filament yarns.

Viscose, cuprammonium and acetate rayons are still produced today with advanced, environmentally friendly processes. They hold small but important market niches.

Protein fibres

Casein fibre (milk protein)

• 1935: Snia Viscosa starts selling Lanital, later improved under the brand Merinova.
• 1938: Courtaulds starts selling a fibre similar to Lanital under the brand Fibrolane.

Other protein fibres developed between 1935 and 1945:

• UK: Ardil, from peanut protein.
• USA: Vicara, from zein (corn).
• Japan: a soy fibre, without a brand name.

Protein fibres were created to imitate wool. They effectively disappeared from the market in the 1960s, when higher-performance synthetic fibres, mainly acrylics, were introduced.

Recent developments: a few years ago a new protein fibre from soy, SPB, was introduced to the market as an imitation of wool and cashmere, produced in China by Xinhui Yuexin Chemical Fibre Co., Ltd.

Man-made fibres from polymers not present in nature: synthetic fibres

Polyvinyl chloride

• 1913: F. Klatte of Griesheim-Elektron produced the first synthetic fibre in Germany, starting from a chlorinated polymer. Production difficulties, in particular the recovery of the spinning solvent (cyclohexanol), prevented its industrial development.
• 1931: R. Hupert of I. G. Farbenindustrie, building on the work of two other German researchers, C. Schoenburg and W. Reppe, produced PeCe, a chlorinated fibre introduced to the market in 1934.

PeCe was the first synthetic fibre made industrially. However, because of its superior technical characteristics, nylon, developed a few years later, is considered “the first true synthetic fibre”.

Polyamide

• 1931: W. H. Carothers, a researcher at Du Pont de Nemours, announced to the American Chemical Society that he had produced a new polymer, “nylon”, from adipic acid and hexamethylenediamine. He described a handful of fibre with a resilience similar to wool and elastic qualities far superior to any known artificial silk.
• 1937: nylon begins industrial production, and it appears on the market in 1939. Because it is made from an acid and an amine that each have 6 carbon atoms, it is known as nylon 6.6.
• 1937: P. Schlack of I. G. Farbenindustrie polymerised caprolactam, creating a fibre called “Perlon”. Produced industrially since 1943, it is known as nylon 6 (6 carbon atoms).

The most common man-made fibres today

Polyester

• 1941: developed in the UK by J. R. Whinfield and J. T. Dickson, building on Carothers’ studies.
• 1948: experimental production starts on a pilot plant.

The patents, which expired in the early 1970s, were acquired by Du Pont for America (the fibre “Dacron”) and by ICI for the rest of the world (the fibre “Terylene”).

Acrylic

• Around 1940 (the date is uncertain because of the war): first experimental production in Germany by H. Rhein, and in the USA by G. H. Latham and R. C. Houtz.
• 1948: Du Pont patents the fibre “Orlon”, and begins marketing it in 1950.

Polypropylene

• 1954: Prof. G. Natta, in the Montecatini laboratories, develops isotactic polypropylene. The invention led first to the plastic material Moplen, followed by the first PP fibre, Meraklon. Natta was later awarded the Nobel Prize in Chemistry for this work.

Man-made fibres for special end uses

Flame retardant fibres

Flame retardant (FR) fibres are mainly produced from three families of base polymers. The limiting oxygen index (LOI) shows the improvement over the standard fibre.

Polymer family	Standard fibre	FR fibre	Example brands
Natural modified polymers	Viscose CV, LOI 20	Viscose FR, LOI 26 to 28	Lenzing FR, Visil
Synthetic modified polymers	Polyester PET/PES, LOI 19 to 21	Polyester FR, LOI 28 to 30	Trevira CS, Securelle
Synthetic modified polymers	Acrylic PAN, LOI 19 to 21	Modacrylic FR (MAC), LOI 28 to 34	Kanecaron, Protex
Intrinsically flame retardant polymers	n/a	Chlorofibre CLF, LOI 38 to 46	Rhovil

Bioactive (antibacterial) fibres

Bioactive fibres are mainly produced from two families of base polymers:

Polymer family	Base fibre	Bioactive fibre	Example brands
Natural modified polymers	Cellulose, modal	Bioactive modal	Modal Fresh
Synthetic modified polymers	Polyester PET	Bioactive polyester	Trevira Bioactive
Synthetic modified polymers	Acrylic PAN	Bioactive acrylic	Amicor, Amicor Plus

High-tech and high-performance fibres

Organic origin. These are produced only from engineered synthetic polymers. The most important from a market point of view are:

Fibre	Polymer	LOI	Brands
Para-aramid (PPTA)	Polyparaphenylene terephthalamide	27 to 29	Kevlar, Twaron
Para-aramid copolymer (PPTA-C)	Copolymer polyparaphenylene / 3,4’-oxydiphenylene terephthalamide	25	Technora
Meta-aramid (PMIA)	Polymetaphenylene isophthalamide	29 to 32	Nomex, Teijinconex
Meta-aramid (PAI)	Polyamide imide	32	Kermel
Meta-aramid (PIC)	Copolyimide	36	P84
Fluoropolymer (PTFE)	Polytetrafluoroethylene	above 90	Teflon, Profilen
Melamine (MF)	Melamine formaldehyde resin	32	Basofil
Phenolic (PHE)	Phenol-aldehyde resin	30 to 34	Kynol
Polybenzimidazole (PBI)	Polybenzimidazole	41	Celanese PBI
PBO	Poly-p-phenylene-2,6-benzobisoxazole	68	Zylon
Polyphenylene sulphide (PPS)	Polyphenylene sulphide	34	Procon, Torcon

Inorganic origin:

• Carbon fibre (CF): above 99.9% carbon.
• Metallic fibre (MTF): 100% stainless steel, 100% silver or 100% copper.
• Others: glass (GF), boron (B), silicon carbide (SiC) and silica (Sil).

Man-made fibre production technology

Apart from some particular exceptions, chemical fibres, both artificial and synthetic, are produced from a polymer turned into a viscous mass (the “dope”) by solution or melting. The dope is extruded through a multi-hole spinneret and the spun filaments are then solidified. The filaments are subsequently oriented at molecular level by drawing, and heat-set.

Three technologies are essentially used in primary spinning.

Wet spinning

The polymer is dissolved in a suitable solvent, extruded, and the filaments are coagulated in a water bath. This was the first technology to be developed. It is still used today for rayon (both continuous filament and staple fibre), most acrylic fibres, modacrylic fibres and aramid fibres.

Dry spinning with solvents

The polymer is dissolved in a suitable solvent and extruded into warm air, at a temperature that allows the solvent to evaporate while the filaments consolidate. This technology is used for acetate, some acrylics and polyvinyl chloride.

Melt spinning (dry spinning by fusion)

The polymer is melted and extruded, and the filaments are solidified by cooling with forced air in a chimney called the “quench”.

This is the most economical and productive technology. It allows high extrusion speeds and requires no washing of the filaments after solidification. It is suitable only for polymers that reach their melting temperature without decomposing, and whose viscosity varies little during melting and extrusion. It is used for polyamides, polyester, polypropylene and polyphenylene sulphide (PPS).

Technology	Artificial fibres	Synthetic fibres
Wet spinning	Cellulose (viscose)	Acrylic, aramid
Dry spinning with solvent	n/a	Acrylic
Melt spinning	n/a	Polyamides, polyester, polypropylene

Electrospinning: a new spinning technology

Electrospinning can be considered a “retrofit and upgrade” of the three traditional technologies. Fibres are extruded using a traditional technology and oriented at molecular level using electrospinning.

In recent years various techniques have been tried to produce single nanofibres and continuous filaments, but electrospinning is the only one available today. The prefix “nano”, from the Greek for “dwarf”, denotes one billionth part (10^-9 m), about 1/80,000 of the diameter of a human hair.

In 1934 Formhals patented a process and outlined an experimental setup for producing polymer filaments using electrostatic force. When used to spin fibres in this way, the process is called electrospinning. In summary, the Formhals description works as follows:

• A high voltage creates an electrically charged jet of polymer solution or melt, which dries or solidifies to leave a polymer fibre. One electrode is placed in the spinning solution or melt, and the other is attached to a collector.
• The electric field is applied to the end of a capillary tube containing the polymer fluid, held by its surface tension. This induces a charge on the surface of the liquid, and mutual charge repulsion creates a force directly opposite to the surface tension.
• As the field intensity increases, the hemispherical surface of the fluid at the tip of the capillary elongates into a conical shape known as the Taylor cone.
• At a critical value, the repulsive electrostatic force overcomes the surface tension and a charged jet of fluid is ejected from the tip of the Taylor cone.
• A solution jet undergoes a whipping process in which the solvent evaporates, leaving a charged polymer fibre that lays itself randomly on a grounded metal collecting screen. A melt jet solidifies as it travels through the air and is collected on the same grounded screen.

In a typical experimental apparatus, the polymer solution or melt is held in a glass tube, usually a pipette, connected to a syringe-like device. A metering pump on the plunger generates a constant pressure and flow of fluid through the pipette. The driving force comes from a high-voltage source, up to 30 kV, through a wire immersed in the solution, and the setup can run on either positive or negative polarity. The spinning rate is controlled by adjusting the fluid flow and the magnitude of the electric field.

Recent and new fibres

A new fibre can come from five types of innovation, each with a different development time and investment.

Type of innovation	Development time	Investment	Examples
Change of the physical-mechanical characteristics of an existing fibre	Short/medium: 6 months to 1 year	n/a	Special cross-section, hollow and multilobal fibres; low or high modulus fibres; cationic dyeable fibres
Conjugation of different existing polymers	Medium: 1 to 5 years	n/a	Low-melt core fibres; some anti-static fibres
Modification of an existing polymer	Medium: 1 to 5 years	Medium/high	FR polyester, FR modacrylic; bioactive polyester, bioactive acrylic
New process for an existing polymer or molecule	Long: 3 to 8 years	Very high	Lyocell, a 100% cellulose solvent-spun fibre (Lenzing, Tencel)
New polymer, new molecule	Long: 5 to 10 years	Very high	PTT (Shell Chemical, Corterra; Du Pont, Sorona); PLA (Cargill Dow, Ingeo)

PTT fibre

PTT (polytrimethylene terephthalate) is a new polymer. Its commercial brand names are Corterra (Shell Chemical) and Sorona (Du Pont).

PLA fibre: a new fibre from a new molecule

PLA (polylactide) is a new polymer developed by Cargill Dow under the brand name NatureWorks; the fibre is marketed as Ingeo.

The raw material for PLA is dextrose, obtained from primary agricultural products such as corn. The Cargill Dow manufacturing process works in steps:

1. Dextrose is converted into lactic acid by fermentation.
2. Lactic acid is transformed by condensation into the basic monomer, “lactide”.
3. PLA is made by ring-opening polymerisation of lactide.

The original paper also compares the physical and mechanical characteristics of a 1.5 dtex polyester (PES) fibre with a 1.5 dtex PLA fibre; see the PDF for the comparison.

Short and medium/long-term forecast: conclusions

Developing a completely new fibre requires a very long time and huge investment before reaching industrial production. To develop PLA Ingeo, Dow Cargill spent about US$200 million from the study phase to the first industrial plant for producing the polymer. All short-term, low-investment projects are therefore directed at further modification and upgrading of existing fibres.

The few long-term projects already in progress are mainly aimed at developing new polymers and new fibres from renewable raw materials of vegetable origin. Not only Ingeo but also Sorona is a synthetic fibre of vegetable origin. Notably, Du Pont sold its entire fibres business but kept Sorona.

The usable vegetable raw materials can vary widely, but the most used today is corn, because of its high worldwide availability. About two years ago a Chinese producer introduced a fibre obtained from soybean, but its diffusion is very limited.

Nanofibres face three big problems before short-term industrialisation:

1. Technology: electrospinning, the technology used today, is still at the level of laboratory apparatus. Designing and building an industrial plant needs high investment in research and engineering.
2. Polymers: the polymers tested so far, only at laboratory level, are very limited, mainly polyester.
3. Market: there is no market ready for this new type of product. Some niche sectors, such as micro-filtration for the sanitary and medical sector, could perhaps begin semi-industrial experimentation today.

Certainly not the traditional textile sector, even at its most advanced. There, even simple “islands-in-the-sea” super-microfibres, on the market for at least 15 years, have a limited market and are used only for very expensive, true niche products such as Alcantara and similar materials.

References

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• Pio Bertoli: Manuale delle fibre tessili, Etas/Kompass.
• Hans J. Koslowski: Chemiefaser-Lexikon: Begriffe, Zahlen, Handelsnamen, Deutscher Fachverlag, 1997.
• Cargill Dow, USA: PLA lactide polymer NatureWorks.
• Prof. Kirill E. Perepelkin, St. Petersburg State University of Technology, Russia, and Dr. Nikolai N. Machalaba, J-S Co “Tverchimvolokno”, Tver, Russia: Para-aramid “world family”: comparison and modification possibilities for different applications.
• A. Piccolini, Centro Tessile Cotoniero e Abbigliamento, Busto Arsizio, Italy: Fibre High Tech e Flame Retardant, 1997.
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