Aramid
Aramid fibers, short for aromatic polyamide, are a class of heat-resistant and strong
The chain molecules in the fibers are highly oriented along the fiber axis. As a result, a higher proportion of the chemical bond contributes more to fiber strength than in many other synthetic fibers. Aramids have a very high melting point (>500 °C (932 °F)).
Common aramid
.Terminology and chemical structure
The term aramid is shortened from
Aromatic in the longer name refers to the presence of aromatic rings of six carbon atoms. In aramids these rings are connected via amide linkages each comprising a CO group attached to an NH group.
In order to meet the FTC definition of an aramid,[4] at least 85% of these linkages must be attached to two aromatic rings.[5] Below 85%, the material is instead classed as nylon.[4]
Para-aramids and meta-aramids
Aramids are divided into two main types according to where the linkages attach to the rings. Numbering the carbon atoms sequentially around a ring, para-aramids have the linkages attached at positions 1 and 4, while meta-aramids have them at positions 1 and 3.[6] That is, the attachment points are diametrically opposite each other in para-aramids, and two atoms apart in meta-aramids. The illustration thus shows a para-aramid.
History
Aromatic polyamides were first introduced in commercial applications in the early 1960s, with a
Meta-aramids are also produced in the Netherlands and Japan by
Based on earlier research by
In 1978, Akzo introduced a similar fiber with roughly the same chemical structure calling it Twaron. Due to earlier patents on the production process, Akzo and DuPont engaged in a patent dispute in the 1980s. Twaron subsequently came under the ownership of the Teijin Aramid Company. In 2011, Yantai Tayho introduced similar fiber which is called Taparan in China (see Production).
Para-aramids are used in many high-tech applications, such as aerospace and military applications, for "bullet-proof"
Both meta-aramid and para-aramid fiber can be used to make aramid paper. Aramid paper is used as electrical insulation materials and construction materials to make honeycomb core. Dupont made aramid paper during the 1960s, calling it Nomex paper. Yantai Metastar Special Paper introduced an aramid paper in 2007, which is called metastar paper. Both Dupont and Yantai Metastar make meta-aramid and para-aramid paper.[citation needed]
Health
During the 1990s, an
Production
World capacity of para-aramid production was estimated at about 41,000 t (40,000 long tons; 45,000 short tons) per year in 2002 and increases each year by 5–10%.[11] In 2007 this means a total production capacity of around 55,000 tonnes per year.[citation needed]
Polymer preparation
Aramids are generally prepared by the reaction between an
Well-known aramid polymers such as Kevlar, Twaron, Nomex, New Star, and Teijinconex) are prepared from diamine and diacid (or equivalent) precursors. These polymers can be further classified according to the linkages on the aromatic subunits. Nomex, Teijinconex, and New Star contain predominantly the meta-linkage. They are called poly-metaphenylene isophthalamides (MPIAs). By contrast, Kevlar and Twaron both feature para-linkages. They are called p-phenylene terephthalamides (PPTAs). PPTA is a product of p-phenylene diamine (PPD) and terephthaloyl dichloride (TDC or TCl).
Production of PPTA relies on a
Spinning
After production of the polymer, the aramid fiber is produced by spinning the dissolved polymer to a solid fiber from a liquid chemical blend. Polymer solvent for spinning PPTA is generally 100% anhydrous sulfuric acid (H2SO4).
Appearances
- Fiber
- Chopped fiber
- Powder
- Pulp
Other types of aramids
Besides meta-aramids like Nomex, other variations belong to the aramid fiber range. These are mainly of the copolyamide type, best known under the brand name Technora, as developed by Teijin and introduced in 1976. The manufacturing process of Technora reacts PPD and 3,4'-diaminodiphenylether (3,4'-ODA) with terephthaloyl chloride (TCl).[12] This relatively simple process uses only one amide solvent, and therefore spinning can be done directly after the polymer production.
Aramid fiber characteristics
Aramids share a high degree of orientation with other fibers such as ultra-high-molecular-weight polyethylene, a characteristic that dominates their properties.
General
- good resistance to abrasion
- good resistance to organic solvents
- nonconductive [ambiguous]
- very high melting point (>500 °C (932 °F))
- low flammability
- good fabric integrity at elevated temperatures
- sensitive to acids and salts [how?]
- sensitive to ultraviolet radiation [how?]
- prone to electrostatic charge build-up unless finished[13]
Para-aramids
- para-aramid fibers, such as Kevlar and Twaron, provide outstanding strength-to-weight properties
- high chord modulus
- high tenacity
- low creep
- low elongation at break (~3.5%)
- difficult to dye – usually solution-dyed[13]
Uses
- flame-resistant clothing
- heat-protective clothing and helmets
- Spectra
- composite materials
- asbestos replacement (e.g. brake linings)
- hot air filtration fabrics
- tires, newly as Sulfron (sulfur-modified Twaron)
- mechanical rubbergoods reinforcement
- ropes and cables[15]
- V-belts (automotive, machinery, equipment, and more)
- wicks for fire dancing
- optical fiber cablesystems
- sail cloth (not necessarily racing boat sails)
- sporting goods
- drumheads
- wind instrument reeds, such as the Fibracell brand
- loudspeaker diaphragms
- boathull material
- fiber-reinforced concrete
- reinforced thermoplastic pipes
- tennis strings, e.g. by Ashaway and Prince tennis companies
- hockey sticks (normally in composition with such materials as wood and carbon)
- snowboards
- jet engine enclosures
- fishing reel drag systems
- asphalt reinforcement
- Prusiksfor rock climbers (which slide along the main rope and can otherwise melt due to friction).
- Snowboardscore reinforcement
See also
Para-aramid
Meta-aramid
- Nomex
- Teijinconex
Others
Notes and references
- S2CID 136433442.
- ISBN 978-0-387-31021-3. Retrieved 16 September 2021.
- ISBN 978-0-87005-198-2.
- ^ a b c Commercial Practices, Part 303, §303.7 Generic names and definitions for manufactured fibers.
- ^ The full definition of aramid fibre is "a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which at least 85% of the amide linkages, ( ) are attached directly to two aromatic rings", with a diagram between the parentheses which shows a vertically oriented CO group attached horizontally to an NH group. There is an incoming bond to the C atom and an outgoing one from the NH group.
- ^ Position 1 is simply chosen as the point where one of the chains is attached. We then count around the ring in the shortest direction until we reach the other one.
- ^ ISBN 978-0-387-27842-1.
- PMID 8062644.
- S2CID 6508943.
- S2CID 218987849.
- ISBN 978-0-309-09614-0.
- .
- ^ a b Kadolph, Sara J. Anna L. Langford (2002). "Textiles". Pearson Education, Inc. Upper Saddle River, NJ.
- .
- ^ "Aramid Cables". FibreMax. Archived from the original on 2021-12-01.
Further reading
- J A Reglero Ruiz; M Trigo-López; F C Garcia; J M Garcia (2017). "Functional Aromatic Polyamides". Polymers. 9 (12): 414. PMID 30965723.
- JWS Hearle (2000). High-performance fibers. Woodhead Publishing LTD., Abington, UK – the Textile Institute. ISBN 978-1-85573-539-2.
- Doetze J. Sikkema (2002). "Manmade fibers one hundred years: Polymers and polymer design". J Appl Polym Sci (83): 484–488.
- Kh. Hillermeier & H.G. Weijland (1977). "An aramid yarn for reinforcing plastics". Plastica (11): 374–380.
- DuPont and Teijin to expand aramid production – September 2004