Aramid

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Aramid fibers are a class of heat-resistant and strong synthetic fibers. Aramid_sentence_0

They are used in aerospace and military applications, for ballistic-rated body armor fabric and ballistic composites, in marine cordage, marine hull reinforcement, and as an asbestos substitute. Aramid_sentence_1

The name is a portmanteau of "aromatic polyamide". Aramid_sentence_2

The chain molecules in the fibers are highly oriented along the fiber axis. Aramid_sentence_3

As a result, a higher proportion of the chemical bond contributes more to fiber strength than in many other synthetic fibers. Aramid_sentence_4

Aramides have a very high melting point (>500 °C). Aramid_sentence_5

Common aramid brand names include Kevlar, Nomex, and Twaron. Aramid_sentence_6

History Aramid_section_0

Aromatic polyamides were first introduced in commercial applications in the early 1960s, with a meta-aramid fiber produced by DuPont as HT-1 and then under the trade name Nomex. Aramid_sentence_7

This fiber, which handles similarly to normal textile apparel fibers, is characterized by its excellent resistance to heat, as it neither melts nor ignites in normal levels of oxygen. Aramid_sentence_8

It is used extensively in the production of protective apparel, air filtration, thermal and electrical insulation, as well as a substitute for asbestos. Aramid_sentence_9

Meta-aramids are also produced in the Netherlands and Japan by Teijin Aramid under the trade name Teijinconex, in Korea by Toray under the trade name Arawin, in China by Yantai Tayho under the trade name New Star, by SRO Group (China) under the trade name X-Fiper, and a variant of meta-aramid in France by Kermel under the trade name Kermel. Aramid_sentence_10

Based on earlier research by Monsanto Company and Bayer, para-aramid fiber with much higher tenacity and elastic modulus was also developed in the 1960s and 1970s by DuPont and AkzoNobel, both profiting from their knowledge of rayon, polyester and nylon processing. Aramid_sentence_11

In 1973 DuPont was the first company to introduce a para-aramid fiber, calling it Kevlar; this remains one of the best-known para-aramids and/or aramids. Aramid_sentence_12

In 1978, Akzo introduced a similar fiber with roughly the same chemical structure calling it Twaron. Aramid_sentence_13

Due to earlier patents on the production process, Akzo and DuPont engaged in a patent dispute in the 1980s. Aramid_sentence_14

Twaron subsequently came under the ownership of the Teijin Aramid Company. Aramid_sentence_15

In 2011, Yantai Tayho introduced similar fiber which is called Taparan in China (see Production). Aramid_sentence_16

Para-aramids are used in many high-tech applications, such as aerospace and military applications, for "bullet-proof" body armor fabric. Aramid_sentence_17

Both meta-aramid and para-aramid fiber can be used to make aramid paper. Aramid_sentence_18

Aramid paper is used as electrical insulation materials and construction materials to make honeycomb core. Aramid_sentence_19

Dupont made aramid paper in 1960s, calling it Nomex paper. Aramid_sentence_20

Yantai Metastar Special Paper introduced an aramid paper in 2007, which is called metastar paper. Aramid_sentence_21

Both Dupont and Yantai Metastar make meta-aramid and para-aramid paper. Aramid_sentence_22

The Federal Trade Commission definition for aramid fiber is: Aramid_sentence_23

Health Aramid_section_1

During the 1990s, an in vitro test of aramid fibers showed they exhibited "many of the same effects on epithelial cells as did asbestos, including increased radiolabeled nucleotide incorporation into DNA and induction of ODC (ornithine decarboxylase) enzyme activity", raising the possibility of carcinogenic implications. Aramid_sentence_24

However, in 2009, it was shown that inhaled aramid fibrils are shortened and quickly cleared from the body and pose little risk. Aramid_sentence_25

A declaration of interest correction was later provided by the author of the study stating that "This review was commissioned and funded by DuPont and Teijin Aramid, but the author alone was responsible for the content and writing of the paper." Aramid_sentence_26

Production Aramid_section_2

World capacity of para-aramid production was estimated at about 41,000 tonnes per year in 2002 and increases each year by 5–10%. Aramid_sentence_27

In 2007 this means a total production capacity of around 55,000 tonnes per year. Aramid_sentence_28

Polymer preparation Aramid_section_3

Aramids are generally prepared by the reaction between an amine group and a carboxylic acid halide group. Aramid_sentence_29

Simple AB homopolymers may look like Aramid_sentence_30

Aramid_description_list_0

  • n NH2−Ar−COCl → −(NH−Ar−CO)n− + n HClAramid_item_0_0

The most well-known aramids (Kevlar, Twaron, Nomex, New Star and Teijinconex) are AABB polymers. Aramid_sentence_31

Nomex, Teijinconex and New Star contain predominantly the meta-linkage and are poly-metaphenylene isophthalamides (MPIA). Aramid_sentence_32

Kevlar and Twaron are both p-phenylene terephthalamides (PPTA), the simplest form of the AABB para-polyaramide. Aramid_sentence_33

PPTA is a product of p-phenylene diamine (PPD) and terephthaloyl dichloride (TDC or TCl). Aramid_sentence_34

Production of PPTA relies on a co-solvent with an ionic component (calcium chloride, CaCl2) to occupy the hydrogen bonds of the amide groups, and an organic component (N-methyl pyrrolidone, NMP) to dissolve the aromatic polymer. Aramid_sentence_35

This process was invented by Leo Vollbracht, who worked at the Dutch chemical firm Akzo. Aramid_sentence_36

Apart from the carcinogenic hexamethylphosphorous triamide (HMPT), still no practical alternative of dissolving the polymer is known. Aramid_sentence_37

The use of the NMP/CaCl2 system led to an extended patent dispute between Akzo and DuPont. Aramid_sentence_38

Spinning Aramid_section_4

After production of the polymer, the aramid fiber is produced by spinning the dissolved polymer to a solid fiber from a liquid chemical blend. Aramid_sentence_39

Polymer solvent for spinning PPTA is generally 100% anhydrous sulfuric acid (H2SO4). Aramid_sentence_40

Appearances Aramid_section_5

Aramid_unordered_list_1

  • FiberAramid_item_1_1
  • Chopped fiberAramid_item_1_2
  • PowderAramid_item_1_3
  • PulpAramid_item_1_4

Other types of aramids Aramid_section_6

Besides meta-aramids like Nomex, other variations belong to the aramid fiber range. Aramid_sentence_41

These are mainly of the copolyamide type, best known under the brand name Technora, as developed by Teijin and introduced in 1976. Aramid_sentence_42

The manufacturing process of Technora reacts PPD and 3,4'-diaminodiphenylether (3,4'-ODA) with terephthaloyl chloride (TCl). Aramid_sentence_43

This relatively simple process uses only one amide solvent, and therefore spinning can be done directly after the polymer production. Aramid_sentence_44

Aramid fiber characteristics Aramid_section_7

Aramids share a high degree of orientation with other fibers such as ultra-high-molecular-weight polyethylene, a characteristic that dominates their properties. Aramid_sentence_45

General Aramid_section_8

Aramid_unordered_list_2

  • good resistance to abrasionAramid_item_2_5
  • good resistance to organic solventsAramid_item_2_6
  • nonconductiveAramid_item_2_7
  • very high melting point (>500 °C)Aramid_item_2_8
  • low flammabilityAramid_item_2_9
  • good fabric integrity at elevated temperaturesAramid_item_2_10
  • sensitive to acids and saltsAramid_item_2_11
  • sensitive to ultraviolet radiationAramid_item_2_12
  • prone to electrostatic charge build-up unless finishedAramid_item_2_13

Para-aramids Aramid_section_9

Aramid_unordered_list_3

  • para-aramid fibers, such as Kevlar and Twaron, provide outstanding strength-to-weight propertiesAramid_item_3_14
  • high chord modulusAramid_item_3_15
  • high tenacityAramid_item_3_16
  • low creepAramid_item_3_17
  • low elongation at break (~3.5%)Aramid_item_3_18
  • difficult to dye – usually solution-dyedAramid_item_3_19

Uses Aramid_section_10

Aramid_unordered_list_4

See also Aramid_section_11

Para-aramid Aramid_sentence_46

Aramid_unordered_list_5

Meta-aramid Aramid_sentence_47

Aramid_unordered_list_6

  • NomexAramid_item_6_51
  • TeijinconexAramid_item_6_52

Others Aramid_sentence_48

Aramid_unordered_list_7


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Aramid.