ARAMID FIBER

ASAD JAMIL 06-NTU-107

TANVEER BALOCH 06-NTU-136

ARAMID FIBER U.S federal trade comission define the

armid fiber as under:“ a manufactured fiber in which fiber

forming substance is a long chain synthetic polyamid e in which atleast 85% of the amide linkage are attached directly to aromatic ring”

ARAMID FIBER A strong, heat-resistant fiber formed of

polymers with repeating aromatic groups branching from a carbon backbone, used in materials for bulletproof vests and radial tires.

They are fibers in which the chain molecules are highly oriented along the fiber axis.

The name is a shortened form of “Aromatic polyamide”.

ARAMID FIBER Aramids share a high degree of

orientation with other fibers such as Ultra high molecular weight polyethylene, a characteristic which dominates their properties. Also called polyaramid.

Para-aramid structure

General Characteristics

No melting point degradation starts from 500°C

Good fabric integrity at elevated temperatures

good resistance to organic solvents nonconductive low flammability sensitive to ultraviolet radiation

General Characteristics prone to static build-up unless finished Para-aramid fibers, which have a slightly

different molecular structure, also provide outstanding strength-to-weight properties, high tenacity and high modulus

Excellent Tensile Strength: 3620 MPa Low Density: 1.44 gm/cm3 (.052 lb/in3) Good Stiffness: 131 GPa (19 msi)

General Characteristics Excellent Toughness. Works well as a hybrid material. Negative Coefficient of linear expansion. Low Dielectric Constant.

Para-aramids

low elongation at break (~3.5%) high Young's modulus high tenacity low creep para-aramid fibers such as Kevlar and

Twaron, provide outstanding strength-to-weight properties

difficult to dye - usually solution dyed 

Uses

heat protective clothing and helmets flame-resistant clothing body armor asbestos replacement (e.g. brake linings) hot air filtration fabrics optical fiber cable systems composite materials

Uses

ropes and cables fiber reinforced concrete reinforced thermoplastic pipes brake pads mechanical rubber goods reinforcement hockey sticks (normally in composition

with such materials as wood and carbon) loudspeaker diaphragms sporting goods.

MANUFACTURING World capacity of aramid production is

estimated at about 41,000 tons/yr in 2002 and increases each year by 5-10%.

In 2007 this means a total production capacity of around 55,000 tons/yr.

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

nNH2+Ar-COCl → -(NH-Ar-CO)n- + nHCl

MANUFACTURING Steps of manufacturing polmerization of Aramid

fiberSTEP 1: dissolve PPD ( poly phenylene diamine) in

mixture of HMPA(hexamethylphosphoramide) and NMP(N-methyl pyrrolidone)

STEP 2: cooling in an ice bath at – 15 c in nitrogen atmosphere.

STEP 3:add TCL(tere phthaloyl chloride) and stirr rapidly- paste like gel formed.

STEP 4: discontinuos stirring and allow the reaction mixture to stand for gradual warming to room temp:

MANUFACTURINGSTEP 5: agitate reaction mixture with water

to wash away solvent and HCLSTEP6: collect the polymer by filteration STEP7: 2:1 ratio by volume of HMPA:NMP

produced PPTA with highest inherent viscosity

STEP 8: optimum reactant (PPI) and TCL concentration ca .25 M.

STEP 9: inherent viscosity decreases rapidly if the reactant concentration is less .25 M

MANUFACTURINGSTEP 10: Inherent viscosity also decreases if

reactant concentration is more than .30 M but the drop is more gradual.

SPINNING OF FIBERS:STEP 1: dissolve PPTA in high strenght H2

SO4 to get liquid crystalline solution.STEP 2: heat the solution upto 80 c

concentration limit of polymer in the solution is 20 % by weight

MANUFACTURINGSTEP 3: degree of orientaion of solution

depends on temperature and polymer concentration

STEP 4: extrude spinning solution through spinnert and draw across small air gap.

STEP 5: wash neutralise, hot draw and dry.

Dyeing of Aramid fiber

The aramid fiber most commonly used for textile purposes is Nomex .

To attain a good color yield, dyeing is carried out at pH 3-4 and 120°C.

Cotton, rayon, and other common fibers are easily dyed in aqueous systems with water dispersable dyes.

However, aramid fibers such as poly-meta-phenyleneisophthalamide, sold by DuPont as Nomex are very difficult to dye without a suitable dye carrier or transfer agent. 

Dyeing of Aramid fiber A solvent with some affinity for these

hydrophobic fibers is required to swell and/or plasticize the fibers, which allows the cationic dye to penetrate beyond the fiber surface.

The solvent should have a low vapor pressure to facilitate dyeing of the fibers at relatively high temperatures without flammability concerns. 

The original solvent used in the dyeing of aramid fibers was acetophenone

Dyeing of Aramid fiber This solvent is a very efficient dye carrier but it

has a very pungent odor.   For this and other reasons, the textile industry

has replaced acetophenone with solvents that have a more favorable odor profile. 

Acetophenone is still used as a standard in laboratory studies when comparing solvent performance. 

A solvent-dyeing process for aramid fibers is described which is capable of producing fiber and fabrics having excellent depth of shades.

Dyeing of Aramid fiber The brightness of the fibers and fabrics is

quite high when the undyed fibers are bright.

When properly selected basic dyes are used, and when heavy shades are developed on the fabrics, good dyed lightfastness values are obtained.

Carpet samples of Aramid dyed via the solvent-dyeing process described are considerably brighter, cleaner, and deeper in shades.

Dyeing Aramid fiber The dyed lightfastness values

(Gray Scale) are considerably higher for these solvent-dyed carpet samples.

THE END