Sulfur fiber
The sulfur fiber or polyphenylene sulfide (PPS) is
characterized by unusual toughness and good load-bearing capabilities. The fiber-forming substance in the case of sulfur fiber is a long-chain synthetic polysulphide
with at least 85% of the sulfide linkages attached directly to two aromatic
rings.
Fiber formation
The raw material for
sulfur fiber is p-dichlorobenzene and sodium sulfide. The conversion of the raw
material into fibers consist of three stages. Those are :
(a)
Production of polyphenylene sulfide polymer.
(b)
Conversion of the polymer into the fiber by melt spinning
(c)
Curing of the fiber for conversion into a tougher material
The polymer is produced
by Wurtz Fitting condensation of p- chlorobenzene and sodium sulfide. The
monomers and solvent, mostly polar, are fed into a polymerization reactor. Polymerization
takes place at elevated temperatures. Once polymerization is complete, the
solvent is stripped and recycled.
The polymer is then washed
with water to remove sodium chloride and dried. The fiber is formed from the
polymer by melt spinning technique at 300°C. The as-spun fiber can be drawn to
3.5 - 4.0 times at 100°C.
After drawing the fiber can be converted into tougher material by curing process. Curing can be done at
250°C - 280°C in the presence of a small amount of air. Curing modifies the
characteristics of the fiber-like
(i) an increase in
molecular weight,
(ii) Cross-linking,
(ii) increase in
toughness,
(iv) resistance to
solvents like a loss in solubility and
(v) change in color
from off-white to brown-black.
Proparties
The physical properties
of sulphur fibre is given in Table
- Density (g/d) 1.37
- Moisture regain (%) 0.6
- Tenacity (g/d) 3 - 3.5
- Breaking Elongation (%) 25 - 30
- Initial modulus (g/d) 30 - 40
- Elastic recovery 100% at 2%; 96% at 5% and 86% at 10%
The fibers exhibit
outstanding resistance to heat, retain more than 70% of original strength after
being exposed to 200°C for 5000 hr. The fiber also shows outstanding resistance
to acids, alkalies, bleaching agents and solvents except hot concentrated
sulphuric acid and nitric acid.
Application
The generic name of this
fiber is Ryton, produced by Philips Petroleum Company, USA. The fiber is used
for fuel gas filtration, wet filtration, flame- retardant clothing and
upholstery.
