Aramid fibers are man-made high-performance fibers, with molecules that are characterized by relatively rigid polymer chains. These molecules are linked by strong hydrogen bonds that transfer mechanical stress very efficiently, making it possible to use chains of relatively low molecular weight.
The term “aramid” is short for “aromatic polyamide”. Aromatic polyamides were first applied commercially as meta-aramid fibers in the early 1960s, with para-aramid fibers being developed in the 1960s and 1970s.
Aramid fibers share some general characteristics that distinguish them from other synthetic fibers:
- High strength
- Good resistance to abrasion
- Good resistance to organic solvents
- No melting point
- Low flammability
- Good fabric integrity at elevated temperatures
These unique characteristics derive from the combination of having stiff polymer molecules with a strong crystal orientation as well as close interaction between the polymer chains due to the hydrogen bonds.
Twaron filament yarns are prepared by dry-jet wet-spinning a liquid crystalline solution of PPTA polymer in concentrated sulfuric acid. After extrusion through spinning holes, the liquid filaments pass through an air gap and enter a coagulation bath containing water. The filaments are subsequently washed, neutralized, dried and wound onto bobbins. Read more on the production process of Twaron.
In the spinning solution, the stiff aramid molecules form liquid crystalline domains in which the polymer molecules are well aligned. During the spinning process itself, the elongational stretching of these domains in the air gap induces the domains and the orientation of the polymer molecules to align with the direction of flow