Polyester Formation

POLYMERIZATION:
First, the polymer is created; in the case of polyester, the polymer is made by heating either dimethyl teraphthalate (DMT)  or terephthalic acid (TPA) with ethylene glycol in the presence of a catalyst (ususally antimony) at 536 º F for 30 minutes at atmospheric pressure and then for 10 hours under vacuum. The excess of ethylene glycol is distilled off.  The resulting chemical, a monomer (single, non-repeating molecule) alcohol, is combined with terephthalic acid and raised to a temperature of 472°F (280°C). Newly-formed polyester, which is clear and molten, is extruded through a slot to form long ribbons.


DRYING: After the polyester emerges from polymerization, the long molten ribbons are allowed to cool until they become brittle. The material is cut into tiny chips and completely dried to prevent irregularities in consistency.

SPINNING:  Fibers are classified according to the type of spinning that the polymer undergoes: this can be melt spinning, dry spinning or wet spinning:

1. Melt spinning is the simplest of these three methods:   In melt spinning, the polymer chips are melted at 500 – 518ºF to form a syrup-like solution.  The solution is put in a metal container called a spinneret and forced through its tiny holes. The number of holes in the spinneret determines the size of the yarn, as the emerging fibers are brought together to form a single strand. Melt spinning is used with polymers such as nylon, polyethylene, polyvinyl chloride, cellulose triacetate, and polyethylene terephthalate, and in the multifilament extrusion of polypropylene.
2. Dry spinning:  the polymer is first dissolved in a solvent. The polymer solution  is then extruded through the spinnerets. The solvent is evaporated with hot air and collected for reuse. The fiber then passes over rollers, and is stretched to orient the molecules and increase the fiber strength. Cellulose acetate, cellulose triacetate, acrylic, modacrylic, aromatic nylon, and polyvinyl chloride are made by dry spinning.
3. In wet spinning, the polymer solution (i.e., polymer dissolved in a solvent as in dry spinning) is spun into a coagulating solution to precipitate the polymer. This process has been used with acrylic, modacrylic, aromatic nylon, and polyvinyl chloride fibers.