Unique thermoplastic monofilament fibers and yarns that exhibit heretofore
unattained physical properties are provided. Such fibers are basically
manufactured through the extrusion of thermoplastic resins that include a
certain class of nucleating agent therein, and are able to be drawn at
high ratios with such nucleating agents present that the tenacity and
modulus strength are much higher than any other previously produced
thermoplastic fibers, particularly those that also simultaneously exhibit
extremely low shrinkage rates. Thus, such fibers require the presence of
certain compounds that quickly and effectively provide rigidity to the
target thermoplastic (for example, polypropylene), particularly after
heat-setting. Generally, these compounds include any structure that
nucleates polymer crystals within the target thermoplastic after exposure
to sufficient heat to melt the initial pelletized polymer and allowing
such an oriented polymer to cool. The compounds must nucleate polymer
crystals at a higher temperature than the target thermoplastic without the
nucleating agent during cooling. In such a manner, the "rigidifying"
nucleator compounds provide nucleation sites for thermoplastic crystal
growth. The preferred "rigidifying" compounds include dibenzylidene
sorbitol based compounds, as well as less preferred compounds, such as
[2.2.1]heptane-bicyclodicarboxylic acid, otherwise known as HPN-68, sodium
benzoate, certain sodium and lithium phosphate salts [such as sodium
2,2'-methylene-bis-(4,6-di-tert-butylphenyl)phosphate, otherwise known as
NA-11]. Specific methods of manufacture of such inventive thermoplastic
fibers, as well as fabric articles made therefrom, are also encompassed
within this invention.
