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.