Improvements in preventing heat- and
moisture-shrink problems in specific
polypropylene tape fibers are provided. Such fibers are basically manufactured through the initial production of
polypropylene films or tubes which are then slit into very thin, though flat (and having very high cross sectional aspect ratios) tape fibers thereafter. Such fibers (and thus the initial films and / or tubes) require the presence of certain compounds that quickly and effectively provide rigidity to the target
polypropylene tape
fiber after heat-setting. Generally, these compounds include any structure that nucleates
polymer crystals within the target polypropylene after
exposure to sufficient heat to melt the initial pelletized
polymer and upon allowing such a melt to cool. The compounds must nucleate
polymer crystals at a higher temperature than the target polypropylene without the nucleating agent during cooling. In such a manner, the "rigidifying" nucleator compounds provide
nucleation sites for polypropylene
crystal growth. Upon slitting of the initial film and / or tube, the
fiber is then exposed to sufficient heat to grow the crystalline network, thus holding the
fiber in a desired position. The preferred "rigidifying" compounds include
dibenzylidene sorbitol based compounds, as well as less preferred compounds, such as
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 tape fibers, as well as fabric articles made therefrom, are also encompassed within this invention.