Polypropylene fibers containing dispersed clays having improved fire performance. I. Effect of nanoclays on processing parameters and fiber properties

Abstract

While the present interest in the use of functionalized nanoclays as additives for improving tensile properties and fire performance in polypropylene thermoplastics has led to a considerable literature, little attention has been given to this polymer in fiber form. In this article, we report the conditions necessary for and the characteristics of filaments and tapes comprising dispersions of functionalized clay in polypropylene–clay prepared by melt compounding polypropylene in a twin screw extruder. A small fraction (1–3% w/w) of modified grafted polypropylene has also been included to improve dispersion of the clay. X-ray diffraction of hot-pressed films, coupled with transmission electron microscopic investigation has been used to assess the degree of dispersion of the clay. Clay dispersion at the nanolevel was observed by TEM, but intercalation was not evident from X-ray study. Compounded samples were melt-extruded into filaments using a single screw extruder and drawn prior to wind up. The physical properties of the clay-containing polypropylene filaments showed that presence of dispersed clay increased filament modulus and was supportive of having achieved some degree of nanodispersion. Selected filament samples had sufficiently acceptable textile properties to enable their knitting into fabric samples. The burning behavior of fabric and film samples were observed by limiting oxygen index and cone calorimetry at 35 kW/m2 external heat flux. While the clay presence did not confer flame retardancy, it did change the burning character and encouraged some char formation