Effects of Fumed Silica and Draw Ratio on Nanocomposite Polypropylene Fibers

Abstract

Abstract:Hydrophylic fumed silica AR974 was tested as a potential nanofiller for the production of composite isotactic polypropylene filaments/fibers (containing 0.25-2 vol % of nanoparticles) via melt compounding and subsequent hot drawing. The objectives of this study were as follows: (i) to investigate the effects of the composition and the processing conditions on the microstructure and the thermal and mechanical properties of the produced fibers; (ii) to separate the effects of silica addition from those produced by fiber drawing; and (iii) to interpret the changes in the matrix molecular mobility (produced by silica and/or drawing). Scanning electron microscopy (SEM) evidenced a good dispersion of nanoparticles at fractions up to 0.5 vol % of the nanofiller. X-ray diffraction (XRD) analyses revealed the increase in crystallinity after drawing of both neat polypropylene (PP) and produced nanocomposite fibers. Consequently, tensile modulus and stress at break of the fibers were enhanced. Drawn fibers containing 0.25-0.5 vol % of nanofiller showed also a remarkable increase in the creep resistance. Loss modulus of drawn fibers showed a pronounced α-relaxation peak at about 65 • C; the higher the draw ratio, the higher the peak intensity. Thermal and mechanical properties of composite fibers were improved due to the combined effects of nanofiller reinforcement and fiber orientation produced during hot drawing. Both fumed silica and draw ratio were significantly effective on tensile modulus and tenacity of nanocomposite fibers up to 0.5 vol % of AR974.

Role of Surface-Treated Silica Nanoparticles on the Thermo-Mechanical Behavior of Poly(Lactide)

“…The effective particle volume fraction φ e generally increased with the filler content, evidencing a relative minimum at 4 vol%. On the other hand, the large initial decrease of the B parameter suggested that the extent of the particle agglomeration increased, as previously determined also in nanocomposite polyolefin fibers with hydrotalcite [69] or fumed silica [32]. However, above 4 vol% the B parameter exhibited an almost constant value until 24 vol% of fumed silica, suggesting a relatively minimum level of aggregation in the tested composition range, in agreement with the results of morphological analysis (see Figure 1).…”

“…Due to its morphological properties, this nanofiller is able to self-aggregate when dispersed in polymer matrices, forming an interconnected network of interacting particles. The role played by silica nanoparticles with different thermoplastic matrices and the consequent thermo-mechanical behavior of nanocomposites produced firstly by melt-compounding and then either by compression molding [23][24][25][26][27][28][29][30] or by fiber spinning [31,32] was extensively investigated by our group in the last years. It was demonstrated how nanosilica addition leads to a strong stiffening effect on the polymer matrices, without impairing their failure properties, improving also the dimensional and thermal degradation stability.…”

Experimental Investigation of Polypropylene Composite Drawn Fibers with Talc, Wollastonite, Attapulgite and Single-Wall Carbon Nanotubes

“…The T max values of this study are in the same range and slightly higher than respective literature values. For example, for PP-fumed silica drawn fibers, values from 300 • C for neat PP up to 330 • C for the composite fibers with 1% silica [39] were reported. For organically modified montmorillonite, values of 348 to 387 • C for T max were reported [40].…”

Effect of the Elongational Flow on the Morphology and Properties of Polymer Systems: A Brief Review

“…This phenomenon is clearly observable in Figure 9A, which displays the trend of the tensile modulus as a function of DR for melt-spun PP fibers [109]. As the draw ratio increases, a severe increment of the fiber stiffness can be observed; furthermore, as documented by the results depicted in Figure 9B, a concurrent increment of the tensile stress and a drastic decrease of the fiber ductility verify as a consequence of drawing.…”