Effects of filament fineness and lubricant additive concentration on the structure and properties of polypropylene BCF yarns

This study investigates the influence of filament fineness and lubricant additive concentration on the structural, thermal, and mechanical properties of polypropylene (PP) bulked continuous filament (BCF) yarns intended for carpet pile applications. Eight yarn samples were produced with a linear density of 1900 dtex using two filament fineness (9.5 and 3.7 denier per filament, dpf) and four lubricant additive concentrations (0, 0.5, 1, and 2 wt%). The yarns were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), tensile test, crimp contraction, and hot air shrinkage measurements. FTIR analysis confirmed that the principal chemical structure of the PP matrix was preserved regardless of filament fineness or additive incorporation, with no new absorption bands emerging at the tested concentration levels. DSC results revealed that 9.5 dpf yarns exhibited higher melting enthalpy and crystallinity compared to 3.7 dpf yarns, indicating differences in crystalline morphology between the two filament fineness levels. Moreover, lubricant additive incorporation tended to promote crystallization and broaden the melting peak width in both fineness groups, indicating changes in the melting behavior and distribution of crystalline regions. TGA demonstrated that all samples underwent a characteristic single-step thermal degradation with decomposition temperatures consistent with isotactic PP. Mechanical characterization showed that the effect of lubricant additive loading depended on filament fineness. Increasing additive concentration reduced tenacity and breaking elongation in the 9.5 dpf yarns, whereas no clear concentration-dependent trend was observed in the 3.7 dpf yarns. Crimp contraction was higher in the 9.5 dpf group, whereas hot air shrinkage was not significantly affected by either filament fineness or additive concentration.