TENSILE VISCOELASTIC PROPERTIES OF SPUNBONDED NONWOVEN POLYPROPYLENE BACKING

The tensile elastic and viscoelastic properties of a nonwoven polypropylene backing, used as the main structural component during the processing of unfinished tufted carpets, are characterized in this study. Since the carpet is subjected to stretching in both the machine and cross-directions during the dyeing and drying processes, the various tensile properties are important material parameters. The average modulus of the untufted nonwoven substrate was 83,100 N/(m width) or 58.8 g/tex with a coefficient of variation of 12% within a roll. Based on the nominal thickness of 0.003 m of the carpet, the modulus was calculated at 27.7 MPa. The average modulus for the tufted substrate was 5.3 MPa (15,900 N/m width or 11.3 g/tex) with a coefficient of variation of 21%. Since the dyeing and drying operations proceed at temperatures in the vicinity of 100-degrees-C, and the stresses and strains are applied for a time ranging up to 10 minutes, the time-dependent tensile properties are also significant at these elevated temperatures. Viscoelastic tests showed that the stress relaxation modulus for the tufted nonwoven substrate was of the order of 1 MPa and rather insensitive to temperatures over the range of 72 to 100-degrees-C. Viscoelastic models consisting of spring and dashpot elements were used to model the creep and stress-relaxation response. Variations observed in tensile modulus, creep compliance, and stress-relaxation modulus suggest that the stress bearing structure, including filament density and bond strength, is not uniform in the nonwoven fabric.