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SynopsisA series of polypropylene (PP)/nylon 6 (N6) blends of composition 75/25,50/50, and 25/75 have been prepared in a screw extruder combined with a Koch static mixer. The phase morphology was observed with a scanning electron microscope. The influence of heating in the reservoir of a rheometer followed by subsequent extrusion through a capillary on the phase morphology was investigated. Phase size growth as a function of time was observed under quiescent and mild deformation rate conditions. The discrete phase size was observed to decrease with increasing extrusion rate through dies. The shear viscosity and principal normal stress difference of the blends were measured as a function of composition. The crystalline orientation of both polypropylene and nylon 6 in blend melt spun fibers was characterized by wide angle X-ray diffraction and interpreted in terms of Hermans-Stein orientation factors. The orientation increases with drawdown ratio. The orientation factors for the polypropylene phase vary with spinline stress in a manner independent of composition and identical to that for pure polypropylene. Extracting melt spun blend fibers with formic acid has produced small-diameter polypropylene minifilaments with diameters of the order of microns.

SynopsisThe effect of fiber structure and morphology on the resultant mechanical and low load deformation properties of thermally bonded nonwoven polypropylene fabrics has been studied. Commercially available staple polypropylene fibers varying in linear density and draw ratio (Herculon and Marvess staple fibers) were used in this study. The orientation of these fibers was characterized by birefrigence measurements. Differential scanning calorimetry measurements were made to determine the heat of fusion and melting point of fibers. Experiments confirm that tensile strength and stiffness of the fabrics correlate with this fiber structure. Under the same bonding conditions fabrics made from fibers with low draw ratios show higher tensile strength and stiffness than do fibers with high draw ratios. The mechanical properties of fabrics were found to be greatly affected by the thermal bonding temperature. The tenacity and flexural rigidity of fabrics made from poorly oriented fibers show higher values than those made from highly oriented fibers. The shrinkage of the fabrics was observed to increase with increasing bonding temperature in both machine and cross machine directions. The changes in fabric thickness due to the thermal bonding are considerably lower for poorly oriented fibers.

A new theory Is presented to predict the tensile behaviour of spun-bonded nonwoven fabrics from the knowledge of the stress-strain behaviour of its constituent fibers, their orientation angle distribution, the fabric's Poisson's ratio and their shear strains.