Mechanical Properties of Polypropylene Multifilament Yarns in Dependence of their Drawing Ratio

Abstract

In the present work we investigated mechanical properties of multifilament PP yarns spun at three spinning regimes and at different drawing ratios to settle the rational spinning parameters of yarns to be used for certain textile purposes. The yarns coded as PP1, PP2 and PP3 were spun in the Laboratory of Fibre Materials Science, Tampere University of Technology on a Fourné laboratory melt spinning unit at corresponding drawing ratios of 3.73, 5.53 and 7.30. The PP granules were supplied by Inka Oy. The spinnerets numbered 10 holes each of 0.5 mm in diameter. Indices of stress-strain behaviour including the ultimate resistance, tensile moduli and yield points, as well as stress relaxation data at three different levels of elongation below the second yield point (2 %, 5 % and 10%) are analysed on the basis of data obtained on a Zwick/Z005 universal testing machine and using testXpert® software. Elongation at break of the yarns greatly decreases while elongation at first yield point shows tendency to decrease with the increase of drawing ratio. Breaking tenacity, initial and secondary moduli of the yarns are in strong linear dependence on drawing ratio. Stress relaxation amount at high drawing ratios and at elongation of 10 % shows the definite tendency to decrease. The attempt is made to interpret stress relaxation data by the parameters of Kohlrausch’s equation