Drawability and attainable mechanical properties of polyamide yarn using true stress – true strain curves

Abstract

The present paper applies the concept of a molecular network to the analysis of melt spun Polyamide 4.6 fibres (Stanyl® from DSM, The Netherlands), obtained at different wind up speeds, and the yarns, subsequently drawn from these. The mechanical properties of the yarns produced are discussed in terms of the network draw ratio, determined by matching true stress–true strain curves. It is shown that analysis of true stress–true strain curves of as-spun yarns of different orientation, can be used to predict their drawability (final tenacity versus draw ratio). Moreover, the maximum attainable tenacity of drawn yarns under given drawing conditions can be forecasted. It is shown that the Edwards–Vilgis rubber elastic model is able to describe the network deformational behaviour of the as-spun yarns over a wide range of draw ratios. The apparent network draw ratio, obtained by curve matching the drawn yarn true stress–true strain curves with those of its precursor yarn, shows discrepancies with the actually applied draw ratio in the drawing process. These discrepancies are discussed in terms of network structural parameters. It is made plausible that growth of existing crystals during hot-drawing is responsible for this, rather than formation of new crystals.