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

The present paper applies the concept of a molecular network to the analysi s of melt spun Polyamide 4.6 fibres (Stanyl (R) from DSM, The Netherlands), obtained at different wind up speeds, and the yarns, subsequently drawn fr om these. The mechanical properties of the yarns produced are discussed in terms of the network draw ratio, determined by matching true stress-true st rain 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 drawa bility (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 describ e the network deformational behaviour of the as-spun yarns over a wide rang e of draw ratios. The apparent network draw ratio, obtained by curve matchi ng the drawn yarn true stress-true strain curves with those of its precurso r yarn, shows discrepancies with the actually applied draw ratio in the dra wing process. These discrepancies are discussed in terms of network structu ral parameters. It is made plausible that growth of existing crystals durin g hot-drawing is responsible for this, rather than formation of new crystal s. (C) 2001 Kluwer Academic Publishers.