Structure-property relationship of modified polypropylene-polycaproamide fiber

The effect of the addition of polyamide on the structure and properties of polypropylene fiber has been studied. Although a good fiber is obtained with a composition containing only a very low concentration of polycaproamide in polypropylene, the increase in polyamide content decreases the drawing strength of the mixed polymer melt due to sudden lowering of melt viscosity and strength. The poor melt strength of the studied polymer mixture is attributed to increased heterogeneity induced in the system with increased concentration of polyamide. Use of an effective interphase modifier, maleic anhydride-grafted polypropylene, however, was found to improve fiber properties of the studied polymer mixtures even with a very high concentration of polyamide as the dispersed phase. Thus, addition of a 1-4 wt % interphase modifier facilitates the formation of good fiber even with 30 wt % polycaproamide in the blend. This improvement is attributed to the improved dispersity of polyamide in the polypropylene matrix as well as improved phase compatibility due to the formation of a chemically modified polyamide during melt extrusion in the presence of maleic anhydride-grafted polypropylene.