DRAWING AND ANNEALING OF NYLON-6 FIBERS - STUDIES OF CRYSTAL-GROWTH, ORIENTATION OF AMORPHOUS AND CRYSTALLINE DOMAINS AND THEIR INFLUENCE ON PROPERTIES

Structural changes in nylon-6 fibres that occur during processing are analysed using X-ray diffraction (X.r.d.), optical birefringence, dens ity and infra-red (i.r.) spectroscopy methods. Amorphous orientation i s described completely by a single parameter, degree of orientation, o n the basis of i.r. and optical birefringence measurements. But an add itional parameter, the fraction of oriented or anisotropic amorphous c omponent, was necessary to fully interpret the X.r.d. data. The amorph ous orientation increases as expected upon drawing, but decreases upon annealing at all temperatures. Crystalline orientation increases rapi dly at small draw ratios (<3) and reaches a plateau at higher draw rat ios. Crystalline orientation decreases upon annealing in highly drawn fibres but increases in others. The crystallinity is similar to 15% in the undrawn fibre, and continues to increase beyond the similar to 50 % value measured for the fibre with the highest (4.5x) draw ratios use d here. Secondary crystallization during drawing occurs at the expense of unoriented amorphous fraction, and in the initial stages of drawin g (3x) is accompanied by the transformation of the gamma into the a cr ystalline form. Secondary crystallization during annealing occurs at t he expense of the oriented amorphous fraction. The ease of gamma to al pha conversion during annealing depends on the initial state of the ga mma form. The glass transition temperature (T-g) appears to be determi ned solely by the amorphous orientation, being higher in fibres with a higher anisotropic component. The improved mechanical properties obse rved at higher draw ratios are attributed to higher crystallinity and lower fraction of the unoriented amorphous component. The shrinkage ob served upon annealing of fibres with smaller draw ratios (similar to 3 ) is likely to be the result of the crystallization of the oriented am orphous chain segments.