Rheology, thermal characteristics, crystallinity, tenacity and density of cationic dyeable polycaproamide/cationic dyeable poly(trimethylene terephthalate) polyblended fibers

Cationic dyeable polycaproamide (CD‐PCA) and cationic dyeable poly(trimethylene terephthalate) (CD‐PTT) polymers were extruded (in ratios 75/25, 50/50, and 25/75) from one melt twin‐screw extruders to prepare three CD‐PCA/CD‐PTT polyblended polymers and then spin fibers. This work examines the rheology, thermal characteristics, crystallinity, tenacity, density, and miscibility parameter μ value of CD‐PCA/CD‐PTT polyblended polymers and fibers using gel permeation chromatography, differential scanning calorimetry, thermogravimetric analysis, potentiometer, rheometer, the density gradient analysis, wide‐angle X‐ray diffraction, and extension stress–strain measurement. The melting behavior of CD‐PCA/CD‐PTT polyblended polymers revealed negative‐deviation blends (NDB). The 50/50 blend of CD‐PCA/CD‐PTT had the lowest melt viscosity. The experimental DSC results demonstrated that CD‐PCA and CD‐PTT molecules constituted an immiscible system. In particular, CD‐PCA, CD‐PTT, and their polyblended fibers yielded a double endothermic peak. The tenacity of CD‐PCA/CD‐PTT polyblended fibers initially declined and then increased as the CD‐PTT content increased. The crystallinities and densities of CD‐PCA/CD‐PTT polyblended fibers were linearly related to the blend ratio. The values of the miscibility parameter μ for all CD‐PCA/CD‐PTT samples were under zero, revealing electrostatic repulsion between CD‐PCA and CD‐PTT molecules. All experimental data supported the immiscibility of CD‐PCA/CD‐PTT polyblended fibers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007