The deformation of carbon nanotube (CNT)-filled PA6 droplets in PP matrix was examined under simple shear flows. The morphology of blends with various CNT contents in PA6 were probed by FE-SEM. Based on the wetting coefficient calculations and rheological measurements, it was noted that the majority of CNTs were selectively located in the PA6 phase for concentrations up to 2 wt%. TEM micrographs evidenced the results for a sample with 0.5 wt% CNT in PA6. Optical microscopy of the blends during simple shear flows revealed the reduced deformability and breakups for filled-droplets. Such observations were ascribed to the increased viscosity ratio and gradual formation of an elastic structure within the droplets. Maffetone-Minale transient droplet deformation model was coupled with a modified capillary number to account for the developed elastic forces. It was shown that the contribution of such forces to the total shape-conserving forces could arise up to 99% in comparison with the well-known interfacial forces. These resisting forces can be so strong that for blends with CNT concentrations above 0.5 wt% in PA6 almost no deformation was observed under the applied shear stresses in this work. POLYM. ENG. SCI., 55:1504-1519, 2015. FIG. 9. Optical micrographs of droplet deformation with time in PP/PA6 sample at a shear-rate of 2 s 21 . The micrographs are captured after startup of shear flow at (a) 0 s, (b) 1 s, (c) 2 s, (d) 5 s, (e) 10 s, (g) 20 s, (h) 50 s, and (k) 120 s. The arrow in (k) indicates the applied flow direction for all micrographs. FIG. 10. Optical micrographs of droplet deformation with time in PP/PA6-0.1 sample at a shear-rate of 2 s 21 . The micrographs are captured after startup of shear flow at (a) 0 s, (b) 1 s, (c) 2 s, (d) 5 s, (e) 10 s, (g) 20 s, (h) 50 s, and (k) 120 s. The arrow in (k) indicates the applied flow direction for all micrographs.
In recent years, 1 H double-quantum NMR (DQ NMR) was established as a suitable molecular-rheology technique to elucidate chain dynamics and to determine entanglement or crosslink densities in linear entangled polymer melts and permanent as well as transient networks. In this work, industrial grade high-density polyethylene, partially cross-linked via electron beam irradiation in the semicrystalline state, is probed in the melt state by low-field DQ NMR and shear rheology. The DQ NMR data is analyzed by two approaches, one assuming the presence of a permanent network and the other considering the potentially complex relaxation spectrum of the studied inhomogeneous systems. A correlation between the DQ NMR results and extent of crosslinking is found. By direct comparison of the rheological results and the NMR-based segmental orientation autocorrelation functions (OACF) via timetemperature superposition (TTS), qualitative consistency between the microscopic and macroscopic observables is established. In this way, the frequency range of shear rheology can be extended by about two decades into the 10 krad/s range. The NMR method is thus a valuable extension of the toolbox of characterization techniques, where gel content measurements by solvent extraction proved to be the least sensitive.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.