Physical and chemical interactions in melt mixed nylon-6/EVOH blends

Nylon-6 (Ny-6) and ethylene-vinyl alcohol copolymer (EVOH) binary blends were prepared in various compositions via dynamic melt blending. In addition, 50/50 blends of EVOH with nylon-6/6.9 (Ny6/6.9) and nylon-11 (Ny-11) were prepared to study the effect of nylon type on the structuring process under melt mixing. The phase morphology and the crystallization behavior of the blends were investigated using differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The insoluble content was studied by solvent extraction. The mixing torque was found to increase with mixing time for intermediate Ny-6 contents, indicating chemical reactions and hydrogen bonds formation between the polymers. Based on FT-Raman spectroscopy chain extension is suggested to be the main chemical reaction between EVOH and Ny-6. The different interaction levels obtained for the Ny-6/EVOH blends affect their properties. The melting temperature of one component decreases as the content of the other component is increased. EVOH has lower crystallization degree when its content is lower; conversely, Ny-6 crystallinity increases foe some compositions compared to the neat polymer. Storage modulus and glass transition temperature values of the blends are between those of the neat polymers according to composition. However, positive deviation was obtained for the 50/50 Ny-6/EVOH blend owing to the chemical reaction between the polymers. SEM micrographs of fractured surfaces exhibit quite uniform, almost as a single-phase morphology, indicating high interaction level between the polymers. SEM/EDS of etched samples revealed that the dispersed particles in the blends are on a submicron scale.