In polarized Fourier-transformed infrared spectroscopy and polarized Raman spectra of drawn poly (ethylene naphthalate)/polypropylene (PP) blends, the intensities of the orientation-sensitive bands of the blend components increased or decreased with increasing elongation, depending on the orientation of the corresponding vibrations. A significantly larger extent of molecular orientation was induced, when localized heating was applied to the blend during elongation (zone-drawing). Greater degree of molecular orientation resulted in a higher strength blend. The strengths of the blends after each stage of microfibrillization, namely fibrillization and isotropization, were measured and correlated with spectral changes. After isotropization, the PP chains were randomized as shown by equal band intensities of the parallel and perpendicular spectra. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1442-1449, 2010