Optical and structural characterization in undrawn, necked, and crazed IPP fibers using multiple-beam interferometry and refined 1D continuous wavelet transform

Abstract This study presents a refined one-dimensional continuous wavelet transform (1D CWT) technique for accurate phase demodulation from multiple-beam interference patterns in the characterization of isotactic polypropylene (IPP) fibers. The research addresses the limitations of traditional phase demodulation methods, specifically the spatial carrier frequency technique’s spectral leakage issues and Phase Shifting Interferometry’s (PSI) requirement for multiple sequential acquisitions. Through comprehensive comparative analysis, the refined 1D CWT algorithm demonstrated superior performance with a minimal standard deviation of 0.09% from the theoretical phase value, significantly outperforming the four-shot PSI technique’s 1.1% deviation and the spatial carrier frequency method’s 4.3% deviation, which also exhibited spectral leakage and phase distortions. The method was validated through detailed characterization of undrawn, necked, and crazed IPP fibers, enabling precise measurement of crucial optical and structural properties including refractive index distribution, birefringence, molecular orientation, and crystallinity. Results revealed significant variations in these properties across different fiber conditions, with necking increasing crystallinity up to 45.50% and molecular orientation to 0.7885, while crazing reduced crystallinity to 10.56% in high craze density regions.