Molecular understanding of the transcrystalline zone in thermoplastic polymers

The transcrystalline zone at the interphase between thermoplastic polymers and reinforcing fibers has been studied experimentally and theoretically. A wide range of matrices such as polyethylene (PE), polypropylene(PP), poly(phenylene sulfide) (PPS), poly({dollar}varepsilon{dollar}-caprolactone) (PCL), polyoxymethylene (POM) were employed and different types of carbon fibers (PE), aramid, and glass fibers were used.; It is shown by wide angle x-ray diffraction, that the b axial orientation is fixed normal to the carbon fiber for transcrystalline zone of PPS and PCL. For PP, the a axis is fixed normal to the fiber. It is shown that the lamella in the transcrystalline zone are twisted.; The transcrystalline zone of these polymers created on carbon fibers is studied by infrared polarized microscopy and Raman microscopy. It is shown that the transcrystalline zone is an oriented zone because of the strong dichroism in this region. The orientation of the zone corresponds to the type of orientation that has been identified from x-ray experiments. For PE, b axial type of orientation in the transcrystalline zone is shown. The infrared spectra of semicrystalline and amorphous polymers are compared.; For both experimental methods the comparison of the transcrystalline zone with uniaxially stretched polymers is done. The reasons for differences in x-ray data between transcrystalline and stretched samples are discussed. Comparison with known row and shish-kebab structures is made.; The case with PPS as the matrix material is especially emphasized. Composite films of different molecular weight poly(phenylene sulfide) (PPS) and three types of carbon fibers (Pitch, PAN, Rayon-based fibers), aramid fibers and glass fibers have been studied. Transcrystallization of growing spherulites is found under all thermal conditions of growth on Rayon and Pitch-based carbon fibers, and aromatic fibers for all types of matrices. For composite films with PAN based carbon fibers the transcrystallization of growing spherulites is not uniform and sometimes is not found at all. Transcrystallization does not occur when glass fibers are used as the reinforcement material. The new induction time quantitative approach is applied to the transcrystalline growth of PPS spherulites on the surface of carbon fibers. The interfacial free energy difference for fiber/crystallite systems and crystallite/heterogeneties in the melt that is defined from growth and nucleation studies are calculated and compared. The relative tendency for a polymer to crystallize at the fiber surface rather than in the bulk is demonstrated.; The crystallization kinetics of two different molecular weight PPS samples is studied by infrared spectroscopy and differential scanning spectroscopy. A method of calculating fractional crystallization from infrared spectra is used to study the kinetics of crystallization both by the Avrami equations and crystallization half-times. The overall rate of crystallization is described by the Avrami equation with an exponent close to 3 for the DSC experiments and close to 2 from the infrared spectroscopy measurements. This difference in the value of Avrami exponent is explained in terms of different types of crystallization in the two cases.