Thermal behavior of drawn poly(lactic acid)-nanocomposite fiber probed by near-infrared hyperspectral imaging based on roundtrip temperature scan

Abstract

Effect of organoclay on drawing of poly(lactic acid) (PLA) was studied by near-infrared (NIR) hyperspectral imaging. A set of PLA fibers was prepared by melt-spinning. While the fiber samples were drawn with the same drawn ratio (DR), they show different mechanical properties depending on the clay content. The difference in the polymer structure between the samples was analyzed by a roundtrip temperature scan of NIR imaging spectra. Namely, the samples underwent heating and then cooling in the opposite way during the spectral measurement. The development of the spectral residuals between the heating and cooling indicated the presence of the hysteresis arising from the thermal relaxation of the crystalline lamellae. Consequently, the result revealed fine details of the drawing. The addition of proper amount of clay increases the frequency of the spontaneous nucleation of the crystals. In contrast, the excessive amount of clay restricts the drawing of the polymer due to the interaction of the clay and PLA, which eventually provides insufficient mechanical property to the PLA fiber.