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The structure and thermal behavior of poly(lactic acid) (PLA) multifilament yarns were studied by complementary techniques of differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, and wide angle X-ray diffraction (WAXD). As for PLA filaments, notable differences in the WAXD patterns, DSC curves, and FTIR spectra were observed. The combination of the WAXD and FTIR results showed that PLA samples with different crystallinity contain a-form crystal structure. The FTIR spectra of the filaments were analyzed to study their crystallinity and crystal structure. The total crystallinity of the PLA filaments was obtained from the percent area loss of the skeletal amorphous band at 955 cm À1. Crystalline fraction from FTIR and DSC were comparable with each other. The C¼ ¼O stretching region, which is sensitive to crystallization and dipole-dipole interactions, was evaluated to provide information about chain conformers and crystallinity of the samples. Depending on the processing conditions, double melting peaks were observed in the DSC curves of the samples. This exhibited the structural reorganization of the crystal phase during heating affected by heating and cooling rate. In the DSC curves of the nearly amorphous multifilament yarn, the exothermic peak observed right above the glass transition temperature (T g ) indicated two relaxed and deformed amorphous regions. However, the multifilament yarn with higher crystallinity showed just endothermic melting peak after its glass transition. V C 2010 Wiley Periodicals, Inc. J Appl

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Natural silk, from Bombyx mori solutions were electrospun into nanofibers, with diameters ranged from 60 to 7000 nm. The effects of electrospinning temperature, solution concentration and electric field on the formation nanofibers were studied. Optical and scanning electron microscope were used to study the morphology and diameter of electrospun nanofibers. It was observed that the nanofibers became flattened with ribbon-like shape with increasing the electrospinning temperature. The nanofiber diameter increases with the increase in the concentration of silk solution at all electrospinning temperature. With increasing the voltage of electric field at 50 C, morphology of the nanofibers changes from ribbon-like structure to circular cross section. Referring to the literature the probable mechanism responsible for the change of morphology is pointed out.

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Physical, thermomechanical, and shape memory properties of two different samples of poly(lactic acid) (PLA) multifilament yarns were determined using various complementary techniques. The birefringence and crystalline fraction of one sample was higher than the other filaments sample indicating higher molecular orientation and compactness. For both filaments, two distinct morphological features with different sizes in the order of few nanometers (less than 50 nm) were found using AFM and SAXS techniques. The glass transition temperature (T g ) of the samples were ranged from 61°C to 76°C depends on the sample and the methods of measurement. Partial storage modulus (E′) increase above T g as well as additional small peak in loss modulus (E″) of the lower crystallinity sample was assigned to recrystallization. The multiple overlapped peaks in the E″ and tan δ curves and subsequent crystallization along with exothermic peak right after T g suggests the existence of both relaxed and oriented amorphous regions. The rigid crystalline regions prevented the shrinkage and enhanced dimensional stability. Multifilament yarn with higher crystallinity and total molecular orientation showed higher modulus (both dynamic and static) and strength and lower elongation at break. The oriented noncrystalline regions in the multifilament yarn sample led to moderate modulus and strength along with high elongation at break. The shape recovery of both samples with different structural parameters stayed almost constant (~50 %) upon the deformation temperature rise.