In situ Synchrotron SAXS/WAXD Study during Uniaxial Drawing of Poly (L-lactic acid)

The structure development of poly(L-lactic acid)(PLLA) during the uniaxial drawing was investigated by means of in-situ simultaneous wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) measurements. When the quenched amorphous film of PLLA was drawn at 77.2 degrees C, which was well above the glass transition temperature of PLLA, two different crystal structures were formed depending on the strain. The mesophase, which has 10(3) helix with large amount of packing disorder, was formed at the early stage of drawing, followed by the crystal transformation into alpha' form (epsilon >= 1.5). SAXS measurement showed that the kebab formation begins at the stage later than that of meso-alpha' transition. It strongly suggests that the transition takes place inside the shish structure. The development of kebab leads to the enhancement of mechanical response, which is found to be the origin of the strain hardening of PLLA.