In Situ Study The Effects Of Temperature On The Cold Crystallization Of PLA And The Microstructure Of Bombyx Mori Silk

The in situ X-ray and FTIR were used to investigate the iso-and nonisothermal crystallization behavior of amorphous polylactic acid (PLA) and the microstructure evolution of Bombyx mori silk upon heating. The dissertation is summerized as following:1. Three kinds of samples were prepared by naturally cooling (NC), liquid nitrogen quenching (NQ), and rapidly compressing (RC) from melts. The microstructure evolution and cold crystallization behavior of samples during heating were studied systematacially. Besides, the effects of rapid compression on the local ordered structrue of amorphous PLA were also discussed in the paper. The contents are as follows:(1). The initial thermostability and microstructure were ivestigated by differential scanning calorimetry (DSC), thermogravimetric (TG), wide angle X-ray diffraction (WAXD) and fourier transform infrared (FTIR) measurements. The results show that the WAXD and FTIR results are similar for all samples, and no crystal was found in them. The TG data indicates that the thermostability of three samples is similar.(2). The isothermal crystallization of NC and RC and the nonisothermal crystallization of NC, NQ and RC were investigated by in situ FTIR and DSC, respectively. It is found that the crystalllization rate of RC samples is higher than that of the others with much lower crystallization temperature.(3). Structure evolution of samples was studied by in situ FTIR and WAXD during cold crystallization. The sequential ordering was investigated during nonisothermal cryatllization by in situ FTIR. The WAXD data show that RC samples possese the similar crystalllite size and crystal growth rate but the higher crystallinity cmpared to NC and NQ samples, suggesting that the higher nucleation density in RC sample. It is concluded that some degree of ordered domains exist in the amorphous RC samples, which turn into nuclei precursor and accelerate the nucleation. Then the high nucleation density enhances the crystallization rate of RC sample.2. The microstructure and surface morphology evolution of degumed Bombyx mori silk was investigated by in situ X-ray diffraction, FTIR microscope and polarization microscope over a broad temperature range from room temperature to thermal denaturation temperature. The results are as follows: The WAXD and POM resules show that the thermal expansion coefficients of lattice are highly anisotropic along a and b axial. The thermal expansion coefficient along a axial is much smaller than that along b axial because of strong hydrogen bonding force along a axial. The crystallinity of baves begins to increase from180℃for the transition from random coil to β-sheet, and decrease significantly at280℃when carbonization occurs. It is also found that the degree of orientation increased slightly during the entire heating process.