Abstract
This thesis studied the microstructure and crystallization behavior of the blends of semicrystalline polymers. Two polymers were investigated here:(1) semicrystalline/amorphous system:poly(L-lactide)(PLLA) /poly(vinylphenol)(PVPh) blend and (2) semicrystalline/semicrystalline system:poly(ethylene oxide)(PEO)/poly(1,4-butylene adipate)(PBA) blend. (1)PLLA/PVPh blend The miscibility, semicrystalline morphology of the PLLA/PVPh blends have been studied by differential scanning calorimetry(DSC),polarized optical microscopy (POM) and small-angle X-ray scattering(SAXS) with the absolute intensity measurement. Blending with PVPh enhanced the SAXS intensity associated with the lamellar stacks. This was attributed the presence of PVPh in the interlamellar regions that enhanced the electron density contrast(Δη) between the crystalline and amorphous layers. We can use the one-dimensional correlation function by defined from Strobl and Schneider, the electron density contrast of the PLLA/PVPh blends in the lamellar stacks was calculated. The electron density contrasts increased as content of PVPh increased. This suggested that PVPh was expelled into interlamellar regions upon the crystallization of PLLA. (2)PEO/PBA blend Miscibility, crystallization behavior, and semicrystalline morphology of blends prepared from two crystalline polymers, PEO and PBA have been studied by POM, DSC and SAXS. PEO and PBA were miscible in the melt. Due to the proximity of Tg and Tm, PEO and PBA crystallized over similar temperature range. However, their respective crystallization rates were very different where PEO usually crystallized prior to PBA. From the isothermal crystallization kinetics stundying, it was found that the crystallization kinetics of PEO was depressed upon blending . Slight dilution with PEO (wPEO≦0.2) promoted the crystallization kinetics of PBA because of enhanced segmental mobility upon blending . Further increase in PEO content reduced the PBA crystallization rate owing to the dominant effect of depression in crystallization driving force. Two kinds of crystallization processes can be identified for the spherulite formation on PEO/PBA blends, i.e.,: sequential and competitive crystallization. When PEO content is rich (wPEO≧70%), the crystallization process is always sequential where the spherulites of PEO formed prior to those of PBA. At low Tc (≦20℃) and PBA-rich composition, the spherulite formation was competitive. The semicrystalline morphology of PEO/PBA blends was probed by SAXS. Blending with PBA (wPBA<40%) shifted the scattering of peak of PEO to higher q. With further addition of PBA, peak located at similar position to that of pure PBA was identified . Base on the SAXS results, the lamellar morphology of PEO/PBA blends can be divided into two categories:(I)insertion mode :for low (wPBA<40%) content ;(II) block mode: for high PBA content (wPBA≧40%) .