| Summary: | 碩士 === 國立臺灣大學 === 高分子科學與工程學研究所 === 99 === The focus of this research is how SiO2-added and architecture affect α and α’crystal structures and morphology of PLLA. PLLA polymer chains packed closely α form crystal structure at higher crystallization temperature, and loosely α’ form crystal structure at lower crystallization temperature. Two crystal structures can co-exist at moderate temperatue. It is investigated by POM, DSC and XRD to observe the crystal structures changes of PLLA/ SiO2 and 3-ram PLLA, then compared with typical linear PLLA system.
When SiO2 is added, it provides heterogenous nucleation surface to accelerate the formation of crystal nuclei; in the contrast, star-shaped PLLA is difficult to form stable nuclei and requires longer crystallization time due to the core unit which is considered as impurity and is excluded from lamellae. The two factors affect the two crystal structures in varying degree, resulting in coexistence zone change. The α and α’ coexistence zone of PLLA/SiO2 system seems the same to pure PLLA system and that is much lower of star-shaped PLLA system. In order to further understand the variations from linear to star-shaped PLLA, different proportion blends of linear and star PLLA are used to link the relationship. Furthermore, it is discussed by the aspects of chain mobility, degree of undercooling and surface free energy of chain folding from the information of glass transition temperature, equilibrium melting temperature and the other basic physical properties.
On the morphology of PLLA, it is typical Maltese cross type spherulite in PLLA/SiO2 system, while there is ring-banded type spherulite appearing in Star-shaped PLLA system. In the blended system of linear and star PLLA, the temperature of ring-banded spherulite appearing is rasing with the proportion of linear PLLA increasing.
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