Structural Evolution in Microbial Polyesters
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- 作者：Kyuyoung Heo ; Jinhwan Yoon ; Kyeong Sik Jin ; Sangwoo Jin ; Harumi Sato ; Yukihiro Ozaki ; Michael M. Satkowski ; Isao Noda ; Moonhor Ree
- 刊名：Journal of Physical Chemistry B
- 出版年：2008
- 出版时间：April 17, 2008
- 年：2008
- 卷：112
- 期：15
- 页码：4571 - 4582
- 全文大小：327K
- 年卷期：v.112,no.15(April 17, 2008)
- ISSN：1520-5207
文摘
The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) (PHB) and its copolymers[P(HB-co-HHx)] containing 2.5, 3.4, and 12 mol % 3-hydroxyhexanoate (HHx) comonomer and the meltingof the resultant crystals were studied in detail using time-resolved small-angle X-ray scattering and differentialscanning calorimetry. The polyesters were found to undergo primary crystallization as well as secondarycrystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to thecrystallization temperature, but no thickening was observed throughout the entire crystallization at a giventemperature. The thickness of the lamellar crystals in the PHB homopolymer was always larger than that ofthe amorphous layers. In the copolymers, by contrast, the randomly distributed HHx comonomer units werefound to be excluded from the lamellar crystals into the amorphous regions during the isothermal crystallizationprocess. This interrupted the crystallization of the copolymer chains, resulting in the formation of lamellarcrystals with thicknesses smaller than those of the amorphous layers. The lamellar crystals in the copolymershad lower electron densities compared to those formed in the PHB homopolymer. On the other hand, secondarycrystallization favorably occurred during the later stage of isothermal crystallization in competition with thecontinuous primary crystallization, forming secondary crystals in amorphous regions, in particular in theamorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formedlamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader sizedistribution, and a lower electron density.