کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
1398515 984392 2007 14 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Crystallization, glass transition and morphology of (R)-3-hydroxybutyrate oligomers
موضوعات مرتبط
مهندسی و علوم پایه شیمی شیمی آلی
پیش نمایش صفحه اول مقاله
Crystallization, glass transition and morphology of (R)-3-hydroxybutyrate oligomers
چکیده انگلیسی

The study focuses on the effect of the molecular length of isotactic hydroxybutyrate oligomers on the crystal morphology, crystallinity, and spherulitic superstructure. Furthermore, the process of solidification of the quiescent melt is evaluated by the analysis of the crystallization kinetics and of the glass transition. Melt-crystallization is strongly controlled by the chain length, and the regime of cooling. Crystallization can completely be avoided by rapid cooling. Slow cooling allows at best incomplete crystallization, with the crystallinity increasing with chain length. Typically, the maximum crystallinity is between 50% and 80% for OHB of molecular weights of 500 and 5000 g mol−1, respectively. The temperatures of the glass transition and of crystallization/melting increase with molecular length, and are discussed in terms of the Fox–Flory and Gibbs–Thomson equations, respectively. For all samples, regardless of the chain length, spherulitic crystallization is observed, with the perfection of spherulites increasing with decreasing crystallization temperature. The transition of formation of extended-chain crystals to formation of folded-chain crystals occurs at a molecular weight of about 2000 g mol−1, which corresponds to chain length of about 7 nm. Analysis of the heat-capacity increment at the glass transition temperature reveals the existence of a rigid amorphous fraction.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: European Polymer Journal - Volume 43, Issue 12, December 2007, Pages 4961–4974
نویسندگان
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