Abstract/Details

Effect of molecular structure on the thermal stability of amorphous and semicrystalline poly(lactic acid)


2007 2007

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Abstract (summary)

Emphasizing on the effect of molecular structure, the issues surrounding the thermal stability amorphous and crystalline states of poly(lactic acid), or PLA, are explored. Enthalpic relaxation, which correlates with physical aging, is investigated for PLA of different tacticities, and we find that a decreased number of configurational defects in the polymer backbone leads to a smaller Kohlrausch-Williams-Watts exponent. On the other hand, specific volume, or equivalently density, does not relate simply to enthalpic stability when comparing the α and stereocomplex forms of PLA crystals. Although the a crystal has the higher density, molecular interactions, as inferred from vibrational spectroscopy and molecular modeling, are stronger in the stereocomplex, a trend consistent with a higher enthalpy of fusion. The methyl-methyl and carbonyl-carbonyl interactions are the main contributors to the α crystal thermal stability, whereas the methyl-methyl and carbonyl-to-α-hydrogen interactions are the important interactions for the thermal stability of the stereocomplex. In addition, good correlation between the post-Tg exotherm and fiber shrinkage can be explained using spectroscopic and calorimetric means. We find that fiber thermal stability is not achieved when crystallizable chains remain largely uncrystallized. During processing, if crystallization is not completed before vitrification sets in, fiber shrinkage will take place, followed by crystallization enhanced due to pre-existing crystallites from processing.

Indexing (details)


Subject
Chemistry;
Polymers;
Materials science
Classification
0494: Chemistry
0495: Polymers
0794: Materials science
Identifier / keyword
Applied sciences; Pure sciences; Amorphous polymers; Biodegradation; Electrospinning; Poly(lactic acid); Thermal stability
Title
Effect of molecular structure on the thermal stability of amorphous and semicrystalline poly(lactic acid)
Author
Aou, Kaoru
Number of pages
242
Publication year
2007
Degree date
2007
School code
0118
Source
DAI-B 68/12, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549383918
Advisor
Hsu, Shaw L.
University/institution
University of Massachusetts Amherst
Department
Polymer Science & Engineering
University location
United States -- Massachusetts
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3293935
ProQuest document ID
304848277
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/304848277
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