Poly(hydroxybutyrate-co-valerate) biodegradable foams : the effects of processing, nanoscale additives, and aging
Abstract/Contents
- Abstract
- Biodegradable polymers can reduce the environmental impact of petroleum-based polymers by eliminating plastic accumulation in nature. Poly(hydroxybutyrate-co-valerate) (PHBV), one such polymer, is completely biorenewable and has potential for significant commercial growth if suitable applications are found. In addition to cost barriers, PHBV has not been widely adopted due to technical challenges associated with melt processing because PHBV has a high melting point and low thermal degradation temperature. These two complications create a narrow processing window in which the melt strength is too low for several common processing techniques, including foaming, blow molding, and film/fiber drawing. The application of interest in this work, foaming, requires high melt strength due to the rapid expansion of molten plastic around growing bubbles in order to prevent unwanted cell coalescence and collapse. Foaming of PHBV with a carbon dioxide producing blowing agent was performed in this thesis research to improve upon the thermodynamic limit witnessed in previous studies with nitrogen-generating blowing agents. The result was an additional decrease in the bulk density of more than 30%, but this was accompanied by a loss of the desired closed-cell morphology. Rapid water quenching at the die in extrusion foaming led to faster cooling and better bubble stabilization in the more expanded foams, as verified by thermal modeling. Next, silica nanoparticles were used as an additive in PHBV foams, and, in addition to bubble nucleation, particles were found to induce crystallization in PHBV. This solidification mechanism stabilized the cell morphology, even in the absence of a water quench. Silica treated with fluorinated silane coupling agents became hydrophobic and also acted as a nucleation agent. However, particle depletion due to aggregation limited the overall nucleation efficiency at high loading with hydrophobic nanoparticles. Ultimately, the rapid quenching of PHBV/silica nanocomposite foams led to synergistic stabilization of heterogeneously nucleated bubbles. As a result, foams with expansion ratios near six and closed-cell morphology were observed under these conditions. Products made from PHBV, including foams, will experience mechanical property degradation as the material ages. Because there is ambiguity as to the specifics of the embrittlement mechanism, the mechanical properties of aged poly(3-hydroxybutyrate) (PHB) and PHBV were examined over a 168 day period. The tensile modulus increased while the ultimate strain decreased, but the thermal characteristics showed no signs of secondary crystallization at 15°C. The aging of PHAs at ambient conditions, near the glass transition, led to a constriction of the rigid amorphous fraction, which decreased the ductility of the samples with little impact on the strength imparted by crystalline regions.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2013 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Wright, Zachary Carl |
|---|---|
| Associated with | Stanford University, Department of Chemical Engineering. |
| Primary advisor | Frank, C. W |
| Thesis advisor | Frank, C. W |
| Thesis advisor | Billington, Sarah L. (Sarah Longstreth), 1968- |
| Thesis advisor | Criddle, Craig |
| Advisor | Billington, Sarah L. (Sarah Longstreth), 1968- |
| Advisor | Criddle, Craig |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Zachary Carl Wright. |
|---|---|
| Note | Submitted to the Department of Chemical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2013. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2013 by Zachary Carl Wright
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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