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Marcos Pantoja Dissertation.pdf (5.61 MB)

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Compounding and Processing Approaches for the Fabrication of Shape Memory Polymers

Pantoja, Marcos
http://orcid.org/0000-0003-1267-5374
http://rave.ohiolink.edu/etdc/view?acc_num=akron1555666527682024

Abstract Details

2019, Doctor of Philosophy, University of Akron, Polymer Engineering.
Shape memory polymers (SMPs) are a type of material capable of indefinitely holding a deformed shape and recovering their original shape upon the application of an external stimulus, such as temperature. SMPs contain at least two networks consisting of a permanent crosslinked polymer matrix and a second reversible, shape fixing network. These networks could be chemically bonded in single chemistry systems such as block copolymers containing elastic and glassy or crystalline phases or be blended together through elastomer and crystalline small molecule mixtures. This dissertation primarily focuses on SMP blends derived from fatty acid-elastomer blends with the aim being to further simplify the fabrication of these materials. The mechanical, thermal, and morphological properties of a series of different blends, along with several styrenic block copolymers, were studied to understand the structure-property relationships between their permanent and reversible networks. In Chapter II, fatty acid swollen natural rubber shape memory polymers were investigated as a function of swelling extent, acid polarity, and applied deformation. The fatty acid-rubber systems demonstrate a 40-50 wt% effective fatty acid solid phase loading range where the fixity of a programmed shape remained > 95% while maintaining structural integrity. The strength of the crystalline fatty acid networks were determined through dynamic mechanical analysis (DMA) moduli measurements where, under large uniaxial deformations, the modulus of the fatty acid was found to increase compared to the unstrained material. This was consistent with preferential alignment of crystal platelets along the strain direction as determined by small angle X-ray scattering (SAXS) measurements. In Chapter III, SMP foams were fabricated by immersing a polyurethane foam inside stearic acid-isopropyl alcohol solutions of varying concentration. Samples were programmed using DMA or a compression press. It was determined that fixity increases with increasing wt% stearic acid, reaching 95% fixity with 29 wt% (1 vol%) stearic acid. Pre- and post-submersion volume measurements reveal that the foam volume increases after the solution treatment. Optical microscopy images illustrate that the stearic acid coats the foam struts, eventually filling the pores at higher stearic acid loading forming a percolating network whose strength increases with increasing stearic acid concentration. Chapter IV demonstrates that neat ABA thermoplastic elastomers are able to act as SMPs without the addition of an additional small molecule additive. It will be discussed how the shape memory properties depend on the molecular weight and shape programming conditions of the SMP, which is in turn related to the chain dynamics and reorganization of the block copolymer morphology under load. The shape memory performance was investigated using DMA. Optimum properties were obtained using a shape programming temperature of 90 oC, yielding fixity (the ability of the polymer to hold the applied deformation) and recovery (the ability of the polymer to recover its original shape) values of ca. 80 and 90%, respectively. Overall, a tradeoff between fixity and recovery was observed for all cases, achieving higher fixities at the expense of recovery and vice versa. Based on these findings a model explaining the shape memory mechanism of neat block copolymer SMPs is proposed. Chapter V presents a different project focusing and the synthesis and characterization of flexible polyimide aerogels. Aliphatic linkages were introduced into the backbone of polyimides through the synthesis of aromatic diamines containing aliphatic spacers. These linkages were varied between 4, 6, and 10 methylene carbons to tune the properties of the resulting aerogels. The density, dielectric constants, thermal and moisture stability, and mechanical properties (including compression, tensile, and three-point bending) of these aerogels were assessed to understand the effect of the amount and length of the methylene spacers on these properties. Overall, the polyimides were flexible at thicknesses up to 2-3 mm.
Kevin Cavicchi (Advisor)
Mukerrem Cakmak (Advisor)
Li Jia (Committee Member)
Jiang Zhe (Committee Member)
Sadhan Jana (Committee Chair)
258 p.
Polymers
shape memory polymers; block copolymers; polymer blends; stearic acid; rubber; SEBS

Recommended Citations

Citations

  • Pantoja, M. (2019). Compounding and Processing Approaches for the Fabrication of Shape Memory Polymers [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555666527682024

    APA Style (7th edition)

  • Pantoja, Marcos. Compounding and Processing Approaches for the Fabrication of Shape Memory Polymers. 2019. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1555666527682024.

    MLA Style (8th edition)

  • Pantoja, Marcos. "Compounding and Processing Approaches for the Fabrication of Shape Memory Polymers." Doctoral dissertation, University of Akron, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1555666527682024

    Chicago Manual of Style (17th edition)

akron1555666527682024
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This open access ETD is published by University of Akron and OhioLINK.