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Supramolecular reinforcement of elastomers using β-sheet nanocrystals

Zhao, Yihong
http://rave.ohiolink.edu/etdc/view?acc_num=akron157305523271555

Abstract Details

2019, Doctor of Philosophy, University of Akron, Polymer Science.
Research into rubber reinforcement using β-sheet nanocrystals in this dissertation is divided into two major parts: thermoplastic elastomer (TPE) and thermoset vulcanizate. The study of β-sheet nanocrystals reinforced thermoplastic elastomers starts from the β-alanine trimer grafted styrene-butadiene rubbers (SBR) with different grafting densities. The nanocrystals in these two samples are rod-like with the longest dimension of a few tens of nanometers. This is in contrast to the fibrous crystals observed in most of the synthetic segmented TPEs. The rod-like nanocrystals are highly effective in reinforcing the elastomers. High strength, and high extensibility are achieved simultaneously. The rod-like morphology observed in the above SBR and in other oligo(β-alanine)-grafted elastomers studied in the Jia laboratory was attributed to the high chain density of a layer of polymer brush covalently attached to the nanocrystal surface. To demonstrate this, β-alanine trimer-grafted polyisobutylenes with different chain densities on the crystal surface were synthesized in order to control the morphology of β-sheet nanocrystals. TEM and SANs were used to confirm the formation of fibrous and particulate crystals in the soft polyisobutylene continuous phase. The SANS data have provided direct evidence of the existence of a layer of brush-like chains on the surface of crystals. The differences in mechanical and dynamic mechanical properties of TPEs containing β-sheet nanocrystals with different morphologies are less significant than expected. The structure change of the nanocrystals during extension is significant, indicated by the hysteretic behaviors of the β-alanine trimer-grafted polyisobutylenes. Surprisingly, IR and DSC indicate a lack of obvious hydrogen-bond breakage and preservation of the β-sheet crystals when the elastomers are stretched to various tensile strains. A fracture recoil model is proposed to explain the reinforcing mechanism of β-sheet crystals. A few crystals break and result in the recoiling of the brush chains. The molecular friction between recoiling chains and the breaking and reformation of hydrogen bonds is proposed to result in the high hysteretic behaviors of the elastomers. The oligo(β-alanine)s was then applied as supramolecular fillers to reinforce SBR vulcanizates. Two fillers are designed and used together to tuning the morphology and changing the mechanical properties of vulcanizates. One is reactive and can form covalent bond with SBR chains to improve filler dispersion. One is not reactive and is able to co-crystalize with the reactive filler and change the morphology of nanocrystals. TEM indicated that the crystal domains dispersed well in rubber matrix for the reactive β-alanine-filled SBR, and aggregation of crystals was observed with increasing amount of the unreactive β-alanine filler. Crystallinity of fillers increased slightly by introducing unreactive β-alanine filler, indicated by deconvolution of the WAXS data. Mechanical properties change with the morphology. Increase in unreactive to reactive filler ratios results in slightly increased modulus, decreased elongation and decreased ultimate strength.
Li Jia (Advisor)
Mark D. Foster (Committee Chair)
Gary R. Hamed (Committee Member)
Abraham Joy (Committee Member)
Kevin Cavicchi (Committee Member)
213 p.
Morphology; Polymer Chemistry; Polymers
thermoplastic elastomers, morphology, reinforcement, reinforcing mechanism, supramolecular fillers, oligo beta-alanine, beta-sheet nanocrystals

Recommended Citations

Citations

  • Zhao, Y. (2019). Supramolecular reinforcement of elastomers using β-sheet nanocrystals [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron157305523271555

    APA Style (7th edition)

  • Zhao, Yihong. Supramolecular reinforcement of elastomers using β-sheet nanocrystals. 2019. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron157305523271555.

    MLA Style (8th edition)

  • Zhao, Yihong. "Supramolecular reinforcement of elastomers using β-sheet nanocrystals." Doctoral dissertation, University of Akron, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron157305523271555

    Chicago Manual of Style (17th edition)

akron157305523271555
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This open access ETD is published by University of Akron and OhioLINK.