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Jiawei Wu final these (Ohio Link).pdf (5.53 MB)

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Study on Epoxidized Poly (Styrene-butadiene-styrene) Modified Epoxy Resins

Wu, Jiawei
http://rave.ohiolink.edu/etdc/view?acc_num=akron1571671436341218

Abstract Details

2019, Doctor of Philosophy, University of Akron, Mechanical Engineering.
The epoxy resins are well known for its advanced mechanical and chemical properties that they have been of significant industrial and commercial importance since decades ago. Nowadays, more and more fields are utilizing it as structure materials where a great toughness is required, which is, however, not an outstanding property for the virgin kind of epoxy resins. Considering this, toughened epoxy resins are awaited to be developed. In this dissertation, we tried epoxidized poly(styrene-butadiene-styrene) as modifiers to ensure a good distribution among the epoxy matrix. And SBSs of different topologies, various molecular weight are prepared to study the corresponding effect on toughening. For samples containing each type of SBS, different composition and epoxidation degree are tried to have a systematic understanding of influences on the toughening effect from these factors. Mechanical behaviors and the toughening mechanisms are summarized according the results obtained. It is found that epoxidized SBS with higher molecular weight and multi-armed structure will enhance the impact resistance more effectively, while a polydispersity of the SBS will result in samples of higher strain at break. The kinetic precipitation of SBS during the epoxy curing is will automatically form the SBS particles, which is of relatively wide distribution. While a general trend is still obtained that SBS with better compatibility with the matrix would be of smaller but narrower-size-distributed particles, and further addition of SBS cause this distribution and average size to be larger. According to the results obtained, we found that cavitation is not necessarily a precondition for inducing of shear yielding, since there exit small particles with whitening borders and semi-induced shear bands around in our epoxidized S4318 containing samples, without a cavitation, however. This indicates that the shear yielding could be formed ahead of the formation of cavitation, although the dilation in shear bands will indeed cause cavitation of the particles later. And that might explain the most commonly seen coexistence of cavitation and shear bands. Compared with smaller particles, which might fail to cavitation, larger particles are of higher possibity to cavitate and induce main shear bands, while smaller particles can induce smaller bands perpendicular to theose main ones, endowing them with better flexibility, and the resulting material are of better ductility, as seen from the results of samples containing bimodal SBS S4318. Generally speaking, addition with more higher epoxidized SBS will have the final samples of better ductility, although this toughening might sacrifice the strength of the materials. An optimum concentration would exist if we want the best toughening effect. For all the samples, the drop in tougheness is observed when the SBS are excessively added, although the mechanisms causing this differ. The inter molecular ligment length is proved to be an important parameter for brittle-ductile transition. However, little correction still need to be added here that even if the critical ligment length is not fulfilled, the isolated rubber particles can still cause local stress concentration and local yielding, as seen from the fractured surface. While meeting the ligment criterion will endow the material of a global scale shear failure. It needs to be noted that the addition of SBS itself causes a decrease in the crosslink density for epoxy resins, and thus the ductility, neglecting the decrease in strength, is always supposed to increase.
Shing-Chung Wong (Advisor)
Xiaosheng Gao (Committee Member)
Kwek Tze Tan (Committee Member)
Rajeev Gupta (Committee Member)
Dmitry Golovaty (Committee Member)
247 p.
Chemistry; Materials Science; Mechanical Engineering; Polymers
Epoxy, rubber particle, toughening, adhesion, epoxidation, fracture, impact, flexural tests, morphology, topology

Recommended Citations

Citations

  • Wu, J. (2019). Study on Epoxidized Poly (Styrene-butadiene-styrene) Modified Epoxy Resins [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1571671436341218

    APA Style (7th edition)

  • Wu, Jiawei. Study on Epoxidized Poly (Styrene-butadiene-styrene) Modified Epoxy Resins. 2019. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1571671436341218.

    MLA Style (8th edition)

  • Wu, Jiawei. "Study on Epoxidized Poly (Styrene-butadiene-styrene) Modified Epoxy Resins." Doctoral dissertation, University of Akron, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1571671436341218

    Chicago Manual of Style (17th edition)

akron1571671436341218
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This open access ETD is published by University of Akron and OhioLINK.
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