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Dissertation Biobased adhesives.pdf (3.97 MB)

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Epoxy Adhesives: Formulation for Sustainability and Mechanism of Adhesion

Patel, Ammar Abbas
http://orcid.org/0000-0001-8882-3121
http://rave.ohiolink.edu/etdc/view?acc_num=case1573254388960149

Abstract Details

2020, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science and Engineering.
Epoxy adhesives constitute a large majority of the structural adhesive market. Most of these adhesives are 2-component systems consisting of a bisphenol A based resin and an amine based hardener. Bisphenol A is an endocrine disruptor and a known carcinogen, as well as derived from petroleum which in itself is a finite resource. Due to these disadvantages, BPA has been banned in multiple countries and replacements for BPA based resins are persistently sought. One of the most common amine curing agents used in epoxy adhesives is petroleum derived isophorone diamine (IPDA) which has been found to be toxic and a skin sensitizer. The need for adhesive systems that can replace bisphenol A based resins and petroleum based IPDA has never been more urgent. A family of biobased epoxies derived from diphenolic acid (DGEDP epoxies) were recently synthesized that have an estrogen binding capacity of an order of magnitude less than BPA but similar thermo mechanical properties to the diglycidyl ether of bisphenol A (DGEBA), the most commonly used epoxy resin derived from BPA. This family of resins, differing amongst each other only in ester chain length in terms of structure exhibited excellent potential as suitable replacements to DGEBA. Their curing kinetics with regards to IPDA were studied to determine which resin would be suitable for adhesive applications. Isoconversional analysis indicated that the resins cured via an autocatalytic mechanism and modeling of the curing behavior using the Kamal Sourour model showed that the methyl ester resin (DGEDP-methyl) exhibited unusually high curing rates. This resin was then chosen for further development as the resin component for a biobased adhesive. However, when lap shear samples on aluminum were prepared, DGEDP-methyl when cured with IPDA exhibited extremely brittle behavior failing at very low stresses. A commercially available highly aliphatic biobased epoxy resin (NC-514) derived from cashew nut shell liquid was hypothesized to increase the energy dissipating ability of the system when blended with DGEDP-methyl. Studying the morphology, thermo mechanical properties and molecular weight between crosslinks of the DGEDP-methyl and NC-514 blend at different ratios, it was found that the 60:40 DGEDP-methyl:NC-514 weight ratio served as a boundary between the 2 components displaying the strength of the DGEDP-methyl and the flexibility of the NC-514. This increase in properties however corresponded to a significant decrease in curing speed with the addition of NC-514. Also, both resins exhibited Newtonian behavior making it difficult to use this adhesive system for vertical configurations. Cellulose nanocrystals (CNC), a biobased filler, were dispersed into the 60:40 resin blend to induce shear thinning and increase curing rate. A percolated network was identified between 0.5 and 1 wt % which also corresponded to an increase in adhesive failure strength. Finally, after optimizing the resin component of the system (60:40 ratio of DGEDP-methyl and NC-514 with 1 wt % CNC) IPDA was replaced by a biobased curing agent: bis(furfurylamine)A. The system cured with a biobased hardener exhibited a very wide glass transition temperature window as well as a transition from brittle to ductile fracture behavior with a crack propagating all through the length of the sample before failure occurred. This led to a significant increase in adhesive failure strength. The completely biobased adhesive system was tested on multiple different substrates with differing surface energies. The wetting of a liquid droplet on a solid surface i.e. spreading coefficient theory was applied to the system to determine compatibility between adhesive and substrate and by extension adhesive failure strength. The value of spreading coefficient was also able to predict the type of failure that occurred. Finally, a novel coating system that increased the strength of epoxy bonded to HDPE was designed. Using silane chemistry, vinyl silane was grafted on the surface of HDPE and an amine silane was condensed via Si-O-Si linkages on the vinyl silane graft in successive steps leaving the amine free to react with the epoxy. In this way, a silane bridge between HDPE and epoxy was formed that led to an increase in adhesive failure strength. This thesis thus investigates the criteria and challenges involved in developing a completely biobased epoxy adhesive system and discusses the mechanism of adhesion used to bond to multiple substrates. Using this information, it then attempts to devise a method to increase adhesive failure strength to difficult to bond substrates.
Ica Manas-Zloczower, Prof. (Committee Chair)
Donald Feke, Prof. (Committee Member)
Gary Wnek, Prof. (Committee Member)
Rigoberto Advincula, Prof. (Committee Member)
200 p.
Materials Science; Polymers; Sustainability
biobased; adhesive; epoxy; bisphenol A; cure kinetics; cellulose; fracture toughness; rheology; morphology; formulation; adhesion; surface energy; spreading coefficient; silane; polyolefin bonding

Recommended Citations

Citations

  • Patel, A. A. (2020). Epoxy Adhesives: Formulation for Sustainability and Mechanism of Adhesion [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1573254388960149

    APA Style (7th edition)

  • Patel, Ammar. Epoxy Adhesives: Formulation for Sustainability and Mechanism of Adhesion . 2020. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1573254388960149.

    MLA Style (8th edition)

  • Patel, Ammar. "Epoxy Adhesives: Formulation for Sustainability and Mechanism of Adhesion ." Doctoral dissertation, Case Western Reserve University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1573254388960149

    Chicago Manual of Style (17th edition)

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This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.