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PhD Defense: Mengfei Huang, "Novel Crosslinking Technologies for Waterborne & Powder Coatings"

Date/Time: 

Friday, October 8, 2021 - 9:00am

Location: 

410 Life Sciences Laboratories, or zoom (email wallace at ecs.umass.edu)

Details: 

ABSTRACT

 

Waterborne coatings and powder coatings are fast-growing sectors of the world coating market due to their environmentally friendliness because they have low or zero of volatile organic compound (VOC) emissions. However, compared to solventborne coatings, significant limitations need to be overcome to enable their broad applications, for example, powder coatings need to be baked at high temperature which require industrial oven. My dissertation will discuss several novel crosslinking strategies for waterborne and powder coatings that could enable curing on-demand at ambient conditions (i.e., at room temperature), with facile polymerization, easy processing, and ultimately, a high degree of crosslinking and excellent performance comparable to solventborne coatings.

For waterborne coatings, we first demonstrated the anionic polymerization mechanism and the high reactivity of the novel monomer diethyl methylene malonate (DEMM). The direct emulsion polymerization of DEMM initiation by water at various pH values and functional groups was evaluated. Furthermore, multi-functional (DEMM)6 was incorporated as a crosslinker into the latex containing carboxyl acid as the functional group to provide a facile crosslinking methodology in improving coating performance. Additionally, a second monomer, hydroxyethyl methacrylate methylene malonate (HEMA- MM) was introduced by first grafting on latex particles via anionic polymerization, leaving the pendent HEMA groups available for the subsequent free radical crosslinking of coating films upon UV-exposure. Systematic investigations were conducted on the structure of encapsulated particle and the film performance, including particle size distribution, water contact angle, grafting efficiency, crosslinking density, pendulum hardness and mechanical strength. The introduction of HEMA-MM into waterborne latex provides a simple post-functionalization approach for the surface modification of latex particles and the preparation of UV-curable coatings.

For powder coatings, we designed and synthesized novel reactive microparticles to address the high- temperature baking limitation required for traditional powder coatings. Here, the particles were designed to have core-shell structures, comprised of a soft-core of thermoset resin bisphenol A diglycidyl ether modified with thermoplastic poly(butyl acrylate) and a protective polyurea shell. The effect of various core chemistries and viscosities on the deposition efficiency and the critical impact velocity were explored. We determined that particles that had a liquid core of epoxy resin yielded a dramatic improvement in both film formation and deposition efficiency up to 56%. Our work represents a significant breakthrough towards achieving reliable, efficient cold spray coatings at room temperature. We also prepared the waterborne latexes by employing a two-component amine-cured epoxy resin chemistry for the formation of thermoset coatings that enable low VOCs, curing at room temperature, longer shelf life and ultimately exhibit excellent mechanical strength ideal for coating applications.

 
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