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Polymer Nanocomposite Protective Coatings Deposited Using Layer-By-Layer Assembly
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Protective coatings with the ability to shield the materials underneath are crucial to packaging, flame retardancy, and corrosion prevention. Amongst all the desired properties, barrier performance is critical for protective coatings. Packaging requires gas barrier and corrosion protection becomes more efficient with a good barrier against corrosive species. Polymer-clay composites have shown great potential as protective coatings due to their cost efficiency, ease of production, and good mechanical properties, and more importantly, good barrier due to the torturous pathway created by impermeable clay. Despite these benefits, further improvements are limited because of clay aggregation and misalignment within polymer matrices. Layer-by-layer assembly (LbL) has proven to be a cost-effective technique that enables high clay loading (> 60 wt%) in thin film coatings. This dissertation is focused on utilizing LbL assembly to achieve a high level of clay alignment and loading in unconventional polymer matrices for varying applications, along with the development of new functionalities. Hydrogen-bonded all-polymer systems are highly stretchable but they suffer from low barrier. In an effort to improve barrier performance while maintaining stretchability, clay platelets were introduced to a hydrogen-bonded system by the alternate deposition of poly(ethylene oxide) (PEO) and polyacrylic acid (PAA) mixed with montmorillonite (MMT) clay. This system, with aligned clay, provides the best stretchable oxygen barrier to-date. In addition to MMT, vermiculite (VMT) clay, with larger aspect ratio, is known to impart better barrier when incorporated into LbL systems. In an effort to improve the barrier and flame resistance of biodegradable polymers such as cellulose, VMT clay is paired with modified cellulose nanofibrils (CNF) (that have positively charged surfaces) using LbL assembly. The resulting nanobrick wall thin film structure imparts great improvement in oxygen barrier, flame resistance, and modulus. LbL-assembled polymer-clay films also demonstrate good corrosion protection. A 30-bilayer waterborne polyurethane and VMT coating, with a thickness of 300 nm, provides 100X improvement in impedance and remains effective for at least five days. This is a result of relatively high hydrophobicity and the nanobrick wall structure, making it a potential environmentally-friendly replacement for toxic chromate conversion coatings (CCCs).
Qin, Shuang (2019). Polymer Nanocomposite Protective Coatings Deposited Using Layer-By-Layer Assembly. Doctoral dissertation, Texas A & M University. Available electronically from