Synthesis and characterization of polyurethane-urea-clay and polyvinylidene fluoride-clay nanocomposites
Chemically-modified clay nanoparticles were incorporated into an acoustically clear, two-part thermosetting polyurethane-urea encapsulant. The dispersion of these platelet-like particles into the polyurethane-urea reduced its water permeability coefficient by 75% at a volume percent clay loading of less than 1%. At this low filler loading level, the density, sound speed, acoustic impedance, modulus, loss tangent and insertion loss of the polyurethane-urea-clay nanocomposites remained essentially unchanged from the values characteristic of the unfilled polyurethane. This study is the first to report the acoustic properties of polymer-clay nanocomposites. Additional data on synthesis/dispersion issues, the adhesive bonding ability of the polyurethane-urea-clay nanocomposites to aluminum substrates, and the thermal conductivity of the nanocomposites, are also presented. These nanocomposites would provide better protection for acoustic sources and sensors from water incursion-induced degradation, thereby significantly increasing their useful service lifetimes in the marine environment. Thinner layers of these nanocomposites applied over miniaturized acoustic devices would provide the same (or better) protection from water incursion as the thicker layers of unfilled polyurethane now used to encapsulate full-sized hardware. ^ Polyvinylidene fluoride (PVDF) is the most widely available and inexpensive electroactive polymer. It does not, however, crystallize directly from the melt in its polar, ferroelectric form—typically, conversion to that form requires mechanical stretching. The addition of treated montmorillonite clay results in the formation of a PVDF-clay nanocomposite that forms polar (β-phase) crystallites directly from the melt. Compared to conventional PVDF homopolymer, this nanocomposite material has improved thermal stability, and similar total percent crystallinity. It also exhibits piezoelectric response up to 6 pC/N. Evidence is presented that the coatings applied to the clay to help with exfoliation/intercalation were not thermally stable at the temperature used to extrude the PVDF-clay nanocomposites. More thermally stable coatings for the clay would have produced better α to β conversion percentages and, therefore, a corresponding increase in piezoactivity. PVDF-clay nanocomposites, once perfected, may allow low-cost piezoelectric polymer skins/coatings to be directly extruded over large areas or surfaces. ^
Chemistry, Polymer|Engineering, Materials Science
Thomas Scott Ramotowski,
"Synthesis and characterization of polyurethane-urea-clay and polyvinylidene fluoride-clay nanocomposites"
Dissertations and Master's Theses (Campus Access).