Browsing by Subject "flame retardant"
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Item Environmentally Benign Flame Retardant Nanocoatings for Fabric(2012-07-16) Li, Yu-ChinA variety of materials were used to fabricate nanocoatings using layer-by-layer (LbL) assembly to reduce the flammability of cotton fabric. The most effective brominated flame retardants have raised concerns related to their toxicity and environmental impact, which has created a need for alternative flame retardant chemistries and approaches. Polymer nanocomposites typically exhibit reduced mass loss and heat release rates, along with anti-dripping behavior, all of which are believed to be due to the formation of a barrier surface layer. Despite these benefits, the viscosity and modulus of the final polymeric material is often altered, making industrial processing difficult. These challenges inspired the use of LbL assembly to create densely layered nanocomposites in an effort to produce more flame-retardant coatings. Laponite and montmorillonite (MMT) clay were paired with branched poly(ethylenimine) to create thin film assemblies that can be tailored by changing pH and concentration of aqueous deposition mixtures. Both films can be grown linearly as a function of layers deposited, and they contained at least 70 wt percent of clay. When applying these films to cotton fabric, the individual fibers are uniformly coated and the fabric has significant char left after burning. MMT-coated fabric exhibits reduced total heat release, suggesting a protective ceramic surface layer is created. Small molecule, POSS-based LbL thin films were also successfully deposited on cotton fabric. With less than 8 wt percent added to the total fabric weight, more than 12 wt percent char remained after microscale combustion calorimetry. Furthermore, afterglow time was reduced and the fabric weave structure and shape of the individual fibers were highly preserved following vertical flame testing. A silica-like sheath was formed after burning that protected the fibers. Finally, the first intumescent LbL assembly was deposited on cotton fabric. SEM images show significant bubble formation on fibers, coated with a 0.5 wt percent PAAm/1 wt percent PSP coating after burning. In several instances, a direct flame on the fabric was extinguished. The peak HRR and THR of coated fabric has 30 percent and 65 percent reduction, respectively, compared to the uncoated control fabric. These anti-flammable nanocoatings provide a relatively environmentally-friendly alternative for protecting fabrics, such as cotton, and lay the groundwork for rendering many other complex substrates (e.g., foam) flame-retardant without altering their processing and desirable mechanical behavior.Item Environmentally-benign Flame Retardant Nanocoating for Foam and Fabric(2014-12-09) Cain, Amanda AshleyHalogen-additives are cost effective flame retardants (FRs) that scavenge H? and OH? radicals in the gas phase, but are under significant scrutiny due to the toxic smoke they release and their potential to leach out into the environment and possibly bio accumulate. One fire retarding solution is using layer-by-layer (LbL) assembly, which is a simple, bottom-up processing technique, to create functional nanocoatings through sequential adsorption of materials with complementary functional groups for the purpose of inhibiting or suppressing the combustion cycle. Inspiration for first applying polymer/clay thin films (i.e., nanobrick walls) as flame retardant (FR) coatings to polyurethane foam via LbL came from the final stage of a proposed flame suppression mechanism in a melt-mixture of polymer and clay, which depicts a physical barrier created from the build-up of impermeable flakes and carbonized char. Intumescing nanobrick wall assemblies comprised of nitrogen and phosphorus-containing polymers (mortar) and clay platelets (bricks) were deposited on flexible polyurethane foam using layer-by-layer assembly. Four trilayers of the poly(allylamine hydrochloride) (PAH)/poly(phosphate sodium salt) (PSP)/montmorillonite (MMT) nanobrick wall assembly (< 3 wt% coating addition) are necessary to cut the pkHRR of polyether-based polyurethane by 54.8%, relative to control, uncoated foam. The influence of clay aspect ratio and composition on fire behavior of coated polyurethane foam was studied as a function of polymer/clay (montmorillonite or vermiculite (VMT)) layers deposited and nanocoating weight addition. A single bilayer (BL) of polyethylenimine (PEI) and formulated-vermiculite clay, which adds only 3.2 wt% to the foam, successfully prevented formation of a melt pool of burning polymer and reduced peak heat release rate and total smoke release by 54% and 31%, respectively. MMT-nanobrick walls require 4 BL to match the fire performance of single BL VMT-nanobrick walls. Aqueous coacervation was investigated as a single step process to deposit flame retardant nanocoatings on textiles quickly. Cotton soaked in environmentally-benign PSP/PEI complex for 1 min resulted in a 16.7% residue after vertical flame testing and a 52.7% reduction in total heat release in comparison to uncoated cotton in micro combustion calorimetry. Nanocoatings produced from a 10 min immersion result in fabric capable of self-extinguishing during vertical flame testing.Item Layer-by-Layer Nanocoatings with Flame Retardant and Oxygen Barrier Properties: Moving Toward Renewable Systems(2012-10-23) Laufer, Galina 1985-Numerous studies have focused on enhancing the flame retardant behavior of cotton and polyurethane foam. Some of the most commonly used treatments (e.g., brominated compounds) have raised concerns with regard to toxicity and environmental persistence. These concerns have led to significant research into the use of alternative approaches, including polymer nanocomposites prepared from more environmentally benign nanoparticles. These particles migrate to the surface from the bulk during fire exposure to form a barrier on the surface that protects the underlying polymer. This theory of fire suppression in bulk nanocomposites inspired the use of layer-by-layer (LbL) assembly to create nanocoatings in an effort to produce more effective and environmentally-benign flame retardant treatments. Negatively charged silica nanoparticles of two different sizes were paired with either positively charged silica or cationic polyethylenimine (PEI) to create thin film assemblies. When applying these films to cotton fabric, all coated fabrics retained their weave structure after being exposed to a vertical flame test, while uncoated cotton was completely destroyed. Micro combustion calorimetry confirmed that coated fabrics exhibited a reduced peak heat release rate, by as much as 20% relative to the uncoated control. Even so, this treatment would not pass the standard UL94 vertical flame test, necessitating a more effective treatment. Positively- charged chitosan (CH) was paired with montmorillonite (MMT) clay to create a renewable flame retardant nanocoating for polyurethane foam. This coating system completely stops the melting of a flexible polyurethane foam when exposed to direct flame from a butane torch, with just 10 bilayers (~ 30 nm thick). The same coated foam exhibited a reduced peak heat release rate, by as much as 52%, relative to the uncoated control. This same nanobrick wall coating is able to impart gas barrier to permeate plastic film. Multilayered thin films were assembled with "green" food contact approved materials (i.e., chitosan, polyacrylic acid (PAA) and montmorillonite clay). Only ten CH-PAA-CH-MMT quadlayers (~90 nm thick) cause polylactic acid (PLA) film to behave like PET in terms of oxygen barrier. A thirty bilayer CH-MMT assembly (~100 nm thick) on PLA exhibits an oxygen transmission rate (OTR) below the detection limit of commercial instrumentation (<= 0.005 cm^3/(m^2*day*atm)). This is the same recipe used to impart flame retardant behavior to foam, but it did not provide effective FR to cotton fabric, so a very different recipe was used. Thin films of fully renewable electrolytes, chitosan and phytic acid (PA), were deposited on cotton fabric in an effort to reduce flammability through an intumescent effect. Altering the pH of aqueous deposition solutions modifies the composition of the final nanocoating. Fabrics coated with highest PA content multilayers completely extinguished the flame and reduced peak heat release (pkHRR) and total heat release of 60% and 76%, respectively. This superior performance is believed to be due to high phosphorus content that enhances the intumescent behavior of these nanocoatings.