Yu-Chin Li

Flame retardant behavior of polyelectrolyte-clay thin film assemblies on cotton fabric.

Cotton fabric was treated with flame-retardant coatings composed of branched polyethylenimine (BPEI) and sodium montmorillonite (MMT) clay, prepared via layer-by-layer (LbL) assembly. Four coating recipes were created by exposing fabric to aqueous solutions of BPEI (pH 7 or 10) and MMT (0.2 or 1 wt %). BPEI pH 10 produces the thickest films, while 1 wt % MMT gives the highest clay loading. Each coating recipe was evaluated at 5 and 20 bilayers. Thermogravimetric analysis showed that coated fabrics left as much as 13% char after heating to 500 degrees C, nearly 2 orders of magnitude more than uncoated fabric, with less than 4 wt % coming from the coating itself. These coatings also reduced afterglow time in vertical flame tests. Postburn residues of coated fabrics were examined with SEM and revealed that the weave structure and fiber shape in all coated fabrics were preserved. The BPEI pH 7/1 wt % MMT recipe was most effective. Microcombustion calorimeter testing showed that all coated fabrics reduced the total heat release and heat release capacity of the fabric. Fiber count and strength of uncoated and coated fabric are similar. These results demonstrate that LbL assembly is a relatively simple method for imparting flame-retardant behavior to cotton fabric. This work lays the foundation for using these types of thin film assemblies to make a variety of complex substrates (foam, fabrics, etc.) flame resistant.

Intumescent All‐Polymer Multilayer Nanocoating Capable of Extinguishing Flame on Fabric

According to the National Fire Protection Association (NFPA), there were an estimated 1.3 million fi res in the United States in 2009, which resulted in 3010 civilian deaths (one every 175 minutes), 17 050 injuries (one every 31 minutes), [ 1 ] and direct property loss estimated at

Polyelectrolyte/Nanosilicate Thin-Film Assemblies: Influence of pH on Growth, Mechanical Behavior, and Flammability

12.5 billion. There were more than 40 000 deaths worldwide from fi re in 2006 and it cost every country an average of 1% of their gross domestic product in property loss, medical services for burn victims, etc. [ 2 ] Firerelated issues continue to drive the development of materials that can reduce fi re risk to save lives and protect property, but any fl ame retardants used to reduce that fi re risk have to meet various safety standards to reduce the deleterious effect on the environment or human health. Textiles in particular require effective anti-fl ammable performance combined with minimal enviornmental impact because they are often washed and fl ame retardant additives can leach out of the fabric and into the environment. [ 3 , 4 ] There are numerous strategies used to make textile fi bers fl ame retardant: surface treatment, fi re-retardant additives or co-monomers in synthetic fi bers, nanocomposite technology, heat-resistant and inherently fi re-retardant fi bers, and fi ber blending. [ 5 ] More recently, layer-by-layer (LbL) assembly has been used as a surface treatment to impart fl ame resistance to cotton fabric by coating each individual fi ber with a claypolymer nanobrick wall. [ 6 ]

Growth and fire protection behavior of POSS-based multilayer thin films

Thin composite films of branched polyethylenimine (BPEI) and Laponite clay platelets were prepared using layer-by-layer assembly. The film thickness was tailored by altering the pH of the aqueous mixtures used to deposit these films, resulting in growth that ranged from 0.5 to 5 nm/bilayer (BL). High-pH BPEI and low-pH clay produced the thickest films. The microstructure of tilted Laponite clay platelet stacks is observed with transmission electron microscopy when using unadjusted BPEI (pH 10.3) and pH 6 Laponite. This recipe resulted in a film with 83 wt % clay and a hardness of 0.5 GPa. In all films, the clay platelets are uniformly deposited and look analogous to a cobblestone path in atomic force microscopy surface images. Several 40-BL films, with thicknesses of 100 nm or more, exhibit reduced moduli ranging from 7 to 10 GPa and hardness of around 0.5 GPa, suggesting that these transparent films could be useful as hard coatings for plastic films. These thin coatings were also deposited onto cotton fabric. Each individual cotton fiber was uniformly coated, and the fabric has significantly more char left after burning than the uncoated fabric. Thermogravimetric analysis results reveal that fabric coated with 10 BLs of BPEI/Laponite produces up to 6 wt % char at 500 degrees C, which is almost 1 order of magnitude greater than that of untreated fabric. This initial study demonstrates that polymer/clay assemblies could improve the thermal stability of cotton and may be useful for fire safety applications.

Controlling polyurethane foam flammability and mechanical behaviour by tailoring the composition of clay-based multilayer nanocoatings

Fully siliceous layer-by-layer assembled thin films, using polyhedral oligomeric silsesquioxanes (POSS) as building blocks, were successfully deposited on various substrates, including cotton fabric. Water-soluble OctaAmmonium POSS ((+)POSS) and OctaTMA POSS ((-)POSS) were used as cationic and anionic components for thin film deposition from water. Aminopropyl silsesquioxane oligomer (AP) was also used as an alternative cationic species. The thickness of the AP/(-)POSS and (+)POSS/(-)POSS film is shown to increase linearly with bilayers deposited. Thermogravimetric analysis (TGA), vertical flame testing (VFT), microscale combustion calorimetry (MCC) and pill testing were performed on cotton fabric coated with 5–20 bilayers of a given recipe. All coated fabrics showed improved preservation (i.e., greater residue following heating to 600 °C) and resistance to degradation from direct flame. With less than 8 wt % added to the total fabric weight, more than 12 wt % char remained following MCC for the 20 bilayers (+)POSS/(-)POSS coated cotton. Furthermore, afterglow time was reduced and the fabric weave structure and shape of the individual fibers were highly preserved following VFT. It is expected that this environmentally-friendly coating could be used to impart flame retardant behavior to a variety of fabrics, for protective clothing and soft furnishings, and other complex substrates like foam.

Rapid growing clay coatings to reduce the fire threat of furniture

This study is a thorough evaluation of clay-based Layer-by-Layer (LbL) coatings intended to reduce the flammability of polymeric materials. Through a systematic variation of a baseline coating recipe, an ideal combination of the coating attributes that provides a rapidly developing coating with an optimum balance of flammability, mechanical, and physical attributes on a complex 3D porous substrate, polyurethane foam (PUF) was identified. Using a unique trilayer (TL) assembly approach, the coating growth was significantly accelerated by the polymer (poly(acrylic acid) (PAA)/branched polyethylenimine (BPEI)) concentration in the formulation. However, to significantly reduce flammability without compromising other performance attributes, the concentration of the nanoparticle fire retardant (nanoFR, clay) suspension was critical. This study has resulted in the most significant reduction in PUF flammability using LbL technology without compromising any of the mechanical or physical attributes of the PUF. More specifically, a reduction in the peak heat release rate (pHRR) and average heat release rate (aHRR) of 33% and 78%, respectively, has been achieved. This reduction in flammability is at least two times more effective than commercial fire retardants and other LbL FR coatings for PUF. The insights gained through this research are expected to accelerate the development of other LbL coatings regardless of the intended application.

Phosphorous-filled nanobrick wall multilayer thin film eliminates polyurethane melt dripping and reduces heat release associated with fire

Layer-by-layer (LbL) assembly coatings reduce the flammability of textiles and polyurethane foam but require extensive repetitive processing steps to produce the desired coating thickness and nanoparticle fire retardant content that translates into a fire retardant coating. Reported here is a new hybrid bi-layer (BL) approach to fabricate fire retardant coatings on polyurethane foam. Utilizing hydrogen bonding and electrostatic attraction along with the pH adjustment, a fast growing coating with significant fire retardant clay content was achieved. This hybrid BL coating exhibits significant fire performance improvement in both bench scale and real scale tests. Cone calorimetry bench scale tests show a 42% and 71% reduction in peak and average heat release rates, respectively. Real scale furniture mockups constructed using the hybrid LbL coating reduced the peak and average heat release rates by 53% and 63%, respectively. This is the first time that the fire safety in a real scale test has been reported for any LbL technology. This hybrid LbL coating is the fastest approach to develop an effective fire retardant coating for polyurethane foam.