Rick D. Davis

Improved Thermal Stability of Organically Modified Layered Silicates

Bromide-containing impurities were found to decrease the thermal stability of quaternary alkyl ammonium-modified layered silicates. Improved purification procedures completely removed bromide and led to a 20°C to >100°C increase in organic modified layered silicate thermal stability. Using mass spectrometry and thermal and electrochemical analysis, N,N-dimethyl-N,N-dioctadecyl quaternary ammonium-modified montmorillonite and fluorinated synthetic mica were found to degrade primarily through elimination and nucleophilic attack by these anions. The nature of residual bromides was identified and quantified, and the efficiency of removing these anions was found to be solvent dependent; sequential extraction, first ethanol then tetrahydrofuran, gave the best results. This exhaustive extraction method represents a viable alternative to the use of expensive, more thermally stable oniumion treatments for layered silicates.

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

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.

Rapid growing clay coatings to reduce the fire threat of furniture

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.

High Throughput Methods for Polymer Nanocomposites Research: Extrusion, NMR Characterization and Flammability Property Screening

A large number of parameters influence polymer-nanocomposite performance and developing a detailed understanding of these materials involves investigation of a large volume of the associated multi-dimensional property space. This multi-dimensional parameter space for polymer-nanocomposites consists of the obvious list of different material types under consideration, such as “polymer” and “nano-additive,” but also includes interphase surface chemistry, and processing conditions. This article presents combinatorial library design and high-throughput screening methods for polymer nanocomposites intended as flame-resistant materials. Here, we present the results of using a twin-screwn extruder to create composition-gradient library strips of polymer nanocomposites that are screened with a solid-state NMR method to rapidly evaluate the optimal processing conditions for achieving nanocomposite dispersion. In addition, we present a comparison of a new rapid Cone calorimetry method to conventional Cone calorimetry and to the gradient heat-flux flame spread method.

A Review of Fire Blocking Technologies for Soft Furnishings

Fire barrier fabrics are expected to play an increasingly important role in complying with existing and proposed soft furnishing flammability regulations in the US. The number of commercial fire blocking technologies is large in order to accommodate the vast requirements of the consumers, manufacturers, and regulatory agencies. Generally, highloft, nonwoven fiber battings are used in residential mattress applications, whereas coated or laminated textiles are more common in institutional and upholstered furnishing applications. Successfully achieving the desired level of fire protection requires appropriate matching of the barrier fabric to the desired characteristics of the soft furnishing. Barrier material selection for soft furnishings is generally a process of trial and error due to significant measurement science gaps.In 2009, the National Institute of Science and Technology and American Fiber Manufacturers Association held a workshop on fire blocking barrier fabrics for soft furnishings to discuss the past, present, and future state of the barrier materials in the US. This manuscript is based on knowledge obtained from the workshop and the subsequent knowledge gathered from literature and stakeholders. Several fire blocking technologies have been explored to reduce the flammability of soft furnishings by preventing or delaying direct flame impingement and heat transfer from the flames or molten polymer to the core components. While previous studies reported on use of fire barriers to comply with full-scale testing of soft furnishing items, they failed to report on assessment of barrier materials as isolated components. In addition to a few examples that demonstrate the complexity that makes a priori selection of fire barrier materials difficult, various fire blocking technologies are discussed in this report with respect to material type, fiber content, and fire blocking mechanisms. Potential test methods for characterizing barrier performance are reviewed. Future trends in fire blocking materials are also briefly described.

High Throughput Flammability Characterization Using Gradient Heat Flux Fields.

The quest for small-scale flammability tests useful for predicting large-scale fire test performance is an enduring undertaking. Often, this work is motivated by limited access to larger quantities of samples, in the case of materials development efforts, and by the slow turn-around and high cost of large scale flammability testing. Use of Cone calorimeter data such as heat release rate (HRR) and ignition data has been coupled with various models to attempt to predict the performance of materials in medium and large scale fire tests. In some instances this has been successful; however, the extensive amount of data that needs to be acquired has motivated the High Throughput (HT) Flammability program at the National Institute of Standards and Technology (NIST) to develop flammability characterization methods which significantly increase the rate of data generation. The goal is to keep pace with our sample preparation rate, which is a significant challenge since our capability to produce samples, either extruded rod, or gradient coatings, has developed to a rate of one sample per minute! The efforts described here are those specifically focused at developing HT flammability analysis methods. The method of evaluating the flammability of a sample at a variety of fluxes simultaneously involves use of a radiant panel to create a gradient heat flux field. Samples are ignited in the high flux region and burned until they self-extinguish. The local flux at this position is termed the minimum flux for flame spread (MFFS). The same general technique has also been accomplished on a smaller scale using the Cone calorimeter. Here MFFS and HRR can be measured concurrently.

Assessment of factors affecting fire performance of mattresses: a review

An in-depth analysis of U.S. residential fire statistics shows that although the total number of fires and deaths due to mattress fires has dropped as a result of several regulatory approaches, the mattress/bedding fires continue to account for one of the largest shares of residential fire deaths and injuries. To address the increasing number of deaths per 1000 mattress/bedding fires, the open flame mattress flammability regulation (16 CFR 1633) was introduced in 2007. The 16 CFR 1633 prescribes performance standards rather than design standards; this allows manufacturers the flexibility to meet the needs of the consumer without sacrificing fire safety. This flammability regulation for residential mattress has generated much interest in understanding the burning behavior of mattresses as well as in developing new materials for mattress construction. To comply with this regulation, it is essential to understand mattress construction, fire performance testing, factors affecting mattress flammability, and compliance solutions.This report reviews the impact of current mattress flammability standards, examines factors affecting mattress flammability, and reviews full-scale and bench-scale test methods that are being developed for mattresses. The construction type, geometry, and size of a mattress are major factors in determining the fire threat of a mattress. The soft materials used in the mattress set, including cushioning materials, fire blocking materials, and tickings, act both individually and collectively to affect the fire performance. The performance of fire barrier materials designed to protect the inner cushioning material from heat and flame is largely dependent on the choice of cushioning material and ticking. When used with an incompatible combination of filling material and ticking, a fire barrier may fail to protect thermal degradation and subsequent burning of filling material. Some of the challenges in designing mattresses have been identified and reported here.

Evaluating smoldering behavior of fire-blocking barrier fabrics

This study reports on the smoldering propensity of commercially available barrier fabrics in a small-scale mock-up configuration. Most barrier fabrics are smolder resistant when tested alone over a standard flexible polyurethane foam. However, when covered with a smolder-prone cover fabric, most barrier fabrics failed the smoldering ignition test described in the Consumer Product Safety Commission’s proposed standard 16 CFR Part 1634. The results of this study suggest that the smolder-prone cover fabrics, when placed on top of a number of barrier fabrics, are capable of releasing sufficient heat to initiate the char oxidation smoldering process of some of the barrier fabrics and subsequently transmit the heat to the underlying flexible polyurethane foam. A smoldering index for barrier fabrics was derived from the measured char volume fraction of the flexible polyurethane foam by varying the barrier fabric component in the flexible polyurethane foam/barrier fabric/cover fabric mock-up systems, while holding the other two components constant. The smoldering index for self-extinguishing barrier fabrics was 0. Barrier fabrics with smoldering index of 1 or more resulted in sustained smoldering in the flexible polyurethane foam. The smoldering propensity of barrier fabrics and the amount of heat transmitted to the flexible polyurethane foam varied depending on the barrier fabric structure, fiber content, air permeability, and bulk density. Flame-retardant treatments and use of char-forming fibers showed a greater tendency for barrier fabric smolder in the presence of the smolder-prone cover fabric. Barrier fabrics with char-forming fiber blends had greater smoldering propensity as compared to barrier fabrics with low charring fiber blends. The lower the smoldering propensity of the barrier fabric, the less likely was the development of sustained smoldering in the flexible polyurethane foam.

Development of High-Throughput Methods for Polymer Nanocomposite Research

This chapter will present an overview of the development of two high-throughput (HT) methods: (1) preparation of formulated polymer libraries using extrusion; (2) screening of flammability properties using flame- spread measurements.

Smoldering and Flame Resistant Textiles via Conformal Barrier Formation

A durable and flexible silicone-based backcoating (halogen free) is applied to the backside of an otherwise smoldering-prone and flammable fabric. When exposed to fire, cyclic siloxanes (produced by thermal decomposition of the backcoating) diffuse through the fabric in the gas phase. The following oxidation of the cyclic siloxanes forms a highly conformal and thermally stable coating that fully embeds all individual fibers and shields them from heat and oxidation. As a result, the combustion of the fabric is prevented. This is a novel fire retardant mechanism that discloses a powerful approach towards textiles and multifunctional flexible materials with combined smoldering/flaming ignition resistance and fire-barrier properties.