BCC Research Flame 2008 Conference Session3

Charles A. Wilkie, Department of Chemistry, Marquette University, Milwaukee, WI

Over the past several years, a great deal of information has been developed on the use of montmorillonite in polymer/clay nanocomposites and its effect on fire retardancy. For instance, we know that good nano-dispersion is necessary to achieve a reduction in the peak heat release rate and we know that the reason for the effectiveness of the nanoclays is due to the nanoconfinement of the degrading radicals by the clay platelets. From the nanocomposite point of view, we know that it is necessary to have an organic modification on the clay which contains at least one long tail, and two are necessary in some circumstances, to obtain good nano-dispersion. What are the requirements for other nano-dimensional materials? What kind of modifications are necessary to obtain good nano-dispersion? Is nano-dispersion important? How much of a difference is there between a well-dispersed nano-dimensional material and a poorly-dispersed material on the PHRR? Questions such as these will be examined for layered double hydroxides and an effort will be made to separate what is now known and what must be known to be able to exploit these nano-dimensional materials in fire retardancy.

10:00-10:30 a.m. Coffee Break

10:30-11:00 a.m.
Flame Retarding Polyamide 6 with Melamine Cyanurate and Layered Silicates
Jin Zhang, Menachem Lewin, Eli Pearce, Polytechnic University, Brooklyn, NY; Mauro Zammarano, Jeffrey W. Gilman, Building and Fire Research Laboratory, National Institute of Standards and Technology, Gaithersburg, MD

The flammability behavior of the system PA6 + melamine cyanurate (MC) with or without organically modified layered montmorillonite (OMMT) or Na+MMT was studied. The high degree of flame retardancy (FR) obtained with 13 wt.% MC is maintained upon adding up to 0.2 wt.% OMMT or Na+MMT. Increase weight percentage of OMMT is antagonistic to the MC effect. The rate of dripping decreases while the size and mass of drops in the UL-94 tests increases with increasing wt.% OMMT, indicating increase in viscosity of the melt and decrease in rate of sublimation of melamine. Addition of PVP decreases the viscosity and partially restores the FR rating. Na+MMT does not increase the viscosity and the FR ratings are partially preserved. The PHRR in the cone calorimeter decreases with increased loading of OMMT. Addition of Na+MMT or PVP has little influence on the PHRR. The time of ignition decreases with increase in OMMT, but is not affected when Na+MMT is used. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. Mechanistic considerations are presented.

11:00-11:30 a.m.
How to Design Polymer Nanocomposites with Flame Retardants?
Serge Bourbigot, Sophie Duquesne, Laboratoire Procédés d'Elaboration des Revêtements Fonctionnels (PERF), LSPES - UMR/CNRS 8008, Ecole Nationale Supérieure de Chimie de Lille (ENSCL), Villeneuve d'Ascq Cedex, France

Polymer nanocomposites usually provide large reduction of heat release rate in specific scenario but they are not able to pass fire tests such as LOI, UL-94, glow wire … required by the legislation to qualify the materials. The incorporation of flame retardants (FR) permits sometimes to create large synergistic effects but also antagonistic effects. The talk will discuss the benefit of combining nanoparticles with FR based on the expertise of our laboratory. Mechanism of action (chemical and physical aspects) on typical examples will be commented with a special emphasis on the nanodispersion of the particles in the presence of FR microparticles. The ultimate goal of the talk will be to give guidelines for designing flame retarded polymer nanocomposites.

11:30 a.m.-12:00 noon
Dimensional Impact of Nanofillers on the Flammability and Thermal Stability of Polymer/Inorganic Nanocomposites Prepared by Extrusion
Feng Yang, Irina Bogdanova, Gordon L. Nelson, College of Science, Florida Institute of Technology, Melbourne, FL

Polymer/silica and polymer/alumina nanocomposites were obtained by a single-screw extrusion approach, and the resulting materials were subjected to comprehensive studies on thermal stability, flammability, as well as physical properties, in terms of additive type and shape, concentration and different surface modification approaches. It was found that the dimension of an additive could greatly affect physical performance. For instance, a 37% increase in tensile strength and a 60% increase in modulus was achieved for alumina in whisker form at 1wt% loading level in polystyrene, while little to no effect on mechanical properties was found for additives of spherical shape. On the other hand, the thermal stability of polymer nanocomposites (PNC) is mainly determined by the chemical nature of nanofillers, which could affect the degradation process of a polymer by three major mechanisms: a catalytic effect, free radical trapping and mobility restriction. While a metal or metal oxide particle can catalyze the cleavage of the carboxyl from a polymer chain, this will not happen with non-metallic additives. The thermal stability of PNCs will not only change, but also the melt flow behavior. The flammability of PNCs was evaluated by UL 94 and Cone Calorimetery. The relationship between thermal stability and melt flow, versus flammability is used to explain the flame retardant mechanism of the PNCs studied.

12:00 noon-12:30 p.m.
Carbonization and Graphitization of Polymer/a-Zirconium Phosphate Nanocomposites
Yuan Hu, Dandan Yang, Lei Song, State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei, Anhui, China

The alpha-zirconium phosphate (a-ZrP) was used as a catalyst to yields several carbon nanostructures in some polymers, which were studied by means of transmission electron microscopy (TEM) and high resolution electronic microscope (HREM). To improve the compatibility between a-ZrP and polymer matrix, the hexadecyl trimethyl ammonium bromide (C16) modified a-ZrP (OZrP) was prepared by cation exchange method. Then polymer/OZrP nanocomposites were prepared by solvothermal methods. Several types of carbon nanomaterials, including graphite, carbon nanoloops and carbon nanotubes, were found after heat treating these nanocomposites. Carbon nanoloops and carbon nanotubes were observed in polymer/OZrP nanocomposites treated at suitable temperature. The experimental results suggested that polymers would have better thermal stability and improved fire performance with the high-crystalization of charred residue in the presence of a-ZrP. The results of this paper indicate possibilities for the future developments in the field of catalyzing carbonization and other flame retardant systems.

12:30-1:30 p.m. Lunch

Chairman: Kelvin K. Shen, Consultant, Saied Kochesfahani and Frederic Jouffret, Rio Tinto Minerals, Denver, CO

1:30-2:00 p.m.
Effect of Nanoparticles on Flammability of Flexible Polyurethane Foams
Mauro Zammarano, Richard Harris Jr., Thomas J. Ohlemiller, John R. Shields, Jeffrey W. Gilman, BFRL, NIST, Gaithersburg, MD

Untreated polyurethane flexible foams (PUFs) are prone to rapid fire growth due to their low density and thermal conductivity. Furthermore, the low viscosity of the decomposition products generates severe dripping that increases the fire hazard related to the combustion of PUFs. In fact, this downward flow of flaming liquid often results in a pool-fire that promotes flame propagation and boosts the rate of heat release (HRR) due to a significant increase in the burning area and to feed-back between the flame on the pool-fire and the residual foam. In this work the effect of nano-additives on the HRR is investigated with special attention given to melt dripping. A modified cone calorimeter test has been developed for this purpose. It is shown that carbon nanofibers form an entangled fiber network which eliminates melt dripping and decreases the HRR. Different combinations of nano-additives and conventional flame retardants are prepared in order to identify potential synergistic formulations.

2:00-2:30 p.m.
Nanotube/Clay Synergy to Obtain Self-Extinguishing Polymer Blends
Seongchan Pack, Miriam H. Rafailovich, Stony Brook University, Stony Brook, NY; Ezra Bobo, University of Pennsylvania, Philadelphia, PA; Kimberley Leonard, Dix Hills High School, Dix Hills, NY; Joshua Rosenbaum, Yeshiva of Flatbush, Brooklyn, NY; Takashi Kashiwagi, NIST, Gathersburg, MD; Menachem Lewin, Brooklyn Polytechnic Institute, Brooklyn, NY

Most polymer blends are known to be immiscible. Upon heating or burning they continue to phase separate changing the distribution of the components. In particular, when the flame retardant formulation is in one of the phases, this will drastically change the flaming characteristics. Here we will show that when clays are added to polymer blends, one obtains the additional benefit that phase segregation is suppressed while burning. Addition of nanotubes further synergizes the reactions and allows for an even greater reduction in the amount of flame retardant material added. These tubes drastically affect the rheological and possible the surface properties of the chars. Here we will discuss the results obtained with the addition of carbon and clay nanotubes. We will show that clay nanotubes also synergize non-halogenated formulations, enabling us to produce new environmentally sensitive, bio-degradable blends with good mechanical properties and UL-94 V0 designation.

2:30-3:00 p.m.
Fire Performance of Polymer + Fiberglass Reinforced Composites With and Without Polymer Nanocomposite Technology
Alexander Morgan, University of Dayton Research Institute, Dayton, OH

In this paper the fire performance of polymer + fiberglass reinforced materials with variables in resin type, nanofiller type/loading level, conventional fillers, and fiberglass loading levels will be discussed. These composites were tested by cone calorimeter at a 50kW/m2 heat flux to see how these materials would perform in a fire risk scenario typical to mass transport/vehicle fire safety needs. The results found that nanofillers did show some reductions in heat release rate, but not the large reductions typically seen for thermoplastic materials. Fiberglass loading had the largest effect on reduction of flammability, but as fiberglass content increased to 85wt% loading, the mechanical durability of the final "char" decreased greatly. The one variable that had the most effect on flammability was the resin type, which strongly suggests that it may be best to focus on a low heat release resin rather than trying to make a commodity epoxy work for this potentially strict fire safety application.

3:00-3:30 p.m. Coffee Break

Chairman: Usman Sorathia, NAVSEA, Carderock Division, West Bethesda, MD

3:30-4:00 p.m.
Flammability and Mechanical Properties of Polypropylene Modified by Nano Clay Compounds and Aluminium Hydroxide Flame Retardant
Maria Wladyka-Przybylak, Henryk Rydarowski, Ryszard Kozlowski, Institute of Natural Fibres, Poland

The very large commercial importance of polypropylene (PP) has also been driving an intense investigation of PP composites reinforced by particulates, fibers, and layered inorganic fillers. Lowering of flammability of polypropylene and maintaining good mechanical properties is most frequently obtained by introducing halogen flame retardants. While burning the flame retardants give off great amounts of smoke containing toxic and corrosive chemical compounds. Used in the research aluminium hydroxide and clay nanoparticles do not have the above mentioned unfavorable properties. Typical metal hydrate formulations must contain very high loadings of the hydrate to meet flammability requirements. Recent work with experimental aluminium hydroxide and nano clay compounds has shown a way to reduce these high loadings to produce formulations with acceptable physical properties, good FR performance, and good processability The article presents the chosen findings of research into flammability of the composite on the polypropylene filled with nano clay and aluminium hydroxide. As well as this, the influence of adhesion upgrader in the mechanical properties was determined. Mechanical properties were determined, whereas flammability by a Cone calorimeter and TGA.

4:00-4:30 p.m.
Variation of Anions in Layered Double Hydroxides: Effects on Fire Properties
LinJiang Wang, Charles A. Wilkie, Department of Chemistry, Marquette University, Milwaukee, WI

Layered double hydroxide are an interesting material for nanocomposite formation because one can vary both the identity of the metals and the anions to see if these variations have an effect on the ability of the nano-material to be well-dispersed in a polymer and to see what effect these have on the fire properties of the polymer. In this study, several anions of either sulfates, sulfonates or phosphates have been utilized as the charge balancing anion to see how the identity of the anion influences dispersion and fire properties.

4:30-5:00 p.m.
Evaluating the Potential of Layered Metal Hydroxides as Nanocomposite Additives for Polymer Fire Retardancy Formulations
Jeanne M. Hossenlopp, Marquette University, Department of Chemistry, Milwaukee, WI

The anionic analogs of smectite clays, such as hydroxy double salts (HDSs), layered double hydroxides (LDHs), and other layered metal hydroxides offer the possibility of tunable physico-chemical properties via changes in the identity and relative stoichiometry of intralayer metals as well as variation in intralayer anions. Key issues in developing this class of materials for polymer fire retardancy include: (a) characterizing the nature of nanodispersion and its effect on polymer thermal and fire properties, (b) evaluating the effect on other physical properties, and (c) quantifying the combined effects of nanomaterials with conventional additives. Recent work in our laboratory on these topics will be discussed.

5:00-5:30 p.m.
Flame Retardancy of Polyamide 6-layered Silicate Nanocomosite Films and Fabrics
Prabir K. Patra, Kadhiravan Shanmuganathan, Qinguo Fan, Paul Calvert, Steve Warner, Yong K. Kim, Department of Materials and Textiles, College of Engineering, University of Massachusetts Dartmouth, North Dartmouth, MA; Nicholas Dembsey, Department of Fire Protection Engineering, Worcester Polytechnic Institute, Worcester, MA

We investigated the effect of quarternary ammonium modified clay (OMMT) as a single additive and in combination with zincborate on the fire retardancy of polyamide 6-layered silicate nanocomposites films, fibers and fabrics to determine the efficacy of condensed phase flame retardant mechanism in relation to OMMT concentration, sample geometry and flame test conditions. Horizontal flame spread conducted on the nanocomposite showed that with an optimum concentration level of 8-10wt% OMMT, the films burned without any dripping. The flame spread rate was reduced by 30-40% as compared to nylon 6 films. Cone calorimeter study on nanocomposite films showed that the peak heat release rate of nylon 6 was reduced by 65-67% with 8-10wt% OMMT. Undrawn nanocomposite mono-filaments with 10wt% MMT burned slowly and steadily in Bunsen flame without dripping. However, in cone calorimeter, nanocomposite fabrics with 8wt% OMMT showed reduced heat release rate and mass loss rate compared to nylon 6 fabrics with increase in fabric tightness factor. The mass loss rate was about 40-60% less compared to nylon 6 fabrics. The fabric char structure remained intact after burning. This demonstrated the interdependence of fabric tightness factor, OMMT concentration, and source of heat flux in forming a protective char and affecting the flammability of fabrics. Dimensionless flame parameters derived from Quintere's model seems to work well to represent that nanocomposites films and fabrics show a deceleratory trend in flaming compared to unfilled nylon 6.

5:30-7:00 p.m.
Reception, all attendees invited

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