Richard E. Lyon

Pyrolysis combustion flow calorimetry

Abstract A method for evaluating the combustibility of milligram samples is described. Pyrolysis-combustion flow calorimetry (PCFC) separately reproduces the solid state and gas phase processes of flaming combustion in a nonflaming test by controlled pyrolysis of the sample in an inert gas stream followed by high temperature oxidation of the volatile pyrolysis products. Oxygen consumption calorimetry is used to measure the heat of combustion of the pyrolysis products. The maximum amount of heat released per unit mass per degree of temperature (J g−1 K−1) is a material property that appears to be a good predictor of flammability.

FIRE RESISTANT ALUMINOSILICATE COMPOSITES

The fire response of a potassium aluminosilicate (Geopolymer) matrix carbon fiber composite was measured and the results compared to organic matrix composites being used for transportation, militar y, and infrastructure applications . At irradiance levels of 50 kW/m 2 typi- cal of the heat flux in a well developed fire, glass- or carbon-reinforced polyeste r, vinylester, epoxy, bismaleimde, cyanate ester, polyimide, phenolic, and engineering thermoplastic laminates ignited readily and released appreciable heat and smoke, while carbon-fiber reinforced Geopolymer com- posites did not ignite, burn, or release any smoke even after extended heat flux exposure . The Geopolymer matrix carbon fiber composite retains sixty-seven percent of its original flexural strength after a simulated large fire exposure.

Thermal properties of phthalonitrile functional polybenzoxazines

Abstract Phthalonitrile functional polybenzoxazines show high thermal stability with temperature at 5% weight loss (T5%) up to 450°C for monofunctional benzoxazine-based polymers, and up to 550°C for polymers from the bifunctional precursors. High char yield up to 80% by weight is obtained by thermogravimetric analysis in an inert atmosphere at 800°C. Char yield up to 70% by weight at 600°C is achieved in air with T5% in the 380–420°C range. Differential scanning calorimetry (DSC) is used to determine curing conditions. These resins do not require ultrahigh curing temperature as it is typical for the other phthalonitrile functional prepolymers and 250°C is used as a maximum post-cure temperature to achieve desired properties. Dynamic mechanical analysis (DMA) reveals unusually broad dependence of loss modulus vs. temperature with the maximum at 300°C for polybenzoxazines from bifunctional precursors and 278°C for polymer from monofunctional precursors. Additionally, these materials exhibit low flammability.

Comparative study of high temperature composites

Abstract Two classes of composite made using either ceramic matrix with high temperature fibers or carbon/carbon have been used for various applications that require high temperature resistance, over three decades. However, their use has been limited to special applications because of the high costs associated with fabrication. Typically the composites are cured at more than 1000°C, and in most instances the heating has also to be carried out in controlled environments. In addition, because of the high processing temperature, only certain type of expensive fibers can be used with the ceramic matrices. A recently developed inorganic matrix, called polysialate can be cured at temperatures less than 150°C, making it possible to use carbon and glass fibers. Composites made using carbon, glass and combinations of carbon and glass fibers have been tested in bending and tension. This paper presents the comparison of processing requirements and mechanical properties of carbon/carbon composites, ceramic matrix composites made with silicon carbide, silicon nitride and alumina fibers and carbon/polysialate composites. The results indicate that carbon/polysialate composite has mechanical properties comparable to both carbon/carbon and ceramic matrix composites at room and high temperatures. Since the polysialate composites are much less expensive, the authors believe that it has excellent potential for more applications in aerospace, automobile and naval structures.

Heats of combustion of high temperature polymers

The heats of combustion for 49 commercial and developmental polymers of known chemical structure were determined using an oxygen bomb calorimeter according to standard methods. The experimental results were compared with thermochemical calculations of the net heat of combustion from oxygen consumption and the gross heat of combustion from group additivity of the heats of formation of products and reactants. The polymers examined were thermally stable, char forming thermoplastics and thermoset resins containing a significant degree of aromaticity and heteroatoms including — nitrogen, sulphur, phosphorus, silicon, and oxygen in linear and heterocyclic structures. The gross and net heats of combustion calculated from polymer enthalpies of formation and oxygen consumption thermochemistry were within 5% of the experimental values from oxygen bomb calorimetry. The heat released by combustion per gram of diatomic oxygen consumed in the present study was E=13.10±0.78 kJ/gO2 for polymers tested (n=48). This value is indistinguishable from the universal value E13.1 kJ/gO2 used in oxygen consumption combustion calorimetry. Published in 2000 by John Wiley & Sons Ltd.

An integral method of nonisothermal kinetic analysis

Abstract A new series solution for the constant heating rate Arrhenius integral is the basis of a method for determining the kinetic parameters of a single-step reaction from temperature scanning experiments. Isoconversion formulas are derived for calculating the Arrhenius activation energy and frequency factor of a reaction independent of the form of the rate law. Thermogravimetry data for pyrolysis of low density polyethylene and differential scanning calorimetry data for the phenylethynyl curing reaction were analyzed and activation energies were determined and found to agree with literature values. In contrast to existing integral methods, frequency factors for the pyrolysis and curing reaction were obtainable using the present approach without any assumptions about the reaction order or the form of the conversion function.

Heat release kinetics

The role of solid-state thermal degradation kinetics in steady-flaming combustion is examined. Expressions for the burning surface temperature, pyrolysis zone depth and fractional mass loss rate are derived from heat transport limited, nonisothermal pyrolysis kinetics. The predicted magnitude of these fire response parameters and their variation with incident heat flux are in qualitative agreement with experimental data from the literature. A material flammability parameter emerges from the analysis that has the units (J/g-K) and significance of a heat release capacity.

Pyrolysis kinetics of char forming polymers

A mechanistic pyrolysis model for char forming polymers is solved analytically and evaluated experimentally. Under conditions of flaming combustion the coupled rate equations for thermal degradation products and reactants reduce to a single-rate law for the residual mass if production of an intermediate species is the rate-limiting step. Exact results are obtained for the mass loss history of a pyrolyzing polymer which include an equilibrium char yield whose value depends only on the relative rates of gas and char formation at a particular temperature. Reaction rate constants for thermolysis of chemical bonds, gas production and char formation are determinable from parametric fits of the mechanistic charring model to thermogravimetric data. Predictions of the nonisothermal mass loss during constant heating rate experiments are in agreement with experimental data over the expected range of validity.

A Thermal Analysis Method for Measuring Polymer Flammability

A thermal analysis method is presented in which controlled heating of polymer samples and complete combustion of the evolved gases are used to separately reproduce the condensed and gas phase processes of flaming combustion in a single laboratory test. Oxygen consumption calorimetry applied to the combustion gas stream gives the heat release rate history of the sample as a function of its temperature. The maximum rate of heat release and the temperature at which it occurs are polymer characteristics related to fire performance and flame resistance.

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.