Black Polymethyl Methacrylate Research Articles

The limiting oxygen volume fraction for opposed flame spread extinction

The limiting oxygen volume fraction (LOC) for flame spread is a parameter used to determine flammability and fire hazard. The LOC depends on the solid material, geometry, and environmental conditions. It is important to understand the relationship between these conditions and the LOC, particularly for environments different than Earth atmospheres. Future spacecraft will have sub-atmospheric cabin pressures designed to reduce preparation time for extravehicular activities. This work attempts to provide further information on this aspect of solid fuel flammability by conducting experiments to determine the effect of ambient pressure and external radiant flux for flames spreading downward over cylindrical samples of black polymethyl methacrylate (PMMA). The experimental methodology is based on test methods ASTM 2863 (LOI) and ASTM E-1321 (LIFT), that are used to determine some aspects of material flammability, specifically extinction and flame spread under external radiant heating. Experiments are conducted in a pressure chamber at pressures from 40 to 100 kPa with radiant heating from 0 to 3.3 kW/m2. Results show that decreasing either the ambient pressure or the external radiant flux increases the LOC of the PMMA. The results are correlated in terms of the ratio of the partial pressure of oxygen, radiant flux, and ambient pressure with an equation that includes the LOC at atmospheric pressure. It is found that the heat transfer and chemical kinetic mechanisms that control the flame spread are primarily dependent on the oxygen molar fraction, explaining the experimental observations. The data from this work will be compared with experiments to be conducted in the International Space Station (ISS) under the SoFIE-MIST project to provide further understanding of the effect spacecraft environments have on the LOC of materials. The results will give further insight into the flammability of materials, particularly at sub-atmospheric ambient pressures found in spacecraft, aircraft, and high-altitude locations.

Experimental study of flame spread underneath photovoltaic (PV) modules

The horizontal flame spread underneath a photovoltaic (PV) module (or a plate) was studied for various gap heights to understand the fundamental fire dynamics between it and a flat roof construction. In a number of experiments, an opaque black polymethyl methacrylate (PMMA) and a black stainless-steel plate were used as surrogate fuel and module, respectively. Additional experiments were conducted with actual PV modules to analyse the reproducibility of the surrogate results and to study the potential effect of the small fuel contribution from the PV modules. PMMA samples (70 cm long) of varying widths (20 cm, 30 cm and 40 cm) were ignited at one end, and flame spread rate, mass loss, radiative heat flux and temperatures were recorded. For the 30 cm wide samples, a reduction in gap height from 20 cm to 17 cm resulted in a significant increase in the flame spread rate (from 0.37 mm/s to 2.41 mm/s). A similar critical gap height (transition into a much faster flame spread rate) was identified for all widths. Thus, introducing gap height requirements into PV installation standards could offer an inexpensive and elegant design that could reduce the fire risk associated with PV modules on flat roofs significantly.

Preparation of Black Poly(Methyl Methacrylate-Ethyleneglycol Dimethacrylate) Microspheres Using Metallic Complex Dyes

In this study, we synthesized polymethyl methacrylate cross-linked microspheres and functionalized the surface of the microspheres with amine groups, and discussed the effect of functionalization and the change of the surface morphology of the microspheres. This research uses 1:2 metal composite acid dye to dye self-synthesized microspheres with uniform particle size, and successfully prepares black polymethyl methacrylate cross-linked microspheres, which are applied to spacer microspheres.

Fire behaviors of vertical and horizontal polymethyl methacrylate slabs under autoignition conditions

AbstractIn this study, horizontal and vertical black polymethyl methacrylate (PMMA) samples were investigated experimentally and theoretically under 25‐70 kW/m2 heat flux with autoignition conditions. An empirical model was developed to predict the autoignition time, where the significance of this model is to unify the prediction for both horizontal and vertical samples. Both horizontal and vertical samples show similar phenomena, such as burning stages and no higher than 2 cm sample expansion. It is obtained that the vertical samples show averagely 21% lower CO yield and also longer ignition time than those of the horizontal samples, while the CO2 yield increases about 24%. However, the vertical samples show a relatively high fire risk. This can be reflected by higher surface temperature, bigger average heat release rate (HRR) and mass loss rate (MLR), higher peak MLR, longer bubbling stage, higher CO2 yield, where the differences become even bigger under a higher external heat flux. A linear relationship was found between the average HRR of vertical and horizontal samples, and also between the ignition temperature and external heat flux for both orientated samples. The research outcomes provide a practical basis and guide for the risk assessment of combustible materials under both vertical and horizontal orientation.

The formation of convex microstructures by laser irradiation of dual-layer polymethylmethacrylate (PMMA)

This work presents the fabrication of convex structures by laser irradiation on dual-layer polymethylmethacrylate (PMMA). The surface PMMA layer can prevent gaseous product from escaping and the high absorption of underlying black PMMA layer can ensure enough gas products produced. It is shown that convex structures can only be formed in a particular focus range. The focus position range for appearance of convex structures is determined in our experiments to be 180–400 μm. And then the dependences of height and diameter of convex structures on pulse energy, pulse number and film thickness of surface layer have been investigated. The result demonstrates that the size (both diameter and height) of convex structures could be tuned by pulse energy; compared with the diameter, the height of convex structures is more sensitive to pulse number and film thickness of surface transparent layer. The formation of convex structures is attributed to the sensitively balanced combination effect between the softening of surface material and expansion of underlying material. Finally, large-area-arrays of convex structures with high consistency and variable tunable sizes were generated. The diameter and height of convex structures were measured to be 149 μm and 43 μm, respectively.

Approximate analytical solutions for transient mass flux and ignition time of solid combustibles exposed to time-varying heat flux

An approximate analytical model was established in this study to predict the transient mass flux and ignition time of solid combustibles exposed to time-dependent exponentially increasing heat flux. Critical mass flux was employed as the ignition criterion in the developed model. A new approximation strategy was used to simplify the complicated exact solution and to derive explicit correlations between ignition time and heat flux. Linear and quadratic heat fluxes were focused and the conclusions under other heat fluxes can be extended through analogy. An equivalent ignition temperature, involving critical mass flux, thermodynamics and chemical kinetics, was found in this study. The negative square root of ignition time is linearly proportional to the heat flux at ignition time. Under linear and quadratic heat fluxes, the ignition heat flux increases with a1/3 and a1/5 (a is a constant in the heat flux expression), respectively, whereas the total heat absorbed by the solid before ignition is proportional to a−1/3 and a−1/5, respectively. The capability of the proposed model was validated by another analytical model, numerical simulations and experimental data of black PMMA (Polymethyl Methacrylate) and pine wood. Furthermore, the effect of surface heat loss on the predictions of the proposed model was estimated and parametric study based on critical mass flux was implemented.

Effects of Combined Surface and In-Depth Absorption on Ignition of PMMA.

A one-dimensional numerical model and theoretical analysis involving both surface and in-depth radiative heat flux absorption are utilized to investigate the influence of their combination on ignition of PMMA (Polymethyl Methacrylate). Ignition time, transient temperature in a solid and optimized combination of these two absorption modes of black and clear PMMA are examined to understand the ignition mechanism. Based on the comparison, it is found that the selection of constant or variable thermal parameters of PMMA barely affects the ignition time of simulation results. The linearity between and heat flux does not exist anymore for high heat flux. Both analytical and numerical models underestimate the surface temperature and overestimate the temperature in a solid beneath the heat penetration layer for pure in-depth absorption. Unlike surface absorption circumstances, the peak value of temperature is in the vicinity of the surface but not on the surface for in-depth absorption. The numerical model predicts the ignition time better than the analytical model due to the more reasonable ignition criterion selected. The surface temperature increases with increasing incident heat flux. Furthermore, it also increases with the fraction of surface absorption and the radiative extinction coefficient for fixed heat flux. Finally, the combination is optimized by ignition time, temperature distribution in a solid and mass loss rate.

Experimental and modelling studies on the kinetics and mechanisms of thermal degradation of polymethyl methacrylate in nitrogen and air

Modelling of spread of fires and their extinguishment in solid materials still present a significant challenge. In order to reliably predict the behaviour of a material in a fire scenario, an adequate description of the processes occurring at the gas/solid interface is highly crucial. In this context, those fire scenarios involving polymeric materials are of primary importance because of their increasing use as components in buildings and in transportation. The purpose of this study is to propose an accurate model for the thermal degradation of polymethyl methacrylate (PMMA) by primarily using thermogravimetric analysis (TGA). TGA in non-isothermal conditions, together with Fourier-transform infrared spectroscopy (FT-IR), was applied to investigate the thermal degradation of black PMMA in inert (nitrogen) and oxidizing (air) atmospheres, at different heating rates. The volatile degradation products as well as mass loss history provided sufficient information regarding the kinetics and possible degradation mechanisms of PMMA. A genetic algorithm (GA) was applied to estimate the kinetic parameters, which showed an excellent agreement with corresponding experimental observations for several heating rates and at different atmospheres (0, 10.5, 15 and 21vol.% O2).

Numerical investigation of the ignition delay time of a translucent solid at high radiant heat fluxes

A one-dimensional numerical model describing the physical and chemical phenomena occurring in a translucent solid fuel up to ignition is used to investigate the failure of the classical ignition theory at radiant heat fluxes above 70 kW/m 2. Comparison with a very large dataset of experimental measurements of time to piloted ignition for black PMMA (PolyMethylMethAcrylate) samples shows that model predictions agree well for heat fluxes from 20 to 200 kW/m 2. The only two available sets of experimental data for ignition at high heat fluxes for black-carbon coated and uncoated samples are used. Predictions of the transient temperature profiles inside the solid at different heat fluxes also agree well with measurements. Among all the mechanisms investigated, agreement with measurements at heat fluxes above 70 kW/m 2 is only possible when in-depth radiation absorption is included in the model. Observed behaviour at high heat fluxes cannot be explained by the reaction scheme, ignition criterion, temperature dependency of material properties, surface heat losses or radiation attenuation by pyrolyzates. The model is also used to show that the traditional coating of black carbon added on the sample does not cancel in-depth radiation absorption but its effect is to absorb at the surface around 35% of the incoming radiation. The work explains the failure of the classical ignition theory at high heat fluxes and it is the first time that the effect of black-carbon coating is explained and quantified.

Effect of oxygen on flame heat flux in horizontal and vertical orientations

A systematic empirical and analytical study was conducted to directly quantify the effect of enhanced ambient oxygen concentration on flame heat flux at bench scale and its ability to represent large-scale flame heat flux of well-ventilated fires. The Advanced Flammability Measurements Apparatus was used to conduct bench scale horizontal and single wall vertical orientation experiments for black polymethylmethacrylate, propylene gas and black polyoxymethylene. The key aspect of this study was direct experimental measurements of flame heat flux back to the burning surface for 20.9–40% ambient oxygen concentrations over a range of applied heat flux. The total flame heat flux, as well as the radiative and convective components, was experimentally measured with various gages. To gain more insight into the effects of oxygen, the flame emissivity, flame height and flame temperature were measured and used to calculate the radiative and convective components of the flame heat flux. Gas burner experiments were conducted to decouple the solid and gas phase effects of the ambient oxygen. Large scale tests of black polymethylmethacrylate were conducted in a horizontal orientation and literature data was used for single wall vertical orientations for comparison to the bench scale, enhanced oxygen results. The main conclusion is that the flame heat flux in enhanced ambient oxygen bench scale does not simulate large-scale flame heat flux in horizontal orientations but simulates a more severe large-scale geometry (parallel wall) in vertical orientations and is useful for evaluation of materials’ vertical flame spread potential.

Experimental and numerical study of autoignition and pilot ignition of PMMA plates in a cone calorimeter

This work presents experimental and numerical results for the autoignition and pilot ignition of horizontal black polymethylmethacrylate (PMMA) plates in a cone calorimeter. Experimentally, the histories of plate surface temperature as well as ignition times have been measured for various radiative heating fluxes. Numerically, a two-dimensional axisymmetric model is proposed to simulate the transient processes in the gas and the solid plate. The radiative absorption by the gas phase monomer is considered in a simplified way. With a set of parameters for the one-step Arrhenius kinetics for the gas-phase reaction and a set of parameters for PMMA pyrolysis, the numerical results of surface temperatures and ignition times agree well with the experimental data for both autoignition and pilot ignition. Both experimental and numerical results indicate that while the pilot ignition is pyrolysis-controlled, the autoignition process depends not only on PMMA pyrolysis but also on gas-phase reaction, especially for lower heating fluxes. According to the numerical calculations for autoignition, the ignition times of thermally thin plates are significantly shorter than those of thermally thick plates. For pilot ignition, there exists a linear 1/ t ig − q rad relation for thermally thick plates, as indicated in the literature.

Cone calorimeter: Initial experiences of calibration and use

The primary objectives after taking delivery of a cone calorimeter were to develop operator skills and to establish the reliability, accuracy and repeatability of the instrument. Since the instrument would be used with a wide range of plastics and rubber materials, for research and development of materials and additives, and also for routine tests, it was necessary to establish the effect of instrument variables on test data and of possible instrument/material interactions. Cast, thick, black polymethyl methacrylate (PMMA) sheet is an ideal calibration material. Attempts to obtain this type of material in usable quantities were unsuccessful and tests were carried out using various adhesives to construct a thermally thick speciment. Alternative systems based on thin black PMMA and transparent PMMA sheets were also evaluated. The cone calorimeter has shown itself to be an extremely useful instrument capable of determining basic fire parameters under present heat flux conditions. Test repeatability can be extremely good depending on the material and test regime. Considerable care is required to interpret data since relatively few materials show pseudo-steady-state burning and data may depend on the selected test end point, sample preparation and size. Difficulties arise with the testing of certain types of materials and products which swell, shrink or melt. These can be accommodated from the research point of view but may present difficulties for the simple comparison or possible specification of end-use products comprising materials of dissimilar behaviour.

Heat Loss to the Interior of a Free Burning Vertical Wall and its Influence on Estimation of Effective Heat of Gasification

Abstract Conduction heat transfer into a vertical free burning slab was measured as a function of time and distance from the leading edge, and its contribution to the known values of effective heat of gasification was analyzed. The present set of experiments was performed using clear and black PMMA (polymethylmethacrylate) samples. The heat conduction into the pyrolyzing surface was deduced from temperature measurements in the interior of burning slabs. The surface conduction heat flux decreased from 14 kW/m2 for clear PMMA and 13kW/m for black PMMA at t = 300s to almost 8kW/m2 at around l = 1000s and then reached a plateau, indicating a substantial degree of unsteadiness in the early part of combustion of slabs. It is concluded that, when estimating burning rates in numerical calculations one has to be careful in selecting a value for the effective heat of gasification because of the generally unsteady nature of heat conduction into the solid interior.