Computational study of how inert additives affect the flammability of a polymer

All polymers are flammable to some degree. For safety, polymer flammability is most commonly reduced through flame retardants that are designed to primarily act chemically as opposed to physically. Here, we investigate computationally using the code Gpyro how inert additives such as hollow glass spheres (HGS) and boron nitride platelets (BNP) alter the flammability properties of glass fibre reinforced polybutylene terephthalate (PBT-GF), in a cone heater and UL94 setup. The Gpyro model is first validated against experiments and another code, both from the literature, for pure PBT-GF. According to the predictions, HGS leads to higher surface temperatures but lower temperatures in-depth, whereas adding BNP yields the opposite effect. Modelling numerically the cone heater setup shows that at 50% HGS loading, the time to ignition is reduced to a quarter while the semi-steady state mass loss rate is reduced to a third; at 50% BNP loading, the time to ignition is doubled while the peak mass loss rate is approximately doubled. In the UL94 setup, where the sample is smaller than cone heater, the effects are similar although less pronounced. A sensitivity study of the thermophysical properties shows that time to ignition is primarily controlled by emissivity, density and specific heat capacity, while peak mass loss rate is controlled by thermal conductivity and specific heat capacity. This work shows how heat transfer within a thermoplastic polymer can be utilised to improve its flammability characteristics through inert additives as well as the limitations of this retardancy approach

Pyrolysis and ignition of a polymer by transient irradiation

Pyrolysis is the thermochemical process that leads to the ignition of a solid fuel and a key mechanism in flame spread and fire growth. Because polymer materials are flammable and ubiquitous in the modern environment, the understanding of polymer pyrolysis is thus essential to tackle accidental fires. In this paper, we used transient irradiation as an external source of heat to study the process of pyrolysis and ignition of a polymer sample. While previous ignition studies use constant irradiation, transient irradiation is the most frequent condition found in accidental fires, but it lacks a theoretical framework since it has been largely ignored in the literature. Moreover, transient irradiation is a more comprehensive case for the understanding of pyrolysis where nonlinear heat transfer effects challenge the validity of solid-phase criteria for flaming ignition developed previously. We propose here that transient irradiation is the general problem to solid fuel ignition of which constant irradiation is a particular solution. In order to investigate how this novel heat source in uences polymer pyrolysis and flammability, numerical simulations and experiments have been conducted on Poly(methyl methacrylate) (PMMA) samples 100mm by 100mm and 30mm deep exposed to a range of parabolic pulses of irradiation. The 1D model, coded in GPyro, uses heat and mass transfer and single-step heterogeneous chemistry, with temperature dependent properties. The predictions are compared to experiments conducted in the Fire Propagation Apparatus using both constant and transient irradiation conditions. The experiments validate the temperature predictions of the model and also provide the time to ignition. The model then complements the experiments by calculating the mass loss rate. A series of 16 parabolic pulses (including repeats) are investigated with a range of peak irradiation from 25 to 45 kW/m2, while the time to peak ranges from 280 to 480s. For these pulses, the time to ignition measurements range from 300 to 483s. The model can predict the in-depth temperature profiles with an average error lower than 9%. Model and experiments are then combined to study the validity of the solid-phase criteria for flaming ignition found in the literature, namely critical temperature, critical mass loss rate, critical energy and critical time-energy squared. We find that of these criteria, the best predictions are provided by the critical mass loss rate followed by the critical temperature, and the worst is the critical energy. Further analysis reveals the novel concept of simultaneous threshold values. While the mass loss rate is below 3g/m2 and the surface temperature is below 305ºC, ignition does not occur. Therefore these threshold values when exceeded simultaneously establish the earliest time possible for ignition

Genome-Wide Influence of Indel Substitutions on Evolution of Bacteria of the PVC Superphylum, Revealed Using a Novel Computational Method

Whole-genome scans for positive Darwinian selection are widely used to detect evolution of genome novelty. Most approaches are based on evaluation of nonsynonymous to synonymous substitution rate ratio across evolutionary lineages. These methods are sensitive to saturation of synonymous sites and thus cannot be used to study evolution of distantly related organisms. In contrast, indels occur less frequently than amino acid replacements, accumulate more slowly, and can be employed to characterize evolution of diverged organisms. As indels are also subject to the forces of natural selection, they can generate functional changes through positive selection. Here, we present a new computational approach to detect selective constraints on indel substitutions at the whole-genome level for distantly related organisms. Our method is based on ancestral sequence reconstruction, takes into account the varying susceptibility of different types of secondary structure to indels, and according to simulation studies is conservative. We applied this newly developed framework to characterize the evolution of organisms of the Planctomycetes, Verrucomicrobia, Chlamydiae (PVC) bacterial superphylum. The superphylum contains organisms with unique cell biology, physiology, and diverse lifestyles. It includes bacteria with simple cell organization and more complex eukaryote-like compartmentalization. Lifestyles range from free-living organisms to obligate pathogens. In this study, we conduct a whole-genome level analysis of indel substitutions specific to evolutionary lineages of the PVC superphylum and found that indels evolved under positive selection on up to 12% of gene tree branches. We also analyzed possible functional consequences for several case studies of predicted indel events

Heat transfer effects in polymer flame retardancy

Product flammability is of particular concern because polymer use in, homes, and industrial premises keeps increasing at a rapid pace. To mitigate the inherent flammability hazard carried by polymers, flame retardant additives are the preferred way to ensure that products can resist ignition for longer and reduce the rate at which fire spreads, thus increasing the evacuation time allowed for people. Most research in the field focusses on the chemical action pathways of the flame retardant additives, with not much research on the role of heat transfer. This thesis studies the heat transfer effects in polymer flame retardancy. All three modes of heat transfer, radiation, convection, and conduction, are studied and quantified. Experimental and numerical methods are combined to complement each other to give a more complete understanding. The effective absorption coefficient of thermal radiation in polybutylene terephthalate (PBT) is studied with systematic additions of flame retardants. It was found that some flame retardants affect the absorption coefficient more than others, but thermal degradation has the strongest effect shown to be likely caused by inducing porosity in the material which increases the absorption coefficient. In convective ignition of flame retarded PBT the time to ignition can be increased by the use of flame retardants. The degradation leading up to ignition reduces the thermal diffusivity of polymers. The reduction in thermal diffusivity was largely unaffected by the flame retardants. Increasing the thermal diffusivity through additives in epoxy showed that the time to ignition increases as the conduction rate increases, reducing the surface temperature. Modelling modifications in thermal diffusivity through additives in PBT showed that there is a trade-off between flammability variables, namely time to ignition and mass loss rate. This thesis shows how heat transfer can be used to reduce flammability and complement the current approaches.Open Acces

Convective ignition of polymers: New apparatus and application to a thermoplastic polymer

A new convective ignition apparatus for polymers has been developed with measured flow and temperature fields. Polymer degradation and ignition is typically studied in fire science under radiative heating or direct contact with a pilot flame but this new apparatus allows for research to be conducted in a convective setting providing a missing piece of knowledge on flammability. Convective heating is a main mode of heat transfer in many real fires such as in the built or natural environment, like building fires or wildfires. The apparatus exposes one side of a sample to air between lab ambient and 735 °C at 0.7 to 5 m/s whilst measuring the sample 2D back side temperature via calibrated infrared. The 2D temperature and flow fields, convective heat transfer, and irradiation were studied under various operating conditions of temperature and flow. Polybutylene terephthalate (PBT) samples with glass fibre were ignited using a 735 °C hot stream. Samples of 2 mm thickness ignited after 30 s with a standard deviation lower than 1 s. The experimental work was augmented with numerical modelling of heat and mass transfer with pyrolysis chemistry in Gpyro, allowing for insight into the temperatures across the sample. Combining experimental with numerical work shows that ignition was observed at a surface temperature of 320 °C. Using this rig, ignition can be studied under a range of temperature and flow conditions filling the gaps of the literature which relies primarily on irradiated samples in natural convection conditions

Hacia una digitalización educativa y social en 25 ciudades colombianas

El objetivo de este proyecto de grado es desarrollar una propuesta piloto de inclusión digital en la ciudad de Buenaventura llamada Carpa de la Conectividad, orientada a la población mayor de cinco años que no tiene acceso al uso de herramientas tecnológicas.Presentación. Marco teórico. Metodología. Resultados. Lista de tablas. Lista de gráficas. Lista de figuras. Lista de anexos.Administrador de EmpresasPregrad

Simultaneous improvements in flammability and mechanical toughening of epoxy resins through nano-silica addition

Polymers in transport, and many other engineering applications, are required to be mechanically tough as well as resistant to ignition and flame spread. These demands are often for many polymer types in competition, especially when adding flame retardants. With nano-silica addition, we show that improvements in both properties of a polymer can be achieved simultaneously. In this study, an epoxy resin is evaluated for its flammability and mechanical properties with step wise additions of nano-silica. The fracture toughness was significantly improved. In the single edge notch bending test, the addition of 36% nano-silica particles doubled the toughness and increased the flexure modulus by 50%. Flammability was studied via time to ignition at constant irradiation, and via a UL94 test coupled with mass loss and surface temperature measurements. Modelling for the heat transport and chemical kinetics in Gpyro was done and yielded good agreement with the temperatures measured. Adding up to 36% nano-silica, the time to ignition increased by 38% although a sharp decrease was observed around 24% SiO2 addition. We show that the increased time to ignition is mostly due to a higher thermal diffusivity, increased inert content, as well as a strengthening of the residue outer skin, which acts as a mass barrier for pyrolysate. This outer skin was analysed using a scanning electron microscope coupled with an energy dispersive X-ray spectrometer. We found that in the skin the nano-silica particles agglomerate at the surface forming a strong continuous structure together with the char residue from the epoxy. Improvements in the flammability as seen in the UL94 test were measured with mass loss showing a 30% reduction after 20 s, and surface temperatures at the ignited end being up to 75 K lower compared to the pure epoxy. Modelling in Gpyro supported the temperature measurements taken. Despite the improvements seen, all samples ignited, failing the test with dripping and showing that the improvements recorded in time to ignition did not fully translate over to the UL94 test. Overall we show that the flammability and toughness of epoxy could be improved simultaneously with nano-silica. Using up to 36% nano-silica, the significant modification of thermal properties could be explored in relation to fire properties for epoxy. Increasing the thermal diffusivity as well as skin formation are the main parameters improving the flammability and show a path for potential improvements in other composites as well

Nutzung des Sedimentationseffektes im Pufferbehaelter beim DIC-SBR-Verfahren Schlussbericht

Available from TIB Hannover: F04B651+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung (BMBF), Bonn (Germany)DEGerman