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Quasi-static dispersion of dusts for the determination of lower explosion limits of hybrid mixtures
(2022)
Knowledge of explosion limiting concentration of explosible materials is necessary forthe design of explosion protection measures. Currently employed methods of testing MEC of a dust cloud or LEL of a hybrid mixture are based on arbitrary assumptionsand possess technical limitations that often lead to values of MEC/LEL, which are unrealistically low or poorly reproducible. This contribution presents an improved method for experimental determination of MEC of a combustible dust cloud or LEL of a flammable gas or hybrid mixture. The new setup operates under laminar conditions and allows a uniform suspension of dust particles in an open top acrylic glass tube. Dust concentration is measured with the help of infrared sensors installed a few centimeters above and below the ignition source. In order to evaluate the dependence of MEC on flow front velocity, MEC of lycopodium was determined at four flow velocities. The results show that the flow field intensity does not significantly influence the MEC of lycopodium for the flow ranges tested in this work. Moreover, LEL of hybrid mixtures of lycopodium and methane was also tested at flow velocities of 4.7 cm/s, 5.8 cm/s, 7 cm/s and 11 cm/s and compared with the values obtained from other sources. The results suggest that the requirement of high energy pyrotechnical igniter may be relinquished, provided that a truly homogeneous suspension of dust particles could be achieved. Moreover, the effect of relative amount of dust and gas, on the course of ignition and flame propagation in hybrid mixtures at their LEL, was studied by the help of high speed videos. For hybrid mixtures of carbonaceous dusts (like lycopodium) at their LEL, ignition occurs in the gas phase, however, flame propagation is only possible through a two-way interaction of dust and gas during the course of combustion.
Mechanical stress often accelerates the failure of polymer materials. The aim of this research is to study the interaction between the sealing material FKM and biofuels B10 (heating oil with 10% biodiesel). The mechanical stress test was carried out in a special apparatus. Both mechanical and non-mechanical stress tests were conducted on specimens at 20, 40, and 70 °C for 28 days to document changes in mass, volume, and tensile properties. Both increasing temperature and mechanical stress have a significant effect on the tensile strength of the FKM polymer when exposed to B10. The combination of increasing temperature and mechanical stress induced rupture within 2 h. It was also established that FKM polymer with pre-exposure in B10 survived longer during mechanical stress compared to specimens exposed only to air. With the support of infrared (IR) spectroscopy, we were able to confirm the penetration of B10 into the FKM polymer.
Several attempts have been made in the past to develop a European harmonized testing and assessment method for façades before the European commission decided to publish a call for tender on the topic. A project consortium from five countries (Sweden, UK, France, Germany and Hungary) applied to the call for tender and was contracted to develop a European approach to assess the fire performance of façades. 24 sub-contractors and 14 stakeholder entities were part of the project. The objective of the European project was to address a request from the Standing Committee of Construction (SCC) to provide EC Member States regulators with a means to regulate the fire performance of façade systems based on a European Approach agreed by SCC. The initial stages of this Project were focused on establishing a Register of the regulatory requirements in all Member States in relation to the fire Performance of façade systems, and to identify those Member States who have regulatory requirements for the fire performance façade systems which go beyond the current EN 13501 (reaction to fire and fire resistance) classification systems and to collate the details of these additional requirements. After having confirmed the regulatory needs a testing and classification methodology based on BS 8414 and DIN 4102-20 was developed to address the identified key performance and classification characteristics.
This paper is a short overview of results the two-year development work, which Final Report published by the European Commission in 2018.
Multifunctional Graphene in Flame Retarded Polybutadiene/ Chloroprene/ Carbon Black Composites
(2021)
Multilayer graphene is investigated as a multifunctional nanofiller to polybutadiene/ chloroprene rubbers (BR/CR) that partially substitutes carbon black (CB) and aluminum trihydroxide (ATH). Loadings of only 3 parts per hundred rubber (phr) MLG replaced 15 phr of CB and/or 3 phr of ATH in BR/CR nanocomposites. Mechanical and fire behavior were investigated, and results point to improved rheological, curing and mechanical properties of MLG-containing rubber composites.
The demands for modern flame retardants are higher than ever: a flame retardant must function effectively in a certain polymer matrix and avoid critical alterations to the material’s properties. Ideally, a flame retardant additive should be easily miscible and show no sign of leaching or blooming from the matrix. Additionally, the flame retardant should be non-toxic, non-accumulating and biocompatible. Hyperbranched polymers are a promising group of multifunctional flame retardants which fulfill these demands: their complex shape enables high miscibility and avoids leaching or blooming, while their high molecular weight potentially increases biocompatibility and lowers accumulation and toxicity. Moreover, they exhibit a low impact on polymer properties and a good flame retardant performance.
This work examines the efficacy and mode of action of phosphorus-based hyperbranched polymeric flame retardants in bisphenol A-based epoxy matrices. To investigate the effect of the complex shape, the hyperbranched polymers are compared to their corresponding monomeric variants. Furthermore, the materials are synthesized to contain systematically varying oxygen-to-nitrogen ratios, allowing for new insight into what role the chemical surrounding of phosphorous plays in flame retardant efficacy.
Using a multi-methodical approach, including thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (FTIR), hot stage FTIR, micro combustion calorimetry, differential scanning calorimetry, oxygen index (LOI), UL-94 tests and cone calorimetry experiments, the decomposition mechanisms and the flame retardant modes of action of these flame retardants in epoxy resins are investigated, shedding new light on the chemistry of flame retardancy.
Most synthetic polymers have a high fire load, and as a result, they require flame retardants (FRs) to ensure their safe use. Phosphorus plays an important role in flame retardancy and has the potential to replace halogenated variants, which are assumed to be harmful to the environment and health. Among phosphorus-based FRs, there exists a trend towards polymeric, high molar mass molecules with complex molecular architectures. In this project, we synthesized a novel series of so-called phosphorus-based hyperbranched polymeric FRs and investigated their use as multifunctional additives to high-performance polymers, i.e. epoxy resins. By cleverly designing the chemical structure to contain varying amounts of P-O and P-N bonds, new insight into the chemical mechanism of flame retardancy was gained, and by comparing the hyperbranched polymers to their monomeric counterparts, a greater understanding of the role of complex architecture was won. This talk aims at presenting some of these results and proposes chemical mechanisms that illustrate what role these novel hyperbranched flame retardants play in molecular firefighting.
The need to develop effective flame retardants that retain polymer properties and are safe for consumers and the environment is a continuous challenge for material scientists. While halogenated flame retardants were once commonplace, the shift to non-halogenated materials has steadily progressed due to concerns over impact on health and the environment. One prominent group of flame retardants has become a viable alternative for halogenated materials, namely phosphorus-based flame retardants. The chemical versatility of phosphorus-based flame retardants and the ability to work as reactive or additive compounds makes them ideally suited for modern materials. There exists a trend toward complex, polymeric, and multifunction flame retardants, as these materials show greater flame retardancy performance than low molecular weight counterparts and affect material properties to a much lesser extent.
One group of organophosphorus flame retardants that shows great potential for high-performance polymers like epoxy resins are hyperbranched phosphorus-based polymers. These additives exhibit great miscibility with the polymer matrix and a significantly decreased diffusion through the material, which greatly reduce leaching or blooming out of the matrix. Moreover, the material’s thermal stability remains intact at elevated temperatures due to its low impact on the glass transition temperature. Finally, following market trends and legislation such as the guidelines for the Restriction of Hazardous Substances Directive implemented by REACH (Registration, Evaluation, Authorization and Restriction of Chemicals) in the EU, these macromolecules are non-accumulating, non-toxic and have a lower risk of leeching or blooming from the matrix, further reducing environmental impact.
The work presented herein focusses on two distinct parts studying hyperbranched polymeric flame retardants and their corresponding monomeric compounds.
The first part, involving the low molecular weight components, investigated the role of the chemical surrounding of phosphorus in terms of flame retardant efficacy. Here, a systematic variance of the surrounding of phosphorus was investigated: by changing the ratio of oxygen to nitrogen (4:0 until 1:3), four materials, namely phosphoester (4:0), phosphoramidate (3:1), phosphorodiamidate (2:2), and phosphoramide (1:3), were synthesized, characterized, and finally added to Bisphenol A based epoxy resins (10 wt.-% loading). Pyrolysis investigations showed that low molecular weight components volatize at lower temperatures than the polymer matrix. Additionally, cone calorimeter measurements and TGA-FTIR investigations show trends in respect to FR efficacy in pyrolysis and full flaming conditions.
The second part involves the hyperbranched variants of the monomeric counterparts and investigates the role of complex shape on flame retardant efficacy. By comparing the low to the high molecular weight compounds, the influence of the complex shape becomes apparent and can be quantified. Cone calorimeter measurements show an increase in flame retardancy for some materials, while for others, the mode of action is altered.
By implementing a multi-methodical approach, various flame retardancy aspects, from pyrolysis behavior in the gas and condensed phase, to ignitability / reaction-to-small-flame performance, to action in forced flammability experiments, are identified and quantified, allowing for a clearer understanding of the behavior in fire of these novel flame retardants. By comprehending the roles of chemical composition and complex shape, it opens the path for new and effective multifunctional, polymeric flame retardants with decreased PBT, higher miscibility, and low impact on Tg.
This work is funded by the Deutsche Forschungsgemeinschaft (DFG: SCHA 730/15-1; WU 750/8-1).
Benefits of hyperbranched structure:
Molecular weight, miscibility, number of FR groups, end-group functionalization, glass transition temperature, decreased PBT.
Examples of hyperbranched FRs:
Charring agent, silicone, triazine, etc.
Systematic study of effect of chemical surrounding and impact of Complex shape of phosphorus-based hyperbranched polymers on flame retardant efficacy in epoxy resins.