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Carbon fibre (CF) and glass fibre (GF) reinforced polymers are used for diverse applications such as electronics/electrical engineering, transportation (railway vehicles, shipping, aviation) and construction. The fire behaviour of composites differs in comparison to polymers. Fibres behave often inert with respect to pyrolysis, but they change the melt flow and dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue and so on. Flame and fire retardancy concepts are needed not only suitable for the different fire protection goals typical for each application, but also tailored for composites. The field is illuminated by examples taken from different projects carried out in the group of the author in the recent years. The examples target on different applications through achieving V0 in UL 94 testing (reaction to small flame controlling the fire risks in the beginning of a fire), reducing heat release rate and fire load in the cone calorimeter (fire risks under forced flaming combusting controlling the contribution to developing fires) and investigating the fire stability when a severe flame is directly applied (key property in fully developed fires). Approaches to halogen-free flame retardancy in GF reinforced thermoplastics and CF reinforced thermosets are presented as well as building up a bench and intermediate scale testing of composites in fire applying mechanical load and direct flame exposure simultaneously.
The understanding of fire behaviour and flame retardancy mode of actions in composites is a promising basis for target-oriented development. The role of flame inhibition, charring and protective layer formation is discussed in composites. Successful concepts are presented for flame retardancy tailored for different application as well as general guidelines for future development. Different phosphorus flame retardants are proposed to achieve halogen-free flame retardancy in applications demanding limited fire risks with respect to ignition and developing fires. Different protective approaches are sketched for addressing the fire resistance of composite that is the most important fire risk for structural applications.
Dripping and melt flow of the pyrolysing polymer melt can be both a benefit and a detriment during a fire. Well-adjusted melt flow and dripping are regularly beneficial to pass small-scale fire tests. Flame retardants often significantly change the melt viscosity of polymeric materials. The influence of certain flame retardants on the dripping behaviour of four commercial polymers is analysed based on experimental monitoring of the mass loss due to dripping, drop size and drop temperature as a function of the furnace temperature applied to a rod-shaped specimen. Investigating the thermal transition, thermal and thermo-oxidative decomposition, as well as the viscosity of the polymer and collected drops accomplish the work and connects dripping and melt flow with physical and chemical processes. Various flame retardant mechanisms affect the dripping behaviour in the UL 94 test. A changed viscosity and reduction in decomposition temperature also play a major role.
This work investigates the fire phenomena of rigid polyurethane foams (RPUF) in detail. To elucidate structure-property relationships systematically varied sets of foams were prepared. RPUF were synthesized with different densities using water and pentane as blowing agent. What is more, a flame retarded RPUF and rigid polyisocyanurate-polyurethane foams were examined. The comprehensive understanding of the processes taking place during combustion is the foundation of customized development of successful flame retardant approaches.
Advanced cone calorimeter investigations provide insight into the fire behavior under forced flaming conditions. Thermocouples in the inside of specimens give information about the temperature gradient and temperature of the pyrolysis zone during combustion. Furthermore, fire phenomena were characterized using SEM, LOI and thermal analysis. By using a multi-methodological approach and systematically varied sets of foam materials, new insights into the burning of RPUF were won. The detailed knowledge of fire phenomena is essential for future development of tailored flame retardant strategies for RPUF.
Carbon fibre (CF) and glass fibre (GF) reinforced polymers are used for diverse applications demaning flame and fire retardancy in the fire scenarios ignition, developing fire and fully developed fire. The fire behaviour of composites differs from polymers, since fibres behave often inert with respect to pyrolysis, change the melt flow / dripping behaviour, the heat absorption and transfer, the amount and properties of the fire residue. Concepts are needed suitable for the different fire protection goals, but also tailored for composites. The field is illuminated by examples carried out in the group of the author in the recent years. Approaches to halogen-free flame retardancy in GF reinforced thermoplastics and CF reinforced thermosets are presented as well as building up a bench and intermediate scale testing of composites in fire applying mechanical load and direct flame exposure simultaneously. The understanding of fire behaviour and flame retardancy modes of action in composites is a promising basis for target-oriented development.
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.
After introducing into the activities and competence of BAM in the field of fire science, several aspects of successful and tailored flame retardancy of polyolefins are discussed. The talk gives an overview of the works relevant for developing flame retardant polyolefins performed in the working group flame retardancy of polymers. The hypothesis of conservation of effective heat of combustion is proposed. The role of charring, inert fillers, protection layer, and intumescence is assessed for flame retarded polyolefins. Distinct routes of optimization sketched. Examples of controlling the dripping and melt flow to obtain the desired fire behaviour are discussed. Finally the cable modul for the cone calorimeter is presented.
The main flame retardant modes of action are known, nevertheless in practise the detailed scientific understanding usually falls short, when it comes to modern multicomponent systems, the important tiny optimizations, or quantifying in terms of specific fire properties. The description of the flame retardant modes of action remains usually vague and fragmentary. This talk tries to deliver thought-provoking impulses how the understanding of the fire behaviour and flame retardancy can be utilized to direct the development of future flame retardant polymer products. Some overseen details are picked up as well as rethinking of concepts memorised long ago is encouraged to discover something new. Furthermore, the talk tries to fill the gap between flame retardant modes of action and fire performance constituting a product. This talk promotes the evidence-based development of flame retardant polymers.
Whereas the degradation of flame retardant polymers has been discussed since decades, only more recently, the lifetime of the flame retardancy itself becomes an important factor, e.g. for cables used as building products. In this work, several kinds of accelerated artificial ageing tests are performed simulating different environmental exposures and thus highlighting different degradation mechanisms: artificial accelerated weathering, climatic chamber, water immersion, salt spray chamber, and autoclave test. The durability is expected to be different for different flame-retardant materials. Thus, various sets of halogen-free fire-retarded polymers were investigated: ethylene vinyl acetate (EVA) with aluminum hydroxide (ATH), boehmite and synergists, ester-based and ether-based thermoplastic polyurethane (TPU) with melamine cyanurate (MC), aluminum diethylphosphinate (AlPi), and boehmite, and glass fiber reinforced polyamide 66 (PA66) with AlPi-based mixtures.
Intensive degradation of the surface was observed, e.g. yielding discoloration and yellowing, EVA showed cracking when weathered. Changes in chemical structure was investigated by ATR-FTIR. The flammability was investigated with the cone calorimeter, UL-94 classification, and oxygen index (LOI). The flame retardancy of most of the materials studied degraded only slightly for the investigated exposure times. EVA/ATH achieved an improved LOI due to flame retardants agglomeration at the surface. Sets of materials, based on EVA and TPU, were also investigated as cable jackets. While flame retarded EVA exhibited no dripping during burning, TPU flame-retarded with MC cables showed pronounced melt-dripping. Cone calorimeter tests were carried out using cable rafts as well as our self-made cable module test, simulating a vertical bundle of cables at the bench scale. The comparison of different fire tests, different exposure conditions, and different materials carved out the specific degradation phenomena with respect to each of these parameters.
Most of this work was supported by the IGF Project (18926 N) of the Fördergemeinschaft für das Süddeutsche Kunststoff-Zentrum e.V., supported by the AiF within the framework of the program “Förderung der Industriellen Gemeinschaftsforschung (IGF)” of the German Federal Ministry for Economic Affairs and Energy based on a decision of the Deutschen Bundestag.
Products and by-products of the invertebrate and vertebrate farming, respectively, are shown to be promising bio-based flame retardant adjuvants in epoxy thermosets. While the addition of bone meal results in the formation of an inorganic shield, protein-based powders from insects provide an intumescent behavior under forced flaming conditions. Combining the latter with a common flame retardant such as ethylene diamine phosphate, the charring efficiency and self-extinguishing properties can be further enhanced.