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Material solutions that meet both circular bioeconomy policies and high technical requirements have become a matter of particular interest. In this work, a prospectively abundant proteinrich waste resource for the manufacturing of flame-retardant epoxy biocomposites, as well as for the synthesis of biobased flame retardants or adjuvants, is introduced. Different biomass fillers sourced from the cultivation of the mealworm beetle Tenebrio molitor are embedded in a bioepoxy resin cured with tannic acid and investigated regarding the fire performance of the thermosets. By means of spectroscopic and thermal analysis (attenuated total reflectance FTIR spectroscopy, thermogravimetric analysis-coupled FTIR spectroscopy, and differential scanning calorimetry), the influence of the biomass microparticles on the curing and thermal degradation behavior is evaluated. The final performance of the biocomposites is assessed based on fire testing methodology (limited oxygen index, UL-94, and cone calorimetry). Providing a high charring efficiency in the specific tannic acid-based epoxy matrix, the protein-rich adult beetle is further investigated in combination with commercial environmentally benign flame retardants in view of its potential as an adjuvant. The results highlight a char forming effect of nonvegan fillers in the presence of tannic acid, particularly during thermal decomposition, and point toward the potential of protein-based flame retardants from industrial insect rearing for future formulations.
Valorizing “non-vegan” bio-fillers: Synergists for phosphorus flame retardants in epoxy resins
(2022)
Sustainable, biogenic flame retardant adjuvants for epoxy resins are receiving increased focus. Zoological products like insects, bone meal, and eggshells are available in large quantities, but remain uninvestigated as functional fillers to epoxy resins, although they are potential synergists to flame retardants. The efficacy and flame retardancy of “non-vegan” additives in combination with flame retardants is investigated and the fire behavior and thermal decomposition of bio-sourced epoxy resin composites is characterized. By comparing the fire performance of composites containing flame retardants or fillers at varying loadings (5, 10, and 20%), their role as synergists that enhance the function of organophosphorus flame retardants in bio-epoxy composites is identified and quantified. Peak heat release rates were 44% lower in composites containing both filler and flame retardant versus those containing only flame retardants, and fire loads were reduced by 44% versus the pure resin, highlighting the ability of “non-vegan” fillers to function as synergists.
The incorporation of nanoparticles like multilayer graphene (MLG) into elastomeric composites boosts their technical performance, such as their mechanical behavior and electrical conductivity. Common filler types (carbon black (CB) and aluminum trihydroxide (ATH)) generally fulfill single, specific purposes and are often used in high loadings. CB typically reinforces rubber mechanically, while ATH increases flame retardancy. Small amounts of MLG reduce these high filler contents and maintain the multifunctional characteristics of rubber composites. In chlorosulfonated polyethylene (CSM) + ATH, an intrinsically flame-retardant rubber was designed to achieve the highest standards such as maximum average of heat emission (MARHE) <90 kW m−2, 3 phrMLG was substituted for 15 phr CB and/or 3 phr ATH via an industrially applicable processing approach. Replacing either CB or ATH resulted in a property profile that was multifunctionally improved in terms of features such as mechanical performance, reduced sorption, and flame retardance. MLG nanocomposites are reported to show promise as an industrially utilizable route to obtain multifunctional high-performance rubbers.
A phosphorous soybean-oil–based polyol was derived via epoxidation and ring opening reaction as an alternative to petrochemical-based polyol for the synthesis of flexible polyurethane foams (FPUFs). 5-wt.% and 10-wt.% of expandable graphite (EG) were added to further improve flame retardancy. The mechanical properties (tensile strength and compression stress) of the foams were investigated. Thermogravimetric analysis (TGA) coupled with Fourier-transform infrared (FTIR) were conducted to evaluate the pyrolysis; limiting oxygen index (LOI), UL 94 and cone calorimeter were performed to analyze the fire performance of the foams; smoke density chamber was used to investigate the smoke released during burning. When 10-wt.% of EG was used, the flame retardancy of the foams was much enhanced due to the synergistic effect between phosphorus and EG. The char yield was three times higher (54wt.%). The fire load MARHE approached 100 kWm−2, half of the value expected for a superposition. The combination of phosphorous polyols and EG is proposed as strategy for future flame retarded FPUFs.
Leather is among the most ancient, widely used materials worldwide. Industrial-scale leather production produces large quantities of organic waste attained during shaving and buffing steps during processing. In this study, leather wastes (LW) are used as fillers in flame retarded polymer composites. LW is investigated as a multifunctional bio-filler that enhances the fire performance of flame retarded poly(ethylene–vinyl acetate) (EVA) containing phosphorus flame retardants (P-FRs) ammonium polyphosphate (APP) or a melamine-encapsulated APP (eAPP). Using LW from tanneries as adjuvants to enhance P-FRs in EVA reduces industrial wastes that otherwise require costly waste management solutions. Materials are characterized multi-methodically via mechanical tests, electron microscopy, rheology, thermogravimetric analysis, evolved gas analysis, and condensed phase FTIR, also reaction-to-small-flames and cone calorimeter tests. EVA containing 10 wt-% LW and 20 wt-% P-FRs achieve 20% reductions in fire loads versus EVA, and up to 10% reduction in effective heats of combustion versus EVA with equal (30 wt-%) P-FR loadings. Enhanced char stabilization of EVA composites with LW and P-FRs lowered peaks of heat release rates up to 53% compared to EVA, and up to 40% compared to equal P-FRs loadings. Synergisms between LW and P-FRs in EVA are quantified. A chemical decomposition mechanism is proposed.
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.
In this work, a series of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative salts containing phosphorus and nitrogen were synthesized, and their effects on mechanical properties, thermal stability and flame retardancy of flexible polyurethane foam (FPUF) were investigated. Studies have shown that the addition of DOPO derivatives will increase the tensile strength, compression set, and compression hardness of FPUF, but it will lead to a decrease in elongation at break. Thermogravimetric analysis showed that the initial decomposition temperature of FPUF containing DOPO derivatives was reduecd, but the char reside was significantly improved. A series of combustion tests indicated that the addition of DOPO derivative salts can improve the flame retardancy of FPUF, of which 10-hydroxy-9,10-dihydro-9-oxa-10 phosphaphenanthrene-10-oxide dicyandiamide salt (D-DICY) exhibited the best flame retardancy. When the load of D-DICY was 20 phr, the limiting oxygen index (LOI) of foam reached 24.5%, and the peak heat release rate and total heat release were decreased by 55.7% and 52.9%, respectively. Furthermore, based on the analysis of the gas phase combustion products and the char residue of the condensed phase, the possible flame retardant mechanism was proposed.
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.
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.
The rapid mass calorimeter (RMC) was used as a screening tool based on accelerated fire testing to assess flame-retarded thermoplastic polyurethane (TPU). The reliability of RMC results was proven with the cone calorimeter as reference fire test. The influence of melamine cyanurate (MC) concentration on the fire performance of TPU was investigated, along with some flame-retardant combinations such as MC with aluminium diethylphosphinate (AlPi), aluminium trihydrate (ATH), and melamine polyphosphate (MPP). The two-stage burning behaviour of TPU was investigated in detail; the first stage corresponds mainly to the hard segments' decomposition and has a much lower effective heat of combustion (EHC) than the second stage, in which mainly the soft segments decompose and an intensive liquid pool fire is observed in the cone calorimeter set-up. In addition to fire testing with the cone calorimeter, RMC, and UL 94 flammability tests, the decomposition of the materials was investigated using thermogravimetric analysis coupled with infrared spectrometry (TGeFTIR). TPU/MC/AlPi shows the most promising results, achieving V-0 classification in UL 94 and reducing the extreme peak heat release rate (PHRR) of the liquid pool fire from 3154 kW/m2 to 635 kW/m2. Using MC/AlPi/MPP enhances the latter PHRR reduction further. The decomposition products identified in the gas phase via TGeFTIR reveal specific MCeAlPi eMPP interactions, as they differ from products seen in systems with MC/AlPi or MC/MPP. Correlations between RMC and cone calorimeter results were examined and presented in the final part of the paper. Several characteristics correlate strongly, pointing out that RMC is a reliable high-throughput fire testing method to screen multicomponent flame-retardant solutions in TPU.