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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 July 2020) | Viewed by 66422

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Dr. Rodolphe Sonnier

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PCH, IMT–Mines Alès, 6, Avenue de Clavières, 30100 Alès, France
Interests: fire behavior; flame retardants; degradation; polymeric materials; fire safety engineering; polymers; materials chemistry; polymer blends; pyrolysis; ionizing radiation
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Prof. Dr. Laurent Ferry

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IMT Mines Ales, Centre des Matériaux des Mines d’Alès (C2MA), 6 Avenue de Clavières, CEDEX, 30319 Alès, France
Interests: flame retardancy; fire behavior; thermal degradation of polymers
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Dr. Henri Vahabi

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Optical Materials, Photonics and Systems Laboratory (LMOPS), Université de Lorraine, F-57000 Metz, France
Interests: flame retardancy; thermal degradation; biobased flame retardants; biopolymers; aging of flame retardant and polymers; fiber-reinforced composites
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The research focuses more and more on the development of biobased materials to attain the requirements of sustainability. Developing biosourced materials in the future includes polymers as well as additives. Among these additives, flame retardants are the most important market. Bioresources are numerous and provide many opportunities to develop innovative flame retardants. Solutions based on carbohydrates, polyphenols, lipids or proteins are currently investigated.

To be commercially successful, biobased flame retardants must obviously be as efficient as oil-based ones. However, cost may also be a major drawback. Indeed, the development of biobased flame retardants often needs various extraction, purification and functionalization steps. A solution to be competitive may be to provide multifunctionalities. For instance, combining flame retardancy with anti-ageing, plasticizing, crosslinking, conductive properties and so on would be highly desirable.

Alongside biobased ones, there are other innovative flame retardants based on various elements or from different classes of materials which offer new opportunities.

This special issue aims to gather high-quality papers about innovative flame retardants. Especially all aspects of biobased flame retardants are considered, i.e. their extraction, synthesis and functionalization as well as the assessment of their fire retardancy properties and their environmental impact. Papers on other innovative flame retardants are also welcomed. Multifunctional additives combining several properties (including flame retardancy) will be privileged.

Dr. Rodolphe Sonnier
Pr. Laurent Ferry
Dr. Henri Vahabi
Guest Editors

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Keywords

Biobased flame retardants
Flame retardancy
Multifunctional flame retardants
Phosphorus functionalization
Lignin
Biophenol
Carbohydrate
Plant-based resources
Resources from sea
Protein

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Published Papers (12 papers)

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18 pages, 18633 KiB

Open AccessArticle

Flame Retardant-Functionalized Cotton Cellulose Using Phosphonate-Based Ionic Liquids

by Karen Al Hokayem, Roland El Hage, Lenka Svecova, Belkacem Otazaghine, Nicolas Le Moigne and Rodolphe Sonnier

Molecules 2020, 25(7), 1629; https://doi.org/10.3390/molecules25071629 - 2 Apr 2020

Cited by 20 | Viewed by 4397

Abstract

Cellulose from cotton fibers was functionalized through a dissolution–regeneration process with phosphonate-based ionic liquids (ILs): 1,3-dimethylimidazolium methylphosphonate [DIMIM][(MeO)(H)PO₂] and 1-ethyl-3-methylimidazolium methylphoshonate [EMIM][(MeO)(H)PO₂]. The chemical modification of cellulose occurred through a transesterification reaction between the methyl phosphonate function of ILs and the primary alcohol functions of cellulose. The resulting cellulose structure and the amount of grafted phosphorus were then investigated by X-ray diffraction, ICP-AES, and ¹³C and ³¹P NMR spectroscopy. Depending on the IL type and initial cotton / IL ratio in the solution, regenerated cellulose contained up to 4.5% of phosphorus. The rheological behavior of cotton cellulose/ILs solutions and the microscale fire performances of modified cellulose were studied in order to ultimately prepare flame retardant cellulosic materials. Significant improvement in the flame retardancy of regenerated cellulose was obtained with a reduction of THR values down to about 5–6 kJ/g and an increase of char up to about 35 wt%. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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15 pages, 4728 KiB

Open AccessArticle

Organo-Inorganic Hybrid Intumescent Fire Retardant Coatings for Thermoplastics Based on Poly(Vinylphosphonic Acid)

by Baljinder K. Kandola, Katherine V. Williams and John R. Ebdon

Molecules 2020, 25(3), 688; https://doi.org/10.3390/molecules25030688 - 6 Feb 2020

Cited by 5 | Viewed by 2855

Abstract

Thin coatings of crosslinked poly(vinylphosphonic acid), PVPA, display good adhesion and excellent intumescent, fire-retardant barrier properties when applied to the surfaces of a typical thermoplastic, such as poly(methyl methacrylate), but perform relatively poorly in water-soak tests. To strengthen and further improve the barrier properties of the intumescent char and to make the coating more hydrophobic, PVPA has been complexed with various inorganic and organic species. The chars formed from coatings of some of these hybrid materials are less friable than chars from coatings synthesized from crosslinked PVPA alone, and show higher levels of water tolerance with no significant reduction in dry adhesion to the substrate. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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13 pages, 4117 KiB

Open AccessArticle

Effective Biobased Phosphorus Flame Retardants from Starch-Derived bis-2,5-(Hydroxymethyl)Furan

by Bob A. Howell and Xiaorui Han

Molecules 2020, 25(3), 592; https://doi.org/10.3390/molecules25030592 - 29 Jan 2020

Cited by 25 | Viewed by 3625

Abstract

A series of biobased phosphorus flame retardants has been prepared by converting starch-derived bis-2,5-(hydroxymethyl)furan to the corresponding diacrylate followed by Michael addition of phosphite to generate derivatives with phosphorus moieties attached via P–C bonds. All compounds behave as effective flame retardants in DGEBA epoxy resin. The most effective is the DOPO derivative, 2,5-di[(3-dopyl-propanoyl)methyl]furan. When incorporated into a DGEBA blend at a level to provide 2% phosphorus, a material displaying a LOI of 30, an UL 94 rating of V0 and a 40% reduction in combustion peak heat release rate compared to that for resin containing no additive is obtained. The analogous compounds generated from bisphenol A and tetrabromobisphenol A exhibit similar flame-retarding properties. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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21 pages, 4803 KiB

Open AccessFeature PaperArticle

Flame Retardancy of Wood Fiber Materials Using Phosphorus-Modified Wheat Starch

by Stefan Gebke, Katrin Thümmler, Rodolphe Sonnier, Sören Tech, André Wagenführ and Steffen Fischer

Molecules 2020, 25(2), 335; https://doi.org/10.3390/molecules25020335 - 14 Jan 2020

Cited by 35 | Viewed by 5987

Abstract

Biopolymer-based flame retardants (FR) are a promising approach to ensure adequate protection against fire while minimizing health and environmental risks. Only a few, however, are suitable for industrial purposes because of their poor flame retardancy, complex synthesis pathway, expensive cleaning procedures, and inappropriate application properties. In the present work, wheat starch was modified using a common phosphate/urea reaction system and tested as flame retardant additive for wood fibers. The results indicate that starch derivatives from phosphate/urea systems can reach fire protection efficiencies similar to those of commercial flame retardants currently used in the wood fiber industry. The functionalization leads to the incorporation of fire protective phosphates (up to 38 wt.%) and nitrogen groups (up to 8.3 wt.%). The lowest levels of burning in fire tests were measured with soluble additives at a phosphate content of 3.5 wt.%. Smoldering effects could be significantly reduced compared to unmodified wood fibers. The industrial processing of a starch-based flame retardant on wood insulating materials exhibits the fundamental applicability of flame retardants. These results demonstrate that starch modified from phosphate/urea-systems is a serious alternative to traditional flame retardants. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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22 pages, 6381 KiB

Open AccessFeature PaperArticle

New Biosourced Flame Retardant Agents Based on Gallic and Ellagic Acids for Epoxy Resins

by Valeriia Karaseva, Anne Bergeret, Clément Lacoste, Hélène Fulcrand and Laurent Ferry

Molecules 2019, 24(23), 4305; https://doi.org/10.3390/molecules24234305 - 26 Nov 2019

Cited by 17 | Viewed by 5383

Abstract

The aim of this work was an investigation of the ability of gallic (GA) and ellagic (EA) acids, which are phenolic compounds encountered in various plants, to act as flame retardants (FRs) for epoxy resins. In order to improve their fireproofing properties, GA and EA were treated with boric acid (to obtain gallic acid derivatives (GAD) and ellagic acid derivatives (EAD)) to introduce borate ester moieties. Thermogravimetric analysis (TGA) highlighted the good charring ability of GA and EA, which was enhanced by boration. The grafting of borate groups was also shown to increase the thermal stability of GA and EA that goes up respectively from 269 to 528 °C and from 496 to 628 °C. The phenolic-based components were then incorporated into an epoxy resin formulated from diglycidyl ether of bisphenol A (DGEBA) and isophorone diamine (IPDA) (72, 18, and 10 wt.% of DGEBA, IPDA, and GA or EA, respectively). According to differential scanning calorimetry (DSC), the glass transition temperature (T_g) of the thermosets was decreased. Its values ranged from 137 up to 108 °C after adding the phenolic-based components. A cone calorimeter was used to evaluate the burning behavior of the formulated thermosets. A significant reduction of the peak of heat release rate (pHRR) for combustion was detected. Indeed, with 10 wt.% of GA and EA, pHRR was reduced by 12 and 44%, respectively, compared to that for neat epoxy resin. GAD and EAD also induced the decrease of pHRR values by 65 and 33%, respectively. In addition, a barrier effect was observed for the resin containing GAD. These results show the important influence of the biobased phenolic compounds and their boron derivatives on the fire behavior of a partially biobased epoxy resin. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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23 pages, 15058 KiB

Open AccessArticle

Development of Bioepoxy Resin Microencapsulated Ammonium-Polyphosphate for Flame Retardancy of Polylactic Acid

by Kata Decsov, Katalin Bocz, Beáta Szolnoki, Serge Bourbigot, Gaëlle Fontaine, Dániel Vadas and György Marosi

Molecules 2019, 24(22), 4123; https://doi.org/10.3390/molecules24224123 - 14 Nov 2019

Cited by 33 | Viewed by 4402

Abstract

Ammonium-polyphosphate (APP) was modified by microencapsulation with a bio-based sorbitol polyglycidyl ether (SPE)-type epoxy resin and used as a flame retardant additive in polylactic acid (PLA) matrix. The bioresin-encapsulated APP (MCAPP) particles were characterized using Fourier transform infrared (FTIR) spectroscopy and Raman mapping, particle size distribution was determined by processing of scanning electron microscopic (SEM) images. Interaction between the APP core and the bioresin shell was revealed by combined thermogravimetric analysis (TGA)‑FTIR spectroscopy. The APP to SPE mass ratio of 10 to 2 was found to be optimal in terms of thermal, flammability, and mechanical properties of 15 wt% additive containing biocomposites. The bioresin shell effectively promotes the charring of the APP-loaded PLA composites, as found using TGA and cone calorimetry, and eliminates the flammable dripping of the specimens during the UL-94 vertical burning tests. Thus, the V-0 rating, the increased limiting oxygen index, and the 20% reduced peak of the heat release rate was reached compared to the effects of neat APP. Furthermore, better interfacial interaction of the MCAPP with PLA was indicated by differential scanning calorimetry and SEM observation. The stiff interphase resulted in increased modulus of these composites. Besides, microencapsulation provided improved water resistance to the flame retardant biopolymer system. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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21 pages, 4626 KiB

Open AccessArticle

Cardanol and Eugenol Based Flame Retardant Epoxy Monomers for Thermostable Networks

by Yvan Ecochard, Mélanie Decostanzi, Claire Negrell, Rodolphe Sonnier and Sylvain Caillol

Molecules 2019, 24(9), 1818; https://doi.org/10.3390/molecules24091818 - 10 May 2019

Cited by 80 | Viewed by 6856

Abstract

Epoxy materials have attracted attention for many applications that require fireproof performance; however, the utilization of hazardous reagents brings about potential damage to human health. Eugenol and cardanol are renewable, harmless resources (according to ECHA) that allow the achievement of synthesis of novel phosphorylated epoxy monomers to be used as reactive flame retardants. These epoxy building blocks are characterized by ¹H NMR and ³¹P NMR (nuclear magnetic resonance) and reacted with a benzylic diamine to give bio-based flame-retardant thermosets. Compared to DGEBA (Bisphenol A Diglycidyl Ether)-based material, these biobased thermosets differ by their cross-linking ratio, the nature of the phosphorylated function and the presence of an aliphatic chain. Eugenol has led to thermosets with higher glass transition temperatures due to a higher aromatic density. The flame-retardant properties were tested by thermogravimetric analyses (TGA), a pyrolysis combustion flow calorimeter (PCFC) and a cone calorimeter. These analyses demonstrated the efficiency of phosphorus by reducing significantly the peak heat release rate (pHRR), the total heat release (THR) and the effective heat of combustion (EHC). Moreover, the cone calorimeter test exhibited an intumescent phenomenon with the residues of phosphorylated eugenol thermosets. Lastly, the higher flame inhibition potential was highlighted for the phosphonate thermoset. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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18 pages, 6514 KiB

Open AccessArticle

The Efficiency of Biobased Carbonization Agent and Intumescent Flame Retardant on Flame Retardancy of Biopolymer Composites and Investigation of Their Melt-Spinnability

by Muhammad Maqsood, Fabian Langensiepen and Gunnar Seide

Molecules 2019, 24(8), 1513; https://doi.org/10.3390/molecules24081513 - 17 Apr 2019

Cited by 28 | Viewed by 3945

Abstract

The objective of this study is to assess the efficiency of biobased carbonization agent in intumescent formulations (IFRs) to examine the flame retardant properties of polylactic acid (PLA) composites and to investigate their melt-spinnability. We used phosphorous-based halogen free flame retardant (FR) and kraft lignin (KL) as bio-based carbonization agent. After melt compounding and molding into sheets by hot pressing various fire related characteristics of IFR composites were inspected and were characterized by different characterization methods. It was fascinating to discover that the introduction of 5–20 wt% FR increased the limiting oxygen index (LOI) of PLA composites from 20.1% to 23.2–33.5%. The addition of KL with content of 3–5 wt% further increased the LOI up to 36.6–37.8% and also endowed PLA/FR/KL composites with improved anti-dripping properties. Cone calorimetry revealed a 50% reduction in the peak heat release rate of the IFR composites in comparison to 100% PLA and confirmed the development of an intumescent char structure containing residue up to 40%. For comparative study, IFR composites containing pentaerythritol (PER) as a carbonization agent were also prepared and their FR properties were compared. IFR composites were melt spun and mechanical properties of multifilament yarns were tested. The analysis of char residues by energy dispersive X-ray spectrometry (EDS) and SEM images confirmed that PLA/FR/KL composites developed a thicker and more homogeneous char layer with better flame retardant properties confirming that the fire properties of PLA can be enhanced by using KL as a carbonization agent. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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Review

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36 pages, 4991 KiB

Open AccessReview

Reactive and Additive Modifications of Styrenic Polymers with Phosphorus-Containing Compounds and Their Effects on Fire Retardance

by Aloshy Baby, Svetlana Tretsiakova-McNally, Malavika Arun, Paul Joseph and Jianping Zhang

Molecules 2020, 25(17), 3779; https://doi.org/10.3390/molecules25173779 - 19 Aug 2020

Cited by 20 | Viewed by 4813

Abstract

Polystyrene, despite its high flammability, is widely used as a thermal insulation material for buildings, for food packaging, in electrical and automotive industries, etc. A number of modification routes have been explored to improve the fire retardance and boost the thermal stability of commercially important styrene-based polymeric products. The earlier strategies mostly involved the use of halogenated fire retardants. Nowadays, these compounds are considered to be persistent pollutants that are hazardous to public and environmental health. Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada. This had triggered a growing research interest in, and an industrial demand for, halogen-free alternatives, which not only will reduce the flammability but also address toxicity and bioaccumulation issues. Among the possible options, phosphorus-containing compounds have received greater attention due to their excellent fire-retarding efficiencies and environmentally friendly attributes. Numerous reports were also published on reactive and additive modifications of polystyrene in different forms, particularly in the last decade; hence, the current article aims to provide a critical review of these publications. The authors mainly intend to focus on the chemistries of phosphorous compounds, with the P atom being in different chemical environments, used either as reactive, or additive, fire retardants in styrene-based materials. The chemical pathways and possible mechanisms behind the fire retardance are discussed in this review. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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47 pages, 106612 KiB

Open AccessReview

Flame Retardant Epoxy Composites on the Road of Innovation: An Analysis with Flame Retardancy Index for Future Development

by Elnaz Movahedifar, Henri Vahabi, Mohammad Reza Saeb and Sabu Thomas

Molecules 2019, 24(21), 3964; https://doi.org/10.3390/molecules24213964 - 1 Nov 2019

Cited by 123 | Viewed by 7646

Abstract

Nowadays, epoxy composites are elements of engineering materials and systems. Although they are known as versatile materials, epoxy resins suffer from high flammability. In this sense, flame retardancy analysis has been recognized as an undeniable requirement for developing future generations of epoxy-based systems. A considerable proportion of the literature on epoxy composites has been devoted to the use of phosphorus-based additives. Nevertheless, innovative flame retardants have coincidentally been under investigation to meet market requirements. This review paper attempts to give an overview of the research on flame retardant epoxy composites by classification of literature in terms of phosphorus (P), non-phosphorus (NP), and combinations of P/NP additives. A comprehensive set of data on cone calorimetry measurements applied on P-, NP-, and P/NP-incorporated epoxy systems was collected and treated. The performance of epoxy composites was qualitatively discussed as Poor, Good, and Excellent cases identified and distinguished by the use of the universal Flame Retardancy Index (FRI). Moreover, evaluations were rechecked by considering the UL-94 test data in four groups as V0, V1, V2, and nonrated (NR). The dimensionless FRI allowed for comparison between flame retardancy performances of epoxy composites. The results of this survey can pave the way for future innovations in developing flame-retardant additives for epoxy. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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27 pages, 11714 KiB

Open AccessReview

Biomacromolecules and Bio-Sourced Products for the Design of Flame Retarded Fabrics: Current State of the Art and Future Perspectives

by Giulio Malucelli

Molecules 2019, 24(20), 3774; https://doi.org/10.3390/molecules24203774 - 20 Oct 2019

Cited by 58 | Viewed by 5388

Abstract

The search for possible alternatives to traditional flame retardants (FRs) is pushing the academic and industrial communities towards the design of new products that exhibit low environmental impact and toxicity, notwithstanding high performances, when put in contact with a flame or exposed to an irradiative heat flux. In this context, in the last five to ten years, the suitability and effectiveness of some biomacromolecules and bio-sourced products with a specific chemical structure and composition as effective flame retardants for natural or synthetic textiles has been thoroughly explored at the lab-scale level. In particular, different proteins (such as whey proteins, caseins, and hydrophobins), nucleic acids and extracts from natural sources, even wastes and crops, have been selected and exploited for designing flame retardant finishing treatments for several fibers and fabrics. It was found that these biomacromolecules and bio-sourced products, which usually bear key elements (i.e., nitrogen, phosphorus, and sulphur) can be easily applied to textiles using standard impregnation/exhaustion methods or even the layer-by-layer technique; moreover, these “green” products are mostly responsible for the formation of a stable protective char (i.e., a carbonaceous residue), as a result of the exposure of the textile substrate to a heat flux or a flame. This review is aimed at summarizing the development and the recent progress concerning the utilization of biomacromolecules/bio-sourced products as effective flame retardants for different textile materials. Furthermore, the existing drawbacks and limitations of the proposed finishing approaches as well as some possible further advances will be considered. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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31 pages, 3972 KiB

Open AccessReview

Phosphorus-Containing Flame Retardants from Biobased Chemicals and Their Application in Polyesters and Epoxy Resins

by Jacob Sag, Daniela Goedderz, Philipp Kukla, Lara Greiner, Frank Schönberger and Manfred Döring

Molecules 2019, 24(20), 3746; https://doi.org/10.3390/molecules24203746 - 17 Oct 2019

Cited by 71 | Viewed by 9747

Abstract

Phosphorus-containing flame retardants synthesized from renewable resources have had a lot of impact in recent years. This article outlines the synthesis, characterization and evaluation of these compounds in polyesters and epoxy resins. The different approaches used in producing biobased flame retardant polyesters and epoxy resins are reported. While for the polyesters biomass derived compounds usually are phosphorylated and melt blended with the polymer, biobased flame retardants for epoxy resins are directly incorporated into the polymer structure by a using a phosphorylated biobased monomer or curing agent. Evaluating the efficiency of the flame retardant composites is done by discussing results obtained from UL94 vertical burning, limiting oxygen index (LOI) and cone calorimetry tests. The review ends with an outlook on future development trends of biobased flame retardant systems for polyesters and epoxy resins. Full article

(This article belongs to the Special Issue Innovative Flame Retardants)

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