Special Issue "Flame Retardancy of Polymeric Materials II- Bio-Inspired and Environmentally-Benign Formulations and Methods"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Applications".

Deadline for manuscript submissions: closed (31 October 2020) | Viewed by 14717

Special Issue Editors

Dr. Svetlana Tretsiakova-McNally
E-Mail Website
Guest Editor
Belfast School of Architecture and the Built Environment, Ulster University, Newtownabbey BT37 0QB, Northern Ireland, UK
Interests: chain-growth polymers; combustion; thermal decomposition; flammability; fire retardants; ligno-cellulosic materials; waste recycling and management; sustainability
Special Issues, Collections and Topics in MDPI journals
Dr. Paul Joseph
E-Mail Website
Guest Editor
Institute of Sustainable Industries and Liveable Cities, Victoria University, P.O. Box 14428, Melbourne, VIC 8001, Australia
Interests: polymer synthesis; environmentally sustainable flame retardant materials; cellulosic combustion and bush fires; waste recycling/management; adaptation of the existing processes/strategies towards more effective means of combustion
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Following on from the success of the recent Special Issue of Polymers, “Flame Retardancy of Polymeric Materials”, we are delighted to launch the second part, entitled as, “Flame Retardancy of Polymeric Materials II—Bio-Inspired and Environmentally-Benign Formulations and Methods”.

The use of fire retardants (FRs) to passively protect solid substrates, including polymeric ones, can be perhaps traced back to the use of their kind first published by Gay-Lussac in 1821 (L. Gay Lussac, Annales de chime, 18(2), (1821) 211). The earlier uses of FRs were mostly aimed at protecting naturally ocurring materials and their derivatives, such as ligno-cellulosics and polymeric components based on polyamides, the latter being mostly of an animal origin. With the emergence of synthetic plastic materials during the turn of the 20th century and their extended use in almost every walks of daily life , such as in dwellings, public places and transportation, brought with it a formidable challenge of their safer use, primarily emanating from their higher flammability and associated hazards.

In spite of the inherent flammability attributes of, and fire hazards associated with, synthetic polymers, their uses and demands  are on the increase. This is primarily due to their ease of production and low cost, light weight, good processability, enhanced weatherability, etc., as opposed to the conventional natural counterparts. One of the main reasons behind the successful use of polymeric-based materials in every-day-life is that, over the past decades, effective means and methods of adequately fire proofing these materials have been also brought in place. However, in an ardent quest to achieve sufficient levels of flame reatrdancy of polymeric materials and components, predominantly synthetic thermoplastics, even the use (or perhaps the misuse!) of certain heavy metal oxides in combination with halogenated moieties became common place. Without much delay, such a practice was severly criticized by the scientific community, and was also concomitantly restricted through legistlative measures. The shift from these toxic formulations to more environmentally-friendly formulations that are based either on metal hydroxides/carbonates, or on phosphorus-containing compounds, or on more recently discovered non-reactive inorganic nano-materials, etc., did not completely eliminate the undesirable side effects like their environmental toxicity and ensuing longer term problems. Naturally, the turn of the century witnessed an upsurge of a huge interest in bio-derived and environmentally-friendly FRs and associated methodologies for fire proofing polymeric materials.

This Special Issue, “Flame Retardancy of Polymeric Materials II- Bio-inspired and environmentally-benign formulations and methods”, predominantly focusses on the recent developments in this area, and the main topics include, but are not limited to, the following:

  1. Sustainable technologies and bio-inspired fire retardants
  2. Novel fire retarded polymeric materials derived from natural resources
  3. Modification/conversion of agricultural products and wastes to serve as FRs
  4. Multicomponent systems incorporating conventional FRs and bio-derived products
  5. Additive/reactive strategies pertaining to bio-inspired FRs
  6. Polymeric hybrid materials and nanocomposites that incorporate natural fibrous materials
  7. Elements of mechanisms of fire retardant action
  8. Elucidation of condensed- and gaseous-phase chemistries
  9. Analytcal correlations of test data at different scales
  10. Mathematical modelling and software simulation of fire behaviour of the modified systems

Whilst original contributions are normally expected, relevant reviews on topical issues in the general subject area are also welcome.

Dr. Svetlana Tretsiakova-McNally
Dr. Paul Joseph
Guest Editors

Keywords

  • Bio-inspired fire retardant materials and formulations
  • Fire retardant coatings, fibres and composites sourced from natural resources
  • Thermal degradation/decomposition and combustion of polymers
  • Calorimetric evaluations
  • Structural and morphological features of materials
  • Mechanisms of flame retardation
  • Characterisation techniques
  • Correlations of empirical parameters
  • Mathematical modelling and computational simulations

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Published Papers (10 papers)

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Research

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Article
Flammability Characteristics and Mechanical Properties of Casein Based Polymeric Composites
Polymers 2020, 12(9), 2078; https://doi.org/10.3390/polym12092078 - 12 Sep 2020
Cited by 1 | Viewed by 1046
Abstract
Even though casein has an intrinsic potential ability to act as a flame retardant (FR) additive, the research regarding the FR performance of casein filled polymeric composites has not been thoroughly conducted. In the present work, two commercial casein products, such as lactic [...] Read more.
Even though casein has an intrinsic potential ability to act as a flame retardant (FR) additive, the research regarding the FR performance of casein filled polymeric composites has not been thoroughly conducted. In the present work, two commercial casein products, such as lactic casein 720 (LAC) and sodium casein 180 (SC), were chosen to investigate their effects on the performances of the polypropylene (PP) composites. The melt compounding and compression moulding processes were employed to fabricate these casein-based composites. Ammonium polyphosphate (APP) was also selected to explore its combined effects in conjunction with casein on the composite’s flammability. The cone calorimeter results showed that the addition of casein significantly reduced (66%) the peak heat release rate (PHRR) of the composite compared to that of neat PP. In particular, the combination of LAC and APP led to the formation of more compact and rigid char compared to that for SC based sample; hence, a further reduction (80%) in PHRR and self-extinguishment under a vertical burn test were accomplished. Moreover, the tensile modulus of the composite improved (23%) by the combined effects of LAC and APP. The overall research outcome has established the potential of casein as a natural protein FR reducing a polymer’s flammability. Full article
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Article
A Kinetic Analysis of the Thermal Degradation Behaviours of Some Bio-Based Substrates
Polymers 2020, 12(8), 1830; https://doi.org/10.3390/polym12081830 - 15 Aug 2020
Cited by 5 | Viewed by 1170
Abstract
In the present paper, we report on a detailed study regarding the thermal degradation behaviours of some bio-sourced substrates. These were previously identified as the base materials in the formulations for fireproofing wood plaques through our investigations. The substrates included: β-cyclodextrin, dextran, potato [...] Read more.
In the present paper, we report on a detailed study regarding the thermal degradation behaviours of some bio-sourced substrates. These were previously identified as the base materials in the formulations for fireproofing wood plaques through our investigations. The substrates included: β-cyclodextrin, dextran, potato starch, agar-agar, tamarind kernel powder and chitosan. For deducing the Arrhenius parameters from thermograms obtained through routine thermogravimetric analyses (TGA), we used the standard Flynn–Wall–Ozawa (FWO) method and employed an in-house developed proprietary software. In the former case, five different heating rates were used, whereas in the latter case, the data from one dynamic heating regime were utilized. Given that the FWO method is essentially based on a model-free approach that also makes use of multiple heating rates, it can be considered in the present context as superior to the one that is dependent on a single heating rate. It is also relevant to note here that the values of energy of activation (Ea) obtained in each case should only be considered as apparent values at best. Furthermore, some useful, but limited, correlations were identified between the Ea values and the relevant parameters obtained earlier by us from pyrolysis combustion flow calorimetry (PCFC). Full article
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Article
Mechanistic Aspects of Condensed- and Gaseous-Phase Activities of Some Phosphorus-Containing Fire Retardants
Polymers 2020, 12(8), 1801; https://doi.org/10.3390/polym12081801 - 11 Aug 2020
Cited by 5 | Viewed by 913
Abstract
As a part of our ongoing investigations on passively fire protecting polymeric materials, we have been employing both reactive and additive routes involving phosphorus-containing compounds. These included inorganic and organic substances, and in the latter case, the phosphorus-bearing groups differed in terms of [...] Read more.
As a part of our ongoing investigations on passively fire protecting polymeric materials, we have been employing both reactive and additive routes involving phosphorus-containing compounds. These included inorganic and organic substances, and in the latter case, the phosphorus-bearing groups differed in terms of the chemical environments (phosphite, phosphate, phosphine, phosphine oxide and phosphonate ester) and oxidation state of the P atom (i.e., III, or V). The overall flammability profiles of wood substrates coated with the phosphorus-containing compounds were obtained through cone calorimetric measurements. The elemental composition, morphology and chemical natures of the char residues, obtained from the cone tests, were analysed through a variety of spectroscopic, chromatographic and spectrometric means. From the complementary information, obtained through these analyses, some probable mechanistic pathways that underpin the condensed- and gaseous-phase activities of the different additives are suggested. It was found that the inorganic solid additive, i.e., (NH4)2HPO4, underwent a two-step degradation, yielding ammonia gas and phosphoric acid. Furthermore, the liquid additives, owing to their volatility as compared to the solid ones, showed a relatively higher presence in the vapour phase than volatile fragments emanating from the latter ones (i.e., from phosphine and the phosphine oxides). Full article
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Article
A Flame-Retardant Phytic-Acid-Based LbL-Coating for Cotton Using Polyvinylamine
Polymers 2020, 12(5), 1202; https://doi.org/10.3390/polym12051202 - 25 May 2020
Cited by 8 | Viewed by 1680
Abstract
Phytic acid (PA), as a natural source of phosphorus, was immobilized on cotton (CO) in a layer-by-layer (LbL) approach with polyvinylamine (PVAm) as the oppositely charged electrolyte to create a partly bio-based flame-retardant finish. PVAm was employed as a synthetic nitrogen source with [...] Read more.
Phytic acid (PA), as a natural source of phosphorus, was immobilized on cotton (CO) in a layer-by-layer (LbL) approach with polyvinylamine (PVAm) as the oppositely charged electrolyte to create a partly bio-based flame-retardant finish. PVAm was employed as a synthetic nitrogen source with the highest density of amine groups of all polymers. Vertical flame tests revealed a flame-retardant behavior with no afterflame and afterglow time for a coating of 15 bilayers (BL) containing 2% phosphorus and 1.4% nitrogen. The coating achieved a molar P:N ratio of 3:5. Microscale combustion calorimetry (MCC) analyses affirmed the flame test findings by a decrease in peak heat release rate (pkHRR) by more than 60% relative to unfinished CO. Thermogravimetric analyses (TGA) and MCC measurements exhibited a shifted CO peak to lower temperatures indicating proceeding reactions to form an isolating char on the surface. Fourier transform infrared spectroscopy (FTIR) coupled online with a TGA system, allowed the identification of a decreased amount of acrolein, methanol, carbon monoxide and formaldehyde during sample pyrolysis and a higher amount of released water. Thereby the toxicity of released volatiles was reduced. Our results prove that PA enables a different reaction by catalyzing cellulosic dehydration, which results in the formation of a protective char on the surface of the burned fabric. Full article
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Article
Synthesis of Novel Polymeric Acrylate-Based Flame Retardants Containing Two Phosphorus Groups in Different Chemical Environments and Their Influence on the Flammability of Poly (Lactic Acid)
Polymers 2020, 12(4), 778; https://doi.org/10.3390/polym12040778 - 01 Apr 2020
Cited by 6 | Viewed by 1537
Abstract
Novel polymeric acrylate-based flame retardants (FR 1–4) containing two phosphorus groups in different chemical environments were synthesized in three steps and characterized via nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS). Polylactic acid (PLA) formulations [...] Read more.
Novel polymeric acrylate-based flame retardants (FR 1–4) containing two phosphorus groups in different chemical environments were synthesized in three steps and characterized via nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mass spectrometry (MS). Polylactic acid (PLA) formulations with the synthesized compounds were investigated to evaluate the efficiency of these flame retardants and their mode of action by using TGA, UL94, and cone calorimetry. In order to compare the results a flame retardant polyester containing only one phosphorus group (ItaP) was also investigated in PLA regarding its flame inhibiting effect. Since the fire behavior depends not only on the mode of action of the flame retardants but also strongly on physical phenomena like melt dripping, the flame retardants were also incorporated into PLA with higher viscosity. In the UL94 vertical burning test setup, 10% of the novel flame retardants (FR 1–4) is sufficient to reach a V-0 rating in both PLA types, while a loading of 15% of ItaP is not enough to reach the same classification. Despite their different structure, TGA and cone calorimetry results confirmed a gas phase mechanism mainly responsible for the highly efficient flame retardancy for all compounds. Finally, cone calorimetry tests of the flame retardant PLA with two heat fluxes showed different flame inhibiting efficiencies for different fire scenarios. Full article
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Article
Waterborne Intumescent Coatings Containing Industrial and Bio-Fillers for Fire Protection of Timber Materials
Polymers 2020, 12(4), 757; https://doi.org/10.3390/polym12040757 - 31 Mar 2020
Cited by 10 | Viewed by 1411
Abstract
Flammability and combustion of softwood treated with intumescent coatings were studied in the present work. The formulations applied onto wood surfaces contained different ratios of industrial fillers, titanium dioxide TiO2 and aluminium trihydroxide Al(OH)3, and/or bio-fillers, eggshell and rice husk [...] Read more.
Flammability and combustion of softwood treated with intumescent coatings were studied in the present work. The formulations applied onto wood surfaces contained different ratios of industrial fillers, titanium dioxide TiO2 and aluminium trihydroxide Al(OH)3, and/or bio-fillers, eggshell and rice husk ash. Combustion behaviours of unprotected and protected wood samples have been examined with the aid of cone calorimetry performed under the varied levels of thermal flux ranging from 30 to 50 kW/m². The char residues obtained after the completion of cone calorimetry test at 40 kW/m² were analysed by the Raman spectroscopy. The fire protective properties of the studied coatings were strongly influenced by the nature of the fillers as well as by the intensity of thermal irradiance. The incorporation of bio-based fillers into the water-based intumescent formulations significantly improved fire resistance of wood substrates. For example, at 30 kW/m², the Effective Heat of Combustion was reduced by more than 40%, whilst the average Peak to Heat Release Rate had dropped from 193.2 to 150.3 kW/m² for the wood sample protected with the formulation incorporating two industrial and two bio-fillers. Moreover, an application of the studied coatings resulted in a notable reduction of the back surface temperature of the wood specimens. Full article
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Article
Incorporation of Comonomer exo-5-(Diphenylphosphato)Isosorbide-2-endo-Acrylate to Generate Flame Retardant Poly(Styrene)
Polymers 2019, 11(12), 2038; https://doi.org/10.3390/polym11122038 - 09 Dec 2019
Cited by 8 | Viewed by 1205
Abstract
A phosphorus containing acrylate monomer has been constructed from isosorbide, a renewable biomaterial. Treatment of isosorbide with diphenylchlorophosphate generates a mixture of phosphorus esters from which exo-5-(diphenylphosphato)isosorbide-2-endo-ol may be isolated using column chromatography. Conversion of the alcohol to the corresponding [...] Read more.
A phosphorus containing acrylate monomer has been constructed from isosorbide, a renewable biomaterial. Treatment of isosorbide with diphenylchlorophosphate generates a mixture of phosphorus esters from which exo-5-(diphenylphosphato)isosorbide-2-endo-ol may be isolated using column chromatography. Conversion of the alcohol to the corresponding acrylate by treatment with acroyl chloride provides a reactive acryloyl monomer containing a diphenylphosphato unit. Copolymerization of this monomer, at levels to provide 1% or 2% phosphorus incorporation, with styrene generates a polymer with substantially diminished flammability compared to that for styrene homopolymer. Full article
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Article
An Alginate Hybrid Sponge with High Thermal Stability: Its Flame Retardant Properties and Mechanism
Polymers 2019, 11(12), 1973; https://doi.org/10.3390/polym11121973 - 30 Nov 2019
Cited by 3 | Viewed by 1367
Abstract
The worldwide applications of polyurethane (PU) and polystyrene (PS) sponge materials have been causing massive non-renewable resource consumption and huge loss of property and life due to its high flammability. Finding a biodegradable and regenerative sponge material with desirable thermal and flame retardant [...] Read more.
The worldwide applications of polyurethane (PU) and polystyrene (PS) sponge materials have been causing massive non-renewable resource consumption and huge loss of property and life due to its high flammability. Finding a biodegradable and regenerative sponge material with desirable thermal and flame retardant properties remains challenging to date. In this study, bio-based, renewable calcium alginate hybrid sponge materials (CAS) with high thermal stability and flame retardancy were fabricated through a simple, eco-friendly, in situ, chemical-foaming process at room temperature, followed by a facile and economical post-cross-linking method to obtain the organic-inorganic (CaCO3) hybrid materials. The microstructure of CAS showed desirable porous networks with a porosity rate of 70.3%, indicating that a great amount of raw materials can be saved to achieve remarkable cost control. The sponge materials reached a limiting oxygen index (LOI) of 39, which was greatly improved compared with common sponge. Moreover, with only 5% calcium carbonate content, the initial thermal degradation temperature of CAS was increased by 70 °C (from 150 to 220 °C), compared to that of calcium alginate, which met the requirements of high-temperature resistant and nonflammable materials. The thermal degradation mechanism of CAS was supposed based on the experimental data. The combined results suggest promising prospects for the application of CAS in a range of fields and the sponge materials provide an alternative for the commonly used PU and PS sponge materials. Full article
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Article
A Novel Inherently Flame-Retardant Composite Based on Zinc Alginate/Nano-Cu2O
Polymers 2019, 11(10), 1575; https://doi.org/10.3390/polym11101575 - 27 Sep 2019
Cited by 11 | Viewed by 1242
Abstract
A novel flame-retardant composite material based on zinc alginate (ZnAlg) and nano-cuprous oxide (Cu2O) was prepared through a simple, eco-friendly freeze-drying process and a sol-gel method. The composites were characterized and their combustion and flammability behavior were tested. The composites had [...] Read more.
A novel flame-retardant composite material based on zinc alginate (ZnAlg) and nano-cuprous oxide (Cu2O) was prepared through a simple, eco-friendly freeze-drying process and a sol-gel method. The composites were characterized and their combustion and flammability behavior were tested. The composites had high thermal stability and achieved nearly non-flammability with a limiting oxygen index (LOI) of 58. The results show remarkable improvement of flame-retardant properties in the ZnAlg/Cu2O composites, compared to ZnAlg. Furthermore, the pyrolysis behavior was determined by pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS) and the flame-retardant mechanism was proposed based on the combined experimental results. The prepared composites show promising application prospects in building materials and the textile industry. Full article
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Review

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Review
Biomolecules as Flame Retardant Additives for Polymers: A Review
Polymers 2020, 12(4), 849; https://doi.org/10.3390/polym12040849 - 07 Apr 2020
Cited by 29 | Viewed by 2714
Abstract
Biological molecules can be obtained from natural sources or from commercial waste streams and can serve as effective feedstocks for a wide range of polymer products. From foams to epoxies and composites to bulk plastics, biomolecules show processability, thermal stability, and mechanical adaptations [...] Read more.
Biological molecules can be obtained from natural sources or from commercial waste streams and can serve as effective feedstocks for a wide range of polymer products. From foams to epoxies and composites to bulk plastics, biomolecules show processability, thermal stability, and mechanical adaptations to fulfill current material requirements. This paper summarizes the known bio-sourced (or bio-derived), environmentally safe, thermo-oxidative, and flame retardant (BEST-FR) additives from animal tissues, plant fibers, food waste, and other natural resources. The flammability, flame retardance, and—where available—effects on polymer matrix’s mechanical properties of these materials will be presented. Their method of incorporation into the matrix, and the matrices for which the BEST-FR should be applicable will also be made known if reported. Lastly, a review on terminology and testing methodology is provided with comments on future developments in the field. Full article
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