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Recent Advances in Flame-Retardant Polymers and Composites

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

Deadline for manuscript submissions: closed (30 April 2021) | Viewed by 27336

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Dr. Nam Kyeun Kim

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Guest Editor

Centre for Advanced Composite Materials, Department of Mechanical Engineering, The University of Auckland, Auckland 1142, New Zealand
Interests: flame retardants; flame retardant composites; fire testing techniques; flammability of natural fibers and biopolymers; fire dynamics simulation

Dr. Oisik Das

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Guest Editor

Structural and Fire Engineering Division, Department of Civil, Environmental and Natural Resources Engineering, Luleå University of Technology, 97187 Luleå, Sweden
Interests: flammability of polymeric composites and bio-based materials; biocomposites development; polymers; biochar; pyrolysis; nanoindentation; natural fibres
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Special Issue Information

Dear Colleagues,

The flame retardant performance of materials has become an increasingly crucial factor for society across a broad range of applications in aircraft, automobiles, civil infrastructure, and consumer products. Both national and international regulations are becoming more stringent, limiting the usage of many polymeric products. Especially, polymeric composites and advanced polymers which have superior specific strength and physical properties are very susceptible to fire. Various flame retardants have been developed and employed to reduce the flammability, but their mechanical and physical performance have been compromised. Moreover, the release of toxic gases during the flame retardant reaction in the gas phase is still one of the critical flammability issues. Therefore, research on the development of novel flame-retardant polymers and composites to enhance fire safety and environmental sustainability with strength is inevitable.

This Special Issue, entitled “Recent Advances in Flame-Retardant Polymers and Composites”, will serve as a platform to focus on the flame-retardant performance of polymers and composites which can be achieved by innovative materials and processing. Potential topics include but are not limited to the following:

Development of environmentally friendly flame retardants;
Novel flame-retardant treatments on fibers, polymers, and composites.
Effects of material systems, structures, or manufacturing processes on the flammability characteristics of composites.
Mechanical performance of polymers and composites at elevated temperatures.
Fire testing techniques.

Dr. Nam Kyeun Kim
Dr. Oisik Das
Guest Editors

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Keywords

flammability
flame retardants
natural fibers and biopolymers
biocomposites
mechanical properties
environmental sustainability

Published Papers (10 papers)

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Editorial

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3 pages, 159 KiB

Open AccessEditorial

Special Issue “Recent Advances in Flame-Retardant Polymers and Composites”

by Nam Kyeun Kim and Oisik Das

Molecules 2021, 26(20), 6167; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26206167 - 13 Oct 2021

Viewed by 1172

Abstract

The flame-retardant performance of materials has become an increasingly crucial factor for society across a broad range of applications in aircraft, automobiles, civil infrastructure, and consumer products [...] Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

Research

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15 pages, 3349 KiB

Open AccessArticle

Effects of Graphene Nanoplatelets on Mechanical and Fire Performance of Flax Polypropylene Composites with Intumescent Flame Retardant

by Imran Ali, Nam Kyeun Kim and Debes Bhattacharyya

Molecules 2021, 26(13), 4094; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26134094 - 05 Jul 2021

Cited by 18 | Viewed by 2628

Abstract

The integration of intumescent flame-retardant (IFR) additives in natural fiber-based polymer composites enhances the fire-retardant properties, but it generally has a detrimental effect on the mechanical properties, such as tensile and flexural strengths. In this work, the feasibility of graphene as a reinforcement additive and as an effective synergist for IFR-based flax-polypropylene (PP) composites was investigated. Noticeable improvements in tensile and flexural properties were achieved with the addition of graphene nanoplatelets (GNP) in the composites. Furthermore, better char-forming ability of GNP in combination with IFR was observed, suppressing HRR curves and thus, lowering the total heat release (THR). Thermogravimetric analysis (TGA) detected a reduction in the decomposition rate due to strong interfacial bonding between GNP and PP, whereas the maximum decomposition rate was observed to occur at a higher temperature. The saturation point for the IFR additive along with GNP has also been highlighted in this study. A safe and effective method of graphene encapsulation within PP using the fume-hood set-up was achieved. Finally, the effect of flame retardant on the flax–PP composite has been simulated using Fire Dynamics Simulator. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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35 pages, 8542 KiB

Open AccessArticle

Durability of Flame-Retarded, Co-Extruded Profiles Based on High-Density Polyethylene and Wheat Straw Residues

by Arne Schirp and Jan Dannenberg

Molecules 2021, 26(11), 3217; https://doi.org/10.3390/molecules26113217 - 27 May 2021

Cited by 2 | Viewed by 2532

Abstract

At present, little information is available in the scientific literature related to the durability (weathering resistance) of fire-retarded wood and natural fiber-reinforced thermoplastics. In this work, thermoplastic profiles for façade applications based on high-density polyethylene, wheat straw particles, and fire-retardants were extruded and their reaction-to-fire performance before and after artificial weathering evaluated. Profile geometries were either solid or hollow-core profiles, and fire-retardants (FR) were added either in the co-extruded layer or in the bulk. Various FR for inclusion in the co-extruded layer were screened based on UL-94 tests. For profile extrusion, two types of FR were chosen: a coated intumescent combination based on ammonium polyphosphate (APP) and an APP coated with melamine and without formaldehyde. Before weathering, the peak heat release rate (pHRR) and the total heat release (THR), which were determined using cone calorimeter measurements, were reduced by up to 64% and 67% due to the FR. However, even before weathering, pHRR of the profiles was relatively high, with best (lowest) values between 230 and 250 kW/m² under the test conditions. After 28 days of artificial weathering, changes in reaction-to-fire performance and color were evaluated. Use of the APP in the co-extruded layer worsened color change compared to the formulation without APP but the pHRR was not significantly changed. The influence of weathering on the fire behavior was small compared to the difference between fire-retarded and non-fire-retarded materials. Results from the cone calorimeter were analyzed with regard to ETAG 028, which provides requirements related to the durability of fire performance of building products. In many formulations, increase in THR was less than 20% compared to before weathering, which would place some of the profiles in class C or better (EN 13501-1). However, due to the high pHRR, at best, class D was obtained under the conditions of this study. In addition to cone calorimeter measurements, results from the single flame source test, limiting oxygen index determination and thermogravimetric analysis, are shown and discussed. Strength properties, water uptake and swelling of the profiles, thermal conductivity, and energy dispersive X-ray data are also presented. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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13 pages, 2013 KiB

Open AccessArticle

Pyrolysis Kinetics and Flammability Evaluation of Rigid Polyurethane with Different Isocyanate Content

by Lin Jiang, Filippo Berto and Dan Zhang

Molecules 2021, 26(8), 2386; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26082386 - 20 Apr 2021

Cited by 5 | Viewed by 1917

Abstract

Polyurethane (PU) is a typical product of the reaction between isocyanate and polyol, whose ratio would greatly influence material properties. In this paper, to investigate the influence of isocyanate on PU thermal stability and flammability, three kinds of rigid polyurethanes (RPUs) with different isocyanate ratio (1.05, 1.1, and 2.0) were manufactured in a laboratory and employed to have a series of TG (thermogravimetry), DSC (differential scanning calorimetry), and cone calorimetry tests. Kissinger’s method was used to calculate the activation energy and judge their stabilities. However, for such a complex degradation which consists of five reactions, it does not make sense by Kissinger method to obtain only two peak active energies. Considering complexity of PU degradation in air, genetic algorithm (GA) was employed to calculate kinetic triplets of five sub-reactions. The effects of isocyanate contents on each sub-reaction stability were obtained and then analyzed. By cone calorimeter testing, we found that great differences in heat release rate data. However, DSC analysis showed a complete opposite changed trend. Such difference is caused by DSC and calorimeter’s sample morphology, the former using grinded polyurethane powders but the latter polyurethane foam block. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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17 pages, 4448 KiB

Open AccessArticle

Thermal Degradation Kinetics and Modeling Study of Ultra High Molecular Weight Polyethylene (UHMWP)/Graphene Nanocomposite

by Iman Jafari, Mohamadreza Shakiba, Fatemeh Khosravi, Seeram Ramakrishna, Ehsan Abasi, Ying Shen Teo, Mohammadreza Kalaee, Majid Abdouss, Ahmad Ramazani S. A, Omid Moradi and Erfan Rezvani Ghomi

Molecules 2021, 26(6), 1597; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26061597 - 13 Mar 2021

Cited by 17 | Viewed by 3673

Abstract

The incorporation of nanofillers such as graphene into polymers has shown significant improvements in mechanical characteristics, thermal stability, and conductivity of resulting polymeric nanocomposites. To this aim, the influence of incorporation of graphene nanosheets into ultra-high molecular weight polyethylene (UHMWPE) on the thermal behavior and degradation kinetics of UHMWPE/graphene nanocomposites was investigated. Scanning electron microscopy (SEM) analysis revealed that graphene nanosheets were uniformly spread throughout the UHMWPE’s molecular chains. X-Ray Diffraction (XRD) data posited that the morphology of dispersed graphene sheets in UHMWPE was exfoliated. Non-isothermal differential scanning calorimetry (DSC) studies identified a more pronounced increase in melting temperatures and latent heat of fusions in nanocomposites compared to UHMWPE at lower concentrations of graphene. Thermogravimetric analysis (TGA) and derivative thermogravimetric (DTG) revealed that UHMWPE’s thermal stability has been improved via incorporating graphene nanosheets. Further, degradation kinetics of neat polymer and nanocomposites have been modeled using equations such as Friedman, Ozawa–Flynn–Wall (OFW), Kissinger, and Augis and Bennett’s. The "Model-Fitting Method” showed that the auto-catalytic nth-order mechanism provided a highly consistent and appropriate fit to describe the degradation mechanism of UHMWPE and its graphene nanocomposites. In addition, the calculated activation energy (E_a) of thermal degradation was enhanced by an increase in graphene concentration up to 2.1 wt.%, followed by a decrease in higher graphene content. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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13 pages, 4244 KiB

Open AccessArticle

Kinetic Modeling and Degradation Study of Liquid Polysulfide Resin-Clay Nanocomposite

by Mohamadreza Shakiba, Arash Kakoei, Iman Jafari, Erfan Rezvani Ghomi, Mohammadreza Kalaee, Davood Zarei, Majid Abdouss, Saeid Shafiei-Navid, Fatemeh Khosravi and Seeram Ramakrishna

Molecules 2021, 26(3), 635; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26030635 - 26 Jan 2021

Cited by 13 | Viewed by 2538

Abstract

Kinetic modeling and degradation study of liquid polysulfide (LPS)/clay nanocomposite is possible through Ozawa–Flynn–Wall (OFW) and Kissinger methods. Comparing the results of these models with experimental data leads to provide an accurate degradation kinetic evaluation of these materials. To this aim, the morphology and distribution of clay nanoparticles (CNPs) within the LPS matrix were investigated using Field Emission Scanning Electron Microscopy (FESEM) and X-ray diffraction (XRD). To evaluate the interaction between the LPS and the CNPs, the Fourier transform infrared (FTIR) identification was utilized. Furthermore, to investigate the kinetics of degradation, the thermal gravimetric analysis (TGA) and derivative thermogravimetry (DTG) of the samples were used in the nitrogen atmosphere with the help of Kissinger and Ozawa–Flynn–Wall (OFW) models. The characterization results confirmed the homogenous dispersion of the CNPs into the LPS matrix. In addition, the presence of CNPs increased the thermal stability and activation energy (E_a) of the samples at different conversion rates. Moreover, the OFW method was highly consistent with the experimental data and provided an appropriate fit for the degradation kinetics. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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12 pages, 3254 KiB

Open AccessArticle

Role of Copper Oxide on Epoxy Coatings with New Intumescent Polymer-Based Fire Retardant

by Riyazuddin, Samrin Bano, Fohad Mabood Husain, Jamal Akhter Siddique, Khadijah H. Alharbi, Rais Ahmad Khan and Ali Alsalme

Molecules 2020, 25(24), 5978; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25245978 - 17 Dec 2020

Cited by 8 | Viewed by 2081

Abstract

Epoxy resins (EP) have been used as a thermos-setting material in the field of coating, casting, bonding agent, and laminating. However, a major drawback associated with its use is the lack of good flaming properties, and it is responsible for heavy smoke along with hazardous gases considerably limiting its uses in various fields. In this study, N-ethanolamine triazine-piperizine, a melamine polymer (ETPMP), was established as a new charring-foaming agent and was successfully synthesized with ethanolamine, piperizine, cyanuric chloride, and melamine as precursor molecules via the nucleophilic substitution reaction method. Elemental analysis and Fourier transform infrared (FTIR) spectroscopy analysis were applied to approve the synthesis of ETPMP and confirmation of its structure and characterization. The epoxy coating of intumescent flame retardant (IFR) was equipped by introducing ETPMP, ammonium polyphosphate (APP), and copper oxide (CuO) in multiple composition ratios. CuO was loaded at various amounts into the IFR-coating system as a synergistic agent. The synergistic action of CuO on IFR coatings was scientifically examined by using different analytical tests such as vertical burning test (UL-94V), limited oxygen index (LOI), thermal gravimetric analysis (TGA), cone calorimeter, and scanning electron microscope (SEM). The results showed that small changes in the amount of CuO expressively amplified the LOI results and enhanced the V-0 ratings in the UL-94V test. The TGA data clearly demonstrate that the inclusion of CuO can transform the thermal deprivation behavior of coatings with a growing char slag proportion with elevated temperatures. Information from cone calorimeter data affirmed that CuO can decrease the burning factors by total heat release (THR) together with peak heat release rate (PHRR). The SEM images indicated that CuO can enrich the power and compression of the intumescent char that restricts the movement of heat and oxygen. Our results demonstrate a positive influence of CuO on the epoxy-headed intumescent flame retardant coatings. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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13 pages, 4193 KiB

Open AccessArticle

Suitability and Modification of Different Renewable Materials as Feedstock for Sustainable Flame Retardants

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

Molecules 2020, 25(21), 5122; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25215122 - 04 Nov 2020

Cited by 10 | Viewed by 2082

Abstract

Due to their chemical structure, conventional flame retardants are often toxic, barely biodegradable and consequently neither healthy nor environmentally friendly. Their use is therefore increasingly limited by regulations. For this reason, research on innovative flame retardants based on sustainable materials is the main focus of this work. Wheat starch, wheat protein, xylan and tannin were modified with phosphate salts in molten urea. The functionalization leads to the incorporation of phosphates (up to 48 wt.%) and nitrogen (up to 22 wt.%). The derivatives were applied on wood fibers and tested as flame retardants. The results indicate that these modified biopolymers can provide the same flame-retardant performances as commercial compounds currently used in the wood fiber industry. Besides, the flame retardancy smoldering effects may also be reduced compared to unmodified wood fibers depending on the used biopolymer. These results show that different biopolymers modified in phosphate/urea systems are a serious alternative to conventional flame retardants. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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11 pages, 3107 KiB

Open AccessArticle

The Effect of Carbon Black on the Properties of Plasticised Wheat Gluten Biopolymer

by Oisik Das, Antonio J Capezza, Julia Mårtensson, Yu Dong, Rasoul Esmaeely Neisiany, Leonardo Pelcastre, Lin Jiang, Qiang Xu, Richard T. Olsson and Mikael S Hedenqvist

Molecules 2020, 25(10), 2279; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25102279 - 12 May 2020

Cited by 14 | Viewed by 2593

Abstract

Wheat gluten biopolymers generally become excessively rigid when processed without plasticisers, while the use of plasticisers, on the other hand, can deteriorate their mechanical properties. As such, this study investigated the effect of carbon black (CB) as a filler into glycerol-plasticised gluten to prepare gluten/CB biocomposites in order to eliminate the aforementioned drawback. Thus, biocomposites were manufactured using compression moulding followed by the determination of their mechanical, morphological, and chemical properties. The filler content of 4 wt% was found to be optimal for achieving increased tensile strength by 24%, and tensile modulus by 268% along with the toughness retention based on energy at break when compared with those of glycerol-plasticised gluten. When reaching the filler content up to 6 wt%, the tensile properties were found to be worsened, which can be ascribed to excessive agglomeration of carbon black at the high content levels within gluten matrices. Based on infrared spectroscopy, the results demonstrate an increased amount of β-sheets, suggesting the formation of more aggregated protein networks induced by increasing the filler contents. However, the addition of fillers did not improve fire and water resistance in such bionanocomposites owing to the high blend ratio of plasticiser to gluten. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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Review

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28 pages, 2709 KiB

Open AccessFeature PaperReview

The Flame Retardancy of Polyethylene Composites: From Fundamental Concepts to Nanocomposites

by Erfan Rezvani Ghomi, Fatemeh Khosravi, Zahra Mossayebi, Ali Saedi Ardahaei, Fatemeh Morshedi Dehaghi, Masoud Khorasani, Rasoul Esmaeely Neisiany, Oisik Das, Atiye Marani, Rhoda Afriyie Mensah, Lin Jiang, Qiang Xu, Michael Försth, Filippo Berto and Seeram Ramakrishna

Molecules 2020, 25(21), 5157; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25215157 - 05 Nov 2020

Cited by 46 | Viewed by 4947

Abstract

Polyethylene (PE) is one the most used plastics worldwide for a wide range of applications due to its good mechanical and chemical resistance, low density, cost efficiency, ease of processability, non-reactivity, low toxicity, good electric insulation, and good functionality. However, its high flammability and rapid flame spread pose dangers for certain applications. Therefore, different flame-retardant (FR) additives are incorporated into PE to increase its flame retardancy. In this review article, research papers from the past 10 years on the flame retardancy of PE systems are comprehensively reviewed and classified based on the additive sources. The FR additives are classified in well-known FR families, including phosphorous, melamine, nitrogen, inorganic hydroxides, boron, and silicon. The mechanism of fire retardance in each family is pinpointed. In addition to the efficiency of each FR in increasing the flame retardancy, its impact on the mechanical properties of the PE system is also discussed. Most of the FRs can decrease the heat release rate (HRR) of the PE products and simultaneously maintains the mechanical properties in appropriate ratios. Based on the literature, inorganic hydroxide seems to be used more in PE systems compared to other families. Finally, the role of nanotechnology for more efficient FR-PE systems is discussed and recommendations are given on implementing strategies that could help incorporate flame retardancy in the circular economy model. Full article

(This article belongs to the Special Issue Recent Advances in Flame-Retardant Polymers and Composites)

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