A phosphorous-based bi-functional flame retardant for rigid polyurethane foam

The improvement of flame retardancy and compatibility of PBAT/PLLA via a hybrid polyurethane

Poly (butylene adipate-co-terephthalate)/poly (L-lactic acid) (PBAT/PLLA) is one of the most important biodegradable polymer combinations; however, they are flammable with heavy melt dripping and incompatible. To achieve the objective of flame retardation and compatibility, a hybrid polyurethane (PU) with multiple flame retardation elements is synthesized via a new ring-opening polymerization (ROP) method and integrated into PBAT/PLLA film. The PU not only dissolves in different organic solvents at mild temperature but also improves the compatibility of PBAT/PLLA. As PU with respect to PBAT/PLLA is 20 wt%, the limiting oxygen index (LOI) and UL-94 reach 25.5 % and V-0 rating, respectively. In cone calorimeter test, the peak heat release rate (pHRR) of PU/PBAT/PLLA is ahead of PBAT/PLLA, and the total heat release (THR) decreases to 25.85 MJ/m2. The fire safety is achieved successfully. The initial pyrolysis of PU promotes the formation of a seed carbon layer; it continuously breaks down into a series of phosphorus‑oxygen radicals and generates different inert gases, while the pyrolytic solid products accelerate the carbonization to form the carbon/silicon composite layer. Then the polymeric combustion is braked completely. Besides, the PU can also tune the mechanical properties of PBAT/PLLA film and enhance its hydrophobicity. This work opens a new window for developing multifunctional flame retardant and paves the way for the richening engineering application of PBAT/PLLA.

Balanced Thermal Insulation, Flame-Retardant and Mechanical Properties of PU Foam Constructed via Cost-Effective EG/APP/SA Ternary Synergistic Modification

To address the challenge of balancing the mechanical, thermal insulation, and flame-retardant properties of building insulation materials, this study presented a facile approach to modify the rigid polyurethane foam composites (RPUFs) via commercial expandable graphite (EG), ammonium polyphosphate (APP), and silica aerogel (SA). The resulting EG/APP/SA/RPUFs exhibited low thermal conductivity close to neat RPUF. However, the compressive strength of the 6EG/2APP/SA/RPUF increased by 49% along with achieving a V-0 flame retardant rating. The residual weight at 700 °C increased from 19.2 wt.% to 30.9 wt.%. Results from cone calorimetry test (CCT) revealed a 9.2% reduction in total heat release (THR) and a 17.5% decrease in total smoke production (TSP). The synergistic flame-retardant mechanism of APP/EG made significant contribution to the excellent flame retardant properties of EG/APP/SA/RPUFs. The addition of SA played a vital role in reducing thermal conductivity and enhancing mechanical performance, effectively compensating for the shortcomings of APP/EG. The cost-effective EG/APP/SA system demonstrates a positive ternary synergistic effect in achieving a balance in RPUFs properties. This study provides a novel strategy aimed at developing affordable building wall insulation material with enhanced safety features.

Bio-Based Alkali Lignin Cooperative Systems for Improving the Flame Retardant and Mechanical Properties of Rigid Polyurethane Foam

Lignin was utilized as an environmentally friendly synergistic agent to augment the fire resistance and mechanical characteristics of rigid polyurethane foam (PUF)/melamine-formaldehyde resin ammonium polyphosphate (MFAPP). The incorporation of lignin significantly enhanced the charring capability and flame retardancy of PUF/MFAPP. Specifically, PUF/MFAPP12/A-lignin3 exhibited a charring residue of 23.1% at 800 °C, accompanied by an increase in the limiting oxygen index (LOI) to 23.1%, resulting in a UL-94 V-0 rating. The cone calorimeter test (CCT) revealed that the peak heat release rate (PHRR), total heat release (THR), smoke production rate (SPR), and total smoke production (TSP) values of PUF/MFAPP12/A-lignin3 were all lower than for pure PUF. MFAPP and alkali lignin exerted a noticeable influence on the physical and mechanical properties, leading to increases in density (35.4 kg/m3), thermal conductivity (32.68 mW/(m·K)), and compressive strength (160.5 kPa). Observations of the morphology and elemental composition of char residues after combustion indicated the formation of an intact, thick, and continuous char layer enriched with nitrogen and phosphorus elements, which acted as a protective shield for the underlying foam.

Advancements in Flame-Retardant Systems for Rigid Polyurethane Foam

The amplified employment of rigid polyurethane foam (RPUF) has accentuated the importance of its flame-retardant properties in stimulating demand. Thus, a compelling research report is essential to scrutinize the recent progression in the field of the flame retardancy and smoke toxicity reduction of RPUF. This comprehensive analysis delves into the conventional and innovative trends in flame-retardant (FR) systems, comprising reactive-type FRs, additive-type FRs, inorganic nanoparticles, and protective coatings for flame resistance, and summarizes their impacts on the thermal stability, mechanical properties, and smoke toxicity suppression of the resultant foams. Nevertheless, there are still several challenges that require attention, such as the migration of additives, the insufficient interfacial compatibility between flame-retardant polyols or flame retardants and the RPUF matrix, and the complexity of achieving both flame retardancy and mechanical properties simultaneously. Moreover, future research should focus on utilizing functionalized precursors and developing biodegradable RPUF to promote sustainability and to expand the applications of polyurethane foam.

Fireproof Nanocomposite Polyurethane Foams: A Review

First introduced in 1954, polyurethane foams rapidly became popular because of light weight, high chemical stability, and outstanding sound and thermal insulation properties. Currently, polyurethane foam is widely applied in industrial and household products. Despite tremendous progress in the development of various formulations of versatile foams, their use is hindered due to high flammability. Fire retardant additives can be introduced into polyurethane foams to enhance their fireproof properties. Nanoscale materials employed as fire-retardant components of polyurethane foams have the potential to overcome this problem. Here, we review the recent (last 5 years) progress that has been made in polyurethane foam modification using nanomaterials to enhance its flame retardance. Different groups of nanomaterials and approaches for incorporating them into foam structures are covered. Special attention is given to the synergetic effects of nanomaterials with other flame-retardant additives.

How Do Phosphorus Compounds with Different Valence States Affect the Flame Retardancy of PET?

This work investigated the effect of different valence states of phosphorus-containing compounds on thermal decomposition and flame retardancy of polyethylene terephthalate (PET). Three polyphosphates-PBPP with +3-valence P, PBDP with +5-valence P and PBPDP with both +3/+5-valence P-were synthesized. The combustion behaviors of flame-retardant PET were studied and the structure-property relationships between the phosphorus-based structures with different valence states and flame-retardant properties were further explored. It was found that phosphorus valence states significantly affected the flame-retardant modes of action of polyphosphate in PET. For the phosphorus structures with +3-valence, more phosphorus-containing fragments were released in the gas phase, inhibiting polymer chain decomposition reactions; by contrast, those with +5-valence phosphorus retained more P in the condensed phase, promoting the formation of more P-rich char layers. It is worth noting that the polyphosphate containing both +3/+5-valence phosphorous tended to combine the advantage of phosphorus structures with two valence states and balance the flame-retardant effect in the gas phase and condensed phase. These results contribute to guiding the design of specified phosphorus-based structures of flame-retardant compounds in polymer materials.

Design of P-decorated POSS towards flame-retardant, mechanically-strong, tough and transparent epoxy resins

Epoxy resins (EPs) are known for their durability, strength, and adhesive properties, which make them a versatile and popular material for use in a variety of applications, including chemical anticorrosion, small electronic devices, etc. However, EP is highly flammable due to its chemical nature. In this study, phosphorus-containing organic-inorganic hybrid flame retardant (APOP) was synthesized by introducing 9, 10-dihydro-9-oxa-10‑phosphaphenathrene (DOPO) into cage-like octaminopropyl silsesquioxane (OA-POSS) via Schiff base reaction. The improved flame retardancy of EP was achieved by combining the physical barrier of inorganic Si-O-Si with the flame-retardant capability of phosphaphenanthrene. EP composites containing 3 wt% APOP passed the V-1 rating with a value of LOI of 30.1% and showed an apparent reduction in smoke release. Additionally, the combination of the inorganic structure and the flexible aliphatic segment in the hybrid flame retardant provides EP with molecular reinforcement, while the abundance of amino groups facilitates a good interface compatibility and outstanding transparency. Accordingly, EP containing 3 wt% APOP increased in tensile strength, impact strength, and flexural strength by 66.0 %, 78.6 %, and 32.3 %, respectively. The EP/APOP composites had a bending angle lower than 90°, and their successful transition to a tough material highlights the potential of this innovative combination of the inorganic structure and the flexible aliphatic segment. In addition, the relevant flame-retardant mechanism revealed that the APOP promoted the formation of a hybrid char layer containing P/N/Si for EP and produced phosphorus-containing fragments during combustion, showing flame-retardant effects in both condensed and vapor phases. This research offers innovative solutions for reconciling flame retardancy & mechanical performances and strength & toughness for polymers.

Research on the Dynamic Response Properties of Nonlethal Projectiles for Injury Risk Assessment

Based on the models already on the market, we have manufactured six types of nonlethal projectiles. We have made convex heads out of polyurethane foam (PUR) filled with mineral fillers like alumina (Al₂O₃) and montmorillonite (MMT). We chose a suitable holder for nonlethal projectiles. Also, we made a custom industrial model and used CAD modeling in SolidWorks to simulate the deformation of the nonlethal projectiles. The polymeric nonlethal projectile holders were then 3D-printed. We performed a dynamic mechanical analysis (DMA) and discussed the results. Likewise, we conducted ballistic impact experiments on nonlethal projectiles (XM1006) and nonlethal projectiles manufactured that were evaluated using a rigid wall and a pneumatic launcher. Furthermore, we looked at cell structure, the spread of the mean pore diameter, and the particle size distributions of the mineral fillers using scanning electron microscopy (SEM). We evaluated and discussed injury risks from nonlethal impacts. Data on nonlethal projectile lethality and safe impact speed are collected. This study explains how lab studies and real-world practice coexist through nonlethal projectile properties.

Emerging trends in flame retardancy of rigid polyurethane foam and its composites: A review

Owing to the superior thermal insulating attributes of rigid polyurethane foam (RPUF) compared to other insulating materials (expanded and extruded polystyrene, mineral wool), it remains the most dominant insulating material and most studied polymer foam. Like other polyurethane foam, RPUF is highly flammable, necessitating the incorporation of flame retardants (FR) during production to lower combustibility, promoting its continuous use as insulation material in construction, transportation, and others. The popular approaches for correcting the high flammability of RPUF are copolymerization and blending (with FR). The second method has proven to be most effective as there are limited trade-offs in RPUF properties. Meanwhile, the high flammability of RPUF is still a significant hindrance in emerging applications (sensors, space travel, and others), and this has continuously inspired research in the flame retardancy of RPUF. In this study, properties, and preparation methods of RPUF are described, factors responsible for the high flammability of PUF are discussed, and flame retardancy of RPUF is thoroughly reviewed. Notably, most FR for RPUF are inorganic nanoparticles, lignin, intumescent FR systems of expandable graphite (EG), ammonium polyphosphate (APP), and hybridized APP or EG with other FR. These could be due to their ease of processing, low cost, and being environmentally benign. Elaborate discussion on RPUF FR mechanisms were also highlighted. Lastly, a summary and future perspectives in fireproofing RPUF are provided, which could inspire the design of new FR for RPUF.

Investigation of the relation between free volume and physico-mechanical performance in rigid polyurethane foam containing turkey feather fibers: Part 2

Rigid polyurethane foams (RPUFs) were modified with 0–15 wt.% turkey feather fibers (TFFs) produced from waste turkey feathers. One-shut free rising method was used for the production of TFFs-filled-RPUFs in a closed mold. The dependence of mechanical performance and water vapor permeability (WVP) feature of the final foams on TFFs loading was evaluated with free volume change. The free volume analysis was performed via Positron Annihilation Lifetime Spectroscopy (PALS), while the mechanical and WVP characteristics were determined with the use of the universal tester machines. PALS findings showed that the incorporation of TFFs with RPUF matrix caused the considerable diminishment in the free volume due to TFFs serving as a filling material and formation of strong secondary bonds between components. Moreover, tensile strength and extension of the foams decreased with the increasing of TFFs, which caused by the occurrence of noteworthy restriction on the spatial alignment and orientation capability of polyurethane chains due to the lack of sufficient free volume allowing the chains to move freely. As for the compression tests, all the TFFs-loaded RPUFs depicted substantially lower performance due to TFFs interfering with the ordered organization of isocyanate domains. Moreover, impact test results showed that the addition of TFFs into RPUF matrix brought about the insufficient impact energy delocalization throughout the matrix due to the restriction on the mobility of polymer chains. Additionally, the remarkable diminishment in WVP was recorded due to the reduction in the number of vacancies and constitution of keratin composed of roundly 60% of hydrophilic protein (especially cystine). All in all, this study established a strong links between free volume and characteristics of TFFs-loaded RPUFs.

Thermal Insulating Rigid Polyurethane Foams with Bio-Polyol from Rapeseed Oil Modified by Phosphorus Additive and Reactive Flame Retardants

In this article, rigid polyurethane foams obtained with the addition of a bio-polyol from rapeseed oil, were modified with the dimethyl propane phosphonate as additive flame retardant and two reactive flame retardants diethyl (hydroxymethyl)phosphonate and diethyl bis-(2-hydroxyethyl)-aminomethylphosphonate. The influence of used flame retardants on the foaming process and characteristic processing times of tested polyurethane systems were determined. The obtained foams were tested in terms of cell structure, physical and mechanical properties, as well as flammability. Modified foams had worse mechanical and thermal insulation properties, caused by lower cellular density and higher anisotropy coefficient in the cross-section parallel to the foam rise direction, compared to unmodified foam. However, the thermal conductivity of all tested foam materials was lower than 25.82 mW/m∙K. The applied modifiers effectively reduced the flammability of rigid polyurethane foams, among others, increasing the oxygen index above 21.4 vol.%, reducing the total heat released by about 41-51% and the rate of heat release by about 2-52%. A correlation between the limiting oxygen index values and both total heat released parameters from the pyrolysis combustion flow calorimetry and cone calorimetry was observed. The correlation was also visible between the value of the heat release capacity (HRC) parameter obtained from the pyrolysis combustion flow calorimetry and the maximum average rate of heat emission (MARHE) from the cone calorimeter test.

A Phosphorous-Based Bi-Functional Flame Retardant Based on Phosphaphenanthrene and Aluminum Hypophosphite for an Epoxy Thermoset

A phosphorous-based bi-functional compound HPDAl was used as a reactive-type flame retardant (FR) in an epoxy thermoset (EP) aiming to improve the flame retardant efficiency of phosphorus-based compounds. HPDAl, consisting of two different P-groups of aluminum phosphinate (AHP) and phosphophenanthrene (DOPO) with different phosphorous chemical environments and thus exerting different FR actions, exhibited an intramolecular P-P groups synergy and possessed superior flame-retardant efficiency compared with DOPO or AHP alone or the physical combination of DOPO/AHP in EP. Adding 2 wt.% HPDAl made EP composites acquire a LOI value of 32.3%, pass a UL94 V-0 rating with a blowing-out effect, and exhibit a decrease in the heat/smoke release. The flame retardant modes of action of HPDAl were confirmed by the experiments of the scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry–Fourier transform infrared spectroscopy–gas chromatograph/mass spectrometer (TG-FTIR-GC/MS). The results indicate that the phosphorous-based FRs show different influences on the flame retardancy of composites, mainly depending on their chemical structures. HPDAl had a flame inhibition effect in the gas phase and a charring effect in the condensed phase, with a well-balanced distribution of P content in the gas/condensed phase. Furthermore, the addition of HPDAl hardly impaired the mechanical properties of the matrix due to the link by chemical bonds between them.

Tuning Electro-Magnetic Interference Shielding Efficiency of Customized Polyurethane Composite Foams Taking Advantage of rGO/Fe3O4 Hybrid Nanocomposites

Electromagnetic interference (EMI) has been recognized as a new sort of pollution and can be considered as the direct interference of electromagnetic waves among electronic equipment that frequently affects their typical efficiency. As a result, shielding the electronics from this interfering radiation has been addressed as critical issue of great interest. In this study, different hybrid nanocomposites consisting of magnetite nanoparticles (Fe₃O₄) and reduced graphene oxide (rGO) as (conductive/magnetic) fillers, taking into account different rGO mass ratios, were synthesized and characterized by XRD, Raman spectroscopy, TEM and their magnetic properties were assessed via VSM. The acquired fillers were encapsulated in the polyurethane foam matrix with different loading percentages (wt%) to evaluate their role in EMI shielding. Moreover, their structure, morphology, and thermal stability were investigated by SEM, FTIR, and TGA, respectively. In addition, the impact of filler loading on their final mechanical properties was determined. The obtained results revealed that the Fe₃O₄@rGO composites displayed superparamagnetic behavior and acceptable electrical conductivity value. The performance assessment of the conducting Fe₃O₄@rGO/PU composite foams in EMI shielding efficiency (SE) was investigated at the X-band (8-12) GHz, and interestingly, an optimized value of SE -33 dBw was achieved with Fe₃O₄@rGO at a 80:20 wt% ratio and 35 wt% filler loading in the final effective PU matrix. Thus, this study sheds light on a novel optimization strategy for electromagnetic shielding, taking into account conducting new materials with variable filler loading, composition ratio, and mechanical properties in such a way as to open the door for achieving a remarkable SE.

A Systematic Review and Bibliometric Analysis of Flame-Retardant Rigid Polyurethane Foam from 1963 to 2021

Flame-retardant science and technology are sciences developed to prevent the occurrence of fire, meet the needs of social safety production, and protect people's lives and property. Rigid polyurethane (PU) is a polymer formed by the additional polymerization reaction of a molecule with two or more isocyanate functional groups with a polyol containing two or more reactive hydroxyl groups under a suitable catalyst and in an appropriate ratio. Rigid polyurethane foam (RPUF) is a foam-like material with a large contact area with oxygen when burning, resulting in rapid combustion. At the same time, RPUF produces a lot of toxic gases when burning and endangers human health. Improving the flame-retardant properties of RPUF is an important theme in flame-retardant science and technology. This review discusses the development of flame-retardant RPUF through the lens of bibliometrics. A total of 194 articles are analyzed, spanning from 1963 to 2021. We describe the development and focus of this theme at different stages. The various directions of this theme are discussed through keyword co-occurrence and clustering analysis. Finally, we provide reasonable perspectives about the future research direction of this theme based on the bibliometric results.

Synergistic Effect of Multifunctional Layered Double Hydroxide-Based Hybrids and Modified Phosphagen with an Active Amino Group for Enhancing the Smoke Suppression and Flame Retardancy of Epoxy

To improve the fire hazard of epoxy resin (EP), phosphomolybdate (PMoA), as a classical Keggin cluster, was successfully intercalated into Mg, Al, and Zn layered double hydrotalcite (LDH) by the reconstruction method, and it was denoted as MgAlZn-LDH-PMoA. The structure and morphology of MgAlZn-LDH-PMoA were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. Subsequently, hexa(4-aminophenoxy)cyclotriphosphazene (HACP) was prepared and characterized as a high-performance organic flame retardant, which is rich in flame elements phosphorus and nitrogen. The synergistic effects of MgAlZn-LDH-PMoA and HACP on the fire safety of EP composites loaded with different amounts of flame retardant hybrids were studied in detail. Thermogravimetric analysis showed that the char residue of these EP composites increased significantly. Compared with the EP matrix filled with only MgAlZn-LDH-PMoA or HACP, the incorporation of MgAlZn-LDH-PMoA and HACP had a synergistic effect on promoting char formation of EP composites. Particularly, the char yield of EP7 is as high as 29.0%. Furthermore, the synergistic effects of incorporation of MgAlZn-LDH-PMoA with HACP were investigated using the cone calorimeter combustion tests. The results showed that the total heat release and peak heat release rate of the EP composites remarkably declined by 35.2 and 50.9%, respectively, with a loading of 7 wt % hybrid flame retardant. Moreover, the hybrid flame retardants also showed an obvious inhibitory effect on the total smoke production and the release of toxic CO gas. The detailed analysis of the residual char indicated that the main mechanism for improving the flame retardancy and smoke suppression performance is due to both the catalytic carbonization of MgAlZn-LDH-PMoA and phosphoric acid compounds and physical barrier function of the char layer. In addition, the molybdenum oxides produced from [PMo₁₂O₄₀]^3- during combustion can not only increase the yield and compactness of the char layer but also reduce the release of CO through a redox reaction, which has important application value to reduce the fire hazard.

It Takes Two to Tango: Synergistic Expandable Graphite–Phosphorus Flame Retardant Combinations in Polyurethane Foams

Due to the high flammability and smoke toxicity of polyurethane foams (PUFs) during burning, distinct efficient combinations of flame retardants are demanded to improve the fire safety of PUFs in practical applications. This feature article focuses on one of the most impressive halogen-free combinations in PUFs: expandable graphite (EG) and phosphorus-based flame retardants (P-FRs). The synergistic effect of EG and P-FRs mainly superimposes the two modes of action, charring and maintaining a thermally insulating residue morphology, to bring effective flame retardancy to PUFs. Specific interactions between EG and P-FRs, including the agglutination of the fire residue consisting of expanded-graphite worms, yields an outstanding synergistic effect, making this approach the latest champion to fulfill the demanding requirements for flame-retarded PUFs. Current and future topics such as the increasing use of renewable feedstock are also discussed in this article.

Functionalized lignin nanoparticles for producing mechanically strong and tough flame-retardant polyurethane elastomers

There is a strong interest in developing environmentally friendly synthesis approaches for making polyurethane elastomers (PUE) with desirable mechanical performance and flame retardancy suitable for a variety of applications. Hence, in this study, a novel nano functionalized lignin nanoparticle (Nano-FL) containing nitrogen (N) and phosphorus (P) moieties was developed via mild grafting reactions combined with the ultrasound method. The Nano-FL incorporated in the PUE acted as both crosslinking agents and flame retardants. The novel Nano-FL showed good compatibility and dispersibility in the PUE matrix, thereby overcoming the weakening effect of adding traditional lignin flame retardants on the mechanical properties of the PUE materials. PUE/Nano-FL exhibited strong tensile properties. Compared with control neat PUE, with 10 wt% of Nano-FL addition, the PUE attained a limiting oxygen index as high as 29.8% and it also passed the UL-94 V-0 rating. Furthermore, Cone Calorimetry Test (CCT) showed that the addition of Nano-FL not only reduced the heat release rate and the total heat release but also decreased the total smoke production rate during combustion. The char residues of PUEs with Nano-FL showed a high oxidation resistance with dense and continuous structural morphologies. The combined barrier and quenching effects of the char layer provided excellent flame retardancy performance. The novel Nano-FL developed in this study showed excellent promises as green functional additives for enhancing mechanical, thermal and flame retardancy performance of a wide range of polymers.

A flame retardant containing biomass-based polydopamine for high-performance rigid polyurethane foam

An inorganic/polymer flame retardant system constructed from biomass can improve the comprehensive properties of rigid polyurethane foam.

Bio-Based Rigid Polyurethane Foams Modified with Phosphorus Flame Retardants

Rigid polyurethane foams (RPURF) containing a bio-polyol from rapeseed oil and different phosphorus-based flame retardants were obtained. Triethyl phosphate (TEP), dimethyl propane phosphonate (DMPP) and cyclic phosphonates Addforce CT 901 (20 parts per hundred polyol by weight) were used in the synthesis of RPURF. The influence of used flame retardants on foaming process, cell structure, and physical-mechanical properties as well as flammability of RPURF were examined. The addition of flame retardants influenced the parameters of the cellular structure and decreased compressive strength. All obtained foam materials had a low thermal conductivity coefficient, which allows them to be used as thermal insulation. The research results of bio-based RPURF were compared with foams obtained without bio-polyol. All modified materials had an oxygen index above 21 vol%; therefore, they can be classified as self-extinguishing materials. The analysis of parameters obtained after the cone calorimeter test showed that the modified RPURF have a lower tendency to fire development compared to the reference foams, which was particularly noticeable for the materials with the addition of DMPP.

Effect of flame retardants on mechanical and thermal properties of bio-based polyurethane rigid foams

A soy oil-based polyol (HSBP) was synthesized from epoxidized soy oil through a ring-opening reaction with distilled water. A phosphorus-containing flame retardant (DOPO–HSBP) was synthesized through the reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and HSBP. A nitrogen-containing flame retardant (T–D) was prepared by the reaction of diethanolamine with glycol diglycidyl ether. The structures of HSBP, DOPO–HSBP, and T–D were characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (¹H NMR). The flame-retardant rigid polyurethane foam (PPUFs and NPUFs) was prepared successfully by mixing HSBP, DOPO–HSBP, and T–D. The effects of DOPO–HSBP content on the mechanical, thermal, and flame-retardant properties of PPUFs and NPUFs were investigated by tensile tests, thermogravimetric analyses (TGA), limiting oxygen index (LOI), and UL-94 vertical burning level. The morphology of PPUFs and NPUFs was studied via scanning electron microscopy (SEM). With the increase in the percentage of DOPO–HSBP added, the flame retardant property of rigid polyurethane foam (RPUF) was greatly improved. When the phosphorus-containing flame retardant DOPO–HSBP was added to 50% of the RPUF with the nitrogen-containing flame retardant T–D, the LOI value of the foam increased from 18.3 to 25.5, and the UL-94 result was classified as “V-0” with almost no effect on the mechanical properties of the RPUF. The results showed that the phosphorus and nitrogen synergistic flame retardants of DOPO–HSBP and T–D can endow excellent flame retardant properties to RPUF without affecting its mechanical properties.

A vegetable oil-based polyurethane rigid foam containing a phosphorus–nitrogen dualflame retardant system was prepared, and the foam exhibited not only excellent flame retardant properties but also good mechanical properties.

New Insights into Antibacterial and Antifungal Properties, Cytotoxicity and Aquatic Ecotoxicity of Flame Retardant PA6/DOPO-Derivative Nanocomposite Textile Fibers

The aim of this study was to evaluate the antibacterial and antifungal activity, cytotoxicity, leaching, and ecotoxicity of novel flame retardant polyamide 6 (PA6) textile fibers developed by our research group. The textile fibers were produced by the incorporation of flame-retardant bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative (PHED) in the PA6 matrix during the in situ polymerization process at concentrations equal to 10 and 15 wt% (PA6/10PHED and PA6/15PHED, respectively). Whilst the nanodispersed PHED provided highly efficient flame retardancy, its biological activity led to excellent antibacterial activity against Escherichia coli and Staphylococcus aureus, as well as excellent antifungal activity against Aspergillus niger and Candida albicans. The results confirmed leaching of the PHED, but the tested leachates did not cause any measurable toxic effect to the duckweed Lemna minor. The in vitro cytotoxicity of the leached PHED from the PA6/15PHED sample was confirmed for human cells from adipose tissue in direct and prolonged contact. The targeted biological activity of the organophosphinate flame retardant could be beneficial for the development of PA6 textile materials with multifunctional properties and the low ecotoxicity profile, while the PHED's leaching and cytotoxicity limit their application involving the washing processes and direct contact with the skin.