Development of an environmentally friendly halogen‐free phosphorus–nitrogen bond flame retardant for cotton fabrics

A novel flame retardant diethyl 4‐methylpiperazin‐1‐ylphosphoramidate (CN‐3) containing phosphorous and nitrogen was prepared. Its chemical structure was confirmed by nuclear magnetic resonance (¹H‐, ¹³C‐, and ³¹P‐NMR), Fourier transform infrared spectroscopy, and elemental analysis. Print cloth and twill fabrics were treated with CN‐3 to achieve different levels of add‐on (7–22 wt% add‐ons for print cloth and 3–18 wt% add‐ons for twill). Thermogravimetric analysis, vertical flame test, and limiting oxygen index (LOI) were performed on the treated cotton fabrics and showed promising results. When the treated print cloth and twill fabric samples were tested using the vertical flame test (ASTM D6413‐08), we observed that the ignited fabrics self‐extinguished and left behind a streak of char. Treated higher add‐ons fabrics were neither consumed by flame nor produced glowing ambers upon self‐extinguishing. LOI (ASTM 2863–09) was used to determine the effectiveness of the flame retardant on the treated fabrics. LOI values increased from 18 vol% oxygen in nitrogen for untreated print cloth and twill fabrics to maximum of 28 and 31 wt% for the highest add‐ons of print cloth and twill, respectively. The results from cotton fabrics treated with CN‐3 demonstrated a higher LOI value as well as a higher char yield because of the effectiveness of phosphorus and nitrogen as a flame retardant for cotton fabrics. Furthermore, FT‐IR and SEM were used to characterize the chemical structure on the treated fabrics as well as the surface morphology of char areas of treated and untreated fabrics. Published 2012. This article is a US Government work and is in the public domain in the USA.     

Synthesis and characterization of a novel phosphorus–nitrogen‐containing flame retardant and its application for textile

The economic and environmentally friendly flame‐retardant compound, tetramethyl (6‐chloro‐1,3,5‐triazine‐2,4‐diyl)bis(oxy)bis(methylene) diphosphonate ( CN‐1 ), was synthesized by a simple two‐step procedure from dimethyl phosphate, and its chemical structure was characterized by ¹H, ¹³C, and ³¹P nuclear magnetic resonance and gas chromatography mass spectroscopy. Using the traditional pad–dry–cure method, we obtained several different add‐ons (wt%) by treating cotton twill fabric with flame retardant ( CN‐1 ). Thermogravimetric analysis, in an air and nitrogen atmosphere, of the modified cotton showed that decomposition occurred ~230°C with 16% residue weight char yield at 600°C, indicating high thermal stability for all treated levels. Limiting oxygen index (LOI) and the vertical flammability test were employed to determine the effectiveness of the flame‐retardant treatments on the fabrics. LOI values increased from ~18 vol% oxygen in nitrogen for untreated fabric to maximum of 34 vol% for the highest treatment level. Fabrics with higher levels of flame retardant also easily passed the vertical flammability test. Furthermore, Fourier transform infrared and scanning electron microscopy were utilized to characterize the chemical structure as well as the surface morphology of the flame‐retardant treated twill fabrics, including char area and the edge between unburned fabric and char area. Copyright © 2011 John Wiley & Sons, Ltd.     

A simple method for determining the total amount of physically and chemically bound water of different cements

A novel environmentally friendly flame-retardant compound, diethyl 3-(triethoxysilanepropyl) phosphoramidate (DTP) was synthesized via a simple one-step procedure with good yield and characterized by FT-IR and ¹H-NMR, ³¹P-NMR and ²⁹Si-NMR. The synthesized compound was coated onto cotton fabrics with different levels of add-ons (5–17 mass%) using the traditional pad-dry-cure method. SEM and XPS were conducted to characterize the surfaces of the coated cotton fabrics. The XPS results showed that DTP was attached to cotton through covalent bond. Cone calorimeter test showed that the cotton fabric treated with DTP became less flammable due to the lower HRR, THR and CO₂/CO ratio. The modified cotton fabrics exhibited efficient flame retardancy, which was evidenced by limiting oxygen index (LOI) and vertical flammability test. Cotton fabrics treated with DTP in 5–17 mass% add-ons had high LOI values of 23–32%. Thermogravimetric analysis results show that the usage of DTP promotes degradation of the cotton fabrics and catalyzes its char formation.     

Preparation of a novel phosphorus‐containing organosilicon and its effect on the flame retardant and smoke suppression of polyethylene terephthalate

A novel phosphorus‐containing silicone flame retardant (PDPSI) was prepared by Mannish reaction, and a series of PDPSI/PET composites were prepared by melt blending method. The nuclear magnetic resonance (¹H NMR), Fourier transformation infrared (FTIR), and the thermogravimetric analyzer (TGA) results indicated that PDPSI showed network structure and owned good thermal stability, with the char residue of 62.2% at 800°C. The flame retardancy of PDPSI/PET composites was characterized by limiting oxygen index (LOI), vertical burning tests (UL‐94), and cone calorimeter (CCT). The results revealed that the addition amount of PDPSI was 5%, the LOI value of PDPSI/PET composites increased to 27.3%, and UL‐94 test passed V‐0 rating. When the PDPSI loading was 3%, PET composites showed excellent flame retardancy and smoke suppression, with a decrease in the peak heat release rate (PHRR) by 71.19% and the total smoke release (TSP) reduced from 14.4 to 11.1m². The scanning electron microscopy (SEM) and FTIR results of char residue demonstrated that the flame‐retardant mechanism of PDPSI was solid phase flame retardant. PDPSI catalyzed the aromatization reaction of PET to promote the formation of a dense and continuous carbon layer, finally improving the flame retardancy and smoke suppression properties of PET.     

Synthesis of siloxane‐containing benzoxazine and its synergistic effect on flame retardancy of polyoxymethylene

A type of trialkoxysilane‐containing naphtholoxazine compound (Naph‐boz) was successfully synthesized and combined with ammonium polyphosphate/melamine (APP/ME) as an intumescent flame retardant (IFR) to improve the flame‐retardant efficiency of polyoxymethylene (POM). The Underwriters Laboratories 94 (UL94) vertical burning test, limiting oxygen index (LOI), cone calorimeter, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and Raman spectral analysis were used to study the flame‐retardant properties and related mechanism. The results showed that the formulation with 20 wt.% of APP, 6 wt.% of ME, and 4 wt.% of Naph‐boz passed UL94 V‐1 rating, and the LOI value was improved to 40.3%. Compared with pure POM, the IFR with Naph‐boz had greater reduction in peak heat release rate (lower 74.9%) and total heat release (lower 40.2%). SEM images showed that compact and reinforcing charred layer was formed during the POM/IFR/4Naph‐boz samples combustion, which was beneficial at reducing and maintaining low combustion parameters throughout the cone calorimeter test. The synergistic flame‐retardant effect between Naph‐boz and APP/ME was considered as the reason for the improvement in flame retardancy POM. Furthermore, because of the Naph‐boz was conducive to the compatibility between the flame retardants and matrix, the notched Izod impact strength of POM/IFR/4Naph‐boz composite was higher than that of POM/IFR system.     

Permanent flame retardant finishing of textile materials by a photochemical immobilization of vinyl phosphonic acid

A new photochemical method for a permanent flame retardant finishing of textiles made of cotton (CO), polyamide (PA) and polyester (PET) is described. Using a mercury vapour UV lamp vinyl phosphonic acid (VPA) can be fixed durable to different fabrics made of CO, PA and PET in the presence of a cross-linking agent and a photo-initiator. After a home laundering cycle up to 50 wt% of the reaction mixture is retained on the fabrics and the absolute phosphorus content was found to be more than 2.0% in all investigated cases. The photochemically modified textiles showed high levels of flame retardant performance and passed a vertical flammability test for protective clothing.     

Effects of melamine polyphosphate and halloysite nanotubes on the flammability and thermal behavior of polyamide 6

Melamine polyphosphate (MPP) and halloysite nanotubes (HNT) were introduced to polyamide 6 (PA6) by melt blending in order to improve the fire resistance. PA6 composite containing 12% flame retardants with good spinnability was obtained. The flammability of PA6 composite was characterized by limiting oxygen index (LOI), UL‐94 vertical burning and cone calorimeter (CONE) tests. The results indicated that the LOI value could reach 24.0 vol.% and UL‐94 rating could achieve V2 level at the presence of 12% flame retardants. CONE data demonstrated that peak heat release rate was significantly reduced from 554 kW/m² of neat PA6 to 368 kW/m² of the sample containing flame retardants. Thermal analysis indicated that the thermal stability and char formation were improved by the presence of flame retardants. The morphology of residue char was characterized by scanning electron microscopy; and it suggested that a network‐structured protective char layer had been formed. The possible synergism between MPP/HNT and their flame retardant mechanism was also analyzed and discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Synergistic improvement of fire retardancy and mechanical properties of ferrocene‐based polymer in intumescent polypropylene composite

The ferrocene‐based polymer (PDPFDE) accompanied with traditional intumescent flame retardant (IFR) system (ammonium polyphosphate (APP)/pentaerythritol (PER) = 3/1, mass ratio) has been used as additive flame retardant in polypropylene (PP), aiming to lower the total loading amount. The thermal stability and fire retardant properties were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), vertical combustion (UL‐94), and cone calorimetry (CONE). The fire retardant mechanism was studied by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The results showed that the PP1 with 25 wt% IFR only passed the UL‐94 V‐1 rating, but the PP6 loaded by 0.5 wt% PDPFDE and 22.5 wt% IFR possessed an LOI value of 28.5% and passed the UL‐94 V‐0 rating; the peak heat release rate (pHRR) and total heat release (THR) are decreased by 63% and 43%, respectively, compared with pure PP. In addition, the char residue of PP6 manifested a very compact and smooth surface, indicating a more effective barrier layer. Meanwhile, it was interesting that the addition of PDPFDE evidently improved the impact strength and elongation at break of PP/IFR composites.     

Flame retardant properties and mechanism of an efficient intumescent flame retardant PLA composites

The charring agent (CNCA‐DA) containing triazine and benzene rings was combined with ammonium polyphosphate (APP) to form intumescent flame retardant (IFR), and it was occupied to modify polylactide (PLA). The flame retardant properties and mechanism of flame retardant PLA composites were investigated by the limited oxygen index (LOI), vertical burning test (UL‐94), thermogravimetric analysis, microscale combustion calorimetry, scanning electron microscopy, laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy. The analysis from LOI and UL‐94 presented that the IFR was very effective in flame retardancy of PLA. When the weight ratio of APP to CNCA‐DA was 3:1, and the IFR loading was 30%, the IFR showed the best effect, and the LOI value reached 45.6%. It was found that when 20 wt% IFR was loaded, the flame retardancy of PLA/IFR still passed UL‐94 V‐0 rating, and its LOI value reached 32.8%. The microscale combustion calorimetry results showed that PLA/IFR had lower heat release rate, total heat release, and heat release capacity than other composites, and there was an obvious synergistic effect between APP and CNCA‐DA for PLA. IFR containing APP/CNCA‐DA had good thermal stability and char‐forming ability with the char residue 29.3% at 800°C under N₂ atmosphere. Scanning electron microscopy observation further indicated that IFR could promote forming continuous and compact intumescent char layer. The laser Raman spectroscopy analysis and X‐ray photoelectron spectroscopy analysis results indicated that an appropriate graphitization degree of the residue char was formed, and more O and N were remained to form more cross‐linking structure. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel intumescent flame retardant imparts high flame retardancy to epoxy resin

Intumescent flame retardant (IFR) has received the considerable attention ascribed to the inherent advantages including non‐halogen, low toxicity, low smoke release and environmentally friendly. In this work, a novel charring agent poly (piperazine phenylaminophosphamide) named as PPTA was successfully synthesized and characterized by Fourier transform infrared spectra (FTIR) and X‐ray photoelectron spectroscopy (XPS). Then, a series of flame‐retardant EP samples were prepared by blending with ammonium polyphosphate (APP) and PPTA. Combustion tests include oxygen Index (LOI), vertical Burning Test (UL‐94) and cone calorimeter testing,these test results showed that PPTA greatly enhances the flame retardancy of EP/APP. According to detailed results, EP containing 10 wt% APP had a LOI value of 30.2%,but had no enhancement on UL‐94 rating. However, after both 7.5 wt% APP and 2.5 wt% PPTA were added, EP‐7 passed UL‐94 V‐0 rating with a LOI value of 33.0%. Moreover, the peak heat release rate (PHRR) and peak of smoke product rate (PSPR) of EP‐7 were greatly decreased. Meanwhile, the flame‐retardant mechanism of EP‐7 was investigated by scanning electron microscopy (SEM), thermogravimetric analysis/infrared spectrometry (TG‐IR) and X‐ray photoelectron spectroscopy (XPS). The corresponding results presented PPTA significantly increased the density of char layer, resulting in the good flame retardancy.     

Thermogravimetric Studies of Deposited Potash Impregnated for Flame-Retardancy into a Cotton Fabric

The effect of potash as a nondurable finish on the flammability of 100% cotton fabric （plain 180 g/m^2） was investigated. The bone-drled weighed fabrics were dipped into suitable concentrations of potash, with a volume of 100 mL at 20-2℃. The impregnation was followed by means of squeeze rolls and drying at 110 ℃. The samples were then reweighed with analytical precision. After conditioning overnight by using our ＂vertical flame tester＂ the optimum add-on values to impart flame-retardancy to cotton fabric was determined and expressed by 0.80 g of potash per 100 g fabric to be an efficient addition. Thermogravimetric analysis of pure cotton, treated cotton with potash at its optimum efficiency for donation of flame-retardancy into cotton fabric was fulfilled and the thermograms were compared and commented. The effectiveness of this hydroxide was attributed to the heat dissipation by the remaining consumed material during the combustion. The results obtained are in favor of ＂Dust or Wall Effect Theory＂.     

Synthesis of a novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano zinc oxide and its application in poly (lactic acid) resin

A novel polyphosphazene/triazine bi‐group flame retardant in situ doping nano ZnO (A4‐d‐ZnO) was synthesized and applied in poly (lactic acid) (PLA). Fourier transform infrared (FTIR), solid state nuclear magnetic resonance (SSNMR), X‐ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive spectrometer (EDS) were used to confirm the chemical structure of A4‐d‐ZnO. The thermal stability and the flame‐retardant properties of the PLA composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), limiting oxygen index (LOI), vertical burning test (UL‐94), and micro combustion calorimeter (MCC) test. The results of XPS showed that A4‐d‐ZnO has been synthesized, and the doping ratio of ZnO was 7.2% in flame‐retardant A4‐d‐ZnO. TGA results revealed that A4‐d‐ZnO had good char forming ability (40 wt% at 600°C). The results of LOI, vertical burning test, and MCC showed that PLA/5%A4‐d‐ZnO composite acquired a higher LOI value (24%), higher UL94 rating, and lower pk‐HRR (501 kW/m²) comparing with that of pure PLA. It indicated that a small amount of flame‐retardant A4‐d‐ZnO could achieve great flame‐retardant performance in PLA composites. The catalytic chain scission effect of A4‐d‐ZnO could make PLA composites drip with flame and go out during combustion, which was the reason for the good flame‐retardant property. Moreover, after the addition of A4‐d‐ZnO, the impaired mechanical properties of PLA composites are minimal enough.     

Flame‐retardant behavior of bi‐group molecule derived from phosphaphenanthrene and triazine groups on polylactic acid

The flame‐retardant polylactic acid (PLA) has been prepared via mixing the flame retardant TGIC‐DOPO derived from phosphaphenanthrene and triazine groups into matrix. The flame retardancy of TGIC‐DOPO/PLA composites was characterized using the limiting oxygen index (LOI), vertical burning test (UL94), and cone calorimeter test. Results reveal that the 10%TGIC‐DOPO/PLA composite obtained 26.1% of LOI and passed UL94 V‐0 rating. The flame‐retardant mechanism of PLA composites was characterized via thermogravimetric analysis (TGA), pyrolysis gas chromatography/mass spectroscopy, and TGA‐Fourier transform infrared. It discloses that TGIC‐DOPO promoted PLA decomposing and dripping early, and it also released the fragments with quenching and dilution effects. These actions of TGIC‐DOPO contribute to reducing the burning intensity and extinguishing the fire on droplets, thus imposing better flame retardancy to PLA. When TGIC‐DOPO was partly replaced by melamine cyanuric with dilution effect and hexa‐phenoxy‐cyclotriphosphazene with quenching effect in composites respectively, the results confirm that TGIC‐DOPO utilize well‐combination in dilution effect and quenching effect to flame retard PLA. Copyright © 2015 John Wiley & Sons, Ltd.     

In situ synthesis of a novel transparent poly (methyl methacrylate) resin with markedly enhanced flame retardancy

A novel phosphorus‐containing monomer, (6‐oxido‐6H‐dibenzo[c,e][1,2]oxaphosphinin‐6‐yl)methyl acrylate (DOPO‐AA), is first synthesized and characterized by Fourier transform infrared spectra (FTIR), ¹H nuclear magnetic resonance (NMR) and ³¹P NMR. The monomer is then introduced into poly (methyl methacrylate) (PMMA) matrix via in situ copolymerization to produce a new PMMA based copolymer (PMMA/DOPO‐AA). From UV–vis spectra, microscale combustion calorimeter (MCC) and thermogravimetric analyses (TGA) results, the as‐fabricated PMMA/DOPO‐AA copolymers not only keep relatively high transparency, but also exhibit remarkable improvements in the flame retardancy and thermal stability, such as increased T_0.5 by 60.2°C and limited oxygen index (LOI) by 4.1, and decreased peak heat released rate (PHRR) by 34.7%. Thermal degradation behaviors investigated by real time Fourier transform infrared spectra (RTIR), char structure analysis studied by scanning electron microscope (SEM) and pyrolysis gaseous products studied by TGA coupled with FTIR (TGA‐FTIR) demonstrate that the catalytic charring function of DOPO‐AA in condensed phase and DOPO flame retardant systems in the gas phase are two key factors for the property enhancements. This work not only provides a promising flame‐retardant monomer for polymers, but also will stimulate more efforts on the development of DOPO‐containing flame‐retardant monomers. Copyright © 2015 John Wiley & Sons, Ltd.     

Durable flame‐retardant finishing for polyamide 66 fabrics by surface hydroxymethylation and crosslinking

This paper describes an attempt to develop a durable finishing method in order to improve the fire performance of polyamide 66 fabrics. Hydroxymethylation with a 36% formaldehyde aqueous solution in association with a pad‐curing process to enable the fabric to react with flame‐retardant solutions was used in the finishing process. The fire performance of treated samples was characterized by limiting oxygen index (LOI) and vertical flammability tests, and the results show that the LOI value can increase from 21.6% to 46.2%. The thermal behavior of untreated and treated polyamide 66 fabrics was investigated by using thermogravimetic analysis and differential scanning calorimetry. Furthermore, residual char of treated fabric sample is much higher than that of untreated fabric sample. Fourier transform infrared spectroscopy proves that the substituted hydroxymethyl groups do exist on the molecular chain of polyamide fabric sample after surface modification. The morphology of residue char of polyamide 66 fabric samples was analyzed by scanning electron microscope, and the mechanical properties were also investigated and discussed. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of anion of polyoxometalate based organic–inorganic hybrid material on intumescent flame retardant polypropylene

In this work, 12‐tungestocobaltic acid based organic–inorganic hybrid material, [Bmim]₆CoW₁₂O₄₀ (CoW) was synthesized and applied as a synergist in polypropylene (PP)/intumescent flame retardant (IFR) composites. The flame retardant properties were investigated by the limiting oxygen index (LOI), UL‐94 vertical burning test, thermal gravimetric analyzer (TGA), cone calorimeter and scanning electron microscopy (SEM) etc. The results showed that the PP composites with 16 wt% IFR and 1 wt% CoW achieves the UL‐94 V‐0 rating and gets a LOI value 28.0. However, only add no less than 25 wt% single IFR, can the PP composites obtain the UL‐94 V‐0 rating, which suggests that CoW has good synergistic effects on flame retardancy of PP/IFR composites. In addition, the SEM and cone calorimeter tests indicated the CoW improves the quality of char layer. The rate of char formation has been enhanced also because of the existence of CoW. It is the combination of a better char quality and a high rate of char formation promoted by CoW that results in the excellent flame retardancy of PP/IFR composites. Copyright © 2016 John Wiley & Sons, Ltd.     

The comparison of differences in flammability and thermal degradation between cotton fabrics treated with phosphoramidate derivatives

The effectiveness of a phosphoramidate tetraethyl piperazine‐1,4‐diyldiphosphoramidate (TEPP) as a flame retardant on cotton twill fabrics was compared with that of a previously studied diethyl 4‐methylpiperazin‐1‐ylphosphoramidate (DEPP). TEPP was formed in a reaction between two phosphonates and a piperazine then cotton twill fabrics were treated with TEPP at different levels of add‐on (2–19 wt%) and characterized using vertical flammability, limiting oxygen index, microscale combustion calorimetry, and thermogravimetric analysis methods. The results showed better flame retardancy and thermal behavior for TEPP fabrics when compared with DEPP fabrics. When the morphological structure of the formed char from the burned areas was examined by scanning electron microscopy, the results revealed a fairly insignificant difference in the mode of action between the two types of fabric. Copyright © 2014 John Wiley & Sons, Ltd.     

Aluminum hypophosphite in combination with expandable graphite as a novel flame retardant system for rigid polyurethane foams

The main aim of this work was to investigate the synergistic effect of expandable graphite (EG) and aluminum hypophosphite (AHP) on the flame retardancy of rigid polyurethane foams (RPUFs). A series of flame retardant RPUF containing EG and AHP were prepared by one‐shot and free‐rise method. The flame retardant, thermal degradation, and combustion properties of RPUF hybrids were characterized through limiting oxygen index (LOI) test, vertical burning (UL‐94) test, thermogravimetric analysis and microscale combustion calorimeter. The LOI and UL‐94 results showed that the RPUF sample with 10 wt% EG and 5 wt% AHP passed UL‐94 V‐0 rating and reached a relatively high LOI value of 28.5%, which is superior over other EG/AHP ratios in RPUF at the equivalent filler loading. Microscale combustion calorimeter results revealed that the incorporation of EG and AHP into RPUF reduced the peak heat release rate and total heat release, thus decrease the fire risk of RPUF significantly. Incorporation of EG and AHP improved the thermal stability of RPUF as observed from the thermogravimetric analysis results and also enhanced the thermal resistance of char layer at high temperature from scanning electron microscopy and Raman spectroscopy. Moreover, it could be seen from thermogravimetric analysis/infrared spectrometry spectra that the addition of EG and AHP significantly decreased the combustible gaseous products such as hydrocarbons and ethers. Finally, the synergistic mechanism in flame retardancy was discussed and speculated. Copyright © 2014 John Wiley & Sons, Ltd.     

A bio‐safe cyclophosphazene derivative flame retardant for polylactic acid composites: Flammability and cytotoxicity

An efficient bio‐safe cyclophosphazene flame retardant, 1,5,9,13,16,20‐Hexaoxa‐7,14,21‐triaza‐6λ⁴,8λ⁴,5λ⁴‐triphosphatrispiro[5.1.5.1.5.1]heneicosa‐6,8(14),15(21)‐triene (HCPO), was synthesized, and then was incorporated into polylactic acid (PLA) to improve the fire safety. The chemical structure of HCPO was confirmed by Fourier‐transformed infrared spectroscopy, mass spectrometry, and nuclear magnetic resonance spectroscopy. The thermal stability of the compound was characterized by thermogravimetric (TG) analyzer. The cytotoxic effects of HCPO to cells were evaluated. Fire behavior and thermal stability of PLA composites were investigated by vertical burning, limiting oxygen index (LOI), TG analysis, and cone calorimeter. The morphology of residual charring was observed by scanning electron microscope. The results showed HCPO was bio‐safe, and highly effective to enhance the flame retardancy of PLA composites. The LOI value was increased from 18.4 to 27.5 and UL‐94 grade achieved V‐0 for the PLA composite containing only 2% HCPO and 2% pentaerythrotol. It was demonstrated that intermolecular cross‐linking reaction between pentaerythrotol and HCPO in high temperature range could accelerate the formation of compact char layers.     

Synthesis of intrinsically flame‐retardant copolyamides and their employment in PA6‐fibers

Flame‐retarded polyamide 6.6 (FR‐PA6.6) was prepared by the cocondensation of hexamethylene diammonium adipate (AH‐salt) with the corresponding salts of hexamethylene diamine and two different organophosphorus compounds, namely, 3‐hydroxyphenylphosphinylpropanoic acid (3‐HPP, 1) and 9,10‐dihydro‐10‐[2,3‐di (hydroxycarbonylpropyl]‐10‐phosphaphenanthrene‐10‐oxide (DDP, 2). The incorporation of the phosphorus comonomers and the thermal and physical properties of the resulting copolyamides have been studied. The phosphorus‐modified FR‐PA6.6 possesses high relative viscosities of 2.0 to 2.4, good thermal stability, and was used for the production of polyamide blends by merging FR‐PA6.6 with commercial PA6. This offered access to flame‐retarded PA6 multifilaments, which possess tensile strengths up to 0.7 GPa and elastic moduli up to 6.2 GPa. Knitted fabrics of FR‐PA6 exhibit high limiting oxygen index (LOI) values between 36 and 38 and executed burning tests demonstrate that the incorporation of phosphorus‐based comonomers improve flame retardancy significantly. The approach presented here offers a straightforward access to effective flame retardancy in nylon 6.