Flame Retardant Polyamide Research Articles

In situ prepared polyamide 6/DOPO-derivative nanocomposite for melt-spinning of flame retardant textile filaments

A novel flame retardant polyamide 6 (PA6)/bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-derivative (PHED) nanocomposite textile filament yarns were developed. The scalable production approach includes in situ water-catalyzed ring-opening polymerization of ε-caprolactam in the presence of the flame retardant PHED followed by melt-spinning of nanocomposite filament yarns and production of knitted fabrics. The specific chemical structure of the PHED additive enabled its excellent miscibility with molten ε-caprolactam and the uninterrupted polymerization of ε-caprolactam. The produced PA6/PHED nanocomposite was characterized by the preserved molecular structure of the polyamide 6 and uniformly distributed nano-dispersed FR at concentrations of 10 and 15 wt %. The PA6/PHED nanocomposite structure was successfully preserved after the melt-spinning processing. The PA6 nanocomposite filament yarns at the applied 15 wt %. loading of PHED showed (a) increased thermo-oxidative stability compared to neat PA6 up to 500 °C, with a 43% higher residue at 500 °C and (b) self-extinguishment of fiber strand and knitted samples within 1 s in standard vertical flame spread tests (ASTM D6413), followed by the significant reduction of the melt-dripping and the melt-drop flammability. Additionally, 1.2 mm-tick PA6/PHED bar samples achieved a V0 rating in UL94 vertical burning test at the applied 10 wt % concentration of PHED. This innovative and scalable approach could pave the way for the production of new-generation nanocomposite PA6 filament yarns with self-extinguishing properties at the macro-scale, which would be highly beneficial for increasing fire safety, whilst maintaining the use of a DOPO derivative at the minimum level.

A facile method to improve thermal stability and flame retardancy of polyamide 6

Abstract Despite great advances for flame-retardant polyamide 6 (PA6), there is still a lack of facile strategies for creating advanced flame-retardant PA6 composites without significantly compromising its thermal stability to date. In this work, flame retardant PA6 nanocomposites were fabricated by incorporation of carbon nanotubes (CNTs) and organic montmorillonite (OMMT) together with aluminum diisobutylphosphinite acid (ABPA) into PA6. CNTs, exfoliated clay sheets and APBA particles are finely dispersed within the PA6 matrix and a physical network is formed. The addition of CNTs can compensate the decrease in thermal stability for the PA6/APBA/OMMT ternary system and further improve the char yield. The PA6/ABPA/5MT/1NT quaternary system containing 6 wt% ABPA, 5 wt% OMMT and 1 wt% CNT achieves a LOI of 31.4% and passes V-0 rating during UL-94 tests. The peak of heat release rate of this PA6 quaternary system decreases by 74.4% as compared to pristine PA6.

Synthesis and characterization of inherently flame retardant polyamide 6 based on a phosphine oxide derivative

To improve the flame retardancy of polyamide 6 (PA 6), 2,3-dicarboxy propyl diphenyl phosphine oxide (DPDPO) as the reactive flame retardant was introduced into the molecular chain of PA 6. The chemical structure, thermal property, mechanical property and flame retardancy of flame retardant PA 6 were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, tensile test, vertical burning test and limiting oxygen index (LOI) test. The flame-retardant mechanism was analyzed by cone calorimetry and pyrolysis-gas chromatography-mass spectrometry. The introduction of DPDPO reduced the melting point and crystallization of flame retardant PA 6, but the flame retardancy of flame retardant PA 6 improved. The flame retardant PA 6 with 5 wt% DPDPO could pass the V-0 rating (UL 94) with the LOI value of 31.7%. The results indicated that DPDPO promotes the degradation of PA 6 at high temperature, and mainly act by the quenching effect of phosphorus-containing radicals in the gas phase. In addition, the reduction of caprolactam produced during degradation also contributes to the improved flame retardancy. The inherently flame retardant PA 6 shows the prospect in the fields of fiber and textile.

Fire retardant mechanism of PA66 modified by a “trinity” reactive flame retardant

ABSTRACTA “trinity” reactive flame retardant (TRFR) was successfully synthesized from pentaerythritol, phosphorus oxychloride (POC), andp‐aminobenzoic acid in two steps. The flame retardant polyamide 66 (PA66) was prepared by polymerizing TRFR with PA66 salt; the structural changes during the heating process, the morphology, and composition after combustion of flame retardant PA66 were analyzed. Fourier transform infrared, scanning electron microscopy, and Raman analysis results showed that the TRFR structure on flame retardant PA66 decomposed at the temperature of 25–550 °C, forming compounds containing phosphorus, carbon, and nitrogen, respectively. These compounds promoted the dehydration of the combustion surface to form char, increased the char formation rate, and produced nonflammable gases, resulting in a dense, porous, noncombustible carbon layer. The carbon layer may isolate oxygen and heat, thereby preventing the polymer from sustainability of combustion. When the TRFR salt content was 3%, TRFR flame retardant PA66 has excellent flame retardancy with limited oxygen index value of 29 and UL94 of V‐0 rating. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 47488.

Rubber toughened flame retardant (FR) polyamide 11 nanocomposites Part 2: synergy between multi-walled carbon nanotube (MWNT) and MMT nanoclay

AbstractIn the previous study, flame retardant (FR) polyamide 11 (PA11) nanocomposites formulations designed for selective laser sintering (SLS)were prepared and characterized. The SEBS-g-MA elastomer successfully improved the material’s ductility. Although the nonhalogenated FR additives and montmorillonite (MMT) nanoclay successfully decreased the heat release capacity (HRC) and peak heat release rate (pHRR) as characterized by microscale combustion calorimeter (MCC). None of the rubber toughened formulations achieved UL 94 V0 rating, which is a bench mark for many FR polymer applications. As part two of this study, we explored the synergism between two nanoparticles, nanoclay and multi-walled carbon nanotubes (MWNTs), to see whether better FR properties can be achieved. TEM micrographs indicate that both nanoclay and MWNTs achieved high level of dispersion. Flammability results showed that all formulations achieved UL 94 V0 rating, which is a significant improvement from the previous formulations without MWNTs. Char morphology characterization indicated that a solid carbonaceous char layer was reinforced by nanoclay and MWNTs.

Silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties.

A facile route of ‘copolymerization/blending’ was proposed to fabricate silicon/nitrogen synergistically reinforced flame-retardant PA6 nanocomposites with simultaneously improved anti-dripping and mechanical properties. Firstly, a persistently inherent flame-retardant PA6 (FR-PA6), with 1,3-bis(3-aminopropyl)tetramethyl disiloxane (MSDS), was synthesized via controllable amidation and a polycondensation reaction. Melamine cyanurate (MCA) nanoparticles as a ‘gas phase’ synergistic agent were then added into FR-PA6 to further improve its flame retardancy. The primarily obtained FR-PA6 could be extinguished after a few melt droplets dropped as ignited, and passed the V-2 rating with enhanced mechanical properties, while PA6 had no rating (NR). The prepared FR-PA6/MCA nanocomposites could attain a limiting oxygen index (LOI) value of 32.7%, and passed the V-0 level with only 1 melting droplet with similar mechanical properties to PA6. Accordingly, the special ‘condensed-gas phase’ synergistic flame-retardant mechanism of FR-PA6/MCA nanocomposites was proposed through studying the residues and pyrolysis volatiles. This work provided a facile route as a model for developing functional PA6 for diverse engineering applications.

Structure and Properties Study of PA6 Nanocomposites Flame Retarded by Aluminium Salt of Diisobutylphosphinic Acid and Different Organic Montmorillonites.

Two different types of organic montmorillonite, namely quaternary ammonium salt intercalated MMT (CMMT) and quaternary phosphonium salt intercalated MMT (PMMT) were used as fillers in the flame-retardant polyamide (PA6) based on aluminium salts of diisobutylphosphinic acid (ABPA). The influence of different types of organic montmorillonite (OMMT) on the structure and properties of flame-retardant PA6 nanocomposites were systematically investigated. The X-ray diffraction and transmission electron microscopy results suggested that the introduction of OMMT improved the dispersion of the flame retardant particles independently of the type of OMMT. The derivative thermogravimetry (DTG) curve transformed to one peak from two peaks (representing the degradation of ABPA and PA6, respectively) after incorporation of the OMMT, which further confirmed better ABPA dispersion. Viscoelastic measurements demonstrated that a mechanically stable network structure was formed with the introduction of OMMT or ABPA and OMMT, while PA6/ABPA/PMMT presented the highest storage modulus and viscosity, suggesting a more efficient network structure. From UL-94 and limited oxygen index (LOI) tests, PA6/ABPA/PMMT presented the best flame performance, with a UL-94 of V-0 and a LOI of 33%. In addition, the PA6/ABPA/PMMT presented the lowest peak heat release rate (pHRR) among the investigated samples. Combined with the char layer analysis, it can be deduced that the introduction of PMMT improved the dispersion of ABPA, and promoted the formation of more efficient network structure, before promoting more compact char structures, which finally resulted in improved flame retardancy.

Enhanced thermal conductivity and flame retardancy of polyamide 6/flame retardant composites with hexagonal boron nitride

Abstract High performance composite of polyamide 6 (PA6)/flame retardant (FR)/hexagonal boron nitride (hBN) was prepared via twin screw extrusion, followed by injection molding. The heat dissipation of the composite was significantly improved by incorporating 40 vol% of hBN, and the corresponding thermal conductivity was up to 5.701 W/(m·K), nearly 17 times that of the PA6/FR composites. In addition, the combination effect of hBN and FR to the flame retardancy of the composites was observed, and the addition of hBN could dramatically enhance the flame retardancy of composites, achieving a UL94 V-0 rating with a limited oxygen index (LOI) value of 37%. This multifunctional modification would broaden the application field of PA6 composites in light-emitting diode (LED) lamps, electronic products, and so on.

Role of caged bicyclic pentaerythritol phosphate alcohol in flame retardancy of PA6 and mechanism study

ABSTRACTA series of PA6/PEPA composites were prepared by mixing caged bicyclic pentaerythritol phosphate alcohol (PEPA) and polyamide 6 (PA6) at different feed ratios by the melt‐blending method in a twin‐screw extruder. The influence of PEPA on the flame‐retardant properties of PA6 was investigated using the limiting oxygen index (LOI), the Underwriters Laboratories UL‐94 test, and the cone calorimeter method. Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, X‐ray photoelectron spectroscopy, thermogravimetry (TG), and TG‐FTIR were conducted to study the influence of PEPA on the thermal decomposition and the mechanism of performance of PA6 from products of condensed and gaseous phases. The results show that the LOI value and the content of residual char of PA6/PEPA composites increased with increasing PEPA content, and an LOI value of 38% could be reached when the feed ratio of PEPA was 30 wt %. The average heat release rate and total heat release drastically decreased with increasing content of PEPA, and the amount of carbon residue increased by 52.9% over neat PA6 after TG tests. The inorganic acid produced by PEPA during combustion can be used as an acid source to promote the dehydration of PA6 and the processes of esterification crosslinking, arylation, and carbonization. Moreover, there was less CO2 released than by PA6, and more carbon‐containing compound remained in the composites so that a stable carbon layer structure was formed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46236.

Thermodynamic Approach for Halogen Free Flame Retarded Polyamide 6 and 66

Background: Halogen free flame retarded Polyamide 6 and 66 are fibres and engineering plastics of great commercial interest. Therefore, an important amount of papers and data as well as technical solutions exist. Nevertheless, for further progress there is a lack of principal results. Methods: Heats of combustion and degradation with their corresponding temperatures and residues were measured on polyamides and their flame retardants. Thermodynamic balances of heat and weight were established. They lead to chemical formulas, which have to be consistent with the balances. This procedure enables the description of degradation and the composition of residues and chars like aluminium phosphate, C3N4 graphite and graphite phosphorous pentoxide. Using the ideal gas equation the amount of evolved gases is estimated. Furthermore, thermodynamic theory can predict the expansion of intumescent flame retardants and indicate the existence of hydrogen bonds between polyamides and melamine cyanurate. Intumescent coatings, which are sprayed or painted on surfaces, are the most efficient flame retardants for devices with low area to volume ratios. Another advantage of intumescent flame retardants is to be seen in their foamed insulating char, which delays the time of failure of the fire protected building part. Conclusion: The thermodynamic procedure allows the quantitative description of decomposition under fire and emphasizes the favourite position of intumescent flame retardants in the ranking of efficiency. Keywords: Combustion, differential scanning calorimetry, extrusion, flame retardants, polyamide, thermodynamics.

Self-Extinguishing and Non-Drip Flame Retardant Polyamide 6 Nanocomposite: Mechanical, Thermal, and Combustion Behavior

AbstractIncorporation of flame-retardant (FR) additives and nanoclay fillers into thermoplastic polymers effectively suppresses materials flammability and melt dripping behavior. However, it largely affects other properties, such as toughness and ductility. In order to recover the lost toughness and ductility of flame retardant polyamide 6, various loadings of maleic anhydride modified SEBS elastomer were added and processed by twin screw extrusion. TEM images showed exfoliated nanoclay platelets and reveals that the clay platelets well dispersed in the polymer matrix. By balancing the ratio of flame retardants, nanoclay and elastomers, formulation with elongation at break as high as 76% was achieved. Combining conventional intumescent FR and nanoclay, UL-94 V-0 rating and the LOI value as high as 32.2 were achieved. In conclusion, effective self-extinguishing and non-drip polyamide 6 nanocomposite formulations with significant improvement in toughness and ductility were achieved.

Preparation and characterization of polyamide 6 fibre based on a phosphorus-containing flame retardant

Intrinsically flame retardant polyamide 6 (FRPA6) was synthesized by melt polycondensation of caprolactam and 9,10-dihydro-10-[2,3-di(hydroxycarbonyl)propyl]-10-phosphaphenanthrene-10-oxide (DDP). Following this, FRPA6 fibres were prepared by melt spinning. The chemical structure, thermal stability, mechanical and combustion properties of FRPA6 were characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, tensile measurements, vertical burning measurements, limiting oxygen index (LOI) measurements, cone calorimetry and scanning electron microscopy. The thermal stability of FRPA6 decreased to a certain extent, but the amount of residual char was improved. FRPA6 containing 5 wt% DDP could achieve a V-0 rating with an LOI value of 33.7%. The spinnability of FRPA6 fibres was good and the tenacity at break reached 3.0 cN dtex−1 which met the requirements of textiles. The flame retardancy of FRPA6 fibres was definitely improved and the LOI value of FRPA6-5 fabric could reach 28.4%, thereby showing good prospect in applications.

Effects of AP and AP-ethyl on the properties of PA6

In this work, the effects of inorganic phosphinate flame retardant of aluminum hypophosphite (AP) and organic phosphinate flame retardant of ethyl substituted phosphinates (AP-ethyl) on the thermal degradation, flame performance, and mechanical properties of polyamide 6 (PA6) were investigated. Scanning electron micrograph showed AP with the shape of bulk and the mean size of 8 μm while AP-ethyl with irregular shape and the mean size of 30 μm. Thermal analysis indicated that the thermal degradation behavior of flame-retardant PA6 was different from pure PA6. Moreover, the cone calorimeter test results revealed that peak heat release rate (PHRR) of PA6/AP (85/15) and PA6/AP-ethyl (85/15) decreased by 51% and 64%, respectively, compared with pure PA6. Furthermore, pure PA6 showed ductile stress–strain curve with the tensile strength of 54.8 MPa. However, PA6/AP and PA6/AP-ethyl displayed brittle stress–strain curve and their tensile strength decreased to 52.3 and 47.1 MPa, respectively. In addition, pure PA6 showed a glossy and tough fracture surface morphology. The rough fracture surface morphologies for PA6/AP and PA6/AP-ethyl were observed, and the interface of PA6/AP was more obscure than that of PA6/AP-ethyl. Consequently, the small particle size of AP had a more uniform dispersion in PA6 matrix.

Simultaneously improving the flame retardancy and mechanical properties for polyamide 6/aluminum diethylphosphinate composites by incorporating of 1,3,5‐triglycidyl isocyanurate

The effect of 1,3,5‐triglycidyl isocyanurate (TGIC) as a synergistic agent on the fire retardancy, thermal, and mechanical properties for polyamide 6/aluminium diethylphosphinate (PA6/AlPi) composites were investigated in detail by limiting oxygen index; vertical burning (UL‐94); cone calorimeter; thermal gravimetric analysis; rheological measurements; and the tests of tensile, flexural, and Izod impact strength. The morphologies and chemical compositions of the char residue were investigated by scanning electron microscopy, X‐ray photoelectron spectroscopy, and Fourier transform infrared spectra. The results demonstrated that AlPi and TGIC exerted an evident synergistic effect for flame retardant PA6 matrix, and the PA6/AlPi/TGIC composites with the thickness of 1.6 mm successfully passed UL‐94 V‐0 rating with the limiting oxygen index value of 30.8% when the total loading amount of AlPi/TGIC with the mass fraction of 97:3 was 11 wt%. However, the samples failed to pass the UL‐94 vertical burning tests when AlPi alone is used to flame retardant PA6 matrix with the same loading amount. The thermal gravimetric analysis data revealed that the introduction of TGIC promoted the char residue formation at high temperature. The rheological measurement demonstrated that the incorporation of TGIC improved the storage modulus, loss modulus, and complex viscosity of PA6/AlPi/TGIC composites comparing with that of neat PA6 and PA6/AlPi composites due to the coupling reaction between TGIC and the terminal groups of PA6 matrix. The morphological structures of char residues demonstrated that TGIC benefited to the formation of more homogenous and integrated char layer with no defects and holes on the surface comparing with that of PA6/AlPi composites during combustion. The higher melt viscosity of composites and the integrated and sealed char layer effectively inhibited the volatilization of flammable gas into the combustion zone and then led to the reduction of the heat release. The results of mechanical properties revealed that the incorporation of TGIC enhanced the mechanical properties for PA6/AlPi/TGIC composites comparing with that of PA6/AlPi composites with the same loading amount of flame retardant caused by the chain extension effect of TGIC. As a result, the flame retardancy and mechanical properties of PA6/AlPi composites simultaneously enhanced due to the introduction of TGIC.

Enhancement of flame retardancy and mechanical properties of polyamide 6 by incorporating an aluminum salt of diisobutylphosphinic combined with organoclay

Polymers with highly effective flame retardancy and optimal mechanical properties remain difficult to achieve. In this study, polyamide 6(PA6)/clay nanocomposites with excellent flame retardancy and mechanical properties were prepared through melt compounding of PA6 and a novel salt of phosphinic acid, namely, aluminum diisobutylphosphinate (ABPA), combined with organically modified layered montmorillonite (OMMT). The dispersion of ABPA and OMMT in the flame retardant composites was characterized by X-ray diffraction, transmission electron microscopy, and viscoelastic measurements. The flame retardancy and thermal degradation behavior of PA6/ABPA and PA6/OMMT/ABPA composites were investigated by limiting oxygen index (LOI) assessment, UL94 testing, cone calorimetry, and thermogravimetric analyses. The morphologies and chemical compositions of the char residue were determined by scanning electron microscopy–energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy analyses. Results demonstrated that the ratio of ABPA and OMMT at a constant total flame retardant level of 12 wt% considerably influenced the thermal stability, flame retardancy, and mechanical properties of the resulting PA6 nanocomposites. When ABPA was introduced solely at a loading amount of 12 wt%, the specimens passed the UL-94 V-0 flammability rating, and the LOI reached 34.8%. When OMMT (ABPA: OMMT 5:1, 12 wt% in total) was incorporated into the ABPA/PA6 composites, the samples passed the UL-94 V-0 flammability rating, and the LOI reached 36.0%. The samples successfully passed the UL-94 V-0 flammability rating when incorporated with OMMT as high as 6 wt% (ABPA: OMMT 1:1, 12 wt% in total; considerable decrease in ABPA loading). The cone test results revealed that the introduction of OMMT efficiently reduced the fire behavior parameters such as heat release rate and total heat release but increased the mean effective heat combustion. Although the substitution of ABPA with OMMT reduced the gas activity of the flame retardants, the amount and thermal stability of the char layers were effectively enhanced. The digital photographs, morphological structures, and composition analysis of char residues verified that OMMT promoted the formation of sufficient, compact, and homogeneous char layer on the material surface during burning. This phenomenon led to increased strength of the char layer and improved flame retardancy of PA6 polymeric materials. Moreover, the flame retardant PA6 nanocomposites showed equal or even superior mechanical properties in terms of flexural strength and modulus than pure PA6.

Preparation and characterization of flame-retarded polyamide 66 with melamine cyanurate by in situ polymerization

In order to improve the flame retardancy and expand the applications of polyamide 66 (PA66), the flame-retarded PA66 (FRPA66) was synthesized by in situ polymerization using nylon salt in the presence of melamine cyanurate (MCA) in an autoclave. The structure and properties of FRPA66 were investigated by Fourier transform infrared spectra (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA), tensile test, scanning electron microscopy (SEM), vertical burning test (UL94), and limiting oxygen index (LOI) test. Experimental results indicated that MCA particles had heterogeneous nucleation effect which contributed the crystallization of PA66 chains at higher temperature and had a higher crystallization degree. The thermal stability and mechanical properties of FRPA66 declined compared to PA66, but the flame retardant properties improved with the loading of MCA. The FRPA66 loaded with 6 wt% of additives can achieve a UL94 V-0 rating with a LOI value of 31.5%. It also can be inferred that both the mechanical property and flame retardancy of FRPA66 prepared by in situ polymerization are better than that of FRPA66 prepared by melt blending at the same dosage.

Preparation and characterizations of flame retardant polyamide 66 fiber

The polyamide 66 (PA66) is one of the most important thermoplastic materials, but it has the drawback of flammability. So the flame retardant PA66 was prepared by condensation polymerization using nylon salt and DOPO-based flame retardant in this paper. Then the flame retardant PA66 fiber was manufactured via melt spinning. The properties of flame retardant PA66 and flame retardant PA66 fiber were investigated by relative viscosity, differential scanning calorimetry (DSC), tensile test, vertical burning test (UL94) and limiting oxygen index (LOI) test. Although the loading of the DOPO-based flame retardant decreased the molecular weight, the melting temperature, the crystallinity and the mechanical properties of flame retardant PA66, the flame retardancy properties improved. The flame retardant PA66 loaded with 5.5 wt% of DOPO-based flame retardant can achieve a UL94 V-0 rating with a LOI value of 32.9%. The tenacity at break decreased from 4.51 cN·dtex–1 for PA66 fiber to 2.82 cN·dtex–1 for flame retardant PA66 fiber which still satisfied the requirements for fabrics. The flame retardant PA66 fiber expanded the application of PA66 materials which had a broad developing prospect.

Flame retardancy of polyamide 6 hybrid fibers: Combined effects of α-zirconium phosphate and ammonium sulfamate

Synergistic effect between α-zirconium phosphate (α-ZrP) and ammonium sulfamate (AS) for enhanced flame retardant properties of Polyamide 6 (PA6) was investigated by using oxygen index instrument, cone calorimeter, thermogravimetric analyzer (TGA), Instron universal test machine and scanning electron microscopy (SEM). PA6/AS/α-ZrP ternary hybrid materials with various contents of α-ZrP and AS were fabricated by melt-mixing method. The result from flammability indicated that the Limiting oxygen index (LOI) and Underwriters Laboratories-94 (UL-94) rating of PA6/AS/α-ZrP were significantly accelerated under the coordinating function of α-ZrP and AS. Moreover, the thermal stability for PA6/AS/α-ZrP studied by TGA also demonstrated this synergistic effect between α-ZrP and AS on the heat resistance. The effects of the usage amount of α-ZrP and AS on mechanical properties were analyzed by using uniaxial tensile test. It was found that the addition of AS provided negative effects on the tensile strength of PA6/AS/α-ZrP, however, the adverse trends that mentioned above could be overcome by using the well dispersed α-ZrP.

Effect of surface chemical modification for aluminum hypophosphite with hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene on the fire retardancy, water resistance, and thermal properties for polyamide 6

The surface chemical modified aluminum hypophosphite (AHP) defined as MAHP was successful prepared through P–H bonds on AHP surface reacted with the aldehyde groups in hexa‐(4‐aldehyde‐phenoxy)‐cyclotriphosphazene made in our lab. The wettability of the flame retardants was evaluated by water contact angle tests, and the water contact angle of the prepared MAHP dramatically increased from 0° for AHP to 145°, which indicated the surface modification made the superhydrophilic AHP into superior hydrophobic MAHP. The prepared MAHP and AHP, respectively, incorporated into polyamide 6 (PA6) matrix to prepare flame retardant PA6 composites and the fire retardancy and thermal degradation behavior of flame retardant PA6 composites were investigated by limiting oxygen index, vertical burning test (UL‐94), cone calorimeter, and thermogravimetric analysis tests. The morphologies and chemical compositions of the char residues for PA6 composites were investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy, respectively. The water resistant properties of flame retardant PA6 composites were evaluated by putting the samples into distilled water at 70°C for 168 hr, and the mechanical properties for flame retardant PA6 composites were investigated by the tensile, flexural, and Izod impact strength tests. The results demonstrated that the PA6/MAHP composites successfully passed UL‐94 V‐0 flammability rating, and the limiting oxygen index value was 27.6% when the loading amount of MAHP was 21 wt%. However, there is no rating in vertical burning tests for PA6/AHP composite with the same amount of AHP, which indicated the surface modification of AHP enhanced the flame retardancy efficiency for PA6 composites. The morphological structures and analysis of X‐ray photoelectron spectroscopy of char residues revealed that the surface modification of AHP benefited to the formation of a sufficient, flame retardant elements rich, more compact and homogeneous char layer on the materials surface during combustion, which prevented the heat transmission and diffusion, limit the production of combustible gases, inhibit the emission of smoke and then led to the reduction of the heat release rate and smoke produce rate. The mechanical properties results revealed that the surface modification of AHP enhanced the mechanical properties, especially the Izod impact strength comparing with that of PA6/AHP composites with the same amount of flame retardant. After water resistance tests, the PA6/MAHP composites remained superior flame retardancy and presented continuous and compact char layer after cone calorimeter tests; however, the fire retardancy for PA6/AHP composite obviously decreased, and the char layer was discontinuous with big hole caused by the extraction of AHP by water during water resistance tests. Copyright © 2017 John Wiley & Sons, Ltd.

An improved method for the durability of the flame retardant PA66 fabric

This paper describes an attempt in order to improve the durability of the flame retardant polyamide 66 (PA66) fabric prepared by the reaction of surface photografting with acrylamide (AM) under UV irradiation. In this study, N,N′-methylene bisacrylamide (MBAAm) combined with acrylamide has been used as a photosensitive monomer during flame retardant finishing of the PA66 fabric sample. “Durable efficiency” has been introduced to evaluate the durability of AM/MBAAm-g-PA66 fabric after 50 times washing with the 0.5 % commercial grade detergent solution. The result indicates that durable efficiency reaches its maximal value of 94.5 % when the MBAAm concentration is 5.0 mass%. The effect of MBAAm on the flame retardancy, thermal stability and tensile properties of the treated PA66 fabric has been investigated, respectively. And an interesting phenomenon shows that although MBAAm could improve the thermal stability of the treated fabric significantly at high temperature, it could have a negative effect on the flame retardancy and tensile properties of the fabric sample when its concentration is high. Its possible mechanism has been discussed here.