Flame Retardancy Of Composites Research Articles

Improving the controlled-release effects of composite flame retardant by loading on porous attapulgite and coating

The attapulgite (ATP) is one of important raw materials of ceramics and often used as a loading carrier. To control the release rate of composite flame retardant (CFR) when exposed to a fire, and to meet the multi-stage flame retarding requirements, the vacuum negative pressure method was adopted to load four kinds of monomer flame retardants on porous ATP as a carrier after activating pretreatment, respectively. Then CFR nanoparticles with controlled-release effects were prepared by the in-situ polymerization reaction on the surface of monomer flame retardants. After that, zinc hydroxyl stannate, styrene, melamine formaldehyde resin and silicon dioxide with high thermal stability and excellent flame retarding properties were selected as the coating layer of four kinds of monomer flame retardants on ATP carrier. Test results of environmental scanning electron microscope and energy dispersive spectrometer show the satisfactory loading and coating results of CFR nanoparticles. Test results of X-ray photoelectron spectroscopy further confirm the excellent loading conditions and coating film formation on ATP carrier. The thermogravimetry-differential thermal scanning calorimetry tests indicate that the flame retarding duration of both loaded and coated CFR nanoparticles on ATP carrier is prolonged and has a satisfactory controlled-release effect.

Improving the Reaction-to-Fire Properties of Thermoplastic Polyurethane by New Phosphazene-Triazinyl-Based Covalent Organic Framework.

In this study, an approach to simultaneously improve fire resistance and mechanical performance of thermoplastic polyurethane (TPU) was introduced through the penetration of a conjugated network containing nitrogen and phosphorus elements. For this purpose, a Bg-HCCP COF was synthesized through a solvothermal method from benzoguanamine (Bg) and hexachlorophosphazene (HCCP) monomers. Then, it was combined with TPU using the wet mixing method. The TPU/Bg-HCCP composites showed better mechanical strength than the untreated sample. The fire safety of TPU/Bg-HCCP composites was greatly improved by increasing the Bg-HCCP contents. The reduction of the peak heat release rate and the total heat release for the TPU/Bg-HCCP composite with 3 wt % Bg-HCCP were about 44.8 and 60.4%, respectively. Besides, the results showed that adding Bg-HCCP to TPU significantly improved the suppression of smoke generation so that 3% by weight of the fire retardant reduced the total smoke released by 53.1%. It also decreased the peak of the carbon monoxide production rate by 26.5%. Generally, our research provides a promising strategy for constructing flame-retardant composites with high performance.

ZIF-67 In Situ Grown on Attapulgite: A Flame Retardant Synergist for Ethylene Vinyl Acetate/Magnesium Hydroxide Composites.

ZIF-67@ATP was prepared by the in situ growth of the zeolite imidazole frame (ZIF-67) on the surface of attapulgite (ATP). The structure and surface morphology of ZIF-67@ATP were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Different mass fractions of ATP and ZIF-67@ATP were added to ethylene vinyl acetate (EVA)/magnesium hydroxide (MH) composites as flame retardant synergists. The flame retardancy of EVA composites was evaluated by the limiting oxygen index (LOI) test, UL-94 test and cone calorimeter test. Composites containing 3 wt% of ZIF-67@ATP reached an LOI value of 43% and a V-0 rating in the UL-94 test, and the ignition time of the composite increased from 38 s to 56 s. The tensile strength and impact strength of the composites did not change significantly, but the elongation at break increased greatly. Typically, for composites containing 4 wt% of ZIF-67@ATP, the elongation at break of the composites increased from 69.5% to 522.2% compared to the samples without the synergist. This study provides novel insights into the application of attapulgite in the field of flame retardant polymer materials.

Flame-retardant properties and mechanism of LGF/PBT/DOPO-HQ-conjugated flame-retardant composites.

In this article, long fiber reinforced polybutylene terephthalate (LGF/PBT/DOPO-HQ) flame-retardant composites were prepared using 10-(2,5-dihydroxy phenyl)-10H-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO-HQ) as the conjugated flame-retardant. The effects of different flame-retardant contents on the combustion properties of the composites were investigated. The results showed that after adding 14% of DOPO-HQ, the flame-retardant effect of the composite reached the V-0 level of UL-94 fire rating with an ultimate oxygen index (LOI) of 26.4%. The average heat release rate (Av-HRR), peak heat release rate (PHRR), and total heat release rate (THR) decreased by 45.9, 56.5, and 32.6%, respectively. This shows that LGF/PBT/DOPO-HQ composite has good flame-retardant properties. Meanwhile, the flame-retardant mechanism of cohesive phase and gas-phase synergy during the combustion of flame retardants was analyzed by carbon layer morphology and dynamic thermal decomposition.

Thermal degradation behavior and flame retardant properties of PET/DiDOPO conjugated flame retardant composites.

PET/DIDOPO conjugated flame retardant composites were prepared by melt blending of styrene bridged DOPO (DIDOPO) into polyethylene terephthalate (PET). The flame retardancy, rheological behavior, and thermal degradation behavior of the composite were characterized by vertical combustion test (UL-94), limit oxygen index test (LOI), rotational rheometer, and thermogravimetry (TG). The results showed that the flame retardant composite with V-0 grade was obtained when the amount of DIDOPO is 12.5wt%, and the corresponding LOI value was 56.87% higher than that of PET. The thermogravimetry-fourier infrared spectroscopy (TG-FTIR) test results showed that DIDOPO could promote the degradation of PET/DIDOPO materials, and release phosphorus-containing free radicals to quench the flame, therefore slowing down the combustion process, and mainly playing the key flame retardant role in gas-phase.

Enhanced flame retardancy of epoxy composites containing melamine polyphosphate‐modified boron nitride

AbstractSurface chemical modification of boron nitride could enhance the compatibility with polymers and improve flame retardancy performances. In this work, the double‐bond active sites were constructed on the surface of boron nitride modified by the γ‐methacryloyloxypropyl trimethoxysilane (KH570). Glycidyl methacrylate (GMA) was further grafted onto the surface of boron nitride via free radical polymerization. Finally, the flame retardancy melamine polyphosphate (MPP) was bonded to the surface of boron nitride by the ring opening reaction. This modification process was proved to be achieved by infrared spectroscopy and thermogravimetric test. The boron nitride modified by flame retardant were added into the epoxy matrix and cured to prepare flame retardant and thermal conductive composites. The flame retardant of the composites was studied by cone calorimetry, UL94 vertical combustion test and limiting oxygen index. The thermal conductivity of the composites was characterized by laser thermal conductivity instrument. The results showed that when the addition amount of flame retardancy MPP modified boron nitride in the composites was 20 wt%, the flame retardant rating of UL94 reached to V1; the limiting oxygen index was increased from 25.1 vol% of pure epoxy resin to 30.3 vol%; the PHRR of pure epoxy resin was reduced from 800 to 510 kW/m2 of composites; the thermal conductivity of the composites was enhanced from 0.21 W/m•K−1 of the pure epoxy resin to 0.82 W/m•K−1of the composites.

Ethylene-propylene-diene (5-ethylidene-2-norbornene) terpolymer/aluminium hydroxide nanocomposites: Thermal, mechanical and flame retardant characteristics

Ethylene-propylene-diene rubber (EPDM) composites were fabricated by incorporating aluminium hydroxide (ATH) and high abrasion furnace (HAF) carbon black using two-roll mill mixing strategy. The thermal stability, flammability and mechanical properties of the composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), horizontal burning test (UL94 HB), mechanical testing (UTM) and dynamic mechanical analysis (DMA). TGA profiles showed that,EPDM/ATH composites presented incremented char residue and reduced mass loss rate compared to control EPDM. The incorporation of ATH was found to benefit the flame retardancy of composites. The storage modulus (E’) of composites peaked due to the increased stiffness of the material with filler loading. Investigation of visco-elastic properties showed the existence of strong polymer - filler interaction. The morphology of the composites under study and the corresponding char residue obtained after their LOI testing were investigated by scanning electron microscopic studies (SEM).

Achieving high flame retardancy, crystallization and biodegradability PLA based on 1 wt% addition of novel fully bio-based flame retardant

In this paper, a bio-based flame retardant PA-AR is synthesized, which endows PLA with good flame retardant and crystallization properties, and at the same time promotes the biodegradability of PLA. Only 1 wt% PA-AR makes the LOI value of PLA reach 26.8% and reaches UL-94 V-0 level. In addition, 1 wt% PA-AR increases the crystallinity of PLA to 23.4%, which increased by 460% compared with PLA. Further, due to the increase of crystallinity, the tensile strength is also improved. Besides, the addition of PA-AR can greatly promote the degradation performance of PLA under specific biological conditions. This work proposed a novel method to obtain completely biodegradable flame retardant composites.

Toughed interface of Mg(OH)2/polymer composites with improved mechanical performance via intramolecular “bridge”

Most commercialized polymers are flammable, which hinders their practical applications. The commonly employed flame retardant magnesium hydroxide (MDH) additives with high loading concentration will deteriorate the composite mechanical properties. Therefore, achieving flame retardant polymer composites without compromising their mechanical strength becomes imperative. Here, we employed a titanate coupling agent (TC) to modify the MDH surface, successfully achieving a 56.8 % enhancement of mechanical strength and improved flame retardancy in TC-MDH@ethylene-vinyl acetate (EVA) composites, compared to pristine MDH/EVA samples. Moreover, molecular dynamic simulation was performed to unravel that TC could function as intramolecular “bridge” to increase the binding energy via hydrogen bonds, which leads to toughed interface of MDH and polymers, as well as better compatibility and homogeneous dispersion between MDH and EVA. Such strategy could be employed to enhance both mechanical strength and flame retardancy of polymer composites.

Synthesis of a novel flame retardant with phosphaphenanthrene and phosphazene double functional groups and flame retardancy of poly (lactic acid) composites

A novel flame retardant hexa (4- (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 -sulfide)-hydroxymethylphenoxy) cyclotriphosphazene (HAP-DOPS) with double functional groups was synthesized, and poly (lactic acid) (PLA) composites were prepared by melt extrusion. The flame retardancy and thermal degradation behavior of flame retardant PLA composites were studied by limiting oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CCT), and thermogravimetric-infrared spectroscopy analysis (TG-IR). The experimental results showed that HAP-DOPS had a good flame-retardant effect on PLA. At flame retardant content of 5 wt%, the PLA/HAP-DOPS composite achieved a V-0 rating (UL-94, 3.2 mm) and a LOI value of 26.6%. The heat release rate (HRR) and total heat release (THR) of PLA composites were decreased by adding HAP-DOPS. The flame retardancy index (FRI) of PLA/HAP-DOPS-7.5 wt% was 1.0257, which showed good flame retardancy. The results of TG-IR showed that HAP-DOPS mainly had a gas-phase flame-retardant effect in PLA.

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.

Construction of a P–N–Si flame retardant coating on the cotton fabric with the integration of biomass carbon dots and ammonium polyphosphate

In order to improve the flame retardancy of cotton fabric, a kind of biomass carbon dots (CDs) particles were interspersed in the ammonium polyphosphate (APP) layer to achieve a new efficient CDs-based APP (CDs-APP) composite flame retardant by the integration technology. Then the CDs-APP layer was coated on the surface of cotton fabric. The microstructure and thermal stability of CDs-APP particle were characterized by the Transmission electron microscopy (TEM), Fourier infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The mass ratio of CDs to APP was 15.52%, which contains the C, O, N, Si and P elements, accounting for the 28.86%, 42.29%, 19.01%, 2.58% and 6.26%, respectively. The flame-retardant mechanism of CDs-APP was investigated by the limiting oxygen index (LOI), vertical combustion, cone calorimeter, thermogravimetric and thermogravimetric-infrared analysis. The results showed that, when the content of CDs-APP was about 10%, the LOI value of cotton fabric rose to 36.1%. The burning time and damage length have reduced to 4.5 s, 5.6 cm, respectively. And the fabric achieved B1 level. The addition of CDs-APP decreased the total heat release, heat release rate, total smoke emission and smoke emission rate of cotton fabric, among the peak-heat release rate has decreased by 55.78%. By quantifying the flame-retardant modes of CDs-APP, it displayed the superposition of physical barrier effect, flame inhibition effect and catalytic charring effect, accounting for 45.96%, 8.62% and 47.85%, respectively.Graphical abstract

Effect of Hygrothermal Ageing on the Mechanical and Fire Properties of a Flame Retardant Flax Fiber/Epoxy Composite.

In engineering applications, natural fiber composites must comply with fire requirements including the use of flame retardant. Furthermore, biocomposites are known to be water sensitive. Whether flame retardants affect the water sensitivity and whether water absorption affects the fire behavior and the mechanical performance of biocomposites are the two main topics addressed in this work. In this study, a flax fiber/epoxy composite flame retardant with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) or aluminum diethyl phosphinate (AlPi) was aged in humid atmosphere or by immersion in water. Water absorption kinetics revealed that DOPO induces an increase in equilibrium water content by approximately a factor of 2 due to its intrinsic hygroscopicity and/or its plasticizing effect on the epoxy matrix. In contrast, AlPi does not significantly change the water sensitivity of the biocomposite. Mechanical testing highlighted that, whatever the FR, the evolution of mechanical properties with ageing is governed by the moisture content. The drop of elastic modulus was attributed to a decrease in fiber rigidity due to plasticization, while the increase in tensile strength was assigned to an increase in fiber/matrix friction due to fiber swelling. As regards flame retardancy, only the highest water contents modified the fire behavior. For the AlPi containing biocomposite, the water release resulted in an increase by 50% of the time to ignition, while for the DOPO flame retardant biocomposite the water release was mainly postponed after ignition.

Synergistic effect of microcrystalline cellulose from oil palm empty fruit bunch waste and tricresyl phosphate on the properties of polylactide composites

Microcrystalline cellulose (MCC) was extracted from oil palm empty fruit bunch (OPEFB) waste by integrated chemical treatments of delignification, bleaching, and acidic hydrolysis. The obtained MCC (OPMC) and tricresyl phosphate (TCP) were used as additives for polylactide (PLA) composites. The influences of OPMC and TCP contents, separately and in combination, were evaluated on the properties of the composites. Characterization studies confirmed the successful extraction of OPMC from OPEFB waste. With regard to the properties of the PLA composite, the appropriate content of OPMC should be 5 phr. The good distribution of OPMC in the polymer matrix changed the failure behavior of the composite from brittle to ductile. All the PLA composites with TCP and OPMC showed flame inhibition and retarded ignition. The synergistic effect of TCP and OPMC resulted in outstanding improvement of impact strength and flame retardancy of composites. The impact toughness of PT10M5 increased to about 218.4 % and 72.3 % that of neat PLA and PT0M5, respectively. Moreover, PT10M5 achieved V-0 rating with high LOI (38.5 %). All these characteristics promise extended applications for PLA composite in bio, circular, and green (BCG) economies and electronics industries.

The piperazine pyrophosphate intumescent flame retardant of polypropylene composites prepared by selective laser sintering

AbstractA highly flame‐retardant PP composite powder suitable for selective laser sintering (SLS) was prepared successfully by mechanical blending, which was composed of pure PP, piperazine pyrophosphate (PPAP), melamine polyphosphate (MPP), and triazine‐based charring‐foaming agent (CFA). The results showed that the flowability of PP composite powder decreased by about 40% and the DSC data indicated the sintering window decreased by about 2°C. Although the flame retardants influenced the processing of SLS, the PP composite powder was still able to be used for printing. The LOI value of PP composites prepared by SLS was 29.2% and the UL‐94 grade was V‐0 rating at the filler loading (16wt% PPAP, 4wt% MPP, 4wt% CFA). The cone calorimeter testing (CCT) data represented that the heat and smoke release significantly decreased. The synergistic effect among flame retardants promoted high‐quality char layers, which is favorable for improving the flame retardancy and thermal stability of PP composites by the test of TGA, SEM, Raman spectra, and FT‐IR. However, the flame retardancy and mechanical properties of PP composites made by SLS were both in varying degrees of decline compared to the ones made by thermo‐compression (TC) because of the higher porosity. An air duct with complex structures was prepared by SLS at last.

Photothermal and fire-safe epoxy/black phosphorene composites: Molecular structure analysis of sutured char

To overcome the high flammability of polymers and endow them with photothermal capability, we fabricate the targeted nanofiller black phosphorus (BP) based SL-EBP-CoP for epoxy. Interestingly, the good ability of photothermal for EP/SL-EBP-CoP2.0 nanocomposite changes with irradiation power can be linearly quantified (r2 > 0.94). Secondly, EP/SL-EBP-CoP2.0 separately reduces peak heat release rate (HRR), total HRR and peak carbon monoxide (CO) production by 59.88%, 39.26% and 36.41% compared with EP, along with the lowest fire growth index. The significantly reduced hazard of heat and CO is attributed to the combined effects of 2D BP, catalysis of CoP and the structure of sutured char. Finally, the pyrolysis of BP-based flame retardants produces P4, P3 and P2 with an abundance of 77.10%, 6.75% and 14.70%. Moreover, flame retardant composites are highly dependent on the final char. This work demonstrates that phosphorus and P-O-P (POx) are nodes and bonding units in the char, POx bonds to the hydrocarbon fragments through P-O-C bonds. Particularly, pyrolysis molecules of suture and rupture of char (CnH2n+2PO4, m/z = 168, 139 and 124) are first discovered. This work booms the path and lays the foundations for the photothermal and fire safety of BP nanocomposites.

Simultaneously improving the flame retardancy and toughness of epoxy composites with hyperbranched phosphorus-containing polysiloxane functionalized halloysite nanotubes

Development of high-performance thermosets with simultaneously improved flame retardancy, toughness and strength but unaffected glass transition temperature (Tg) has been a great challenge. In this work, hyperbranched phosphorus-containing polysiloxane functionalized halloysite nanotubes (HBPPSi-HNTs) were synthesized to prepare flame-retarding, mechanically-strong and tough epoxy composites. The tensile and impact strengths of the composites with 5.0phr HBPPSi-HNTs were improved by 23.7 % and 48.8 % respectively compared with the neat epoxy resin. The epoxy composites also exhibited excellent flame-retardancy due to the instantaneous gas-phase and condensed-phase flame retardant behavior of HBPPSi-HNTs. The composite with 10.0phr HBPPSi-HNTs passed UL-94V-0 rating, with an LOI value as high as 42.6 %. And compared with neat epoxy resin, the peak of heat release rate (PHRR), total heat release (THR), total smoke production (TSP) and CO generated per second (COY) were reduced by 50.1 %, 32.6 %, 30.1 % and 39.5 %, respectively. This work presented a general approach to prepare epoxy composites with simultaneously improved flame retardancy and mechanical properties without sacrificing the glass transition temperature.

Multi-element synergistic effects to improve the flame retardancy of high impact polystyrene

Pure high impact polystyrene (HIPS) is widely used, but it is flammable. During combustion, it produces black smoke, drips, and poses other hazards to human safety, making it necessary to study flame-retardant HIPS. In this study, nitrogen-phosphorus-silicon flame retardants were prepared by using melamine cyanurate (MC), aluminum hypophosphite (ALHP), and nano-silica (nano-SiO2) to improve the flame retardancy of HIPS. The flame retardancy and mechanism of HIPS composites were studied. The results showed that when the ratio of MC to ALHP was 1:4 and nano-SiO2 was 1.5 wt%, the limiting oxygen index (LOI) value of HIPS composite was 26.9%, and PHRR and THR were reduced to 254 kW/m2 and 85 MJ/m2, respectively. The smoke production decreased by 32%, and the carbon residue increased by 70%. ALHP and nano-SiO2 mainly play a flame retardant role in the condensed phase. MC mainly plays a flame retardant role in the gas phase, as well as the condensed phase.

Simultaneously Improving Flame Retardant Performance, Thermal Stability and Conductivity of Copolymers of Polyethylene‐octene by Addition of a Ternary Composite Flame Retardant System

AbstractThe development of high efficiency and low‐cost refractories has always been a subject that attract people‘s attention. Although polyethylene‐octene copolymers (POE) has excellent mechanical properties, it is easy to be ignited, which seriously hinders its multi‐field applications. In this paper, a novel ternary composite flame retardant system, ammonium polyphosphate (APP)/expanded graphite (EG)/sepiolite (SEP), was proposed and applied to POE to prepare high flame‐retardant POE composites. The experimental results showed that the addition of SEP could play a good reinforcing role, so as to improve the mechanical properties of POE/APP composites. Thermogravimetric analysis (TGA) showed that when the ratio of EG and SEP was 1 : 1, the initial thermal decomposition temperature decreased significantly, which was conducive to the early degradation and carbonization of POE/APP composites. The thermal conductivity test showed that the addition of SEP can reduce the thermal conductivity of POE/APP composites. In addition, the flame retardant test results revealed that when the ratio of EG and SEP was 1 : 1, the oxygen index (LOI) increased to 25.3 %, the heat release rate (HRR) decreased to 140 kW/m2, the total heat release (THR) decreased to 70 MJ/m2, and the carbon layer produced by combustion was dense and uniform, which contribute to the great heat insulation. In conclusion, the addition of an appropriate amount of ternary compound flame retardant (EG/SEP/APP) could have an excellent synergistic flame retardant effect on POE/APP composites, and the processing method was simple and efficient, which would benefit to broad application of the prepared POE composites.

Effects of intumescent flame retardant based on THEIC-based oligomeric ester as char forming agent on thermal，mechanical and flame retardant properties of HDPE composites

In this study, a new phosphor-ester (TPE) was prepared by one-spot polycondensation of tris (2-hydroxyethyl) isocyanurate (THEIC) and phenyl phosphonic dichloride (PPDC) and used as a charring agent in combination with ammonium polyphosphate (APP) to develop new intumescent flame retardant (IFR) for high-density polyethylene (HDPE). The thermal and flame retardant properties of composites were investigated by thermogravimetric analysis (TGA), limiting oxygen index measurement (LOI), and cone calorimetry (CCT). At the same time, the morphology and chemical structure of the char residue were analyzed by scanning electron microscopy, Fourier transfer infrared spectroscopy, and laser Raman spectroscopy. The results showed the LOI value of the composite HD/APP/TPE containing 25 wt. % of APP/THE reaches 28.2 %. The CCT test suggested that the peak heat released rate (PHRR) of the flame retardant composite is decreased by 37 % compared to that of pure HDPE. The use of IFR based on APP and TPE produces a compact char residue that acts as a barrier for heat, oxygen, and volatile combustibles and protects the underlying polymer. Besides TPE can produce the PO-type radicals that show some gas phase flame retardant action. However, the tensile strength of the composites is still lower than that of pure polymer.