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.     

Effect of natural basalt fiber for EVA composites with nickel alginate‐brucite based flame retardant on improving fire safety and mechanical properties

The natural basalt fiber (BF) was incorporated into EVA composites with environmental‐friendly nickel alginate‐brucite based flame retardant (NiFR), to further improve the flame‐retardant effect and mechanical properties. The flame retardancy of EVA composites were characterized by LOI, UL 94, and cone test. With 55 wt% loading, 3BF/52NiFR had the highest LOI value of 31.9 vol.% in all fiber reinforced composites and pass UL 94V‐0 ratting. And comparing to 55B composite with untreated brucite, 3BF/52NiFR decreased peak of heat release rate by 47.8%, total heat release by 21.9%, and total smoke production by 35.5% and kept more residue 54.0% during cone test. Moreover, 3BF/52NiFR also enhanced the mechanical properties of composites by better compatibility with EVA matrix. BF/NiFR exert synergistic flame‐retardant effect major in promoting charring effect in condensed phase during combustion. The fire‐resisted and rigid BF into the char layer reinforced the intensity of protective barrier which prolonged the residence time of pyrolysis carbonaceous groups degraded from EVA matrix, resulting in less heat and smoke release.     

Zeolitic imidazolate frameworks‐8 modified graphene as a green flame retardant for reducing the fire risk of epoxy resin

A novel hybrid material of ZIF‐8/RGO (zeolitic imidazolate frameworks‐8 loaded the surface of graphene) was synthesised by a simple method and characterized. Then, ZIF‐8/RGO was added into epoxy resin (EP), and the flame retardancy and smoke suppression of the EP composites were studied. Compared with pure EP, the peak heat release rate and the total heat release of the EP composites were reduced remarkably, and their LOI and UL94 vertical burning rating were also improved. In addition, their smoke production rate and total smoke production were decreased drastically. The improved flame retardancy and smoke suppression were mainly attributed to the physical barrier effect of graphene. Meanwhile, the metal oxide decomposed from ZIF‐8 could contribute to the production of char residue and enhance the compactness of the char layer.     

Flame retardancy mechanisms of poly(1,4‐butylene terephthalate) containing microencapsulated ammonium polyphosphate and melamine cyanurate

The flame retardancy mechanisms of poly(1,4‐butylene terephthalate) (PBT) containing microencapsulated ammonium polyphosphate (MAPP) and melamine cyanurate (MC) were investigated via pyrolysis analysis (thermogravimetric analysis (TGA), real‐time Fourier transform infrared (FTIR), TG‐IR), cone calorimeter test, combustion tests (limited oxygen index (LOI), UL‐94), and residue analysis (scanning electron microscopy (SEM)). A loading of 20 wt% MC to PBT gave the PBT composites an LOI of 26%, V‐2 classification in UL‐94 test and a high peak heat release rate (HRR) in cone calorimeter test. Adding APP to PBT/MC composites did not improve their flame retardancy. In comparison with the addition of ammonium polyphosphate (APP) to PBT, MAPP with silica gel shell and MAPP with polyurethane shell both promoted the intumescent char‐forming and improved the flame retardancy of PBT through different mechanisms in the presence of MC. These two halogen‐free PBT composites with V‐0 classification according to UL‐94 test were obtained; their LOI were 32 and 33%, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

A novel intumescent flame‐retardant LDPE system and its thermo‐oxidative degradation and flame‐retardant mechanisms

A carbonization agent, 3,9‐di (2‐hydroxyisopropyl)‐2,4,8,10‐tetraoxa‐3,9‐diphosphaspiro‐[5,5]‐undecane (SPEPO), was synthesized from pentaerythritol (PER), phosphorus trichloride, formic acid, and acetone as raw materials. The structure of SPEPO was characterized by FTIR and ¹H‐NMR. As a carbonization agent and an acid source, SPEPO can form a novel intumescent flame‐retardant (IFR) system for low density polyethylene (LDPE) together with ammonium polyphosphate (APP) and melamine phosphate (MP). The flame retardancy and thermal behavior of the IFR system for LDPE were investigated by limiting oxygen index (LOI), UL‐94 test, and thermogravimetric analysis (TGA). When the weight ratio of SPEPO, APP, and MP is 7:7:1 and their total loading level is 30%, the IFR‐LDPE presents the optimal flame retardancy (LOI value of 27.6 and UL‐94 V‐0 rating). However, SPEPO, APP, or MP can only show a very poor flame‐retardant performance when used alone. This indicates that there is a synergistic effect among SPEPO, APP, and MP. TGA results obtained in air demonstrate that SPEPO has an ability of char formation itself, and the char residue of SPEPO can reach 24 wt% at 700°C. The IFR can change the thermal degradation behavior of LDPE, enhance T_max of the decomposition peak of LDPE, and promote LDPE to form char based on the calculated and the experimental data of residues. According to the results of Py‐GC/MS in combination with FTIR of the char residues at different temperatures, a possible flame‐retardant mechanism has been proposed. Copyright © 2008 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.     

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.     

Flame‐retardant performance and mechanism of epoxy thermosets modified with a novel reactive flame retardant containing phosphorus,nitrogen, and sulfur

A novel phosphorus‐containing, nitrogen‐containing, and sulfur‐containing reactive flame retardant (BPD) was successfully synthesized by 1‐pot reaction. The intrinsic flame‐retardant epoxy resins were prepared by blending different content of BPD with diglycidyl ether of bisphenol‐A (DGEBA). Thermal stability, flame‐retardant properties, and combustion behaviors of EP/BPD thermosets were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), limited oxygen index (LOI) measurement, UL94 vertical burning test, and cone calorimeter test. The flame‐retardant mechanism of BPD was studied by TGA/infrared spectrometry (TGA‐FTIR), pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS), morphology, and chemical component analysis of the char residues. The results demonstrated that EP/BPD thermosets not only exhibited outstanding flame retardancy but also kept high glass transition temperature. EP/BPD‐1.0 thermoset achieved LOI value of 39.1% and UL94 V‐0 rating. In comparison to pure epoxy thermoset, the average of heat release rate (av‐HRR), total heat release (THR), and total smoke release (TSR) of EP/BPD‐1.0 thermoset were decreased by 35.8%, 36.5% and 16.5%, respectively. Although the phosphorus content of EP/BPD‐0.75 thermoset was lower than that of EP/DOPO thermoset, EP/BPD‐0.75 thermoset exhibited better flame retardancy than EP/DOPO thermoset. The significant improvement of flame retardancy of EP/BPD thermosets was ascribed to the blocking effect of phosphorus‐rich intumescent char in condensed phase, and the quenching and diluting effects of abundant phosphorus‐containing free radicals and nitrogen/sulfur‐containing inert gases in gaseous phase. There was flame‐retardant synergism between phosphorus, nitrogen, and sulfur of BPD.     

Synergistic effect of boron containing substances on flame retardancy and thermal stability of clay containing intumescent polypropylene nanoclay composites

The functions of nanoclay and three different boron containing substances, zinc borate (ZnB), borophosphate (BPO₄), and boron silicon containing preceramic oligomer (BSi), were studied to improve the flame retardancy of polypropylene (PP)‐nanoclay‐intumescent system composed of ammonium polyphosphate (APP) and pentaerythritol (PER). The flame retardancy of PP composites was investigated using limiting oxygen index (LOI), UL‐94 standard, thermogravimetric analysis (TGA), and cone calorimeter. According to the results obtained, the addition of 20 wt% intumescent flame retardant (IFR) improved the flame retardancy by increasing the char formation. Addition of clay slightly increases the LOI value and reduces the maximum heat release rate (HRR). Addition of clay also increases the barrier effect due to intumescent char, especially in thin samples. Boron compounds show their highest synergistic effect at about 3 wt% loading. According to UL‐94 test and LOI test, 3 wt% ZnB containing composite shows the highest rating (V0) and BPO₄ containing sample shows the highest LOI value (26.5). Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal stability and flame retardancy of PET/magnesium salt composites

Nano-Mg(OH)₂ (nanometre magnesium hydroxide, nano-MH) was successfully introduced into the esterification and polycondensation system by in situ polymerization to obtain PET/magnesium salt composites (PETMS). The thermal properties and flame retardancy of PETMS were investigated by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UL-94 vertical burning and limited oxygen index (LOI) test. The DSC and TGA results show that magnesium salts in the PET matrix have little effect on the thermal properties of PET, but a significant effect on the thermal stabilities of the composites. The results of LOI and UL-94 test show PETMS have higher LOI values (≥25%) and V-0 rating without melt dripping in the UL-94 test, indicating that PETMS have good flame retardancy and anti-dripping property. Moreover, the residues of magnesium salts and composites after TGA test were also studied by Fourier transform infrared spectroscopy (FTIR) to better understand the mechanism of flame retardancy, which reveals that magnesium salts accelerate the degradation of PET and catalyze the formation of char. The SEM results show the morphological structures of the char effectively protect the composites’ internal structures and inhibit the heat, smoke transmission and reduce the fuel gases when the fire contacts them.     

Synergistic effects of β‐cyclodextrin containing silicone oligomer on intumescent flame retardant polypropylene system

The effects of β‐cyclodextrin containing silicone oligomer(CDS), as a synergistic agent, on the flame retardancy and mechanical properties of intumescent flame retardant polypropylene composites were studied by adding different amounts of CDS in intumescent flame retardants. The limiting oxygen index (LOI), UL‐94 test, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) were utilized to evaluate the synergistic effects of CDS in the composites. It was found that after a little amount of CDS partially replaced a charring‐foaming agent (CFA) in IFR, LOI values of the composites were enhanced and they obtained a UL‐94 V‐0 rating. IFR system containing 6.25wt% CDS presented the best flame retardancy in PP. The experimental results obtained from LOI and UL‐94, TGA, SEM, and mechanical properties indicated that the combination of CDS and CFA presents synergistic effects in flame retardancy, char formation, and mechanical properties of the composites. This is probably due to different structures of polyhydroxyl macromolecules (CDS and CFA), the existence of dimethyl silicone group in CDS, and the toughness of epoxy silicon chain in CDS. SEM results proved that the interfacial compatibility between IFR and PP was improved by CDS. Copyright © 2009 John Wiley & Sons, Ltd.     

Synergistic effects of 4A zeolite on the flame retardant properties and thermal stability of a novel halogen‐free PP/IFR composite

The synergistic effects of 4A zeolite (4A) on the thermal degradation, flame retardancy and char formation of a novel halogen‐free intumescent flame retardant polypropylene composites (PP/IFR) were investigated by the means of limiting oxygen index (LOI), vertical burning test (UL‐94), digital photos, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), cone calorimeter test (CCT), laser Raman spectroscopy (LRS) and X‐ray photoelectron spectroscopy (XPS). It was found that a small amount of 4A could dramatically enhance the LOI value of the PP/IFR systems and the materials could pass the UL‐94 V‐0 rating test. Also, it could enhance the fire retardant performance with a great reduction in combustion parameters of PP/IFR system from CCT test. The morphological structures observed by digital and SEM photos revealed that 4A could promote PP/IFR to form more continuous and compact intumescent char layer. The LRS measurement, XPS and TGA analysis demonstrated that the compactness and strength of the outer char surface of the PP/IFR/4A system was enhanced, and more graphite structure was formed to remain more char residue and increase the crosslinking degree. Copyright © 2013 John Wiley & Sons, Ltd.     

Synergistic effects of cerium phosphate and intumescent flame retardant on EPDM/PP composites

An intumescent flame retardant system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) was used for flame retarding ethylene–propylene–diene‐modified elastomer (EPDM)/polypropylene (PP) blends. Cerium phosphate (CeP) was synthesized and the effect on flame retardancy and thermal stability of EPDM/PP composites based on intumescent flame retardant (IFR) were studied by limiting oxygen index (LOI), UL‐94, and thermogravimetic analysis (TGA), respectively. Scanning electron microscopy (SEM) and Fourier transform infrared spectrometry (FTIR) were used to analyze the morphological structure and the component of the residue chars formed from the EPDM/PP composites, and the mechanical properties of the materials were also studied. The addition of CeP to the EPDM/PP/APP/PER composites gives better flame retardancy than that of EPDM/PP/APP/PER composites. TGA and RT‐FTIR studies indicated that an interaction occurs among APP, PER, and EPDM/PP. The incorporation of CeP improved the mechanical properties of the materials. Copyright © 2010 John Wiley & Sons, Ltd.     

Modified boron nitride as an efficient synergist to flame retardant natural rubber: preparation and properties

A new flame retardant system with organic modified boron nitride (m‐BN) and intumescent flame retardant (IFR) was used in this paper, and the synergistic flame retardancy of m‐BN and IFR on natural rubber (NR) was studied. NR/IFR/m‐BN composites were characterized by X‐ray photoelectron spectroscopy(XPS), Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis, UL‐94, limiting oxygen index (LOI), tensile testing, cone calorimeter testing, and thermal conductivity testing. When 4 wt% m‐BN was added, the flame retardancy and mechanical properties of the composites were improved. The LOI value of NR/IFR/4 phr m‐BN reached 26.8%, and suppressed fire spread in a UL‐94 test. Compared with pure NR, the peak heat release rate (pHRR) was reduced by 52.2%, the total heat release (THR) was reduced by 27.6%, and CO yields were reduced by 51.4%. As a key aspect of fire safety, the ignition time is effectively delayed to 23 seconds due to the increased thermal conductivity of NR/IFR/m‐BN. Since the synergistic effect of m‐BN effectively improves the flame retardancy of NR, it provides a feasible method for improving the fire safety of polymers.     

Flame retardancy and smoke suppression of molybdenum trioxide doped magnesium hydrate in flexible polyvinyl chloride

In this paper, an effective flame retardant consisting of hierarchical magnesium hydrate (MH) nanosheets doped with molybdenum trioxide nanoparticles (MO@MH) was successfully synthesized via a hydrothermal process. Then, MO@MH, MH, and MH/MO were respectively incorporated into flexible polyvinyl chloride (fPVC) to prepare a series of composites via melt blending. The results of limiting oxygen index (LOI), UL‐94, and cone calorimetry test showed that MO@MH exhibited better flame retardancy and smoke suppression than MH and MH/MO due to the synergistic effect of MO and MH, and the hierarchical structure of MO@MH. With the addition of 20 phr MO@MH, LOI value of fPVC was increased from 23.9% to 33.8% , and UL‐94 reached V0 rating. The peak heat release rate, total heat release, peak smoke production rate, and total smoke production were decreased to 143.0 kW/m², 44.9 MJ/m², 0.0093 m²/s and 29.4 m², respectively. The thermogravimetric analysis results suggested that MO@MH greatly promoted the dehydrochlorination of fPVC at lower temperature, so that more compact and continuous char residues were formed. The Fourier transform infrared spectroscopy results indicated that MO@MH can prevent chain scission and oxidation of fPVC carbonaceous backbone, and as a result less smoke was released.     

Combustion properties and thermal degradation behavior of polylactide with an effective intumescent flame retardant

An intumescent flame retardant spirocyclic pentaerythritol bisphosphorate disphosphoryl melamine (SPDPM) has been synthesized and its structure was characterized by Fourier transformed infrared spectrometry (FTIR), ¹H and ³¹P nuclear magnetic resonances (NMR). A series of polylactide (PLA)-based flame retardant composites containing SPDPM were prepared by melt blending method. The combustion properties of PLA/SPDPM composites were evaluated through UL-94, limiting oxygen index (LOI) tests and microscale combustion calorimetry (MCC) experiments. It is found that SPDPM integrating acid, char and gas sources significantly improved the flame retardancy and anti-dripping performance of PLA. When 25 wt% flame retardant was added, the composites achieved UL-94 V0, and the LOI value was increased to 38. Thermogravimetric analysis (TGA) showed that the weight loss rate of PLA was decreased by introduction of SPDPM. In addition, the thermal degradation process and possible flame retardant mechanism of PLA composites with SPDPM were analyzed by in situ FTIR.     

Roles of organic intercalation agent with flame retardant groups in montmorillonite (MMT) in properties of polypropylene composites

Three kinds of organic intercalation agent containing flame retardant groups, melamine (MA), triphenylphonium (TPP) chloride, and tetradecyl trihexyl phosphonium (TTP) bromide were intercalated into montmorillonite (MMT) via cation exchange reactions. These modified MMTs are combined with intumescent systems and compounded with PP. The flame retardant and thermal properties of the PP composites are studied. The organic intercalation agents in the layers of MMT play important roles in the char formation and flame retardant properties of PP composites. MA shows a better performance in limiting oxygen index (LOI) value and TPP helps to increase UL‐94 properties, whereas TTP maintains or deteriorates the flame retardancy of polypropylene/intumescent flame retardant (IFR) composites. The LOI and UL‐94 properties increase firstly and then decrease as the content of MMT increases. The MA acts as a blowing agent and emits an inert gas to provide migration impetus, which results in a better intumescent structured and stronger char to endure heat erosion. Although TPP and TTP emit combustible gas that burn, especially for TTP as it has a more flammable aliphatic chain. The synergistic effect between MA‐MMT and IFR is better than that for TPP‐MMT and TTP‐MMT. 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 retardancy and smoke suppression of silicone foams with microcapsulated aluminum hypophosphite and zinc borate

The flame‐retardant microcapsules were successfully fabricated with an aluminum hypophosphite (AHP) core. Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) were used to verify that AHP was encapsulated in the microcapsules, and thermogravimetry analysis showed that microencapsulated AHP (MAHP) possessed higher thermal stability than that of AHP. Then, a flame‐retardant and smoke suppression system for silicone foams (SiFs) was obtained through a synergistic effect of MAHP and zinc borate (2ZnO·3B₂O₃·3.5H₂O). The mechanical properties, flame retardance, and smoke suppression of SiFs with MAHP and zinc borate were tested using the tensile test, limiting oxygen index (LOI) test, UL‐94 test, and cone calorimeter test. The mechanical properties indicated that the tensile strength and elongation at break of SiFs could evidently improve with the incorporation of MAHP. Compared with pure SiF, SiF8 with 4.5‐wt% MAHP and 1.5‐wt% zinc borate could achieve an LOI value of 30.7 vol% and an UL‐94 V‐0 rating, the time to ignition amplified almost six times, the peak heat release rate and total heat release were 51.10% and 46.00% less than that of pure SiF, respectively, the fire performance index increased nearly 13 times, and the fire growth index value was only 13.18% of pure SiF. Moreover, the partial substitution of zinc borate imparted a substantial improvement in both flame retardancy and smoke suppression. Especially, the peak smoke production rate and total smoke production of SiF8 were merely 38.46% and 38.84% of pure SiF.     

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.