Intumescent Flame Retardant Polypropylene Composites Research Articles

Preparation and flame retardant properties of organic montmorillonite synergistic intumescent flame retardant polypropylene

Ammonium polyphosphate (APP) and aluminium diethylphosphonate (ADP) were mixed according to the mass ratio of 4:1, compounded with dipentaerythritol (DPER) to construct a novel intumescent flame retardant (IFR), and organo-montmorillonite (OMMT) as a synergistic flame retardant, then melt blended to prepare intumescent flame retardant polypropylene (PP) composites. The flame retardancy, thermal stability, and mechanical properties of flame retardant polypropylene composites were examined using the limiting oxygen index (LOI), vertical combustion test, thermogravimetric analysis, and cone calorimetry test. The results showed that the LOI value of the flame retardant composite PP3 reached 31.3%, UL-94 reached V-0 level, the peak heat release rate (pHRR) and the total heat release (THR) decreased by 87.8% and 33.7%, respectively, compared with the original sample of PP, and the break elongation increased by 216.4% compared with that of the sample PP1 without the addition of OMMT. The findings demonstrated that adding OMMT to IFR in the right dosage can have a positive synergistic flame retardant impact.

Effect of hollow glass microsphere on the processing and flame retardancy of intumescent flame retardant polypropylene composites prepared by selective laser sintering

Effect of hollow glass microsphere on the processing and flame retardancy of intumescent flame retardant polypropylene composites prepared by selective laser sintering

Synergistic effects of zeolitic imidazolate frameworks (ZIFs) with different transition metals on intumescent flame-retarded polypropylene composites: A comparative study

The use of intumescent flame retardants (IFRs) is considered an environmentally friendly and cost-effective strategy to suppress potential fire hazards from synthetic polymers. However, some conventional IFRs are neither efficient in developing a thermally stable char layer nor reducing the release of toxic byproducts during polymer combustion. In this work, we aim to discuss the effects of zeolitic imidazolate frameworks (ZIFs) on synergistically improving the flame retardancy behaviors in polypropylene (PP) composites, including thermal degradation (evolved gas analysis), free radical reactions in the gaseous phase (in-situ chemiluminescent image analysis), and carbonaceous structure in the condensed phase (micro-morphology and composition analysis). It is found that the transition metals in ZIFs can catalytically accelerate the crosslinking reaction at a lower initial temperature and decrease the amount of hydrocarbon volatiles in the gaseous phase. Once ignited, the embedded ZIFs can firstly bridge adjacent phosphorus chains in the polymer matrix to expand crosslinking degrees and then they are anchored in the developed N-doped phospho-carbonaceous networks after pyrolysis. As a result, more compact char residue structures are observed in the condensed phase for ZIF-reinforced composites. For example, by replacing 2 wt% of IFR with ZIF-67, the peak heat release rate, peak smoke production rate, and peak CO production rate are reduced by 69%, 80%, and 72%, respectively, when compared to the conventional composite. These results indicate an excellent solution to resolve inherent fire hazards associated with IFRs in polymers and achieve necessary efficiency for industrial applications. It also provides a new strategy for determining flammability characteristics and combustion mechanisms of polymer composites using in-situ chemiluminescence analysis.

The effect of boric acid on flame retardancy of intumescent flame retardant polypropylene composites including nanoclay

In this study, different amounts of boric acid (BA, 1.25, 2.5, 3.75 and 5.0 wt%) were used to enhance the effectiveness of an intumescent flame retardant (IFR) system composed of ammonium polyphosphate (APP) and pentaerythritol (PER) in polypropylene (PP) including 2 wt% montmorillonite nanoclay (MMT). Meanwhile, metaboric acid and boron oxide which were generated by the decomposition of BA appeared in the melt compounding and the burning processes, respectively. Extensive experimental studies were performed to investigate the effects of BA/boron oxide and MMT combinations on the properties of PP/IFR. The fire resistances of the composites were studied by UL 94, limiting oxygen index (LOI) and cone calorimetry tests. The thermal properties were determined by using thermogravimetric analysis, differential scanning calorimetry and thermal conductivity measurements. In addition, the mechanical properties of the composites were examined. The experimental results revealed that although the additions of 1.25 and 2.5 wt% BA with 2 wt% MMT significantly enhanced thermal and flame resistances of PP composites, 3.75 and 5.0 wt% BA additions generated antagonistic effects and deteriorated the fire resistance of the composites. The sample including 2.5 wt% BA addition achieved the best flame retardancy. The LOI value was increased from 18 to 31% with UL 94 V-0 rating. In addition, the peak heat release rate was reduced from 668.6 to 150.0 kW/m2 and the total heat release value was decreased from 247.9 to 98.4 MJ/m2. In the meantime, the thermal conductivity was increased from 0.22 up to 0.28 W/mK. Furthermore, CO, CO2 and the smoke productions were significantly decreased with respect to PP. NO generation was decreased with BA replacements. At the same time, although there was a slight decrease in the tensile strength, the flexural strength significantly increased with BA and MMT additions.

Intumescent flame retardant behavior of charring agents with different aggregation of piperazine/triazine groups in polypropylene

To explore the structure mode of charring agent with higher flame retardant efficiency, two charring agents (PT-Cluster and PT) with different aggregation structure of piperazine/triazine groups were synthesized and characterized, and then were applied to preparing intumescent flame retardant polypropylene (PP) composites with ammonium polyphosphate (APP). Both PT-Cluster/APP/PP and PT/APP/PP composites performed excellent intumescent flame retardant effects. The values of LOI reached over 32% while the mass ratio of charring agent was only 3 wt% in the case of 25 wt% IFR loading. The pk-HRR values of 5%PT-Cluster/20%APP/75%PP and 5%PT/20%APP/75%PP were 242 kW/m2 and 330 kW/m2, respectively, which were all decreased by over 73% compared with neat PP. Besides, the total heat release (THR) and average effective heat of combustion (av-EHC) of charring agent/APP/PP were also decreased. More importantly, the aggregated piperazine/triazine groups in PT-Cluster further raised the flame retardant efficiency of charring agent/APP system. PT-Cluster/APP system brought higher residue yields and lower THR, av-EHC and total smoke release than PT/APP in cone calorimeter test, implying that PT-Cluster/APP exhibited better charring and barrier effect, and more effective quenching effect than PT/APP during combustion. The enhanced flame retardant effect was resulted by the aggregated piperazine/triazine groups in PT-Cluster. By means of the macromolecular structure of PT-Cluster, more residues were remained in condensed phase and more phosphorus-containing components were released to gas phase. Accordingly, PT-Cluster/APP performed better condensed-phase and gas-phase effects than PT/APP.

Effect of hollow glass microsphere on the flame retardancy and combustion behavior of intumescent flame retardant polypropylene composites

Nowadays, increasing the fire safety of polypropylene (PP) is an important research direction. In this article, the investigation mainly focuses on the effect of hollow glass microsphere (HGM) on improving the fire safety of PP/intumescent flame retardants (IFR) composites. The flame retardancy, smoke suppression and thermal stability of PP/IFR/HGM system were studied by limiting oxygen index (LOI), vertical burning (UL-94), cone calorimeter tests (CCT) and thermogravimetric analysis. All the results demonstrated that the incorporation of HGM into PP/IFR system can clearly improve the fire safety of PP/IFR materials. The result of the LOI can be as high as 36.5% with only 1 wt% HGM and 24 wt% IFR addition. Scanning electron microscope–energy-dispersive spectrometer (SEM–EDS) and CCT results illustrated that during the combustion, HGM would migrate onto the surface of the sample to form a compact char layer and prevent further combustion of the material. Furthermore, the CCT results indicated that HGM can slow down the peak heat release rate (from 94.9 to 61.6 kW/m2) and make the total smoke release (TSR) decrease from 1210 m2/m2 (PP/IFR) to 544 m2/m2 (PP/IFR/HGM), reduced by 55.0%. In addition, HGM can improve the thermal stability of PP/IFR systems.

Fire hazard suppression of intumescent flame retardant polypropylene based on a novel Ni‐containing char‐forming agent

Reducing the fire hazard of polypropylene (PP) is an important research direction in the fields of fire safety materials. In this article, a novel Ni‐containing char‐forming agent (TTPN) was successfully synthesized, using tris(2‐hydroxyethyl) isocyanurate (THEIC), terephthalic acid, and nickel dihydrogen phosphate. Then, TTPN was combined with the silica‐gel microencapsulated ammonium polyphosphate (OS‐MCAPP) to prepare intumescent flame retardant PP composites. From the results of the limiting oxygen index (LOI) test and cone calorimeter, the composite containing 30% IFR (OS‐MCAPP: TTPN = 3:2) shows the highest LOI value of 33.5%, and its peak heat release rate is 275.5 kWm−2, decreased by 79.0% and 37.4% than those of pure PP and the composite containing the char‐forming agent without Ni. Meanwhile, the composite containing TTPN present the best smoke and CO2/CO suppression. The results indicate that TTPN has an excellent ability to dramatically reduce the fire hazard of PP.

Morphology Influence of Nanoporous Nickel Phosphate on Intumescent Flame Retardant Polypropylene Composites

Abstract The morphology of nanoporous nickel phosphate (NP) has a close relationship with its properties, so in this work NP with needle-like and mushroom-like shape was synthesized. Then NP with needle-like and mushroom-like shape was applied in intumescent flame retardant polypropylene (PP) composites. With the addition of suitable content of NP, both mushroom-like and needle-like NP can improve the combustion and thermal properties of intumescent flame retardant PP composites. Needle-like NP shows a better thermal ant flame retardant synergist effect with intumescent flame retardants compared to mushroom-like NP. However, mushroom-like NP shows a better effect on smoke suppression. With the addition of suitable content of needle-like NP, the peak heat release rate of flame retardant PP composite decreases by 68.2 % comparing with that of the pure PP, and decreases by 23.8 % comparing with that of flame retardant PP composite without NP. The maximum weight loss temperature of PP composites can be increased from 408 °C to 485 °C with the addition of needle-like NP. Furthermore, the pyrolysis products of flame retardant PP composite with needle-like NP were investigated. From the research, it provides a further understanding of the influence on synergic effects in intumescent flame retardant systems.

Synthesis and characterization of a novel organic-inorganic hybrid char-forming agent and its flame-retardant application in polypropylene composites

A novel organic-inorganic hybrid char-forming agent (SCTCFA-ZnO) was synthesized and characterized by Fourier transform infrared spectrometry (FTIR) and solid state nuclear magnetic resonance (SSNMR). SCTCFA-ZnO was combined with ammonium polyphosphate (APP) to prepare intumescent flame retardant polypropylene (PP) composites. The flame retardancy and thermal degradation behaviour of composites were investigated by the means of limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test (CONE) and thermogravimetric analysis (TGA). The flame retardant pattern and mechanism of PP composites were studied by thermogravimetric analysis/infrared spectrometry (TG-IR), scanning electron microscopy (SEM), laser Raman spectroscopy analysis (LRS), FTIR and X-ray photoelectron spectroscopy (XPS). The results indicated APP/SCTCFA-ZnO system with the mass ratio of 2:1 showed the best flame retardant properties and smoke suppression performance in PP composites. TGA results showed that APP/SCTCFA-ZnO could clearly improve the thermal stability of composites and promote the char residue formation. The residue analysis results further revealed higher graphitic cross-linking structures containing more P, O, N and Si in PP/APP/SCTCFA-ZnO consequently resulted in more obvious reduction of the combustion and smoke production than PP/APP/SCTCFA/ZnO.

Studies on intumescent flame retardant polypropylene composites based on biodegradable wheat straw

SummaryWheat straw (WS) has numerous advantages compared with traditional bioadditives such as starch and lignin. So in this work, based on WS and silica microencapsulated ammonium polyphosphate, flame retardant polypropylene/wheat straw (WSP) composites were prepared by melted blend method. Flame retardant and thermal properties of WSP composites have been investigated. The results of cone calorimeter show that peaks of heat release rate and total heat release of the flame retardant WSP composite decrease substantially compared with those of pure polypropylene. The peak of heat release rate value of the flame retardant WSP composite decreases from 1290.5 to 247.9 kW/m2, and the total heat release value decreases from 119.4 to 46.3 MJ/m2. Meanwhile, thermal degradation and gas products of the flame retardant WSP composite were monitored by thermogravimetric analysis and thermogravimetric analysis‐infrared spectrometry. The result of thermal analysis shows that the flame retardant WSP composite has a high thermal stability and has a 30.0 wt% residual char at 600°C. From this work, we hope to provide a method to prepare flame retardant polymer composites with a biodegradable natural material‐WS.

Preparation of novel phosphorus-nitrogen-silicone grafted graphene oxide and its synergistic effect on intumescent flame-retardant polypropylene composites.

Due to the poor dispersion in polymer matrix, graphene can hardly be used alone as a flame-retardant additive for polymers. In this paper, a novel halogen-free flame retardant – the ternary graft product of silsesquioxane, graphene oxide and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (PMGO) with a structure of graphene oxide layers modified with the synergistic flame retardant multiple elements of phosphorous, nitrogen and silicon was synthesized and then used in combination with traditional intumescent flame retardant (IFR) to enhance the flame retardancy of polypropylene (PP). The experimental results show that the thermal and flame retardant properties of flame-retardant (FR) PP composites are significantly improved by introducing 5 wt% PMGO as well as 20 wt% IFR. The peak heat release rate and total heat release of the FR PP composite are reduced 61.5% and 40.2%, respectively, compared to neat PP. Based on the char layer observation and thermal analysis, the enhancement in flame retardancy is mainly attributed to the outstanding intumescent char layers with high strength and thermal stability formed under the synergistic effect of PMGO and IFR. Besides, the introduced phosphorous, nitrogen and silicon hydrophilic groups do not show the negative effects on the surface hydrophobicity of flame retardant PP materials, which could broaden its scope of application.

The effects of graphene on the flammability and fire behavior of intumescent flame retardant polypropylene composites at different flame scenarios

This work explores the feasibility of using graphene as an effective synergist for intumescent flame retardant (IFR). The flammability test and fire behavior under different fire scenarios are investigated. The incorporation of graphene results in different responses of IFR/polypropylene (PP) composites to small fire tests and burning under forced-flaming condition. The addition of graphene weakens the reaction of flame retardant PP to small flame. Lower loading of graphene is observed to improve the swelling of char, resulting in better insulation of the char and decrease in heat and smoke release. The further increase of graphene leads to the worsened fire safety. Flame retardant mechanism and model are proposed on the basis of the analyses of thermal decomposition products and process, and melt viscosity change. This works provides a solution to comprehensively assess the synergistic or antagonistic effect of graphene, and will be beneficial to developing its flame retardant mechanism.

Investigation on pyrolysis of intumescent flame-retardant polypropylene (PP) composites based on synchrotron vacuum ultraviolet photoionization combined with molecular-beam mass spectrometry

The pyrolysis of intumescent flame-retardant polypropylene (PP) composites was studied by synchrotron vacuum ultraviolet photoionization combined with molecular-beam mass spectrometry (SVUV-PIMS). Pyrolytic products of intumescent flame-retardant PP composite formed at certain temperature have been identified by the measurement of photoionization mass spectra at different photon energies. By using SVUV-PIMS, some isomers were identified. Meanwhile, the effect of high-efficient flame-retardant synergist–nanoporous nickel phosphate on pyrolytic products of intumescent flame-retardant PP composite was also studied. By analyzing the pyrolysis of the intumescent flame-retardant PP composites with or without the flame-retardant synergist, the synergistic flame-retardant mechanism was discussed as the condensed-phase flame-retardant mechanism not gas flame-retardant mechanism as expected. The studies in this work are much helpful for further understanding the flame-retardant mechanism of intumescent flame-retardant PP composites.

Effects of Zinc Phytate on Flame Retardancy and Thermal Degradation Behaviors of Intumescent Flame-retardant Polypropylene

ABSTRACTIn this paper, zinc phytate was prepared and used as a synergist in intumescent flame-retarded polypropylene composites. The results showed that the polypropylene composites with 17 wt% intumescent flame retardant and 2 wt% zinc phytate have a limiting oxygen index 29.2 and achieve the UL-94 V-0 rating. Moreover, the peak heat release rate of the polypropylene composites decreases from 374 to 275 kW/m2. Real-time Fourier-transform infrared spectroscopy showed that the zinc phytate delays the emission of carbon dioxide indicating that zinc phytate slows the degradation of polypropylene which regulates the suitability of intumescent flame-retardant system in polypropylene.

Functional organoclay with high thermal stability and its synergistic effect on intumescent flame retardant polypropylene

In this work a novel functional modifier for clay with increased thermal stability and synergistic effect on the flame retardancy of intumescent flame retardant polypropylene (IFR PP) composites was developed. First, triphenyl(undec-10-enyl)phosphonium bromide (TPB) was synthesized and characterized by FT-IR and 1H NMR spectroscopy. TPB has a high thermal stability with an initial decomposition temperature of about 270°C. Subsequently, TPB was used to prepare functional organoclay (OC) by cation exchange reaction. OC was characterized by thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). The interlayer distance of novel OC increased to 1.85nm. OC was used in IFR PP nanocomposites prepared by melt mixing. The morphology, thermal stability and fire behavior of these IFR PP nanocomposites were investigated by SEM, TEM, TGA, limiting oxygen index (LOI), vertical burning test (UL94), and cone calorimeter (CC) test. In comparison to IFR (18wt%) PP composites, IFR (16wt%)+OC (2wt%) PP nanocomposites passed the UL94 V-0 rating and showed no dripping. The LOI value decreased from 30.5 to 28.8 due to the use of low molar mass TBP. It was shown by cone calorimeter tests that the additional used of 1 or 2wt% OC leads to a reduced heat release rate, smoke production rate and total smoke production. All these experimental results showed that this novel OC provided an excellent synergistic effect on the flame retardancy of IFR PP composites. Finally, electron beam treatment was used to enhance the thermal stability of flame retardant nanocomposites.

Synergism effect of CeO2 on the flame retardant performance of intumescent flame retardant polypropylene composites and its mechanism

The synergism of CeO2 on the flame retardancy and char-forming mechanism of efficient intumescent flame retardant polypropylene composites (PP/IFR) are investigated. It is found that CeO2 enhances the limited oxygen index (LOI) value of the PP/IFR composites dramatically and the materials pass the vertical burning test (UL-94) V-0 rating test. The catalytic effectivity (CAT-EFF) results show that when 1wt% CeO2 is introduced into PP/IFR composite, it has the highest CAT-EFF, and the LOI value of the composites increases from 27.1 to 32.6%. The presence of CeO2 enhances the fire retardant performance, resulting consequently in a great reduction in peak heat release rate (p-HRR), total heat release (THR), heat release capacity (HRC) of the PP/IFR composite obtained from microscale cone calorimeter (MCC) tests. CeO2 reduces the initial decomposition temperature of the IFR and PP/IFR, and it improves the thermal stability and char formation ability. When CeO2 is incorporated into IFR, it forms numerous closed foams without holes, and the char contains more P. The morphological structures observed by digital photos and scanning electron microscopy (SEM) demonstrated that CeO2 promotes to form the more continuous and more compact intumescent char layer. The Energy dispersive X-ray spectrometry (EDX) results indicate that it remains more P and O elements for PP/IFR/1%CeO2 composite. The Laser Raman spectroscopy (LRS) measurements reveal that the strength of the char residue with CeO2 is enhanced with lower R value. The X-ray photoelectron spectroscopy (XPS) analysis demonstrates that CeO2 helps to form crosslinking network containing more O and P in the char layer. Thus, a suitable amount of CeO2 plays a critical role in the flame retardancy and char-forming behavior of PP/IFR, and promotes the formation of more compact char structures in the PP/IFR composites.

Study of the synergistic effect of nickel phosphate nanotubes (NiPO-NT) on intumescent flame retardant polypropylene composites

The nickel phosphate nanotubes (NiPO-NT) were synthesized by hydrothermal method, and its structure was characterized. Then NiPO-NT was added to intumescent flame retardants system in polypropylene (PP) matrix for the first time,and the synergistic effect of NiPO-NT with intumescent flame retardants was studied. The results show that only small content of NiPO-NT can obviously improve the flame retardant and thermal properties of intumescent flame retardant PP composite. With the addition of 0.3 % NiPO-NT, the peak heat release rate of intumescent flame retardant PP composite decreases from 374.7 to 255.5 kW m−2, and the limit oxygen index value increases from 29.9 to 33.9. Meanwhile, the maximum mass loss temperature under N2 atmosphere is increased from 408 to 483 °C.

Synergistic flame retardant effect of BiFeO3 in intumescent flame‐retardant polypropylene composites

The BiFeO3 was used to intumescent flame retardant (IFR) polypropylene (PP) composites as a synergist. The limiting oxygen index (LOI) and UL‐94 tests indicated that there is an optimum synergistic concentration of BiFeO3 in the PP/IFR composites. Thermogravimetric analysis (TG) results of flame retardant PP showed that the moderate of BiFeO3 can reduce the decomposition rate of sample at high temperatures. TG of APP/PER/BiFeO3 showed that BiFeO3 main affects the third mass loss stage of APP/PER. So the morphology and composition of the char residue of APP/PER/BiFeO3 composites were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and laser Raman spectroscopy (LRS). An appropriate amount of BiFeO3 can react with APP/PER forming BiOP and FeOP bond, and so more P elements was involved in a crosslinking reaction to form more stable char residue, which can effectively increase the flame retardant properties of PP. POLYM. COMPOS., 38:2771–2778, 2017. © 2015 Society of Plastics Engineers

Influence of zinc borate on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites

The influence of zinc borate (ZB) on the flame retardancy and thermal stability of intumescent flame retardant polypropylene composites (PP/IFR) containing ammonium polyphosphate (APP) and charring-foaming agent (CNCA-DA) were characterized by limiting oxygen index (LOI), UL-94 measurement, cone calorimeter test (CCT), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and thermogravimetry analysis (TGA). The results revealed that a small amount of ZB could effectively improve the LOI value, UL rating of the PP/IFR systems, and reduce the combustion performance of PP/IFR systems from CCT test, including heat release rate (HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP). The catalytic effectivity (CAT-EFF) results showed that when 1% ZB was added to PP/IFR, it had the highest CAT-EFF, and could enhance the LOI value from 27.1 to 30.7. The morphological structures observed by digital photos and SEM indicated that ZB could promote to remain more P and O, and B could participate the connecting reaction to form the more continuous and more compact intumescent char layer on the char surface to hinder heat diffusion and oxygen transmission effectively. The TGA data revealed that ZB could change the degradation behavior of the IFR and PP/IFR, improve the thermal stability of the PP/IFR systems at high temperature and increase the char residue.

Synergistic effect of allophane with intumescent flame retardants on thermal behavior and fire retardancy of polypropylene

The effects of allophane (ALL) as a synergistic agent on the flame retardancy and thermal stability of intumescent flame-retardant (IFR) polypropylene composites were studied by limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CONE) and thermogravimetric analysis. The incorporation of ALL led to enhanced thermal stability, LOI value and UL-94 ratings. CONE tests indicated that heat release rate, peak rate of heat release, smoke production rate, total smoke production and mass loss values of PP/IFR/ALL sample were much lower than those of PP/IFR and pure PP samples. Fourier transform infrared spectrometry result proved the presence of silicoaluminophosphate which can act as a catalytic agent to enhance the oxidative dehydration crosslinking charring process. Scanning electron microscopy and Raman spectra observation demonstrated that ALL could promote forming homogenous and compact char layer. The mechanical properties of PP composites were also improved by the loading of ALL.