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.     

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.     

Preparation and properties of an efficient smoke suppressant and flame‐retardant agent for thermoplastic polyurethane

APP@ETA, as a new type of flame retardant, was prepared by chemically modifying ammonium polyphosphate (APP) with ethanolamine (ETA) and applied to thermoplastic polyurethane (TPU) in this study. Then, the smoke suppression properties and flame‐retardant effects of APP@ETA in TPU composites were evaluated using smoke density test, cone calorimeter test, etc. And, the thermal degradation properties of flame‐retardant TPU composites were investigated by thermogravimetric analysis/infrared spectrometry. The smoke density test results indicated that APP@ETA could obviously improve the luminous flux of TPU composites in the test with or without flame. The cone calorimeter test results showed that total smoke release, smoke production rate and smoke factor of the composites with APP@ETA were significantly decreased than those of the composites with APP. For example, when the loading of APP@ETA or APP was 12.5 wt%, the total smoke release of the sample with APP@ETA decreased to 3.5 m²/m² from 6.0 m²/m², which was much lower than that of the sample with APP, reduced by 41.7%. The thermogravimetric analysis results demonstrated that APP@ETA could decrease the initial decomposition temperature and improve the thermal stability at high temperature for TPU composites. Copyright © 2017 John Wiley & Sons, Ltd.     

Mechanical and flame‐retardant properties and thermal decomposition of vinyl ester resin modified by different phenyl silsesquioxanes

The mechanical properties and fire resistance of vinyl ester resin (VER) composites containing cage‐shaped octaphenyl silsesquioxane (OPS), incompletely cage‐shaped phenyl silsesquioxane (PhT₇POSS), and ladder‐shaped phenyl silsesquioxane (PPSQ) were investigated. The POSS structure and dispersion have a great influence on the mechanical properties, thermal stability, and decomposition process of VER composites. The bending strength at break and modulus of the VER‐POSS composites were enhanced obviously, especially for VER‐PPSQ composite and VER‐OPS composite, respectively. In addition, PhT₇POSS‐based VER composites revealed the lower values of the peak heat release rate, total heat release, and total smoke release in cone calorimetry tests due to the formation of dense carbon/silica protective layers that acted as a barrier to heat and mass transfer. Moreover, the flame‐retardant mechanisms of condensed phase and gas phase were also investigated in detail. These results illustrate VERs modified by OPS, PhT₇POSS, and PPSQ are providing an applicable method to fabricate the composites with excellent flame‐retardant and mechanical properties.     

Hugely enhanced flame retardancy and smoke suppression properties of UHMWPE composites with silicone‐coated expandable graphite

In this paper, silicone‐coated intumescent flame retardants was prepared by an efficient and simple approach, aiming at enhancing the flame‐retardant efficiency and smoke suppression properties. The surface of expandable graphite (EG) was treated prior to the coverage of nonflammable silicone. The resultant silicone‐modified EG hybrid (SEG) was combined with ammonium polyphosphate (APP) and applied as a flame‐retardant and smoke‐suppressant for ultrahigh molecular weight polyethylene (UHMWPE). Compared with UHMWPE/APP/EG (with 15 wt% APP/EG), UHMWPE/APP/SEG (with 15 wt% APP/SEG) gives decrement by 18.5% in the peaks of the heat release rate, 6.33% in total heat release and 13.6% in total smoke release, whereas increment by 23% in tensile strength and 12.1% in elongation at break, respectively. It is suggested that the introduction of silicone on the surface of EG can improve the interfacial compatibility between EG and UHMWPE. Moreover, it can lead to forming more char residue and reducing the release of smoke particulates during combustion process of the composites.     

Effects of graphene nanosheets decorated by cerium stannate on the enhancement of flame retardancy and mechanical performances of flexible polyurethane foam composites

As one of the most used polyurethane, flexible polyurethane foam (FPUF) still confronted highly flammable problems. However, current flame retardant employed in FPUF deteriorated the other utilization performances, such as mechanical properties. In this work, cerium stannate decorated graphene nanosheets (GNS@Ce₂Sn₂O₇, GCSO) was prepared to fabricate flame retardant FPUF composites. Compared to pure FPUF, the tensile strength and average compression strength of FPUF composites accomplished 100 and 412% increase, respectively, while the average rebound was basically maintained. In contrast to pure FPUF, total heat release and total smoke production of FPUF composites displayed a 42.2 and 75.1% reduction, respectively. Furthermore, the released toxic gases (such as, CO₂, CO and NO_x) during combustion were greatly decreased. These results were due to the catalytic and barrier effect of GCSO promoting the formation a high-quality char residue with a compact, intact and dense morphology. Therefore, it provides a facile method to fabricate FPUF composites with advanced comprehensive performance for the furniture field.     

纳米阻燃高分子材料:现状、问题及展望

纳米阻燃体系是一种新型的聚合物阻燃体系,被誉为阻燃技术的革命.极少量(≤5wt%)纳米阻燃剂的加入即能显著降低高分子材料燃烧时的热释放速率(HRR)和烟密度(SEA),延缓其燃烧过程,还能不同程度地提高材料的力学性能.本文总结了近年来国内外纳米阻燃领域的进展,介绍了本课题组在纳米阻燃方面所做的工作,探讨了纳米阻燃研究中存在的问题,并对其未来的发展进行了展望.     

Thermal degradation and flame retardancy of fumaric acid in thermoplastic polyurethane elastomer

In this paper, fumaric acid (FA) which was a new type of environmental and low‐cost flame retardant was applied for thermoplastic polyurethane elastomer (TPU). The flame‐retardant properties of TPU were tested using limiting oxygen index, cone calorimeter test, smoke density test, and thermogravimetric/Fourier transform infrared spectroscopy. It has been proved that FA could improve the difficulty of the ignition of the sample; the limiting oxygen index value of the sample (FA‐4) increased by 29.7% when 2.0 wt% FA was added to TPU. The cone calorimeter test showed that FA can greatly reduce heat release and smoke production during the combustion process of TPU composites. For example, compared with the pure TPU, the peak heat release rate and total smoke release of the sample (FA‐4) with 2.0 wt% FA were decreased by 50.8% and 51.5% respectively. The results of smoke density test showed that the luminous flux of the samples contained 0.5 wt% FA was increased by 79.2% compared with the pure TPU. The TG results revealed that the sample of FA‐4 had higher char residue content compared with the sample of TPU. The results of thermogravimetric/Fourier transform infrared spectroscopy proved that FA could decrease the initial decomposition temperature for TPU composites and increase the release of CO₂ and H₂O. All results of test illustrated that FA had good flame‐retardant effect on TPU.     

Flame retarded polymer nanocomposites: Development,trend and future perspective

Polymer nanocomposites are a new class of flame retarded materials which have attracted much attention and considered as a revolutionary new flame retardant approach.A very small amount of nano flame retardants (normally < 5 wt%) can significantly reduce the heat release rate (HRR) and smoke emission (SEA) during the combustion of polymer materials.Moreover,the addition of nano flame retardants can also improve the mechanical properties of polymer materials compared with the deterioration of traditional fla...     

Effect of boric acid on properties of high‐alumina phosphate‐bonded plastic refractory materials

The effect of boric acid on the properties of high‐alumina phosphate‐bonded plastic refractory materials at medium temperature is investigated in this work. Powder X‐ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TG/DTA), and scanning electron microscopy (SEM) techniques are used to investigate the compositions and microstructures of the Al₂O₃–H₃BO₃ sintering products, in order to study the influence of the generated aluminum borate on the high‐aluminum refractories. Additionally, the effect of the addition of H₃BO₃ on the densification and mechanical strength of high‐aluminum phosphate‐bonded plastic refractories is studied by the permanent linear change, apparent porosity, cold compressive strength, flexural strength, and scanning electron microscopy pattern. The densification and mechanical strength of the refractories can be improved significantly by the optimal addition of H₃BO₃. However, excess H₃BO₃ will bring about a large amount of bound water into the refractories, and superabundant aluminum borate whiskers will be generated by the excess addition of H₃BO₃, both of them resulting in the reduction of the densification and mechanical strength of the refractory. In conclusion, the optimum dosages of H₃BO₃ in the powder system of high‐alumina phosphate‐bonded plastic refractories are 5, 4, and 3 wt%, sintered at 700, 900, and 1100 °C, respectively.     

The study of mechanical behavior and flame retardancy of castor oil phosphate-based rigid polyurethane foam composites containing expanded graphite and triethyl phosphate

The goal of this work was the synthesis of novel flame-retarded polyurethane rigid foam with a high percentage of castor oil phosphate flame-retarded polyol (COFPL) derived from renewable castor oil. Rigid flame-retarded polyurethane foams (PUFs) filled with expandable graphite (EG) and diethyl phosphate (TEP) were fabricated by cast molding. Castor oil phosphate flame-retarded polyol was derived by glycerolysis castor oil (GCO), H₂O₂, diethyl phosphate and catalyst via a three-step synthesis. Mechanical property, morphological characterization, limiting oxygen index (LOI) and thermostability analysis of PUFs were assessed by universal tester, scanning electron microscopy (SEM), oxygen index testing apparatus, cone calorimeter and thermogravimetric analysis (TGA). It has been shown that although the content of P element is only about 3%, the fire retardant incorporated in the castor oil molecule chain increased thermal stability and LOI value of polyurethane foam can reach to 24.3% without any other flame retardant. An increase in flame retardant was accompanied by an increase in EG, TEP and the cooperation of the two. Polyurethane foams synthesized from castor oil phosphate flame-retarded polyol showed higher flame retardancy than that synthesized from GCO. The EG, in addition to the castor oil phosphate, provided excellent flame retardancy. This castor oil phosphate flame-retarded polyol with diethyl phosphate as plasticizer avoided foam destroy by EG, thus improving the mechanical properties. The flame retardancy determined with two different flame-retarded systems COFPL/EG and EG/COFPL/TEP flame-retarded systems revealed increased flame retardancy in polyurethane foams, indicating EG/COFPL or EG/COFPL/TEP systems have a synergistic effect as a common flame retardant in castor oil-based PUFs. This EG/COFPL PUF exhibited a large reduction of peak of heat release rate (PHRR) compared to EG/GCO PUF. The SEM results showed that the incorporation of COFPL and EG allowed the formation of a cohesive and dense char layer, which inhibited the transfer of heat and combustible gas and thus increased the thermal stability of PUF. The enhancement in flame retardancy will expand the application range of COFPL-based polyurethane foam materials.     

Influence of flame retardant additives on the processing characteristics and physical properties of ABS

Antimony trioxide (Sb₂O₃) is a common additive in flame retardant formulations and a study has been made to determine the effects of adding different grades into ABS polymer either alone or with commercial brominated materials bis(Tribromophenoxy)ethane (BTBPE) or Tetrabromobisphenol A (TBBA). The results consider mechanical, microscopical and flame retardant properties, and the effects of different Sb₂O₃ grades with average particle sizes of 0.1μm, 0.52μm and 1.31μm. The Sb₂O₃ was added at 4wt% loadings and the bromines at 20wt% loadings. Additions of different grades of antimony trioxide showed that standard grades (0.52 and 1.31μm) had a detrimental effect on impact and flexural properties when added at a 4wt% loading. The use of a new sub‐micron particle size product (0.1μm) had little effect on impact properties and only a slight detrimental effect on the flexural modulus and flexural strength when added to the ABS. Additions of either of the two brominated materials also caused a large drop in impact properties when added at 20wt% loadings. The addition of TBBA BA‐59P into ABS caused an increase in both flexural modulus and flexural strength which was contrary to expectations. When formulated with 4wt% 1.31μm Sb₂O₃ these bromine containing compounds suffered a further reduction in impact energies. Using the 0.1μm material improved both impact and flexural properties but impact values were still below those of unfilled ABS. The addition of the 0.1μm grade resulted in improvements in fire resistance as measured by the UL‐94 properties.     

Synergistic effect of bismuth oxide and mono‐component intumescent flame retardant on the flammability and smoke suppression properties of epoxy resins

A novel mono‐component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS)‐hybrid bismuth oxide (PPMS‐Bi₂O₃) was synthesized and carefully characterized by FTIR, ¹H NMR, ³¹P NMR, SEM‐EDS, and TG analyses. Then, PPMS‐Bi₂O₃ was utilized as flame retardant for epoxy resins (EPs), and the thermal stability, flame retardancy, and smoke suppression properties of EP composites were investigated. TG results show that PPMS‐Bi₂O₃ is more conducive to enhance the thermal stability and char forming ability of EP composites compared with the same addition of PPMS or the mixture of PPMS and Bi₂O₃, and this positive effect is enhanced with the increasing Bi₂O₃ content. Cone calorimeter test reveals that the PPMS‐Bi₂O₃ can effectively reduce the heat release and smoke production in comparison with PPMS or the mixture of PPMS and Bi₂O₃ due to the formation of a more compact and intumescent char against fire, as judged by digital photographs and SEM images. EDS analysis indicates that the combination PPMS and Bi₂O₃ by hydrogen bonds promotes to generate more phosphorus‐rich and aromatization structures in the condensed phase that enhance the barrier effect and anti‐oxidation ability of the char, thus imparting higher flame retardant and smoke suppression efficiencies to EP composites.     

Highly efficient multielement flame retardant for multifunctional epoxy resin with satisfactory thermal,flame‐retardant,and mechanical properties

Multifunctional epoxy resins with excellent, thermal, flame‐retardant, and mechanical properties are extremely important for various applications. To solve this challenging problem, a novel highly efficient multielement flame retardant (PMSBA) is synthesized and the flame‐retardant and mechanical properties of modified epoxy resins are greatly enhanced without significantly altering their and thermal properties by applying the as‐synthesized PMSBA. The limiting oxygen index value reaches up to 29.6% and could pass the V‐0 rating in the UL‐94 test with even low P content (0.13%). Furthermore, cone calorimetry results demonstrate that 30.3% reduction in the peak heat release rate for the sample with 10.0 wt% PMSBA is achieved. X‐ray photoelectron spectroscopy and scanning electron microscopy indicate that Si‐C, Si‐N, and phosphoric acid derivative can be transformed into a multihole and intumescent char layer as an effective barrier, preserving the epoxy resin structure from fire. More importantly, mechanical properties such as impact strength, tensile strength, and flexural strength are also increased by 63.86%, 33.54%, and 15.65%, respectively, which show the incorporation of PMSBA do not deteriorate the mechanical properties of modified epoxy resins. All the results show that PMSBA is a promising strategy for epoxy resin with satisfactory, thermal, flame‐retardant, and mechanical properties.     

Effect of Fe3O4‐doped sepiolite on the flammability and thermal degradation properties of epoxy composites

As‐received sepiolite/epoxy systems and Fe₃O₄‐doped sepiolite/epoxy systems were prepared, and the contents of sepiolite and Fe₃O₄‐doped sepiolite were kept as 2 and 4 wt%, respectively. Compared with sepiolite, the effect of Fe₃O₄‐doped sepiolite on the flame retardancy, combustion properties, thermal degradation, thermal degradation kinetics and thermomechanical properties of epoxy resin was investigated systematically by limiting oxygen index (LOI), cone calorimeter (Cone), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Some interesting results had been acquired. The addition of sepiolite decreased heat release rate, total smoke production and smoke production rate, and obviously improved LOI values of epoxy composites. Compared with sepiolite, the addition of Fe₃O₄‐doped sepiolite further reduced parameters mentioned above of epoxy composites, and further enhanced LOI values and char residues after cone test. There might be a synergistic effect between sepiolite and Fe₃O₄ on flame retardant epoxy composite. TGA results indicated that the addition of sepiolite had a slight effect on the thermal degradation of epoxy composites; however, the addition of Fe₃O₄‐doped sepiolite accelerated the thermal degradation of epoxy composites. DMA results showed that the addition of both sepiolite and Fe₃O₄‐doped sepiolite increased the glass transition temperature (T_g) of epoxy composite. The results obtained in this paper supplied an effective solution for developing excellent flame retardant properties of polymeric materials. Copyright © 2015 John Wiley & Sons, Ltd.     

Construction of crosslinking network structures by adding ZnO and ADR in intumescent flame retardant PLA composites

Different proportion of nano zinc oxide (nano ZnO) and chain extender (ADR) were combined with the intumescent flame retardant and then added into the PLA matrix. The thermal stability, flame retardant performance, and mechanical properties were studied. The gel content results showed that crosslinking structures were obtained after the addition of nano ZnO and ADR, which were generated by the catalytic chain scission effect of nano ZnO and chain extension effect of ADR. With addition of 1% nano ZnO and 1.6% ADR, the gel content of flame retardant PLA composite reached the highest value (14.2%). Meanwhile, the corresponding flame retardant PLA composite with 1% nano ZnO and 1.6% ADR, named FRPLA/ZnO/ADR-1, exhibited an overall improved properties including the flame retardant properties and mechanical performance, which passed the UL94 V-0 level with a limiting oxygen index value of 40.1%. Compared to FRPLA (flame retardant PLA without ZnO and ADR), the peak heat release rate and the total smoke production of FRPLA/ZnO/ADR-1were reduced by 60% and 67% respectively, and the final mass improved from 12% to 38%. In addition, the tensile strength and elongation at break of FRPLA/ZnO/ADR-1 increased by 25%, 14% compared with that of FRPLA. The impact strength was 15.1 kJ/m², which is similar to the pure PLA (15.6 kJ/m²). It indicated that the addition of nano ZnO and ADR could balance the flame retardant performance and the mechanical properties of the flame retardant PLA.     

Preparation and characterization of phenolic foams with eco-friendly halogen-free flame retardant

The high solid resol phenolic resin was prepared via step polymerization of formaldehyde, paraformaldehyde, and phenol using sodium hydroxide and calcium oxide as catalysts, and employed to prepare the phenolic foams (PFs) by the introduction of retardant additives including eco-friendly halogen-free flame retardants (ammonium polyphosphate), char-forming agents (pentaerythritol), and synergists (zinc oxide, molybdenum trioxide, cuprous chloride, and stannous chloride). The effects of these additives on flame retardancy, heat resistance, and fire properties of flame-retardant composite phenolic foams (FRCPFs) were evaluated by limiting oxygen index (LOI) tests, thermogravimetric analyzer, and cone calorimeter tests. It was found that the flame retardan significantly increased the LOIs of FRCPFs. Compared with PF, heat release rate, total heat release, effective heat of combustion, production or yield of carbon monoxide (COP or COY), and Oxygen consumption (O₂C) of FRCPFs all remarkably decreased. However specific extinction area and total smoke release significantly increased, which agreed with the gas-phase mechanism of the flame-retardant system. The results indicate that FRCPFs have excellent fire-retardant performance and less smoke release. APP/PER/ZnO is shown to be better flame-retardant system for PFs.     

Novel tetrapotassium azo diphosphonate (INAZO) as flame retardant for polyurethane adhesives

An inorganic azo diphosphonate (INAZO), (KO)₂(O)P-NN-P(O)(OK)₂·4H₂O, was synthesized and tested as a novel type of flame retardant additive for castor oil and oligomeric methylene diphenyl diisocyanate (PMDI) based two component polyurethane adhesive with or without using dolomite ((CaMg(CO₃)₂) as filler. Flammability according to UL 94 test and performance under forced-flaming conditions (cone calorimeter) were investigated at the additive loadings of 5, 10 and 20 wt %. It was shown that INAZO improves flame retardancy by significantly reducing heat release rate (HRR), maximum average rate of heat emission (MARHE) and total smoke release (TSR) values in comparison to CaMg(CO₃)₂ filled polyurethane adhesives. The macroscopic structure of the sample residues after cone calorimeter measurement was also analysed. The action mechanism of the developed INAZO flame retardant is suggested to be mainly in the condensed phase. UL 94 V-0 rating was achieved in the vertical burning test when 10 wt % loading of INAZO was used, whereas the reference flame retardant ammonium polyphosphate (APP) required a loading of 20 wt % to reach the V-0 classification.     

Thermal and flame retardant properties of novel intumescent flame retardant polypropylene composites

Novel intumescent flame retardant polypropylene (PP) composites were prepared based on a char forming agent (CFA) and silica-gel microencapsulated ammonium polyphosphate (Si-MCAPP). The thermal and flame retardancy of flame retardant PP composites were investigated by limiting oxygen index, UL-94 test, cone calorimetry, thermogravimetric analysis, scanning electron micrograph, and water resistance test. The results of cone calorimetry show that the flame retardant properties of PP with 30 wt% novel intumescent flame retardants (CFA/Si-MCAPP = 1:3) improve greatly. The peak heat release rate and total heat release decrease, respectively, from 1,140.0 to 156.8 kW m^?2 and from 96.0 to 29.5 MJ m^?2. The PP composite with CFA/Si-MCAPP = 1:3 has the excellent water resistance, and it can still obtain a UL-94 V-0 rating after 168 h soaking in water.     

A biobased flame retardant towards improvement of flame retardancy and mechanical property of ethylene vinyl acetate

A new biobased flame retardant (MHPA) with remarkable compatibility was synthesized via a facile and low-cost neutralization reaction of magnesium hydroxide (MH) and phytic acid (PA). By blending the prepared MHPA into ethylene vinyl acetate (EVA), the fire retardancy, smoke suppression and mechanical properties of the composites were significantly improved. When 50 wt% of MH was added into EVA matrix, the value of limiting oxygen index (LOI) reached 26.1%. Whereas, when 10 wt% MH in the EVA composites (with initial 50 wt% MH) was replaced by MHPA, the resulted EVA composites had a LOI value of 30.8%, indicating high efficiency of addition of MHPA to improve flame retardancy. Moreover, the heat release rate (HRR) and total smoke production (TSP) of the EVA composites reduced by 54.4% and 27.6%, respectively, suggesting that incorporation of MHPA could effectively hinder rapid degradation of EVA composites during burning process. The fire-retardant mechanism may reside in that the MHPA combined with MH can present the excellent carbonization and expansion effects. This study illustrates that the biobased MHPA has a broad application prospect to develop flame-retardant EVA composites.