Flame retardancy of different‐sized expandable graphite particles for high‐density rigid polyurethane foams

The effects of expandable graphite (EG) of different particle sizes, on the fire‐retardant properties of high‐density rigid polyurethane foam (RPUF) (0.45 g cm^?3) were studied. Samples of EG with different particle sizes were obtained by pulverization in an ultra‐high‐speed mixer for 4 and 13 min, respectively. It was shown that as received (EG0) and 4 min pulverized EG (EG4) efficiently improved the fire‐retardant properties of RPUF composites, while 13 min pulverized EG (EG13) did not. The char of the burned composites filled with EG0 and EG4 covered the whole surface of the samples and formed a complete physical barrier. This barrier material prevented combustible gases from feeding the flame and also isolated oxygen efficiently from the burning material. EG13 did not produce enough char to cover the whole surface of the burning sample, resulting in poor fire‐retardant property of the RPUF composites. Thermal degradation tests of the foams by thermogravimetric analysis indicated that EG showed negligible effects on the thermal stability of the RPUFs. Copyright © 2006 Society of Chemical Industry     

Flame‐retardant and mechanical properties of high‐density rigid polyurethane foams filled with decabrominated dipheny ethane and expandable graphite

The article reported the flame‐retardant and the mechanical properties of expandable graphite (EG), an intumescent type, and decabrominated dipheny ethane (DBDPE), a gas‐phase type of flame‐retardant‐containing high‐density rigid polyurethane foams (RPUF) with a constant density of 0.5g/cm³. The results indicated that both EG and DBDPE could effectively interdict the burning of RPUF, besides, the EG exhibited more effective flame retardancy than the DBDPE. When the flame‐retardant loadings were 20 wt %, the LOI value of DBDPE‐filled RPUF increased to 33 vol %, while, surprisingly, the EG‐filled RPUF reached 41 vol %. Unfortunately, when they were both simultaneously added into RPUF, there was not any flame‐retardant synergistic effect. Although EG had outstanding flame retardancy, the compressive strength and modulus of 20 wt % EG‐filled RPUF dropped to only 9.1MPa and 229.7MPa respectively, which were lower than those of DBDPE (12.4 MPa and 246.8 MPa). The phenomena were ascribed to the different flame‐retardant mechanisms of EG and DBDPE, which were verified by scanning electronic microscope (SEM) observation of the burned surfaces. Besides, the dynamical mechanical analysis (DMA) demonstrated that the additions of EG and DBDPE made the glass transition temperature shift to the high temperatures, and the EG‐filled RPUF had the higher storage modulus. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dependence of flame‐retardant properties on density of expandable graphite filled rigid polyurethane foam

Different density rigid polyurethane foams (RPUF) filled with various expandable graphite loadings were fabricated by cast molding. The flame retardant properties of these composites were assessed by limiting oxygen index and horizontal and vertical burning tests. The results showed that the flame retardant efficiency got better with increase in the foam density at the fixed EG weight percent or with increase in the EG weight percent at the fixed foam density. After burning, the low density (0.065 g/cm³) pure burned RPUF produced the highly collapsed and carbonized material, while the high density (0.510 g/cm³) pure RPUF had little change in size and had reduced destruction of the material. Moreover, the scanning electronic microscope (SEM) observation showed that the higher density EG/RPUF composites had a more compact outer layer (burned layer) after burned, in which more wormlike materials composed of expanded graphite particles appeared. In addition, higher foam density led to less plastic deformation in the interface layer between the burned and the inside layers. These results indicated that a weight percent of a flame retardant additive that achieves satisfactory flame retardancy for a certain density foam cannot effectively be applied for another density foam. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Flame retardancy of ceramic-based rigid polyurethane foam composites

In this work, ceramic fillers zirconia and alumina powder were incorporated in the rigid polyurethane foams derived from modified castor oil and their impact on the mechanical, thermal, and fire performances of composite foams have been analyzed. It was observed that the addition of ceramic filler showed improved mechanical and thermal properties and best properties were shown by 6% zirconia with compressive strength of 6.61 MPa and flexural strength of 5.72 MPa. Zirconia also demonstrated an increase in T_5% up to 260 °C. Cone calorimetry shows a decrease in peak of heat release from 118 to 84 kW m⁻² and 94 kW m⁻² by the incorporation of alumina and zirconia powder, respectively. Furthermore, total heat release (THR), smoke production rate (SPR), and total smoke release (TSR) were also found to decrease remarkably on the incorporation of ceramic fillers. So, these fillers have a great potential as an additive to incorporate good mechanical, thermal, and fire properties in bio-based rigid PU foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48250.     

Effects of expandable graphite and ammonium polyphosphate on the flame‐retardant and mechanical properties of rigid polyurethane foams

In this work, the effect of expandable graphite (EG) and ammonium polyphosphate (APP) on the flame retardancy and mechanical properties of the rigid polyurethane foam (RPUF) was studied. The results indicated that both EG and APP could effectively improve the flame retardancy of RPUF, while the retardancy of EG was better than APP. When the flame‐retardant loading was 15 wt %, the limited oxygen index (LOI) values of APP‐ and EG‐filled RPUF were 24.5 and 32 vol %, respectively. According to the LOI test, the optimal ratio of APP to EG in RPUF composites was 1 : 1 by weight, at which the LOI value of 15 wt % (APP + EG)/RPUF was 30.5 vol %. Thermal degradation test of RPUF composites by thermogravimetric analysis indicated that the addition of APP and EG to RPUF could lead to an increase in the amount of high‐temperature residue. Under the same conditions, the residue amount of EG/RPUF was less than that of APP/RPUF at the same temperature. Compression test and dynamic thermal mechanical analysis indicated that both the compressive strength and modulus decreased at a certain extent with the EG‐ or APP‐filled into RPUF, respectively, but with the mixture of EG and APP added into RPUF, the mechanical properties of these materials increased. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Addition flame‐retardant effect of nonreactive phosphonate and expandable graphite in rigid polyurethane foams

A series of flame‐retardant rigid polyurethane foams (RPUFs) containing nonreactive phosphonate (5‐ethyl‐2‐methyl‐1,3,2‐dioxaphosphorinan‐5‐yl) methyl dimethyl phosphonate P‐oxide (EMD) and expandable graphite (EG) were prepared by water blown. The flame‐retardant properties and mechanism of EMD/EG on RPUFs were systematically investigated. The EMD/EG system effectively increased the limiting oxygen index (LOI) value and decreased the values of total heat release (THR), av‐effective heat of combustion (EHC), pk‐heat release rate (HRR), total smoke release (TSR) of RPUFs. The impact values of LOI, THR, and av‐EHC resulted by EMD/EG system are nearly equal to the sum of the impact values by EMD and EG individually in RPUFs, which implies the addition flame‐retardant effect from EMD and EG. EMD alone exerted excellent gas‐phase flame‐retardant effect by releasing PO fragments with quenching effect. The firm residue produced by EMD combined well with the loose and worm‐like expanded graphite from EG further to form compact and expanded char layer, which brought excellent barrier effect and filtration effect to matrix. That's why pk‐HRR and TSR values of RPUF reduced. Depending on the simultaneous actions of EMD/EG system in gas phase and condensed phase during combustion, the flame‐retardant effects from nonreactive phosphonate and EG on RPUFs were added together. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45960.     

Flame retardation and thermal stability of novel phosphoramide/expandable graphite in rigid polyurethane foam

A novel flame retardant named diethylene N,N',N''‐tri (diethoxy)phosphoramide (DTP) was synthesized using diethyl phosphate and diethylenetriamine via Atherton–Todd reaction. Then, series of flame‐retardant water‐blown rigid polyurethane foams (RPUFs) with expandable graphite (EG) and DTP were prepared through box‐foaming. The results of thermogravimetric analysis showed that DTP/EG changed thermal degradation process of RPUF and promoted enhancing char residues. The complex flame‐retardant system (EG/DTP) endowed RPUF higher limiting oxygen index (LOI) values (29.1%–30.2%) and lower heat release rate peak (PHRR) values according to LOI and microscale combustion calorimeter tests. More importantly, the synergistic flame‐retardant effect between EG and DTP in RPUF was proved by the analysis of synergistic effectivity values. Based on the analysis of cone calorimetric tests, EG/DTP revealed remarkable effects to inhibit the fire intensity and smoke release of RPUF with decreased PHRR and total smoke production due to good char‐forming action. To further investigate the char‐residues of the foams after combustion, scanning electron microscope and energy dispersive X‐ray spectroscopy analyses were conducted. The results suggested that EG/DTP flame‐retardant system promoted RPUF forming a compact, continuous and phosphorus‐rich char layer as a good fire barrier in combustion. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46434.     

Synergistic effect of aluminum hydroxide and expandable graphite on the flame retardancy of polyisocyanurate–polyurethane foams

For the first time, expandable graphite (EG) and aluminum hydroxide (ATH) was combined to improve the flame retardancy of polyisocyanurate–polyurethane (PIR–PUR) foam. The limited oxygen index increased from 26.5 for the PIR–PUR matrix to an incredible value of 92.8 when 24 phr (parts per 100 of matrix) EG and 60 phr ATH were incorporated into the matrix. Based on morphology observation and thermogravimetric analysis, it was speculated that two factors contributed to the improvement of flame retardancy primarily. First, ATH could effectively induce “villi” like particles, which was useful to form a dense char. The compact char layer could effectively impede the transport of bubbles and heat. Second, ATH and EG accelerated the initial degradation and fluffy char was quickly generated on the surface of the composites. Thus, the degradation of the composite was slowed down and the diffusion of volatile combustible fragments to flame zone was delayed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39936.     

Expandable graphite in polyurethane foams: The effect of expansion volume and intercalants on flame retardancy

Several expandable graphites (EGs), differing in expansion volume but with the same mean size, are compared as flame retardants in polyurethane (PUR) foams. Not only common sulfur‐intercalated graphites are investigated but also a new one intercalated with phosphorus. The main aim of this article is to understand which properties of EG are important for its flame retardancy effectiveness in PUR foams. Thermal stability, flammability, and fire behavior are analyzed through limiting oxygen index and cone calorimeter tests. Detailed characterization of the phosphorus‐intercalated graphite is also provided as well as physical–mechanical characterization. The results show that the well‐known sulfur‐intercalated graphites and the one with phosphorus both enhance the residue yield, induce a protective layer, and thus efficiently flame‐retard PUR foams. While the expansion volume of the EGs had a surprisingly limited influence on the performance of the foams, at least in the range tested, the most important feature controlling the effectiveness of EG in terms of flame retardant PUR foams was the type of intercalant. The presence of EG affected the physical–mechanical properties of the foams; however, no significant effect of the expansion volume or intercalant type has been revealed on the physical–mechanical properties of the foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45173.     

Mechanical and flame-resistance properties of polyurethane-imide foams with different-sized expandable graphite

Polyurethane-imide (PUI) composite foams with expandable graphite (EG) of different sizes were prepared by a polyimide prepolymer method. EG particles were treated with a silane coupling agent to improve compatibility with the foam. The effect of EG particle size on cell morphology, thermal degradation, flame-resistance and mechanical properties of PUI foams was investigated. Results showed that the mean cellular diameter of foams with EG particle was much higher than that of foams with surface-modified EG particle at the same filler loading. When filler particle diameter increased from 20 to 90 μm, the compressive strength, density and closed-cell ratio of foams increased, and then decreased when filler particle diameter further increased from 90 to 150 μm. Thermal stability of foams increased with the increasing filler particle diameter from 20 to 50 μm, and decreased with the increasing filler particle diameter from 50 to 90 μm. The limited oxygen index (LOI) value of foams with surface-modified EG increased from 24.8% to 32.1% when EG particle diameter was below 90 μm. Foams with surface-modified EG exhibited enhanced mechanical properties, thermal stability and flame resistance than foams with neat EG at the same loading.     

A facile strategy to fabricate microencapsulated expandable graphite as a flame‐retardant for rigid polyurethane foams

A facile strategy is reported for one‐step preparation of reactive microencapsulated expandable graphite (EG) for flame‐retardant rigid polyurethane foams (RPUF), which is based on in situ emulsion polymerization and the use of poly(glycidyl methacrylate) (PGMA) as reactive polymer shell. FTIR and SEM observations well demonstrate the formation of PGMA microencapsulated EG (EG@PGMA) particles. The encapsulation of PGMA shell significantly improves the expandability of EG particles from 42 to 70 mL g^?1. RPUF/EG@PGMA composite with only 10 wt % EG@PGMA loading reaches the UL‐94 V‐0 rating. The limiting oxygen indexes increase remarkably from 21.0 to 27.5 vol %. Additionally, the improved chemical and physical interaction enhance the interfacial bonding between EG and matrix, thus resulting in improved mechanical properties of RPUF/EG@PGMA. These attractive features suggest that the strategy proposed here can serve as a promising means to prepare highly efficient, reactive microencapsulated EG and corresponding good flame‐retarding RPUF with high mechanical properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42364.     

Influence of expandable graphite on flame retardancy and thermal stability property of unsaturated polyester resins/organic magnesium hydroxide composites

An eco-friendly flame retardant unsaturated polyester resin (UPR) material was prepared by combination organic magnesium hydroxide (OMH) and expandable graphite (EG). Different from direct addition of magnesium hydroxide (MH) in UPR matrix-like traditional method, OMH as a reactive monomer participates in the polycondensation reaction of UPR was more effective in improving the compatibility of flame retardant with matrix. Interestingly, the flame retardant UPR composites exhibited a more satisfactory flame retardant effect when a certain amount of 8 wt % EG was added into UPR/OMH matrix because of the synergistic effect between OMH and EG, resulted in the limited oxygen index from 21.7 to 28.5% and UL-94 test passed V-0 rating. Moreover, the peak heat release rate, total heat release, and smoke production rate of flame retardant UPR composites significantly reduced. The excellent flame retardancy was due to the formation of a dense and continuous carbon layer in the later stages of combustion. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 47881.     

Preparation and characterization of microencapsulated ammonium polyphosphate and its synergistic flame‐retarded polyurethane rigid foams with expandable graphite

A facile and effective method for the preparation of microencapsulated ammonium polyphosphate (MAPP) by in situ surface polymerization was introduced. The ‘polyurethane‐like’ shell structure on the surface of MAPP was characterized by using Fourier transform infrared spectroscopy. The hydrophobicity and thermal behavior of MAPP were studied by using water contact angle tests and thermogravimetric analysis. The foam density and mechanical properties of polyurethane (PU) rigid foams were investigated. The flame retardancy of PU rigid foams formulated with MAPP was evaluated by using limiting oxygen index and cone calorimetry. The results show that MAPP can greatly increase the flame retardancy of PU materials. Also, there is a synergistic effect between MAPP and expandable graphite in flame retarding PU rigid foams. Moreover, the water resistance property of PU/MAPP composites is better than that of PU/ammonium polyphosphate. The morphology and chemical structure of PU/MAPP rigid foams after burning were systematically investigated. © 2013 Society of Chemical Industry     

Core–shell structure design of pulverized expandable graphite particles and their application in flame‐retardant rigid polyurethane foams

Pulverized expandable graphite (pEG) and melamine ? formaldehyde (MF) resin core ? shell structure particles (pEG@MF) as specific flame retardants for rigid polyurethane foam (RPUF) were synthesized by encapsulating pEG particles with a layer of MF resin via in situ polycondensation. The initial feed weight ratio of pEG and MF prepolymer was found to be the key factor affecting the shell forming process, and the shell growth can be regarded as a combination of ‘raspberry‐like’ and conventional ‘core–shell’ formation mechanisms. With the encapsulation of a well formed MF shell, the expandability of pEG particles was significantly enhanced from 42 mL g^–1 to 76 mL g^–1 and thus the pEG@MF particles showed good flame‐retardant performance in RPUF. The RPUF/pEG@MF composites passed the V‐0 rate and the limiting oxygen index was remarkably increased from 21 to 28 vol% by adding only 10 wt% pEG@MF particles; both the expandability and available expandable graphite content played an important role in controlling the flame‐retardant performance of pEG@MF particles. With a loading of fine sized pEG@MF particles, desirable mechanical and thermal insulation properties of RPUF/pEG@MF composites were achieved by preserving the complete cell structure of RPUF and screening the high thermal conductivity of the pEG particles with the thermally inert MF resin shell. The exciting application of the novel pEG@MF particles indicates that the core–shell structure design of expandable graphite can serve as promising solution for fabricating halogen‐free flame‐retardant RPUF composites with high performance. © 2013 Society of Chemical Industry     

Bi-phase flame-retardant effect of hexa-phenoxy-cyclotriphosphazene on rigid polyurethane foams containing expandable graphite

The flame-retardant rigid polyurethane (PU) foams with hexa-phenoxy-cyclotriphosphazene/expandable graphite (HPCP/EG) were prepared through box-foaming in our laboratory. The flame retardancy of PU foams was characterized using the limiting oxygen index and cone calorimeter. The results show that the incorporation of HPCP into the PU foams containing EG enhanced flame retardancy. The main degradation process of HPCP in PU foams was investigated by pyrolysis gas chromatography/mass spectroscopy. HPCP during combustion generated phenoxyl and PO₂ free radicals, which could quench the flammable free radicals produced by the matrix and hamper the free radical chain reaction of combustion. This observation shows that HPCP produced a gas-phase flame-retardant effect in this specimen. Additionally, micro-morphology, elemental composition and content of residual char of the flame-retardant PU foams after the cone calorimeter test were also characterized using scanning electron microscope and energy dispersive X-ray microanalyser. The results exhibit that the partial phosphorus from HPCP remained in the residual char, and HPCP significantly enhanced the strength and compatibility of the char layer formed by the PU foams containing EG. These results indicate the important function of HPCP in condensed phase. Thus, HPCP exhibited gas-phase and condensed-phase flame-retardant effects on the PU/EG foams.     

Blast furnace slag or fly ash filled rigid polyurethane composite foams: A comprehensive investigation

Ground granulated blast furnace slag (BFS) and fly ash (FA) are iron-making industry and power plant byproducts, respectively. Although their use in concrete is quite common, investigation of the effects of these inorganic compounds on polymer properties is quite new, and their use as fillers in polymer foam composites has not yet been really explored. Their properties, such as high electrical resistivity, make them a good asset for use in rigid polyurethane foams that are widely used for insulation. In this study, a comprehensive investigation of the effect of BFS and FA on morphology, electrical and thermal conductivity, and rheological and mechanical properties of water-blown rigid polyurethane foams was performed. The relationship between these properties was examined. A relative enhancement of the properties is observed for filled foams, especially up to the percolation threshold. The results highlight a noticeable effect of the electrical percolation threshold on the different properties of foams. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47433.     

Synergistic effect between zeolitic imidazolate framework-8 and expandable graphite to improve the flame retardancy and smoke suppression of polyurethane elastomer

Zeolitic imidazolate framework-8 (ZIF-8) was synthesized at room temperature, and then added with expandable graphite (EG) to polyurethane elastomer (PUE) to study their flame retardancy and smoke suppression of PUE. The results showed that when the total flame retardant was 3 wt % and the ratio of ZIF-8 and EG was 1:3, it had the best effect on the flame retardancy and smoke suppression of PUE. Compared with pure PUE, the peak heat release rate, the total heat release, and the maximum smoke density values of Z1E3 decreased by 83.4, 42.6, and 22.4%, respectively. Moreover, the limited oxygen index value of Z1E3 increased to 30.2% and its UL-94 vertical burning test reached V-1 rating. This was because ZIF-8 synergized with EG to make the intumescent char layer compact, resulting in improved flame retardancy and smoke suppression of PUE. The specific mechanism of flame retardancy and smoke suppression is also discussed in this article. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48048.     

膨胀石墨对乙烯基硅橡胶的阻燃作用研究

将可膨胀石墨(EG)添加到乙烯基硅橡胶中并采用过氧化物硫化制备了硅橡胶材料,对其阻燃性能和燃烧行为进行了研究.结果表明,当EG的添加量为5份时,材料在垂直燃烧测试中通过了UL 94 V-0级,且能离火自熄,极限氧指数达到了33.0％;与纯硅胶材料相比,EG的加入有效降低了材料的热释放和烟释放;材料与火焰接触区域,EG完...     

Synthesis and characterization of starch-based polyurethane foams

Starch-based polyurethane foams were synthesized by reacting a mixture of starch and polycaprolactone triol with an aliphatic diisocyanate, in the presence of water as blowing agent. Some foams were also prepared by adding a certain amount of polyethyleneglycol. The reaction kinetics is affected by the presence of starch due to the higher viscosity related to the presence of the high molecular weight polysaccharide. Starch-based polyurethanes show higher glass transition temperatures and lower thermal stability. Cellular materials with different mechanical properties can be obtained by varying the amount of starch and by controlling the relative amount of polycaprolactone triol and polyethyleneglycol in the composition. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:739–745, 1998     

Flame retardant polyurethane foam prepared from compatible blends of soybean oil‐based polyol and phosphorus containing polyol

A phosphorus containing polyether polyol (THPO‐PO) was synthesized by polymerization between tris(hydroxymethyl) phosphine oxide (THPO) and propylene oxide (PO). A soybean oil‐based polyol(SBP) was synthesized from epoxidized soybean oil by ring‐opening reaction with lactic acid. The corresponding polyurethane foams (PUFs) were prepared by mixing SBP with THPO‐PO. The density of these foams decreased as the content of THPO‐PO increased. The yield strength of PUFs was observed to be decreased firstly and then increased with the addition of THPO‐PO. Microphotographs of PUFs were examined by scanning electron microscope which displayed the cells as spherical or polyhedral. The thermal degradation and fire behavior of PUFs were investigated by thermogravimetric analysis, limiting oxygen index (LOI), and UL‐94 test. Although the thermal stability of PUFs were decreased with increasing THPO‐PO percentage, the flame retardancy of PUFs were improved. The LOI value increased to 27.5 with 40% THPO‐PO. THPO‐PO in sequence worked in inhibiting flame and forming phosphorus‐rich char layer, thus endowing PUFs with the increased flame‐retardant performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45779.