Synthesis and thermal behavior of a novel UV‐curable transparent flame retardant film and phosphorus‐nitrogen synergism of flame retardancy

A novel phosphorus monomer (PDHA) has been synthesized through phenyl dichlorophosphate (PDPC) reacting with 2‐hydroxyethyl acrylate (HEA). The structure of PDHA was characterized by Fourier transform infrared spectroscopy (FTIR) and ¹H nuclear magnetic resonance spectroscopy (¹H NMR). A series of UV curable resins were manufactured by blending PDHA with triglycidyl isocyanurate acrylate (TGICA) at different weight ratios. The fire performance was examined by micro‐scale combustion calorimeter (MCC) and limiting oxygen index (LOI). The results obtained from MCC indicated that the addition of PDHA to TGICA reduced the HRR and HRC. In addition, the LOI values varied from 28 to 34. The char residues of the composites were observed by scanning electron microscopy (SEM). Their thermal degradation behavior was investigated by thermogravimetric analysis and real time FTIR analysis (RT‐FTIR). The test results indicated that when the weight ratio of PDHA/TGICA = 1:1, the onset temperature of the composite was highest and the most char residue at 700°C was observed. RT‐FTIR showed that the phosphate group of PDHA first degraded to form poly(phosphoric acid)s at around 300°C, which had the major contribution to form the compact char to protect the sample from further degradation. Copyright © 2010 John Wiley & Sons, Ltd.     

Flame retardancy and thermal degradation of intumescent flame retardant polypropylene with MP/TPMP

The performances of the novel intumescent flame retardant (IFR) polypropylene (PP) composites containing melamine phosphate (MP) and tris(1‐oxo‐2,6,7‐trioxa‐1‐phosphabicyclo[2,2,2]methylene‐4)phosphate (TPMP) were investigated. The flame retardancy of IFR‐PP system was characterized by limiting oxygen index (LOI) and UL 94 and cone calorimeter. The morphology of the char obtained after cone calorimeter testing was studied by scanning electron microscopy (SEM). The thermal oxidative degradation (TOD) of the composites was investigated by using thermogravimetric analysis (TGA) and real‐time Fourier transform infrared spectroscopy (RT‐FTIR). Compared with the PP/ TPMP or PP/ MP binary composite, at the same addition level, the LOI values of the PP/MP/TPMP ternary composites increase and reach V‐0 at the suitable MP/TPMP ratio. The results of TGA and RT‐FTIR showed the existence of the interaction between IFR and PP. Copyright © 2008 John Wiley & Sons, Ltd.     

Flammability and thermal degradation of epoxy acrylate modified with phosphorus‐containing compounds

A series of UV‐curable flame retardant resins was obtained using epoxy acrylate (EA) modified with 1‐oxo‐4‐hydroxymethyl‐2,6,7‐trioxa‐1‐phosphabicyclo[2.2.2]octane (PEPA). The flammability was characterized by limiting the oxygen index (LOI), UL 94 and cone calorimeter, and the thermal degradation of the flame retardant resins was studied using thermogravimetric analysis (TGA) and real time Fourier transform infrared (RTFTIR). The results indicated that the flame retardant efficiency increases and the heat release rate (HRR) decreases greatly with the content of PEPA. The TG data showed that the modified epoxy acrylates (MEAs) have lower initial decomposition temperatures and higher char residues than pure EA. The RTFTIR study indicates that the MEAs have lower thermal oxidative stability than the pure EA. Copyright © 2009 John Wiley & Sons, Ltd.     

聚苯氧基磷酸联苯二酚酯/聚磷酸铵膨胀阻燃剂对环氧树脂阻燃性能影响研究

以聚苯氧基磷酸联苯二酚酯(PBPP)与聚磷酸铵(APP)组成复合阻燃剂,对环氧树脂(EP)进行阻燃改性.通过氧指数(LOI)、垂直燃烧(UL-94)、热失重(TGA)、锥形量热(CONE)和扫描电镜(SEM)等方法研究改性环氧树脂的阻燃性能和阻燃机理.结果表明,PBPP/APP体系对EP具有较好的阻燃性能,阻燃剂添加量为10%时能使环氧树脂的氧指数提高到29.6%,垂直燃烧等级达到UL94 V-0级,残炭量大大增加;平均热释放速率下降45.7%,热释放速率峰值下降51.0%,有效燃烧热平均值下降21.1%;TGA、CONE、SEM等综合分析显示了PBPP/APP改性后的环氧树脂比纯环氧树脂具有更高的热稳定性,燃烧后能够形成连续、致密、封闭、坚硬的焦化炭层,在聚合物表面产生有效覆盖、隔绝了氧气,改善了环氧树脂的燃烧性能.     

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.     

Preparation and thermal properties of a novel flame-retardant coating

A novel silicone and phosphate modified acrylate (DGTH) was synthesized and characterized by ¹H NMR and FTIR. It was found that DGTH could be cured both by UV radiation and moisture mode with FTIR. The flammability and thermal behavior of the cured film were studied by the limited oxygen index (LOI), thermogravimetric analysis (TG) and real time Fourier transform infrared (RT-FTIR). The LOI value of the cured film is 48 and the TG data shows that the cured film has three characteristic degradation temperature regions, attributing to the decomposition of phosphate and polyurethane to alcohols and isocyanates, thermal pyrolysis of alkyl chains, and decomposition of unstable structures in char, respectively. The RT-FTIR data implies that the degraded products of phosphate form poly(phosphoric acid) further catalyse the breakage of carbonyl groups to form an intumescent char, preventing the samples from further burning.     

Synthesis and thermal degradation behaviors of hyperbranched polyphosphate

A novel epoxy-terminated hyperbranched polyphosphate (E-HBPP) was synthesized by employing an A₂ + B₃ polycondensation and characterized by FTIR, ¹H NMR and GPC. E-HBPP was used as a reactive-type flame retardant for diglycidyl ether of bisphenol-A/m-phenylene diamine (DGEBA/mPDA) system. A series of flame retardant resins were prepared and their flame retardancy was monitored by the limiting oxygen index (LOI). The results showed that the LOI value of the cured samples and the degree of expansion of the formed char after burning increased along with the E-HBPP content. Their thermal degradation behaviors were investigated by thermogravimetric analysis and in situ FTIR and showed that the phosphate group of E-HBPP first degraded to form poly(phosphoric acid)s at around 300 °C, which had a major contribution to form the compact char to protect the sample from further degradation. The dynamic mechanical thermal properties were studied by dynamic mechanical thermal analysis (DMTA) and the results showed a good miscibility between E-HBPP and DGEBA. The mechanical properties of the cured films were also investigated. Less than 20% E-HBPP addition improved both the tensile strength and elongation at break.     

Thermal degradation behavior of hyperbranched polyphosphate acrylate/tri(acryloyloxyethyl) phosphate as an intumescent flame retardant system

The hyperbranched polyphosphate acrylate (HPPA) was blended in different ratios with tri(acryloyloxyethyl) phosphate (TAEP) to obtain a series of UV curable intumescent flame retardant resins. The thermal degradation mechanism of their cured films in air was studied by thermogravimetric analysis and in situ Fourier-transform infrared spectroscopy. The results showed that the addition of HPPA reduced the initial decomposition temperature (T_di) but increased the char residue. Moreover, the decomposition was considered to be divided into three stages: firstly the degradation of phosphate group, secondly ester group and finally alkyl chain. The morphological structure of the formed char was observed by scanning electron microscopy, demonstrating the formation mechanism of the intumescent charred crust.     

Thermal and flame retardant properties of epoxy resin cured by a novel phosphorus-containing 4,4′-bisphenol novolac curing agent

A novel flame retardant curing agent for epoxy resin (EP), i.e., a DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing 4,4'-bisphenol novolac (BIP-DOPO) was synthesized and characterized by Fourier transform infrared (FTIR), ¹H NMR, ³¹P NMR spectroscopy, and gel permeation chromatography. The epoxy resin cured by BIP-DOPO itself or its mixture with a commonly used bisphenol A-formaldehyde novolac resin (NPEH720) was prepared. The flame retardancy of the cured EP thermosets were studied by limiting oxygen index (LOI), UL 94 and cone calorimeter test (CCT), and the thermal properties by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results show that the cured epoxy resin EPNP/BI/3/1, which contains 2.2% phosphorus, possesses a value of 26.2% and achieves the UL 94 V-0 rating. The data from cone calorimeter test demonstrated that the peak release rate, average heat release rate, total heat release decline sharply for the flame retarded epoxy resins, compared with those of pure ones. DSC results show that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA indicates that the incorporation of BIP-DOPO promotes the decomposition of epoxy resin matrix ahead of time and leads to higher char yield. The surface morphological structures of the char residues reveal that the introduction of BIP-DOPO benefits to the formation of a continuous and solid char layer on the epoxy resin material surface during combustion.     

Poly (diallyldimethylammonium) and polyphosphate polyelectrolyte complexes as an all‐in‐one flame retardant for polypropylene

Poly (diallyldimethylammonium chloride) (PDDA) and ammonium polyphosphate (APP) deionized chloride ions and ammonium ions by ionizing in aqueous solution respectively, then combined to form poly (diallyldimethylammonium) and polyphosphate (PAPP) polyelectrolyte complexes as an all‐in‐one flame retardant for polypropylene and its composites were characterized by Fourier transform infrared (FTIR) spectroscopy and X‐ray photoelectron spectroscopy. One flame retardant system composed of PAPP and PP, the other flame retardant system composed of PAPP, Polyamide‐6 (PA6) and PP were tested by limiting oxygen index (LOI), UL‐94, cone calorimeter tests and thermogravimetric analysis (TGA) and compared with pure PP. The results showed that the LOI value of PP/PAPP composite can reach 27.5%, and UL‐94 V‐2 rating can be reached at 25 wt% PAPP loading. Meanwhile the cone calorimetry results displayed that the peak heat release rate (PHRR) and total heat release (THR) were reduced up to 69.3% and 22.5%, respectively, compared with those of pure PP. After adding 5 wt% PA6, the carbon source missing due to the early PAPP decomposition can be made up, and PHRR and THR can be further reduced slightly. The flame retardant mechanism of PAPP was studied by FTIR spectroscopy and X‐ray photoelectron spectroscopy. Six‐membered ring of C─N containing conjugate double bonds, cross‐linked phosphate structure formed stable, intumescent, compact char layer which greatly improved the flame retardancy of PP.     

A flame-retardant epoxy resin based on a reactive phosphorus-containing monomer of DODPP and its thermal and flame-retardant properties

A flame-retardant epoxy resin (EP) was synthesized based on a novel reactive phosphorus-containing monomer, 4-[(5,5-dimethyl-2-oxide-1,3,2-dioxaphosphorinan-4-yl)oxy]-phenol (DODPP), and its structures were characterized by FTIR, ¹H NMR and ³¹P NMR spectra. The DODPP-EP₃/LWPA (low molecular weight polyamide), which contains 2.5% phosphorus, can reach UL-94 V-0 rating and a limiting oxygen index (LOI) value of 30.2%. The thermal properties and burning behaviours of cured epoxy resins were investigated by differential scanning calorimeter (DSC), thermogravimetry (TG), LOI, UL-94 tests and cone calorimetry. The morphologies of residues of cured epoxy resins were investigated by scanning electron microscopy (SEM). DSC shows that the glass-transition temperatures of cured epoxy resins decrease with increasing phosphorus content. TGA shows that the onset decomposition temperatures and the maximum-rate decomposition temperatures decrease, while char yields increase, with the increase of phosphorus content. The data from the cone calorimeter tests give the evidence that heat release rate (HRR), peak heat release rate (PHRR), average heat release rate (Av-HRR), average mass loss rate (Av-MLR) and the fire growth rate index (FIGRA) decrease significantly for DODPP-EP₃/LWPA. SEM shows that the DODPP-EP₃/LWPA forms lacunaris and compact charred layers which inhibit the transmission of heat during combustion.     

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.     

Flame-retarded mechanism of SEBS/PPO composites modified with mica and resorcinol bis(diphenyl phosphate)

The flame retardancy of styrene-b-ethylene/butylene-b-styrene triblock polymer (SEBS)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends was greatly improved by the combined use of mica and resorcinol bis(diphenyl phosphate) (RDP). The limiting oxygen index (LOI), vertical burning and cone calorimeter test were performed to evaluate the flame-retarded effect. The composite of SEBS/PPO/maleic anhydride grafted SEBS (SEBS-g-MAH) with a mass ratio of 11/11/3 passed a V-0 rating in the UL94 test by the addition of 10–15 wt% mica and 15–10 wt% RDP with total amount of 25 wt%. The synergism was confirmed by the mathematical evaluation of the synergistic effect index (SE) in LOI, the residue, the peak heat release rate (PHRR) and the total heat evolved (THE) per mass loss (THE/ML). The flame-retarded mechanism of the composite was also proposed on the results of cone calorimeter test, TGA-FTIR, SEM micrographs and SEM/EDS analysis of the residues. It was found that the degradation rate of SEBS/PPO/SEBS-g-MAH matrix was slowed down, a more consolidated char layer with higher residue was promoted by the combination of RDP and mica. The flame-retardancy of RDP with mica in SEBS/PPO/SEBS-g-MAH matrix was synergistic through gas and condensed phase action.     

Synergistic effect between expandable graphite and ammonium polyphosphate on flame retarded polylactide

Synergistic effect was observed between expandable graphite (EG) and ammonium polyphosphate (APP) on flame retarded polylactide (PLA) in this paper using limiting oxygen index (LOI), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray spectroscopy (XPS) and cone calorimeter tests etc. In the experiments, PLA composites with 15 wt% of APP/EG(1:3) combinations showed a LOI value of 36.5 and V-0 rating in UL-94 tests, greatly improved flame retardant properties from composites with APP or EG alone. Results from TGA and cone calorimeter demonstrated that APP/EG combination could retard the degradation of polymeric materials above the temperature of 520 °C by promoting the formation of a compact char layer. This char layer protects the matrix effectively from heat penetrating inside and prevents its further degradation, resulting in lower weight loss rate and better flame retarded performance.     

Synthesis and effect of hyperbranched (3-hydroxyphenyl) phosphate as a curing agent on the thermal and combustion behaviours of novolac epoxy resin

A novel type of hyperbranched (3-hydroxyphenyl) phosphate (HHPP) with high functionality as a curing agent of epoxy resins was synthesized and characterized by FTIR, ¹H NMR and vapor phase osmometry (VPO). The cured epoxy resin with HHPP possessed improved glass transition temperature. The thermostability and flame retardancy of O-cresol novolac epoxy resin cured with different contents of HHPP were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI) and cone calorimetry. The obtained results show that the samples containing a higher percentage of HHPP exhibit relatively lower thermostability at lower temperature while higher thermostability at elevated temperature and more char was formed compared with those containing a lower percentage of HHPP. The LOI value increased from 22.0 to 30.0 when HHPP, instead of 1,3-dihydroxybenzene, was used as a curing agent. The 25 wt% addition of HHPP in the curing agent complex effectively decreased the heat release rate and improved the char yield to the content nearly similar as those of the epoxy resin cured with pure HHPP.     

Flame retardancy of epoxy resin nanocomposite with a novel polymeric nanoflame retardant

A wrapped nanoflame retardant, designated as polyhedral oligomeric silsesquioxane (POSS)‐poly(4‐bromostyrene) (PBS)‐carbon nanotubes (CNTs), was synthesized via π‐π stacking interactions between the walls of multiwalled carbon nanotubes and the silicon‐bromine containing hybrid copolymer (designated as POSS‐PBS) that was copolymerized by 4‐bromostyrene and acryloyloxyisobutyl polyhedral oligomeric silsesquioxane. The POSS‐PBS‐CNTs exhibited good dispersibility in epoxy resin (EP) without obvious aggregation. Furthermore, the fire behaviors of this flame‐retardant EP (FR‐EP) nanocomposites were examined via limited oxygen index (LOI) and cone calorimeter (CONE) tests. The FR‐EP had an ideal LOI value of 35.3% and its residual char yield obtained from CONE test was significantly enhanced from 5.9% to 15.3% with the incorporation of 4 wt% POSS‐PBS‐CNTs and 1.33 wt% Sb₂O₃ into EP matrix. Additionally, the addition of 4 wt% POSS‐PBS‐CNTs or POSS‐PBS can efficiently decrease the peak heat release rate (PHRR) of EP matrix by 41.0% or 45.6%, respectively.     

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.     

Synthesis of a novel phosphorus‐containing curing agent and its effects on the flame retardancy,thermal degradation and moisture resistance of epoxy resins

A novel phosphorus‐containing compound diphenyl‐(1, 2‐dicarboxylethyl)‐phosphine oxide defined as DPDCEPO was synthesized and used as a flame retardant curing agent for epoxy resins (EP). The chemical structure of the prepared DPDCEPO was well characterized by Fourier transform infrared spectroscopy, and ¹H, ¹³C and ³¹P nuclear magnetic resonance. The DPDCEPO was mixed with curing agent of phthalic anhydride (PA) with various weight ratios into epoxy resins to prepare flame retardant EP thermosets. The flame retardant properties, combustion behavior and thermal analysis of the EP thermosets were respectively investigated by limiting oxygen index (LOI), vertical burning tests (UL‐94), cone calorimeter measurement, dynamic mechanical thermal analysis and thermogravimetric analysis (TGA) tests. The surface morphologies and chemical compositions of the char residues for EP thermosets were respectively investigated by scanning electron microscopy and X‐ray photoelectron spectroscopy (XPS). The water resistant properties of the cured EP were evaluated by putting the samples into distilled water at 70°C for 168 hr. The results revealed that the EP/20 wt% DPDCEPO/80 wt% PA thermosets successfully passed UL‐94 V‐0 flammability rating and the LOI value was as high as 33.2%. The cone test results revealed that the incorporation of DPDCEPO effectively reduced the combustion parameters of the epoxy resin thermosets, such as heat release rate and total heat release. The dynamic mechanical thermal analysis test demonstrated that the glass transition temperature (Tg) decreased with the increase of DPDCEPO content. The TGA results indicated that the incorporation of DPDCEPO promoted the decomposition of epoxy resin matrix ahead of time and led to a higher char yield and thermal stability at high temperatures. The surface morphological structures and analysis of the XPS of the char residues of EP thermosets revealed that the introduction of DPDCEPO benefited the formation of a sufficient, compact and homogeneous char layer with rich flame retardant elements on the epoxy resin material surface during combustion. The mechanical properties and water resistance of the cured epoxy resins were also measured. After water resistance tests, the EP/20 wt% DPDCEPO/80 wt% PA thermosets retained excellent flame retardancy, and the moisture adsorption of the EP thermosets decreased with the increase of DPDCEPO content in EP thermosets because of the existence of the P–C bonds and the rigid aromatic hydrophobic structure in DPDCEPO. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on flame-retardant mechanism of polycarbonate containing sulfonate-silsesquioxane-fluoro retardants by TGA and FTIR

The flame retardancy of bisphenol A polycarbonate (PC) containing potassium diphenylsulfone sulfonate (KSS), poly(aminopropyl/phenylsilsesquioxane) (PAPSQ) and poly(vinylidenefluoride) (PVDF) was measured by limited oxygen index (LOI) and examined according to UL94. A high LOI and UL94 V-0 rating for 1.6 mm thickness samples were obtained by a combined use of equivalent KSS, PAPSQ and PVDF at 0.1-0.3 wt% loading, respectively. The improvement in flame retardancy of PC compositions arose from the synergistic interaction of three additives. Thermogravimetric analysis (TGA) indicated that the combination decreased the activation energy (E) of PC degradation and elevated the thermal degradation rate of PC to ensure the formation of an insulating carbon layer. FTIR analysis showed that the LOI char of PC containing the three additives took on a highly cross-linking aromatic ester and ether structure.     

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.