The effect of different impact modifiers in halogen-free flame retarded polycarbonate blends - I. Pyrolysis

In this first of two papers, the thermal decomposition of bisphenol A bis(diphenyl phosphate)-flame retarded polycarbonate (PC) blends with different impact modifiers was studied. The impact modifiers were an acrylonitrile-butadiene-styrene (ABS), a poly(n-butyl acrylate) (PBA) rubber with a poly(methyl methacrylate) (PMMA) shell and two silicone-acrylate rubbers consisting of PBA with different amounts of polydimethylsiloxane (PDMS) and different shells (PMMA and styrene-acrylonitrile, SAN). The focus of this work was to study the impact of the acrylate and silicon-acrylate rubbers with respect to pyrolysis and flame retardancy in comparison to common ABS. Thermogravimetry (TG) was performed to investigate the pyrolysis behaviour and reaction kinetics. TG in combination with FTIR identified the pyrolysis gases. Solid residues were investigated by FTIR-ATR. PC/ABS shows two-step decomposition, with PC decomposing independently from ABS at higher temperatures. Pure acrylate rubber destabilises PC due to interactions between the rubber and PC, which leads to earlier decomposition of PC. Using silicone-acrylate rubbers led to similar results as PC/ABS with respect to pyrolysis, reaction kinetics and analysis of the solid residue; hence the exchange of ABS for the silicone-acrylate rubbers is possible.     

Thermal properties and combustion behaviors of UV‐cured phosphate triacrylate/star poly(urethane acrylate) oligomer blends

A series of UV‐curable intumescent flame retardant resins was obtained by blending phosphate triacrylate (TAEP) in certain ratios with star poly(urethane acrylate) (SPUA) oligomer. The flammability of the cured films was characterized by limited oxygen index (LOI), UL 94, and the cone calorimeter. The results showed that the cured TAEP/SPUA samples greatly expanded while burning. A distinct synergistic effect was found between TAEP and SPUA. TAEP2 sample showed the highest LOI value (41) among all resins. The cone calorimeter results showed that the peak heat release rates and carbon monoxide yield decreased to the approximate level. The degradation was monitored by thermogravimetric analysis and real‐time Fourier transform infrared spectroscopy. A degradation mechanism is suggested in which the phosphate group in TAEP first degraded to form poly(phosphoric acid)s, which further catalyzed the degradation of the material to form char with emission of carbon dioxide and nitrogen volatiles from SPUA, leading to the formation of expanding char. The morphologic structures of crusts of the formed chars were observed by scanning electron microscopy, demonstrating the synergistic effect between TAEP and SPUA. Copyright © 2008 John Wiley & Sons, Ltd.     

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

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

A novel intumescent flame retardant: Synthesis and application in ABS copolymer

A novel phosphorous-nitrogen structure containing intumescent flame retardant, poly(4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB) was synthesized and characterized. Thermal stability and flammability properties of ABS/PDSPB composites were investigated by thermogravimetric analysis (TGA) and cone calorimeter test, respectively. The results showed that the addition of PDSPB enhanced the thermal stability and flame retardancy of ABS significantly. The weight of residues improved greatly with the addition of PDSPB. FTIR and SEM investigations revealed that the residual chars contain polyphosphoric or phosphoric acid, which plays an important role in the process of carbonization. The intumescent chars formed from PDSPB and ABS/PDSPB composites were intact, multicellular and strong. It is confirmed that the char structure was a critical factor for flame retardancy of ABS resin.     

Poly(lactic acid) nanocomposites with improved flame retardancy and impact strength by combining of phosphinates and organoclay

To minimize the loading level of the char-forming phosphorus based flame retardants in the poly(lactic acid) (PLA) with reduced flammability, we have developed the flame-retarded PLA nanocomposites by melt blending method incorporating organically modified montmorillonite (OMMT) and aluminium diethylphosphinate (AlPi) additives. The influence of AlPi and OMMT on flame retardancy and thermal stability of PLA was thoroughly investigated by means of the limiting oxygen index (LOI), UL94 test, cone calorimeter, X-ray diffraction (XRD), thermogravimetric analysis and scanning electronic microscopy (SEM). The experimental results show that the PLA/AlPi/OMMT system has excellent fire retardancy. The LOI value increases from 19% for pristine PLA to 28% for the flame-retarded PLA. Cone calorimeter analysis of the PLA/AlPi/OMMT exhibits a reduction in the peak heat release rate values by 26.2%. Thermogravimetric analysis and SEM of cone calorimeter residues indicate that OMMT significantly enhances the thermal stability, promotes char-forming and suppresses the melt dripping. The research of this study implies that the combining of the flame retardant and organoclay results in a synergistic effect. In addition, the flame-retarded PLA nanocomposite also exhibits notable increase in the impact strength and the elongation at break.     

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.     

Flame retardancy mechanisms of aryl phosphates in combination with boehmite in bisphenol A polycarbonate/acrylonitrile-butadiene-styrene blends

The influence of nano-dispersed 5 wt.% boehmite (AlOOH) and 5 wt.% AlOOH combined with bisphenol A bis(diphenyl phosphate) (BDP) in bisphenol A polycarbonate/acrylonitrile-butadiene-styrene (PC/ABS) + poly(tetrafluoroethylene) (PTFE), and 1 wt.% AlOOH with and without BDP, resorcinol bis(diphenyl phosphate) (RDP), and triphenyl phosphate (TPP), on PC/ABS + PTFE has been investigated. Possible flame retardancy mechanisms are revealed. Thermogravimetry (TG) and evolved gas analysis (TG-FTIR) are used to study pyrolysis, a cone calorimeter applying different external heat fluxes is used to investigate fire behaviour, and LOI and UL 94 are used to investigate flammability. Fire residues were investigated using ATR-FTIR.Adding 5 wt.% AlOOH decreases the peak heat release rate, as also has been reported for polymer nanocomposites with other layered structures. AlOOH releases water, and adding 5 wt.% AlOOH crucially influences thermal decomposition by enhancing the hydrolysis of PC and of BDP. For PC/ABS + PTFE + BDP + 5 wt.% AlOOH, the formation of AlPO₄, for instance, results in antagonistic effects on the charring of PC + BDP, whereas synergy is observed in LOI. When only 1 wt.% AlOOH is added to the PC/ABS + PTFE with and without BDP, RDP and TPP, respectively, no significant influence is observed on thermal decomposition, UL 94, LOI or performance in the cone calorimeter.     

Synthesis of a novel phosphate‐containing highly transparent PMMA copolymer with enhanced thermal and flame retardant properties

A novel poly(methyl methacrylate) (PMMA)‐based copolymer (PMMA‐co‐BDPA) rich in aromatic rings was synthesized via radical copolymerization between a phosphorus‐containing acrylic monomer (BDPA) and methyl methacrylate (MMA). UV‐vis spectroscopy demonstrated that the copolymer had high transparency. Thermogravimetric analysis (TGA) and a differential scanning calorimeter (DSC) were used to test the thermal properties of the composites. Additionally, the PMMA‐co‐BDPA‐15 copolymer exhibited a 23% increase in the limited oxygen index (LOI) value. A cone calorimeter test indicated that the peak heat release rate (pk‐HRR) of PMMA‐co‐BDPA was reduced by 29.2% compared with that of pure PMMA, and the carbon yield of burning was obviously increased. The combined test results demonstrated that the prepared copolymer material had good transparency, thermal stability, and flame retardancy.     

Effect of anionic organoclay with special aggregate structure on the flame retardancy of acrylonitrile-butadiene-styrene/clay composites

Two organoclays, octadecylammonium modified montmorillonite (COM) and an anionic surfactant modified montmorillonite (AOM), were used to prepare acrylonitrile-butadiene-styrene (ABS)/clay composites. The flammability of these composites was evaluated by cone calorimetry. COM enhanced the flame retardancy of ABS/COM composite due to the catalysis by acidic sites originating from COM. Interestingly, AOM presented a similar flame retardancy to ABS/AOM composite, although AOM did not form the acidic sites. The morphology observation showed that the dispersion degree of AOM in ABS resin was lower than that of COM, which was also confirmed by the rheological properties of ABS composites. The investigations on the surface of the residue after cone calorimeter tests showed that the better flame retardancy of ABS/AOM composite was mainly due to the special structure of AOM.     

交联核壳结构PBA/PS和PBA/PMMA纳米微球的制备与应用

考察了聚丙烯酸丁酯/聚苯乙烯(PBA/PS)以及聚丙烯酸丁酯/聚甲基丙烯酸甲酯(PBA/PMMA)交联核壳结构纳米高分子微球的制备方法,并对其在尼龙复合材料中的应用进行了初步研究.结果表明,通过交联剂的引入使粒子核层和壳层内部均形成了高度交联的结构,可以限制亲水性较小的聚苯乙烯(PS)壳层向粒子内部迁移的趋势;制备出的微球平均粒径为40~50 nm,粒径分布很窄.采用饥饿态加料方式加入第二单体不仅可以使微球具有较高的产率和凝胶率,而且可以使其具有更理想的核壳结构和更窄的粒径分布.此外,将合成出的PBA/PMMA核壳粒子对尼龙6基体进行复合的结果表明,由于该微球表面与尼龙6基体之间具有较强的界面相互作用且微球具有较大的形变能力,可以在基体中形成良好的分散,在保持材料强度的同时有效地提高了其刚性和韧性.     

Flame retardancy mechanisms of phosphorus‐containing polyhedral oligomeric silsesquioxane (DOPO‐POSS) in polycarbonate/acrylonitrile‐butadiene‐styrene blends

The flame retardancy mechanisms of a novel polyhedral oligomeric silsesquioxane containing 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO‐POSS) in polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) blends are discussed. The thermal stability of PC/ABS composites with different DOPO‐POSS loadings are investigated by TGA and the enhancement of the thermal stability could be found at high temperature range. Their fire behavior is tested by the LOI, UL‐94, and cone calorimeter. Excellent flame retardancy of PC/ABS composites have been discovered with 10 wt% DOPO‐POSS loading. TGA‐FTIR, FTIR, XPS, and SEM, respectively, are used to characterize the gaseous products and the condensed residue in thermal decomposition, and the micro‐structure of the chars from cone calorimeter tests. The decomposition of PC/ABS with 10 wt% DOPO‐POSS shows significant changes compared with PC/ABS by TGA, FTIR, TGA‐FTIR, and XPS analysis. The enhancement of the thermal‐oxidative stability of PC/ABS with DOPO‐POSS is attributed to the interaction between DOPO‐POSS and PC/ABS at high temperature, which might be the key for improvement of the flame retardancy. Copyright © 2011 John Wiley & Sons, Ltd.     

Silicone‐based impact modifiers for poly(vinyl chloride), engineering resins,and blends

Silicone‐based impact modifiers were prepared in a previous study. The modifiers were composed of silicone/acrylic rubber cores and grafted acrylic shells. They improved the toughness of poly(vinyl chloride) (PVC) and poly(methyl methacrylate). The silicone emulsion that was used to produce the silicone‐based impact modifiers was prepared via two routes: emulsion polymerization and bulk polymerization of octamethyltetracyclosiloxane. Many silicone‐based impact modifiers were produced that had different silicone/acrylic rubber characteristics. Through a toughness examination of modified PVC, the best composition of the silicone‐based impact modifiers was obtained, and the silicone content in the rubber composition was 25 wt %. The morphology of the silicone‐based impact modifiers, determined by transmission electron microscopy, was as follows: core and second shell polymers were mainly poly(butyl acrylate), and the first shell polymer was silicone. The silicone‐based impact modifiers were blended with engineering resins such as PVC, polycarbonate (PC), poly(butylene terephthalate) (PBT), and PC/PBT mixtures. The impact strength under standard conditions and after weathering test conditions for blends of the silicone‐based impact modifiers were investigated with respect to two commercially available acrylic and methyl methacrylate/butadiene/styrene impact modifiers. The results showed good weatherability and good toughness under low‐temperature conditions for the silicone‐based impact modifiers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1112–1119, 2004     

纳米二氧化硅表面接枝9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物以及对聚甲基丙烯酸甲酯复合材料阻燃性能和透明性的影响

聚甲基丙烯酸甲酯(PMMA)是一种重要的透明高分子材料,但是PMMA的易燃性限制了其应用。 本工作在纳米二氧化硅表面接枝含磷阻燃剂9,10-二氢-9-氧杂-10-磷杂菲-10-氧化物(DOPO),并用于聚甲基丙烯酸甲酯(PMMA)的改性。 极限氧指数(LOI)、垂直燃烧(UL-94)和锥形量热(CCT)测试结果表明,制备的PMMA复合材料的阻燃性能大幅度提高,这主要归因于纳米粒子和含磷阻燃剂的协同阻燃作用,形成致密的炭保护层结构。 同时,二氧化硅接枝DOPO的加入可以保持PMMA良好的透明性,这有利于材料在光学透明性要求较高的领域的应用。     

Halogen-free flame retarded poly(butylene terephthalate) (PBT) using metal oxides/PBT nanocomposites in combination with aluminium phosphinate

The flame retardancy of poly(butylene terephthalate) (PBT) containing aluminium diethlyphosphinate (AlPi) and/or nanometric metal oxides such as TiO₂ or Al₂O₃ was investigated. In particular the different active flame retardancy mechanisms were discovered. Thermal analysis, evolved gas analysis (TG-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analyses of residues (ATR-FTIR) were used. AlPi acts mainly in the gas phase through the release of diethylphosphic acid, which provides flame inhibition. Part of AlPi remains in the solid phase reacting with the PBT to phosphinate-terephthalate salts that decompose to aluminium phosphate at higher temperatures. The metal oxides interact with the PBT decomposition and promote the formation of additional stable carbonaceous char in the condensed phase. A combination of metal oxides and AlPi gains the better classification in the UL 94 test thanks to the combination of the different mechanisms.     

Cone calorimeter analysis of flame retardant poly (methyl methacrylate)-silica nanocomposites

Nanocomposite is a promising method to reduce fire hazards of polymers. Specifically due to increased interfacial area between polymer and nanofillers, polymer nanocomposites have an advantage in reducing fire hazards efficiently even when the flame retardant additives are at a concentration of 5 mass% or less. In theory, crosslinking between the polymer chains can create a carbon-dense structure to enhance char formation, which can further promote the flame retardancy. However, little research has been done to explore the flammability of crosslinking polymer nanocomposites with a low concentration of nanosilica particles. In this study, crosslinked and non-crosslinked poly (methyl methacrylate) (PMMA) nanocomposites of a low concentration of nanosilica particles have been prepared via an in situ method. Their fire properties were tested by using the cone calorimeter at the heat flux of 50 kW m^?2. Although silica-containing flame retardants tend to negatively affect the ignitability and soot production especially at a high concentration, through the condensed phase mechanism, the samples of high loading rate of nanosilica particles show better fire retardancy performance in the aspect of flammability, including decreased heat release rate, mass loss rate, and total heat release. Additionally, crosslinking indeed attributes to the less intensive combustion of crosslinked PMMA samples, especially at a low concentration of nanosilica. The combination of nanosilica particles with the modification of the internal structure of the polymer nanocomposites might be a good strategy to improve fire retardancy.     

高密度聚乙烯/蒙脱土纳米复合材料膨胀阻燃体系的性能

使用以乙烯/醋酸乙烯共聚物(EVA)为相容剂的高密度聚乙烯/蒙脱土(HDPE/OMT)纳米复合材料作为基体,制备了含不同成炭剂的聚磷酸铵(APP)膨胀阻燃体系,对其阻燃性能进行了比较和研究,并分析了蒙脱土与膨胀阻燃剂协效作用的机理。热重分析(TGA)、垂直燃烧(UL-94)、极限氧指数(LOI)、锥形量热计结果表明:APP/季戊四醇(PER)体系熔融过程较短可形成蒙脱土增强炭层;PER/PA/OMT体系中较高的有机物含量有利于蒙脱土迁移和堆积。     

Synthetic hydromagnesite as flame retardant. Evaluation of the flame behaviour in a polyethylene matrix

Synthetic hydromagnesite obtained from an industrial by-product was evaluated as a non-halogenated flame retardant. It was used in combination with aluminium hydroxide (ATH) and compared with commercial flame retardants like magnesium hydroxide (MH) and natural hydromagnesite-huntite (U) in a polyolefin system of low-density polyethylene/poly(ethylene-co-vinyl acetate) (LDPE/EVA).The thermal stability and flame behaviour of the halogen free flame retarded composites were studied by thermogravimetric and differential thermal analysis (TG-DTA), limiting oxygen index (LOI), epiradiateur and cone calorimeter. It has been shown that synthetic hydromagnesite could be an alternative solution to the use of MH in non-halogenated flame retardant systems in EVA.     

Preparation and Characterization of Core/Shell-like Intumescent Flame Retardant and its Application in Polypropylene

With a shell of starch-melamine-formaldehyde (SMF) resin, core/shell-like ammonium polyphosphate (SMFAPP) is prepared by in situ polymerization, and is characterized by SEM, FTIR and XPS. The shell leads SMFAPP a high water resistance and flame retardance compared with APP in polypropylene (PP). The flame retardant action of SMFAPP and APP in PP are studied using LOI, UL 94 test and cone calorimeter, and their thermal stability is evaluated by TG. The flame retardancy and water resistance of the PP/SMFAPP composite at the same loading is better than that of the PP/APP composite. UL 94 ratings of PP/SMFAPP can reach V-0 at 30 wt% loading. The flame retardant mechanism of SMFAPP was studied by dynamic FTIR, TG and cone calorimeter, etc.     

Bubbles and collapses: Fire phenomena of flame‐retarded flexible polyurethane foams

Flexible polyurethane foams (FPUF) are easy to ignite and exhibit rapid flame spread. In this paper, the fire phenomena of two standard foam formulations containing tris(1,3‐dichloro‐2‐propyl) phosphate (FR‐2) and a halogen‐freepoly (ethyl ethylene phosphate) (PNX), respectively, as flame retardants are compared. A multi‐methodological approach is proposed which combines standard fire tests as well as new investigatory approaches. The thermophysical properties of the foams were determined by thermogravimetric analysis (TG), reaction to small flames was studied by means of the limiting oxygen index (LOI) and UL 94 HBF test, and the burning behavior was investigated with the cone calorimeter. Further, temperature development in burning cone calorimeter samples was monitored using thermocouples, and rheological measurements were performed on pyrolyzed material, delivering insight into the dripping behavior of the foams. This paper gives comprehensive insight into the fire phenomena of flame‐retarded FPUFs that are driven by the two‐step decomposition behavior of the foams. LOI and UL 94 HBF tests showed a reduced flammability and reduced tendency to drip for the flame‐retarded foams. TG and cone calorimeter measurements revealed that the two‐step decomposition behavior causes two stages during combustion, namely structural collapse and pool fire. The flame‐retardant mode of action was identified to take place primarily during the foam collapse and be based mainly on flame inhibition. However, some condensed‐phase action was been measured, leading to significantly increased melt viscosity and improved dripping behavior for foams containing PNX.     

Preparation of Polylactide Composite with Excellent Flame Retardance and Improved Mechanical Properties

Despite the good biodegradable and mechanical properties, poly(lactic acid) still suffers from a highly inherent flammability, which restricts its applications in the electric and automobile fields. In order to improve the flame retardancy of PLA, in this work, melamine polyphosphate (MPP) and zinc bisdiethylphosphinate (ZnPi) were firstly incorporated into PLA, and the synergistic effect of them on flame retardance of PLA was investigated using limiting oxygen index (LOI), UL-94 vertical measurement, scanning electron microscopy (SEM) and cone calorimeter tests etc. The results showed that PLA composite with 15 wt% of MPP/ZnPi (3:2) had the best flame-retardant efficiency with LOI value of 30.1 and V0 rating in UL-94 tests, which was far better than using MPP or ZnPi alone. What is more, although a wide range of flame retardants have been developed to reduce the flammability, so far, they normally compromise the mechanical properties of PLA. On the premise of maintaining good flame-retardant performance, we improved the toughness of flame-retardant PLA composite, and the impact strength of flame-retardant PLA composite was more than tripled (8.08 kJ/m²) by adding thermoplastic urethanes (TPU). This work offers an innovative method for the design of the unique integration of extraordinary flame retardancy and toughening reinforcement for PLA materials.