Characterisation of soot particulates from fire retarded and nanocomposite materials, and their toxicological impact

Polyamide 6 (PA 6) and polypropylene (PP) containing fire retardants, nanofillers or a combination of both additives have been investigated using the steady state tube furnace (ISO TS 19700). The samples were tested under three different fire conditions, to determine the effect of additives on the soot production or toxic product yields. The particle size distribution of the soot was investigated with a cascade impactor, and the separated soot fractions examined by SEM. The predicted deposition based on aerodynamic size of particulates in the human respiratory tract shows clear differences between the pure polymer and its additive counterparts. In all ventilation conditions the virgin polymer produces the least amount of soot, both the additives used (fire retardant and nanoclay) increase the amount of soot, mainly within 0.5-1.0 μm range, for each fire condition. A large contribution to the total soot mass originated particles smaller than 0.5 μm.     

Self-extinguishing polymer/organoclay nanocomposites

We demonstrated that self-extinguishing polymer nanocomposites, which can pass the stringent UL 94 V0 standard, can be successfully prepared by combining modified organoclays with traditional flame retardant (FR) agents. Using secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we determined that the addition of modified clays, which can intercalate or exfoliate in the matrix, also improved the dispersion of the FR agents. Dynamic mechanical analysis (DMA) indicated that the clays increased the modulus of the polymer above T_g, which prevented dripping during burning. Cone calorimetry test showed that the nanocomposites with both FR and organoclay, had a lower peak heat release rate (PHRR) and average mass loss rate (MLR) than those with only clay or the FR agents. Extended X-ray absorption fine structure (EXAFS) data confirmed that no FR/clay interactions occurred in the solid phase, and that the synergistic effects were due to gas phase reactions. Since this mechanism is not specific, it opens the possibility of formulating self-extinguishing materials from a large class of polymers.     

Catalytic fire retardant nanocomposites

In this paper the chemical activity of carbon nanotubes and polyhedral oligomeric silsesquioxane during thermal degradation and combustion of polymer nanocomposites is addressed. Indeed, polymer-nanofiller systems may exhibit chemical effects capable of thermal stabilisation of polymers as well as reduction of combustion rate and heat released, owing to catalytic effects induced by the nanofillers at high temperature.Carbon nanotubes in the presence of oxygen are shown to promote oxidative dehydrogenation in polyethylene with production of a stable surface layer of carbon char that provides an effective oxygen barrier effect. A similar action is performed by metal-containing polysilsesquioxanes dispersed in polypropylene.With either carbon nanotubes or metal POSS, partial carbonisation of the polymer matrix occurs during combustion, subtracting part of the organic polymer from combustion, targeting one of the major fire retardancy aim.     

Mechanical and fire retardant properties of EVA/clay/ATH nanocomposites - Effect of particle size and surface treatment of ATH filler

Mechanical and flame retardant properties of ethylene vinyl acetate (EVA) copolymer/organoclay/alumina trihydrate (ATH) nanocomposites have been studied. ATH with different particle sizes, ATH1 (2.2-5.2 μm) and ATH2 (1.5-3.5 μm), and three different surface treatments, uncoated, fatty acid coated and silane coated, have been used. A synergistic effect was observed in EVA/organoclay/ATH nanocomposites with the total heat evolved (THE) and the heat release rate (HRR) lower than that of EVA/ATH composite. It was also found that mechanical and flame retardant properties are affected in different ways by the particle size and the surface treatment of ATH fillers. Improvements in tensile and flame retardant properties were observed in nanocomposites when uncoated ATH fillers and fatty acid coated ATH2 filler were used. On the other hand, silane coating on ATH1 and ATH2 improves limiting oxygen index (LOI) and leads to higher t_ignition and the best char stability after cone calorimeter test.     

Flammability of styrenic polymer clay nanocomposites based on a methyl methacrylate oligomerically-modified clay

Nanocomposites of polystyrene, high impact polystyrene, acrylonitrile-butadiene-styrene terpolymer, polypropylene, and polyethylene were prepared using a methyl methacrylate oligomerically-modified clay by melt blending and the thermal stability and fire retardancy were studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed morphology, depending on the polymer.     

Styrenic polymer nanocomposites based on an oligomerically-modified clay with high inorganic content

Clay was modified with an oligomeric surfactant containing styrene and lauryl acrylate units along with a small amount of vinylbenzyl chloride to permit the formation of an ammonium salt so that this can be attached to a clay. The oligomerically-modified clay contains 50% inorganic clay, and styrenic polymer nanocomposites, including those of polystyrene (PS), high-impact polystyrene (HIPS), styrene-acrylonitrile copolymer (SAN) and acrylonitrile-butadiene-styrene (ABS), were prepared by melt blending. The morphologies of the nanocomposites were evaluated by X-ray diffraction and transmission electron microscopy. Mixed intercalated/delaminated nanocomposites were formed for SAN and ABS while largely immiscible nanocomposites were formed for PS and HIPS. The thermal stability and fire properties were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The plasticization from the oligomeric surfactant was suppressed and the tensile strength and Young's modulus were improved, compared to similar oligomerically-modified clays with higher organic content.     

The effects of intralayer metal composition of layered double hydroxides on glass transition, dispersion, thermal and fire properties of their PMMA nanocomposites

A series of aluminum-containing layered double hydroxides (LDHs), containing Mg, Ca, Co, Ni, Cu and Zn as the divalent metals, have been prepared by the co-precipitation method and used to prepare nanocomposites of PMMA by in situ bulk polymerization. The additives were characterized by Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy (XRD) and thermogravimetric analysis while the polymer composites were characterized by XRD, transmission electron microscopy, differential scanning calorimetry and cone calorimetry. Polymerization of methyl methacrylate in the presence of these undecenoate LDHs results in composites with enhanced thermal stability. The glass transition temperatures of the composites and the pristine polymers are found to be around 110 °C; this suggests that the presence of these additives has little effect on the polymer. It is found that the additive composition and the dispersion state of LDHs agglomerates in the polymer matrix influence the fire properties of composites as measured by cone calorimetry.     

Thermal and flame properties of polyethylene and polypropylene nanocomposites based on an oligomerically-modified clay

An oligomerically-modified clay was made using a surfactant which is the ammonium salt of an oligomer. The newly modified clay contains 37.5% inorganic clay and 62.5% oligomer. Polyethylene and polypropylene nanocomposites were made by melt blending the polymer with the oligomerically-modified clay in a Brabender mixer at various clay loadings. The structure of the nanocomposites was characterized by X-ray diffraction and transmission electron microscopy. Mechanical testing showed that the polyethylene nanocomposites had an enhanced Young's modulus and slightly decreased elongation, while the changes for polypropylene nanocomposites are small compared with the virgin polymers. The thermal stability and flame properties were evaluated using thermogravimetric analysis and cone calorimetry, respectively. The plasticising effect of the oligomer was suppressed because of the increased inorganic content. The maximum reduction in peak heat release rate is about 40%.     

Structure-property relationships of new polystyrene nanocomposites prepared from initiator-containing layered double hydroxides of zinc aluminum and magnesium aluminum

Polystyrene/layered double hydroxides (PS/LDHs) nanocomposites were prepared by free radical polymerization of styrene monomer in the presence of LDHs intercalated with 4,4′-azobis(4-cyanopentanoate) anions (LDH-ACPA). XRD and ATR-IR are used to confirm that the materials produced are layered and the presence of the azo-initiator anions in these LDHs. These LDHs were used successfully to polymerize styrene and both XRD and TEM images of the composites support the formation of a mixed exfoliated-intercalated nanocomposite for ZnAl-ACPA but a microcomposite for MgAl-ACPA. The magnesium-containing LDHs decreased the glass transition temperature (T_g) of the composites while ZnAl-ACPA did not affect T_g significantly. The T_g depression is related to enhanced polymer dynamics due to the extra free volume at the LDH additive-polymer interface. A reduction in the onset of thermal decomposition temperature was observed in PS/LDH compared to neat PS, likely due to the early decomposition of the LDH. The fire performance, as evaluated by the cone calorimeter, reveal that PS-ZnAl-ACPA shows enhanced fire properties compared to PS-MgAl-ACPA.     

Rheology of polymer layered silicate nanocomposites

Layered silicate based polymer nanocomposites have gained significant technological interest because of the recent commercialization of nylon 6 and polypropylene based materials. Aside from the natural interests in understanding and improving the processing of these hybrids, viscoelastic measurements have also proven to be a sensitive tool to probe the mesoscale structure and the strength of polymer–nanoparticle interactions.     

Fire behavior of flame retarded unsaturated polyester resin with high nitrogen content additives

The novel flame retarded unsaturated polyester resins have been developed and prepared by introduction of high nitrogen content additives into the polymer matrix in order to verify their effectiveness in the formation of swollen carbonaceous char inhibiting the burning process of the polymer. The intumescent flame retardants (IFRs) based on mixture or metal complex were developed and characterized by particle size distribution, Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), powder X-ray diffraction (XRD), elemental analysis (CHN) and thermogravimetric analysis (TGA). The evaluation of the efficiency of IFRs addition on the flammability and smoke emission of the unsaturated polyester resins (UP) was carried out using the fire hazard (UL-94), limiting oxygen index (LOI) and cone calorimeter (CC) tests, as well as smoke density chamber tests. The volatile compounds evolved during the burning of materials were determined using a steady state tube furnace and a gas chromatograph with mass spectrometer. Furthermore, the prepared materials were subjected to differential scanning calorimetry (DSC), thermogravimetric analysis and water resistance tests. The mechanical properties of the materials were investigated using Shore D hardness and dynamic mechanical thermal analysis (DMA). The structural evaluation of the manufactured materials and samples after the cone calorimetry tests was carried out using scanning electron microscopy (SEM). It was found that the incorporation of new intumescent flame retardants led to the formation of carbonaceous char layers’ inhibiting the decomposition process and limiting the smoke emission. The most promising results were obtained for the resin containing complex designated as ZN3AT, for which the highest reduction in maximum values of heat release rate (419 kW/m²) compared to unmodified polymer (792 kW/m²) were recorded. Apart from that, the prepared intumescent flame retardants affect the cross-linking process as well as the thermal and mechanical properties of the UP.     

A review of candidate fire retardants for polyisoprene

Polyisoprene elastomer, as natural rubber (NR) or manufactured synthetically (IR), is used in rubber compounds for applications such as tyres, dampers and suspension elements. NR/IR compounds without fire retardants have a low resistance to burning, and emit large quantities of dense smoke. This is because polyisoprene readily decomposes upon heating, by random chain scission, vaporising into a mixture of small aromatic chemical species, which ignite readily and form smoke particles with negligible char residue formation. The effects of commonly used additives on the thermal decomposition and burning of polyisoprene are reviewed; whilst cross-linking agents have significant effects on physical and ageing properties, they have little effect on thermal decomposition and burning. Fillers such as carbon black and silicas reduce the fuel content by dilution of the polymer and the formation of a stabilising residue.Potential approaches for fire retarding IR are reviewed, identifying two main approaches; halogenated additives, or high loadings of aluminium hydroxide (ATH), neither of which are satisfactory. Other potential approaches are identified, including the use of phosphorus and nitrogen based additives as intumescent char formers, and with zeolites as char catalysts. Alternative inorganic fire retardants to ATH are identified for use, and zinc hydroxystannate and zinc borate are considered as synergists with ATH. Expandable graphite (EG) is identified for use in other elastomers and has potential for polyisoprene. Nano-scale fire retardants such as montmorillonite clay and multi-walled carbon nanotubes are reported typically as a secondary additive to hydrated fillers, but have yet to make a successful transition to industrial processing.     

Fire properties of styrenic polymer-clay nanocomposites based on an oligomerically-modified clay

An oligomerically-modified clay has been used to fabricate nanocomposites with styrenic polymers, such as polystyrene, high-impacted polystyrene, poly(styrene-co-acrylonitrile) and acrylonitrile-butadiene-styrene by melt blending. The clay dispersion was evaluated by X-ray diffraction and bright field transmission electron microscopy. All of the nanocomposites have a mixed delaminated/intercalated structure. The fire properties of nanocomposites were evaluated by cone calorimetry a nd the mechanical properties were also evaluated.     

Styrenic nanocomposites prepared using a novel biphenyl-containing modified clay

Montmorillonite was organically modified using an ammonium salt containing 4-acetylbiphenyl. This clay (BPNC16 clay) was used to prepare polystyrene (PS), acrylonitrile butadiene styrene (ABS) and high impact polystyrene (HIPS) nanocomposites. Polystyrene nanocomposites were prepared both by in situ bulk polymerisation and melt blending processes, while the ABS and HIPS nanocomposites were prepared only by melt blending. X-ray diffraction and transmission electron microscopy were used to confirm nanocomposite formation. Thermogravimetric analysis was used to evaluate thermal stability and the flammability properties were evaluated using cone calorimetry. By thermogravimetry, BPNC16 clay was found to show high thermal stability, and by cone calorimetry, a decrease in both the peak heat release rate and the mass loss rate was observed for the nanocomposites.     

Characterisation of the dispersion in polymer flame retarded nanocomposites

Flame retardant nanocomposites have attracted many research efforts because they combine the advantages of a conventional flame retardant polymer with that of polymer nanocomposite. However the properties obtained depend on the dispersion of the nanoparticles. In this study, three types of polymer flame retarded nanocomposites based on different matrices (polypropylene (PP), polybutadiene terephtalate (PBT) and polyamide 6 (PA6)) have been prepared by extrusion. In order to investigate the dispersion of nanoparticles in the polymer containing flame retardant, conventional methods used to characterise the morphology of composites have been applied to FR composites containing nanoclays. XRD, TEM and melt rheology give useful information to describe the dispersion of the nanofiller in the flame retarded nanocomposite. In the PA6-OP1311 (phosphorus based flame retardant) materials, the clay is well dispersed unlike in PBT and PP materials where microcomposites are obtained with some intercalation. The poor dispersion is also highlighted by NMR measurements but the presence of flame retardant particles interferes in the quantitative evaluation of nanoclay dispersion and underestimations are made.     

Polystyrene nanocomposites based on an oligomerically-modified clay containing maleic anhydride

An oligomerically-modified clay containing maleic anhydride was used to prepare polystyrene-clay nanocomposites by melt blending and the effect of this modified clay on the thermal stability and fire performance was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed immiscible/intercalated/delaminated morphology. The maleic anhydride modified clay improved the compatibility between the clay and the polystyrene.     

New aspects of migration and flame retardancy in polymer nanocomposites

Annealing of pristine polypropylene blended with the organomontmorillonite (OMMT) at temperatures of 180-340 °C under a stream of nitrogen and of nitrogen-air mixtures is investigated. The oxidative annealing brings about the dispersion of the OMMT in the polypropylene and the formation of a nanocomposite structure. This is evidenced by the increase in the interlayer distance ‘d’ as measured by small angle XRD, with time of annealing and with the weight percent of air. This indicates progressive intercalation of the polymeric matrix into the clay gallery and subsequently exfoliation. The degree of exfoliation is estimated by the extent of migration determined spectroscopically on the surface of the annealed sample. The accumulated clay on the surface due to migration hinders the penetration of the oxygen into the annealing melt as expressed by the decrease in the rate of migration with the increase in the air concentration. This indicates the increase in ageing and storage stability of nanocomposites with increase in the extent of migration. The extent of migration is proportional to the polar carbonyl groups formed on the matrix. The energy of activation of the migration was found to be 37.82 kJ/mol indicating that the rate-determining step of migration is diffusion controlled reaction. The penetration of oxygen into the melt is the first of five steps, followed by oxidation, intercalation, exfoliation and migration. Monitoring the migration with increase in the temperature enables the observation at 275 °C of the transition of the nanocomposite structure to noncolloidal microcomposite. Increasing the annealing temperature above 300 °C brings about a slow, low-temperature combustion and formation of a new kind of char on the surface of the sample.     

含改性硅微粉硅橡胶阻燃抑烟研究

为进一步提升硅橡胶(SR)的阻燃性能,利用硅烷偶联剂对硅微粉(SF)进行表面改性,以改性后的SF为阻燃剂,制备出SR样品。通过扫描电子显微镜(SEM)对改性前后SF表面形貌进行表征,通过极限氧指数(LOI)、水平垂直测试、锥形量热仪(CCT)、烟密度测试(SDT)等手段研究SR复合材料力学性能、阻燃性能、抑烟性能。研究表明:添加相同质量的SF和改性SF时,含改性SF的SR力学性能明显提升。其中,含21%(wt)改性SF/SR复合材料的力学、阻燃性能综合最佳。与纯SR相比,改性SF/SR复合材料的LOI增加了15%,热释放速率峰值降低86%,火灾增长指数降低了58%,最大烟密度降低43%。     

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...     

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.