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 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.     

Methyl methacrylate oligomerically-modified clay and its poly(methyl methacrylate) nanocomposites

A methyl methacrylate oligomerically-modified clay was used to prepare poly(methyl methacrylate) clay nanocomposites by melt blending and the effect of the clay loading level on the modified clay and corresponding nanocomposite was studied. These nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis and cone calorimetry. The results show a mixed intercalated/delaminated morphology with good nanodispersion. The compatibility between the methylacrylate-subsituted clay and poly(methyl methacrylate) (PMMA) are greatly improved compared to other oligomerically-modified clays.     

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%.     

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.     

Polyethylene and polypropylene nanocomposites based on a three component oligomerically-modified clay

Polyethylene and polypropylene nanocomposites were prepared using a novel oligomerically-modified clay that contains three components, styrene, lauryl acrylate and vinylbenzyl chloride. The nanocomposites were prepared by directly melt blending the polymers with the clay and they were characterized by X-ray diffraction and transmission electron microscopy, to understand their morphology, and their thermal stability, flammability and mechanical properties were evaluated using thermogravimetric analysis, cone calorimetry and mechanical testing, respectively. The reduction in peak heat release rate is about 60% at 5% inorganic clay loading and 70% at 8% inorganic clay loading.     

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.     

Fire retardancy of bis[2-(methacryloyloxy)ethyl] phosphate modified poly(methyl methacrylate) nanocomposites containing layered double hydroxide and montmorillonite

Copolymer nanocomposites were prepared by suspension copolymerization of bis[2-(methacryloyloxy)ethyl] phosphate and methyl methacrylate, together with bis(2-ethylhexyl) phosphate layered double hydroxide and a montmorillonite, Cloisite 93A. X-ray diffraction and transmission electron microscopy were used to characterize the morphology of nanocomposites and the dispersion of additives in the polymer. The thermal stability of the nanocomposites has been assessed by thermogravimetric analysis and cone calorimetry has been used to study the fire properties. Bis[2-(methacryloyloxy)ethyl] phosphate not only copolymerized with MMA, but also aids in the dispersion of additives in PMMA. The copolymer nanocomposites have better dispersion and higher degradation temperature and more char mass than the corresponding PMMA nanocomposites. The largest peak reduction in the heat release rate of the copolymer nanocomposites are 52 and 65% for LDH and MMT additives, respectively.     

Benzimidazolium surfactants for modification of clays for use with styrenic polymers

Nanocomposites of polystyrene (PS), acrylonitrile-butadiene-styrene copolymer (ABS) and high impact polystyrene (HIPS) were prepared with two new homologous benzimidazolium surfactants used as organic modifications for the clays. The morphology of the polymer/clay hybrids was evaluated by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing good overall dispersion of the clay. The thermal stability of the polymer/clay nanocomposites was enhanced, as evaluated by thermogravimetric analysis. From cone calorimetric measurements, the peak heat release rate of the nanocomposites was decreased by about the same amount as seen for other organically-modified, commercially available clays.     

Fire retardant systems in poly(methyl methacrylate): Interactions between metal oxide nanoparticles and phosphinates

In the course of our investigations on halogen-free fire-retardant solutions for PMMA, the influence of oxide nanoparticles (TiO₂, Al₂O₃) on the thermal stability and fire behaviour of PMMA blended with phosphinate additives (Exolit OP930 and OP1311) has been studied by thermogravimetric analysis and cone calorimetry. For each mixture, the residues obtained after combustion were examined and characterized by SEM, X-ray diffraction and X-ray microprobe analysis. Some synergistic effects were obtained between nanometric alumina and OP930 additive leading to the reduction of peak of heat released rate and of total heat released up to 30% and to the increase of time to ignition. From the results obtained, it can be proposed that OP930 and OP1311 act principally in the condensed phase, the presence of oxides playing a reinforcement role in the carbonaceous layer promoted by the phosphinate additives.     

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.     

Smoke and hydrocarbon yields from fire retarded polymer nanocomposites

Polypropylene (PP) and Polyamide 6 (PA6) samples, with and without fire retardants (FR) (ammonium polyphosphate in PP, and a mixture of organic aluminium phosphinate and melamine polyphosphate (OP 1311) in PA 6) and nanofillers (NC) were burned under different fire conditions in order to compare their toxic product yields. Fire effluents (CO, smoke and hydrocarbons) were generated using a steady state tube furnace (BS 7900, ISO TS 19700) for the separate materials and fire retarded and nanocomposite modifications of these materials under flaming conditions. Under well-ventilated conditions yields of carbon monoxide (CO) for all PP samples are similar, whereas for PA6 samples much higher yields of CO for PA6 + FR and PA6 + NC are observed. The highest yields of CO occur for both pure polymers in under-ventilated fire conditions when fire retardant and nanoclay are combined together. For PP the smoke is fairly independent of fire condition, but the PP + FR + NC shows less agglomeration. For PA6 the sample containing OP 1311 shows consistently higher smoke yields. For hydrocarbon yields similar effects are observed for both PP and PA6 polymers; the highest yields are for PA6 + NC, except under-ventilated fires where PA6 + FR produce the most; for PA6 + FR + NC samples the lowest yields are observed, compared to either NC or FR formulations.     

Polystyrene nanocomposites based on quinolinium and pyridinium surfactants

In this paper pyridine and quinoline-containing salts were employed to modify montmorillonite. TGA analysis shows that the quinolinium modified clay has a higher thermal stability than the pyridinium modified clay. Polystyrene nanocomposites were prepared by in situ bulk polymerisation and direct melt blending using both clays. The X-ray diffraction and transmission electron microscopy results show the formation of intercalated structures. The 50% degradation temperature of the nanocomposites is increased and so is the amount of char from TGA analysis compared to the virgin polymer. Cone calorimetric results indicate that clay reduces the peak heat release rate and average mass loss rate and thus lowers the flammability of the polymer.     

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.     

Flammability, microhardness and transparency of nanocomposites based on functionalized polyethylenes

The flammability, microhardness and transparency of nanocomposites based on poly(ethylene-co-acrylic acid) copolymers having different concentration of acrylic acid and different molar mass, their Zn ionomer and ethylene-glycidylmethacrylate copolymer as matrixes and on organically modified montmorillonite as a nanofiller have been investigated. The presence and the increase in the content of the clay lead to the increase in the limiting oxygen index and to significant reduction of the burning rate of all materials. The results from the Vickers microhardness measurements have shown that the addition of the clay to matrixes of polar functionalized polyethylenes leads to a significant increase in the microhardness of the materials, while the creep constant does not decrease significantly. The UV spectra show that the light transmittance of the materials does not change significantly in the presence of the clay, i.e., the nanocomposite films preserve the polymer transparency. The results have been interpreted by the intercalated structures of the nanocomposites investigated.     

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.     

Flammability performance of poly(vinyl alcohol) nanocomposites with zirconium phosphate and layered silicates

Nanocomposites of poly(vinyl alcohol) with α-type zirconium phosphate (PVA/ZrP) and with layered silicates (montmorillonite and hectorite) were prepared by solution blending. Thermal properties and flame retardancy of the materials were characterized by thermogravimetric analysis and microscale combustion calorimetry. PVA/ZrP nanocomposite showed a faster charring process in temperature range between 200 and 350 °C but higher thermal stability and greater char yields above 350 °C and a different heat release rate feature, compared to clay-based samples. Observation of the micrographs of the chars from the nanocomposites present two distinct structures; one constituted by the stacked clay layers on the surface combined with clay-reinforced foams in the interior residue, and the other formed by carbon covered on the tightly curled ZrP nanoplatelets. The results indicated different flame retardant mechanisms of the two nanocomposites, which depend on the chemical/physical effects from the inherent properties of the nanofillers.     

A novel method for preparation of exfoliated UV-curable polymer/clay nanocomposites

The half adduct of isophorone diisocyanate and 2-hydroxyethyl acrylate (IPDI-HEA), as a reactive organic modifier, was used to functionalize Na-montmorillonite (Na-MMT) clay. Unlike the electronic interaction in the conventional cation-exchange method, the driving force for the organic modification came from the chemical reaction between IPDI-HEA and framework hydroxyl groups on the surface of clay. With high degree of organic modification (48%), the d-spacing of clay layer was greatly enlarged to 3.32 nm, and the clay became more organophilic. After in situ photopolymerization among the IPDI-HEA grafted MMT clay, monomers and oligomers, the exfoliated polymer/clay nanocomposites were obtained. X-ray diffraction and transmission electron microscopy were used to detect the structure and morphology of the clay dispersed in the polymer matrix. Compared with the pure polymer materials, the exfoliated polymer/clay nanocomposites exhibited enhancements in mechanical and thermal properties.     

Fire retardancy behavior of PLA based nanocomposites

To understand and improve the fire retardancy behavior of polylactic acid, we have incorporated two structurally different additives, sepiolite and organically modified montmorillonite. A novel approach (combination of electrospinning and extrusion/injection molding) is employed to address critical issues like char enhancement as well as the homogeneity/uniformity of the inorganic barrier during combustion of polymer nanocomposites. Fundamental knowledge is gained on the mechanisms of fire retardancy, particularly with samples of different thicknesses (thermally thin versus thermally intermediate/thick). Volumetric imaging of the residues provided a deeper understanding of the formation or the evolution of the inorganic barrier. Considerable insight on the dependency of biodegradation on the environment (primarily) and on the compromising effect of high aspect ratio nanoparticles is also obtained. This knowledge has a broader scientific impact and is critical to design the new generation of eco-benign flame retardant and biodegradable polymer nanocomposites.     

Fire retardancy of melamine and zinc aluminum layered double hydroxide in poly(methyl methacrylate)

The thermal and fire properties of PMMA modified with various loadings of melamine or zinc aluminum undecenoate LDH were evaluated using TGA, DTA and cone calorimetry. The additives were characterized by X-ray diffraction, TGA, FT-IR and elemental analysis. While the two additives are very effective with this polymer, a higher loading of melamine (30%) is required to reach a good reduction in PHRR (47%) relative to the pure polymer, while with the LDH, 10% loading is enough to obtain a similar reduction. The combinations of these additives in PMMA reveal that the time to PHRR and the amount of smoke produced are the key differences, with melamine increasing the first parameter and leading to less smoke production relative to LDH-rich PMMA systems at similar total additive loadings. Analysis of the residue shows that melamine is completely lost during combustion while the LDH forms ZnO and ZnAl₂O₄.