Synergistic effects of metal hydroxides and fumed nanosilica as fire retardants for polyethylene

This work aims to study the synergistic effect of aluminum/magnesium hydroxide microfillers and organomodified fumed silica nanoparticles as flame retardants (FRs) for linear low-density polyethylene (LLDPE), and to select the best composition to produce a fire-resistant polyethylene-based single-polymer composite. The fillers were added to LLDPE at different concentrations, and the prepared composites were characterized to investigate the individual and combined effects of the fillers on the thermo-oxidation resistance and the fire performance, as well as the microstructural, physical, thermal and mechanical properties. Both filler types were homogeneously distributed in the matrix, with the formation of a network of silica nanoparticles at elevated loadings. Melt flow index (MFI) tests revealed that the fluidity of the material was not considerably impaired upon metal hydroxide introduction, while a heavy reduction of the MFI was detected for silica contents higher than 5 wt%. FRs introduction promoted a noticeable enhancement of the thermo-oxidative stability of the materials, as shown by thermogravimetric analysis (TGA) and onset oxidation temperature (OOT) tests, and superior thermal properties were measured on the samples combining micro- and nanofillers, thus evidencing synergistic effects. Tensile tests showed that the stiffening effect due to a high content of metal hydroxide microparticles was accompanied by a decrease in the strain at break, but nanosilica at low concentration contributed to preserve the ultimate mechanical properties of the neat polymer. The fire performance of the samples with optimized compositions, evaluated through limiting oxygen index (LOI) and cone calorimetry tests, was strongly enhanced with respect to that of the neat LLDPE, and also these tests highlighted the synergistic effect between micro- and nanofillers, as well as an interesting correlation between fire parameters and viscosity.

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title: Flame retardancy and smoke suppression of magnesium hydroxide filled polyethylene
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title: Discolouration of polypropylene-based compounds containing magnesium hydroxide
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title: Tensile properties and stress whitening of polypropylene/polyolefin elastomer/magnesium hydroxide flame retardant composites for cable insulating application
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title: Improving the flame-retardant efficiency of aluminum hydroxide with fullerene for high-density polyethylene
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title: Synergistic effect of aluminum hydroxide and nanoclay on flame retardancy and mechanical properties of EPDM composites
abstract: The composites based on ethylene–propylene–diene monomer rubber (EPDM) with aluminum hydroxide (ATH), nanoclay, vulcanizing agent, and curing accelerator were prepared by conventional mill compounding method. The thermal stability and the flame retardant properties were evaluated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, cone calorimeter, and smoke density chamber tests. The results indicated that the substitution of the nanoclay in the EPDM/ATH composites increased the 50% weight loss temperature and the LOI value, and reduced the peak heat release rate (pk-HRR), the extinction coefficient (Ext Coef), the maximal smoke density (Dm), and the whole smoke at the first 4 min (VOF4) of the test specimens. The synergistic flame retardancy of the nanoclay with ATH in EPDM matrix could imply that the formation of a reinforced char/nanoclay layer during combustion prevents the diffusion of the oxygen and the decomposed organic volatiles in the flame. The mechanical properties of the composites have been increased by replacing more of the nanoclays into the EPDM/ATH blends. The best loading of the nanoclay in EPDM/ATH composites is 3 wt %, which keeps LOI in the enough value, the V-0 rating in the UL-94 test, and the improved mechanical properties with better dispersion and exfoliation of the nanoclays shown by transmission electron microscopy (TEM) micrographs.

title: Flame retardant and mechanical properties of polyethylene/magnesium hydroxide/montmorillonite nanocomposites
abstract: Polyethylene (PE) provides good flexibility at low temperatures, chemical stability, and electrical performance that makes it an ideal insulating material for wire and cable, but it has low melting point and is flammable. In fire events, PE must be modified with additives to enhance its flame retardancy and satisfy the fire safety standards. In this study, we used the LDPE and cross-linked polyethylene (XLPE) as the matrix, added nanoclay montmorillonite (MMT), flame retardant magnesium hydroxide (MH) and compatibilizer LDPE grafted maleic anhydride (LDPE-g-MA). The PE/PE-g-MA/MH/MMT nanocomposites were compounded using the twin screw extruder, then were injection molded into the standardized specimens. The properties of nanocomposites were characterized with XRD, TGA, and DSC techniques and LOI, tensile, and impact examinations. The results showed that the interlayer of OMT (modification of organoclay) modified with dodecylamine expanded to about 4.1 A and there was no 2θ peaks between 1.5° and 10°, indicating that the dispersion of nanocomposites were exfoliation structure from XRD pattern. The tensile and impact strengths were enhanced with LDPE-g-MA and clay added. The increase in char residual of nanocomposites indicated that the thermal stability at elevated temperatures improved. The XLPE nanocomposites achieved the effective level of flame retardancy.

title: Effect of zinc borate on flammability/thermal properties of ethylene vinyl acetate filled with metal hydroxides
abstract: In this work, zinc borate was used as a flame retardant in ethylene vinyl acetate/magnesium hydroxide or aluminum hydroxide flame-retardant formulations. High content zinc borate leads to significant improvements of flame retardancy through limiting oxygen index, UL-94 and cone calorimeter experiments. The protective char formation revealed significant structural modifications due to the presence of zinc borate. It was demonstrated that during polymer heating, aluminum hydroxide and magnesium hydroxide decomposed to Al2O3 and MgO which resulted an increase in ignition time. Moreover, formation of Al2O3 or MgO in situ from aluminum hydroxide or magnesium hydroxide during polymer combustion is the first event. Concurrently, zinc borate degraded and formed a vitreous protective coating, which yielded the substrate with an efficient char which acted as a physical barrier and a glassy cage for better protection of polymer substrate.

title: Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer
abstract: The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/ talc) has been investigated. The release of water from Mg(OH) 2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH) 2 , appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH) 2 loading in ternary compositions.

title: Reflections on migration of clay and structural changes in nanocomposites
abstract: The profound effect on flame retardancy of the blending of small amounts of clay with polymers is believed to be due to the formation of a protective clay-rich char barrier on the surface of the pyrolyzing polymer during combustion. The mode of formation of this barrier is discussed, in view of recent results. Evidence is reviewed, showing that the organically layered silicon particles migrate to, and accumulate on the surface of the molten polymer at temperatures far below pyrolysis temperature. The causes of the migration are: temperature and viscosity gradients of the melt with regard to heat source; propelling the organically layered silicon to the surface by gas bubbles from the decomposing surfactant and polymer; and by the difference in surface free energy between the polymer and the polymer/clay aggregate. The interfacial tension of the clay/polymer aggregates is calculated for a number of polymers, and shown to be much lower than the surface tension of the low surface free energy ingredient. It is suggested that these aggregates migrate to the surface. The decomposition of the surfactant in the clay above 200°C brings about, in the case of polypropylene/nanocomposite, two simultaneous and opposing phenomena: the migration of the clay; and the conversion of the nanocomposite into a non-colloidal microcomposite. The decomposition of the surfactant is accompanied by an increase in interlayer distance, and internal pressure in the clay particles, culminating either in a separation of the external layers (i.e. exfoliation), or in their collapse into each other, forming a microcomposite. Mechanistic considerations are presented.

title: Nanocomposites at elevated temperatures: migration and structural changes
abstract: The possible effect of temperature stability of organic layered silicates (OLSs) on the structure and flammability behavior of polymer/montmorillonite (MMT) nanocomposites has been discussed in a previous publication. Above 200°C, the OLS begins to decompose, and the nanocomposite structure is gradually destroyed even before pyrolysis and combustion. Data on the decomposition of polymer/OLS mixtures upon isothermal thermogravimetric analysis (TGA) experiments are presented, and include rates and energies of activation at a range of temperatures from 200 to 400°C. Decomposition of OLSs in the presence of polymer is discussed in view of the decomposition of clay, pristine surfactant, and OLS. Accumulation of clay by migration to the surface of samples at a range of temperatures is indicated by X-ray diffraction (XRD) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) measurements on the isothermally heated samples. Mechanistic considerations concerning changes in the structure of the nanocomposite, the decomposition of OLS, and migration of clay will be presented.

title: Fire retardancy of ethylene-vinyl acetate composites – Evaluation of synergistic effects between ATH and diatomite fillers
abstract: In the present work, diatomite was used as co-filler in aluminium hydroxide/ethylene-vinyl acetate composites (ATH/EVA). This silica-based marine sediment acts as a synergistic agent with ATH, to increase the flame retardant properties of EVA composites. When diatomite was used with ATH the formation of an expanded layer during cone calorimetry tests was observed. This layer presents a complex structure which better insulates the sample and reduces the heat release rate (HRR). Rheological measurements, such as complex viscosity obtained with an ARES apparatus, suggest an influence of the viscosity of the sample melt. We assume that the viscosity of the EVA composites is influenced by the porosity of the diatomite. Better residue cohesion was also obtained in presence of diatomite.

title: Flame-retardant properties of ethylene-vinyl acetate/oil sludge/ fumed silica composites
abstract: Ethylene-vinyl acetate (EVA)/oil sludge (OS)/fumed silica (SiO2) composites were synthesized using OS containing CaCO3 as raw material. Flame retardant and thermal degradation properties of the composites were characterized via limiting oxygen index (LOI), cone calorimetry test (CCT), scanning electronic microscopy (SEM), smoke density test (SDT), and thermogravimetry Fourier transform infrared spectrometry (TG-FTIR). Addition of a certain amount of SiO2 could evidently increase LOI values. The heat release rates (HRR) of the composites were much lower than those of EVA and EVA/OS composites. The morphologies and structures of the residues, revealed by SEM, ascertained that the formed char layers on the composites were denser than those of the EVA/OS composites. SiO2 in the material can help smoke suppression. The composites also assumed a higher thermal stability than the EVA/OS composites.

title: Smoke suppression properties of fumed silica on flame-retardant thermoplastic polyurethane based on ammonium polyphosphate
abstract: In this paper, fumed silica has been used as smoke suppression and flame-retardant synergism in thermoplastic polyurethane (TPU) composites based on ammonium polyphosphate (APP). And, the synergistic smoke suppression property and flame-retardant effect of fumed silica in flame-retardant TPU composites are mainly intensively investigated by several methods, including smoke density test (SDT), cone calorimeter test (CCT), scanning electron microscopy (SEM), limiting oxygen index, and thermogravimetric analysis. The results of SDT show that fumed silica can significantly decrease smoke production of flame-retardant TPU composites. The results of CCT present that the addition of fumed silica can effectively reduce smoke production rate, total smoke release, smoke factor, heat release rate, and mass loss in the combustion process of flame-retardant TPU composites. The SEM results show that fumed silica can improve the quality of char residue after cone calorimeter test. All the results show that fumed silica is an effective smoke suppression agent and a good flame-retardant synergism with APP in TPU composites.

title: Effect of phosphorous-modified silica on the flame retardancy of polypropylene based nanocomposites
abstract: Surface modification of various silicas by phosphorous agents was carried out with the aim to use these particles as flame retardant additive in a polypropylene matrice (PP) at low content (10 wt%). Thermal and flammability properties of PP/modified silica (PP-Tm-10%, PP-Zm-10%) were studied using TGA, PCFC and cone calorimeter and compared to those conferred by pure silica (PP-T-10%, PP-Z-10%). Quite surprisingly the untreated fillers induce the most significant reduction of peak of Heat Release Rate (50% decrease) while the surface modification by phosphorous agents does not lead to the expected effect on the fire behavior of PP composite. This phenomenon was related to the morphology and rheological behavior of the various PP composites. Indeed, the higher the storage modulus at low frequencies is, the better the fire behavior is, because of the induced barrier effect. Moreover, the addition of non modified silicas leads to a decrease of 10 s of the TTI. This phenomenon was related to the formation of bubbles after the PP melting during cone calorimeter test.

title: Synergistic flame retardant mechanism of fumed silica in ethylene-vinyl acetate/magnesium hydroxide blends ☆
abstract: The flammability characterization and synergistic flame retardant mechanism of fumed silica in the ethylene-vinyl acetate/magnesium hydroxide (EVA/MH) blends were studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI), and UL-94 test. The results showed that the addition of a given amount of fumed silica apparently increased the LOI value and decreased the loading of MH in EVA blends while keeping the V-0 rating in the UL-94 test. The data obtained from the CCT indicated that the addition of fumed silica not only greatly reduced the heat release and mass loss rates, but also depressed the smoke release during the combustion of EVA/MH blends. The morphological and TGA data showed further evidence that this synergistic flame retardant mechanism of fumed silica in the EVA/MH materials is mainly due to the physical process of fumed silica acting as enhanced char/silica layers in the condensed phase which prevents the heat and mass transfer in the fire. By adding fumed silica into EVA/MH blends and reducing the total amount of fillers, the elongation at break of samples is doubled, while the fire resistance of the blends is maintained.

title: Influence of fumed silica on the flame-retardant properties of ethylene vinyl acetate/aluminum hydroxide composites
abstract: The flammability and synergistic flame-retardant effects of fumed silica (SiO2) in ethylene vinyl acetate (EVA)/aluminum hydroxide (ATH) blends were studied with limiting oxygen index measurements, UL 94 testing, cone calorimeter testing (CONE), and thermogravimetric analysis (TGA). The results show that the addition of a given amount of fumed SiO2 can apparently improve UL 94 rating. The CONE data indicated that the addition of fumed SiO2 greatly reduced the heat release rate. The TGA data showed that this synergistic flame-retardant mechanism of fumed SiO2 in the EVA/ATH materials was mainly due to the physical process.

title: Thermal stability of high density polyethylene–fumed silica nanocomposites
abstract: High-density polyethylene-based nanocomposites were prepared through a melt compounding process by using surface functionalized fumed silica nanoparticles in various amounts, in order to investigate their capability to improve both mechanical properties and resistance to thermal degradation. The fine dispersion of silica aggregates led to noticeable improvements of both the elastic modulus and of the stress at yield proportionally to the filler content, while the tensile properties at break were not impaired even at elevated filler content. Thermogravimetric analysis showed that the selected nanoparticles were extremely effective both in increasing the decomposition temperature and in decreasing the mass loss rate, even at relatively low filler loadings. The formation of a char enriched layer, limiting the diffusion of the oxygen through the nanofilled samples, was responsible of noticeable improvements of the limiting oxygen index, especially at elevated silica loadings. In contrast with commonly reported literature results, cone calorimeter tests also revealed the efficacy of functionalized nanoparticles in delaying the time to ignition and in decreasing the heat release rate values. Therefore, the addition of functionalized fumed silica nanoparticles could represent an effective way to enhance the flammability properties of polyolefin matrices even at low filler concentrations.

title: Polyethylene-based single polymer laminates: Synergistic effects of nanosilica and metal hydroxides
abstract: This work aims to investigate the fire performance of novel polyethylene-based single polymer composites. Fumed silica nanoparticles and magnesium hydroxide microfiller were added at an optimized concentration to a linear low-density polyethylene matrix, which was then reinforced with ultra-high molecular weight polyethylene fibers. Through the optimization of the production process, it was possible to limit the porosity inside the single polymer composites, thus retaining the pristine mechanical properties of the fibers. The addition of SiO2 and magnesium hydroxide determined an increase in the elastic modulus in both the longitudinal and transversal direction, but it concurrently led to a reduction in ductility, especially in the transversal direction. The fillers were proved to bring interesting improvements of the thermal degradation resistance and of the flame behaviour. Thermogravimetric analysis tests highlighted an increase in the onset degradation temperature and in the temperature associated to the maximum degradation rate. Moreover, both the oxidation onset temperature and limiting oxygen index were considerably improved. Cone calorimetry tests evidenced that filled single polymer composites were characterized by lower peak heat release rate and total heat released with respect to neat single polymer composites.

title: High performance polyethylene nanocomposite fibers
abstract: A high density polyethylene (HDPE) matrix was melt compounded with 2 vol% of dimethyldichlorosilane treated fumed silica nanoparticles. Nanocomposite fibers were prepared by melt spinning through a co-rotating twin screw extruder and drawing at 125°C in air. Thermo-mechanical and morphological properties of the resulting fibers were then investigated. The introduction of nanosilica improved the drawability of the fibers, allowing the achievement of higher draw ratios with respect to the neat matrix. The elastic modulus and creep stability of the fibers were remarkably improved upon nanofiller addition, with a retention of the pristine tensile properties at break. Transmission electronic microscope (TEM) images evidenced that the original morphology of the silica aggregates was disrupted by the applied drawing.

title: Tensile creep behaviour of polymethylpentene–silica nanocomposites
abstract: For the first time, poly(4-methyl-1-pentene) (PMP) nanocomposites were prepared by melt compounding 2 vol% of fumed silica nanoparticles, in order to study the role of the nanofiller surface area and functionalization on the tensile mechanical response of the material, with particular focus on its creep behaviour. The high optical transparency of the polymer matrix was substantially preserved in the nanocomposites, while the mechanical properties (in particular the creep stability) were improved. Dynamic mechanical thermal analysis showed an improvement of the storage modulus, more evident above the glass transition temperature of the polymer matrix. Uniaxial tensile tests evidenced that the elastic modulus of the material was positively affected by the presence of silica nanoparticles, even if a slight reduction of the strain at break was detected. The reduction of the tensile creep compliance was proportional to the surface area of the nanofiller, being more evident at high stresses and elevated temperatures. Findley's law furnished a satisfactory fitting of the creep behaviour of the composites, even at high temperatures. It clearly emerges that the incorporation of fumed silica nanoparticles in PMP can be an effective way to overcome the problem of the poor creep stability of polyolefins, especially at high temperatures and high stresses. Moreover the possibility of retaining the original transparency of the material is fundamental for the production of completely transparent PMP components.

title: Cycloolefin copolymer/fumed silica nanocomposites
abstract: We prepared cycloolefin copolymer (COC)/ fumed silica nanocomposites by melt compounding to study the effect of the filler dimensions (filler surface area) on the physical properties, with particular attention to their thermal, mechanical, and optical behaviors. Thermogravi- metric analysis revealed a positive contribution of silica nanoparticles to the thermal degradation resistance of COC, as the decomposition temperature of the nanofilled samples increased by 40 � C with respect to that of the unfilled matrix. Dynamic mechanical thermal analysis and quasi-static ten- sile tests of the nanocomposites evidenced a slight stiffening effect, proportional to the nanofiller surface area, without any reduction in the fracture toughness. Creep resistance of the nanocomposites was increased by the addition of silica nanoparticles, especially when high-surface-area nano- particles were used. The positive effect of the nanoparticles on the viscoelastic and fracture behavior was related to the uni- form dispersion of silica aggregates in the matrix. Ultraviolet- visible spectrometry measurements evidenced that the original transparency of neat COC was practically maintained after the addition of silica nanoparticles.   2011

title: Linear low-density polyethylene/silica micro- and nanocomposites: dynamic rheological measurements and modelling
abstract: Linear low-density polyethylene (LLDPE) based composites were prepared by melt compounding with 1, 2, 3 and 4 vol% of various kinds of amorphous silicon dioxide (SiO2) micro- and nanoparticles. Dynamic rheological tests in parallel plate configuration were conducted in order to detect the role of the filler morphology on the rheological behaviour of the resulting micro- and nanocomposites. A strong dependence of the rheological parameters from the filler surface area was highlighted, with a remarkable enhancement of the storage shear modulus (G') and of the viscosity (η) in fumed silica nanocomposites and in precipitated silica microcomposites, while glass microbeads only marginally affected the rheologi- cal properties of the LLDPE matrix. This result was explained considering the formation of a network structure arising from particle-particle interactions due to hydrogen bonding between silanol groups. A detailed analysis of the solid like behav- iour for the filled samples at low frequencies was conducted by fitting viscosity data with a new model, based on a modifi- cation of the original De Kee-Turcotte expression performed in order to reach a better modelling of the high-frequency region.

title: Effect of Silica Nanoparticles on the Mechanical Performances of Poly(Lactic Acid)
abstract: Various kinds of fumed silica nanoparticles, different in terms of specific surface area and surface functionalization, were melt compounded with a poly(lactic acid) biodegradable matrix, with the aim to investigate the thermo-mechanical and optical properties of the resulting materials. Untreated nanoparticles at elevated surface area resulted to be effective in increasing elastic modulus, because of the extended filler–matrix interaction, while the finer dispersion of silica aggregates at the nanoscale obtained with surface treated nanoparticles led to noticeable improvements of the tensile properties at yield and at break, both under quasi-static and impact conditions. Also the fracture toughness and the creep stability were substantially enhanced by nanosilica addition, without impairing the original optical transparency of the matrix.

title: Rheological and dynamic mechanical characteristics of rotationally moldable linear low‐density polyethylene fumed silica nanocomposites
abstract: In rotational molding process, polymer powders undergo a cycle of heating, melting, cooling, and subsequent solidification in the mold. Resins, like linear low-density polyethylene (LLDPE), are used in this process on a large scale mainly because of its good mechanical properties and excellent thermal stability. Yet, incorporation of additives is necessary to further improve the visco-elastic, thermal as well as melt flow properties of the resin. This study investigates the effects of nanocomposites of fumed silica (FS) with rotationally moldable LLDPE. Thermal transitions in the LLDPE-FS nanocomposites were investigated and correlated with their melt flow characteristics. The effect on melt processing during rotational molding and compounding, were analyzed by melt flow index and torque rheometry studies. A suitable blend of FS in LLDPE has been recommended for rotational molding based on rheological studies and Dynamic mechanical analysis.

title: Fire retardancy of polypropylene/kaolinite composites
abstract: In this study the influence of surface modification of kaolinite with trisilanolisooctyl Polyhedral OligoSilSesquioxane (POSS) in polypropylene composites was evaluated in terms of thermal stability and fire retardancy and compared with talc. Thermogravimetric analysis showed that incorporating 30 wt% of kaolinite enhanced the thermal stability by ca. 20 °C compared to neat polymer. Cone calorimeter results demonstrated that kaolinite can greatly reduce the pHRR but not unmodified kaolinite. Rheological measurements showed that surface treatment of kaolinite leads to a decrease in viscosity, which could enhance processability. Finally, a correlation between viscosity and pHRR was found and the fire behavior of PP containing modified kaolinite could be explained.

title: Relation between the viscoelastic and flammability properties of polymer nanocomposites
abstract: Previous work has shown that the formation of a network structure of nanoparticles within a polymer matrix can significantly reduce nanocomposite flammability and that viscoelastic properties could be utilized to predict their flammability reduction. The present work extends this type of investigation to the study of clay and carbon nanotube nanocomposites. In particular, we study PS/clay, PS/MWNT, PMMA/clay, and PMMA/SWNT nanocomposites. At a clay level of about 10% by mass, the network structure is formed for the PS and the PMMA clay nanocomposites; it requires a level of about 0.5% with the SWNT and 2% with the MWNT. These samples showed significantly reduced mass loss rates of PS and PMMA. However, the solid residues collected from radiative gasification tests of PS/clay and PMMA/clay showed many small cracks, despite the network formation within the initial sample. This is in contrast to the smooth, continuous residues (no cracks or openings) for PS/MWNT and PMMA/SWNT nanocomposites. The cracks in the clay samples are probably formed due to weaker network at elevated temperatures due to weaker bridging interaction between clay platelets as compared to stronger network resulting from dense entanglement and bridging of carbon nanotubes.

title: Nonlinear Tensile Creep of Linear Low Density Polyethylene/Fumed Silica Nanocomposites: Time-Strain Superposition and Creep Prediction
abstract: The main objectives of the study were (i) to quantitatively describe the nonlinear viscoelastic creep of model nanocomposites, (ii) to construct the generalized compliance curve by means of the tensile compliance vs. internal time superposition for a pseudo iso-free-volume state, and (iii) to predict the compliance vs. real time curves for selected stresses. To this end, the free volume theory of nonlinear viscoelastic creep developed for thermoplastics and their blend was successfully employed. Linear low density polyethylene/fumed silica nanocomposites, showing notable enhancement of the creep resistance in proportion to the surface area of incorporated nanofillers, were taken as simple model materials.  2010. a 2010 Society of Plastics Engineers

title: Mechanical, thermal and flammability properties of polyethylene/clay nanocomposites
abstract: Polyethylene/clay composites were prepared by melt compounding polyethylene and montmorillonite clay organically modified with different intercalating agents. Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) revealed that PE/clay nanocomposites formed when using a reactive intercalating agent, while only conventional microcomposites were obtained from the common alkylammonium intercalated clay. Mechanical testing indicated that the reinforcement in the nanocomposites was more effective than that in their conventional counterparts. The thermal stability and flammability of the PE/clay nanocomposites were measured by thermogravimetric analysis (TGA) and cone calorimetry. By adding only 2 phr organoclay, the peak heat release rate of the nanocomposite was reduced by 54%. Further studies indicated that the improvement of flammability is due to the formation of a clay-enriched protective char during combustion.

title: Comparing the effect of nanofillers as thermal stabilizers in low density polyethylene
abstract: A study of the thermal degradation under inert and oxidative conditions of LDPE and three 5-wt% nanocomposites has been performed. The bases of comparison were the geometries of the nanofillers (spherical, fibrous and laminar) and the sample thickness. Homogeneous and well-dispersed materials were obtained with the three nanoparticles, ensuring a relevant comparative analysis. The thermal degradation curves obtained from TGA under nitrogen flow did not show significant differences in behaviour within the nanocomposites and the reference LDPE. However, the results for the thermo-oxidation study showed a strong stabilization effect for both fibrous and laminar silicates, but not for the spherical silica nanoparticles. A kinetic study of the degradation under isothermal conditions showed that the nanocomposites made from fibrous and laminar silicates degraded following the mechanisms observed for thin films independent of the sample thickness. These results suggested the occurrence of a protective layer against thermo-oxidation on the film surface. Chemical analysis of the degraded surfaces by IR and EDX measurements gave data to explain these differences in behaviour.

title: Polymer/montmorillonite nanocomposites with improved thermal properties Part I. Factors influencing thermal stability and mechanisms of thermal stability improvement
abstract: The results of recent research indicate that the introduction of layered silicate – montmorillonite – into polymer matrix results in increase of thermal stability of a number of polymer nanocomposites. Due to characteristic structure of layers in polymer matrix and nanoscopic dimensions of filler particles, several effects have been observed that can explain the changes in thermal properties. The level of surface activity may be directly influenced by the mechanical interfacial adhesion or thermal stability of organic compound used to modify montmorillonite. Thus, increasing the thermal stability of montmorillonite and resultant nanocomposites is one of the key points in the successful technical application of polymer–clay nanocomposites on the industrial scale. Basing on most recent research, this work presents a detailed examination of factors influencing thermal stability, including the role of chemical constitution of organic modifier, composition and structure of nanocomposites, and mechanisms of improvement of thermal stability in polymer/montmorillonite nanocomposites.

title: Effect of aramid regenerated fibers on thermo-mechanical behaviour of polyamide 12 composites
abstract: Aramid regenerated short fibers, obtained from the production scrap of as-produced aramid yarns, were utilized as reinforcement in a commercial polyamide (PA12) at different contents, ranging from 10 wt% to 30 wt%, in order to evaluate the effect of the fiber loading on the mechanical and dynamic behaviour of the resulting materials. Differential scanning calorimetry tests revealed how the crystallinity slightly decreased with the fiber content, while quasi-static tensile tests evidenced that the introduction of aramid fibers provided an interesting stiffening effect on the resulting composites, proportionally to the filler content. On the other hand, the presence of agglomerated fibers led to an embrittlement of polyamide composites, with a progressive reduction of the deformation at break. Tensile dynamic tests confirmed the stabilizing effect provided by the recycled fibers, while the coefficient of linear thermal expansion was progressively reduced both under and above the glass transition temperature. Isothermal creep compliance of the material was substantially reduced upon fiber addition, especially at elevated testing temperatures. Accordingly, Vicat softening temperature was increased of 10–20℃ in dependence on the fiber content. Also, the thermal degradation stability was slightly improved upon fiber addition. Morphological analysis on the cryofractured surfaces revealed a quite good fiber-matrix interfacial adhesion.