199545717
Synergistic effects of metal hydroxides and fumed nanosilica as fire retardants for polyethylene
Abstract 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.
136974058
Flame retardant polymer composites
In this review article, different approaches of enhancing flame retardancy of polymeric composite material and their effect on different composite properties are analysed critically. The mechanisms of fire spreading on composite materials are also discussed. Flame retardancy of polymeric composite material can be enhanced either by enhancing the fire performance of constituents of composite i.e. matrices and reinforcing agents or by providing a protective flame retardant (FR) coating around the composite material. Fire performance of reinforcing material is improved by treating with FR-chemicals while the fire performance of polymer matrices can be improved by incorporating micro and nano FR-fillers or by introducing FR-compound into polymer backbone. The flammability of micro and nano filler added polymeric composites and newly developed polymer derivatives and their effect on composite properties like mechanical, thermal have been discussed. However, the development of flame retardant polymer composite is still at nascent stage and for further development, it is necessary to work on the development of non-health hazardous, environment friendly flame retarding agents which will be able to enhance the fire performance of composite materials at very low concentration levels.
5012018
(Re)processing effects on linear low-density polyethylene/silica nanocomposites
A linear low density polyethylene matrix was melt compounded with a given amount (2 vol.%) of both untreated (hydrophilic) and surface treated (hydrophobic) fumed silica nanoparticles with the aim to investigate the influence of the time under processing conditions on the microstructure and thermo-mechanical properties of the resulting materials. Crosslinking reactions induced by thermal processing caused a remarkable increase of the melt viscosity, as revealed by the melt flow index values of both neat matrix and nanocomposites. Thermal oxidation of the matrix was slightly reduced by the introduction of fumed silica nanoparticles, especially for long compounding times. Differential scanning calorimetry evidenced how silica nanoparticles had a nucleating effect on the matrix, while both the melting temperature and the relative crystallinity were decreased by the compounding process. Nanosilica addition promoted a general improvement of the tensile properties, that progressively decreased with the processing time.
136021241
Overview of fire retardant mechanisms
Abstract The flammability of polymeric materials depends on thermal degradation processes which occur on exposing them to heat. Fire retardant systems have been developed which reduce polymer flammability by various mechanisms which are not yet fully understood. Innovations to the traditional fire retardant approach are required by recent recognition of hazards which have previously been neglected or underestimated. This challenging task is likely to be satisfactorily accomplished only if more detailed information on mechanistic aspects becomes available. Thermal degradation mechanisms which take place in the polymer matrix are of paramount importance in the understanding of polymer combustion and fire retardance. The parameters which affect the thermal behaviour of polymeric materials, such as oxygen concentration, pressure and heating rate, are examined in relation to combustion conditions. Examples of recent mechanistic studies of intumescent and halogen based fire retardants are reviewed and discussed.
136515259
New prospects in flame retardant polymer materials: From fundamentals to nanocomposites
Abstract The objective of this review is to make the field of “flame retardants for polymer materials” more accessible to the materials science community, i.e. chemists, physicists and engineers. We present the fundamentals of polymer combustion theory, the main flame retardant properties and tests used to describe fire behavior, together with the nature and modes of action of the most representative flame retardants and the synergistic effects that can be achieved by combining them. We particularly focus on polymer nanocomposites, i.e. polymer matrices filled with specific, finely dispersed nanofillers, which will undoubtedly pave the way for future materials combining physicochemical and thermo-mechanical performances with enhanced flame retardant behavior.
3888561
Chemical alternatives assessment of different flame retardants – A case study including multi-walled carbon nanotubes as synergist☆
Flame retardants (FRs) are a diverse group of chemicals used as additives in a wide range of products to inhibit, suppress, or delay ignition and to prevent the spread of fire. Halogenated FRs (HFRs) are widely used because of their low impact on other material properties and the low loading levels necessary to meet the required flame retardancy. Health and environmental hazards associated with some halogenated FRs have driven research for identifying safer alternatives. A variety of halogen-free FRs are available on the market, including organic (phosphorus and nitrogen based chemicals) and inorganic (metals) materials. Multi-walled carbon nanotubes (MWCNT) have been demonstrated to act as an effective/synergistic co-additive in some FR applications and could thereby contribute to reducing the loading of FRs in products and improving their performance. As part of the FP7 project DEROCA we carried out a chemical alternatives assessment (CAA). This is a methodology for identifying, comparing and selecting safer alternatives to chemicals of concern based on criteria for categorising human and environmental toxicity as well as environmental fate. In the project we assessed the hazard data of different halogen-free FRs to be applied in 5 industrial and consumer products and here we present the results for MWCNT, aluminium diethylphosphinate, aluminium trihydroxide, N-alkoxy hindered amines and red phosphorus compared to the HFR decabromodiphenylether. We consulted the REACH guidance, the criteria of the U.S.-EPA Design for Environment (DfE) and the GreenScreen® Assessment to assess and compare intrinsic properties affecting the hazard potential. A comparison/ranking of exposure reference values such as Derived No Effect Levels (DNELs) showed that FRs of concern are not identified by a low DNEL. A comparison based on hazard designations according to the U.S.-EPA DfE and GreenScreen® for human health endpoints, aquatic toxicity and environmental fate showed that the major differences between FRs of concern and their proposed alternatives are the potential for bioaccumulation and CMR (carcinogenic, mutagenic or reprotoxic) effects. As most alternatives are inorganic chemicals, persistence (alone) is not a suitable criterion. From our experiences in carrying out a CAA we conclude: i) REACH registration dossiers provide a comprehensive source of hazard information for an alternative assessment. It is important to consider that the presented data is subject to changes and its quality is variable. ii) Correct identification of the chemicals is crucial to retrieve the right data. This can be challenging for mixtures, reaction products or nanomaterials or when only trade names are available. iii) The quality of the data and the practice on how to fill data gaps can have a huge impact on the results and conclusions. iv) Current assessment criteria have mainly been developed for organic chemicals and create challenges when applied to inorganic solids, including nanomaterials. It is therefore crucial to analyse and report uncertainties for each decision making step.
20573319
Halogenated Flame Retardants: Do the Fire Safety Benefits Justify the Risks?
Since the 1970s, an increasing number of regulations have expanded the use of brominated and chlorinated flame retardants. Many of these chemicals are now recognized as global contaminants and are associated with adverse health effects in animals and humans, including endocrine and thyroid disruption, immunotoxicity, reproductive toxicity, cancer, and adverse effects on fetal and child development and neurologic function. Some flame retardants such as polybrominated diphenyl ethers (PBDEs) have been banned or voluntarily phased out by manufacturers because of their environmental persistence and toxicity, only to be replaced by other organohalogens of unknown toxicity. Despite restrictions on further production in some countries, consumer products previously treated with banned retardants are still in use and continue to release toxic chemicals into the environment, and the worldwide use of organohalogen retardants continues to increase. This paper examines major uses and known toxic effects of commonly-used organohalogen flame retardants, replacements for those that have been phased out, their combustion by-products, and their effectiveness at reducing fire hazard. Policy and other solutions to maintain fire safety while reducing toxicity are suggested. The major conclusions are: (1) Flammability regulations can cause greater adverse environmental and health impacts than fire safety benefits. (2) The current options for end-of-life disposal of products treated with organohalogens retardants are problematic. (3) Life-cycle analyses evaluating benefits and risks should consider the health and environmental effects of the chemicals, as well as their fire safety impacts. (4) Most fire deaths and most fire injuries result from inhaling carbon monoxide, irritant gases, and soot. The incorporation of organohalogens can increase the yield of these toxic by-products during combustion. (5) Fire-safe cigarettes, fire-safe candles, child-resistant lighters, sprinklers, and smoke detectors can prevent fires without the potential adverse effects of flame retardant chemicals. (6) Alternatives to organohalogen flame retardant chemicals include using less flammable materials, design changes, and safer chemicals. To date, before evaluating their health and environmental impacts, many flame retardant chemicals have been produced and used, resulting in high levels of human exposure. As a growing literature continues to find adverse impacts from such chemicals, a more systematic approach to their regulation is needed. Before implementing new flammability standards, decision-makers should evaluate the potential fire safety benefit versus the health and environmental impacts of the chemicals, materials, or technologies likely to be used to meet the standard. Reducing the use of toxic or untested flame retardant chemicals in consumer products can protect human and animal health and the global environment without compromising fire safety.
42419139
Persistence, bioaccumulation, and toxicity of halogen-free flame retardants.
Polymers are synthetic organic materials having a high carbon and hydrogen content, which make them readily combustible. Polymers have many indoor uses and their flammability makes them a fire hazard. Therefore, flame retardants (FRs) are incorporated into these materials as a safety measure. Brominated flame retardants (BFRs), which accounted for about 21% of the total world market of FRs, have several unintended negative effects on the environment and human health. Hence, there is growing interest in finding appropriate alternative halogen-free flame retardants (HFFRs). Many of these HFFRs are marketed already, although their environ- mental behavior and toxicological properties are often only known to a limited extent, and their potential impact on the environment cannot yet be properly assessed. Therefore, we undertook this review to make an inventory of the available data that exists (up to September 2011) on the physical-chemical properties, pro- duction volumes, persistence, bioaccumulation, and toxicity (PBT) of a selection of HFFRs that are potential replacements for BFRs in polymers. Large data gaps were identified for the physical-chemical and the PBT properties of the reviewed HFFRs. Because these HFFRs are currently on the market, there is an urgent need to fill these data gaps. Enhanced transparency of methodology and data are needed to reevaluate certain test results that appear contradictory, and, if this does not provide new insights, further research should be performed. TPP has been studied quite extensively and it is clearly persistent, bioaccumulative, and toxic. So far, RDP and BDP have demonstrated low to high ecotoxicity and persistence. The compounds ATH and ZB exerted high toxicity to some species and ALPI appeared to be persistent and has low to moderate reported ecotoxicity. DOPO and MPP may be persistent, but this view is based merely on one or two studies, clearly indicating a lack of information. Many degradation studies have been performed on PER and show low persistence, with a few exceptions. Additionally, there is too l ittle information on the bioaccumulation potential of PER. APP mostly has low PBT properties; however, moderate ecotoxicity was reported in two studies. Mg(OH)₂, ZHS, and ZS do not show such remarkably high bioaccumulation or toxicity, but large data gaps exist for these compounds also. Nevertheless, we consider the latter compounds to be the most promising among alternative HFFRs. To assess whether the presently reviewed HFFRs are truly suitable alternatives, each compound should be examined individually by comparing its PBT values with those of the relevant halogenated flame retardant. Until more data are available, it remains impossible to accurately evaluate the risk of each of these compounds, including the ones that are already extensively marketed.
95106935
Flame retardant effects of magnesium hydroxide
Abstract Magnesium hydroxide has all the characteristics required for use as a flame retardant filler. It can be made synthetically with high purity and in a range of useful morphologies, responds well to surface modifiers and decomposes endothermically with release of water at temperatures close to those of polymer degradation and high enough to allow incorporation into most polymer types. Crystal growth is difficult and, until recently, particles with suitable morphologies were too expensive for other than niche applications. New production methods are now available that offer the prospect of improved morphology control and better cost effectiveness. Use of this filler enables high levels of flame retardancy to be achieved in a wide range of polymer types, including ethylene vinyl acetate, polypropylene and polyamides.
96208830
Fire retardant action of mineral fillers
Endothermically decomposing mineral fillers, such as aluminium or magnesium hydroxide, magnesium carbonate, or mixed magnesium/calcium carbonates and hydroxides, such as naturally occurring mixtures of huntite and hydromagnesite are in heavy demand as sustainable, environmentally benign fire retardants. They are more difficult to deploy than the halogenated flame retardants they are replacing, as their modes of action are more complex, and are not equally effective in different polymers. In addition to their presence (at levels up to 70%), reducing the flammable content of the material, they have three quantifiable fire retardant effects: heat absorption through endothermic decomposition; increased heat capacity of the polymer residue; increased heat capacity of the gas phase through the presence of water or carbon dioxide. These three contributions have been quantified for eight of the most common fire retardant mineral fillers, and the effects on standard fire tests such as the LOI, UL 94 and cone calorimeter discussed. By quantifying these estimable contributions, more subtle effects, which they might otherwise mask, may be identified.
139547518
Influence of flame retardant magnesium hydroxide on the mechanical properties of high density polyethylene composites
The effects of incorporating magnesium hydroxide as a flame retardant on the mechanical properties of high density polyethylene which include tensile, flexural, compressive, shear and fracture toughness behaviours were investigated. The weight fraction of the filler material ranges from 10 to 50 wt %. The effects of filler weight percent and strain rate during tensile testing by means of a universal testing machine were both studied to identify the behaviour of the produced composites. It was observed that the flexural modulus and Young's modulus increased steadily while the tensile fracture strength and the tensile yield strength were inversely proportional to the weight fraction of magnesium hydroxide. The tensile yield strength showed a steady decrease with the loading of filler material until 10% then it showed a plateau until 50%. The tensile elongation at break decreased sharply between zero and 10% weight fraction, followed by a slight decrease until 50% weight fraction. The flexural strength peaked with the increase of magnesium hydroxide weight fraction. The strain rate showed a dramatic effect on the tensile properties of the samples. The compressive strength and shear strength of specimens were directly proportional to Mg(OH)2 until 40% and 30%, respectively. The novelty in optimizing between filler content and testing configurations reveal wide range of applications.
96745065
Ecological issue of polymer flame retardancy
The use of polymer flame retardants has an important role in saving lives. The main flame retardant systems for polymers currently in use are based on halogenated, phosphorous, nitrogen, and inorganic compounds. All of these flame retardant systems basically inhibit or even suppress the combustion process by chemical or physical action in the gas or condensed phase. Conventional flame retardants, such as halogenated, phosphorous, or metallic additives, have a number of negative attributes. An ecological issue of the application of conventional flame retardants demands the search of new polymer flame retardant systems. Among the new trends of flame retardancy are intumescent systems, polymer nanocomposites, preceramic additives, low-melting glasses, different types of char formers, and polymer morphology modification processing. The brief explanations on the three major types of flame retardant systems (intumescent systems, polymer nanocomposites, and polymer organic char formers) are the subject of this overview. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2449–2462, 2002
136427361
Effect of particle size and content of magnesium hydroxide on flame retardant properties of asphalt
The flame-retardant properties of asphalt for some building applications are very important. This article is mainly focused on the influence of particle size and content of magnesium hydroxide (MH) on the flame-retardant properties of asphalt. The limit oxygen index and cone calorimeter results indicate that as the MH content and mesh number increase, the flame-retardant properties of MH-filled flame-retardant asphalt show a rising trend. But the role of particle size in smoke suppression is not obvious. Several tests confirm that the dispersion of the MH have some influence on the flame-retarding effect of asphalt. The 3000 mesh MH for the preparation of flame-retardant asphalt shows optimal performance. The experimental data show that the softening point of flame-retardant asphalt increases, but the ductility and penetration decrease with increasing MH content. MH affects the asphalt viscosity, but not affects the adhesion of the asphalt to gravel. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
98496355
Flame retardancy and smoke suppression of magnesium hydroxide filled polyethylene
In this work, halogen-free, flame-retarded polyethylene was investigated to study the effect of inorganic fillers on the improvement of flame retardancy and the suppression of smoke density. Through analyses on the thermal stability and smoke density, it was found that the flame retardancy developed by magnesium hydroxide could effectively be increased by the additional incorporation of zinc borate and talc. Furthermore, a synergistic effect was observed when zinc borate and talc were incorporated together. This result was confirmed by the observation of fire performance with cone calorimetry. A morphological study supported the idea that the improvement in the flame retardancy and the suppression of smoke density was due to hard and compact charred layers formed by the interactions between polymer and inorganic fillers. The charred layers provided a good thermal and flame barrier.
94481570
Discolouration of polypropylene-based compounds containing magnesium hydroxide
Abstract Magnesium hydroxide is extensively used in the plastics industry as a flame retardant and smoke suppressant in various polymeric matrices (polyolefins, nylons etc.). However, it was found that compounding Mg(OH) 2 with polymers leads to the formation of various colours ranging from light grey to rather dark beige. The effect of the temperature and processing technology, and of various properties of Mg(OH) 2 (impurities, particle size and morphology) on colour formation was investigated in this work. One of the causes for the discolouration appears to be the interaction between the Mg(OH) 2 and antioxidants containing phenolic groups. This reaction takes place rapidly when the former is added to the polymer melt containing the antioxidant. The amount and type of coating, and its continuity over the particles surface (dependent on the powder morphology and coating technology) may represent a way to prevent the chemical interaction between the filler and plastics components and avoid discolouration. A method for the quantitative evaluation of coating quality and continuity was developed. Based on this research, ways to improve the quality of magnesium hydroxide as a fire retardant were suggested. One of these ways, namely the addition of TiO 2 , is particularly interesting. We found that besides its pigmentation effect, TiO 2 is synergistic with magnesium hydroxide in terms of flame retardancy and improves the thermal stability of polypropylene.
98331967
Tensile properties and stress whitening of polypropylene/polyolefin elastomer/magnesium hydroxide flame retardant composites for cable insulating application
Flame retardant polypropylene (PP) composites were prepared by combining random polypropylene with uncoated and surface-treated forms of magnesium hydroxide filler and elastomeric modifiers, with and without maleic anhydride functionalization. Four types of magnesium hydroxide (MDH) with different surface treatments were compounded at amounts up to 60% by weight to PP/polyolefin elastomer (POE) matrix resin to obtain a series of composites. The tensile strength and elongation at break were measured. MDH coated with polymeric material was found to give a high elongation at break value compared with the values obtained with uncoated and vinyl silane and amino silane coated MDH. Two types of POE, i.e., neat and maleic anhydride grafted POE (POEgMA), were used to investigate the stress whitening of composites in bending deformation. POEgMA used composites showed no stress whitening while neat POE used composites showed whitening when bended. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2311–2318, 2005
100545266
Improving the flame-retardant efficiency of aluminum hydroxide with fullerene for high-density polyethylene
The influence of fullerene (C60) on the flame retardancy and thermal stability of high-density polyethylene (HDPE)/aluminum hydroxide (ATH) composites was studied. After the addition of three portions of C60 to an HDPE–ATH (mass ratio = 100:120) composite, a V-0 rating in the UL-94 vertical combustion test was achieved, and the limiting oxygen index increased by about 2%. The results of cone testing also showed that the addition of C60 effectively extended the time to ignition and the time to maximum heat-release rate while cutting down the peak heat-release rate. Thus, fewer flame retardants were needed to achieve a satisfactory flame retardance. Consequently, the adverse effects on the mechanical properties because of the high level of flame-retardant loading was reduced, as evidenced by the obvious enhancements in the tensile strength, elongation at break, and flexural strength. Electron spin resonance spectroscopy proved that C60 was an efficient free-radical scavenger toward HO· radicals. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy demonstrated that in both N2 and air atmospheres, C60 increased the onset temperature of the matrix by about 10 °C because of its enormous capacity to absorb free radicals evolved from the degradation of the matrix to form crosslinked network, which was covered by aluminum oxide. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44551.
137418785
Synergistic effect of aluminum hydroxide and nanoclay on flame retardancy and mechanical properties of EPDM composites
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. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2042–2048, 2013
97606365
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.
137040244
Effect of zinc borate on flammability/thermal properties of ethylene vinyl acetate filled with metal hydroxides
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.
98624258
Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer
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.
96293872
Reflections on migration of clay and structural changes in nanocomposites
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. Copyright © 2006 John Wiley & Sons, Ltd.
94392810
Nanocomposites at elevated temperatures: migration and structural changes
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. Copyright © 2006 John Wiley & Sons, Ltd.
138653309
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.
100217727
Flame-retardant properties of ethylene-vinyl acetate/oil sludge/ fumed silica composites
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.
97159258
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.
137692503
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.
95490179
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.
96711210
Influence of fumed silica on the flame-retardant properties of ethylene vinyl acetate/aluminum hydroxide composites
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. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011
73713553
Thermal stability of high density polyethylene–fumed silica nanocomposites
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.
139604028
Polyethylene-based single polymer laminates: Synergistic effects of nanosilica and metal hydroxides
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.
5034350
High performance polyethylene nanocomposite fibers
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.
40421525
Tensile creep behaviour of polymethylpentene–silica nanocomposites
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. Copyright © 2010 Society of Chemical Industry
5022837
Cycloolefin copolymer/fumed silica nanocomposites
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. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 3393-3402, 2011
16649850
Linear low-density polyethylene/silica micro- and nanocomposites: dynamic rheological measurements and modelling
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.
88504153
Effect of Silica Nanoparticles on the Mechanical Performances of Poly(Lactic Acid)
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.
137123679
Rheological and dynamic mechanical characteristics of rotationally moldable linear low‐density polyethylene fumed silica nanocomposites
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. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers
138588229
Fire retardancy of polypropylene/kaolinite composites
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.
52840595
Relation between the viscoelastic and flammability properties of polymer nanocomposites
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.
5034304
Nonlinear Tensile Creep of Linear Low Density Polyethylene/Fumed Silica Nanocomposites: Time-Strain Superposition and Creep Prediction
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. POLYM. COMPOS., 31:1947–1955, 2010. a 2010 Society of Plastics Engineers
136526526
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.
137100185
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.
59396035
Polymer/montmorillonite nanocomposites with improved thermal properties Part I. Factors influencing thermal stability and mechanisms of thermal stability improvement
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.
138248210
Effect of aramid regenerated fibers on thermo-mechanical behaviour of polyamide 12 composites
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.