Polymer Degradation and Stability (v.82, #2)
Advert Details (III).
Editorial by Norman Billingham (143).
Influence of testing conditions on the performance and durability of polymer stabilisers in thermal oxidation by J Pospı́šil; Z Horák; J Pilař; N.C Billingham; H Zweifel; S Nešpůrek (145-162).
Information on the efficiency of stabilisers in protecting polymers against thermal oxidation under service conditions is essential for selection and development of appropriate stabilizing systems. Accelerated tests are necessary to get data in an acceptable time and need carefully selected failure criteria. Appropriate testing severity, avoiding misuse of accelerated methods and understanding of the limitations of the methods are essential if reliable data are to be obtained. The potential and limitations of oven ageing tests, oxygen uptake measurements, differential scanning calorimetry (DSC) and chemiluminescence (CL) in stabiliser testing are reviewed.
Keywords: Accelerated tests; Long-term heat ageing; Oven ageing; Differential scanning calorimetry; Chemiluminescence; Antioxidant testing;
Photodegradation of polypropylene nanocomposites by Bénédicte Mailhot; Sandrine Morlat; Jean-Luc Gardette; Sylvain Boucard; Jannick Duchet; Jean-François Gérard (163-167).
The photochemical behaviour of polypropylene–clay nanocomposites was studied. The samples were prepared by blending in the molten state isotactic polypropylene, organo-modified montmorillonite, i.e. layered silicate or clay modified with alkyl ammonium cations, and maleic anhydride-grafted polyprolylene as compatibilizer. The montmorillonite dispersion state within the iPP matrix was analyzed by Transmission Electron Microscopy. Accelerated photoageing of nanocomposites carried out at λ>300 nm and 60 °C was analysed by infrared spectroscopy. The oxidation products formed have been identified and the contribution of each component of the nanocomposite evaluated by studying different formulations. The presence of stabilisers in the formulation has also been analysed from the comparison of the rates of oxidation of several stabilised and non-stabilised nanocomposites.
Keywords: Nanocomposite; Photo-oxidation; Polypropylene; Layered silicates;
Estimation of parameters that correlate molecular structure of hindered amines with their stabilizing efficiency by Leonid Yu. Smoliak; Nikolay R. Prokopchuk (169-172).
Substances of a hindered amine (HA) class were studied as stabilizers of polyethylene. The diffusion and solubility of HAs were measured by the stack method. The correlation between physical parameters, structure of stabilizer molecules and efficiency was investigated. It was shown that both chemical and physical aspects could affect the efficiency depending on the structure of the molecule. The inverse character of changes in efficiency on Moisan's plot for a pair of hindered amines, based on mono- and bis-substituted phthalic acid esters, was discovered and the reasons for such a phenomenon are discussed.
Keywords: Polyethylene; Stabilization; Hindered amine; Molecular structure; Correlation; Efficiency;
Effect of the polymer type and experimental parameters on chemiluminescence curves of selected materials by Lyda Matisová-Rychlá; Jozef Rychlý; Kristian Slovák (173-180).
Oxidation of a series of common polymers and some low-molecular mass compounds has been examined by chemiluminescence. An oxidation test involving temperature ramp experiments in oxygen in the temperature range 40–220 °C has been used, enabling us to compare the oxidizability of different materials over a large temperature interval from the viewpoint of their chemiluminescence intensity and to discuss the observed discrepancies. According to this approach polymers can be divided into three groups. In the first, there are strongly luminescent polymers like polyolefins, polyamides, etc., in the second, medium luminescent polymers like cellulose, poly (2,6-dimethyl-1,4-phenylene oxide), etc., and in the third, weakly luminescent polymers like polystyrene, poly(methyl methacrylate), poly(ethylene terephthalate), etc. Different mechanisms of initiation may be seen in different temperature regions of polymer oxidation from the chemiluminescence intensity–temperature run depending on the polymer quality and on the physical state of the polymer matrix. The temperature coefficient of the chemiluminescence increase, as derived from the corresponding Arrhenius’ graphs is usually rather low below the T g of the polymer (around 40–60 kJ/mol) while at high temperatures it reflects the oxidation of the polymer matrix (around 100–150 kJ/mol or more). Any previous oxidation of the polymer may affect the chemiluminescence intensity–temperature run significantly.
Keywords: Chemiluminescence; Thermal oxidation; Degradation; Polyolefins; Polyamides; Polysaccharides;
Multi-cell imaging chemiluminescence to map heterogeneous degradation of polypropylene plaques by Mikael Hamskog; Björn Terselius; Pieter Gijsman (181-186).
The heterogeneity of the degradation of stabilized polypropylene (PP) plaques was studied using a recently designed multi-cell imaging chemiluminescence instrument. Mapping of the degradation of unaged PP plaques showed randomly distributed oxidation induction times (OIT), indicating random initiation presumably at polymerization catalyst residues. Contrary to this, hot-air oven aged PP plaques showed position related degradation. Zero OIT values were found at the edges, indicating complete oxidation, whereas the OIT increased towards the centre of the plaque. This non-random OIT distribution can be explained by a difference in evaporation rate of the stabilizer at different positions in the plaque.
Keywords: Imaging chemiluminescence; Oxidation; Degradation; Stabilization; Oven ageing;
Techniques for the analysis of aging signatures of silica-filled siloxanes by Bryan Balazs; Steve DeTeresa; Robert Maxwell; Ed Kokko; Tait Smith (187-191).
Degradation mechanisms for complex polymer systems are often subtle and difficult to detect, yet a precise understanding of their effect on a polymer component's macroscopic performance is necessary for understanding aging behavior. Furthermore, predictions of the engineering performance of aged components are prone to large errors when the service lifetimes are much greater than the duration of laboratory aging tests, especially when multiple degradation mechanisms contribute to the overall aging. In order to avoid these errors, lifetime-performance models for components are needed that acknowledge the changes brought about by aging or damage over many size domains, from the macroscopic to the molecular level. We are studying a silica-filled siloxane foam using techniques which link aging and damage over several size domains in order to improve our material/component lifetime predictions. Parameters such as radiation-induced crosslinking, changes in motional dynamics caused by desiccation, and mechanical damage are incorporated into Finite Element Analysis codes and combined with computed tomographic data to provide “age-aware” models and predictive capability at the component level.
Keywords: Modeling; Siloxane; Computed tomography; Finite element analysis;
NMR analysis of γ-radiation induced degradation of halthane-88 polyurethane elastomers by Robert S. Maxwell; David Chambers; Bryan Balazs; Rebecca Cohenour; William Sung (193-196).
We report 1H and 13C NMR analysis of changes in chain dynamics in a polyurethane elastomer system, Halthane 88-3, caused by exposure to 1.2 MeV gamma radiation from a Co-60 source. 1H NMR relaxation measurements clearly discriminate between interfacial, soft segment, and sol domains in the polymer. The 1H T 2 of the interfacial domain and the soft segment domain increased with the increased dose of γ-radiation. 13C CPMAS experiments also show that the hard segment domain remained unchanged up to cumulative dose of 100 kGray. The 1H and 13 C NMR results strongly suggest that the Halthane 88-3 elastomer undergoes chain scission, primarily in the long chains that make up the soft segments of the polymer. The NMR results are compared to results from DMA and a direct correlation between observables has been demonstrated.
Keywords: Polyurethane; NMR; Radiation; Degradation; DMA;
Polymer additive analysis at the limits by J.C.J. Bart (197-205).
Polymer/additive analysis is a complex problem. Analysis of additives in polymers takes advantage of all current instrumental tools featuring techniques based on low/high temperature, pressure, speed, wavelength, voltage, performance, sensitivity, selectivity, resolution, mass, fragmentation, dimensionality, orthogonality, equipment size, column technology, instrumental complexity, cost, timeliness, etc. with allowance for the use of extreme operating parameters in terms of volume, solvent use, temperature variation, time, speed, wavelength dependency, destructiveness, spatial resolution, remoteness, angular dependency, modulation, etc. Historically, analysis of polymer/additive packages has experienced a long series of tool development. Nowadays the experimentalist disposes of powerful tools with a proven record of being efficient in industrial problem solving. High-performance polymer/additive analysis does benefit from on-line, simultaneous analysis, fast screening, high sensitivity and high resolution. The future of in-polymer additive analysis will be strongly affected by developments in many instrumental disciplines. General trends are higher sensitivity, more information, faster and further automation. Some future needs are more reliable quantitation, reference materials and simplification of data management. A particular problem in additive analysis concerns accuracy and traceability. There are still many quantitative analytical methods waiting to be developed. It is here that the field will advance. The paper concludes with various proposals for (r)evolutionary developments in polymer/additive analysis.
Keywords: Polymer additives; Additive analysis;
Production of lifetime controlled plastics: copolymers of styrene and substituted butadienes by P.C. Frangiosa; L.H. Catalani (207-210).
This work was directed to the study of the UV radiation effects on samples of polystyrene (PS) and copolymers of styrene with different proportions of 2-substituted-1,3-butadienes, in the presence of air and in solution, aiming at the optimisation of the degradation of the PS when exposed to the natural environment. Polymers were prepared by free-radical polymerization in solution, using azo-bis-isobutyronitrile as initiator, resulting in an average molecular weight, M ̄ W of about 30.0 kg/mol for the homo- and copolymers. The polymers were separated and characterized by infrared spectroscopy, elemental analysis, light scattering and gel permeation chromatography. The degradation rates were directly related to the increase in the comonomer contents of the polymers.
Keywords: Polystyrene; Photodegradation; Copolymers; Macroketone; Amplified degradation;
Hydrolytic stability of phenolic antioxidants and its effect on their performance in high-density polyethylene by Kornél Nagy; Edina Epacher; Peter Staniek; Béla Pukánszky (211-219).
Comparative experiments were carried out with two hindered phenolic antioxidants of different chemical structures to determine their hydrolytic stability and performance in the presence of extractive media. Hostanox O10® (HO10) and Hostanox O3® (HO3) were hydrolysed in solution and the reaction products were identified by HPLC-ESI-MS analysis. The efficiency of the two additives was checked by standard multiple extrusion test in HDPE. Samples were stored in water for a year to determine their hydrolytic stability under more practical conditions. The results proved that Hostanox O10 is a better processing stabilizer than HO3, while the latter performs much better under the effect of extractive media. Besides hydrolysis other reactions, mainly the splitting off one or more alkyl groups from the original molecule, may also take place during storage at 80 °C in water, which may also lead to a decrease in stabilizer efficiency. The results clearly prove that high efficiency in a short-term laboratory test is not the only criterion to rank a stabilizer. Under long term conditions such as storage in an extractive environment HO3 outperforms HO10.
Keywords: Polyethylene; Pipes; Stabilizer; Hydrolysis; HPLC-ESI-MS;
Effect of gamma irradiation on the ductile-to-brittle transition in ultra-high molecular weight polyethylene by João Carlos Miguez Suarez; Ronaldo Sergio de Biasi (221-227).
Ultra-high molecular weight polyethylene (UHMWPE) is used in the manufacture of medical applications due to its excellent mechanical properties, abrasion resistance and biocompatibility. The products are usually sterilized by gamma radiation. It is well known that gamma irradiation introduces structural changes that may be detrimental to the integrity and performance of the polymer, limiting its useful life. Therefore, it is imperative to have a fundamental understanding of the fracture behaviour of the material. A commercial general grade ultra-high molecular weight polyethylene (UHMWPE) was irradiated with several total doses and the effects of gamma radiation on the mechanical behaviour of the polymer and its morphology were evaluated by tensile tests, electron spin resonance spectroscopy (ESR) and scanning electron microscopy (SEM). The experimental data show that the gamma irradiation changes the molecular structure of UHMWPE, degrades its tensile properties and produces a gradual ductile-to-brittle transition.
Keywords: Ultra-high molecular weight polyethylene; UHMWPE; Gamma irradiation; Fracture; Tensile properties; Ductile-to-brittle transition; Scanning electron microscopy;
UV stability and radiation-crosslinking of linear low density polyethylene and low density polyethylene for greenhouse applications by Ahmed A Basfar; K.M Idriss Ali; S.M Mofti (229-234).
Ultraviolet (UV) radiation stability and γ-radiation crosslinking of linear low density polyethylene (LLDPE) and low density polyethylene (LDPE) for greenhouse film applications was investigated. Various combinations of primary antioxidant (i.e. Irganox 1010), secondary antioxidant (i.e. Irgafos 168), UV absorber (i.e. Chimassorb 81) and hindered amine light stabilizer (HALS) were used to prepare thin PE films (60 μm thick). The films were cross-linked by γ-rays with doses of 20–200 kGy. Accelerated weathering test up to 1146 h and natural (outdoor) weathering up to 165 days were performed for the prepared films. In addition, gel content and mechanical properties of these films were determined. Improved UV stability was achieved with films of LLDPE and LDPE containing HALS along with other additives.
Keywords: LLDPE; LDPE; Weathering; Radiation; UV; Gel content;
Artificial accelerated weathering of poly(vinyl chloride) for outdoor applications by Luis Pimentel Real; Adélia Pereira Rocha; Jean-Luc Gardette (235-243).
We have performed artificial accelerated ageing in xenon light and a natural exposure in Lisbon (hot, Mediterranean climate), using four different types of TiO2 pigmented PVC formulations, containing various other additives. The experimental results obtained permit us to compare the performance of the additives present in the different formulations and give us information about the sensitivity of each analytical technique used to evaluate the effects of degradation in the PVC samples, originated by the weathering from light, referred to previously.
Keywords: Poly(vinyl chloride); Weathering; Infrared microscopy; Colorimetry; Mechanical proprieties;
Stabilization of PVC by epoxidized sunflower oil in the presence of zinc and calcium stearates by M.T. Benaniba; N. Belhaneche-Bensemra; G. Gelbard (245-249).
Sunflower oil was epoxidized and characterized. Epoxidized sunflower oil (ESO) was used as an organic thermal co-stabilizer for plasticized polyvinyl chloride (PVC) in the presence of Zn and Ca stearates. The thermo-oxidative degradation of PVC was studied in the presence of this ternary stabilizer system at 170 °C. The rates of dehydrochlorination were measured by potentiometric titration and the extents of discoloration were evaluated. The formation of polyene sequences was investigated by UV–visible spectroscopy. The influence of the ratio of Zn and Ca stearates (1/2,1/1 and 2/1) and of the amount of oxirane oxygen in the HTE were considered. Synergistic effects were found.
Thermal ageing of conducting polymeric composites by Mária Omastová; Silvia Podhradská; Jan Prokeš; Ivica Janigová; Jaroslav Stejskal (251-256).
The electrical properties of polymer composites—polyethylene/carbon black (PE/CB), polyethylene/carbon black modified by polypyrrole (PE/CB-PPy), and polyethylene/carbon black modified by polyaniline (PE/CB-PANI)—were investigated during slow cyclic heating and cooling thermal ageing. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16 to 125 °C. Scanning electron microscopy was used for morphology study of surface of modified CB particles. It was found that the thermal treatment resulted in a conductivity increase in all composites when heated below the melting point of PE. This effect was explained by increased crystallinity in the polymer matrix of thermally treated composites and confirmed by DSC analysis. The thermal ageing during the heating above the melting point of polymer matrix caused decrease in conductivity of PE/CB composites, but increase of conductivity in composites containing CB-PPy or CB-PANI as a filler. The modified fillers create more perfect and thermally resistant conducting network in PE matrix. The temperature of decomposition maximum of PE/CB-PPy and PE/CB-PANI composites into higher compared with PE/CB composite as observed by thermogravimetric analysis.
Keywords: Polypyrrole; Polyaniline; Carbon black; Polyethylene; Composites; Conductivity; Thermal ageing;
Modification of surface and mechanical properties of polyethylene by photo-initiated reactions by F. Fallani; G. Ruggeri; S. Bronco; M. Bertoldo (257-261).
Low density polyethylene thin films were crosslinked in the bulk and on the surface by means of photo-initiated reactions. The purpose of these experiments was to study if there is a direct relationship between the distribution of crosslinks in the depth of the films and the mechanical properties of the films themselves. By bulk treatment with a PI1 photoinitiator and a dimethacrylate, samples with enhanced Young's modulus values were obtained. The addition of an inorganic filler had no significant influence on the rate of the crosslinking reaction, but resulted in an enhancement of the oxygen barrier of the treated films. Samples with enhanced modulus and hydrophilicity were obtained by hot-surface treatment with a PI2 photoinititator and multifunctional allylic and acrylic monomers.
Keywords: Photocrosslinking; Polyethylene; Mechanical properties;
Effects of talc and gamma irradiation on mechanical properties and morphology of isotactic polypropylene/talc composites by Matjaž Denac; Vojko Musil; Ivan Šmit; Franjo Ranogajec (263-270).
Although isotactic polypropylene (iPP) has become one of the largest and fastest growing polymeric materials, some disadvantages in its properties, like poor stability to gamma (γ) irradiation, may impede its growth in commercial use. The popularity of γ irradiation use to sterilize iPP and iPP composites devices is increasing. The purpose of our research work was to examine the effects of talc and low dose γ irradiation on mechanical properties and the morphology of iPP and iPP/talc composites. The samples were prepared in a Brabender kneading chamber and by compression molding on a laboratory press. The iPP and iPP/talc composites were characterized by tensile testing, measurements of notched impact strength, FTIR spectroscopy, differential scanning calorimetry, optical microscopy, scanning electron microscopy and wide angle X-ray diffraction. The role of untreated talc or talc surface treated with aminosilanes as well as the influence of γ irradiation on mechanical properties and the morphology of modified iPP is discussed.
Keywords: Isotactic polypropylene; Talc; Composites; Gamma irradiation; Mechanical properties; Morphology;
Effect of hygrothermal aging on the essential work of fracture response of amorphous poly(ethylene terephthalate) sheets by T. Bárány; J. Karger-Kocsis; T. Czigány (271-278).
The toughness of amorphous poly(ethylene terephthalate) (PET) sheets before and after hygrothermal aging was determined by the essential work of fracture (EWF) concept. Hygrothermal aging at 60 °C for 100 h of the specimens was performed in hot water and soft drink (Coca-Cola), respectively. The EWF parameters were determined using the energy partitioning method of Karger-Kocsis et al., at various testing temperatures (T=−20 °C, +23 °C, +60 °C, respectively) at constant deformation rate (v=2 mm/min). It was found that the specific essential work of fracture terms are more sensitive for the test conditions than the plastic ones. Changes in the former terms were assigned to an alteration in the viscoelasticity of PET owing to temperature and the plasticising effect of water.
Keywords: PET; Hygrothermal aging; Ductile fracture mechanism; Viscoelasticity;
Thermal degradation of recycled polypropylene toughened with elastomers by R. Navarro; L. Torre; J.M. Kenny; A. Jiménez (279-290).
Commercial polyolefins, such as polypropylene (PP), are widely used because of their easy processing and their excellent properties. Although their recycling is well established, the mechanical and thermal properties of the recycled products are normally lower than those of the virgin material. The introduction of an elastomeric additive can improve the toughness, without compromising the processability and recycling capabilities. However the thermal properties of these blends should be assessed in order to limit degradation during recycling. This work presents a study of the thermal degradation of blends based on recycled PP with different elastomeric systems. Thermogravimetric analysis in dynamic and isothermal modes is used to develop a kinetic model for the decomposition reaction of the studied blends. The effect of the introduction of the elastomer is analysed through the variation of the apparent activation energies as well as the reaction order and pre-exponential factor. The correspondence between experimental and calculated results demonstrates the validity of the proposed model.
Keywords: Recycled polypropylene; Elastomers; Additives; TGA; Kinetic modelling;
Iron compounds in non-halogen flame-retardant polyamide systems by Edward D. Weil; Navin G. Patel (291-296).
An effective flame retardant system for polyamide 4,6 was found based on inorganic iron compounds with polyphenylene oxide and zinc borate. Iron compounds have been known as flame retardant synergists in halogen systems but their utility in non-halogen systems has been largely unrecognized. The iron compounds appear to improve char morphology. Polyphenylene oxide provides the char-forming component. Evidence was developed for a positive interaction between the polyphenylene oxide, the iron compound and zinc borate. Favorable results from more recent studies of iron compounds in non-halogen systems are also briefly reviewed.
Keywords: Polyamide 4,6; Flame retardant; Iron; Polyphenylene oxide; Zinc borate; Char; Morphology; Synergism;
Heat and mass transport in developing chars by J.E.J. Staggs (297-307).
The physics of heat and mass transport in chars is explored in the context of a developing char layer. The most important features of the problem are discussed and a section of the relevant literature is briefly reviewed. A mathematical model is then developed and analysed in order to illustrate some of the important phenomena. The model relates to the simplified case of a polymer which degrades to produce char and volatile gases in a single step at a critical temperature. Transport of gas through the char is modelled by Darcy's law and for simplicity it is assumed that there is no overall volume change as char is formed. Conservation of mass, Darcy's law and the perfect gas law are combined to give a non-linear diffusion equation describing the evolution of pressure in the developing char. This equation, together with equations expressing conservation of energy in the char and the virgin polymer and appropriate boundary/initial conditions complete the description. Exact solutions are derived for isothermal conditions in the char and these are used to frame the numerical results for the full model. A key parameter in the model is a dimensionless number λ akin to the Lewis number, namely the ratio of pressure diffusivity to thermal diffusivity. Generally, for realistic parameter values, λ is very large and the results show that under such conditions the developing char offers no resistance to the flow of gases. In other words, one may effectively assume that the mass flux of volatile gases through the char is uniform. Numerical solutions of the full model are presented and discussed and the question of integrity of the char is briefly explored.
Keywords: Developing char; Mathematical model; Polymer; Mass transport; Char formation;
A stibonium-modified clay and its polystyrene nanocomposite by Dongyan Wang; Charles A. Wilkie (309-315).
Triphenylhexadecylstibonium trifluoromethylsulfonate has been prepared and ion-exchanged with sodium montmorillonite to obtain a new organically-modified clay. The clay has higher thermal stability than an ammonium clay; only a portion of the alkyl chain is lost during degradation and all of the antimony is retained. This clay has been used to prepare a polystyrene nanocomposite in which the clay is not uniformly distributed throughout the polymer. Nonetheless the polymer does insert into the clay layers and the d-spacing of the clay expands from 2.0 to 3.0 nm. The enhanced thermal stability of this system may mean that it could be useful for polymers which must be processed at temperatures above that at which the ammonium clays undergo degradation.
Keywords: Nanocomposite; Polystyrene; Antimony;
Selective phosphorylation of hydroxyphenols for forming reactive flame retardants by A. Toldy; P. Anna; Gy. Marosi; Gy. Keglevich; X. Almeras; M. Le Bras (317-323).
Monophosphorylated hydroxy phenols were synthesized in a selective way and incorporated in different percentages into epoxy resins as reactive flame retardants. The LOI values of the epoxy resin samples could be increased this way up to 28%. The DSC results show that by increasing the percentage of incorporated monophosphorylated hydroquinone (HMP), the exothermic effect of the curing is decreased, which implies lower network density. An optimum balance is necessary between the flame retardant effect, determined by percentage of HMP, and the lower degree of crosslinking.
Keywords: Monophosphorylated hydroxyphenols; Reactive flame retardant; Epoxy resin;
Effect of fillers on the fire retardancy of intumescent polypropylene compounds by X Almeras; M Le Bras; P Hornsby; S Bourbigot; Gy Marosi; S Keszei; F Poutch (325-331).
The effects of fillers (talc and calcium carbonate) were investigated on polypropylene /ammonium polyphosphate/polyamide-6 (PP/APP/PA-6) intumescent system by using mechanical testing, LOI method, cone calorimetry and thermoanalytical techniques. Calcium carbonate and talc affect the fire protective properties of PP/APP/PA-6 system in different ways. It is shown that talc induces an increase in the Young's modulus and a decrease in the elongation at break. Calcium carbonate leads to a decrease in the elongation at break, but there is no improvement in the Young's modulus. Talc increases fire protective performance due to forming a ceramic like protective shield at the surface, whereas calcium carbonate decreases it because of a reaction with APP. Effects of talc and calcium carbonate were furthermore investigated on PP/APP/PA-6 system by measuring Rate of Heat Release (RHR), Total Heat Emitted (THE), CO/CO2 evolution and residual mass. Results are interpreted by means of decomposition, chemical reaction between components and formation of a protective shield at the surface at ignition.
Keywords: Intumescence; Fire retardancy; Polypropylene; Polyamide-6; Ammonium polyphosphate; Cone calorimetry; Talc and CaCO3;
Effect of various combinations of flame-retardant fillers on flammability of radiation cross-linked poly(vinyl chloride) (PVC) by A.A Basfar (333-340).
Various formulations of radiation cross-linked poly(vinyl chloride) (PVC) were prepared to improve the flame retardancy for wire and cable insulation applications. Limiting oxygen index (LOI) was used to characterize the flammability of the developed formulations. The effect of different plasticizers, dioctyl phthalate (DOP), di-isodecyl phthalate (DIDP) and tri-2-ethylhexyl trimellitate (TOTM) and various combinations of different flame-retardant additives, namely Sb2O3, zinc borate, Al(OH)3 and Mg(OH)2 on the mechanical properties and flammability was investigated. The influence of radiation dose on the mechanical properties was minimal at room temperature, but more prominent after thermal aging for 168 h at 136 °C. The highest LOI was 31% for PVC formulations containing DOP as a plasticizer and TMPTA at an absorbed dose of 60 kGy. Both DTG peak maxima and temperature for loss of 50% mass were investigated for selected formulations. No apparent influence of plasticizer type or irradiation dose on these thermal properties was observed.
Keywords: Flammability; PVC; Wire; Radiation cross-linking; Flame-retardant;
Fire retardant mechanism in intumescent ethylene vinyl acetate compositions by A. Riva; G. Camino; L. Fomperie; P. Amigouët (341-346).
The thermal and combustion behaviour of an intumescent fire retardant system based on Polyamide 6 (PA6) and Ammonium Polyphosphate (APP), used to improve flame retardant properties of poly(ethylene-co-vinyl acetate) (EVA), loaded with Mg(OH)2 (MH) was examined. The study of the interactions between the additives introduced in EVA was focused in particular on the MH-APP interaction. The evolution of water from MH takes place at about 400 °C, with a fair overlap with ammonia and water evolution from APP degradation. Ammonia evolution from APP is facilitated by the presence of MH, in their mixture heated alone or in the polymer matrix. UL94 test shows that the interaction between MH and APP modifies the combustion behaviour of the intumescent mixture.
Keywords: EVA; Intumescence; Ammonium polyphosphate; Polyamide 6; Magnesium hydroxide; Flame retardancy;
Thermal degradation of methyl methacrylate polymers functionalized by phosphorus-containing molecules—II: initial flame retardance and mechanistic studies by A. Gentilhomme; M. Cochez; M. Ferriol; N. Oget; J.L. Mieloszynski (347-355).
The thermal behaviour of methyl methacrylate polymers functionalized by phosphorus-containing molecules was investigated by TGA/FT-IR and Py-GC–MS under air and argon atmosphere. Three homopolymers and four copolymers with methyl methacrylate (MMA) were prepared and studied. The gases emitted during the degradation of these materials were unambiguously identified, allowing us to suggest a degradation mechanism very different to that of PMMA. The measurement of the LOI values show that the polymers have potential flame retardant properties.
Keywords: Thermal degradation; Poly(methyl methacrylate); Functionalization; Phosphorus; Mechanism; LOI; TGA; Py-GC–MS;
Red phosphorus/aluminium oxide compositions as flame retardants in recycled poly(ethylene terephthalate) by F Laoutid; L Ferry; J.M Lopez-Cuesta; A Crespy (357-363).
The mechanical properties and fire resistance of a recycled poly(ethylene terephthalate) were improved by using a specific treatment of the waste material and the incorporation of encapsulated red phosphorus in combination with co-additives. The use of red phosphorus has to be limited due to a negative influence on impact resistance and rate of heat release. Among several metal oxides, Al2O3 acts as a good co-synergist at a total loading of 5 wt.% due to its reactivity, high specific surface area and aluminium phosphate formation. The complementary use of glass fibres can also generate intumescence by improving the mechanical stability of the char layer.
Keywords: PET recycling; Fire resistance; Red phosphorus; Aluminium oxide; Intumescence;
An investigation into the decomposition and burning behaviour of Ethylene-vinyl acetate copolymer nanocomposite materials by T.Richard Hull; Dennis Price; Yan Liu; Claire L. Wills; Joan Brady (365-371).
Ethylene-vinyl acetate copolymer (EVA) is a widely used material, particularly as a zero-halogen material in the cable industry. It is frequently formulated with large quantities of inorganic filler material, such as aluminium trihydroxide (ATH). Used alone, EVA is known to form a protective layer which can inhibit combustion under well ventilated conditions, though this effect is not observed when used in formulations with ATH. The incorporation of nanoscale clay fillers into EVA appears to reinforce the protective layer. The stages of the decomposition under different conditions is described both for the 10 mg (TGA) and 200 mg (small tube furnace) scales. The latter allows the residues formed to be subjected to further analysis, to elucidate the mechanism of the reduction of decomposition and flammability. Enhancements in the thermo-oxidative stability of the EVA clay material were evident from both tube furnace and TGA experiments. The polymer-organoclay materials, prepared on a two-roll mill, showed poor dispersion when studied by SEM, suggesting that a significant portion was present as a microcomposite. However, when the char was analysed by SEM, layers of protective material were clearly evident on the char surface. From XRD spectra, there was no evidence of order within the polymer-organoclay, but ordering of the outer layer of char was demonstrated. This suggests that for EVA, which melts before burning, organoclay layers become nanodisperse at the surface of the burning polymer. These materials have also been studied in the Purser furnace, designed to replicate the conditions found in fully developed fires. This allows effluent yields, such as O2, CO2 and CO to be determined as a function of fire condition, by controlling the rate of burning and the ventilation rate. The effect of both the nanofillers and the protective layers are reported and discussed, under different ventilation conditions. Specifically, the relationship between equivalence ratio and hydrocarbon and carbon monoxide yield is focussed upon.
Keywords: Ethylene-vinyl acetate; EVA; ATH; Nanocomposite; Fire; Fire retardant; Fire toxicity; Purser furnace; BS 7990;
Intumescence in fire retardancy of lignocellulosic panels by Ondrej Grexa; Franck Poutch; Desana Manikova; Helena Martvonova; Andrea Bartekova (373-377).
At present there is growing interest in using wood and wood-based products for applications in various industries (mainly building and transportation). One of the limitations to use of wood is its flammability. The most usual way to improve the fire performance of wood is by chemical treatment with flame retardants. The “classical” mechanisms for flame retardancy of wood require relatively high load of flame retardants in the wood, which was connected with some problems (durability, higher sensitivity to moisture etc.). This paper deals with the intumescing concept of flame retardancy of wood based panels. Particleboard with improved fire performance was prepared in a laboratory conditions. Flame retardant formulations were used with the ability to form an intumescent layer during exposure to heat. This way it was possible to decrease the content of flame retardants in the body of the board. The heat release rate and the mass loss rate characteristics were measured by cone calorimetry. The results were promising in comparison to the classical way of flame retardancy of wood.
Keywords: Intumescence; Heat release rate; Fire retardancy; Particleboard;
Fire retardancy effect of migration in polypropylene nanocomposites induced by modified interlayer by Gy. Marosi; A. Márton; A. Szép; I. Csontos; S. Keszei; E. Zimonyi; A. Toth; X. Almeras; M. Le Bras (379-385).
Montmorillonite nanoparticles were found to be inefficient in polypropylene because of the lack of a heat insulating char layer and the decomposition of the compatibilising surfactant layer on their surface. Combination with an ammonium polyphosphate-based intumescent system showed some synergism due to modified rheology. The effect of surface and interface modification was analysed using Raman microscopy and X-ray photoelectron spectroscopy. Forming a heat resistant coating layer of low surface energy around the nanoparticles promotes their migration to the surface and formation of a flexible barrier layer, and thus leads to better performance.
Keywords: Nanoparticles; Flame retartdant;