Polymer Degradation and Stability (v.93, #11)

Calendar (I).

FRPM'07 special edition by Baljinder K. Kandola; T. Richard Hull (1985).

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

Study of the thermal decomposition of flame-retarded unsaturated polyester resins by thermogravimetric analysis and Py-GC/MS by Everson Kandare; Baljinder K. Kandola; Dennis Price; Shonali Nazaré; Richard A. Horrocks (1996-2006).
The thermal degradation behaviours of flame-retarded unsaturated polyester resin formulations containing ammonium polyphosphate (APP), Cloisite 25A nanoclay and zinc based smoke suppressants have been studied using thermogravimetric analysis (TGA) combined with infrared analysis of the evolved gases (EGA) and pyrolysis/gas chromatography–mass spectrometry (GC/MS). In TGA–EGA experiments, the mass loss as a function of temperature has been correlated with the evolution of carbon monoxide (CO) and carbon dioxide (CO2) and oxygen (O2) consumption as measured by an oxygen analyser. The effect of APP, Cloisite 25A and the smoke suppressants on the evolution of CO and CO2 has been examined. The decomposition behaviour of flame-retarded polyester resins under isothermal pyrolytic conditions was investigated and the evolved gaseous products were collected and qualitatively and semi-quantitatively analysed via GC/MS. The addition of APP does not yield many new gaseous products relative to the unmodified polyester resin neither does the presence of zinc borate (ZB) and zinc stannate (ZS) together with APP. Possible chemical interactions are discussed in an attempt to explain the observed results.
Keywords: Pyrolysis-GC/MS; Unsaturated polyester resin; Flame-retardant additives; Ammonium polyphosphate; Smoke suppressants;

Intrinsically flame retardant epoxy resin – Fire performance and background – Part II by A. Toldy; A. Szabó; Cs. Novák; J. Madarász; A. Tóth; Gy. Marosi (2007-2013).
The flame retardant mechanism of a newly synthesized phosphorus-containing reactive amine, which can be used both as crosslinking agent in epoxy resins and as flame retardant, was investigated. The mode of action and degradation pathway were investigated by in situ analysis of the gases evolved during the degradation by thermogravimetric measurements coupled online with infrared (TG-EGA–FTIR) and mass spectroscopy (TG/DTA-EGA–MS) and by solid residue analysis by infrared (ATR) spectroscopic methods and X-ray photoelectron spectroscopy (XPS). It was observed that the main difference in the degradation of the reference and the flame retardant system is that the degradation of the latter begins at lower temperature mainly with the emission of degradation products of the phosphorus amine, which act as flame retardants in the gas phase slowing down the further degradation steps. At the high temperature degradation stage the solid phase effect of the phosphorus prevails: the formation of phosphorocarbonaceous intumescent char results in a mass residue of 23.4%. The ratio of phosphorus acting in gas phase and solid phase, respectively, was determined on the basis of thermogravimetric and XPS measurements.
Keywords: Epoxy resin; organophosphorous reactive amine flame retardant; Flame retardancy; Mode of action; Degradation mechanism by TG-EGA–FTIR, TG/DTA-EGA–MS, ATR-IR, XPS;

Catalyzing carbonization function of α-ZrP based intumescent fire retardant polypropylene nanocomposites by Dandan Yang; Yuan Hu; Lei Song; Shibin Nie; Shuqin He; Yibing Cai (2014-2018).
The catalyzing carbonization function of alpha-zirconium phosphate (α-Zr(HPO4)2·H2O, α-ZrP) based on an intumescent fire retardant (IFR) polypropylene (PP) system is reported. The IFR system consists of ammonium polyphosphate and pentaerythritol. The morphology of the PP/organophilic ZrP nanocomposites is characterized by X-ray diffraction and high resolution transmission electron microscopy (HRTEM). The results indicate that an intercalated structure is formed. Thermogravimetric analysis, limiting oxygen index (LOI) and UL-94 are used to characterize the thermal stability and the flame retardant properties. It is found that there is a transformation of the char microstructure and an increment of LOI value in the PP systems with the OZrP, and the UL-94 level is improved, from failure, to a V-0 rating. The synergistic effect improves the flame retardant properties of PP remarkably. The morphology and structure (HRTEM and selected area electron diffraction) of the char residue also indicate the presence of graphite sheets. A possible mechanism for catalyzing carbonization is discussed.
Keywords: Polypropylene; Alpha-zirconium phosphate; Intumescent fire retardant; Nanocomposites; Catalyzing carbonization; Graphite sheets;

Fire retardancy of polymer clay nanocomposites: Is there an influence of the nanomorphology? by Fabienne Samyn; Serge Bourbigot; Charafeddine Jama; Séverine Bellayer (2019-2024).
The obvious aspect of nanodispersion and its role when investigating fire retardancy is not often clearly commented upon in the literature. Polymer clay nanocomposites can exhibit different morphologies and these might have consequences for their fire behaviour. Using solid state NMR to quantify the nanodispersion of organoclay in polyamide-6 (PA-6), we have prepared by melt blending PA-6/clay nanocomposite exhibiting different nanomorphologies. NMR results are consistent with transmission electron microscopy (TEM) images but the advantage of NMR is that it is representative of the whole sample and provides a precise quantification. PA-6 nanocomposites exhibit significant reduction of PHRR but the nanomorphology (exfoliation, intercalation and presence of tactoids) does not play any significant role. In other words, we have clearly shown that if nanodispersion is achieved, polymer/clay nanocomposite should exhibit fire retardant properties.
Keywords: Polyamide-6; Nanocomposite; Fire retardant; Solid state NMR; Dispersion;

Preparation, thermal properties and flame retardancy of phosphorus- and silicon-containing epoxy resins by M. Spontón; L.A. Mercado; J.C. Ronda; M. Galià; V. Cádiz (2025-2031).
Phosphorus- and silicon-containing epoxy resins were prepared from (2,5-dihydroxyphenyl)diphenyl phosphine oxide (Gly-HPO), diglycidyloxy methylphenyl silane (DGMPS) and 1,4-bis(glycidyloxydimethyl silyl)-benzene (BGDMSB) as epoxy monomers and diaminodiphenylmethane (DDM), bis(3-aminophenyl)methyl phosphine oxide (BAMPO) and bis(4-aminophenoxy)dimethyl silane (APDS) as curing agents. Epoxy resins with different phosphorus and silicon content were obtained. Their thermal, dynamic mechanical and flame retardant properties were evaluated. The high LOI values confirmed that epoxy resins containing hetero-atoms are effective flame retardants, but a synergistic efficiency of phosphorus and silicon on flame retardation was not observed.
Keywords: Flame retardance; Epoxy; Phosphorus-containing resins; Silicon-containing resins;

Mechanical and fire retardant properties of EVA/clay/ATH nanocomposites – Effect of particle size and surface treatment of ATH filler by M.A. Cárdenas; D. García-López; I. Gobernado-Mitre; J.C. Merino; J.M. Pastor; J. de D. Martínez; J. Barbeta; D. Calveras (2032-2037).
Mechanical and flame retardant properties of ethylene vinyl acetate (EVA) copolymer/organoclay/alumina trihydrate (ATH) nanocomposites have been studied. ATH with different particle sizes, ATH1 (2.2–5.2 μm) and ATH2 (1.5–3.5 μm), and three different surface treatments, uncoated, fatty acid coated and silane coated, have been used. A synergistic effect was observed in EVA/organoclay/ATH nanocomposites with the total heat evolved (THE) and the heat release rate (HRR) lower than that of EVA/ATH composite. It was also found that mechanical and flame retardant properties are affected in different ways by the particle size and the surface treatment of ATH fillers. Improvements in tensile and flame retardant properties were observed in nanocomposites when uncoated ATH fillers and fatty acid coated ATH2 filler were used. On the other hand, silane coating on ATH1 and ATH2 improves limiting oxygen index (LOI) and leads to higher t ignition and the best char stability after cone calorimeter test.
Keywords: Alumina trihydrate; Organoclay; Nanocomposites; TGA; Mechanical properties; Fire retardant properties;

Synthesis and thermal behaviour of polyamide 6/bentonite/ammonium polyphosphate composites by J.B. Dahiya; M. Muller-Hagedorn; H. Bockhorn; B.K. Kandola (2038-2041).
In order to achieve acceptable levels of flame retardancy of polymers, phosphorus-based flame retardant (FR) additives at about 20–30% w/w are required which is too high for conventional synthetic fibres. To know whether more finely sized particles of conventional FRs with or without nanoclay are more effective at the same concentration, composites of PA6 with bentonite and ammonium polyphosphate (APP) have been prepared by melt processing in a twin-screw extruder. XRD peaks and TEM images of PA6/Org-bentonite composite show partially ordered intercalation and ordered exfoliation. Thermal analysis in He shows that thermal stability of PA6 nanocomposite has increased by 18 °C compared with pure PA6 during degradation after 425 °C but it has decreased by 100 °C on inclusion of APP in PA6/nanoclay composites. The char yield is increased by 20% in PA6/bentonite/APP composites. No effect on thermal stability or char yield is observed by reducing the particle size of APP.
Keywords: Nylon 6; Bentonite; Composite; Thermal degradation; TEM; TG;

Synthesis and performance of cyclic phosphorus-containing flame retardants by DongQuy Hoang; Jinhwan Kim; Bok Nam Jang (2042-2047).
A series of organo-cyclic phosphorus compounds were synthesized in an attempt to find an efficient flame retardant (FR) for acrylonitrile–butadiene–styrene (ABS). The success of synthesis was confirmed by 1H and 31P NMR. Thermogravimetric analysis (TGA) results reveal that cyclic phosphorus compounds synthesized in this study show almost one step degradation between 250 and 400 °C and are believed to work in the vapour phase rather than in the condensed phase. From UL-94 test, V-0 rating was achieved at 15–35 wt% loading of cyclic or cyclic alkyl phosphonate FR and no rating at 35 wt% loading of cyclic phosphate for ABS. On the other hand, a much lower loading (7.5%) was needed to obtain V-0 rating for polycarbonate when 3,9-diphenyl-3,9-dioxa-2,4,8,10-tetraoxa-3,9-diphosphaspiro-5,5-undecane (PBPP) was added as FR. All the results show that the flame retarding effect is strongly dependent on the P content of the FR incorporated. The flame retardant mechanism of cyclic phosphorus compounds is also discussed.
Keywords: Organo phosphorus; Flame retardant; ABS; Polycarbonate; Spirobisphosphonate; Spirobisphosphate;

A composite laminate based on natural sisal fibre and polypropylene was prepared by compression moulding. The mechanical properties of the composite were assessed under tensile, flexural and impact loading. Changes in the stress–strain characteristics, yield stress, tensile strength, and tensile (Young's) modulus, due to ageing have been analysed. Important findings with the fresh and aged fibres and their behaviour in composites have been reported and analysed.
Keywords: Sisal; Natural fibre; Polypropylene; Composite; Compression moulding; Ageing;

Effective additives are required to impart a measure of fire retardancy to polymeric materials used in a variety of applications. Traditionally, these have been gas-phase active additives, most commonly organohalogen compounds or solid-phase active agents, often organophosphorus compounds. Organosphosphorus flame retardants are often very effective but may suffer from a cost disadvantage when compared with their organobromine counterparts. Organohalogen flame retardants are usually quite effective but their use is a subject to several environmental concerns. The development of additives that could simultaneously promote both types of fire retardant action could make available flame retardants that are both more cost effective and more environmentally friendly than those currently in use. Several sets of compounds with the potential to display both solid-phase and gas-phase flame retardant activities have been prepared and evaluated.
Keywords: Dual-functional flame retardants; Bromine-phosphorus flame retardants; Nitrogen-phosphorus flame retardants; Low-halogen flame retardants; Environmentally-friendly flame retardants;

Characterisation of the steady state tube furnace (ISO TS 19700) for fire toxicity assessment by Anna A. Stec; T. Richard Hull; Krzysztof Lebek (2058-2065).
The steady state tube furnace (Purser furnace, ISO TS 19700) has been developed specifically to replicate the generation of toxic products from real fires under different fire conditions on a bench-scale. Steady state burning is achieved by driving the sample into a furnace of increasing heat flux at a fixed rate and recording the product yields over a steady state period in the middle of the run. The furnace, sample, and effluent dilution chamber temperature profiles are presented to characterise the conditions in the apparatus. The distribution of smoke in the mixing chamber has been investigated to demonstrate the efficiency of mixing in the effluent dilution chamber. The heat flux applied to the sample at various points through the furnace has been measured, showing that conditions vary from those typical of pre-flaming to fully developed fires. An initial investigation of the repeatability and interlaboratory reproducibility has been undertaken, showing acceptable low levels of uncertainty in the toxic product yields.
Keywords: Fire; Toxicity; Fire toxicity; Steady state tube furnace; ISO 19700; Purser furnace;

In order to compare their inherent flame retardancy and thermal stability, two phosphorus-containing thermotropic liquid crystalline copolyesters (P-TLCP) were synthesized by melting transesterification. Additionally based on the facts that the P-TLCP can work as a functional additive to enhance the flame retardancy and mechanical property of PET, we further studied the flame retardant mechanism. Scanning Electronic Microscope (SEM) observations show that the char from PET/P-TLCP is more compact, therefore more efficiently resists fire and heat attack than pure PET. Moreover, Fourier Transform Infrared Spectroscopy (FTIR) measurements of evolved gas, indicate that P-TLCP decomposes to produce phosphorus-containing small molecular compounds during the pyrolysis process, such that P-TLCP could play a flame retardant role in vapour phase. Furthermore, P-TLCP strongly inhibits the generation of combustible compounds in the pyrolysis of PET, which also helps to resist fire propagation.
Keywords: Fire retardant; Thermotropic liquid crystal copolymer; PET; TG–FTIR;

New developments in chemical modification of fire-safe rigid polyurethane foams by Wojciech Zatorski; Zbigniew K. Brzozowski; Andrzej Kolbrecki (2071-2076).
This work reports the preparation of polyurethane–polyisocyanurate (PUR–PIR) foams containing different amounts of flame retardants (FRs) and a layered silicate nanoclay. An environmentally friendly blowing agent, a mixture of 1,1,1,3,3-pentafluorobutane and 1,1,1,2,3,3,3-heptafluoropropane (HFC 365/227), with small amount of water was used. The flame retarded PUR–PIR foams showed better fire resistance in comparison to classical PUR and unmodified PUR–PIR foams without deterioration of their functional properties. It was observed that when nanoclay was used in conjunction with flame retardants containing reactive bromine and phosphorus compounds, and zinc stannate, the flammability was significantly reduced. Expandable graphite was also used in some samples. As control samples for reference purposes three foam systems without any flame retardant were frothed: PUR, PUR–PIR and foams PUR–PIR modified by carbodiimide groups.
Keywords: Layered silicate nanoclay; Polyurethane–polyisocyanurate foam; Flame retardant; Reactive bromine; Reactive phosphorous; Zinc stannate;