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The multicomponent flame retardant system of melamine polyphosphate (MPP), melamine cyanurate (MC) and aluminum diethylphosphinate (AlPi) is proposed and investigated for thermoplastic polyurethane (TPU). The synergy between those additives and the resulting superior fire performance are discussed. Systematically varied sets of flame retarded TPU with various MPP/MC/AlPi ratios were investigated in terms of fire behavior, pyrolysis products and mechanical properties. The total amount of the additives was always 30 wt.-%. Further, the influence of various AlPi concentrations was investigated. The optimal MPP:MC ratio was determined while keeping the amount of AlPi constant. The combination of 8 wt.-% MPP, 12 wt.-% MC and 10 wt.-% is proposed as the most promising halogen free flame retardant formulation for TPU, because it yielded a reduction in PHRR from 2660 kW/m2 (TPU) to 452 kW/m2 and enabled V-0 classification in the UL 94 test. Combinations of MPP and MC as well a high concentration of AlPi are beneficial for the mechanical properties e.g. tensile strength and elongation at break of the formulations and could be a strong competitor to commercial flame retarded TPUs.

The compositional and stereochemical heterogeneity of copolymers are key molecular metrics, and their knowledge is of pivotal importance for evidence based material development. Yet, while it is state of the art to determine these parameters for many petroleum based polymers, little insight exists in that regard for bio-based materials. Towards this end, size exclusion chromatography (SEC) was hyphenated with nuclear magnetic resonance spectroscopy (NMR) in an offline manner and a blend of poly(lactic acid) (PLA) and poly(butylene succinate-co-adipate) (PBSA) investigated. Thus, the microstructural heterogeneity could be shown with regard to tacticity of the PLA and regioregularity of the PBSA component. The results show, that the highest molar mass fraction differs in stereochemical com position from the others. It may be assumed that this is the result of misinsertions with regard to stereochemistry occurring during the catalytic polymerization of the lactide. While the content of both constituent polymers along the molar mass axis could be well studied using a univariate analysis of the infrared (IR) spectra, this method failed to profile the adipate and succinate content individually. For this purpose, SEC was coupled to IR spectroscopy in online mode and the spectra were evaluated by a multivariate protocol. Thus, the content of each monomer along the molar mass distribution could be mapped with high chromatographic resolution.

Linear economy models are no longer acceptable for the plastic industry and a change to a sustainable circular plastic economy must take place. In the field of thermoplastic foams, the biopolymer poly(lactic acid) (PLA) is a suitable alternative for fossil based foams like polystyrene. However, the production ofPLA bead foams is still a challenge. In regards to circular plastic economy products, a reduction of the needed polymer additives is aspired to simplify the union of end-of-life plastic streams. Flame retardants (FR) are required in many applications and are often the largest proportion of additives. It turns out that the removal of FRs, for example the removal of the REACh registered FR hexabromocyclododecane for polystyrene foams, requires a great effort. This paper shows that PLA bead foams require no FR to achieve a class E classification for construction products. Therefore, nine PLA types are analyzed by differential scanning calorimetry, thermogravimetric analysis, gel permeation chromatography, and rheotens measurements. From five types, PLA bead foams could be produced with two different densities. In addition, PLA bead foams containing 1.5 wt% alkoxy amine FR were produced. The flammability of the PLA bead foams was investigated by LOI, DIN-4102-1-B2, and cone calorimeter tests.

The rapid mass calorimeter (RMC) was used as a screening tool based on accelerated fire testing to assess flame-retarded thermoplastic polyurethane (TPU). The reliability of RMC results was proven with the cone calorimeter as reference fire test. The influence of melamine cyanurate (MC) concentration on the fire performance of TPU was investigated, along with some flame-retardant combinations such as MC with aluminium diethylphosphinate (AlPi), aluminium trihydrate (ATH), and melamine polyphosphate (MPP). The two-stage burning behaviour of TPU was investigated in detail; the first stage corresponds mainly to the hard segments' decomposition and has a much lower effective heat of combustion (EHC) than the second stage, in which mainly the soft segments decompose and an intensive liquid pool fire is observed in the cone calorimeter set-up. In addition to fire testing with the cone calorimeter, RMC, and UL 94 flammability tests, the decomposition of the materials was investigated using thermogravimetric analysis coupled with infrared spectrometry (TGeFTIR). TPU/MC/AlPi shows the most promising results, achieving V-0 classification in UL 94 and reducing the extreme peak heat release rate (PHRR) of the liquid pool fire from 3154 kW/m2 to 635 kW/m2. Using MC/AlPi/MPP enhances the latter PHRR reduction further. The decomposition products identified in the gas phase via TGeFTIR reveal specific MCeAlPi eMPP interactions, as they differ from products seen in systems with MC/AlPi or MC/MPP. Correlations between RMC and cone calorimeter results were examined and presented in the final part of the paper. Several characteristics correlate strongly, pointing out that RMC is a reliable high-throughput fire testing method to screen multicomponent flame-retardant solutions in TPU.

The current article deals with the development of different novel, tailor-made polyolefin formulations exhibiting both low flammability and high weathering resistance, so as to provide value-added polyethylene grades with extended service lifetime. Two low-density (LDPE) and one linear low-density (LLDPE) polyethylene grades were modified via melt compounding with an additive system comprising: (a) a nitrogen-phosphorous intumescent system for flame retardance and (b) a hindered amine light stabilizer and a benzophenone-type UV absorber for UV/heat stabilization, at a total loading of 30-35 wt%. The target was to reach V0 classification in UL94V flammability tests, while to a large extent maintaining the mechanical properties, such as, tensile and impact strength of the investigated polymers, thus ensuring that the additives do not interfere significantly with the material quality. Subsequently, the compounds were subjected to separate artificial UV and heat aging at 100 C for 1500 h; the formulations showed good flame retardance, even after prolonged artificial weathering, but there was an observable, although acceptable, decrease in the mechanical properties. Nevertheless, all the results show that the developed polyethylene compounds are very promising for outdoor applications, such as, irrigation piping and profiles, where long-term weathering stability is important, and where flame retardance is important for safety during storage. This publication was made possible by the NPRP award (NPRP 9-161-1-030) from the Qatar National Research Fund (a member of The Qatar Foundation). We are also grateful to BASF and Sabo for supplying the additives at no cost. We further express our gratitude to Dr. Mabrouk Ouederni from QAPCO for providing us with the three polyethylene grades. The statements made herein are solely the responsibility of the author(s). Scopus

Novel bifunctional antioxidants (AO) with high molecular weight were successfully synthesized by two-step free-radical thiol-ene click reaction and transesterification. The structures of the stabilizers were confirmed by 1H NMR spectra and Fourier Transform Infrared Spectrometry (FTIR). Thermal gravimetric analysis (TGA) showed high temperature stability above 300 °C, proving suitability as potential stabilizers for standard and technical polymers. The performance of the bifunctional antioxidants was investigated through oxidation induction time (OIT) and accelerated heat aging of PP compounds in comparison to state of the art stabilizers represented through 2,2′-thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] and a binary mixture of pentaerythritol tetrakis(3,5-di-tert-butyl-4-hydroxyhydrocinnamate) and dioctadecyl 3,3′-thiodipropionate. Reduced degradation and extended maintenance of mechanical values of PP stabilized through the novel antioxidants during heat aging are due to the high amount of alkyl sulfide groups. Furthermore, a low migration tendency of the high-molecular AO could be determined by FTIR mapping of heat-treated samples.

The potential of thirteen aliphatic, aromatic, thiuram and heterocyclic substituted organic disulfide derivatives of the general formula R–S–S–R′ as a new group of halogen-free flame retardants (FR) for polypropylene films have been investigated. According to DIN 4102-1 standard ignitibility test, for the first time it has been demonstrated that many of the disulfides alone can effectively provide flame retardancy and self-extinguishing properties to polypropylene (PP) films at already very low concentrations of 0.5 wt%. In an effort to elucidate the mechanism of the thermal decomposition of disulfide derivatives the fragmentation patterns of the evolved gases from a thermogravimetric analyzer (TGA) have been analyzed by simultaneous mass spectrometry (MS) and Fourier transform infrared spectrometry (FTIR). The main decomposition products initiated by homolytic scission of the S–S bond and/or scission of the C–S bond were identified as thiols, aliphatic and aromatic hydrocarbons, isothiocyanates (depending on the disulfide structures) with further evolution of elemental sulfur and sulfur dioxide at temperatures of above 300 °C and 450 °C, respectively. Based on this preliminary study, we have shown that disulfides represented by e.g. diphenyl disulfide ( 1 ), 5,5′-dithiobis(2-nitrobenzoic acid) ( 2 ), bis(1-phenyl-1H-tetrazol-5yl)-disulfide ( 4 ), 2-bisbenzothiazole-2,2′-disulfide ( 6 ) and N , N -dithiobis-(phtalimide) ( 10 ) constitute a new halogen-free family of additives for flame retarding of polypropylene.

The effect of six halogen-free flame retardant (FR) formulations was investigated on the thermal stability of two low-density polyethylenes (LDPE) and one linear low-density polyethylene (LLDPE), by means of thermogravimetric analysis (TGA) under nitrogen and air atmosphere. The relative data were combined with flammability properties and the overall performance of the FRs was correlated with the type of branching in the polyethylene grades and to their processing behavior. The thermal degradation kinetics was further determined based on the Kissinger and Coats-Redfern methods. In terms of flammability, the addition of a triazine derivative and ammonium polyphosphate at a loading of 35 wt. %. was found to be the most efficient, leading to UL 94 V0 ranking in the case of the LDPE grade produced in an autoclave reactor. - 2019 by the authors. Funding: This publication was made possible by the NPRP award [NPRP 9-161-1-030] from the Qatar National Research Fund (a member of The Qatar Foundation). The statements made herein are solely the responsibility of the author(s). Scopus

Poly(lactic acid) (PLA) was submitted to solid state polymerization (SSP) in a fixed bed reactor under nitrogen flow, so as to examine technique efficiency for increasing the molecular weight and hence permitting the reduction of the melt polymerization residence times. In order to use a suitable starting material, SSP prepolymers of low and medium molecular weight were first prepared through solid state hydrolysis of commercial PLA grade under acidic and alkaline conditions. During these degradation runs, hydrolysis involved the random scission of ester groups in the polymer backbone, while the relevant kinetics and the resulting thermal properties were also examined. In a subsequent step, the prepolymers obtained were subjected to SSP at three temperatures, approximately 2.5–25.0 °C below their melting point. The process achieved an increase of up to 1.7 times the initial molecular weight, however, with different trends depending on the prepolymer characteristics, reaction temperature and time, as well as the pH of the hydrolysis medium. In addition to molecular weight build up, the effect of the SSP process on end product thermal properties was also investigated.

Various analogs of (1-alkoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (AZONOR), symmetric and asymmetric (1,2,2,6,6 pentamethylpiperidin-4-yl)diazene flame retardants such as (N-t-butyl-N′-1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (1), (N-cyclohexyl-N′-1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (2), bis(1,2,2,6,6 pentamethylpiperidin-4-yl)diazene (3), bis(1-methoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (4), bis(1-ethoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (5), bis(1-propoxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (6), bis(1-octyloxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (7), bis(1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl)diazene (8), bis(1-methoxy-2,2,6,6-tetramethyl-4-piperidone)azine (9) have been prepared and tested as either flame retardants alone or as flame retardant synergists in different polyolefin formulations. The flame retardant efficacy increased in the following order in polypropylene films DIN 4102 B2 test standard 4, 5 > 7, 6, 8> FLAMESTAB NOR116, 9, 2 > 1, 3. Only AZONOR flame retardants were capable of preventing burning dripping. Whereas in polyethylene films the best performance was recorded for 6 followed by FLAMESTAB NOR116 and 9 had clearly the lowest performance in this test series. The long term flame retardant efficacy in polypropylene plaques after accelerated weathering (WOM Ci 65 A, BPT 63 °C, 60% relative humidity. water spray) was also studied and the results showed that all AZONOR compounds exhibited excellent and unchanged flame retardant performance even after extended weathering for 2000 h. In polypropylene plaques a strong synergistic effect between 6 and brominated flame retardants and alumina trihydrate (ATH) were observed. Thus, the addition of AZONOR allowed for a significant reduction of the commercial flame retardants while still achieving a UL94 V-2 rating for 1.6 mm polypropylene plaques. The synergistic effect in high-impact polystyrene films was also evident, although it was much weaker than in polypropylene plaques.

In this study, the flame retardancy and physical properties of polyamide 6, melt processed in a twin-screw extruder with various amounts of melamine polyphosphate and layered silicates, were examined. Generally, there were indications that exfoliated nanocomposites were produced. During compounding, the presence of layered silicates was found to result in polymer degradation, which was further enhanced by the addition of the flame retardant. The additives were also shown to restrain the ability of polyamide 6 for crystallization. Tensile modulus and tensile strength were substantially improved, however polymer's ductility deteriorated. The incorporation of the additives exerted a positive effect also on the flame retardancy of polyamide 6, leading to materials of UL94 V-2 classification.

Four triazene derivatives have been synthesized, i.e. bis-4,4′-(3,3′-dimethyltriazene)-diphenyl ether ( 1 ), bis-4,4′-(3,3′-diethyltriazene)-diphenyl ether ( 2 ), 2,2,6,6,-tetramethyl-1-phenylazo-piperidine ( 3 ) and 4-hydroxy-2,2,6,6-tetramethyl-1-phenylazopiperidine ( 4 ). Their thermal properties were determined by differential scanning calorimetry (DSC) and the fragmentation patterns were analysed by simultaneous mass spectrometry (MS) and Fourier transform infrared (FTIR) spectrometry of off-gases from a thermogravimetric analyser (TGA). The triazenes exhibited an exothermic decomposition peak at temperatures between 230 and 280 °C when the triazene units were homolytically cleaved into various aminyl, resonance-stabilized aryl radicals and different CH fragments with simultaneous evolution of elemental nitrogen. The potential of triazenes as a new class of flame retardants for polypropylene films was investigated by performing ignitability test in accordance to DIN 4102-1/B2 standard. Polypropylene samples containing very low concentration of only 0.5 wt% of any of these triazene (R–N 1 = N 2 –N 3 R’R″) additives passed the test with B2 classification. Notably, no burning dripping could be detected. The average burning times are very short with exceptionally low weight losses. Based on this preliminary FR testing we have shown that the triazene compounds constitute a new and interesting family of radical generators for flame retarding of polymeric materials.

An inorganic azo diphosphonate (INAZO), (KO)2(O)P-N N-P(O)(OK)2·4H2O, was synthesized and tested as a novel type of flame retardant additive for castor oil and oligomeric methylene diphenyl diisocyanate (PMDI) based two component polyurethane adhesive with or without using dolomite ((CaMg(CO3)2) as filler. Flammability according to UL 94 test and performance under forced-flaming conditions (cone calorimeter) were investigated at the additive loadings of 5, 10 and 20 wt %. It was shown that INAZO improves flame retardancy by significantly reducing heat release rate (HRR), maximum average rate of heat emission (MARHE) and total smoke release (TSR) values in comparison to CaMg(CO3)2 filled polyurethane adhesives. The macroscopic structure of the sample residues after cone calorimeter measurement was also analysed. The action mechanism of the developed INAZO flame retardant is suggested to be mainly in the condensed phase. UL 94 V-0 rating was achieved in the vertical burning test when 10 wt % loading of INAZO was used, whereas the reference flame retardant ammonium polyphosphate (APP) required a loading of 20 wt % to reach the V-0 classification.

In this work, we report the synthesis and use of an innovative multifunctional radical generator, i.e., bis(1-propyloxy-2,2,6,6-tetramethylpiperidyl)-4-diazene (AZONOR) that alone can effectively provide flame retardancy and self-extinguishing properties to both polypropylene films and plaques. Polypropylene samples containing very low concentrations of 0.25–1 wt% of this additive can successfully pass not only the fire standard tests of DIN 4102 B2 and NF P92-505 but also the more challenging UL94 VTM-2 standard. Besides relative low levels of addition and having no detrimental effect on polypropylene appearance or its mechanical and processing properties another great advantage offered by this flame retardant is its multifunctionality, i.e., high flame retardant durability after artificial weathering. Thus, even after 2000 h of artificial weathering no significant decrease in flame retardant efficacy could be observed.

The potential synergy of melamine polyphosphate and layered silicates for enhancing the flame retardancy and physical properties of polyamide 6 is investigated. Through melt blending, exfoliated nanocomposites were prepared, suffering, however, from polymer degradation. In the presence of the additives, the ability of polyamide 6 to crystallize was restrained and its thermal stability was deteriorated. Nevertheless, the stiffness of the polymer was increased, yet at the expense of ductility. Apart form stiffness, the additives exerted a positive effect on the fire resistance of polyamide 6; melamine polyphosphate and layered silicates cooperated during combustion to provoke the formation of a superficial protective barrier, yielding materials of inferior flammability.

A number of symmetrical and unsymmetrical azoalkanes of the general formula R(SN¼NSR and related azoxy,hydrazone as well as azine derivatives have been synthesized in order to assess their potential as novel flameretardants for polypropylene alone or in combination with commercially available flame retardants such as aluminatrihydrate (ATH), decabromodiphenyl ether (DecaBDE) and tris(3-bromo-2,2-bis(bromomethyl)-propyl)phosphate(TBBPP). The experimental results show that in the series of different sized azocycloalkanes the flame retardantefficacy decreased in the following order: R¼cyclohexyl>cyclopentyl>cyclobutyl>cyclooctanyl>>cyclododecanyl.Whereas in the series of aliphatic azoalkanes compounds the efficacy decreased in the following order:R¼n-alkyl>tert-butyl>tert-octyl. In addition, also some of the prepared azoxy, azine, and hydrazone derivativesprovide flameretardancy to polypropylenefilms atalready very lowconcentrations (0.25–1wt%). Noteworthyis thatin contrast to other halogen-free radical generators, the azoalkanes are also very effective as flame retardants inpolypropylene thick moldings. Interestingly, it was found that 4,4(-bis(cyclohexylazocyclohexyl)-methane) shows astrong synergistic effect with ATH. Thus, in the presence of 0.5wt% of azoalkane the ATH loading could be reducedfrom60to25wt%andstillUL94V-2ratingcouldbereached.Furthermore,thefiretestingdatarevealthatazoalkanesshow a synergistic effect with DecaBDE and when used in conjunction with very low loadings of TBBPP. Copyright 2010 John Wiley & Sons, Ltd.Keywords: additives; azo compound; radical (generator); non-halogenated flame retardants; poly(propylene)

The efficiency of melamine cyanurate and a clay filler for improving the flame retardancy and other physical properties of polyamide 6 was examined. Partially intercalated-exfoliated morphologies were obtained. Nanocomposites suffered from polymer degradation during compounding, while the molecular weight was enhanced in the case of the flame retarded samples. Silicates were shown to restrain crystallization, whereas melamine cyanurate induced heterogeneous nucleation. Both additives positively influenced the tensile modulus of the prepared samples, decreasing their ability to elongate. With respect to the UL94 flammability test, melamine cyanurate was proved to be not sufficiently capable of increasing the tendency of nanocomposites to drip, negatively affecting flammability.

A series of symmetrical and unsymmetrical azoalkanes were synthesized and their potential as a free-radical source for rheology modification of polyolefins was investigated. The experimental results show that unsymmetrical azoalkanes, in particular N-cyclohexyl-N'-tert-octyldiazene (13), can be successfully used for manufacturing controlled-rheology poly(propylene) and cross-linked high-density polyethylene. For example, the melt flow rate of a general-purpose poly(propylene) (MFR =14) could be increased to a value of 800 when 0.75 wt.-% of azoalkane 13 was added during reactive processing. In parallel, it was found that 13 has a remarkable efficiency for free-radical-induced cross-linking of high-density polyethylene, resulting in similar gel contents to dicumyl peroxide.

The effectiveness of the reactive extrusion technique was investigated for poly(ethylene terephthalate) to promote the concept of closed-loop recycling, that is, the reuse of waste material in the initial application. More specifically, a chain-extender system, consisting of pyromellitic dianhydride, polyol, and a catalyst, was employed, and its efficiency regarding the improvement of the recyclate quality was evaluated. Accordingly, rheological and thermal characterizations were performed and used as criteria of the modification induced in the polymer molecular structure during processing due to the counteracting degradation and chain-extension reactions. In particular, the molecular weight, related to intrinsic viscosity and melt flow rate measurements, of modified poly(ethylene terephthalate) samples was found to increase with the additive content. Simultaneously, a decrease in the crystallinity was observed, attributed to the branching effect of the chain extender, which restricted the ability of the macromolecules to organize in the crystal structure. Beyond a critical concentration of the additive system, the molecular weight of the treated samples started to decrease again, and this was accompanied by a small increase in the crystallinity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1671–1678, 2007

Beyond traditional polymer stabilization, sterically hindered piperidine derivatives move into new application areas where radical functions are key elements. Recent achievements in using nitroxyl derivatives in degradation, polymerization and grafting processes are discussed together with the involved chemical reactions and the resulting material properties. The examples shown cover selected nitroxylethers (NORs) performing as flame retardants and flame retardant synergists or replacing peroxides in manufacturing controlled rheology polypropylene (PP). Furthermore, NORs and nitroxyl radicals mediate radical polymerization processes resulting in tailor-made intermediates for polymer modification via radical and condensation steps and offer access to complex polymer architecture. To cite this article: R. Pfaendner, C.R. Chimie 9 (2006).

The synthesis of azoalkanes such as azocyclohexane (1) and 4,4'-bis(cyclohexylazocyclohexyl)methane (2) and their use as flame retardansts in polymer substrates is reported. For the first time it is demonstrated that azoalkanes alone can effectively provide flame retardancy and self-extinguishing properties to poly(propylene) films at a very low concentration of 0.25 to 0.5 wt.-%. All the poly(propylene) formulations passed DIN 4102-1/B2 standards and the instant azoalkane-containing poly(propylene) blends.

Controlled free radical polymerization (CFRP) of vinyl chloride (VCM) and copolymerization with several comonomers have been studied in aqueous suspension. Therefore di-tert-butylnitroxide and three novel nitroxyl radicals were used as mediating agents. Copolymerization of VCM with styrene, partly combined with acrylonitrile, maleic acid anhydride and maleic acid imide as well as methyl methacrylate, n-butyl methacrylate, butyl acrylate and butadiene have been achieved, demonstrating an efficient route for novel vinyl chloride copolymer architecture.

Artificial weathering was performed for 4000 h to evaluate the light stability of postused, CaCO3-filled polypropylene material recycled from garden chairs. The old chair material was recycled by applying the remelting–restabilization technique while using different stabilization systems in selected concentrations. To study the role of restabilization in the material performance, the tensile impact strength was monitored during the artificial weathering exposure. The data were compared to microphotographs of the specimens' surfaces. The effect of light on the material was further studied through yellowness index (Y.I.) determinations. The results revealed that the appropriate restabilization of the postconsumer chair material is mandatory for improving its light stability, ensuring its reuse in the original application. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1311–1318, 2003

The long-term thermal stability of postused CaCO3-filled Polypropylene was evaluated through accelerated heat aging tests for about 2000 h. The material from old garden chairs was recycled by applying the remelting-restabilization technique while using different stabilization systems in selected concentrations. To study the effect of heat aging on the material properties, crystallinity content, tensile strength, and tensile impact strength together with time to embrittlement were monitored. The results illustrate that the restabilization recipe is of crucial importance for improving the long-term thermal stability of the postused chair material, ensuring its reuse in the original application. Best long-term performance is achieved by combining a filler deactivator with appropriate heat and light stabilizer systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3033–3044, 2003

Wire and cable coverings are potentially a major cause of fire in buildings and other installations. As they need to breach fire walls and are frequently located in vertical ducting, they have significant potential to increase the fire hazard. It is therefore important to understand the ignition and burning characteristics of cables by developing a model capable of predicting their burning behaviour for a range of scenarios. The fire performance of electrical cables is usually dominated by the fire performance of the sheathing materials. The complexity of the problem increases when cable sheathing incorporates fire retardants. One-dimensional pyrolysis models have been constructed for cable sheathing materials, based on milligram-scale and bench-scale test data by comparing the performance of three different software tools (ThermaKin, Comsol Multiphysics and FDS, version 6.0.1). Thermogravimetric analysis and differential scanning calorimetry were conducted on powdered cable coatings to determine the thermal degradation mechanism, the enthalpy of decomposition reactions, and the heat capacities of all apparent species. The emissivity and the in-depth absorption coefficient were determined using reflectance and transmittance measurements, with dispersive and non-dispersive spectrometers and integrating spheres. Bench-scale tests were conducted with a mass loss calorimeter flushed with nitrogen on samples in a horizontal orientation, for comparison with the pyrolysis model of non-flaming decomposition at an external heat flux of 50 kW m-2. The parameters determined through analysis of the milligram-scale data were used to construct a pyrolysis model that predicted the total mass loss from calorimeter tests in anaerobic conditions. A condensed phase pyrolysis model that accurately predicts in-depth temperature profiles of a solid fuel, and the mass flux of volatiles evolved during degradation of the fuel, is an essential component of a comprehensive fire model, which when coupled to a computational fluid dynamics code can be used to predict the burning processes in a fire scenario. Pyrolysis models vary considerably in complexity based on the assumptions incorporated into the development of the model.

Postconsumer recycled polypropylene, filled with 15% CaCO3 was restabilized at various degrees utilizing different processing stabilizers, one of which is especially prepared to counter the deactivating effects of fillers and other moieties. The polymer was then subjected to multiple extrusion cycles for the purpose of studying the effects of the extent and temperature of reprocessing on its chemical stability. The relative effectiveness of the various restabilization recipes used was also examined. The process-induced material degradation is primarily due to chain scission, which causes an average molecular weight reduction; its progression was monitored by measuring the decrease in viscosity. It is determined that degradation increases linearly with the extent of

Post-use high-density polyethylene, almost devoid of any stabilizing agents, was restabilized in various degrees and subjected to multiple extrusion cycles at different reprocessing temperatures for assessing its chemical stability. The process-induced material degradation was attributed primarily to long-chain branching caused by crosslinking. It was monitored by an increase in viscosity and evaluated on the basis of an approximate expression derived using fundamental principles of macromolecular rheology. It was determined that long-chain branching increases with temperature and the extent of processing, while decreasing with the amount of restabilizing agent added. A simple model was developed to quantitatively describe the progress of the chemical change by relating it to key material and operational variables. Besides constituting a useful method of monitoring and controlling polymer modification during processing, this model suggests ways of optimizing stabilization according to the particular processing and product requirements. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2207–2217, 2001

Artificial weathering was applied for about 8000 h to evaluate the light stability of postconsumer high-density polyethylene (HDPE) material recycled from bottle crates. For recycling the remelting-restabilization technique was applied. To study the effect of the restabilization, the tensile impact strength was monitored during the artificial weathering exposure. The data were compared with microphotographs of the specimens' surface. Repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The repigmented grades were further studied by colorimetric determinations of the color difference (ΔE) during artificial weathering. The results illustrate that the restabilization is mandatory for improving the light stability of the postconsumer crate material, ensuring its re-use in the original application. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1118–1127, 2000

The remelting–restabilization technique was applied for the recycling of post-used, polyethylene packaging film. A multiple extrusion cycles procedure was performed at different reprocessing temperatures for monitoring the processing stability of the restabilized material. Furthermore, at different film blowing conditions mechanical properties were evaluated, to study the effect of restabilization on the mechanical performance of the recycled material. The results illustrate that the restabilization of PE film is very impressive in limiting the degradation effect, which is an essential prerequisite for the re-use in the original application, i.e. for closed-loop recycling.

A remelting–restabilization technique was applied for the recycling of postused, yellow-pigmented high-density polyethylene (HDPE) bottle crates. Multiple extrusion cycles procedure, at different reprocessing temperatures, was performed for monitoring the processing stability of the restabilized and nonrestabilized material as reference. In addition, mechanical properties measurements were carried out, to study further the effect of restabilization on the performance of the recycled material. Finally, repigmentation was used to investigate the role of new pigments on the final recycled product. The results illustrate that restabilization of postused crates leads to careful reprocessing without severe degradation, which is an essential prerequisite for reuse in the original application. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1775–1785, 1999

A series of bis-(1,3,5)triazinyl diazenes and two metal complexes thereof were synthesized and tested as new flame retard- ants in polypropylene films. It was observed that electron withdrawing triazinyl ring substituent (i.e., Cl and phenyl moieties) improved the thermal stability of diazene compounds, whereas electron donating groups (i.e., methoxy, dimethylamino, and ethylthio moieties) had a destabilizing effect. TGA, DTA/DSC, NMR, and ATR-FTIR were used for the characterization. Quantum mechanical modeling (Gaussian 09) was also utilized to facilitate the interpretation of the NMR data. Bis-(4,6-dichloro-(1,3,5)triazin-2-yl)-dia- zene 1 and bis-(4,6-dimethoxy-(1,3,5)triazin-2-yl)-diazene 2 were found to be effective flame retardants in polypropylene films and DIN4102-1 B2 classification was reached already at a loading of 0.5 wt %. Interestingly, the copper complex of 2 showed even higher fire retardant activity than its precursor 2, whereas the corresponding zinc complex exhibited lower flame retardant efficacy than its precursor. V C 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40413.

The desire to reduce the load on the ecosystem has in recent years driven flame retardant research toward halogen-free systems or at least toward combinations that permit a substantial reduction in the percentage of halogenated substances. This review provides a comprehensive and chronological insight into some novel developments within the family of nitrogen-based flame retardants and their structure–property relationships. It focuses on a series of different N -alkoxy hindered amines (NOR), azoalkanes (AZO) of the general formula R′–N N–R, and related compounds such as azoxy, hydrazone, azine, triazene, tetrapotassium azo diphosphonate (INAZO), and bis(1-alkoxy-2,2,6,6-tetramethylpiperidyl)-4-diazene compounds. These nitrogen-containing flame retardants mainly exhibit self-extinguishing properties for polypropylene and polyethylene films or even in some cases for polypropylene moldings, polyurethane adhesives, and polystyrene. In addition, their performance in combination with various conventional flame retardant classes is discussed. Contrary to other nitrogen-containing flame retardants, such as melamines, the presented nitrogen-based flame retardants are effective at very low additive levels (

The use of various copolymers as dispersants/intercalants/exfoliants in polypropylene (PP)-clay nanocomposites based on unmodified montmorillonite clays (NaMMT) has been explored. The primary objective of this research has been to find dispersants that allow PP nanocomposites to be formed by direct melt mixing, that are effective with unmodified clays and that comprise only a minor component of the overall composition both with respect to both clay and PP. Two classes of dispersants were investigated: PEO-based nonionic surfactants and amphiphilic copolymers based on a long chain (meth)acrylate (e.g. octadecyl acrylate) and a more polar comonomer (e.g. maleic anhydride, N-vinylpyrrolidone, methyl methacrylate). The state of dispersion achieved and the properties of the derived nanocomposites were found to depend strongly on both on the level of dispersant and its overall composition but interestingly properties are not particularly dependent on the dispersant architecture (i.e. whether statistical, gradient or block copolymer). The nanocomposites possess a tensile modulus up to 40% greater that the precursor PP while elongation at break and impact strength are significantly improved over clay alone composites and reference organoclay-based nanocomposites. Also notable are significantly better thermal and thermo-oxidative stability as compared to both PP and clay alone composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20-50 wt-%) of the composition with respect to clay.

Summary: Poly(propylene) (PP)-clay nanocomposites were prepared from unmodified montmorillonite clays (NaMMT), with poly(ethylene oxide)-based nonionic surfactants as dispersants/intercalants/exfoliants. The primary objective of this research was to find dispersants that (a) allow PP nanocomposites to be formed by direct melt mixing; (b) are effective with unmodified clays and (c) comprise of only a minor component with respect to both the clay and the overall composition. Linear, branched, gemini and sugar-based surfactants and structures containing poly(dimethyl siloxane) and poly(methyl methacrylate) blocks were examined. These additives were found to be effective in breaking down the clay agglomerates to tactoids, giving some expansion of the clay structure and partial exfoliation and providing substantially improved clay dispersion. The properties of the derived nanocomposites depend on the level of additive and its structure. Tensile and impact properties show significant improvement over the precursor PP. Also notable are the significantly better thermal and thermo-oxidative stabilities, as compared to both PP and “clay alone” composites. For optimal properties, it is both necessary and desirable that the surfactant should only be a minor constituent (20–50%) of the composition, with respect to the clay. A preferred surfactant is linear PE-block-PEO, with a short PEO block and an alkyl chain with approximately 30 carbon atoms (C30).