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This study provides insight into the accelerated hydrolysis of polyester PLA through the addition of phosphites based on pentaerythritol. To control hydrolysis and ensure processing stability, different types of phosphites and combinations of phosphites with acid scavengers were studied. Therefore, commercially available PLA was compounded with selected additives on a twin-screw extruder, and hydrolysis experiments were performed at 23 °C, 35 °C and 58 °C in deionized water. Hydrolysis of PLA was evaluated by the melt volume rate (MVR) and size-exclusion chromatography (SEC). For example, after 4 days of water storage at 58 °C, the number average molecular weight of the PLA comparison sample was reduced by 31.3%, whereas PLA compounded with 0.8% phosphite P1 had a 57.7% lower molecular weight. The results are in good agreement with the expected and tested stability against hydrolysis of the investigated phosphite structures. 31P-NMR spectroscopy was utilized to elucidate the hydrolysis of phosphites in the presence of lactic acid. With the addition of phosphites based on pentaerythritol, the hydrolysis rate can be enhanced, and faster biodegradation behavior of biodegradable polyesters is expected. Accelerated biodegradation is beneficial for reducing the residence time of polymers in composting facilities or during home composting and as litter or microplastic residues.

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.

In this study, the flame retardant effect of the Zn salt of 10-hydroxy-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (Zn-DOPOx), melamine polyphosphate (MPP) and their mixture was investigated towards the mode of action in glass fiber-reinforced polyamide 66 (PA 66 GF). The flammability was evaluated using UL 94 V and cone calorimetry. Influence on char formation was analyzed by SEM. Thermal decomposition of Zn-DOPOx and MPP was studied by TGA and ATR-FTIR. The release of gaseous PA 66 decomposition products was investigated using TGA-DTA-FTIR. Combining Zn-DOPOx and MPP leads to an improvement in flame retardancy, most pronounced for equal parts of weight. Mode of action changes significantly for Zn-DOPOx:MPP (1:1) compared to the sole components and a strong interaction between Zn-DOPOx and MPP is revealed, resulting in a more open char structure. Fuel dilution as well as less exothermic decomposition are essential for the mode of action of the combination. Through low HRR values and high CO/CO2 ratio during cone calorimetry measurements, a significant increase in gas phase activity was proven. Therefore, it is concluded that Zn-DOPOx:MPP (1:1) leads to a significant increase in flame retardancy through a combination of mode of actions in the gas and condensed phase resulting from the change in thermal stability.

Thermo-oxidative aging of dipentaerythritol (DPE) stabilized, glass fibre reinforced PA66 compounds was studied at 200°C. The influence of DPE as a thermo-oxidation stabilizer on the retention of tensile properties, molecular weight, crystallinity, oxidized layer thickness as well as the specimen surface and fracture morphology was analysed. Moreover, the impact of DPE on the intrinsic humidity inside the test specimens before aging was examined due to its hygroscopic behaviour. The reduction of the extractable amount of DPE from test granules over the aging time proved the existence of chain extension or crosslinking reactions between the polyamide or its degradation products and DPE. Whereas DPE improves the retention of mechanical characteristics during aging only slightly, the combination of DPE and glass fibres reaches retention of mechanical characteristics above 50 % after 1000 h of aging at 200°C in air. DPE raises the intrinsic humidity during processing and before aging resulting in an increase of PA66 degradation during processing and in the first aging phase due to additional hydrolysis. Both the ensuing shorter chain length and water-induced post-crystallisation give rise to higher crystallinity after processing, increasing the oxygen diffusion limitation which results in slower thermo-oxidation. In addition, DPE accelerates the formation of the oxidized layer on the PA66 surface but slows down its growth during the later aging phase.

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.

The commercially available partially bio-based poly(butylene succinate) (PBS) and poly(butylene succinate-co-adipate) (PBSA) are subjected to prolonged and multiple extrusion cycles to investigate their thermal behavior. Empirically, both PBS and PBSA form branches at 190°C, with PBS possessing a higher tendency for branching than PBSA as studied by rheology and size exclusion chromatography (SEC). In each case, the branching is favored by fumaric acid moieties, making both PBS and PBSA susceptible to accelerated thermal oxidation. Indeed, the NMR signal attributed to fumaric acid disappears upon thermal processing of PBS and PBSA. Presumably, the bio-based succinic acid used contains minor quantities of fumaric acid, yet still sufficient to cause this surprising processing behavior. The branching of both polymers is suppressed by stabilizers such as phenolic antioxidants, as proven by rheology and SEC. This is complemented by nuclear magnetic resonance (NMR), revealing that the fumaric acid signal is still well-resolved in the stabilized processed samples.

An IR-camera is used for investigating flame retarding mode of actions during UL94 standard flammability test. Commonly used UL94 tests give qualitative results of burning behavior and are improved by taking temperature profiles with an IR-camera. Analysis of these profiles leads to new insights into the underlying mechanism of the flame retardant. Lower peak temperatures and faster cooling are a hint for a cooling mechanism. A shorter time range to reach the peak temperature is significant for dilution. Every flame retarding mode of action has its own specific influence on the temperature profile. Therefore, a more detailed conclusion of the flame retarding behavior of flame retardants can be obtained by the method described here.

Accelerated (artificial) weathering and thermal aging tests were performed to investigate the effectiveness of different formulations in reducing the UV/heat degradation extent for two low-density polyethylene types (LDPE-A, LDPE-T). The two LDPEs differ in the type and extent of branching due to the applied polymerization process, with LDPE-A being produced in an autoclave and LDPE-T in a tubular reactor. Oligomeric or high molecular weight hindered amine light stabilizer (HALS), and two UV absorbers of benzophenone or hydroxyphenyl-triazine types were equally introduced to both the LDPE grades at a total content of 0.2 wt%. The surface morphology, as well as thermal and mechanical properties, were examined during aging showing a significant degradation extent for the neat samples. In particular, a mechanism of chain scission/branch-ing that resulted in crosslinking was assumed for the neat polyethylenes, after combining the decrease of molecular weight observed in the GPC analysis with the increase in Young's modulus after UV exposure. LDPE-T presented higher photo-ox-idation rates due to its comb-like branched structure and its higher possibility of intermolecular reactions between adjacent chains. Little or no degradation was observed for the stabilized grades, confirming the effectiveness of the selected UV/heat systems in improving the weathering resistance of the two LDPE grades and enhancing their useful lifetime. 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. The statements made herein are solely the responsibility of the author(s). Scopus

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.

Additives for plastics based on natural raw materials (“bio‐additives”) are well‐known substances that have been used as such or in chemically modified form in the plastics industry for many years. However, interest in new bioadditives is increasing in line with the goal of replacing petrochemical raw materials and promoting a circular economy, as well as with the increasing demand for biopolymers. Since practically all polymers require additives to guarantee their properties, processing and application, it is logical for biopolymer formulations to also be developed entirely on the basis of renewable raw materials, i.e. both the polymer and the additive. The most important additives include plasticizers, antioxidants and flame retardants.

Oxyimides have gained wide interest in different applications because of radical generating properties, such as flame retardants in various polymers. As polyamide-6 (PA6) is highly flammable and shows burning dripping during incineration the mentioned issues have to be overcome by the use of a flame retardant. All previously developed oxyimides already show these properties, but this is based on the ester structure with the consequence of transesterification/transamidation in polyesters/polyamides. In this work, a new class of oxyimides based on ether bonds is synthesized. Oxyimide ethers do not degrade PA6, only sometimes slightly increase MVR, and show excellent flame retardancy in PA6. Depending on the structure, UL 94 V-0 can be reached with very low loadings. This makes oxyimide ethers an alternative to commonly used flame retardants for PA6.

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

Additive fur Kunststoffe auf der Basis naturlicher Rohstoffe („Bio-Additive“) sind einerseits altbekannte Substanzen, die als solche oder in chemisch modifizierter Form seit vielen Jahren in der Kunststoffwelt eingesetzt werden. Andererseits steigt das Interesse an neuen Bioadditiven mit dem Ziel, petrochemische Rohstoffe zu ersetzen und eine Kreislaufwirtschaft zu begunstigen, sowie auch mit der zunehmenden Nachfrage nach Biopolymeren. Da nahezu alle Polymere Additive benotigen, um Eigenschaften, Verarbeitung und Anwendung sicherzustellen, ist es folgerichtig, auch Biopolymer-Formulierungen vollstandig auf der Basis nachwachsender Rohstoffe zu entwickeln, also sowohl das Polymer als auch das Additiv. Zu den wichtigsten Additiven gehoren Weichmacher, Antioxidantien und Flammschutzmittel.

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.

Most flame-retarded polymer products need to be highly durable throughout their service lifetime in many demanding applications areas such as construction, transportation, electric equipment, and textiles, where low flammability in combination with high resistance toward oxidative deterioration triggered by the action of light, heat, and/or mechanical stress is a mandatory quality. To achieve this, it is essential to better understand the overall interplay (both physical and chemical processes) between different components such as different flame retardant structures in their respective polymers and in the presence of coadditives such as processing stabilizers, antioxidants, light stabilizers, metal deactivators, filler deactivators, ultraviolet absorbers, and so on, in the flame-retarded polymer product. In this article, the key difficulties in improving weathering resistance of flame-retarded polymers are reviewed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

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.

Polymer nanocomposites based on organically modified layered silicates are an area of substantial scientific interest and of emerging industrial practice. Despite the proven benefits of nanocomposites such as mechanical properties, barrier properties and contribution to fire retardancy, polymer nanocomposites are used today only in niche applications. The reasons for the limited growth of nanocomposites are explained through the availability of alternative solutions, processing and dispersion challenges and inferior oxidative and photooxidative stability. Recent developments show the improved dispersion of unmodified nanoclays in polyolefins with the help of selected copolymer structures. The (photo)oxidative instability of nanocomposites is compensated with adjusted stabilizer systems.

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)

Organically modified clay-reinforced polyamide 6 was subjected to accelerated heat aging to estimate its long-term thermo-oxidative stability and useful lifetime compared to the virgin material. Changes in molecular weight, and thermal and mechanical properties were monitored and connected to the polymer modification encountered during aging. The incorporation of the clay filler was found to result in moderate polymer degradation during processing, which became more pronounced with aging time at elevated temperature, imparting discoloration. Post-crystallization was favoured by short periods of heat exposure, leading to an increase of crystalline content. Conversely, extended chain scission occurring after prolonged residence time negatively affected crystallites' size, lowering the degree of crystallinity. The aging-induced transformations of crystal structures correlated well with materials' mechanical performance, yielding initially hard and brittle specimens which gradually adopted a softening behavior. Relative to the unfilled polymer, the loss of ductility during aging was milder in the case of nanocomposite, indicating that the clay filler restricted degradation, prolonging durability.

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

The current study is focused on key experiments on catalyzed SSP, examining the effect of selected phosphonates on the overall process rate. Catalyst incorporation was achieved through melt blending in a single screw extruder, providing a suitable and homogenous starting material for the reaction in the solid phase. More specifically, the post-polycondensation runs were performed in a fixed bed reactor under flowing nitrogen at 160 and 200 °C. The additives used were found to catalyze the reaction in the solid phase, resulting even in tripling the solution relative viscosity after 4 h of SSP. Differences in the catalytic performance of the added materials were observed and correlated to the catalysts properties and morphology. An indicative potential catalysis mechanism is suggested, in which reactivity enhancement through partial attachment of the phosphorus compounds on the polyamide chain is the key step. Finally, the kinetics of the process were examined based on a power-law rate expression, which was further modified so as to relate the apparent SSP rate constant with the phosphorus concentration.

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).

Additives are essential components of plastic formulations providing maintenance and/or modification of polymer properties, performance and long-term use. The extension of polymer properties by additives has played a substantial role in the growth of plastics. At the beginning of the plastics age additives were used mainly to maintain polymer properties and to help plastics to survive heat treatment during transforming processes. The next generation of additives provided extension of service life as well as modification of mechanical and physical properties. These well-established additives – antioxidants, heat stabilizers, light stabilizers and others – cover the requirements of standard plastics and today's mass applications. The more recent developments of high-performance additives address more stringent or new requirements, more severe processing and use conditions and/or environmental concerns, but still with the main target of maintaining plastic properties. The future will introduce more and more new effects and functionalities through additives in plastic applications tailoring the properties of polymers and offering a vast potential of innovation in the plastics area. Recent examples of emerging technologies show that additives will not only modify the polymer itself and add new properties, but can also, when incorporated into the plastic, beneficially impact properties, which are of high value for the user. The paper shows the role of additives used in plastics from the past to the present with the focus on stabilization and performance of additives incorporated during melt processing, and outlines future trends.

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

A remelting-restabilization technique was applied for the recycling of post-used, yellow pigmented high density polyethylene (HDPE) bottle crates. In order to evaluate the potential of the recyclate to be used in the original apllication, the most important parameters were investigated: processing stability, long-term heat stability and light stability. A multiple extrusion cycles procedure at different reprocessing temperatures was performed for monitoring the processing stability of the restabilized and non-restabilized material. Oven aging was applied for about 8000 h (i.e., more than one year) to evaluate the long term thermal stability of the crate material, as manifested by melt flow rate, tensile impact strength, and time until embrittlement measurements. To evaluate the light stability of the recycled material artificial weathering was applied for about 8000 h, whereas the tensile impact strength was monitored. The latter data were enriched with microphotographs of the specimens surface. Finnaly, repigmentation was used to investigate the role of new pigments on the final performance of the recyled product. The results illustrate that restabilization is mandatory for the quality improvement of post-used crates ensuring its re-use in the original application and thus making closed loop recycling.

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

A kinetic model based on a detailed reaction mechanism for the nitroxide-mediated radical polymerization (NMRP) of styrene is presented. The reaction mechanism includes the following reactions: chemical initiation, reversible nitroxyl ether decomposition, monomer dimerization, thermal initiation, propagation, reversible monomeric and polymeric alkoxyamine formation (production of dormant species), alkoxyamine decomposition, rate enhancement, transfer to monomer and dimer, as well as conventional termination. By simple manipulation of the ODEs initial conditions and tuning of the model by turning on/off the appropriate kinetic steps via their corresponding kinetic rate constants, the model presented here is capable of representing two technologically important variations of nitroxyl mediated polymerization techniques: 1) use of traditional radical initiator together with a nitroxide-type stable radical; and 2) use of a nitroxyl ether or alkoxyamine compound as controller. Model predictions are validated ag...

Oven aging was applied for about 8800 hours (more than one year) to evaluate the long-term thermal stability of post-used HDPE material recycled from bottle crates. For recycling, the remelting-restabilization technique was applied. To study the effect of restabilization, crystallinity and melt flow rate were monitored during heat aging. Furthermore, tensile strength and tensile impact strength were followed together with the time until embrittlement. These data were enriched with microphotographs of the specimens' surfaces. Finally, repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The results illustrate that restabilization is mandatory for improving the long-term thermal stability of the post-used crate material, enabling its reuse in the original application.