Disulfides – Effective radical generators for flame retardancy of polypropylene

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 oC and 450 oC, 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

Estabilizante orgánico para PVC. Alternativa eficiente para tubos de PVC

Se describen los estabilizantes con base orgánica como alternativa en la fabricación de tubos de PVC en respuesta a consideraciones ambientales y políticas, las cuales exigieron el reemplazo del plomo por alternativas menos contaminantes.

Mode of Action of Zn-DOPOx and Melamine Polyphosphate as Flame Retardants in Glass Fiber-Reinforced Polyamide 66

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

Halogen-free flame-retardant compounds. Thermal decomposition and flammability behavior for alternative polyethylene grades

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)

An Integrated Characterization Strategy on Board for Recycling of poly(vinyl butyral) (PVB) from Laminated Glass Wastes

: Polyvinyl butyral (PVB) is widely used as an interlayer material in laminated glass applications, mainly in the automotive industry, but also for construction and photovoltaic applications. Post-consumed laminated glass is a waste that is mainly landfilled; nevertheless, it can be revalorized upon efficient separation and removal of adhered glass. PVB interlayers in laminated glass are always plasticized with a significant fraction in the 20-40% w/w range of plasticizer, and they are protected from the environment by two sheets of glass. In this work, the aim is to develop a thorough characterization strategy for PVB films. Neat reference PVB grades intended for interlayer use are compared with properly processed (delaminated) post-consumed PVB grades from the automotive and construction sectors. Methods are developed to open opportunities for recycling and reuse of the latter. The plasticizer content and chemical nature are determined by applying well-known analytical techniques, namely, FT-IR, TGA, NMR. The issue of potential aging during the life cycle of the original laminated material is also addressed through NMR. Based on the findings, a sensor capable of directly sorting PVB post-consumer materials will be developed and calibrated at a later stage

Zukunftsbild Hochschullehre 2025

Das Diskussionspapier zur Hochschullehre 2025 zeichnet sich methodisch durch seine partizipative Entstehung aus: In einem der HFDcon 2022 zeitlich vorgelagerten Prozess trafen sich 21 angemeldete Teilnehmer:innen aus dem deutschen Hoch- schulumfeld, um den Wandel der Hochschullehre für das Jahr 2025 zu skizzieren und Thesen für eine neue Denkkultur zu formu- lieren. In mehreren virtuellen Sitzungen wurden zunächst die Ziele des Papiers definiert, Themen geclustert und erste Forderungen ent- wickelt. Innerhalb der folgenden vier Wochen wurde dann – teils in Kleingruppen – kontrovers diskutiert, formuliert und überarbeitet, bis das Papier am 30. Juni 2022 in seiner ersten Fassung auf der Konferenz HFDcon 2022 vorgestellt wurde

Benefits of radical generators in flame retarded polymers: Review and new developments

Radical generators as synergists in flame retarded polymers have been used in combination with brominated flame retardants for decades. However, due to the low thermal stability of radical generators under the usual polymer processing conditions the use was limited to selected applications e.g. in polystyrene foams. The need to find efficient halogen free flame retardants resulted inter alia in the discovery and commercialization of hindered amine light stabilizers based on alkoxyamines (NOR-HALS). NOR-HALS provide flame retardancy of polypropylene and polyolefin fibers, non-wovens and films. The performance of the NOR molecules depends on their structure i.e. the capability to degrade into nitroxyl plus alkyl or aminyl plus alkoxy radicals. Through formation of radicals a fast degradation of the polymer chain is induced and flame retardancy is achieved by removing the substrate from the flame. On the other hand, the formed radicals are involved in the free radical chemical reactions during the combustion process. Furthermore, alkoxy amines can interact with brominated flame retardants and facilitate the release of bromine, consequently increasing the overall FR performance. Therefore, it is possible with NORs to design flame retardant polyolefin molding compositions with lower levels of halogenated flame retardants and, in addition, to eliminate antimony trioxide. Moreover the hindered amine (HALS) structure provides light and long-term thermal stability of flame retarded formulations. Following the success of NOR based flame retardants a number of alternative radical generator molecules have been identified namely azo compounds, triazenes, hydrazones and azines. Especially combinations of Azo and NOR structures in one molecule show increased performance at loadings as low as 0.5 % in polypropylene films, including light and long-term thermal stability, and act synergistically with halogen, phosphorus and inorganic flame retardants. Although the performance of alkoxyamines in thin sections such as films is well documented and the UL 94 V-2 classification is often obtained in moldings, formulations usually fail in achieving the UL 94 V-0 classification as burning drips cannot be avoided despite short burning times. For the first time a new class of nitrogen based radical generators can be presented whereas in combination with selected phosphorus derivatives flame retarded polypropylene with UL 94 V-0 classification is accessible. Thermal stability and degradation of the new class into radicals is correlated to the molecular structure and can be adjusted in line with the degradation of the polymer and the synergist. Moreover the necessary loadings to achieve UL 94 V-0 are below 10 %

(Photo)oxidative stabilization of flame-retarded polymers

Flame-retarded polymer formulations are mainly used in long-term applications whereas antioxidants, light stabilizers, and other additives provide the requested lifetime of plastic materials. However, many flame retardants influence the oxidative and photooxidative stability of polymers often in a negative way resulting in early failure and loss in value. On the other side, insufficient (photo)oxidative stability of the flame retardant itself may reduce the flame retardance performance over time. Therefore, depending on the type of flame retardant used, the polymer substrate and the intended application adjusted stabilizer systems have to be selected or developed.In this chapter, challenges of the stabilization of flame-retarded polymers are analyzed with regard to the components and mutual interactions with focus on "green" flame retardants. Processing and long-term thermal stabilization of flame-retarded polymers are discussed and strategies of improving the light sta bility of flame-retarded polymers are provided. Additionally, the specific requirements of the stabilization of nanocomposites as potential flame-retardant components are covered