Disulfides – Effective radical generators for flame retardancy of polypropylene

Abstract

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 o C and 450 o 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.

Arylthio‐ and Arylseleno‐Substituted s‐Heptazines

“…The incorporation of 5 wt% of compound 1 , increased the LOI value from 18.4±0.15 O 2 % to 20.0±0.23 O 2 % , whereas the addition of 10 wt% of melem increased the LOI value of PP by only 19.1±0.30 O 2 % . The LOI values observed for compound 1 were similar to those reported for DTBB in PP, which rises from 17.0 O 2 % to 19.8 O 2 % (0.5 wt.% DTBB), 20.6 O 2 % (1 wt.% DTBB), 20.3 O 2 % (3 wt.% DTBB), 20.4 O 2 % (5 wt.% DTBB), and 20.4 O 2 % (10 wt.% DTBB) . According to these results, compound 1 shows flame‐retardant effects, but further investigations are required and are currently being performed.…”

“…Wilen et al. showed that radical generators based on alkyl disulfides (structure type: R−S−S−R) had promising flame‐retardant properties in polypropylene (PP) . Furthermore, the flame retardancy of such disulfides was proved by Döring et al.…”

Synthesis of a novel PEPA-substituted polyphosphoramide with high char residues and its performance as an intumescent flame retardant for epoxy resins

“…Although there are few reports on the use of sulfur as flame retardant in some polymers [51,52], there is seldom report about polyphosphoramide containing sulfur flame retardant epoxy resins.…”

Sulfides and Disulfides of s‐Triazine: Potential Thermal Thiyl Radical Generators

“…Disulfide bonds connecting two s‐triazine rings have also been reported . However, this bond type is not the subject of our present study.…”

“…In a previous paper, we presented the first representatives of a new class of arylthio‐substituted s‐heptazines . Arylthiocyamelurates are able to release thiyl radicals during thermal decomposition, and thiyl radicals are known to be a species with flame‐retardant effects . Our model arylthio‐substituted s‐heptazine molecule, triphenylthiocyamelurate (C 6 H 5 S) 3 C 6 N 7 , decomposes thermally at around 393 °C .…”