Synergism of free radical initiators with self‐extinguishing additives in vinyl aromatic polymers

Abstract

SynopsisVinyl aromatic polymers such as polystyrene can be made nonflammable by the addition of halogen compounds. The amount of halogen required to make such polymers nonflammable can now be greatly reduced by the addition of small amounts of certain free radical initiators. Normally about 5 phr of acetylene tetrabromide (parts of additive per hundred parts of polymer) must be added to polystyrene to obtain a self-extinguishing polymer. Only 0.5 phr of acetylene tetrabromide is required if 0.5 phr dicurnyl peroxide is added. This synergistic effect has been observed with a series of peroxides, hydroperoxides, azo compounds, quinone imines, benzothiazole sulfenamides, disulfides, and a bibenzyl compound. The synergistic mechanism seems to be based on a series of reactions involving attack of the polymer by the initiator and subsequent reaction between polymer fragments and the halogen compound. The result is a delay in the loss of halogen from the polymer mass and thus a more efficient use of the halogen additive for flame quenching. Known inhibitors of free radical reactions have a detrimental effect on the synergistic mechanism.

Azoalkanes: A Novel Class of Flame Retardants

“…He proposed that the radical precursors trigger the decomposition of the halogenated flame retardant whereby halogen radicals are rapidly liberated that effectively interrupt the combustion process. [16] It is worth noting that all of the used radical precursors have very limited thermal stabilities and no indication has been given that they will exhibit flame retardancy properties on their own. In contrast, our studies have clearly demonstrated that alkyl radicals generated by the diazene radical precursors have the ability to effectively interrupt the combustion process at the right point by themselves.…”

Molecular basis of flame inhibition

“…Thus it appears that at least part of the synergism associated with this system derives from the ability of Sb203 to moderate the release of halogen to the gas phase and over a considerable temperature range. This effect has a parallel in the use of substrate free radical initiators, such as dicumyl peroxide [34], which are believed to delay the Joss of haloge, n from the decomposing polymer.…”

Disulfides – Effective radical generators for flame retardancy of polypropylene

“…From the viewpoint of flame retardancy of polymers mainly radical generators triggered by thermolysis or redox systems have been successfully used to suppress and retard the fire response of polymeric materials [21,22]. In the past it has been demonstrated that certain peroxides can be used as synergists to enhance the action of brominated flame retardants (BFR) [23][24][25][26][27][28][29], whereas azo compounds [30] and alkoxyamines [12,31] have been shown to provide self-extinguishing properties to polymers even by themselves. Thus, it has been established that radical precursors that are capable of generating various carbon (e.g.…”

“…For example some disulfides presented in this paper (e.g. disulfide 6) are claimed to be effective flame retardant synergists with halogens in polystyrene [23]. Moreover, elemental sulfur and other polysulfides are also known as effective flame retardant components [41][42][43][44][45].…”