Abstract
The role of various additives (emulsifier, anti-dripping agent) and formulation procedures (pre-dispersion of solid additives in polyol via milling) which influence the flame retardancy of 6,6′-[ethan-1,2-diylbis(azandiyl)]bis(6H-dibenzo[c,e][1,2]oxaphosphin-6-oxid) (EDA-DOPO) containing flexible polyurethane foams has been investigated in this work. For comparison, the flame retardancy of two additional structurally-analogous bridged 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-based compounds, i.e., ethanolamine-DOPO (ETA-DOPO) and ethylene glycol-DOPO (EG-DOPO) were also evaluated together with EDA-DOPO in flexible PU foams of various formulations. The flame retardancy of these three bridged-DOPO compounds depends on the type of PU formulation. For certain PU formulations containing EDA-DOPO, lower fire performance was observed. Addition of emulsifier and polytetrafluoroethylene (PTFE) to these PU formulations influenced positively the flame retardancy of EDA-DOPO/PU foams. In addition, dispersion of EDA-DOPO and PTFE via milling in polyol improved the flame retardancy of the PU foams. Mechanistic studies performed using a microscale combustion calorimeter (MCC) and its coupling to FTIR showed no difference in the combustion efficiency of the bridged-DOPO compounds in PU foams. From MCC experiments it can be concluded that these bridged-DOPO compounds and their decomposition products may work primarily in the gas phase as flame inhibitors. The physiochemical behavior of additives in PU formulation responsible for the improvement in the flame retardancy of PU foams was further investigated by studying the dripping behavior of the PU foams in the UL 94 HB test. A high-speed camera was used to study the dripping behavior in the UL 94 HB test and results indicate a considerable reduction of the total number of melt drips and flaming drips for the flame retardant formulations. This reduction in melt drips and flaming drips during the UL 94 HB tests help PU foams achieve higher fire classification.
Highlights
Polyurethanes are inherently flammable materials and their flammability is generally reduced by addition of flame retardant additives [1]
Three different structurally analogous bridged DOPO compounds namely EDA-DOPO, ETA-DOPO, and ethylene glycol-DOPO (EG-DOPO) were investigated for their flame retardant behavior in foams obtained from two different PU formulations
Further work was carried out to understand this difference in flame retardant efficacy of the three DOPO additives and improve the fire performance of EDA-DOPO in formulation B
Summary
Polyurethanes are inherently flammable materials and their flammability is generally reduced by addition of flame retardant additives [1]. The influence of addition of flame retardant additives in the thermal decomposition process as well as in improving their flame retardancy is well studied [1,2,3,4]. PU foams are manufactured using a variety of raw materials and process additives. Little has been reported which reflects the influence of these materials on thermal decomposition and fire behavior of the polyurethanes. It is known that increased concentration of some PU components (silicone additives and metal catalysts) in the PU foams have a detrimental effect on fire behavior. It has been found that MDI based PU foams display better fire performance compared to that of TDI based PU foams and the chemistry of polyols influences the fire performance of the PU foams [5]
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