Thermal Stability of Fire Retardants:* V. Decomposition of Haloalkyl Phosphates under Polyurethane Processing Conditions

Abstract

The thermal decomposition of a series of commercial FR agents used in polyurethane was studied in dilute solution in bibenzyl at temperatures commonly found in the center of large, slab stock buns. At 216°C all of the haloalkyl phosphates containing the XCH 2 CYHOgroups, where X is Cl or Br and Y is H or ClCH 2 -, decomposed at similar rates, i.e., they all gave first order rate constants between 1.0 and 5.8 x 10 -4 min -1 . The addition of toluene diamine to the solution increased the rate of acid evolution from the reacting mixture by a factor of at least ten and in one case by a factor of sixty. The amine is postulated to attack the C-X bond to produce a secondary amine hydrohalide salt which releases hydrogen halide at elevated temperatures.Pentabromodiphenyl oxide was found to be stable under both sets of conditions. Tris (2,3-dibromopropyl) phosphate, in contrast, undergoes decomposition via a free radical mechanism similar to that of vicinal dibromoalkanes.

Thermal decomposition, combustion and fire‐retardancy of polyurethanes—a review of the recent literature

“…In a typical foam formulation, the water content of the mixture is about 2.5 wt% of the total weight 14. This amount of water is sufficient to react with about 38% of the initial isocyanate groups.…”

“…Since some FR additives tend to promote scorch, we will discuss this phenomenon in detail. Larsen and Ecker14 and Tokuyasu15 studied the effect of haloalkyl phosphates, the most common class of flame‐retardants in PU foams, on foam discolouration. The haloalkyl phosphates were shown to decompose thermally in the temperature range between 160 and 230 °C with loss of hydrogen halide (other studies show alkylene dichlorides are also major products—see below).…”

“…The presence of an amine caused a large increase in the rate of decomposition—about a tenfold increase 14. The primary reaction appears to be a nucleophilic displacement on the CX bond by the amine to give rise to a secondary amine hydrogen halide salt.…”

Thermogravimetric and qualitative analysis of thermal decomposition characteristics of polyurethane foams based on polyols with carbamide or oxamide and borate groups

“…A typical amount of water applied to foaming is about 2.5 wt% . It was found empirically that 2 wt% water with regard to the polyol is sufficient for the foaming of polyols with urea or oxamide groups (Table ).…”

Foamed polyurethane plastics of reduced flammability

“…Usually about 2.5 wt % water is used for the foaming process. 7,32 We found empirically that polyols with borate groups needed more water in the foam preparation process ( Table V).…”