A new mechanism of flame retardancy for polyurethanes

Abstract

synopsisA chemical model is outlined which gives a simple description of flameretardant &-ciency of organic bromides in flexible polyurethane foam systems. The mechanism suggests dehydrobromination by an interplay of S N~ and SN2 reactions in intramolecular and intermolecular processes. Evidence is presented to demonstrate that flameretardant efficiency is directly related to the facility of dehydrohalogenation by an intramolecular process in which cyclic urethanes (five to ten membered rings) are formed by either S N~ and/or sN2 reactions. The requirement for a nucleophile, such as carbamate nitrogen, in halogen systems is suggested. In other mechanistic aspects, it was shown that flame retardancy passes through a maximum as a function of bromide content in the foam. It is believed that this behavior reflects certain undefined combustion aspects in the solid phase. It is also shown that unlike additive flame retardants, the TGA's of neither the starting brominecontaining alcohols nor their model N-phenylcarbamates correlate with the weight loas cuwes of the control foam. Instead, the TGA's of both flame retardant and nonflameretarded foams from the reactive bromide alcohols all fall in about the decomposition range of the control foam. As a practical consequence of the rwults reported herein, it is now possible to correlate flame retardancy and structure as well as formulate new flame retardants with greater assurance of success.

Ignition, combustion, toxicity, and fire retardancy of polyurethane foams: A comprehensive review

“…A series of bromine-containing polyols such as 3,4-dibromocyclohexane-1,1-dimethanol, brominated propylene oxide adducts of 3-cyclohexene-1,1-dimethanol, tetrabromophthalic anhydride/diethanolamine propylene oxide amide-ester adducts, b,c-dihydroxypropyl 2,3,7,8-tetrabromooctyl ether, and 1,2,5,6-tetrabromo-3,4-dihydroxyhexane have been studied for their fire-retarding efficiency when incorporated as part of the polymer in flexible and rigid urethane foams. 173 The LOI values of 2.0% and 2.5% bromine-containing urethane foams increase to 21.0 and 21.2, respectively, and they are rated self-extinguishing by ASTM D 1692. Urethane foams containing about 3.0% bromine from brominated polyols show slightly lower porosity, 91% compression sets, and somewhat greater load-bearing properties and tensile strength.…”

“…These foams produce 58% char at 300°C and 25% char at 500°C and are rated self‐extinguishing by ASTM D 1692‐67T. A series of bromine‐containing polyols such as 3,4‐dibromocyclohexane‐1,1‐dimethanol, brominated propylene oxide adducts of 3‐cyclohexene‐1,1‐dimethanol, tetra‐ bromophthalic anhydride/diethanolamine propylene oxide amide–ester adducts, β,γ‐dihydroxypropyl 2,3,7,8‐tetrabromooctyl ether, and 1,2,5,6‐tetrabromo‐3,4‐dihydroxyhexane have been studied for their fire‐retarding efficiency when incorporated as part of the polymer in flexible and rigid urethane foams 173. The LOI values of 2.0% and 2.5% bromine‐containing urethane foams increase to 21.0 and 21.2, respectively, and they are rated self‐extinguishing by ASTM D 1692.…”

Fire retardancy, thermal, and physico-mechanical properties of semi-rigid water-blown polyurethane foam from palm oil-based polyol

“…33 Even with higher LOI value, PEG-PU is still considered readily combustible in open air as the value is lower than the oxygen content in atmosphere at ∼ 21%. Papa and Proops 34 claimed that PU foams with LOI values higher than 21.2 may possess superior flame-retardancy.…”

Synthesis and spectroscopic data of 3,3',5,5'-tetrabromo-4,4'-diaminodiphenyldibromomethane

“…TB-DADPM is also reported to decompose at its melting point (12). HBr is known' to be an effective agent for the cleavage of C-C and C-H bonds in many polymers (16,17).…”