Highly flame‐retardant polyurethane foam based on reactive phosphorus polyol and limonene‐based polyol

Abstract

Polyurethane foams are in general flammable and their flammability can be controlled by adding flame-retardant (FR) materials. Reactive FR have the advantage of making strong bond within the polyurethane chains to provide excellent FR over time without compromising physico-mechanical properties. Here, phenyl phosphonic acid and propylene oxide-based reactive FR polyol was synthesized and used along with limonene based polyol for preparation of FR polyurethanes. All the obtained foams showed higher closed cell content (above 96%). By the addition of FR-polyol, the compressive strength of the foams showed 160% increment which could be due to reactive nature of FR-polyol. Moreover, 1.5 wt % of phosphorus (P) content reduced the self-extinguishing time of the foam from 81 (28% weight loss) to 11.2 s (weight loss of 9.8%). Cone test showed 68.6% reduction in peak heat release rate along with 23.4% reduction in thermal heat release. The change in char structure of carbon after burning was analyzed using Raman spectra which, suggests increment in the graphitic phase of the carbon over increased concentration of phosphorus. It can be concluded from this study that phosphorous based polyol could be blended with bio-based polyols to prepare highly FR and superior physico-mechanical rigid polyurethane foams.

Castor‐oil derived nonhalogenated reactive flame‐retardant‐based polyurethane foams with significant reduced heat release rate

“…As the concentration of FR polyol increases, onset decomposition temperature reduces to about 270 °C. This could be due to the low thermal stability of P‐O‐C and P‐C bonds within the FR polyol . In principle, phosphorus compound contributes to flame retardancy in two distinct ways, namely, condensed phase and gas phase .…”

“…In principle, phosphorus compound contributes to flame retardancy in two distinct ways, namely, condensed phase and gas phase . At higher temperature, thermal decomposition of P‐O‐C and P‐C bonds result in phosphinic acid within the condensed phase of the foams, causing transesterification reaction accelerating dehydration of the foams and forming intumescent barrier char structure . Barrier char layered over the surface of the foams, prevents the direct contact of the oxygen, thermal energy and combustible media providing flame retardancy.…”

“…On the other hand, phosphorus compounds also form PO*, PO 2 *, and OHPO* radicals responsible for inhibiting potentially flame promoting H* and OH* radicals, thereby providing flame retardancy . Although both possibilities exist, major contribution over flame retardancy mechanism of RFR occurs in solid phase resulting in high final char content and can be observed from the TGA curve . Differential TGA (DTGA) curves [Figure (b)], clearly show the narrowing of derivative curves with added phosphorus concentration using FR‐polyol during foam fabrication.…”

“…In previous studies, bromine‐based RFRs required about 5–6 wt % Br in the foam to obtain optimum flame retardancy . While phosphorus‐based RFR provides better flame retardancy with just 1.5 wt % P concentration . Very few studies are reported for bio‐linked phosphorus‐based RFRs for rigid polyurethane foams.…”

Bi‐phase flame‐retardant effect of dimethyl methylphosphonate and modified ammonium polyphosphate on rigid polyurethane foam

“…The common methods include introduction of reactive or addition flame retardant into RPUF matrix. The reactive flame retardants generally are the modified polyol with flame retardant chemical structure . And the addition flame retardants with no reaction groups cannot react with other component during the formation of RPUF, such as Al (OH) 3 , Mg (OH) 2 , expanded graphite (EG), and melamine .…”