Synthesis and synergistic flame‐retardant effects of rigid polyurethane foams used reactive DOPO‐based polyols combination with expandable graphite

Abstract

Flame retardant rigid polyurethane foams (FR‐RPFs) were prepared by a one‐pot and free‐rise method with reactive DOPO‐based polyols and expandable graphite (EG) as flame retardants. The flame retardancy, thermal stability and morphological of FR‐RPFs were investigated by some characterization testing techniques. Less than 10 wt% EG incorporated in the FR‐RPF‐0 can improve the mechanical strength due to forming a chemical bond between FR‐RPF and EG. With addition of 1.5 wt% P and 12.5 wt% EG, the FR‐RPF achieved the LOI of above 30%, meeting the standard of combustible stage B1. Thermal stability and residual mass of FR‐RPFs effectively increased as the increase EG by TGA analysis. EG could help to form a more thermally stable and compact char layer during combustion by SEM analysis. Cone calorimeter tests indicated that the obvious synergistic flame‐retardant effects between DOPO‐based polyols and EG could be concluded in FR‐RPFs. The co‐existence of DOPO‐based polyols enabled EG adhere more smoke fragments and the combination of DOPO‐based polyols and EG better strengthened char layer, so as to enhance the barrier and protective effect of residue. The synergistic flame‐retardant effects from the combination system of DOPO‐based polyols/EG endowed themselves with high flame‐retardant efficiency.

Bio-Based Rigid Polyurethane Foams Modified with Phosphorus Flame Retardants

“…Modifications should reduce all fire hazards, such as total heat release, smoke generation, the toxicity of gaseous decomposition products, and the rate of combustion. The application of proper flame retardants should allow for the safe evacuation of people, as well as reducing material losses caused by the fire [ 9 ]. Currently, the most common method of reducing the flammability of PUR materials is the addition of additive flame retardants during synthesis [ 2 , 10 ].…”

“…In the gas phase, the radicals resulting from the decomposition of the flame retardant recombine with the hydrogen (H • ) and hydroxide (OH • ) radicals, stopping the oxidation reactions [ 16 ]. Expanded graphite [ 9 , 17 ], aluminum hydroxide [ 18 ], magnesium hydroxide [ 19 ], ammonium polyphosphate [ 20 ], as well as layered clay [ 21 ] are also frequently used substances. However, to achieve an acceptable reduction in the flammability of PUR, inorganic substances often have to be used in large amounts, which adversely affect the structure of the material and the physical and mechanical properties [ 22 ].…”

Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes

“…This phosphonate-containing diol promoted char formation during combustion. Moreover, most of the studies dealt with the synthesis of novel polyol structures containing phosphinate 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) as a reactive flame retardant for PU foams, materials or coatings [ 29 , 30 , 31 , 32 ].…”

It Takes Two to Tango: Synergistic Expandable Graphite–Phosphorus Flame Retardant Combinations in Polyurethane Foams

“…This approach has become legendary for the excellent flame retardancy it provides to polyurethane foams (PUFs) [11][12][13][14]. In this feature article, we turn the scientific spotlight on the concept, mechanisms, and role of Polymers 2022, 14, 2562 2 of 24 the synergistic combinations of EG and P-FRs in PUFs in order to evoke the applause this approach deserves [15][16][17][18].…”