Waterborne polyurethane conjugated with novel diol chain-extender bearing cyclic phosphoramidate lateral group: synthesis, flammability and thermal degradation mechanism

Abstract

A diol bearing a cyclic phosphoramidate pendant group, namely 2-(5,5-dimethyl-2-oxo-2l 5 -1,3,2-dioxaphosphinan-2-ylamino)-2-methyl-propane-1,3-diol (PNMPD) was synthesized and characterized by FTIR and NMR. Subsequently, PNMPD was applied as a flame-retardant chain extender to prepare phosphorus-nitrogen containing waterborne polyurethane (PNWPU), and the influence of PNMPD on the hydrolysis, thermal and flame-retardant properties of PNWPU was investigated. The fabricated PNMPDbased PNWPU shows controllable mechanical properties and maintains the good hydrolysis-resistance property of polyurethane. Thermal stability and flammability analysis demonstrate that though the covalent conjugation of PNMPD induces a slight thermal destabilization effect, it efficiently promotes char formation in PNWPU, as a result, a 27.2% limiting oxygen index (LOI) value and a UL-94 V-0 rating can be achieved with only 12 wt% PNMPD incorporated. Compared with WPU, the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR) and total smoke release (TSR) of PNWPU-12, evaluated with cone calorimetry, are decreased by 44.7%, 39.0%, 42.9% and 36.1%, respectively. In addition, the flame retarding mechanism of PNWPU was comprehensively investigated by SEM microscopy, EDX analysis, real time FTIR and TG-FTIR, and results elucidate that these notable reductions in fire hazards are probably attributed to the formation of polyphosphoric acid-rich rugged and intumescent char in the condensed phase, which behaves as a "labyrinth effect" to effectively inhibit the transmission of heat, oxygen and volatile fragments from entering into the flame zone and shield the underlying PNWPU matrix against flame.

Synthesis of a phosphorus‐ and nitrogen‐containing flame retardant and evaluation of its application in waterborne polyurethane

“…The waterborne polyurethane dispersions were synthesized according to Zhang et al . First, 19.9 g of IPDI, 30.0 g of PPG 2000, 2.8 g of DMPA, and 0.05 wt % DBTDL were put into a 250 mL three‐necked flask with a Teflon mechanical stirrer, thermometer, nitrogen inlet, and reflux condenser, and heated up to 80 °C for 3 h. After completion of the reaction, the temperature was cooled to 60 °C.…”

Hydroxyl-decorated ammonium polyphosphate as flame retardant reinforcing agent in solvent-free two-component polyurethane

“…. The typical absorption bands of PU are located at 3420 cm −1 (NH stretching), 2869–2969 cm −1 (CH stretching), 1708 cm −1 (urethane carbonyl groups), 1530 cm −1 (urethane NH bending), 1373 cm −1 (CH bending) and 1106 cm −1 (COC stretching) . The intensity of the characteristic bands gradually diminishes above 200 °C and disappears entirely above 400 °C ( T max2 ), indicating that the main degradation of PU chains occurs within this region.…”

Recent developments in P(O/S)–N containing flame retardants

“…57 Rigid PU foam (RPUF) is often used as an insulation material, especially in buildings, due to its superior physical and mechanical properties and low thermal conductivity, while flexible foams are used for application in a variety of consumer and commercial products, including bedding, furniture, automotive interiors, carpet underlay, and packaging. Phosphoramidates [64][65][66] and phosphonates 67 are well studied as FRs for PU foams. It is required that these FRs should not have negative influence on the physical properties of the materials and the environment.…”

“…It is required that these FRs should not have negative influence on the physical properties of the materials and the environment. Phosphoramidates [64][65][66] and phosphonates 67 are well studied as FRs for PU foams. These compounds produce active PO species in the gas phase during the thermal decomposition process, which interferes with the combustion process of the flammable volatiles.…”