Peikun Zhang

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

A diol bearing a cyclic phosphoramidate pendant group, namely 2-(5,5-dimethyl-2-oxo-2λ5-1,3,2-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 PNMPD-based 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.

Synergistic effect of phosphorus–nitrogen and silicon-containing chain extenders on the mechanical properties, flame retardancy and thermal degradation behavior of waterborne polyurethane

With the aim to keep a balance between the flame retardancy and thermal stability as well as mechanical properties of waterborne polyurethane (WPU), a novel phosphorus–nitrogen–silicon containing flame retardant WPU (FRWPU) was synthesized by conjugating with a cyclic phosphoramidate lateral group bearing diol (named as PNMPD) and silane coupling agent KH-602 in the chain-extension and post-chain extension process, respectively. Significant enhancement in tensile strength (6.1 MPa) is obtained with the combined covalent incorporation of PNMPD and KH-602 rather than using PNMPD alone. A limiting oxygen index (LOI) value of 27.7% and a UL-94 vertical burning V-0 rating is achieved for FRWPU-12.6 with 12 wt% PNMPD and 60% post-chain extension ratio by KH-602, while the peak heat release rate (PHRR), total heat release (THR), peak smoke produce rate (SPR) and total smoke production (TSP) characterized by a cone calorimeter (CC) markedly reduce by 36.0%, 42.9%, 40.1% and 35.4%, respectively, compared to those of pure WPU, which is more efficient in flame retardancy than FRWPU-12.0 merely loaded with 12 wt% PNMPD. Meanwhile, the thermal degradation behaviors and flame-retardant mechanism of FRWPU were consistently confirmed by thermogravimetric analysis (TGA), scanning electron microscopy (SEM), thermogravimetry-Fourier transform infrared (TG-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. All results indicate that the interactions between phosphorus and silicon elements in the condensed phase are mainly responsible for the dramatically reduced fire hazards, which inhibits the heat and flammable gas release and facilitates the formation of a more thermally stable graphitized char layer consisting of –P(O)–O–Si– structures.

Synthesis and Application of Phosphorus-containing Flame Retardant Plasticizer for Polyvinyl Chloride

A novel phosphorus-containing flame retardant plasticizer (PFRP) derived from castor oil acid methyl ester (COME) was synthesized to substitute dioctyl phthalate (DOP) for plasticizing polyvinyl chloride (PVC) products. The chemical structures of PFRP were confirmed by fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR). Meanwhile, the plasticizing effect, flammability and thermal stability of plasticized PVC films were investigated by dynamic mechanical analyzer (DMA), limiting oxygen index (LOI) test, scanning electron microscope (SEM) and thermogravimetric analysis (TGA). As the PFRP content increasing from 0 wt% to 50 wt% amount of plasticizers, the plasticizing efficiency and the mechanical properties showed a slightly decreasing tendency compared with that of DOP, while the LOI value of plasticized PVC increased remarkably from 21.5 % to 25.2 %, showing a combined plasticizing efficiency and flame retardancy. SEM and TGA analysis indicated that PFRP had little effect on thermal stability but was effective to promote the formation of compact carbon residue.