Saiqi Tian

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.

A photochromic long persistent luminescent polyurethane based on a colour conversion process

A photochromic long persistent luminescent polyurethane (PLPLPU) is prepared via incorporating amino-functionalized phosphors (NH2-SrAl2O4:Eu2+,Dy3+) and the red fluorescer 1-[(2-hydrocyethly)amino]anthraquinone (HAA) based on a colour conversion process. X-ray Diffraction (XRD), UV-vis absorption spectroscopy (UV), thermogravimetric analysis (TG), a fluorescence spectrophotometer and an afterglow brightness tester as well as the percentage of the migration test were utilized to characterize the structure and properties of the resultant samples. The photoluminescence emission spectrum of phosphors is overlapped with the excitation spectrum of HAA, which demonstrates that HAA can be selected as a colour conversion agent and can be excited by phosphors in the dark. PLPLPU shows red emission in daylight and yellow in the dark, exhibiting a pleasant photochromic long persistent luminescence effect. Furthermore, HAA in PLPLPU was confirmed to have a better thermal migration stability than the blend samples due to the chemical combination.

A thermochromic luminous polyurethane based on long persistent luminescent phosphors and thermochromic pigment

A thermochromic luminous polyurethane (TLPU), which can reversibly change its color and can exhibit fluorescence emission with the change in temperature, was prepared through incorporating long persistent luminescent phosphors (SrAl2O4:Eu2+,Dy3+) and thermochromic pigment (TP). X-Ray Diffraction (XRD) patterns, differential scanning calorimetry (DSC) curves, thermogravimetic analysis results (TG), UV-vis absorption spectra (UV), reflectance spectra and fluorescence spectra were obtained to characterize the properties of the resultant samples. The phosphorescence colors were directly related to the temperature because of the inner phase transition of the thermochromic pigment on heating. TLPU was red in daylight under low temperature conditions and turned white as the temperature rose. After the stoppage of excitation and in the dark, it emitted yellow light while cooling and turned green as the temperature increased.