Phosphorus Ester Containing Mesoporous Silica as Novel High‐Effective Flame Retardant in Polyurethane and Polyester Coatings

How Do Phosphorus Compounds with Different Valence States Affect the Flame Retardancy of PET?

This work investigated the effect of different valence states of phosphorus-containing compounds on thermal decomposition and flame retardancy of polyethylene terephthalate (PET). Three polyphosphates-PBPP with +3-valence P, PBDP with +5-valence P and PBPDP with both +3/+5-valence P-were synthesized. The combustion behaviors of flame-retardant PET were studied and the structure-property relationships between the phosphorus-based structures with different valence states and flame-retardant properties were further explored. It was found that phosphorus valence states significantly affected the flame-retardant modes of action of polyphosphate in PET. For the phosphorus structures with +3-valence, more phosphorus-containing fragments were released in the gas phase, inhibiting polymer chain decomposition reactions; by contrast, those with +5-valence phosphorus retained more P in the condensed phase, promoting the formation of more P-rich char layers. It is worth noting that the polyphosphate containing both +3/+5-valence phosphorous tended to combine the advantage of phosphorus structures with two valence states and balance the flame-retardant effect in the gas phase and condensed phase. These results contribute to guiding the design of specified phosphorus-based structures of flame-retardant compounds in polymer materials.

Metal-organic framework-derived bird's nest-like capsules for phosphorous small molecules towards flame retardant polyurea composites

The loading treatment of phosphorus flame retardants can mitigate their migration and plasticization effect. However, designing suitable carriers has remained a great challenge. Herein, two kinds of Co-based isomers, namely cobalt-cobalt layered double hydroxides (CoCo-LDH) and cobalt basic carbonate (CBC), were synthesized by employing ZIF-67 as a self-template, assemblied into two different nanostructures namely multi-yolk@shell CBC@CoCo-LDH (m-CBC@LDH) and solid CBC nanoparticles by facilely tuning the reaction time, which were employed as carriers, respectively. Subsequently, triphenyl phosphate (TPP)-loaded m-CBC@LDH (m-CBC-P@LDH) was prepared using TPP as the guest. The m-CBC@LDH with high specific surface area and hollow structure exhibited up to more than 30% of TPP loading. The peak of heat release rate and total heat release of polyurea composite blended with 5 wt% m-CBC-P@LDH reduced by 41.7% and 20.6% respectively, and the mechanical properties were less damaged. This work complements a feasible approach for preparation of metal-organic frameworks-derived flame retardant carriers.

A High-Phosphorus-Content Polyphosphonate with Combined Phosphorus Structures for Flame Retardant PET

A high-phosphorus-content polyphosphonate (PBDA), containing two phosphorus-based structures: phosphaphenanthrene (DOPO) and phenyl phosphonate groups, was synthesized and used in flame retardant polyethylene terephthalate (PET). Good self-extinguishing property (high UL 94 grade and LOI value), superior flame retardancy (lower heat/smoke release), and high quality retention (high carbon residue) were endowed to PET by PBDA. When 10 wt% PDBA was added, the peak heat release rate (pHRR), total heat release (THR), and total smoke rate (TSR) of PDBA/PET were found to be significantly reduced by 80%, 60.5%, and 21%, respectively, compared to the pure PET, and the LOI value jumped from 20.5% for pure PET to 28.7% with a UL-94 V-0 rating. The flame-retardant mode of action in PET was verified by thermogravimetric analysis-Fourier transform infrared (TGA-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), real-time FTIR, and scanning electron microscopy (SEM). Phosphaphenanthrene and phosphonate moieties in PDBA decomposed in sequence during heating, continuously releasing and keeping high-content PO· and PO2· radicals with a quenching effect and simultaneously promoting the formation of viscous crosslinked char layers causing a high barrier effect. PDBA mainly acted in the gas phase but the condensed-phase flame retardant function was also considerable.