Facile Synthesis of a Highly Efficient, Halogen-Free, and Intumescent Flame Retardant for Epoxy Resins: Thermal Properties, Combustion Behaviors, and Flame-Retardant Mechanisms

A novel branched poly­(phosphonamidate-phosphonate) (BPPAPO) oligomer was synthesized from the polycondensation of phenylphosphonic dichloride and tri­hydroxy­methyl­phosphine oxide followed by end-capping with aniline in a one-pot synthesis. BPPAPO exhibited excellent flame-retardant efficiency in epoxy resins (EP). With only 5.0 wt % loading, the EP composite reached UL-94 V-0 rating with a limiting oxygen index (LOI) value of 35.5%. BPPAPO catalyzed the early degradation of EP and promoted the formation of more char residue. Glass transition temperatures were partially lowered. When 7.5 wt % BPPAPO was incorporated, the peak heat release rate and total heat release were decreased by 66.2% and 37.3%, respectively, with a delayed ignition and the formation of a highly intumescent char residue. Combination of gas-phase and condensed-phase flame-retardant mechanisms was verified

Effect of Rare Earth Hypophosphite Salts on the Fire Performance of Biobased Polylactide Composites

In this work, two kinds of rare earth hypophosphites (REHP), lanthanum hypophosphite (LaHP) and cerium hypophosphite (CeHP), were synthesized and characterized. Subsequently, LaHP and CeHP were added into polylactide to improve its flame retardant properties. Thermal gravimetric analysis was employed to investigate the thermal decomposition behavior of REHP and flame retardant polylactide composites (FR-PLA). The fire performance evaluated by microscale combustion calorimetry and cone calorimeter clearly demonstrated that the addition of LaHP and CeHP resulted in significant reduction of the heat release rate, low total heat release, and compact intumescent char layer. Thermogravimetric analysis–infrared spectrometry testing indicated that the addition of REHP significantly decreased the yields of pyrolysis products. Furthermore, the crystallization behaviors of FR-PLA composites were investigated by differential scanning calorimetry. The char residue of FR-PLA composites after cone calorimeter testing were also be investigated by scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy

Influence of g‑C₃N₄ Nanosheets on Thermal Stability and Mechanical Properties of Biopolymer Electrolyte Nanocomposite Films: A Novel Investigation

A series of sodium alginate (SA) nanocomposite films with different loading levels of graphitic-like carbon nitride (g-C₃N₄) were fabricated via the casting technique. The structure and morphology of nanocomposite films were investigated by X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis results suggested that thermal stability of all the nanocomposite films was enhanced significantly, including initial thermal degradation temperature increased by 29.1 °C and half thermal degradation temperature improved by 118.2 °C. Mechanical properties characterized by tensile testing and dynamic mechanical analysis measurements were also reinforced remarkably. With addition of 6.0 wt % g-C₃N₄, the tensile strength of SA nanocomposite films was dramatically enhanced by 103%, while the Young’s modulus remarkably increased from 60 to 3540 MPa. Moreover, the storage modulus significantly improved by 34.5% was observed at loadings as low as 2.0 wt %. These enhancements were further investigated by means of differential scanning calorimetry and real time Fourier transform infrared spectra. A new perspective of balance was proposed to explain the improvement of those properties for the first time. At lower than 1.0 wt % loading, most of the g-C₃N₄ nanosheets were discrete in the SA matrix, resulting in improved thermal stability and mechanical properties; above 1.0 wt % and below 6.0 wt % content, the aggregation was present in SA host coupled with insufficient hydrogen bondings limiting the barrier for heat and leading to the earlier degradation and poor dispersion; at 6.0 wt % addition, the favorable balance was established with enhanced thermal and mechanical performances. However, the balance point of 2.0 wt % from dynamic mechanical analysis was due to combination of temperature and agglomeration. The work may contribute to a potential research approach for other nanocomposites