Preparation and flame-retardant mechanism of polyheptazine/PA6 nanocmposites

Terminal group effects of DOPO-conjugated flame retardant on polyamide 6: Thermal stability, flame retardancy and mechanical performances

Two DOPO-conjugated flame retardants with or without amino terminal groups (DOPO-NH₂ and DIDOPO, respectively) were synthesized and incorporated into polyamide 6 (PA6). Results demonstrated the DOPO-NH₂ endowed superior thermal, flame retardant and mechanical performances to PA6 composites. With the same loading of 15 wt%, DOPO-NH₂ can catalyze the PA6 matrix more effectively and result in more residues at high temperature. The PA6 composites containing DOPO-NH₂ exhibited higher LOI (28.0%) compared to 25.0% for the sample containing DIDOPO, and the lower heat release capacity and peak heat release rate. Furthermore, the overall mechanical properties of PA6 composites containing DOPO-NH₂ outperformed the samples containing DIDOPO, even superior to that for PA6. Such a significant difference can be mainly attributed to the existence of amino-terminal group, which can interact with carboxyl group in PA6 as confirmed by dynamic mechanical analysis, improving the compatibility between the flame retardant and PA6 matrix.

A top-down design for easy gram scale synthesis of melem nano rectangular prisms with improved surface area

An unprecedented top-down design for the preparation of melem by 1 h stirring of melamine-based g-C₃N₄ in 80 °C concentrated sulfuric acid (95-98%) was discovered. The melem product was formed selectively as a monomer on the gram scale without the need for controlled conditions, inert atmosphere, and a special purification technique. The as-prepared air-stable melem showed a distinctive nano rectangular prism morphology that possesses a larger surface area than the melems achieved by traditional bottom-up designs making it a promising candidate for catalysis and adsorption processes.

Preparation of Flame-Retardant Polyurethane and Its Applications in the Leather Industry

As a novel polymer, polyurethane (PU) has been widely applied in leather, synthetic leather, and textiles due to its excellent overall performance. Nevertheless, conventional PU is flammable and its combustion is accompanied by severe melting and dripping, which then generates hazardous fumes and gases. This defect limits PU applications in various fields, including the leather industry. Hence, the development of environmentally friendly, flame-retardant PU is of great significance both theoretically and practically. Currently, phosphorus-nitrogen (P-N) reactive flame-retardant is a hot topic in the field of flame-retardant PU. Based on this, the preparation and flame-retardant mechanism of flame-retardant PU, as well as the current status of flame-retardant PU in the leather industry were reviewed.

State of the Art in the Preparation and Properties of Molecular Monomeric s-Heptazines: Syntheses, Characteristics, and Functional Applications

This review gives an account on the fast expanding field of monomeric (or molecular) heptazines, at the exclusion of their various polymeric forms, often referred to as carbon nitrides. While examples of monomeric heptazines were extremely limited until the beginning of this century, the field has started expanding quickly since then, as has the number of reports on polymeric materials, though previous reviews did not separate these fields. We provide here a detailed report on the synthetic procedures for molecular heptazines. We also extensively report on the different achievements realized from these new molecules, in the fields of physical chemistry, spectroscopy, materials preparation, (photo)catalysis, and devices. After a comprehensive summary and discussion on heptazines syntheses and characteristics, we show that starting from well-defined molecules allows a versatility of approaches and a wide tunability of the expected properties. It comes out that the field of monomeric heptazines is now emerging and possibly heading toward maturity, while diverging from the one of polymeric carbon nitrides. It is likely that this area of research will quickly surge to the forefront of the search for active organic molecules, with special attention to the domains of catalysis and organic-based functional materials and devices.

Construction of Charring-Functional Polyheptanazine towards Improvements in Flame Retardants of Polyurethane

Nitrogen-containing flame retardants have been extensively applied due to their low toxicity and smoke-suppression properties; however, their poor charring ability restricts their applications. Herein, a representative nitrogen-containing flame retardant, polyheptanazine, was investigated. Two novel, cost-effective phosphorus-doped polyheptazine (PCN) and cobalt-anchored PCN (Co@PCN) flame retardants were synthesized via a thermal condensation method. The X-ray photoelectron spectroscopy (XPS) results indicated effective doping of P into triazine. Then, flame-retardant particles were introduced into thermoplastic polyurethane (TPU) using a melt-blending approach. The introduction of 3 wt% PCN and Co@PCN could remarkably suppress peak heat release rate (pHRR) (48.5% and 40.0%), peak smoke production rate (pSPR) (25.5% and 21.8%), and increasing residues (10.18 wt%→17.04 wt% and 14.08 wt%). Improvements in charring stability and flame retardancy were ascribed to the formation of P-N bonds and P=N bonds in triazine rings, which promoted the retention of P in the condensed phase, which produced additional high-quality residues.