Influence of the Crystal Structure of Melamine Trimetaphosphate 2D Supramolecules on the Properties of Polyamide 6

Organic-inorganic hybrid functionalized chitosan/ammonium polyphosphate (APP): A synergistic strategy for flame-retardant and high-mechanical-strength epoxy thermosets

Epoxy resin (EP) is an industrially essential polymer widely used in electronic packaging, adhesives, and construction. Despite its utility, the high flammability of EP poses a significant safety risk. In this study, a novel chitosan-derived organic-inorganic hybrid flame retardant (CPMM) was synthesized, which was then combined with ammonium polyphosphate (APP) and added to epoxy resin (EP) to produce high-performance flame-retardant epoxy thermosets. Samples containing 7.5 wt% CPMM and 7.5 wt% APP reached a limiting oxygen index (LOI) of 30.5 % and a V-0 rating, along with a marked decrease in peak heat release rate from 1447.0 kW/m2 to 267.1 kW/m2 compared to pure EP. Thermogravimetric analysis indicated that the synergistic effect of CPMM and APP promotes the formation of more complete intumescent char structures, thereby enhancing the flame-retardant properties of the epoxy thermosets. Furthermore, mechanical performance tests showed improvements in both tensile and flexural strengths due to the robust interaction between CPMM and the matrix. This study provides a promising strategy for the design of bio-based organic-inorganic hybrid flame retardants and epoxy thermosets with enhanced performance.

Bimetallic Effect of Hybrid Flame Retardant on Flame Retardant Performance in Polypropylene

Polypropylene composites are widely used for their excellent properties, but poor flame retardance is a major concern. The phosphorus content of the material in intumescent flame retardant (IFR) has a direct effect on retarding smoke and dehydrating to carbon during combustion. This study presents a hybrid flame retardant (MPA@ZrP-Zn) synthesized by noncovalent bonding between melamine and phytic acid molecules, containing a large number of phosphorus atoms in the system. Theoretical calculations confirm that the structure formed by zinc ions and melamine phytate (MPA) is more stable, and the overall electrophilicity index is at the level of a moderate Lewis acid. In addition, the Zr-Zn bimetallic effect significantly improves the drip resistance of IFR and reduces smoke emissions during combustion. UL-94 and LOI tests have shown that PP composites with MPA@ZrP-Zn (PPZn30) can achieve a V-0 rating and 33.5% of the LOI value. The THR and PHRR were 15.1% and 54.2% lower, respectively, for PPZn30 (compared to pure PP), and the ID/IG curves further indicate a higher degree of graphitization of the carbon layer in the combustion residue, which should be ascribed to the bimetallic effect. Therefore, this work puts forward a strategy to achieve high-performance PP composites with excellent flame retardant properties, which exhibit huge applications in electrical appliances and energy vehicles.

Three-Dimensional Cross-Linking Network Coating for the Flame Retardant of Bio-Based Polyamide 56 Fabric by Weak Bonds

Weak bonds usually make macromolecules stronger; therefore, they are often used to enhance the mechanical strength of polymers. Not enough studies have been reported on the use of weak bonds in flame retardants. A water-soluble polyelectrolyte complex composed of polyethyleneimine (PEI), sodium tripolyphosphate (STPP) and melamine (MEL) was designed and utilized to treat bio-based polyamide 56 (PA56) by a simple three-step process. It was found that weak bonds cross-linked the three compounds to a 3D network structure with MEL on the surface of the coating under mild conditions. The thermal stability and flame retardancy of PA56 fabrics were improved by the controlled coating without losing their mechanical properties. After washing 50 times, PA56 still kept good flame retardancy. The cross-linking network structure of the flame retardant enhanced both the thermal stability and durability of the fabric. STPP acted as a catalyst for the breakage of the PA56 molecular chain, PEI facilitated the char formation and MEL released non-combustible gases. The synergistic effect of all compounds was exploited by using weak bonds. This simple method of developing structures with 3D cross-linking using weak bonds provides a new strategy for the preparation of low-cost and environmentally friendly flame retardants.