Self-extinguishing and transparent epoxy resin modified by a phosphine oxide-containing bio-based derivative

Preparation of High-Transparency Phosphenanthrene-Based Flame Retardants and Studies of Their Flame-Retardant Properties

Transparency is an important property for polymer flame retardants, especially epoxy resin (EP) flame retardants, and flame-retardant epoxy resins that maintain a high transparency and low chromatic aberration play important roles in the optical, lighting, and energy industries. Herein, a DOPO-based flame retardant 6,6'-((sulfonylbis(4,1-phenylene))bis(oxy))bis(dibenzo[c,e][1,2]oxaphosphinine 6-oxide) with a high transparency and low chromatic aberration was prepared via the classical Atherton-Todd reaction and named SBPDOPO. Its chemical structure was characterized with Fourier IR spectroscopy and NMR spectroscopy. An EP loaded with 7 wt% SBPDOPO passed the UL-94 V-0 rating with an LOI value of 32.1%, and the peak heat release rate, total heat release, and total smoke production were reduced by 34.1%, 31.6%, and 27.7%, respectively, compared with those of pure EP. In addition, the addition of SBPDOPO improved the thermal stability, residual mass, and glass transition temperature of the EP. On this basis, the EP containing 7 wt% SBPDOPO maintained a high transparency and low color aberration, with a transmittance of 94% relative to that of pure EP and a color aberration ΔE of 1.63. Finally, the flame-retardant mechanism of SBPDOPO was analyzed, which demonstrated that it exerted both gas-phase and condensed-phase flame-retardant effects, and that SBPDOPO/EP had high potential for application scenarios in which both flame retardancy and transparency are needed. SBPDOPO/EP has great potential for applications requiring both flame retardancy and transparency.

Flame-retardant poly(L-lactic acid) with enhanced UV protection and well-preserved mechanical properties by a furan-containing polyphosphoramide

Despite good biodegradability and mechanical strength, the intrinsic flammability of poly(L-lactic acid) (PLA) impede its practical application. Introducing phosphoramide is an effective method to enhance the flame retardancy of PLA. However, most of the reported phosphoramides derive from petroleum resources, and their addition tends to deteriorate the mechanical properties, especially toughness, of PLA. Herein, a bio-based, furan-containing polyphosphoramide (DFDP) with high flame-retardant efficiency was synthesized for PLA. Our study found that 2 wt% DFDP enabled PLA to pass a UL-94 V-0 rating, and 4 wt% DFDP increased the limiting oxygen index (LOI) to 30.8 %. DFDP effectively maintained the mechanical strength and toughness of PLA. The tensile strength of PLA with 2 wt% DFDP reached 59.9 MPa, and its elongation at break and impact strength were increased by 15.8 % and 34.3 %, respectively, relative to those of virgin PLA. The UV protection of PLA was significantly enhanced by introducing DFDP. Hence, this work provides a sustainable and comprehensive strategy for the creation of flame-retardant biomaterials with improved UV protection and well-preserved mechanical properties, which possess a broad prospect in industrial application.

Flame-Retarded Rigid Polyurethane Foam Composites with the Incorporation of Steel Slag/Dimelamine Pyrophosphate System: A New Strategy for Utilizing Metallurgical Solid Waste

Rigid polyurethane (RPUF) was widely used in external wall insulation materials due to its good thermal insulation performance. In this study, a series of RPUF and RPUF-R composites were prepared using steel slag (SS) and dimelamine pyrophosphate (DMPY) as flame retardants. The RPUF composites were characterized by thermogravimetric (TG), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared coupling (TG-FTIR). The results showed that the LOI of the RPUF-R composites with DMPY/SS loading all reached the combustible material level (22.0 vol%~27.0 vol%) and passed UL-94 V0. RPUF-3 with DMPY/SS system loading exhibited the lowest pHRR and THR values of 134.9 kW/m² and 16.16 MJ/m², which were 54.5% and 42.7% lower than those of unmodified RPUF, respectively. Additionally, PO· and PO₂· free radicals produced by pyrolysis of DMPY could capture high energy free radicals, such as H·, O·, and OH·, produced by degradation of RPUF matrix, effectively blocking the free radical chain reaction of composite materials. The metal oxides in SS reacted with the polymetaphosphoric acid produced by the pyrolysis of DMPY in combustion. It covered the surface of the carbon layer, significantly insulating heat and mass transport in the combustion area, endowing RPUF composites with excellent fire performance. This work not only provides a novel strategy for the fabrication of high-performance RPUF composites, but also elucidates a method of utilizing metallurgical solid waste.