Flame-retardant behavior of a phosphorus/silicon compound on polycarbonate

Selectively self-recyclable, highly transparent and fire-safe polycarbonate plastic enabled by thermally responsive phosphonium-phosphate

Both the circular economy and fire-safety of polymer plastics have become a global consensus. Herein, an integrated strategy for selectively self-recyclable, highly-transparent and fire-safe polycarbonate plastic is proposed by thermally responsive phosphonium-phosphate (DP). During its service life, DP, as a flame-retardant with good compatibility, enables polycarbonate plastic with high transparency in visible light, excellent self-extinguishing and high fire-safety. After consumption, DP, as a catalyst, triggers the selective self-recycling of DP-containing polycarbonate in mixed plastics and even in same-kind polycarbonate plastics without an external catalyst. Importantly, the oxygen-consuming mechanism at high temperature in fire accidents (>350 °C) and the double hydrogen bond catalysis mechanism at a lower temperature (180 °C) of DP are key to the life cycle management of polycarbonate from use-stage to post-consumption. This work inspires a new solution to plastic pollution by designing sustainable plastics that satisfy both service-stage and end-of-life criteria, striving towards a zero-waste circular economy.

Synthesis and Characterization of DOPO-Containing Poly(2,6-dimethyl-1,4-phenylene oxide)s by Oxidative Coupling Polymerization

A set of polyphenylene oxides incorporating DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) functionality, denoted as DOPO-R-PPO, was synthesized by copolymerization of 2,6-dimethylphenol (2,6-DMP) with various DOPO-substituted tetramethyl bisphenol monomers. In the initial step, a Friedel-Crafts acylation reaction was employed to react 2,6-DMP with different acyl chlorides, leading to the formation of ketone derivatives substituted with 2,6-dimethylphenyl groups. Subsequently, the ketones, along with DOPO and 2,6-DMP, underwent a condensation reaction to yield a series of DOPO-substituted bisphenol derivatives. Finally, polymerizations of 2,6-dimethylphenol with these DOPO-substituted bisphenols were carried out in organic solvents using copper(I) bromide/N-butyldimethylamine catalysts (CuBr/DMBA) under a continuous flow of oxygen, yielding telechelic PPO oligomers with DOPO moieties incorporated into the polymer backbone. The chemical structures of the synthesized compounds were characterized using various analytical techniques, including Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR), phosphorus nuclear magnetic resonance (31P NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). When compared to conventional poly(2,6-dimethyl-1,4-phenylene oxide)s with a similar molecular weight range, all DOPO-PPOs exhibited higher glass transition temperatures, enhanced thermal degradability, and increased char yield formation at 800 °C without compromising solubility in organic solvents.

Polyimide Copolymers and Nanocomposites: A Review of the Synergistic Effects of the Constituents on the Fire-Retardancy Behavior

Carbon-based polymer can catch fire when used as cathode material in batteries and supercapacitors, due to short circuiting. Polyimide is known to exhibit flame retardancy by forming char layer in condensed phase. The high char yield of polyimide is attributed to its aromatic nature and the existence of a donor–acceptor complex in its backbone. Fabrication of hybrid polyimide material can provide better protection against fire based on multiple fire-retardancy mechanisms. Nanocomposites generally show a significant enhancement in mechanical, electrical, and thermal properties. Nanoparticles, such as graphene and carbon nanotubes, can enhance flame retardancy in condensed phase by forming a dense char layer. Silicone-based materials can also provide fire retardancy in condensed phase by a similar mechanism as polyimide. However, some inorganic fire retardants, such as phosphazene, can enhance flame retardancy in gaseous phase by releasing flame inhibiting radicals. The flame inhibiting radicals generated by phosphazene are released into the gaseous phase during combustion. A hybrid system constituted of polyimide, silicone-based additives, and phosphazene would provide significant improvement in flame retardancy in both the condensed phase and gas phase. In this review, several flame-retardant polyimide-based systems are described. This review which focuses on the various combinations of polyimide and other candidate fire-retardant materials would shed light on the nature of an effective multifunctional flame-retardant hybrid materials.

Synthesis of a Compound Phosphorus-Nitrogen Intumescent Flame Retardant for Applications to Raw Lacquer

Raw lacquer (RL) is a natural polymer compound with highly promising applications; however, its inflammable attribute restricts the industrial applications. In this study, melamine is used to formulate tri (1-melamine-2-propanol) phosphate (FR-1), after which it is synthesized with ammonium phosphate (FR-2) and diatomite to form a compound phosphorus-nitrogen intumescent flame retardant (IFR). Next, IFR is used as the filling agent that then cross-links with RL, and as such RL/IFR membranes are formed after the curing. The limiting oxygen index (LOI) measurement, the vertical combustion test (UL-94), the microshape calorimetric analysis (CCT), and the thermal gravimetric analysis (TGA) are conducted to examine the combustion resistance and thermal stability of the membranes. Fourier transform infrared spectroscopy (FT-IR) and electron scanning microscope (SEM) are performed to separately characterize the structure and compatibility; the mechanical properties of the membranes are also evaluated. The vertical combustion test results confirm that with 30 wt% of IFR, RL/IFR membranes acquire 12.3% higher LOI and a vertically combustion of V-0 level. The TGA indicates that RL/IFR membranes demonstrate a greater adhesion level, a higher rigidity, and better luster than pure RL membranes.

Synthesis of a novel modified chitosan as an intumescent flame retardant for epoxy resin

According to the concept of fire life cycle assessment (LCA), a new type of intumescent flame retardant was designed and synthesized by chemically bonding chitosan, phosphorus pentoxide and melamine. The resultant compound, chitosan ethoxyl melamine phosphate (CEMP), was characterized by FTIR, 1H NMR, 31P NMR, XRD and SEM. The performance of CEMP and organic montmorillonite (OMMT) was evaluated in the substrate of epoxy resin (EP) with limited oxygen index (LOI), UL-94, cone calorimetric test (CCT), TGA and TG-IR. As a result, intumescent flame retardant EP (EP3) containing 30.6% LOI and V-0 rating was prepared by adding 3 wt% OMMT and 15 wt% CEMP. The CCT results indicated that CEMP and OMMT reduced the peak of heat release rate (PHRR) to about one fourth that of pure EP and total heat release (THR), 1/2. Decomposition of EP and EP3 was traced from 100 to 600°C by TG-IR.

A novel DOPO-g-KH550 modification wood fibers and its effects on the properties of composite phenolic foams

A novel 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) graft γ-amino propyl triethoxy silane (KH550) was synthesized and introduced on the surface of wood fiber. Finally DOPO-g-KH550 treated wood fiber (DKTWF) was used to prepare DKTWF composite phenolic foams (DKTWFCPF). The structures of DOPO-g- KH550 was acknowledged by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H-NMR). The structures of DKTWF were confirmed by FT-IR. Compared with wood fiber, the diffraction peaks’ position was basically unchanged, but the crystallinity was slightly increased and thermal stability were dramatically improved, T5% and Tmax increased by 21.9o and 36.1o respectively. But the char yield (800o) was slightly reduced. With the dosage of DKWF, there were different degrees of improvement including the mechanical properties, flame retardancy and microstructure of DKTWFCPF. Comprehensive analysis, the interfacial compatibility was significantly improved between DKTWF and phenolic resin, and the suitable content of DKTWF was 4%.