Cyclotriphosphazene-Based Intumescent Flame Retardant against the Combustible Polypropylene

Hexakis[p-(hydroxymethyl)phenoxy]cyclotriphosphazene as an Environmentally Friendly Modifier for Polyurethane Powder Coatings with Increased Thermal Stability and Corrosion Resistance

Protection against fire and the corrosion of metals is necessary to ensure human safety. Most of the fire and corrosion inhibitors do not meet the ecological requirements. Therefore, effective and ecological methods of protecting metals are currently a challenge for researchers. In this work, the influence of hexakis(4-(hydroxymethyl)phenoxy)cyclotriphosphazene (HHPCP) on the characteristics of powder coatings was examined. The coatings' properties were investigated by measuring the roughness, hardness, adhesion to the steel surface, cupping, gloss, scratch resistance, and water contact angle. The thermal stability was studied by furnace test and TGA analysis. The corrosion resistance test was carried out in a 3.5% NaCl solution. The distribution of phosphazene-derived segments in the coating was examined by GD-EOS analysis. Modified coatings show better corrosion and thermal resistance and can be used for the protection of the steel surface. Their better corrosion resistance is due to the electroactive properties of the phosphazene ring and its higher concentration at the coating surface, confirmed by GD-EOS analysis. The increase in thermal resistance is due to the effect of the formation of phosphoric metaphosphoric and polyphosphoric acids during the decomposition of HHCPC, which remain in the condensed char phase and play a crucial role in surface protection.

Halogen-free layered double hydroxide-cyclotriphosphazene carboxylate flame retardants: effects of cyclotriphosphazene di, tetra and hexacarboxylate intercalation on layered double hydroxides against the combustible epoxy resin coated on wood substrates

The development of halogen-free flame retardants as environmentally friendly and renewable materials for heat and fire-resistant applications in the field of electronics is important to ensure safety measures. In this regard, we have proposed a simple and halogen-free strategy for the synthesis of flame retardant LDH-PN materials to decrease the fire hazards of epoxy resin (EP), via a co-precipitation reaction between Mg(NO₃)₂ and Al(NO₃)₃ and the subsequent incorporation of different cyclotriphosphazene (PN) carboxylate anions. The cyclotriphosphazene-based di, tetra and hexacarboxylate-intercalated layered double hydroxides are designated as LDH-PN-DC, LDH-PN-TC and LDH-PN-HC, respectively. Furthermore, the intercalation of cyclotriphosphazene carboxylate anions into the LDH layers was confirmed by PXRD, FT-IR, TGA, solid-state ³¹P NMR, nitrogen adsorption and desorption analysis (BET), HR-SEM and XPS. Evaluation of the flame retardant (vertical burning test and limiting oxygen index) properties was demonstrated by formulating the LDH-PN materials with epoxy resin (EP) in different ratios coated on wood substrates to achieve the desired behaviour of the EP/LDH-PN composites. Structure–property analysis reveals that EP/LDH-PN-TC-20 wt% and EP/LDH-PN-HC-20 wt% achieved a V₀ rating in the UL-94 V test and achieved higher LOI values (27.7 vol% for EP/LDH-PN-TC-20 wt% and 29 vol% for EP/LDH-PN-HC-20 wt%) compared to the epoxy-coated wood substrate (23.2 vol%), whereas EP/LDH-PN-DC failed in the vertical burning test for various weight percentages of LDH-PN-DC from 5 wt% to 20 wt% in the composites, with a lower LOI value of 22.1 vol%. Excellent flame retardancy was observed for EP/LDH-PN-TC and EP/LDH-PN-HC due to the presence of more binding sites of carboxylate anions in the LDH layers and less or no spiro groups in cyclotriphosphazene compared to that in EP/LDH-PN-DC. In addition, the synergistic flame retardant effect of the combination of LDH and cyclotriphosphazene on the epoxy resin composites remains very effective in creating a non-volatile protective film on the surface of the wood substrate to shelter it from air, absorb the heat and increase the ignition time, which prevents the supply of oxygen during the combustion process. The results of this study show that the proposed strategy for designing flame-retardant properties represents the state-of-the-art, competent coating of inorganic materials for the protection and functionalization of wood substrates.

The flame retardant properties of the different types of cyclotriphosphazene carboxylate-intercalated LDH materials are emphasized by increasing the number of binding sites and decreasing the number of spiro groups in the cyclotriphosphazene core.

Synthesis of the first 2-hydroxyanthraquinone substituted cyclotriphosphazenes and their cytotoxic properties

New 2-hydroxyanthraquinone based cyclotriphosphazenes were prepared and their cytotoxic effects were investigated in MCF-7 (breast cancer), MCF-12A (normal breast epithelium), DLD-1 (colon cancer), and CD-18Co (normal colon epithelium) cell lines.

Synergistic Flame Retardant Effect of an Intumescent Flame Retardant Containing Boron and Magnesium Hydroxide

In this study, to develop an organic/inorganic synergistic flame retardant and to reduce the dosage and cost of flame retardants, organic/inorganic synergistic flame retardants, hexakis(4-boronic acid-phenoxy)-cyclophosphazene (CP-6B), and magnesium hydroxide (MH) were chosen. The flame retardant properties of CP-6B/MH in epoxy resin (EP) were discussed. EP/CP-6B/MH had better flame retardancy and heat resistance compared with EP/CP-6B and EP/MH. A limiting oxygen index of EP/3.0%CP-6B/0.5%MH of 31.9% was achieved, and vertical burning V-0 rating was achieved. Compared with EP, the cone calorimeter dates of EP/CP-6B/MH decreased. CP-6B/MH inhibited combustion and did little to damage mechanical properties. Besides, the flame retardant mechanism was studied by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography-mass spectrometry. CP-6B/MH exerted good synergistic effects.

Molecular Firefighting-How Modern Phosphorus Chemistry Can Help Solve the Challenge of Flame Retardancy

The ubiquity of polymeric materials in daily life comes with an increased fire risk, and sustained research into efficient flame retardants is key to ensuring the safety of the populace and material goods from accidental fires. Phosphorus, a versatile and effective element for use in flame retardants, has the potential to supersede the halogenated variants that are still widely used today: current formulations employ a variety of modes of action and methods of implementation, as additives or as reactants, to solve the task of developing flame-retarding polymeric materials. Phosphorus-based flame retardants can act in both the gas and condensed phase during a fire. This Review investigates how current phosphorus chemistry helps in reducing the flammability of polymers, and addresses the future of sustainable, efficient, and safe phosphorus-based flame-retardants from renewable sources.

Facile one-pot synthesis of multifunctional polyphosphazene nanoparticles as multifunctional platform for tumor imaging

By integrating imaging and drug-delivery in a single system, fluorescent nano-multifunctional imaging platforms can offer simultaneous diagnosis and therapy to diseases like cancer. However, the synthesis of such system involves a tedious, time-consuming, and multi-step process. Herein we report a facile method based on simple ultrasonication to synthesize highly cross-linked, monodispersed fluorescent polyphosphazene nanoparticles from hexachlorocyclotriphosphazene (HCCP) and dichlorofluorescein (FD). Various functional groups (folic acid, PEG-NH₂, and methylene blue) can be "fastened" in situ onto the poly(cyclotriphosphazene-co-dichlorofluorescein) (PCTPDF) nanoparticles to expand its application as nano-multifunctional platform. All the nanoparticles were characterized spectrophotometrically, and morphology was established by the images obtained from scanning electron microscope (SEM). The synthesized multifunctional nanoparticles exhibited low toxicity and penetrated through the cytomembranes of human colon cancer (HCT 116) cells. When applied to in vivo tumor imaging using biologically engineered mouse model, methylene blue functionalized (PCTPDF@MB) nanoparticles exhibited excellent photodynamic activity and imaging ability. Thus, PCTPDF nanoplatform based on multi-functional fluorescent nanoparticles might offer an efficient solution to new age theranostics. Apart from diagnostics application, PCTPDF, as a nanoplatform, could also be utilized to achieve more comprehensive application in modern analytic chemistry. Graphical Abstract The table of contents.

Superior flame retardancy and smoke suppression of epoxy-based composites with phosphorus/nitrogen co-doped graphene

Phosphorus and/or nitrogen doping is an effective method of improving the physical and chemical properties of reduced graphene oxide (rGO). In this work, phosphorus and nitrogen co-doped rGO (PN-rGO), synthesized using a scalable hydrothermal and microwave process, was used as an additive to improve the flame retardancy of epoxy resin (EP) for the first time. Chemical structure and morphology characterization confirmed that the nitrogen and phosphorus atoms were doped into the graphite lattice adopting pyrrolic-N, pyridinic-N, quaternary-N and pyrophosphate and metaphosphate forms. Doping increased the oxidization resistance of rGO and the thermal-oxidative stability of its composites' char, while also improving the catalytic charring ability of polymer. Both effects resulted in the formation of a stable char protective layer during burning and to a significant improvement in flame retardation and smoke suppression in the final composites. The peak heat release rate (PHRR), total heat release (THR) and total smoke production (TSP) for the EP-based composite (containing 5 wt% PN-rGO) decreased by 30.9%, 29.3% and 51.3%, respectively, compared to neat EP. Our work has produced a promising graphene-based flame retardant additive for the mass production of high-performance composites, also expended the application of heteroatom-doped graphene.

Cyclotriphosphazene core-based dendrimers for biomedical applications: an update on recent advances

This review is focused on the recent use of cyclotriphosphazene-based dendrimers in biomedicine. Since its synthesis for the first time in 1834, cyclotriphosphazene has been an important compound of phosphorus chemistry as a scaffold, and a large number of cyclotriphosphazene derivatives have been synthesized and applied in various fields such as biology, catalysis, fluorescence, nanomaterials, etc. Today, one of the most important uses concerns its biomedical applications. In this review, the recent developments (since 2012) of cyclotriphosphazene for major pharmaceutical applications are highlighted and analyzed.

Preparation of dual-functionalized graphene oxide for the improvement of the thermal stability and flame-retardant properties of polysiloxane foam

Polysiloxane foam (PSF) is a foam material with outstanding performance. However, the limiting oxygen index (LOI) of pure PSF is only 22.0 vol%, which can be attributed to combustible materials.