Influence of microencapsulated red phosphorus on the flame retardancy of high impact polystyrene/magnesium hydroxide composite and its mode of action

Preparation and characterization of polydopamine/melamine microencapsulated red phosphorus and its flame retardance in epoxy resin

Polydopamine/melamine composite microencapsulated red phosphorus (RP@PDA/MA) was prepared and applied as the flame retardant for epoxy resin (EP) in this work. For comparison, polydopamine (PDA) coated red phosphorus (RP@PDA) was also prepared. The microstructure, chemical composition and thermal decomposition of the as prepared samples were systematically characterized. The results showed that PDA and PDA/MA shell structures were fabricated successfully via convenient water-based processes at room temperature. The flame retardance of red phosphorus (RP), RP@PDA, and RP@PDA/MA on EP was evaluated. The results showed that EP blending with 7 wt% RP@PDA/MA passed V-0 degree in the vertical burning test (UL-94), reached a limited oxygen index (LOI) of 30.9% and decreased the peak heat release rate of EP by 65.1% in the cone calorimeter test. The satisfactory flame retardance can be attributed to the intumescent flame retardant system consisting of RP@PDA/MA. The PDA and PDA/MA shell structures also improved the compatibility between RP and EP, thus RP@PDA and RP@PDA/MA had less significant impact on the tensile-strain properties of EP.

Construction of few-layered black phosphorus/graphite-like carbon nitride binary hybrid nanostructure for reducing the fire hazards of epoxy resin

Black phosphorus (BP) and graphite-like carbon nitride (g-C₃N₄) were combined to prepare BP-CN hybrid nanostructure through a simple self-assembly method assisted by ultra-sonication, and as-obtained materials were further used as fire retardants introduced into epoxy resin to fabricate EP/BP-CNx nanocomposites. It was found that the introduction of 2 wt% BP-CNx into EP contributed to considerable decrements in peak heat release rate (up to 47.72%) and total heat release (utmost to 49.60%) of composites, and LOI value increased from 25% to 31%. SSTF results revealed that the introducing of BP-CN can distinctly reduce the production of smoke. TG-IR results demonstrated that the addition of BP-CN0.5 and BP-CN2.0 into EP matrix exert different influences on the decomposition of resin. Analyses of residual chars further validated through adjusting the proportion of BP and CN can achieve different fire performances of matrix. This work illustrates that BP can reduce the fire hazards of EP, and the hybridization of CN can achieve better flame retarded efficiency, which provides a new strategy for black phosphorus to be used as a flame retardant.

Barrier function of graphene for suppressing the smoke toxicity of polymer/black phosphorous nanocomposites with mechanism change

Recently, black phosphorous (BP) nanosheets as an emerging nanomaterial have presented significant fire safety improvement in polymer nanocomposites. However, as elemental phosphorus, fire safety improvement effect of BP nanosheets on polymer composites builds on the conversion of gaseous pyrolysis products into smoke particles, which inevitably promotes the formation and release of smoke particles. From the perspective of overall fire safety improvement, it is vital to simultaneously suppress the heat release and smoke production of polymer/BP composites. Herein, melamine-mediated graphene/black phosphorous nanohybrids (GNS/MA/BP) were fabricated through electrostatic-driving self-assembly process and introduced into polyether thermoplastic polyurethane (TPU). During combustion, the barrier function provided by thermally stable layered structure of graphene (GNS) enables more pyrolysis products of BP nanosheets to be kept within condensed phase and react with polymer matrix. Compared to pure TPU, the incorporated hierarchical nanostructure (GNS/MA/BP-2) decreases PHRR, THR, and total CO₂ release of TPU composite by 54.7%, 23.5%, and 32.5%, respectively. Beside, in contrast to TPU-BP composite, the release rate of toxic smoke and CO gas of TPU-GNS/MA/BP-2 composite are reduced by 46.7% and 49.4%. With barrier function of graphene, the heat and smoke release behavior of polymer/BP nanocomposites is effectively suppressed.

Reactive and Additive Modifications of Styrenic Polymers with Phosphorus-Containing Compounds and Their Effects on Fire Retardance

Polystyrene, despite its high flammability, is widely used as a thermal insulation material for buildings, for food packaging, in electrical and automotive industries, etc. A number of modification routes have been explored to improve the fire retardance and boost the thermal stability of commercially important styrene-based polymeric products. The earlier strategies mostly involved the use of halogenated fire retardants. Nowadays, these compounds are considered to be persistent pollutants that are hazardous to public and environmental health. Many well-known halogen-based fire retardants, regardless of their chemical structures and modes of action, have been withdrawn from built environments in the European Union, USA, and Canada. This had triggered a growing research interest in, and an industrial demand for, halogen-free alternatives, which not only will reduce the flammability but also address toxicity and bioaccumulation issues. Among the possible options, phosphorus-containing compounds have received greater attention due to their excellent fire-retarding efficiencies and environmentally friendly attributes. Numerous reports were also published on reactive and additive modifications of polystyrene in different forms, particularly in the last decade; hence, the current article aims to provide a critical review of these publications. The authors mainly intend to focus on the chemistries of phosphorous compounds, with the P atom being in different chemical environments, used either as reactive, or additive, fire retardants in styrene-based materials. The chemical pathways and possible mechanisms behind the fire retardance are discussed in this review.

Application of calcium montmorillonite on flame resistance, thermal stability and interfacial adhesion in polystyrene nanocomposites

To exploit the application of calcium montmorillonite (CaMt) and improve the flame resistance of polystyrene (PS), two kinds of long carbon chain quaternary ammonium bromides with different spatial effect (i.e., cetyltrimethyl ammonium bromide (CTAB) and didodecyl dimethyl ammonium bromide (DDAB)) were used to intercalate CaMt for yielding corresponding organic calcium montmorillonite (CaOMt). The PS nanocomposites containing CaOMt (PS/CaOMt) were prepared by melt blending method. The effects of CaOMt on flame resistance, thermal stability, tensile properties and interfacial adhesion of PS/CaOMt were investigated. The results showed that both CTAB and DDAB were intercalated into CaMt to get CaOMt with an exfoliated/intercalated structure, which could endue good interfacial adhesion and thermal stability for PS/CaOMt. All peak values of flame resistance parameters of PS/CaOMt decreased and corresponding combustion times were postponed obviously. Moreover, Young’s modulus of DDAB-intercalated PS/CaOMt was improved by 49.1% while its tensile strength kept at the same level as PS.

Self-Extinguishing Resin Transfer Molding Composites Using Non-Fire-Retardant Epoxy Resin

Introducing fire-retardant additives or building blocks into resins is a widely adopted method used for improving the fire retardancy of epoxy composites. However, the increase in viscosity and the presence of insoluble additives accompanied by resin modification remain challenges for resin transfer molding (RTM) processing. We developed a robust approach for fabricating self-extinguishing RTM composites using unmodified and flammable resins. To avoid the effects on resin fluidity and processing, we loaded the flame retardant into tackifiers instead of resins. We found that the halogen-free flame retardant, a microencapsulated red phosphorus (MRP) additive, was enriched on fabric surfaces, which endowed the composites with excellent fire retardancy. The composites showed a 79.2% increase in the limiting oxygen index, a 29.2% reduction in heat release during combustion, and could self-extinguish within two seconds after ignition. Almost no effect on the mechanical properties was observed. This approach is simple, inexpensive, and basically applicable to all resins for fabricating RTM composites. This approach adapts insoluble flame retardants to RTM processing. We envision that this approach could be extended to load other functions (radar absorbing, conductivity, etc.) into RTM composites, broadening the application of RTM processing in the field of advanced functional materials.

A Geometry Effect of Carbon Nanomaterials on Flame Retardancy and Mechanical Properties of Ethylene-Vinyl Acetate/Magnesium Hydroxide Composites

This study was aimed at investigating the effects of carbon nanomaterials with different geometries on improving the flame retardancy of magnesium hydroxide⁻filled ethylene-vinyl acetate (EM). The thermal stability and flame retardancy were studied by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 test, and cone calorimeter test (CCT). The in situ temperature monitoring system and interrupted combustion offered direct evidence to link flame retardancy and composite structure. Results demonstrated that carbon nanomaterials enhanced the thermal stability and fire safety of EM. The geometry of carbon nanomaterials played a key role in synergistic flame retardancy of EM, with the flame-retardant order of carbon nanotube > nanoscale carbon black > graphene. Based on an online temperature monitoring system and interrupted combustion test, one-dimensional carbon nanotube was more inclined to form the network structure synergistically with magnesium hydroxide in ethylene-vinyl acetate, which facilitated the generation of more continuous char structure during combustion. In parallel, the mechanical property was characterized by a tensile test and dynamic mechanical analysis (DMA). The incorporation of carbon nanomaterials presented a limited effect on the mechanical properties of the EM system.

In situ reactive zone with modified Mg(OH)2 for remediation of heavy metal polluted groundwater: Immobilization and interaction of Cr(III), Pb(II) and Cd(II)

Mg(OH)₂ dissolves slowly and can provide a long-term source of alkalinity, thus a promising alternative reagent for the in situ remediation of heavy metal polluted groundwater. However, the application of Mg(OH)₂ on in situ reactive zone (IRZ) for heavy metal polluted groundwater has never been investigated. In this study, the behaviors of heavy metals in a Mg(OH)₂ IRZ were monitored for 45d. The heavy metals show a sequential precipitation by modified Mg(OH)₂ due to the difference of K_sp. Column tests were conducted to investigate the temporal and spatial distribution of heavy metals in Mg(OH)₂ IRZ and evaluate the stabilization effect for multi-heavy metal polluted groundwater. Experimental results indicate that there exist interactions between different heavy metals, and their zoning distribution is attributed either to the competitive adsorption onto porous media (control column) or to the sequential precipitation of heavy metal ions (IRZ column). In contrast with the control column, heavy metal contaminated area in Mg(OH)₂ IRZ significantly shrinks. According to the chemical speciation analysis, when water containing Pb(II), Cd(II) and Cr(III) flows through Mg(OH)₂ IRZ, exchangeable fraction of total concentration significantly reduce and the proportion of carbonate and Fe/Mn oxides fraction increase, indicating the decrease of their mobility and toxicity.

Black Phosphorus Based Photocathodes in Wideband Bifacial Dye-Sensitized Solar Cells

Ultrasmall black phosphorus quantum dots (BPQDs) serve as the near-infrared light absorber and charge transfer layer in the photocathode of a bifacial n-type dye sensitized solar cell. Wideband light absorption and ≈20% enhancement in the light-to-electron efficiency are accomplished due to the fast carrier transfer and complementary light absorption by the BPQDs demonstrating that BP has large potential in photovoltaics.

Improved ceramifiable properties of EVA composites with whitened and capsulized red phosphorus (WCRP)

Phase separation between SGFs and phosphates promotes formation of cristobalite at high temperature, which leads to improvements in ceramifiable properties.