Hydroxide Composites Research Articles

4,4−Diaminodiphenyl methane functionalized reduced graphene oxide/CoFe−layered double hydroxide obtained by in−situ hydrothermal as a high−performance absorber

The self−assembly among different two−dimensional materials could effectively improve the self−stacking effect and promote repeated reflection and refraction of incident electromagnetic wave (EMW). The polarization effect caused by the heterogeneous contact also helps the attenuation of EMW. In this study, the in−situ hydrothermal approach was used to effectively fabricate petal−like CoFe−layered double hydroxide sheets (CoFe−LDH) grown on reduced graphene oxide (RGO) functionalized by 4,4−diaminodiphenyl methane (DDM). The microwave absorption properties of DDM−functionalized RGO/CoFe−layered double hydroxide composites (DDM−RGO/LDH) were investigated. When the loading of DDM−RGO is 40.0 ​mg, the reflection loss reached −60.0 ​dB at 5.28 ​GHz, resulting in great EMW absorption performance. The effective absorption bandwidth at 2.00 ​mm is 5.28 ​GHz. The results show that DDM−RGO/LDH has a wide microwave absorption bandwidth and strong absorption capability, thus could be applied as an advanced EMW absorbing material.

Enhanced flame retardancy, smoke suppression, and acid resistance of polypropylene/magnesium hydroxide composite by expandable graphite and microencapsulated red phosphorus

AbstractLow flame retardant efficiency and poor acid resistance of filled polymer composites are two main drawbacks of magnesium hydroxide (MH) as a flame retardant (FR). To solve these problems, expandable graphite (EG) and microencapsulated red phosphorus (MRP) were introduced into polypropylene/magnesium hydroxide (PP/MH) composite by melt compounding. The obtained PP/MH/EG/MRP quadruple composite was studied regarding its fire behavior as well as acid resistance. Obvious flame retardant synergism among MH, EG, and MRP is found in PP, which diminishes the loading of FR from 63.0 to 37.5 wt% to obtain V‐0 rating in UL‐94 test and low smoke release. Compact intumescent char with high thermo‐oxidative stability was generated on composite surface, which plays a vital role in flame retardancy. The removal of MH by acid erosion on PP/MH/EG/MRP composite surface does not affect production of intumescent char and fire behavior of this composite. The composite displays good fire retardancy, smoke inhibition, and acid resistivity concurrently. This article renders an easy and cheap route to overcome the main faults of MH.

Preparation of lignin–MgAl layered double hydroxide composites by hydrothermal method using lignin as carrier and intercalation modifier agent

To improve the dispersion and crystallization of layered double hydroxides (LDHs), black liquor lignin was used as both the carrier and the intercalation modifier agent to prepare lignin–MgAl layered double hydroxide (Lignin-LDH) composites by a hydrothermal method. Fourier-transform infrared spectroscopy showed that the amount of NO3− inserted into the LDH interlayers decreased significantly with the increase of the lignin content. X-ray diffraction revealed that the crystallization of LDH in the Lignin-LDH composites was enhanced by the hydrothermal treatment, and the crystal structure of the LDH was more disordered with the increase of the lignin content. Thermogravimetric analysis showed that hydrothermal treatment and the addition of lignin were beneficial for enhancing the thermal stability of the Lignin-LDH composites. The basal spacing of the LDH was unchanged based on Bragg equation calculations. Based on the infrared and thermogravimetric analysis results, it can be inferred that the molecules of dissolved hydroxyl compounds were inserted into the LDH interlayers. Scanning electron microscopy showed that the hydrothermal treatment promoted the growth of LDH crystals, and the increase of the lignin amount resulted in the dispersion of LDH in lignin and a decrease of the LDH thickness.

Metal-organic framework derived nickel‑cobalt layered double hydroxide nanosheets cleverly constructed on interconnected nano-porous carbon for high-performance supercapacitors

The ingenious use of renewable and degradable biomass glucose materials to replace traditional organic synthetic materials can create huge economic benefits and potential ecological environmental protection. In this work, interconnected nano-porous carbon/nickel‑cobalt layered double hydroxide (INPC/NiCo-LDH) composites were successfully fabricated through calcination and solvothermal techniques, by first depositing 2-methylimidazole cobalt salt (ZIF-67) nanoparticles on the surface of INPC using glucose as the carbon source, followed by an in situ growth of NiCo-LDH nanosheets by controlling ion etching and co-deposition. The obtained INPC/NiCo-LDH composite exhibited high mass capacitance (1712 F g−1 at 0.5 A g−1), good rate capability and cycling performance (86.1 % after 5000 cycles). The assembled INPC/NiCo-LDH//INPC asymmetric supercapacitor (ASC) showed excellent capacitive performance (115.9 F g−1 at 0.5 A g−1) and high energy density (41.2 Wh kg−1 at 400 W kg−1). The three prefabricated all-solid-state INPC/NiCo-LDH//INPC ASCs linked in series could successfully light up a small light bulb, showing a potential application in real life.

Optimization of adsorption of methyl orange from aqueous solution by magnetic CoFe2O4/ZnAl-layered double hydroxide composite using response surface methodology

The CoFe2O4/ZnAl-layered double hydroxide (LDH) composite was successfully developed through a facile co-precipitation method, characterized, and applied as an effective adsorbent for the removal of methyl orange (MO) dye from aqueous solutions. The central composite design (CCD) of the response surface methodology (RSM) was employed to estimate and optimize process variables such as initial MO concentrations, solution pH, adsorbent dosage, and contact time. 98.878% adsorption efficiency was obtained at an initial concentration of 18.747 mg l−1 of MO, with an adsorbent dosage of 0.048 g, a solution pH of 2.770, and a contact time of 85.890 min. Analysis of variance (ANOVA) confirmed the significance of the predicted model (R2 = 0.9844). Kinetic and equilibrium studies indicated that the experimental data for MO adsorption were best described by pseudo-second-order kinetic and Langmuir models. The maximum monolayer adsorption capacity of the CoFe2O4/ZnAl-LDH for MO was 42.3 mg g−1.

Anchored growth of highly dispersed LDHs nanosheets on expanded graphite for fluoride adsorption properties and mechanism.

In this study, a new composite with layered double hydroxides (LDHs) anchored grown on expanded graphite (EG) interlayers was prepared by vacuum-assisted intercalation and hydrothermal method. Both sides of EG were completely covered by highly dispersed LDHs nanosheets and formed a sandwich-like structure. The unique structure made expanded graphite/layered double hydroxides (EG/LDHs) composites which had excellent F- adsorption performance. The adsorption performance of F- on EG/LDHs was evaluated, and the results indicated that the adsorption process was consistent with the pseudo-second-order kinetic model and the Langmuir model. Pseudo-second-order kinetic model indicated that the adsorption sites were the main factor in the adsorption process. Moreover, the maximum adsorption capacity (Qm) reached 63.21mg·g-1 at 30min at room temperature, which was better than most of the same type of adsorbents. The highly dispersed of LDHs anchored growth on EG overcame the disadvantage of aggregation, which exposed more adsorption sites and improved the removal efficiency of F-. In addition, the effects of pH, anion interference, different water quality, and regeneration tests on the EG/LDHs composites were also analyzed, showing that the composites have good stability.

Decoration of polystyrene with nanoparticles of cobalt hydroxide as new composites for the removal of Fe(iii) and methylene blue from industrial wastewater.

Effluent water from different industries is considered one of the most serious environmental pollutants due to its non-safe disposal. Therefore, proper treatment methods for such wastewater are strongly stimulated for its potential reuse in industries or agriculture. This study introduces a composite fabricated via doping of polystyrene with nanoparticles of cobalt hydroxide as a novel adsorbent for dye and heavy metal decontamination from wastewater. The adsorbent fabrication involves the preparation of polystyrene via high-internal phase emulation (HIPE) polymerization followed by its intercalation with particles of alkali cobalt. The chemical composition and structural properties of the synthesized composite were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and energy-dispersive X-ray spectroscopy (EDX). Moreover, scanning electron microscopy (SEM) and N2 adsorption-desorption surface area analysis were performed to identify the surface and morphological characteristics of the composite. Then, the ability of this structure toward the removal of methylene blue dye (MB) and heavy metal (iron iii) species from waste aqueous solutions was investigated. Successful elimination for both MB and Fe(iii) was achieved by the presented composite. Elevated adsorption capacities of 75.2 and 112.3 mg g-1, toward MB and Fe(iii) respectively, were detected for the presented polymer-metal hydroxide composite. The increased values of the composite are attributed to the presence of both organic and inorganic functional groups within its structure. Kinetic and isotherm studies for the removal of both cationic species revealed that adsorption processes fit the pseudo-second-order kinetic model and Langmuir isotherm model. Additionally, thermodynamics measurements indicated that the adsorption process of methylene blue and Fe ions is feasible, spontaneous, physisorption, and endothermic.

Efficient ZnCr LDH/monoclinic‐WO3 composites for Degradation of Tetracycline under Visible Light

AbstractRecently, efficient removal of antibiotics like Tetracycline (TC) from wastewater is emerging as a crucial problem. However, low adsorption capacity and high cost of photocatalysts limit their utility. In this context, monoclinic tungsten trioxide (WO3) loaded ZnCr layered double hydroxide (LDH) composites (ZnCr‐xWO3 x=10 and 20 %) are prepared by co‐precipitation method and characterized by several techniques viz. X‐Ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Raman, Photoluminescence (PL), Field‐Emission Scanning Electron Microscopy (FE‐SEM), Brunauer Emmett Teller (BET), Diffuse Reflectance Spectroscopy (DRS) and Dynamic Light Scattering (DLS). The XRD pattern confirms the formation of ZnCr LDH and its composites with monoclinic‐WO3. Bond vibrations and phase transitions were explored with the help of FTIR and Raman spectra. The BET analysis for ZnCr LDH and ZnCr‐10WO3 composite shows surface area as 27.439 m2/g and 47.691 m2/g. The higher photocatalytic performance of the composites formed is due to enhanced specific surface area and better separation efficiency of photo‐generated electrons and holes through conventional class II hetero junction between ZnCr LDH and monoclinic‐WO3. The kinetics studies performed shows better fit for pseudo first order reaction with maximum degradation efficiency and rate constant for ZnCr‐10WO3 (i. e., 86.7 % and 1.5×10−2 min−1).

Insights into the heavy metal adsorption and immobilization mechanisms of CaFe-layered double hydroxide corn straw biochar: Synthesis and application in a combined heavy metal-contaminated environment

Biochar is an emerging eco-friendly and high-efficiency heavy metal (HM) adsorbent that exhibits satisfactory HM remediation effects in both water and soil environments. However, few studies have investigated the mechanisms and application of biochar in the remediation of combined HM-contaminated environments. Therefore, in the present study, a novel corn straw biochar-loaded calcium-iron layered double hydroxide composite (CaFe-LDH@CSB) was synthesized via the coprecipitation method and applied as a remediation adsorbent to remove HMs in both water and soil environments. The results indicated that the HM adsorption mechanism of CaFe-LDH@CSB in the aquatic phase involved a chemical endothermic adsorption process of functional group-complexed monolayers, dominated by precipitation, ion exchange, complexation and π bond interactions. The maximum adsorption capacity for Cd(II), Pb(II), Zn(II) and Cu(II) in the aqueous phase reached 24.58, 240.96, 57.57 and 39.35 mg g−1, respectively. In addition, application of CaFe-LDH@CSB in the combined HM-contaminated soil treatment helped to increase the soil pH, which increased by 5.1–17.9% in low-contamination (LC) soil and by 7.0–13.9% in high-contamination (HC) soil. Moreover, application of CaFe-LDH@CSB effectively decreased the acid-soluble fraction of HMs and increased the HM residual fraction. The immobilization mechanism of CaFe-LDH@CSB in the soil was concluded to involve pore filling, functional group action and electrostatic interactions. Overall, this study provided a novel LDH biochar composite that can be effectively applied in the remediation of combined HM-contaminated water and soil environments.

Polyoxometalate‐Incorporated Host‐Guest Framework Derived Layered Double Hydroxide Composites for High‐Performance Hybrid Supercapacitor†

Comprehensive SummaryMetal organic frameworks have been employed as high‐performance layered double hydroxide (LDH) composite supercapacitor electrode materials but have shown unsatisfactory redox ability and stability. Herein, a host‐guest CuMo‐based polyoxometalate‐based metal organic framework (POMOF) with copious electrochemically active sites and strong electrochemical redox activities has been effectively coupled with POM‐incorporated CoNi‐LDH to develop a nanocomposite (NENU‐5@CoNi‐LDH) by a simple solvothermal method. The designed electrode shows a high specific capacity of 333.61 mAh·g–1 at 1 A·g–1. In addition, the novel hybrid symmetric supercapacitor NENU‐5@CoNi‐LDH/active carbon (AC) demonstrated a high energy density of 80.8 Wh·kg–1 at a power density of 750.7 W·kg–1. Interestingly, the nanocomposite of NENU‐5@CoNi‐LDH exhibits an outstanding capacitance retention of 79% after 5000 charge‐discharge cycles at 10 A·g–1. This work provides a new strategy and will be the backbone for future energy storage research.

N, F Codoped FeOOH Nanosheets with Intercalated Carbonate Anions Rich in Oxygen Defects for Enhanced Alkaline Electrocatalytic Water Splitting

Alkaline water splitting is a highly efficient and clean technology for hydrogen energy generation. However, in alkaline solutions, most catalysts suffer from extreme instability. Herein, a cross-nanostructured N, F, and CO32- codoped iron oxyhydroxide composite (N,F-FeO(OH)-CO3-NF) rich in oxygen defects is designed for water splitting in the alkaline solution. X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations show that the introduction of F and CO32- can induce electron redistribution around the active center Fe, accelerate the four-electron transfer process, and optimize the d-band center, thereby improving the efficiency and stability of HER and OER. In a 1 M KOH solution, N,F-FeO(OH)-CO3-NF only needs the overpotential of 248 mV for OER and the overpotential of 199 mV for HER to reach the current density of 10 mA·cm-2. Meanwhile, it can reach 100 mA·cm-2 current density at 1.55 V vs RHE and maintains a current density of 10 mA·cm-2 for 120 h in a two-electrode electrolytic water device. Compared with bulk hydroxides, the heteroatom and anion codoped composite hydroxides are more stable and have dual functions in the electrolyte solution. This is of great significance for designing a new stable water-splitting electrocatalyst.

Construction of the composites of nitrogen and sulfur-doped porous carbon and layered double hydroxides and the synergistic removal of heavy metal pollutants

• High dispersion and stable attachment of LDH on nitrogen and sulfur doped porous carbon (NSPC). • The synergistic effect of LDH and NSPC enhances the adsorption of heavy metal ions. • The adsorption mechanism was attributed to surface complexation. Layered double hydroxides (LDHs) composites (NSPC@LDH) were successfully prepared on nitrogen and sulfur-doped porous carbon (NSPC) by a simple co-precipitation method. The synergistic effect between the modified porous carbon and LDH enhanced its adsorption performance. Compared with pure LDH, the composite had a larger specific surface area (188.78 m 2 /g) and pore structure with a smaller crystallite size (4.56 nm). The porous carbon carrier effectively mitigated the aggregation effect of LDH. The maximum adsorption capacities of NSPC@LDH for Zn 2+ (100 ppm) and Cu 2+ (100 ppm) were 125.7 mg/g and 137.5 mg/g, respectively, which were 2.85 and 2.39 times the original LDH. The XRD and XPS studies of the adsorbent after adsorption revealed that surface complexation and physical adsorption played a dominant role in the removal of Zn 2+ and Cu 2+ , and the introduction of N, S heteroatoms provided more active centers for heavy metal ions. Moreover, after five desorption cycles, NSPC@LDH still exhibited high removal efficiency. The results indicated that the synthesized NSPC@LDH composites have great potential for removing Zn 2+ and Cu 2+ from aqueous solutions.

ZIF-67 In Situ Grown on Attapulgite: A Flame Retardant Synergist for Ethylene Vinyl Acetate/Magnesium Hydroxide Composites.

ZIF-67@ATP was prepared by the in situ growth of the zeolite imidazole frame (ZIF-67) on the surface of attapulgite (ATP). The structure and surface morphology of ZIF-67@ATP were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Different mass fractions of ATP and ZIF-67@ATP were added to ethylene vinyl acetate (EVA)/magnesium hydroxide (MH) composites as flame retardant synergists. The flame retardancy of EVA composites was evaluated by the limiting oxygen index (LOI) test, UL-94 test and cone calorimeter test. Composites containing 3 wt% of ZIF-67@ATP reached an LOI value of 43% and a V-0 rating in the UL-94 test, and the ignition time of the composite increased from 38 s to 56 s. The tensile strength and impact strength of the composites did not change significantly, but the elongation at break increased greatly. Typically, for composites containing 4 wt% of ZIF-67@ATP, the elongation at break of the composites increased from 69.5% to 522.2% compared to the samples without the synergist. This study provides novel insights into the application of attapulgite in the field of flame retardant polymer materials.

Exploration of metal-layered double hydroxide composite material for hybrid capacitor produced by facile and efficient electrodeposition process

Manganese cobaltite (MCO) with an empirical formula Mn2−x Co1+x O4 and cobalt-nickel layered double hydroxide (CN-LDH) composite were synthesized through a dual-step electrodeposition approach. This process commenced with cyclic voltammetry (CV) electrodeposition of manganese cobaltite (MCO) on nickel foam (NF) followed by annealing in air. The next step was the CV electrodeposition of CN-LDH on MCO. The enhanced composite material MCO-2.5 @CN-LDH yielded a remarkable specific capacity of 415.9 mAh g−1 at a specific current of 1 A g−1 in a three-electrode configuration using 2 M KOH electrolyte. The electrodeposition method is credited for producing these competitive results, since the method excludes polymeric binders which would make it necessary to include conductive additives to compensate for the increased resistivity in the electrode materials. This positive electrode and the activated carbon from cooked chicken bone waste (CCBW) as the negative electrode were assembled into hybrid supercapacitor device (MCO-2.5 @CN-LDH//CCBW) using the same electrolyte. The device generated a specific energy of 55.8 Wh kg−1 corresponding to a specific power of 940.4 W kg−1 at 1 A g−1. A device stability measurement at 10,000 galvanostatic charge-discharges (GCD) at 7 A g−1 produced a capacity retention of 81.6% and coulombic efficiency of 99.8%. Owing to these promising results, the fabricated materials proved to be capable to be employed as high specific energy supercapacitor.

Synergistic Effect of Cerium Oxide for Improving the Fire-Retardant, Mechanical and Ultraviolet-Blocking Properties of EVA/Magnesium Hydroxide Composites.

Rare earth oxide particles have received important attention in recent years, and due to the wide diversity of promising applications, the need for this kind of material is predicted to expand as the requirements to use the current resources become more demanding. In this work, cerium oxide (CeO2) was introduced into ethylene-vinyl acetate (EVA)/magnesium hydroxide (MDH) composites for enhancing the flame retardancy, mechanical properties and anti-ultraviolet aging performance. The target EVA/MDH/CeO2 composites were prepared by extrusion and injection molding, and the effects of the addition of the CeO2 were explored by thermogravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), limiting oxygen index (LOI), UL-94, cone calorimetry test, and anti-ultraviolet aging test. Typically, the incorporation of the CeO2 allows a significant increase of the elongation at break and Young’s modulus compared with EVA/MDH by 52.25% and 6.85%, respectively. The pHRR remarkably decreased from 490.6 kW/m2 for EVA/MDH to 354.4 kW/m2 for EVA/MDH/CeO2 composite. It was found that the CeO2 presents excellent synergism with MDH in the composites for the anti-UV properties in terms of mechanical properties preservation. Notably, the combination of CeO2 with MDH is a novel and simple method to improve the filler–polymer interaction and dispersion, which resulted in the improvement of the mechanical properties, flame retardancy and the anti-ultraviolet aging performance of the composites.

Enhancement of thermal stability and flame retardancy of ethylene vinyl acetate/magnesium hydroxide composite by carbon black

AbstractNano‐sized carbon black (CB) was introduced to ethylene vinyl acetate/magnesium hydroxide (EVA/MH) composite by melt compounding and the EVA/MH/CB ternary composites were investigated in terms of their thermal, flame retardant, mechanical, and electrical properties. The results indicate that the introduction of MH and CB has no impact on thermal degradation mechanism of EVA, but inhibits its degradation substantially. The presence of CB can hinder thermo‐oxidative degradation and increase thermal stability of the EVA/MH composite significantly. The addition of CB increases the flame‐retardant efficiency of MH effectively. The EVA/MH/CB composite with 3.6% CB can achieve V‐0 rating and its peak heat release rate is 23% smaller than that of the EVA/MH composite, which only achieves V‐2 rating in UL‐94 test. The improvement in flame retardancy happens in condensed phase. On the whole, the introduction of proper CB can enhance the thermal and flame‐retardant properties of EVA/MH composite considerably without damaging its mechanical and electrical performances. This work provides a simple and cost‐effective method to further increase the properties of EVA/MH composite for wire and cable industry.

Designed formation of 2D/2D hierarchical V2CTx MXene/NiV layered double hydroxide heterostructure with boosted electrochemical performance for asymmetric supercapacitors

Designing exceptional hierarchical structure of nanocomposites has far-reaching significance for improving the electrochemical performance. Herein, a new 2D/2D hierarchical structure of V2CTx MXene/NiV layered double hydroxide (V2CTx/NiV-LDH) composite was successfully constructed by in-situ synthesis method. The introduction of V2CTx MXene with high electrical conductivity can suppress the aggregation of NiV-LDH nanosheets and relieve the volume change, which significantly improves the electrical conductivity of the composites and provides more active sites. The synergistic effect of NiV-LDH and V2CTx effectively enhances the charge storage capacity. The specific capacitance of V2CTx/NiV-LDH-10 electrode at 1 A g−1 is 1658.19 F g−1. Meanwhile, V2CTx/NiV-LDH-10 exhibits excellent stability with 80.95 % capacity retention after 10,000 cycles. Moreover, the asymmetric supercapacitor based on V2CTx/NiV-LDH-10 (positive electrode) and AC (negative electrode) assembled achieves a maximum energy density of 54.19 Wh kg−1 at a power density of 750 W kg−1. The results show that V2CTx/NiV-LDH-10 is a promising electrode candidate material for green energy storage.

Facile and Controllable Synthesis of CuS@Ni-Co Layered Double Hydroxide Nanocages for Hybrid Supercapacitors.

The synthesis of battery-type electrode materials with hollow nanostructures for high-performance hybrid supercapacitors (HSCs) remains challenging. In this study, hollow CuS@Ni-Co layered double hydroxide (CuS-LDH) composites with distinguished compositions and structures are successfully synthesized by co-precipitation and the subsequent etching/ion-exchange reaction. CuS-LDH-10 with uniformly dispersed CuS prepared with the addition of 10 mg of CuS shows a unique hollow polyhedral structure constituted by loose nanosphere units, and these nanospheres are composed of interlaced fine nanosheets. The composite prepared with 30 mg of CuS addition (CuS-LDH-30) is composed of a hollow cubic morphology with vertically aligned nanosheets on the CuS shell. The CuS-LDH-10 and CuS-LDH-30 electrodes exhibit high specific capacity (765.1 and 659.6 C g–1 at 1 A g–1, respectively) and superior cycling performance. Additionally, the fabricated HSC delivers a prominent energy density of 52.7 Wh kg–1 at 804.5 W kg–1 and superior cycling performance of 87.9% capacity retention after 5000 cycles. Such work offers a practical and effortless route for synthesizing unique metal sulfide/hydroxide composite electrode materials with hollow structures for high-performance HSCs.

Role of expandable graphite on flame retardancy, smoke suppression, and acid resistance of polypropylene/magnesium hydroxide composites

AbstractIn this work, expandable graphite (EG) was introduced to the composite of polypropylene/magnesium hydroxide (PP/MH) by melt compounding, fire performance, thermal degradation behavior, and acid resistance of the PP/MH/EG composites were investigated. The results demonstrate that the flame retardant efficiency of MH is very low by itself and there is a noticeable synergism between MH and EG in PP. The addition of proper EG can enhance flame retardancy, smoke suppression, and acid resistance of the PP/MH composite significantly at the same time. Replacing 8.7 wt% MH with 8.7 wt% EG reduces the filling grade needed for V‐0 from 63 wt% MH to 56.5 wt% MH/EG mixture. The presence of EG on the composite surface hinders acid erosion of MH. There is no chemical reaction between MH and EG. Continuous intumescent char can be produced on the composite surface upon combustion, which is responsible for the much‐improved flame retardancy and smoke suppression, regardless of the presence of MH on the surface area.

Synthesis and flame retardant behavior of siloxane functionalized polyethylene

AbstractTo improve the flame retardancy of polyethyelene (PE), this work realized an effective in‐situ synthesis of siloxane functionalized PE via continuous process with two stages: in the first stage, reactive olefin monomers containing dichlorosilane group were designed and utilized in ethylene copolymerization catalyzed by Ziegler‐Natta catalyst; in the second stage, by injecting dimethylsilanediol (DMS) directly into the unterminated polymerization solution, siloxane was grafted onto PE side group via the reaction between the pendant chlorosilane groups on PE and hydroxyl on DMS. Owing to the carbonization effect of silica produced by siloxane combustion, the combustion residue of PE was significantly increased to 20.8 wt% in the TGA test after grafting 0.58 mol% DMS. The siloxane functionalized PE was then added into PE/magnesium hydroxide (MH) composites to investigate the materials burning behavior. By grafting 0.15 wt% siloxane, the limited oxygen index of PE was increased from 18% to 21% and that of PE/MH increased from 28% to 30%, indicating the flame retardancy of PE was improved with grafted siloxane modification. It was also found that the nanoscale silica in‐situ generated by the graft siloxane groups efficiently assisted the formation of a dense residual layer of MgO and amorphous carbon.