Synthesis of a Novel Flame Retardant and Its Synergistic Effect With a Phosphapheanthrene Flame Retardant in Polypropylene/Polyethylene Vinyl Acetate Blends

A novel flame retardant (NSiB) containing nitrogen, silicon and boron was synthesized through reacting of N-(β-aminoethyl)-γ-aminopropyl trimethoxy-silane (KH-792) and boric acid. The structure of NSiB was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy with energy dispersive spectrometry (SEM-EDS). The effects of NSiB on the flame retardancy and thermal behaviors of polypropylene (PP)/polyethylene vinyl acetate (EVA) blends were investigated by limiting oxygen index value (LOI), vertical burning tests (UL-94) and thermal gravimetric analysis tests (TGA). The results showed that the flame retardancy and thermal stability of PP/EVA blends were improved with the addition of NSiB. When 7.5 wt% DOPO (phosphaphenanthrene) and 0.5 wt% NSiB were incorporated, the LOI value of the PP/EVA blends was 26.9%, and the class V-0 of UL-94 test was passed, as compared to the LOI value of 22.4% and class V-2 of UL-94 test for 8.0 wt% DOPO only and 16.7% and fail, respectively, for the PP/EVA blends alone. The char structure observed by SEM indicated that the surface of the char for the PP/EVA/7.5 wt% DOPO/0.5 wt% NSiB blends had a denser and continuous char structure when compared with that of the PP/EVA blends and PP/EVA/8.0 wt% DOPO blends. These results indicated that there was a good synergistic effect for NSiB and DOPO.     

Synergistic Effect of Phosphorus-Containing Montmorillonite with Intumescent Flame Retardant in Polypropylene

Phosphorus-containing montmorillonite (P-MMT) was successfully prepared via intercalating resorcinol bis(diphenyl phosphate) (RDP) into montmorillonite (MMT) layers, and was utilized as a synergistic agent in the polypropylene/melamine pyrophosphate/pentaerythritol (PP/MPP/PER) intumescent flame retardant (IFR) system. The synergistic effect of P-MMT and IFR was investigated by dynamic mechanical analysis (DMA), thermogravimetry (TG), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), and scanning electron microscopy (SEM). It was found that P-MMT could significantly improve the thermostability and flame retardancy of the PP/IFR composite. When 2.0 wt% P-MMT replaced the same amount of IFR in the composite, both the onset decomposition temperature (T _onset) and the maximum-rate decomposition temperature (T _max) of the PP/IFR composite were increased by more than 14°C. Meanwhile, the LOI value was increased from 29.5% to 32.5%, the UL-94 rating was enhanced from V-1 to V-0, and the heat release rate (HRR), total heat release (THR), and mass lose rate (MLR) were decreased dramatically, which proved that P-MMT had a good synergistic effect with IFR in flame retardant PP.     

Effect of Polyborosiloxane on the Flame Retardancy and Thermal Degradation of Intumescent Flame Retardant Polypropylene

A novel synergistic flame retardant agent containing boron and silicon, namely polyborosiloxane (PBSil), was prepared via the condensation reaction of boric acid (BA), tetraethoxysilane (TEOS), and octamethyl cyclotetrasiloxane (OMCTS). The obtained PBSil was then combined with an intumescent flame retardant (IFR) to flame retard polypropylene (PP), and the effects of PBSil on the flame retardancy and thermal degradation of the PP/IFR composite were investigated. It was found that PBSil could improve the compatibility between the IFR and the PP matrix, thereby improving the mechanical properties of the composite. Compared with zinc borate, zeolite, and nano-silica, PBSil showed much better flame retardancy and smoke suppression in the PP/IFR composite. When the content of PBSil was 3.0 wt%, the limiting oxygen index (LOI) value of the flame retardant PP was increased from 29.0% to 35.0%, and the UL-94 rating was improved from V-1 to V-0 rating. Simultaneously, the heat release rate (HRR) and smoke production rate (SPR) of the composite were decreased dramatically. The thermogravimetric (TG) analysis, Fourier transform infrared (FTIR), and thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR) results showed that, PBSil could enhance the thermostability of the IFR, and promote the char formation. Furthermore, the compactness and thermostability of the intumescent char were significantly improved, contributing to the improvement of the flame retardancy of the composite.     

Preparation and Flammability of a Flame-Retardant Poly(Butyl Acrylate-Vinyl Acetate) System Based on Gemin-Surfactant Modified Montmorillonite and Ammonium Polyphosphate

Gemin-surfactant modified montmorillonite (G-MMT) was successfully prepared by an ion exchange reaction and characterized via Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The P(BA-VAc)/G-MMT emulsion was prepared via an in-situ polymerization method using potassium persulfate (K₂S₂O₈, KPS) as an initiator. Ammonium polyphosphate (APP) was introduced for obtaining P(BA-VAc)/APP/G-MMT flame-retardant latex with a constant total content of 15 wt% of APP and G-MMT in P(BA-VAc). The flame retardancy and thermal behavior of the latex films were investigated by limiting oxygen index (LOI), vertical burning test (UL-94) and thermal gravimetric analysis (TG/DTA). Compared with the P(BA-VAc)/APP composite, the LOI value of P(BA-VAc)/APP/G-MMT containing 0.5 wt% G-MMT at the same total additive loading increased to 29.1 from 20.0 and its UL-94 increased from no rating to V-0. Thermal gravimetric (TG) data showed that the amount of residues increased significantly with the loading of G-MMT. In addition, the LOI values increased with the increase in char residues. The morphology and microstructure of the residues generated during LOI testing were investigated by scanning electron microscopy (SEM). The outer surfaces of P(BA-VAc)/APP/G-MMT charred layers were more continuous and compact than those of P(BA-VAc)/APP.     

Pyridine-thermal synthesis and high catalytic activity of CeO2/CuO/CNT nanocomposites

Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO₂ composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO₂ composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO₂/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH⁻ ions around the surface of CNTs. Subsequently, the metal ions such as Ce³⁺ and Cu²⁺ in situ react with the OH⁻ ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO₂/CuO/CNT nanocomposites are obtained. The T₅₀ depicting the catalytic activity for CO oxidation over CeO₂/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO₂/CNT or CuO/CNT nanocomposites or CNTs.     

Effect of Phosphorus Compounds on Flame Retardancy and Thermal Degradation of Polycarbonate and Acrylonitrile–Butadiene–Styrene

Phosphorus flame retardants, bis(2,6-dimethylphenyl) phenyl phosphonate (BDMPP) and poly(bisphenol S phenyl phosphonate) (PBSPP), were synthesized and their structures were characterized with Fourier transform infrared spectroscopy, and ¹H and ³¹P nuclear magnetic resonance. The phosphorus compounds were used to impart flame retardancy to polycarbonate (PC) and acrylonitrile–butadiene–styrene (ABS). Combustion behaviors and thermal degradation properties of the systems were assayed by limiting oxygen index (LOI), vertical burning test (UL-94), and thermogravimetric analysis. PC/7 wt.% BDMPP and PC/5 wt.% PBSPP pass UL-94 V-0 rating; their LOI values were 32.7% and 33.6% respectively. ABS/35 wt.% BDMPP and ABS/30 wt.% PBSPP also pass the UL-94 V-0 rating and their LOI values were 28.9% and 28.3% respectively. Scanning electron microscopy revealed that the char properties had direct effects on flame retardancy.     

Synergistic Effect Between Organically Modified Montmorillonite and Ammonium Polyphosphate on Thermal and Flame-Retardant Properties of Poly(Butyl Acrylate/Vinyl Acetate) Copolymer Latex

Hexadecyl trimethyl ammonium bromide modified montmorillonite (1631-MMT) was successfully synthesized via an ion exchange reaction and characterized through Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Various poly(butyl acrylate/vinyl acetate) P(BA-VAc) copolymer P(BA-VAc)/1631-MMT emulsions were prepared via in-situ polymerization method using potassium persulphate (K₂S₂O₈, KPS) as an initiator. Ammonium polyphosphate (APP) was introduced for obtaining P(BA-VAc)/APP/1631-MMT flame-retardant latex. The flame retardancy and thermal behavior of the latex films were investigated through limiting oxygen index (LOI) and vertical burning test (UL-94) and thermo-gravimetric analysis (TGA/DTA [differential thermal analysis]) analysis. Compared with the P(BA-VAc)/APP composite, the LOI value of P(BA-VAc)/APP/1631-MMT sample was increased from 27.7 to 30.3 with a concentration of 1631-MMT 0.5 wt% in composition, and its UL-94 was raised to V-0 from no rating. TG date showed that the amount of residues increased significantly when 1631-MMT was added. The morphology and microstructure of the residues generated during LOI testing were investigated by scanning electron microscopy (SEM). The outer surface of the P(BA-VAc)/APP/1631-MMT charred layer was more continuous and compact than that of P(BA-VAc)/APP.     

Large scale intercalated growth of short aligned carbon nanotubes among vermiculite layers in a fluidized bed reactor

Short aligned carbon nanotubes (CNTs) were intercalated grown among vermiculite layers from ethylene using a simple fluidized bed chemical vapor deposition (CVD) process. The length of CNTs ranged from 0.5 to 1.5 μm after a synthesizing duration of 1-5 min at 650 °C. The as-grown CNTs vertically aligned to the vermiculite layers were with the mean outer and inner diameter of 6.7 and 3.7 nm, respectively. A CNT yield of 0.22 g/g_cat was obtained for a 5-min growth. Those indicated that the fluidized bed CVD was an effective way for mass production of short CNTs.     

Synthesis and Application of a Novel Charring Agent Poly(p-ethylene terephthalamide)

A novel charring agent poly(p-ethylene terephthalamide) (PETA) was synthesized by using terephthaloyl chloride and ethylenediamine through solution polycondensation at low temperature. Poly(p-ethylene terephthalamide) was used together with ammonium polyphosphate (APP) to prepare a novel intumescent flame retardant (IFR) for acrylonitrile–butadiene–styrene (ABS). The thermal degradation behavior and flame retardancy were investigated by thermogravimetric analysis and limiting oxygen index (LOI) tests, and the morphology and structures of residues generated in different conditions were investigated by scanning electron microscopy and Fourier transform infrared spectra. The results showed that PETA could be effective as a charring agent, the flame retardancy of ABS and the weight of residues improved greatly with the addition of IFR. When the content of APP was 25 wt% and PETA was 12.5 wt%, the LOI value of IFR–ABS system was found to be 33, and class V-0 of UL-94 test was passed. The microstructures observed by scanning electron microscope indicated that the charring agent (PETA) can promote formation of uniform and compact intumescent charred layers in IFR–ABS system after burning.     

A comparative study of thermionic emission from vertically grown carbon nanotubes and tungsten cathodes

Thermionic emission from vertically grown carbon nanotubes (CNTs) by water-assisted chemical vapor deposition (WA-CVD) is investigated. I-V characteristics of WA-CNT samples exhibit strong Schottky effect leading to field proportionality factor β ∼ 10⁴ cm⁻¹in contrast to β ∼ 200 cm⁻¹ for the bare tungsten substrate. Non-contact atomic force microscopy imaging of CNT samples show propensity of nanoasperities over a scale of micron size over which the tungsten surface is seen to be atomically smooth. The values of root mean-square roughness for CNTs and W were found to be 24.2 nm and 0.44 nm respectively. The Richardson-Dushman plots yield work function values of Φ_CNT ? 4.5 and Φ_W ? 4.3 eV. Current versus time data shows that CNT cathodes are fifteen times noisier than tungsten cathode presumably due to increased importance of individual atomic events on the sharp CNT tips of bristle like structures. Power spectral density of current exhibited 1/f^ξ behavior with ξ ? 1.5, and 2 for W and CNTs. The former suggests surface diffusion whereas the latter indicates adsorption/desorption of atomic/molecular species as a dominant mechanism of noise generation.     

Fabrication and characterization of magnetic Fe3O4-CNT composites

Carbon nanotubes (CNTs) decorated with magnetite nanoparticles on their external surface have been fabricated by in situ solvothermal method, which was conducted in benzene at 500 °C with ferrocene and CNTs as starting reagents. The as-prepared composites were characterized using XRD, FTIR, SEM and TEM. It has been found that the amount of magnetite nanoparticles deposited on the CNTs can be controlled by adjusting the initial mass ratio of ferrocene to CNTs. The Fe₃O₄-CNT composites display good ferromagnetic property at room temperature, with a saturation magnetization value (M_s) of 32.5 emu g⁻¹ and a coercivity (H_c) of 110 Oe.     

Mechanical and Flame Retardant Properties and Microstructure of Expandable Graphite/Silicone Rubber Composites

Flame-retardant expandable graphite (EG)/silicone rubber (SR) composites were prepared using nano-CaCO₃ particles as reinforcement filler. In addition to mechanical measurements, limited oxygen index (LOI), UL-94 and cone calorimeter tests (CCT), the thermal properties were tested by thermogravimetric analysis (TGA). The results showed that the content and particle size of the EG both had large effects on the flammability and mechanical properties of the EG/SR blends. The composites that contained 25 phr EG (50–80 mu) had excellent LOI values, 47–48, and achieved the UL-94 V-0 level while the pure SR sample had the LOI value of 25 and achieved the UL-94 V-2 level. The data obtained from the CCT indicated that the addition of EG decreased remarkably the heat release rate, smoke emission, and mass loss rate of the composites. SEM microphotographs of the EG/SR composites before and after combustion demonstrated that EG underwent a large volume expansion, and the multiporous char structure blocked heat transfer and protected the substrate from fire.     

Effect of SnO2 coating on the magnetic properties of nanocrystalline CuFe2O4

Nanocrystalline CuFe₂O₄ and CuFe₂O₄/xSnO₂ nanocomposites (x=0, 1, 5 wt%) have been successfully synthesized by one-pot reaction of urea-nitrate combustion method. The transmission electron microscope study reveals that the particle size of the as synthesized CuFe₂O₄ and CuFe₂O₄/5 wt%SnO₂ are 10 and 20 nm, respectively. The SnO₂ coating on the nanocrystalline CuFe₂O₄ was confirmed from HRTEM studies. The resultant products were sintered at 1100 °C and characterized by XRD and SQUID for compound formation and magnetic studies, respectively. The X-ray diffraction pattern shows the well-defined sharp peak that confirms the phase pure compound formation of tetragonal CuFe₂O₄. The zero field cooled (ZFC) and field cooled (FC) magnetization was performed using SQUID magnetometer from 2 to 350 K and the magnetic hysteresis measurement was carried out to study the magnetic properties of nanocomposites.     

Magnetoelectric characterization of xNi0.75Co0.25Fe2O4-(1−x)BiFeO3 nanocomposites

Magnetoelectric (ME) nanocomposites containing Ni_0.75Co_0.25Fe₂O₄-BiFeO₃ phases were prepared by citrate sol-gel process. X-ray diffraction (XRD) analysis showed phase formation of xNi_0.75Co_0.25Fe₂O₄-(1−x)BiFeO₃ (x=0.1, 0.2, 0.3 and 0.4) composites on heating at 700 °C. Transmission electron microscopy revealed the formation of powders of nano order size and the crystal size was found to vary from 30 to 85 nm. Dispersion in dielectric constant (ε) and dielectric loss (tan δ) in the low-frequency range have been observed. It is seen that nanocomposites exhibit strong magnetic properties and a large ME effect. On increasing Ni_0.75Co_0.25Fe₂O₄ contents in the nanocomposites, the saturation magnetization (M_S) and coercivity (H_C) increased after annealing at 700 °C. The large ME output in the nanocomposites exhibits strong dependence on magnetic bias and magnetic field frequency. The large value of ME output can be attributed to small grain size of ferrite phase of nanocomposite being prepared by citrate precursor process.     

Low-temperature sintering and microwave dielectric properties of Ca2Zn4Ti15O36 ceramics

The sintering behavior, microstructures, and microwave dielectric properties of Ca₂Zn₄Ti₁₅O₃₆ ceramics with B₂O₃ addition were investigated. The crystalline phases and microstructures of Ca₂Zn₄Ti₁₅O₃₆ ceramics with 0-10 wt% B₂O₃ addition were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The sintering temperature of Ca₂Zn₄Ti₁₅O₃₆ ceramic was lowered from 1170 to 930 °C by 10 wt% B₂O₃ addition. Ca₂Zn₄Ti₁₅O₃₆ ceramics with 8 wt% B₂O₃ addition sintered at 990 °C for 2 h exhibited good microwave dielectric properties, i.e., a quality factor (Qf) 11,400 GHz, a relative dielectric constant (ε_r) 41.5, and a temperature coefficient of resonant frequency (τ_f) 94.4 ppm/°C.     

On the thermal stability of Co2Z hexagonal ferrites for low-temperature ceramic cofiring technologies

Co₂Z hexaferrite Ba₃Co₂Fe₂₄O₄₁ was prepared by a mixed oxalate co-precipitation route and the standard ceramic technology. XRD studies show that at T<1300 °C different ferrite phases coexist with the M-type hexaferrite as majority phase between 1000 and 1100 °C and the Y-type ferrite at 1230 °C. The Z-type material has its stability interval between 1300 and 1350 °C. Both synthesis routes result in almost single-phase Z-type ferrites after calcination at 1330 °C, intermediate grinding and sintering at 1330 °C. The permeability of Co₂Z-type ferrite of about μ=20 is stable up to several 100 MHz, with maximum losses μ′′ around 700 MHz. Addition of 3 wt% Bi₂O₃ as sintering aid shifts the temperature of maximum shrinkage down to 950 °C and enables sintering of Z-type ferrite powders at 950 °C. However, the permeability is reduced to μ=3. It is shown here for the first time that Co₂Z ferrite is not stable under these conditions; partial thermal decomposition into other hexagonal ferrites is found by XRD studies. This is accompanied by a significant decrease of permeability. This shows that Co₂Z hexagonal ferrite is not suitable for the fabrication of multilayer inductors for high-frequency applications via the low-temperature ceramic cofiring technology since the material is not compatible with the typical process cofiring temperature of 950 °C.     

Short time synthesis of high quality carbon nanotubes with high rates by CVD of methane on continuously emerged iron nanoparticles

We report the variation of yield and quality of carbon nanotubes (CNTs) grown by chemical vapor deposition (CVD) of methane on iron oxide-MgO at 900-1000 °C for 1-60 min. The catalyst was prepared by impregnation of MgO powder with iron nitrate, dried, and calcined at 300 °C. As calcined and unreduced catalyst in quartz reactor was brought to the synthesis temperature in helium flow in a few minutes, and then the flow was switched to methane. The iron oxide was reduced to iron nanoparticles in methane, while the CNTs were growing.TEM micrographs, in accordance with Raman RBM peaks, indicate the formation of mostly single wall carbon nanotubes of about 1.0 nm size. High quality CNTs with I_G/I_D Raman peak ratio of 14.5 are formed in the first minute of CNTs synthesis with the highest rate. Both the rate and quality of CNTs degrades with increasing CNTs synthesis time. Also CNTs quality sharply declines with temperature in the range of 900-1000 °C, while the CNTs yield passes through a maximum at 950 °C. About the same CNTs lengths are formed for the whole range of the synthesis times. A model of continuous emergence of iron nanoparticle seeds for CNTs synthesis may explain the data. The data can also provide information for continuous production of CNTs in a fluidized bed reactor.     

Oxygen contaminants affecting on the electronic structures of the carbon nano tubes grown by rapid thermal chemical vapor deposition

Oxygen-related electronic structures of CNTs (carbon nanotubes) grown by rapid thermal chemical vapor deposition (RT-CVD) have been investigated by using partial electron yield near edge X-ray absorption spectroscopy (PEY-NEXAFS) and X-ray photoelectron spectroscopy (XPS). On the CNT surface with increased oxygen resulting from e-beam irradiation under the O₂ gas environment, C k-edge NEXAFS spectra showed an increase of the oxygen-related resonance peaks ranging from 287 to 289 eV whereas the sp² related peak at 285.4 eV was nearly unchanged. After the complete removal process of the oxygen atom on the surface by annealing the sample at 500 °C for 30 min, C K-edge spectra showed an abrupt decrease of the oxygen-related resonance peaks in 287-289 eV and an increase of the sp² related peak at 285.4 eV, indicating that the degree of crystallinity in the CNT sample was improved.     

The Flame Retardancy,Thermal Properties,and Degradation Mechanism of Zinc Alginate Films

The coordination structure, flame retardancy, thermal stabilities, and degradation mechanism of zinc alginate films were studied by Fourier transform infrared spectroscopy (FTIR), limiting oxygen index (LOI), vertical burning (UL-94), and thermogravimetric analysis (TGA) tests. The FTIR results showed that the structure of zinc alginate was correlated to its bidentate bridging coordination. The LOI (49.3) and UL-94 (V-0 rating) results indicated that zinc alginate was an inherent flame retardant material. The TG results showed that zinc alginate had better thermal stabilities than sodium alginate in the lower temperature zones; however, the thermal stabilities of zinc alginate were worse than those of sodium alginate at higher temperatures because of the decomposition of zinc oxalate formed in the degradation process of zinc alginate. Based on the TG results and FTIR of the residues at different temperatures, the effect of zinc ions on the degradation process of alginate was different from that of sodium ions. The zinc ions can catalyze alginate to form the residues and increase the amount of the residues, finally forming zinc oxide. Further, it could decrease the release of flammable gases and increase the flame retardancy of alginate.     

Magnetic phases in lanthanum-strontium manganite-cobaltite La1.25Sr0.75MnCoO6

Two methods—the solid-phase high-temperature (1300 °C) and the liquid-phase low-temperature (750 °C) routes—were used to synthesize the complex oxide La_1.25Sr_0.75MnCoO₆, which has the structure of rhombohedral perovskite and is characterized by a disordered distribution of Mn and Co in structural sites. It was found by means of X-ray absorption near edge spectroscopy (XANES) at the K-edge that mixed valence states of Co²⁺/Co³⁺ and Mn³⁺/Mn⁴⁺, exist in both phases. Measurements of dc magnetization and real (χ′) and imaginary (χ″) parts of the ac susceptibility showed that the magnetic properties of these oxides are determined by a ferromagnetic transition at T_C=217 K and a frequency-dependent transition at T_g<100 K. The high frequency dependence of T_g is indicative of the cluster-glass behavior of La_1.25Sr_0.75MnCoO₆ (7 5 0) at T<T_C within the ferromagnetic state.