Expanded polystyrene foams containing ammonium polyphosphate and nano-zirconia with improved flame retardancy and mechanical properties

Expanded polystyrene (EPS) foams were flame retarded using ammonium polyphosphate (APP) and nano-zirconia (nano-ZrO₂) by means of phenolic resin as a binder. It is found that the incorporation of a small amount (5 phr) of nano-ZrO₂ into the APP flame-retarded EPS foams leads to 19% increase in flexural strength and 38% increase in compressive strength. Flame-retardant properties of the flame-retarded EPS foams were investigated by limiting oxygen index (LOI), UL-94 and cone calorimetry test (CCT). The LOI of the APP flame-retarded EPS foams in presence of nano-ZrO₂ is above 31%, and the UL 94 V-0 rating can be reached. The CCT test results indicate that the APP flame-retarded EPS foams containing nano-ZrO₂ have lower peak heat release rate, average effective heat of combustion and average specific extinction area. Moreover, thermal decomposition of the flame-retarded EPS foams was investigated by thermogravimetric analysis (TGA) and the TGA results illustrated clearly that the addition of nano-ZrO₂ into the APP flame-retarded EPS foams leads to an increase in the residual char yield. The reason for the increase is possibly because ZrO₂ may react during combustion process with pyrophosphoric acid produced from the thermal decomposition of APP to form zirconium pyrophosphate (ZrP₂O₇) confirmed by XRD studies of the char, which is helpful to improve the formation of the char. The XPS results showed that the ratio of oxidized carbons in the char increases with the presence of nano-ZrO₂.     

Near net-shape fabrication and properties of graphitic carbon foam with a continuous network of graphite nanosheets

A near net-shape graphitic carbon foam (GCF) with a continuous network of graphite nanosheets was prepared by direct carbonization of epoxy resin filled with nano-Al₂O₃. The effects of carbonization temperature on the properties of the resulting carbon foams were investigated by SEM, TEM, XRD, Raman, thermal conductivity and compression strength test. The results show that the as-prepared GCF can maintain well dimensional stability upon carbonization. The carbothermal reaction between the nano-Al₂O₃ and carbon foam matrix greatly influences the microstructure of carbon foam and promotes its growth of the continuous network of graphite nanosheets. In addition, the GCF prepared at 1700 °C possesses a compressive strength of 2.34 MPa with a bulk density of 0.19 g cm^-3, and meanwhile presents a high graphitization degree of 65.12% and a thermal conductivity of 2.02 W/mK. The continuous network of graphite nanosheets favors the enhancement of thermal conductivity of carbon foam and simultaneously prevents the decline of compressive strength further.     

A novel polyurethane prepolymer as toughening agent: Preparation,characterization, and its influence on mechanical and flame retardant properties of phenolic foam

A novel phosphorus‐ and silicon‐containing polyurethane prepolymer (PSPUP) was synthesized by the chemical reaction of phenyl dichlorophosphate with hydroxy‐terminated polydimethylsiloxane (HTPDMS) and subsequently with toluene‐2,4‐diisocyanate. The structure of PSPUP was confirmed by Fourier transform infrared spectroscopy and ¹H nuclear magnetic resonance. Afterward, a series of phenolic foams (PF) with different loadings of PSPUP toughening agent were prepared. The apparent density and scanning electron microscopy results showed that the addition of PSPUP can increase the apparent density of phenolic foam. The compressive, impact and friability test results showed that the incorporation of PSPUP into PF dramatically improved the compressive strength, impact strength, and reduced the pulverization ratio, indicating the excellent toughening effect of PSPUP. The limiting oxygen index of PSPUP modified phenolic foams remained a high value and the UL‐94 results showed all samples can pass V0 rating, indicating the modified foams still had good flame retardance. The thermal properties of the foams were investigated by thermogravimetric analysis under air atmosphere. Moreover, the thermal degradation behaviors of the PF and PSPUP/PF were investigated by real‐time Fourier transform infrared spectra. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Correlation of microstructure and mechanical properties of Al2O3-C bodies containing Nano-Al2O3 and Nano-TiO2 additives

Al₂O₃-C foam filters have been successfully used for steel and aluminum melts filtration. Improving the high-temperature mechanical properties enhances the capability and application of these filters for the filtration of large steel casting parts along with ingot casting or continuous casting of steel for long periods of time. In this study, adding nano-Al₂O₃ and/or nano-TiO₂ to the composition of Al₂O₃-C filters was investigated. Uniaxially pressed Al₂O₃-C samples containing additives in the range from 0 to 1.0 wt% of nano-oxides were prepared. The physical and mechanical properties, as well as microstructural analysis, were measured after sintering at 1600°C for 5 hours under a petroleum coke bed. The results showed that the presence of nano-Al₂O₃ particles in the composition led to an increase in the cold crushing strength (CCS) due to the formation of the Al₃CON phase which acts as a chemical bonding between Al₂O₃ particles and the carbonaceous matrix. On the other hand, the addition of 1.0 wt% of nano-TiO₂ in the composition caused an increase of 50% in the hot modulus of rupture (HMOR), attributed to the formation of columnar Al₂O₃ grains in the microstructure.     

Curing Characteristics,Morphological, Tensile and Thermal Properties of Bentonite-Filled Ethylene-Propylene-Diene Monomer (EPDM) Composites

Bentonite (Bt) with irregular shape and surface morphology was used as a new type of filler in EPDM. EPDM/Bt composites were prepared using a laboratory size two-roll mill by adding 0 to 70 phr Bt. The effects of Bt loading on curing characteristics, morphology, tensile and thermal properties of EPDM/Bt composite were studied. Scorch and curing time were decreased with 0 to 30 phr loading and increased subsequently at 50 and 70 phr. Tensile strength and elongation at break (E_b) were increased with increasing Bt loading from 0 to 50 phr and decreased at 70 phr, whereas the tensile modulus (M100%) shows an increasing trend with increasing Bt loading. Thermogravimetric analysis shows the enhancements of thermal properties with increasing Bt loading. Morphological studies of tensile fracture surfaces of EPDM/Bt composite proves good interaction between Bt particles and EPDM at 50 phr and formation of Bt agglomerates at 70 phr.     

Interfacial origin of enhanced energy density in SrTiO3-based nanocomposite films

SrTiO₃-based films doped with different Al-precursors were prepared by sol-gel methods and the dielectric strengths and leakage currents of the materials were investigated. The best performance was found in SrTiO₃ films doped with Al₂O₃ nanoparticles (nano-Al₂O₃). When 5 mol% of nano-Al₂O₃ was added to SrTiO₃ films with Al electrodes, the dielectric strength was enhanced to 506.9 MV/m compared with a value of 233.5 MV/m for SrTiO₃ films. The energy density of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films was 19.3 J/cm³, which was also far higher than that of the SrTiO₃ films (3.2 J/cm³). These results were attributed to interfacial anodic oxidation reactions, which were experimentally confirmed by cross-sectional transmission electron microscope studies and theoretically modelled based on Faraday's laws. The films with added nano-Al₂O₃ featured many conducting paths at the interfaces between the host phase and the guest nano-Al₂O₃, which promoted ion transport and contributed to the strong anodic oxidation reaction capability of the 5 mol% nano-Al₂O₃ doped SrTiO₃ films.     

Water absorption,residual mechanical and thermal properties of hydrothermally conditioned nano-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> enhanced glass fiber reinforced polymer composites

The durability of the nano-Al₂O₃ enhanced glass fiber reinforced polymer (GFRP) composites in hydrothermal environment is necessary for hydro/hygro thermal applications. The present investigation emphasizes the effect of nano-Al₂O₃ filler concentration on moisture absorption kinetics, residual mechanical and thermal properties of hydrothermally treated GFRP nano-composites. Nano-Al₂O₃ particles were mixed with epoxy matrix through temperature assisted magnetic stirrer and followed by ultrasonic treatment. It has been observed that, the addition of 0.1 wt% of nano-Al₂O₃ into the GFRP nano-composites reduces the moisture diffusion coefficient by 10%, as well as improves the flexural residual strength by 16% and interlaminar residual shear strength by 17% as compared to the neat epoxy GFRP composites. However, the glass transition temperature has not been improved by the addition of nano-Al₂O₃ filler. Weibull design parameters have been determined for dry and hydrothermally conditioned nano-composites. A good agreement between the experimental and the simulated stress–strain results has been observed. The interface failure mechanism has been evaluated by field emission scanning electron microscope to support the new findings.     

Mechanical and thermal properties of phenolic/glass fiber foam modified with phosphorus‐containing polyurethane prepolymer

Phenolic foam exhibits outstanding flame, smoke and toxicity properties, good insulation properties and low production costs. However, the brittleness and pulverization of phenolic foam have severely limited its application in many fields. In this study, a novel phosphorus‐containing polyurethane prepolymer (DOPU) modifier was firstly synthesized, and then the foaming formula and processing of toughening phenolic foam modified with DOPU and glass fiber were explored. The structure and reactive behavior of prepolymer and phenolic resin were investigated using Fourier transform infrared spectroscopy. The effects of DOPU and glass fiber on the apparent density, compressive strength, bending strength and water absorption were investigated. The results suggested that the apparent density, compressive strength and bending strength of modified phenolic foam tended to increase irregularly with increasing content of DOPU. The addition of DOPU led to lower water absorption of glass fiber‐filled foam. Thermal stability and flame retardancy were examined using thermogravimetric analysis and limiting oxygen index (LOI) tests. It was found that foam with 3% DOPU and 0.5% glass fiber added exhibited good thermal stability and high char yields. The LOI value of modified phenolic foams decreased with increasing DOPU content, but it still remained at 41.0% even if the amount of modifier loaded was 10 wt%. © 2012 Society of Chemical Industry     

Thermal and electrical properties of epoxy composites at high alumina loadings and various temperatures

Epoxy microcomposites with high loading micro alumina (Al₂O₃, 100–400 phr) were prepared by casting method and their thermal and electrical properties were studied at temperatures from 25 to 150 °C. The electric resistance device and the dielectric electrode device were designed to measure the electrical properties of the composites. Thermogravimetric analysis (TGA) and scanning electron microscopic proves the homodispersion of Al₂O₃ microparticles in epoxy. TGA indicates that the temperature of 5 % weight loss of epoxy/Al₂O₃ (100 phr) composite is 366 °C, 34 °C higher than that of pure epoxy. Differential scanning calorimetry shows that the glass transition temperature of epoxy/Al₂O₃ composite (400 phr) increases to 114.7 °C, 9.2 °C higher than that of pure epoxy. Thermal conductivity test demonstrated that with increasing Al₂O₃ content at 25 °C, thermal conductivity of epoxy/Al₂O₃ composites increased to 1.382 W/(m K) which is 5.62 times that of pure epoxy. Electrical tests demonstrate that by increasing of Al₂O₃ content and temperature, the electric resistance and dielectric properties of the composites show great dependencies on them. Resistivities of all the specimens decreased with the increasing of temperature owing to the increasing molecular mobility in the higher temperature. Resistivity of pure epoxy at 25 °C is about 9.56 × 10¹⁶ Ω cm, about one order of magnitude higher than that of pure epoxy at 125 °C and two orders of magnitude higher than that of pure epoxy at 150 °C. These results can give some advice to design formulations for practical applications in power apparatus.     

Properties of Ferrite-Filled Natural Rubber Composites

Nickel zinc ferrite (Ni-ZnFe₂O₄)-filled natural rubber (NR) composite was prepared at various loading of ferrite. The tensile properties included in this study were tensile strength, tensile modulus and elongation at break. The tensile strength and elongation at break of the composites increased up to 40 parts per hundred rubber (phr) of ferrite and then decreased at higher loading whereas the tensile modulus was increased gradually with increasing of ferrite loading. Scanning electron microscopy (SEM) was used to determine the wettability of filler in rubber matrix. From the observation, the increase of filler loading reduced the wettability of the filler. Thermal stability of the composites was conducted by using a thermogravimetry analyser (TGA). The incorporation of ferrite in NR composites enhanced the thermal stability of NR composites. The swelling test results indicate that the swelling percentage of the composites decreased by increasing of ferrite loading. The initial permeability, μ_i and quality factor, Q of magnetic properties of NR composites achieved maximum value at 60 phr of ferrite loading for frequency range between 5000–40,000 kHz. The maximum impedance, Z _max of the NR composites was at the highest value at 80 phr ferrite loading for frequency range between 200–800 MHz.     

Semi-rigid foams of calcium silicate (CaSiO3) embedded in natural rubber latex

Semi-rigid foams were prepared by NR latex with 0, 2, 5, 10, 20 and 30?phr CaSiO₃ added in a sulphur-curing system. The main composition of eggshell is made of 96.23%wt of CaCO₃ and 3.77%wt of other oxide compounds. The CaSiO₃ induced a spontaneous polarisation and reinforced the NR matrix due to ionic charge contents of Ca²⁺, Si⁴⁺ and O^2? in its structure. Furthermore, the CaSiO₃ was found to enhance the mechanical, thermal and physical properties of the composite foams. The suitable condition to prepare the semi-rigid composite foams was by adding 30?phr CaSiO₃ in the NR latex with the sulphur-curing system. The obtained bulk density, the relative composite foam density, the compressive strength, the contact angle with water, and acetone at the water to acetone ratio of 1:1 were found to be 1.2230?g?cm^?3, 0.3611, 588.10?kPa, 103.3°, 26.5° and 85.3°, respectively.     

Effect of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanofiller on ion conductivity,transmittance, and glass transition temperature of PEI:LiTFSI:PC:EC polymer electrolytes

In the present study, ion conductivity, optical properties, and glass transition temperatures are characterized for polymer electrolytes composed of poly(ethyleneimine) (PEI), lithium bis(trifluoromethane)sulfonylimide (LiTFSI) salt, propylene carbonate (PC), and ethylene carbonate (EC). It was doped with nanoceramic particles in different ratio (0–15 wt.%) to see the effect of ceramic particles. The salt concentration was fixed as 1.04 mol.kg^?1. Although valuable improvement in ion conductivity could not be achieved due to nano-Al₂O₃ fillers, ion conductivity results are placed between 10^?2 and 10^?4 S/cm. Differential scanning calorimetry (DSC) measurements and optical measurements of all electrolytes were performed between ?80 and 140 °C, in the wavelength range between 400 and 700 nm for sample with 80 μm thickness, respectively. The results showed that transmittance of electrolytes decreased monotonically for increasing Al₂O₃ contents. In particular, its transmittance value at 550 nm where human sight is at its greatest sensitivity went from 100% without nanoparticles to 50% for 15 wt% of Al₂O₃.     

A novel method for preparation of interconnected pore-gradient ceramic foams by gelcasting

A novel approach was introduced to prepare pore-gradient Al₂O₃ ceramic foams with association of gelcasting process and polymer sphere template. This approach allows the design of pore connectivity and gradient height of ceramic foams by the appropriate selection of sphere sizes and numbers. The limitation of ceramic foams fabricated by polymeric sponge process on sponge carrier can be resolved by this approach. Epispastic polystyrene (EPS) spheres with different sizes were employed to array ordered templates. Influence of solid content and dispersant on the viscosity of Al₂O₃ slurry was studied. EPS spheres modified by oxygen plasma to increase the hydrophilicity of surfaces and influence of pre-removal of EPS template on the integrity of networks were investigated. Results showed that 55?vol.% Al₂O₃ slurries with 0.5?wt% dispersant kept good fluidity for casting and permeability in template. Water contact angle of EPS surface decreased from 95.2° to 20°. Some defects in green bodies such as edge-delamination and micropores disappeared after surface modification. The perfect structure and morphology of the ceramic foams were ascribed to the pre-removal of template by solvent. The hierarchical pore structure was fabricated with EPS spheres of 2.1, 2.6 and 3.2?mm diameters. Porosity and compressive strength of the pore-gradient Al₂O₃ ceramic foam were 68.5% and 3.06?MPa at 1,500?°C, respectively.     

Using the Mass Method to Produce PVC/Clay Nanocomposite Foams: The Effect of Nano-clay and Foaming Conditions on Density and Cell size

Nanocomposite foams contain very fine cells because of the fillers in nano scale. Due to the limited size of the cells, the mechanical and physical properties of nanocomposite foams are improved compared to polymer foams. In this study PVC/clay nanocomposite foams containing various concentrations of nano-clay (1, 3 and 5 phr) were successfully prepared. The samples were placed under CO₂ gas pressure at 5 MPa, by immersing in glycerin bath at 60, 70, 80 °C and 20, 30, 40 s, respectively, to form foams. The density and the cell size as a factor of nano-clay content, foaming time and temperature were investigated using Archimedes method and scanning electron microscopy, respectively. The minimum density was obtained in the sample containing 1 phr nanoclay prepared at 80 °C and 40 s. The minimum cell size was related to the sample containing 5 phr nanoclay at 60 °C and 20 s.     

Preparation and properties of a novel flame retardant polyurethane quasi‐prepolymer for toughening phenolic foam

A novel phosphorus‐ and nitrogen‐containing polyurethane quasi‐prepolymer (PNPUQP) was synthesized and incorporated into phenolic foam (PF) in different ratios in order to improve the toughness. The structure of PNPUQP was confirmed by Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance (NMR). The effects of PNPUQP on the flame retardant properties, thermal stability and mechanical properties of modified PF were investigated. The results suggested that the addition of 3 wt % PNPUQP increased the toughness of PF and improved the flame retardancy. The investigation on the morphology of PF and modified PF by scanning electron microscope (SEM) certified the good toughness of the PNPUQP on PF. Additionally, the thermal properties of the foams were investigated by thermogravimetric analysis (TGA) under N₂ atmosphere. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42424.     

木质素基PF泡沫的发泡工艺与性能

利用低廉的木质素部分取代苯酚制备木质素基酚醛树脂(PF)泡沫,采用正交试验对木质素基PF发泡工艺进行了研究,研究了表面活性剂(吐温–80)用量、发泡剂(正戊烷)用量、发泡温度三个因素对木质素基PF泡沫性能的影响,从而优化发泡工艺。实验结果表明,对木质素基PF泡沫的极限氧指数(LOI)和导热系数影响最大的是发泡温度,而对于压缩强度影响最大的是表面活性剂用量。木质素基PF泡沫的最佳发泡工艺为:表面活性剂(吐温–80)用量为8%、发泡剂(正戊烷)用量为12%,发泡温度为90℃,所得泡沫具有较好的热稳定性,其LOI为39%,压缩强度为0.32 MPa,导热系数为0.025 W/(m·K)。     

Thermo-mechanical behaviors of epoxy resins reinforced with nano-Al2O3 particles

This study examined the thermo-mechanical behavior of epoxy resins/nano-Al₂O₃ composites including the curing behavior, thermal stability, dynamic mechanical properties and thermal mechanical properties. The DSC curve peak temperature of the composites was decreased by the addition of nano-Al₂O₃. The thermal stability of the composites was similar to that of the neat epoxy resins. Dynamic mechanical analysis (DMA) indicated the glass transition temperature of the composites to be approximately 11 °C higher than that of the neat epoxy resins. The coefficient of thermal expansion (CTE) of the composites decreased with increasing nano-Al₂O₃ content.     

Preparation and properties of nano ZnO toughed phenol–urea-formaldehyde foam

Urea formaldehyde (UF) and phenol formaldehyde (PF) foam possess outstanding flame-retardant properties, excellent insulation, and low thermal conductivity. These properties make them suitable for thermal insulation in buildings. However, the mechanical properties still need to be improved. In this study, orthogonal test was designed to optimize the level components of PF/UF composite foam first, then nano ZnO was added to the PF/UF composite foam to improve its toughness. The effects of nano ZnO on the morphology, apparent density, pulverization rate, thermal conductivity and thermal degradation property, flame retardancy, and mechanical properties of the ZnO/PF/UF nanocomposite foam were studied. The addition of nano ZnO improved the bending and compressive strength and decreased the pulverization rate of the composite foam significantly. The ZnO/PF/UF nanocomposite foam also presented better flame retardant properties than PF/UF composite foam. The largest oxygen index values of ZnO/PF/UF nanocomposite foam could reach 39.31%, while the thermal conductivity and the maximum rate of weight loss temperature were increased to 0.036 W/(m∙K) and 279°C, respectively. Moreover, ZnO/PF/UF nanocomposite foam showed low apparent density property (0.27 g/cm³).     

Effect of zinc oxide on properties of phenolic foams/halogen‐free flame retardant system

A halogen‐free flame retardant system consisting of ammonium polyphosphate (APP) as an acid source, blowing agent, pentaerythritol (PER) as a carbonific agent and zinc oxide (ZnO) as a synergistic agent, was used in this work to enhance flame retardancy of phenolic foams. ZnO was incorporated into flame retardant formulation at different concentrations to investigate the flammability of flame retardant composite phenolic foams (FRCPFs). The synergistic effects of ZnO on FRCPFs were evaluated by limited oxygen index (LOI), thermogravimetric analysis (TGA), cone calorimeter tests, and images of residues. Results showed that the flame retardant significantly increased the LOI of FRCPFs. Compared with PF, heat release rate (HRR), total heat release (THR), effective heat of combustion (EHC), production or yield of carbon monoxide (COP or COY) and Oxygen consumption (O₂C) of FRCPFs all remarkably decreased. However specific extinction area (SEA) and total smoke release (TSR) significantly increased, which agreed with the gas‐phase flame retardancy mechanism of the flame retardant system. The results indicated that FRCPFs have excellent fire‐retardant performance and less smoke release. And the bending and compression strength were decreased gradually with the increase of ZnO. The comprehensive properties of FRCPFs were better when the amount of ZnO was 1～1.5%. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42730.     

Effects of zinc borate loading on thermal stability,flammability, crystallization properties of magnesium oxide/(90/10) mLLDPE/(NR/ENR-50) blends

Effects of different zinc borate (ZB) loadings on thermal, flammability and crystallinity properties of blends of 10 % rubber (9/1) natural rubber (NR)/epoxidised natural rubber (ENR)/metallocene linear low density polyethylene/N,N-m-phenylenebismaleimide/MgO were investigated. Fourier transform infrared spectroscopy revealed that –C=O and –OH groups appeared while C–O–C and C=C groups disappeared in all blend samples. ZB increased the activation of HVA-2 by changing the reaction mechanism and increasing the concentration of the –C=O groups in the blends due to the peak at 1,714–1,718 cm^?1. The crystallinity of all blends was increased by ZB loading increase; therefore, it played the heterogeneous nucleation center and maximum crystallinity was observed at 6 phr ZB blend. The thermal stability of NR improved with increase of zinc borate loading and the highest thermal stability was determined for 8 phr ZB blend. Good compatibilization between the two rubbers (NR/ENR-50) was achieved in the presence of ZB, which was revealed by the presence of only one peak for their decomposition. The limiting oxygen index value of mLLDPE was decreased by two rubbers loading increase, while it was increased by ZB loading increase to provide fire barriers to protect flammable materials from thermal damage. It was concluded that ZB has a synergistic effect on the LOI values of flame retardant mLLDPE/rubber containing MgO.