Pulverized polyurethane foam particles reinforced rigid polyurethane foam and phenolic foam

Polyurethane consumption has been increasing in recent years, raising concerns about how to deal with the polymer waste. Post‐consumer rigid polyurethane foams or polyurethane foam scraps (PPU) ground into particles were utilized to strengthen mechanical properties of rigid polyurethane foam (PUF) and phenolic foam (PF). Viscosity of prepolymer with PUF was measured and PPU was well dispersed in prepolymer, as observed by optical microscope. Microstructures and morphologies of the reinforced foam were examined with scanning electron microscope (SEM) while cell diameter and density were measured by Scion Image software. Universal testing machine was employed to optimize compressive properties at various weight ratios of PPU. Both PUF and PF with 5 wt % PPU, respectively, exhibited considerable improvement in mechanical properties especially compressive property. The compressive modulus of PUF with 5 wt % PPU was 12.07 MPa, almost 20% higher than pure PUF while compressive strength of PF with 5 wt % PPU reached 0.48 MPa. The thermal stability of the reinforced foam was tested by thermal gravity analysis (TGA) and the result shows no obvious impact with PPU. The decomposition temperatures of PUF with PPU and PF with PPU were 280°C, because PPU has relatively weak thermal stability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39734.     

A study of the properties of carbon foam reinforced by clay

A novel carbon foam with high strength and very low thermal conductivity was prepared by thermal treating of coal tar based mesophase pitch mixed with montmorillonite clay. SEM observation showed that less micro-cracking appeared on the cell wall of foam by adding of clay-montmorillonite. Foam mechanical properties were improved and its thermal conductivity was markedly decreased. The compressive strengths were increased by 64%, 96% and 100% when the additive amounts of clay were 2%, 5% and 10% (wt%), respectively. Due to the high thermal insulation and lamellar structure of clay, the thermal conductivity of carbon foam decreases from 2 W/m K to 0.25 W/m K.     

Irradiation effects on graphite foam

The solid state reactor is an advanced reactor concept that takes advantage of newly developed materials with enhanced heat transfer characteristics to provide an inherently safe, self-regulated heat source. High conductivity graphite foam, developed and produced at Oak Ridge National Laboratory, is being evaluated as a candidate material for the core of basic heat source modules.Irradiation studies at the Oak Ridge National Laboratory High Flux Isotope Reactor were conducted to obtain preliminary data on the effects of neutron damage on the thermal properties and volume change behavior of the graphite foam as a function of neutron dose up to 2.6 displacements per atom at an irradiation temperature of ∼740 °C. Samples were characterized for dimensional and structural changes, and thermal transport as a function of dose. Following the initial effects of the irradiation, the samples were annealed at 1000 and 1200 °C and the thermal diffusivity measured as a function of temperature. A simple microstructural model was developed for graphite foam and, by coupling this model to the known single crystal and polycrystalline irradiation behavior of graphite; a mechanism by which the irradiation-induced volume and dimensional changes in graphite foam may be explained is postulated.     

Thermomechanical behavior of a graphite foam

The thermomechanical behavior of a graphite foam derived from pitch for use in thermal management was studied in air up to 150 °C. The damping capacity or loss tangent under flexure was 0.17 at 30 °C for the graphite foam, compared to 0.02 for conventional graphite (not a foam), 0.15 for flexible graphite and 0.22 for PTFE. The loss tangent of the graphite foam decreased with increasing temperature, whereas that of conventional graphite did not. The compressive strain of the graphite foam strongly depended on time, compressive stress and temperature. Due to creep at 30 °C, it reached 3% at 200 kPa, in contrast to 0.7% for conventional graphite. Thermal softening increased the compressive strain in the graphite foam upon heating and subsequent cooling, such that the thermal expansion phenomenon was overshadowed. In contrast, thermal softening was less in conventional graphite. The storage modulus of the graphite foam under flexure was lower than that of conventional graphite. Its fractional decrease with increasing temperature was more than that of conventional graphite.     

Nacre-like alumina composites reinforced by zirconia particles

Nacre-like alumina is a class of bio-inspired ceramic composite manufactured by field-assisted sintering of green bodies made primarily of alumina platelets with an anisotropic microstructure. Here we investigate the addition of zirconia particles to enhance the mechanical properties of the composite. The resulting structure is a nacre-like anisotropic structure which features deflection and reinforcement during crack propagation. Monoclinic zirconia has no impact on the mechanical properties of the composite while tetragonal zirconia improves its fracture resistance properties. Both types of zirconia seem to slow down grain growth during sintering. The addition of zirconia stabilised in the tetragonal phase is thus a good option to obtain a composite with a fine microstructure and higher mechanical properties than a standard nacre-like alumina, with a flexural strength of 626 ± 39 MPa and a crack initiation toughness of 6.1 ± 0.6 MPa.m^0.5.     

Graphite foam from pitch and expandable graphite

Graphite foams were prepared from a coal tar pitch that was partially converted into mesophase. Expandable graphite was used instead of an inert gas to “foam” the pitch. The resulting foam was subjected to a series of heat treatments with the objective of first crosslinking the pitch, and thereafter carbonizing and graphitizing the resulting foam. XRD confirmed that the graphitization at 2600 °C resulted in a highly graphitic material. The porosity of this foam derives from the loose packing of the vermicular exfoliated graphite particles together with their internal porosity. During the foaming process the pitch tends to coat the outside surface of the expanding graphite flakes. It also bonds them together. The graphite foam prepared with 5 wt.% expandable graphite had a bulk density of 0.249 g cm⁻³, a compressive strength of 0.46 MPa and a thermal conductivity of 21 W m⁻¹ K⁻¹. The specific thermal conductivity (thermal conductivity divided by the bulk density) of this low-density carbon foam was 0.084 W m² kg⁻¹ K⁻¹ which is considerably higher than that of copper metal (0.045 W m² kg⁻¹ K⁻¹) traditionally used in thermal management applications.     

Shape modification of graphite particles by rotational impact blending

To modify particle shape of graphite materials, a rotational impact-blending machine was utilized and the effect of operational conditions was investigated in relation to the size and shape of particles. It was also examined on the specific surface area and the crystal structure of particle surface.As a result, a particle shape index, defined as a ratio of short to long axis of an approximated ellipse by Fourier analysis, got large, whereas the particle size became small a bit, as the peripheral velocity of a rotor and the treatment time increased. The specific surface area more or less increased after treatments, and R value of Raman spectroscopy also increased with the treatment time as the lattice defects grow on the particle surface by surface milling or impact. Then, it temporarily decreased due to the generation of new surfaces with a few defects by volumetric grinding. Finally, two regression analyses were carried out on the relationship between the operational conditions and the particle properties like the diameter and the shape index so as to get proper particles.     

A review on the mechanical and electrical properties of graphite and modified graphite reinforced polymer composites

Carbon materials particularly in the form of sparkling diamonds have held mankind spellbound for centuries, and in its other forms, like coal and coke continue to serve mankind as a fuel material, like carbon black, carbon fibers, carbon nanofibers and carbon nanotubes meet requirements of reinforcing filler in several applications. All these various forms of carbon are possible because of the element's unique hybridization ability. Graphene (a single two-dimensional layer of carbon atoms bonded together in the hexagonal graphite lattice), the basic building block of graphite, is at the epicenter of present-day materials research because of its high values of Young's modulus, fracture strength, thermal conductivity, specific surface area and fascinating transport phenomena leading to its use in multifarious applications like energy storage materials, liquid crystal devices, mechanical resonators and polymer composites. In this review, we focus on graphite and describe its various modifications for use as modified fillers in polymer matrices for creating polymer-carbon nanocomposites.     

Carbon nanotube reinforced shape memory polyurethane foam

Multiwalled carbon nanotube (MWCNT)/polyurethane (PU) foams have been synthesized from polypropylene glycol and 2,4/2,6-toluene diisocyanate following the one-shot foaming method in the presence of water as the chemical blowing agent. The effects of CNT content on the performances of the foams have been analyzed in terms of reactivity, mechanical and dynamic mechanical properties, and shape memory properties of the foams. It was found that the cream time, rise time, tensile, and compressive strengths at room temperature, glassy and rubbery state moduli, glass-transitional temperature (T _g), and shape fixity and shape recovery increased with the addition and increasing amount of MWCNT.     

Multiscale analysis of composite material reinforced by randomly-dispersed particles

A multiscale analysis method is presented in which detailed information on the microscopic level is incorporated into macroscopic models capable of simulating damage evolution and ultimate failure. The composite considered is reinforced by randomly-dispersed particles, which reflects the statistical characteristics of real materials, such as cement-based materials. Specifically, a three-dimensional material body is decomposed into many unit cells. Each unit cell is reinforced by a cylindrical particle, the orientation of which is characterized by three Euler angles generated by the random number generator. Based on a detailed finite element analysis, the material properties of the representative volume element are obtained. As verification, the properties of the cylindrical particles are set equal to those of the matrix and the computed ‘composite’ properties reduce exactly to those of the ‘isotropic’ material, as expected. Through coordinate transformation, the effective material properties of each unit cell are calculated. The assembly of stiffness matrices of all unit cells leads to the stiffness matrix of the whole specimen. Under the simple tension loading condition, the initial damaged unit cell can be identified according to the von Mises yield criterion. The stiffness of the damaged unit cell will then be reduced to zero and it will cause stress redistribution and trigger further damage. It was found that the reinforcement is effective to mitigate and arrest the damage propagation, and therefore prolongs the material's lifetime. These results suggest that the hierarchical coupling approaches used here may be useful for material design and failure protection in composites.     

Modeling the principle physical parameters of graphite carbon foam

Graphite carbon foam, a mesophase, pitch-based material, portrays highly ordered topology structures which exhibit superior mechanical and thermal properties. Typical graphite carbon foam with dimensions 5 cm³, can have a surface area greater than 11 m², making it an excellent candidate for heat transfer applications. Accurate three dimensional modeling of carbon foams is necessary to study and predict their properties in simulation. This paper describes a computer algorithm for modeling POCO Foam® and similar carbon foams. The algorithm, written in MATLAB, captures the principle physical parameters of the carbon foam including bubble and pore diameter ranges and overall foam void percentage while retaining the random dispersal of spherical bubbles found in manufactured foams.     

Dielectric properties of exfoliated graphite reinforced flouroelastomer composites

Dielectric relaxation behavior of nano graphite reinforced flouroelastomer composites has been studied as a function of variation in filler in the frequency range of 0.01–10⁵ Hz. The effect of variation in filler loadings on the complex and real parts of impedance was distinctly visible which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The electric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The frequency dependence of AC conductivity has been investigated by using Percolation theory. The phenomenon of percolation in the composites has been discussed based on the measured changes in electric conductivity and morphology of composites at different concentrations of the filler. The percolation threshold as studied by DC conductivity occurred in the vicinity of 2.5–3.5 phr of filler loading. Scanning electron microscope microphotographs showed agglomeration of the filler above this concentration and formation of a continuous network structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

VARI成型泡沫夹层复合材料界面质量控制方法研究

采用本体树脂涂覆、胶膜和辅助织物粘贴在泡沫加工表面的方法分别改善胶接界面,解决了真空树脂浸渗工艺(VARI)制备的非屈曲碳纤维织物(NCF)/聚甲基丙烯胺(PMI)泡沫夹芯复合材料中泡沫与蒙皮的脱粘问题。结果表明,在相同VARI工艺参数条件下,采用890树脂涂覆的方法可以达到大约80%区域面积的良好粘接界面,对应的抗平拉强度提高了30%;同时胶膜和辅助织物粘贴方法则可达到接近100%改善胶接界面质量的效果,其对应的抗平拉强度则分别提高了76%和56%。     

The fatigue behavior of graphite fiber reinforced nylon

The fatigue lives of graphite fiber reinforced nylon composites were related uniquely to the tensile strengths of the materials. The distributions of tensile strength and fatigue life were measured and correlated with either two- or three-parameter Weibull functions. For a specific population, there existed a unique relationship between the two cumulative distributions. Thus, if the effect of an environmental variable on the distribution of strength is measured, the effect on the fatigue life can be estimated. It was also found that the mechanism of fatigue failure was influenced by the technique of fabrication. Compression molded materials failed through an isothermal, brittle mode of fracture, while injection molded materials failed in a ductile, thermal mode.     

Electrochemical production of graphite salts using a three-dimensional electrode of graphite particles

Electrochemical production of graphite salts by intercalation of pure sulfuric acid has been performed using a three-dimensional packed bed of graphite particles percolated by the electrolyte. The first stage compound of graphite bisulfate in which all the layers are intercalated (C₂₄⁺ HSO₄^?, 2.5 H₂SO₄) was detected by the colour change to blue and X-ray diffractometry. The influence of the most important parameters (operating intensity, packed bed height, electrolyte percolation, type of graphite particles and electrode potential) has been deduced from experimental results, which show that formation of the first stage compound occurs first at the top of the bed and moves progressively downwards. A modelization allows to determine first the reaction rate, which appears to be constant during operation, and second an electrochemical kinetics law of intercalation.     

A sandwich structure graphite block with excellent thermal and mechanical properties reinforced by in-situ grown carbon nanotubes

A graphite block derived from natural graphite flakes (NGF) has high thermal conductivity (TC) but poor mechanical properties. An effort to overcome this shortcoming was made by introducing carbon nanotubes (CNTs) onto the NGF surface by chemical vapor deposition (CVD). A block with a CNT–NGF–CNT sandwich structure was then prepared by hot-pressing at 2973 K. The new structure improved bend strength (increasing 52.2%) of the block, while maintaining the TC in the direction perpendicular to hot-pressing.