Electrical conductivity and major mechanical and thermal properties of carbon nanotube‐filled polyurethane foams

The carbon nanotubes (CNTs)/rigid polyurethane (PU) foam composites with a low percolation threshold of ～ 1.2 wt % were prepared by constructing effective conductive paths with homogeneous dispersion of the CNTs in both the cell walls and struts of the PU foam. The conductive foam presented excellent electrical stability under various temperature fields, highlighting the potential applications for a long‐term use over a wide temperature range from 20 to 180°C. Compression measurements and dynamical mechanical analysis indicated 31% improvement in compression properties and 50% increase in storage modulus at room temperature in the presence of CNTs (2.0 wt %). Additionally, the incorporation of only 0.5 wt % CNTs induced remarkable thermal stabilization of the matrix, with the degradation temperature increasing from 450 to 499°C at the 50% weight loss. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New Polyurethane‐based magnetostrictive composites: Dynamical mechanical properties

Polyurethane‐based magnetostrictive composites containing between 30 and 70 wt% Terfenol‐D have been prepared in order to obtain better and tailored dynamic‐mechanical properties. The thermal and mechanical properties of polyurethanes with different chemical compositions were first analyzed to determine the most adequate one to prepare the composite materials. Calorimetric analysis indicates that the amount of crystallites increased in presence of Terfenol‐D. Dynamic‐mechanical properties have also been determined for the chosen composite, showing that the damping peak at glass transition increased by the addition of the magnetostrictive material while it became simultaneously broader. However, the storage modulus showed a drop with the increase in the filler content from 2200 MPa for pure polyurethane to 400 MPa for polyurethane with 60 %wt Terfenol‐D. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Polyurethane–cement‐based foams: Characterization and potential uses

The production of a new lightweight composite material based on polyurethane and Portland cement was investigated. The composite was obtained by the mixture of polyurethane foam precursors with different amounts of cement and water. To allow cement hydration, samples were aged in water and characterized through scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, and compressive testing. We studied the cement hydration reactions and the effect of the organic phase on hydration by determining the amount of chemically bonded water by calcination. The results showed that the amount of water affected the morphology and porosity of the foams and thereby affected the cement hydration reaction. Furthermore, the mechanical properties of the hybrid composite varied in a wide range, depending on the cement and water contents and on whether the hydrated cement particles behaved as fillers or were allowed to interact to form stronger inorganic networks within the polymeric matrix forming the bubble walls. The polyurethane–cement composite foams showed an increase in the stiffness and the yield strength. In addition, the ductile behavior of the polymeric foams was preserved, even at high filler loadings, due to the chemical compatibility between the hydroxyl groups of the polyol and the cement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polyurethane‐modified epoxy resin: Solventless preparation and properties

A polyurethane‐modified epoxy resin system with potential as an underfill material in electronic packaging and its preparation procedure were studied. The procedure enabled the practical incorporation of an aliphatic polyurethane precursor, synthesized from poly(ethylene glycol) and hexamethylene diisocyanate without a solvent, as a precrosslinking agent into a conventional epoxy resin. With a stoichiometric quantity of the polyurethane precursor added to the epoxy (ca. 5 phr), the polyurethane‐modified epoxy resin, mixed with methylene dianiline, exhibited a 36% reduction in the contact angle with the epoxy–amine surface, a 31% reduction in the cure onset temperature versus the control epoxy system, and a viscosity within the processable range. The resultant amine‐cured thermosets, meanwhile, exhibited enhanced thermal stability, flexural strength, storage modulus, and adhesion strength at the expense of a 5% increase in the coefficient of thermal expansion. Exceeding the stoichiometric quantity of the polyurethane precursor, however, reduced the thermal stability and modulus but further increased the coefficient of thermal expansion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Chemical vapour infiltration and mechanical properties of carbon open-cell foams

In order to improve their mechanical properties, carbon open-cell foams of two different pore sizes were infiltrated with pyrocarbon by chemical vapour deposition at reduced pressure and using pure propane as precursor. The optimal conditions in terms of deposition rate and uniformity in coating thickness, structure and anisotropy were first investigated. Foam specimens were infiltrated at various stages, with two pyrocarbons of distinct microtextures and their morphology, relative density and geometrical features were evaluated.Compressive crushing tests were conducted to determine the influence of the pore size, the pyrocarbon type and the relative density on the mechanical properties of the pyrocarbon-infiltrated foams. They retain their non-brittle and dissipating behaviour up to relative densities of 0.15. The stiffness, crushing strength and dissipated energy increase significantly with the relative density. The crushing behaviour of the pyrocarbon-foam specimens can be essentially explained using simple structural models and failure mechanisms, according to the Gibson & Ashby’s approach for brittle cellular solids.     

Polyurethane–polyaniline conducting graft copolymer with improved mechanical properties

The crosslinking effects on the mechanical and electrical properties of a conducting copolymer obtained by grafting polyaniline on a carboxylated polyurethane were investigated. The synthesis and characterization of the polyurethane–polyaniline copolymer (PEUAPAN) were previously reported. The crosslinking process was carried out by reacting ethylenediamine with those polyurethane residual carboxylic groups not involved in the amide binding to the conducting chains. The insoluble material obtained (PEUAPANc) shows a marked elastomeric feature, as evidenced in stress–strain and stress–relaxation measurements. Although the crosslinked graft copolymer conductivity is lower than that of the pristine material, its variation during deformation cycles is reversible because the chain relaxation and viscous flow phenomena are drastically suppressed by the crosslinks. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2516–2521, 2003     

Preparation and physico‐mechanical,thermal and acoustic properties of flexible polyurethane foams based on hydroxytelechelic natural rubber

Novel flexible polyurethane foams were successfully prepared from a renewable source, hydroxytelechelic natural rubber (HTNR) having different molecular weights (1000–3400 g mol^?1) and variation of epoxide contents (EHTNR, 0–35% epoxidation) by a one‐shot technique. The chemical and cell structures as well as physico‐mechanical, thermal, and acoustic properties were characterized and compared with commercial polyol analogs. The obtained HTNR based foams are open cell structures with cell dimensions between 0.38 and 0.47 mm. The HTNR1000 based foam exhibits better mechanical properties but lower elongation at break than those of commercial polyol analog. However, the HTNR3400 based foam shows the best elastic properties. In a series of EHTNR based foams, the tensile and compressive strengths show a tendency to increase with increasing epoxide content and amount of 1,4‐butanediol (BD). The HTNR based foams demonstrate better low temperature flexibility than that of the foam based on commercial polyol. Moreover, the HTNR based polyurethane foams was found to be an excellent absorber of acoustics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physico‐mechanical properties of NBR/CPVC blend vulcanizates and foams

Foams were prepared from acrylonitrile‐butadiene rubber (NBR)/chlorinated polyvinyl chloride (CPVC) blend compounds using a chemical blowing agent during compression molding. The effect of varying NBR/CPVC blend ratio and the time on the foams were investigated. The curing parameters showed that both the maximum torque and the difference between the maximum and minimum torque decreased with increase of CPVC content. The limiting oxygen index (LOI) of the blend vulcanizate increased with increase of CPVC content, reached up to 30% for the NBR/CPVC blend with blend ratio 50/50. The SEM micrographs of the NBR/CPVC blend indicate semi‐compatibility between the blend phases. The NBR/CPVC foams prepared using a chemical blowing agent, showed closed cell structures, which were uniformly distributed across the blend phases. The average cell sizes increased and foam density decreased with increase of CPVC content. Tensile strength and tear strength of both vulcanizates and foams increased with increase CPVC content. Hardness of the foams increased but resilience of the foams decreased with increase of CPVC content. Density, tensile strength, tear strength, and hardness of the foams increased but resilience decreased when the compression molding time of the foam was increased. J. VINYL ADDIT. TECHNOL., 25:182–188, 2019. © 2018 Society of Plastics Engineers     

Mica reinforced nylon‐6: Effect of coupling agents on mechanical,thermal, and dielectric properties

The effects of applying titanate (TYZOR® TPT) and silane (DYNASYLAN VTMO) coupling agents to wet ground muscovite mica in nylon‐6 composites are described. Nylon‐6 composites of 5–40 wt % filler loadings were compounded using an APV Baker twin‐screw extruder. Mica (25 wt %) brought about an increase in the Young's modulus, flexural strength, and flexural modulus but did not produce significant variations in tensile and impact strength. Hence different coupling agents were employed. It was observed that titanate coupling agent improved the tensile strength and the Young's modulus of the composites much while the impact properties were enhanced by the silane coupling agent. An attempt was made to use ?‐caprolactum in improving the interfacial adhesion of the filler and the matrix. It was observed that ?‐caprolactum improved the flexural modulus of the composites most. The effect of coupling agents on the dielectric strength, heat distortion temperature, and morphology were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4074–4081, 2006     

Mechanical and thermal properties of modified red mud‐reinforced phenolic foams

A new type of composite based on phenolic foams reinforced with red mud microparticles was prepared using a thermal foaming method. Red mud was ground into ultrafine particles with grain diameters ranging from 1 to 1.5 μm. Silane coupling agent γ‐ureidopropyltriethoxysilane was used to modify the red mud microparticles to improve particle dispersion and adhesion between the particles and the phenolic matrix. The effects of the modified red mud microparticles on the mechanical and thermal properties of the composite were investigated at weight ratios ranging from 0 to 21%. The phenolic foams incorporating 15 wt% of the filler exhibited the best integrated performance. In comparison with native phenolic foams, tensile strength and impact strength were increased by 81.8 and 82.3%, respectively. Furthermore, the addition of modified red mud microparticles to the phenolic foam significantly decreased its thermal conductivity while increasing its limiting oxygen index. A morphological analysis using scanning electron microscopy indicated that incorporation of the modified red mud microparticles into the foam produced relatively small and uniformly sized cells within the material, which indicated that the observed improvements in mechanical and thermal properties were primarily due to the chemical adhesion between the particles and the matrix and good dispersion of particles in the matrix. The reinforced foams described in this study can be used in a variety of applications in the field of heat insulation. © 2018 Society of Chemical Industry     

Intrinsically flame retarded foams based on melamine − formaldehyde condensates: thermal and mechanical properties

Two kinds of foam based on melamine ? formaldehyde (MF ) condensates (PVA /MF (PVA , polyvinyl alcohol), PVA /APTES /MF (APTES , 3‐triethoxysilylpropylamine)) were prepared by chemical modification. Pure MF foam has the serious disadvantage that it is very hard and brittle, breaks easily and crumbles when handled. After modification, PVA /MF and PVA /APTES /MF display excellent resilience. The structures of the foams were characterized by Fourier transform infrared (FTIR ), SEM and XRD . XRD data indicate that modifiers hinder the crystallization of MF , which might contribute to the improvement of resilience. Flame retardancy of the foams was characterized by limiting oxygen index testing, and the thermal degradation behavior was studied using TGA . The mode of flame retardant action is suggested by gaseous and solid phase analysis. TGA‐FTIR results demonstrate that the sublimation of the melamine of MF and foams based on MF occurs during thermal decomposition, which contributes to the high flame retardancy. © 2016 Society of Chemical Industry     

GMA‐based emulsion‐templated solid foams: Influence of co‐crosslinker on morphology and mechanical properties

Highly open porous polymer foams formed from high internal phase emulsions (polyHIPEs) are attracting significant interest because of their potential applications in many areas of advanced materials science. In this work, the influence of the crosslinker or co‐crosslinkers of different molecular weights on the morphology and mechanical properties of polyHIPEs containing glycidyl methacrylate (GMA) was studied. Several poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinkers were considered. The results show that introducing higher molecular weight crosslinkers into polyHIPEs produces a more open structure, with significantly increased compression strength and deformation at breakage. This eliminated the undesirable brittleness and chalkiness commonly found in polyHIPE materials. The Young's modulus of GMA‐based polyHIPEs containing 40% poly(ethylene glycol) dimethacrylate increased by 50% and the crush strength by 400% when compared with traditional GMA/ethylene glycol dimethylacrylate polyHIPEs. This improvement in mechanical properties is expected to improve the suitability of polyHIPEs for use in a wide range of applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46295.     

PVC‐clay nanocomposites: Preparation,thermal and mechanical properties

PVC‐clay nanocomposites were prepared by melt blending of the polymer with an organically modified clay, both in the presence and in the absence of di(2‐ethylhexyl) phthalate (DOP). The clay can serve as a plasticizer for PVC in the absence of DOP. The nanocomposites were characterized by using X‐ray diffraction and transmission electron microscopy, and the materials were found to be largely intercalated. Thermal properties were evaluated by using thermogravimetric analysis, and the thermal stability was determined to be variable, depending upon the amounts of clay and DOP that were present. The fraction of polymer that remained at 600°C was significantly reduced in the presence of the clay, a result indicating that the clay had an effect on the course of the degradation of the PVC. The tensile strength of the nanocomposites increased as the fraction of clay increased, and the addition of a small amount of clay increased the elongation, but when additional clay was added, the elongation decreased.     

Effects of expandable graphite and dimethyl methylphosphonate on mechanical,thermal, and flame‐retardant properties of flexible polyurethane foams

Expandable graphite (EG) and dimethyl methylphosphonate (DMMP) were added to polyurethane to form flame‐retardant high‐resilience flexible polyurethane foam (FPUF) in one‐step. The effects of EG and DMMP on cell morphology, mechanical properties, dynamic mechanical properties, thermal degradation, and flame‐retardant properties of FPUF were studied. The results indicated that adding proper amount EG or/and DMMP would not seriously damage cell morphology and mechanical properties. Dynamic mechanical analysis (DMA) demonstrated that there were two tan δ peaks attributed to soft and hard segment seperately and 15 pbw EG or/and 15 pbw DMMP could enhance damping property of FPUF. Thermogravimetric analysis–Fourier transform infrared spectroscopy (TGA–FTIR) results indicated that 15 pbw EG or 15 pbw DMMP could improve the thermal stability of the second degradation step but there were no synergistic effect between the two. DMMP made FPUF composites produce more toxic gases such as CO, however, EG displayed an opposite effect. Both EG and DMMP could effectively improve the flame retardant properties of FPUF, and there was synergistic effect between the two. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 916‐926, 2013     

Orientation‐dependent mechanical and thermal properties of plasma‐sprayed ceramics

Due to droplet‐based assembly, microstructure anisotropy is expected in atmospheric plasma‐sprayed coatings (APS), with lamellar separations and interfaces having critical effects on properties. Quantitative determination of these anisotropic properties is difficult due to geometric test constraints. This has been overcome in the literature through a variety of indirect, local, or modeled evaluation, however direct measurement on like‐dimensioned coatings is not available. In this work, 25‐mm thick ceramic coating variants, deposited at two different feed rates, were obtained from industry and macroscopic mechanical and thermal properties were evaluated in both in‐plane and out‐of‐plane orientations using identical specimen geometries. As expected, and confirming select past work, coating anisotropy has a direct influence on measured properties. The response of each property is microstructure‐dependent, highlighting the specific interaction: for instance, the fracture toughness is 120% higher in the through‐thickness orientation versus in‐plane after thermal aging, while the thermal conductivity was 24% lower in the through‐thickness. The former benefits from the lamellar interfaces that provide obstacles to crack propagation while the latter sees these interfaces as efficient phonon scatters. The results provide insights for design through robust property measurements and into operational mechanisms in this class of highly defected ceramics.     

Nanoclay‐reinforced syntactic foams: Flexure and thermal behavior

Syntactic foams containing 60 vol% of hollow glass microballoons in epoxy matrix are modified with untreated nanoclays using combined mechanical and ultrasonication methods. Effects of nanoclays on flexure and thermal behavior of syntactic foams are investigated by adding different amount of nanoclays in the range of 1–3% by weight. Microscopic examinations and physical property characterization are performed to determine the interactions among constituent materials and the void formation during fabrication. It is found that the syntactic foams with 2 wt% nanoclays show the highest improvement in flexural properties (∼42% strength and ∼18% modulus) and dynamic mechanical properties (∼30% storage modulus and ∼28% loss modulus) properties. Thermal decomposition temperature is found to be unaffected by the addition of nanoclays, whereas a continuous reduction in the coefficient of thermal expansion (CTE) is observed. An examination of failure surface indicates that the failure is initiated on the tension side of the flexure sample due to fracturing of microballoons. POLYM. COMPOS., 31:1332–1342, 2010. © 2009 Society of Plastics Engineers     

New alginate foams: Box‐Behnken design of their manufacturing; fire retardant and thermal insulating properties

A new method for preparing alginate foams with progressive release of copper in the presence of sodium lauryl sulfate (SLS, foaming agent) has been designed. Copper acts as the ionotropic gelling agent through the reaction of copper carbonate with gluconolactone. The process does not require freeze‐drying contrarily to the conventional method used for preparing macroporous alginate foams. The new materials investigated in this study have remarkable thermal properties, including thermal conductivity lower than 0.041 W m^?1 K^?1 and low heat release (below 2 kJ g^?1), which allows labeling these foams self‐extinguishing materials. An experimental design methodology, based on a Box‐Behnken plan with three parameters and three levels, is successfully used for evaluating the impact of the amounts of alginate, SLS, and copper carbonate on the productivity, apparent density, and shrinking at air‐drying. It yielded an optimization of the process for the manufacturing of light, and stable/rigid insulating and thermally stable materials. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45868.     

Synthesis and mechanical properties of lightweight hybrid geopolymer foams reinforced with carbon nanotubes

A lightweight hybrid geopolymer foams reinforced with carbon nanotubes (CNTs) was exploited by adding the CNTs into geopolymeric matrix through hydrogen peroxide method. The synergistic effects of nanotubes and foaming agent on the phase evolution, microstructure, and mechanical properties were investigated. After introduction of nanotubes, the geopolymer foams reinforced with CNTs (CNTs/KGP) still showed amorphous structure. Porosity of the foams increased with the H₂O₂ content and decreased with the increase in CNTs content. The addition of CNTs (1-9 wt%) in foams refined the distribution of pore size from 523 to 352 μm. Compression strength of the CNTs/KGP samples elevated with the increasing content of CNTs, which was contributed to the crack propagation and bridging of CNTs in foams. The CNTs/KGP foams with considerable porosity show potential applications in adsorption, filtration, membrane supports, other industries, etc     

Effect of organoclay content on the mechanical properties of ethylene‐vinyl acetate copolymer/ multi‐walled carbon nanotube/organoclay foams

The main objective of this study is to obtain ethylene‐vinyl acetate copolymer (EVA)/multi‐walled carbon nanotube (MWCNT)/organoclay foams with improved mechanical properties without increase of their density, compared with EVA/MWCNT foams. MWCNT content was fixed at 5 phr in this study. To achieve the objective, EVA was melt‐mixed with MWCNTs and organoclays in a bench kneader. And the obtained EVA/MWCNT/organoclay mixtures were mixed with chemical blowing agent and cross‐linking agent in a two roll‐mill. After being mixed in a two roll‐mill, the mixtures were put in a mold and the foams were obtained by compression‐molding. The effect of organoclay content on the mechanical properties and surface resistivity of EVA/MWCNT (5 phr)/organoclay foams was investigated. The addition of 1 phr organoclays to the EVA/MWCNT (5 phr) foams resulted in the improvement of tensile strength, 100% tensile modulus, tear strength, and compression set without increase of the density. However, further increase in content of organoclay (3 phr) leaded to a deterioration of mechanical properties. Therefore, determining the optimal content of organoclay was very important in order to achieve the main objective of this study. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers