Compressive response of composite ceramic particle-reinforced polyurethane foam

Quasi-static and dynamic compressive tests are undertaken on the polyurethane (PU) foam and fumed silica reinforced polyurethane (PU/SiO₂) foam experimentally. The ceramic microspheres with varying mass fractions are adopted to mix with the PU/SiO₂ foam to fabricate the composite particle-reinforced foams. The effects of strain rate and particle mass fraction are discussed to identify and quantify the compressive response, energy-absorbing characteristic, and the associated mechanisms of the composite foams. The results show the initial collapse strength and plateau stress of the foams are improved significantly by reinforcing with the ceramic microsphere within 60 wt% at quasi-static compression. The rate sensitivity is observed on all the foams, but in different patterns due to the influence of ceramic microsphere. The compressive response affected by ceramic microsphere can be attributed to the particle cluster effect and stress wave propagation. Together with the deformation, the compressive characteristic experiences non-monotonic change from the low to high strain rates. The specific energy absorption (SEA) of the foam with 41 wt% ceramic microsphere show the largest magnitude at quasi-static compression. With the increasing strain rate, the ceramic reinforced foam exhibits superior energy absorption efficiency at high strain rates to that of the pure foams.     

Fingerprinting of bottle-grade poly(ethylene terephthalate) via matrix-assisted laser desorption/ionization mass spectrometry

Matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) has been shown to provide a valuable technique to study the thermomechanical degradation of poly(ethylene terephthalate) (PET). MALDI-MS has been tested to monitor both the admixture of post-consumption bottle-grade PET (PET_pc-btg) with virgin bottle-grade PET (PET_v-btg) and the thermomechanical degradation effects on the chemical properties of PET_v-btg. Principal component analysis of MALDI-MS data classify the samples into groups with specific features: a) PET-btg with intrinsic viscosities of 0.80 or 0.65-0.60 dL g⁻¹); b) processed or virgin PET with the same intrinsic viscosity; c) PET_v-btg from PET containing PET_pc-btg; and d) PET_v-btg from different manufacturers. MALDI-MS data is therefore able to reveal the quality of PET-btg resins preventing frauds and illegal use of recycled PET-btg.     

Study of syneresis in thin foam layers by creating pressure drops in the liquid phase

The method of creating pressure drops in liquid phases of foams (foam pressure drop technique) is employed to study the influence of Plateau-Gibbs border radius and surface viscosity on the velocity of liquid flows through foams. Sodium dodecyl sulfate-stabilized foams with Newtonian black films and foams stabilized with 9,6-ethoxylated nonylphenol (Triton X-10 0) are investigated. A method is developed for determining the velocities of nonstationary syneresis in local layers of foams. The measured flow velocities correspond to those calculated through the Nguyen equation for sodium dodecyl sulfate solution foams with constant curvature radii and for local layers of foams at curvature radii varying in the range of 20–80 fum and variable pressure drops. In Triton X-100 solution foams, experimentally measured syneresis velocities are higher than those calculated by the Lemlich and Nguyen equations but agree with the velocities calculated via the Koehler equation at permeability K ₀ ⁿ varying in the range of 0.5 × 10^-3-2 × 10^-3 under the assumption that the key factor is the hydrodynamic resistance in foam knots.     

Lignin as a Partial Polyol Replacement in Polyurethane Flexible Foam

This study was focused on evaluating the suitability of a wide range of lignins, a natural polymer isolated from different plant sources and chemical extractions, in replacing 20 wt.% of petroleum-based polyol in the formulation of PU flexible foams. The main goal was to investigate the effect of unmodified lignin incorporation on the foam’s structural, mechanical, and thermal properties. The hydroxyl contents of the commercial lignins were measured using phosphorus nuclear magnetic resonance (³¹P NMR) spectroscopy, molar mass distributions with gel permeation chromatography (GPC), and thermal properties with differential scanning calorimetry (DSC) techniques. The results showed that incorporating 20 wt.% lignin increased tensile, compression, tear propagation strengths, thermal stability, and the support factor of the developed PU flexible foams. Additionally, statistical analysis of the results showed that foam properties such as density and compression force deflection were positively correlated with lignin’s total hydroxyl content. Studying correlations between lignin properties and the performance of the developed lignin-based PU foams showed that lignins with low hydroxyl content, high flexibility (low T_g), and high solubility in the co-polyol are better candidates for partially substituting petroleum-based polyols in the formulation of flexible PU foams intended for the automotive applications.     

Mechanical properties of polyurethane foams modified by polymer-polyols

The mechanical properties of polyurethane foams based on tolylene diisocyanate and polyether modified by polymer-polyol, which is a styrene-acrylonitrile copolymer grafted onto polyol, were studied. The breaking stress, the hardness at 40% compression, the elongation at break, and the density depend on the amount of both the hard phase in the polymer-polyol and the polymer-polyol component in the polyurethane foam composition. Samples with a density of ～30 kg/m³ were prepared to have other mechanical properties practically identical to those of standard samples with a density of ～37–47 kg/m³.     

THE RESEARCH AND APPLICATION OF COLLOID AS LUBRICANTS

Foam generated by sparging of aqueous solutions of the block copolymers P85 (PEO₂₆‐PPO₃₉‐PEO₂₆), F88 (PEO₁₀₃‐PPO₄₀‐PEO₁₀₃), F127 (PEO₉₉‐PPO₆₅‐PEO₉₉), and L64 (PEO₁₃‐PPO₃₀‐PEO₁₃), has been characterized by foam volume measurements. Uniform wet foam formed, which, after drainage of the major part of the liquid, transformed to polyhedral dry foam. Conductance jumps across the foam column indicated that structural changes occur at a certain liquid fraction. The dry foams of P85 were less stable than those of F88 and F127. The latter copolymers showed similar foam stability over a period of one hour. The L64 foam was very unstable. It is suggested that the stability of the dry foams is determined by the resistance to rupture of the foam films. Foam stability is discussed in relation to earlier studies on surface rheology and to the thickness of thin foam films. A general relationship for all PEOx‐PPOy‐PEOx block copolymers between the dilatational modulus and the foam stability could not be found. However, the ability to form thick adsorption layers, accompanied by steric repulsive forces across foam films, appears to be a general foam‐stabilizing factor. Surface diffusion coefficients of a fluorescent probe in single‐block copolymers foam films are also reported for a brief discussion on Gibbs‐Marangoni stabilization.     

Fabrication‐controlled morphology of poly(butylene succinate) nano‐microcellular foams by supercritical CO2

Poly(butylene succinate) urethane ionomer (PBSUIs) foams with nano‐microcellular morphology were fabricated using supercritical CO₂ (sc‐CO₂) at different parameters. Effect of urethane ionic group (UIG) content (ranged from 1% to 5%) on the rheology and crystallization of PBSUIs were evaluated by intrinsic, dynamic rheological, X‐ray diffraction, and differential scanning calorimetry measurements. The results show that the complex viscosity of PBSUIs vastly improved, while their intrinsic viscosity and crystallinity decreased. They also evidenced that CO₂ promoted the formation of crystallites in the amorphous and increased the X_c of PBSU and PBSUIs foams. Scanning electron microscope was employed to explore the influences of UIG content and foaming parameters on the morphologies of PBSUIs microcellular foams, and it revealed that UIG content was the dominated factor. The cell size and cell densities of PBSUIs microcellular foams were smaller than 5.0 micrometers and higher than 1.5 × 10¹⁰ cells/cm³, respectively, even foamed at diverse variations of foam temperature and pressure. Interestingly, PBSUIs with 3% and 5% UIG content achieved microcellular foams in nano‐cells, high‐stretched elliptical shape. The mechanism was ascribed that these PBSUIs with high melt viscosities could retard the CO₂ bubbles to merge during the foam process and induce the cells to stretch and orient in depressururization direction. This study proposed a novel method for fabricating PBS nano‐microcellular foams.     

Studying the Suitability of Nineteen Lignins as Partial Polyol Replacement in Rigid Polyurethane/Polyisocyanurate Foam

In this study, nineteen unmodified lignins from various sources (hardwood, softwood, wheat straw, and corn stover) and isolation processes (kraft, soda, organosolv, sulfite, and enzymatic hydrolysis) were used to replace 30 wt.% of petroleum-based polyol in rigid polyurethane/polyisocyanurate (PUR/PIR) foam formulations. Lignin samples were characterized by measuring their ash content, hydroxyl content (Phosphorus Nuclear Magnetic Resonance Spectroscopy), impurities (Inductively Coupled Plasma), and pH. After foam formulation, properties of lignin-based foams were evaluated and compared with a control foam (with no lignin) via cell morphology, closed-cell content, compression strength, apparent density, thermal conductivity, and color analysis. Lignin-based foams passed all measured standard specifications required by ASTM International C1029-15 for type 1 rigid insulation foams, except for three foams. These three foams had poor compressive strengths, significantly larger cell sizes, darker color, lower closed-cell contents, and slower foaming times. The foam made with corn stover enzymatic hydrolysis lignin showed no significant difference from the control foam in terms of compressive strength and outperformed all other lignin-based foams due to its higher aliphatic and p-hydroxyphenyl hydroxyl contents. Lignin-based foams that passed all required performance testing were made with lignins having higher pH, potassium, sodium, calcium, magnesium, and aliphatic/p-hydroxyphenyl hydroxyl group contents than those that failed.     

X-ray computed tomography-based modeling of polymeric foams: The effect of finite element model size on the large strain response

A hybrid numerical–experimental approach is used to characterize the macroscopic mechanical behavior of polymeric foams. The method is based on microstructural characterization of foams with X-ray computed tomography (CT) and conversion of the data to finite element (FE) models. The 2D models are created from a 3D close-celled foam and subjected to compression loads. Since the large strain regime is explored, contact between elements is incorporated. It is shown that, for calculating the effective Young's modulus, a model consisting of at least 11²–12² cells in the model should be used, whereas for the large strain regime 12²–14² cells in the model are needed. Discretization had a significant influence on the results, where relatively coarse elements caused loss of connectivity in the cell walls and thickening of the cell walls. It is shown that at least three to four elements should be taken over the thickness of the cell walls for these structures. Finally, a good qualitative agreement is observed between the deformations found with the FE models and in situ compression experiments of an open-celled foam during X-ray CT. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1473–1482, 2010     

Competitive adsorption of -α-lysophosphatidylcholine/β-lactoglobulin mixtures at the interfaces of foams and foam lamellae

The stability of foams formed with the protein β-lactoglobulin as a function of increasing concentration of the lipid analogue -α-lysophosphatidylcholine were investigated using a microconductivity technique. The drainage, surface diffusion and thickness properties of thin liquid films (foam lamallae) were also studied using optical microscopy including epi-illumination, fluorescence recovery after photobleaching and film interferometry techniques. In addition, the surfactant binding properties of the protein were examined. The addition of small quantities of -α-lysophosphatidylcholine to β-lactoglobulin (molar ratio, R < 7:1) increased the foam stability, whereas a slightly higher concentration of surfactant in the mixture (R = 10) caused foam destabilisation. The explanation of these observations is based on changes in the composition and structure of the adsorbed interfacial layers of the thin films caused by competitive displacement of the protein by the surfactant.     

Constructing a bio-based flame retardant coating through co-depositing polydopamine and guanosine 5′-monophosphate disodium salt (GMP) for flexible polyurethane foam

The fire hazard posed by the inherent flammability and smoke toxicity of flexible polyurethane foam (FPUF) often necessitates the incorporation of flame retardants to meet stringent regulations. The development of environmentally friendly strategies to enhance the fire resistance of FPUF is of increasing importance and a significant amount of research has been devoted to this end. In this work, a bio-based coating was constructed by co-depositing polydopamine and guanosine 5′-monophosphate disodium salt (GMP) to increase the fire safety of FPUF. The coating significantly improved the flame retardancy of FPUF. The FPUF@PDA-GMP samples showed an LOI value of 24.5% with a self-extinguishing effect and exhibited reduced release of heat, smoke, CO, CO₂, and HCN due to their compact and strong char. The compressive strength at 70% strain of FPUF@PDA-GMP was 8 times higher than that of the control FPUF sample. The coating had a little negative effect on the resilience and improved its elongation at break. This investigation has provided a useful method for designing and producing high-performance foams.     

Layering Optimization of the SrFe0.9Ti0.1O3−δ–Ce0.8Sm0.2O1.9 Composite Cathode

Cathode thickness plays a major role in establishing an active area for an oxygen reduction reaction in energy converter devices, such as solid oxide fuel cells. In this work, we prepared SrFe_0.9Ti_0.1O_3−δ–Ce_0.8Sm_0.2O_1.9 composite cathodes with different layers (1×, 3×, 5×, 7×, and 9× layer). The microstructural and electrochemical performance of each cell was then explored through scanning electron microscopy and electrochemical impedance spectroscopy (EIS). EIS analysis showed that the area-specific resistance (ASR) decreased from 0.65 Ωcm² to 0.12 Ωcm² with the increase in the number of layers from a 1× to a 7×. However, the ASR started to slightly increase at the 9× layer to 2.95 Ωcm² due to a higher loss of electrode polarization resulting from insufficient gas diffusion and transport. Therefore, increasing the number of cathode layers could increase the performance of the cathode by enlarging the active area for the reaction up to the threshold point.     

Retention profile, kinetics and sequential determination of selenium(IV) and (VI) employing 4,4'-dichlorodithizone immobilized-polyurethane foams

Polyurethane foams (PUFs) loaded with the chromogenic reagent 4,4′-dichlorodithizone (Cl₂H₂D_Z) have been investigated for the quantitative retention, chemical speciation and sequential determination of traces of inorganic selenium(IV) and (VI) from aqueous media containing bromide ions. The retention profile of selenium(IV) onto the reagent loaded foam followed a dual-mode sorption mechanism involving both absorption related to “solvent extraction” and an added component for surface adsorption. The kinetics and thermodynamic characteristics of selenium(IV) uptake onto PUFs have been studied. The kinetics of selenium(IV) sorption onto PUFs was found fast, reached equilibrium in few minutes and followed a first-order rate constant in presence of bromide ions in the extraction media. The thermodynamic parameters, ΔH, ΔS and ΔG, indicated the exothermic and spontaneous nature of the sorption process. The sorption and the recovery percentages of inorganic selenium(IV) from fresh water by the proposed loaded foam columns were achieved quantitatively. The height equivalent to theoretical plate (HETP), the number of layers (N), breakthrough capacity and the critical capacity for selenium(IV) uptake onto Cl₂H₂D_Z loaded foams columns were found to be 1.3, 103, 8.6 and 7.2 mg/g, respectively. The method was successfully applied for the chemical speciation and sequential determination of inorganic selenium(IV) and/or (VI) species spiked to fresh and industrial wastewaters.     

Foaming in aqueous solutions of zwitterionic surfactant: Effects of oil and salts

This paper reports a study on the stability of foams generated from the aqueous solutions of the zwitterionic surfactant, N-Dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, in presence of NaCl, CaCl₂ and AlCl₃. The effect of oil (i.e. n-hexane) on foam was also studied. The surface and interfacial tensions were measured. These tensions and the CMC decreased upon salt addition, signifying an increased adsorption of the surfactant molecules at the interface. The quantity of salt required for reducing the surface tension and CMC was in the sequence: NaCl > CaCl₂ > AlCl₃. The salts had a pronounced effect on the foaming characteristics, i.e. they reduced the initial foam volume. The effectiveness of salts in reducing the foam stability followed the sequence: AlCl₃ > CaCl₂ > NaCl. However, the foam collapse rate was reduced in the presence of salt. The presence of oil decreased the foam volume and reduced its stability. The entering, bridging, and spreading coefficients were calculated, which explained the stability of foams in presence of oil.     

“Cooperative” Effects in the Destruction of Foam Column. Comparison of the Behavior of Polyhedral Two- and Three-Dimensional Foams

The kinetics of the destruction of polyhedral monolayer and bulk (three-dimensional) foams from solutions of nonionic surfactants and protein (lysozyme) was studied at various pressure drops Pand constant temperaturetand at various temperatures at P= const in order to elucidate the role of cooperative effects in a foam stability. It was established that lifetimes _p of monolayer and bulk foams prepared from surfactants at t= const decrease with an increase in pressure drop; however, the values of _p are always larger for the monolayer than for bulk foams. Avalanche-like destruction typical of foam prepared from surfactant solutions, which is observed at certain pressure drops in foam liquid phase and temperature, was not disclosed in the monolayer foam formed from the same solutions. For foams with structured adsorption layers (the foam from lysozyme solution), the lifetimes and character of destruction practically do not differ for monolayer and bulk foams. It was established that cooperative effect appears in very thin foam layers beginning with the bubble bilayer.     

Melamine,silica, and ionic liquid as a novel flame retardant for rigid polyurethane foams with enhanced flame retardancy and mechanical properties

Rigid polyurethane (PU) foams were successfully filled with different weight ratios of melamine (1 wt%, 5 wt%, 10 wt%), silica (0.1 wt%) and ionic liquid, 1-Ethyl-3-methylimidazolium chloride, [EMIM]Cl (0.3 wt%). The aim of this study was to improve the flame retardancy of PU foams and to develop the synergistic effect between melamine, silica and ionic liquid on the flame-retardant PU foams. The influence of different loadings of the fillers was examined. The results showed that in comparison with unfilled foam, all modified compositions are characterized by higher density (41–46 kg m⁻³), greater compression strength (134–148 kPa), and comparable thermal conductivity (0.023–0.026 W m⁻¹ K⁻¹). Moreover, the reaction to fire of the PU composites has been investigated by the cone calorimeter test. The results showed that the fire resistance of PU foams containing as little as 1 wt% of melamine is significantly improved. For example, the results from the cone calorimeter test showed that the incorporation of the melamine, silica and ionic liquid significantly reduced the peak of heat release rate (pHRR) by ca. 84% compared with that of unmodified PU foam. SEM results showed that incorporated fillers can form an intumescent char layer during combustion which improves the reaction to fire of the composite foams.     

The selective oxidation of ethanol to CO2 at Ptpc/Ir/Pt metallic multilayer nanostructured electrodes

In this work, Pt_pc/Ir/Pt metallic multilayer nanostructured electrodes were prepared. The composition and number of the constituent metal layers were varied and the number of Ir and Pt layers studied were: 1.5:1.5, 1.5:10, 10:1.5, 10:10 and 250:250 Ir and Pt monolayers. The ethanol electrooxidation reaction and its products was studied using electrochemical in situ FTIR technique and could be observed as a selective cleavage of the ethanol CC bond in acidic electrolyte. Neither acetaldehyde nor acetic acid IR band could be observed for ethanol electrooxidation at 1.5 V vs. RHE over Pt_pc/Ir₂₅₀/Pt₂₅₀ metallic multilayer electrodes. Also, the enhancement on CO₂ production over this electrode was more than six times the amount observed using the Pt_pc electrodes. Thus, the complete CC cleavage bond in ethanol molecule was observed, leading only CO₂ as reaction product.     

Trace analysis of chlorofluorocarbons/partially halogenated chlorofluorohydrocarbons (CFC/HCFC) in polymeric foams by headspace capillary gas chromatography with electron-capture detection or ion trap detection combined with preconcentration on a cold trap

Two headspace-methods were developed for the detection and determination of traces of CFC/HCFC in polymeric foams. These methods consist of capillary gas chromatography using an electron-capture detector (ECD method) or an ion trap detector combined with preconcentration on a cold trap (ITD method). Different CFC/HCFC such as R115, R22, R12, R142b, R114, R11, R141b and R113 were investigated in polyethylene and flexible polyurethane foams. Conditions for sample preparation (e.g. thermostating time and temperature) were optimized. Determination of the detection limits and quantitation of the amount of CFC/HCFC released from the foam were performed with gas standards prepared with the help of mass flow controllers. Quantitative analyses of the total amount of CFC/HCFC present in the foam were performed using multiple headspace extraction. Longterm studies were performed on the rate of release of some CFC/HCFC from the foams. Additionally a method for distinguishing a CFC/HCFC-contaminated foam from an old CFC/HCFC-blown foam is presented. Both methods can be used individually; however, best results are achieved by using the ECD method for screening and the ITD method for confirmation. This combination was used for routine analysis enforcing legal restrictions on the use of CFC/HCFC in foams.Abbreviations CFC chlorofluorocarbon - HCFC partially halogenated chlorofluorohydrocarbon - PUR polyurethane - PS polystyrene - PE polyethylene - MHE multiple headspace extraction - ECD electron capture detector - ITD ion trap detector - FID flame ionization detector - TCD thermal conductivity detector - MS mass spectrometry - WCOT wall coated, open tubular (column) - ppm parts per million (1:10⁶ v/v) - ppb parts per billion (1:10⁹ v/v) - ppt parts per trillion (1:10¹² v/v) - DL detection limit - RSD relative standard deviation - CO₂ carbon dioxide - R115 C₂ClF₅ - R22 CHClF₂ - R12 CCl₂F₂ - R142b C₂H₃ClF₂ - R114 C₂Cl₂F₄ - R11 CCl₃F - R141b C₂H₃ClF - R113 C₂Cl₃F₃     

Rigid polyurethane foams reinforced with disilanolisobutyl POSS: Synthesis and properties

This work reports the synthesis of rigid polyurethane (PU) foams modified by disilanolisobutyl polyhedral oligomeric silsesquioxane (DSIPOSS). This open‐cage nanostructure silsesquioxane has 2 hydroxyl groups and therefore can be chemically built directly in the PU backbone to form hybrid polyurethane‐POSS foam. Synthesis procedure using polymeric 4,4′‐diphenylmethane diisocyanate, polyetherol, and DSIPOSS has been elaborated, and the influence of POSS on the cell structure, closed cell content, apparent density, thermal conductivity, and compression strength of the rigid polyurethane composites has been evaluated. The hybrid composite foams containing 1.5 and 2.0 wt% DSIPOSS showed a reduced number of cells and an increased average area of foam cells in comparison with the unmodified PU, while the addition of 0.5wt% of DSIPOSS causes an increase in the number of cells of the foam as compared with the reference and thus a reduction in the average area of cells. X‐ray microtomography provided data on the porous structure of polyurethane hybrid materials, including reduction of the pore surface area. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy analysis revealed a good homogenization of DSIPOSS in polyurethane matrix. Thermogravimetric analysis results have shown that incorporation of POSS nanoparticles into PU foam does not significantly change the degradation process. The compressive strength of PUF‐POSS hybrids in the direction parallel and perpendicular to the direction of foam rise is greater than the strength of the reference foam already for the lowest DSIPOSS content.     

Foaming of trans‐polyisoprene using N2 as the blowing agent

Foaming of trans‐1,4‐polyisoprene (TPI) polymer was carried out through a batch process using nitrogen (N₂) as the blowing agent. TPI vulcanizates having varying crosslink densities were prepared by varying crosslinking agent content and curing time. The vulcanizates were then saturated with N₂ inside a pressure vessel at a pressure of 14 MPa and varying temperatures for 5 hours before effecting the foaming by rapidly quenching the pressure. The effects of varying the crosslinking agent content, silica filler content, and precuring time of the vulcanizates and the effects of varying the gas saturation temperature of foaming on the cell characteristics and physical properties of the foam prepared were investigated. The cells of the TPI foams had a spherical, closed structure. The density, expansion ratio, cell size, cell density, and tensile properties of the foams varied with varying crosslink density of the TPI vulcanizates as well as the saturation temperature of foaming. The important effects of crosslink density and saturation temperature on the N₂ solubility in the TPI matrix and thus on the foam expansion were discussed. The silica filler was found to be acting as a cell nucleating agent and reinforcing filler for the TPI foams.