Microcellular Polyurethane Research Articles

Sustainable castor oil-based microcellular polyurethane foam with desirable flame retardancy, vibration damping performance and recyclability

Microcellular polyurethane foam (MPUF) is extensively utilized as a vibration dampening material. However, its long chain and porous composition render it highly susceptible to combustion. Herein, we grafted the flame retardant 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO) onto the castor oil by a simple method to obtain a bio-based flame-retardant polyester polyol (COBH). Then, a bio-based flame-retardant MPUF was synthesized by one-pot synthesis of COBH, polyether polyol, and isocyanate. The target MPUF exhibits excellent flame retardancy, with the limiting oxygen index (LOI) sharply increasing from 19.3 % to 27.6 % and the peak of heat release rate (PHRR) decreasing significantly by 60.1 % as compared to MPUF prepared using unmodified castor oil. In addition, the MPUF shows good vibration dampening performance with a maximum loss factor of 5.2 and a maximum Sc-factor of 250. Moreover, the MPUF can be processed into MPU film by compression molding. The MPU film has adjustable mechanical properties and reusability. This study provides a feasible method for the preparation of flame-retardant, recyclable, bio-based MPUF with good vibration damping properties, thus expanding the practical applications of MPUF in the automotive, aerospace, and packaging and transportation industries.

Soundproofing properties of open- cell microcellular polyurethane foam containing styrene-grafted polyester polyol

Both soundproofing and mechanical strength present significant challenges in the context of sound-insulating materials. Herein, to take advantage of higher intermolecular interactions of ester groups, a soundproofing open-cell Microcellular Polyurethane Foam (MPUF) was developed using polymer-grafted polyester polyol (POP) and saturated polyester polyol. The POP was synthesized by grafting polystyrene on unsaturated polyester polyol (UNPES) in a saturated polyester polyol media. The amount of styrene monomer and UNPES were changed and the POP with optimum properties was selected. The successful synthesis of POP was approved by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance spectroscopy (1H NMR), and gel permeation chromatography (GPC). The spherical morphology of selected POP with a diameter of about 500 nm was confirmed by scanning electron microscopy (SEM) and dynamic light scattering (DLS) analysis. MPUFs containing different amounts of POP (10, 30, 50, and 100 %) as polyester polyol parts were prepared. It was found that mechanical properties including tensile strength: 3500 KPa, elongation at break%: 350% and soundproofing properties with acoustic activity of 0.72 were obtained when the POP content of the MPUF was fixed at 30%. The cell-opening behavior of POP in polyester-based MPUF was studied using SEM. It was found that the average of the open cells’ size and their population were increased as the POP content increased. Such MPUFs can be effective in successful mechanical and acoustic damping in the automotive industry.

Statistical characterization of microcellular polyurethane foams microstructure based on 2D and 3D image analysis

This paper presents protocols developed to quantitatively characterize the cellular microstructure of microcellular polyurethane foams, from scanning electron microscopy (2D) and X-ray micro-computed tomography (2D and 3D) data. The objectives are to provide, for both techniques: (i) a detailed description of the analysis steps based on open source Python algorithms; (ii) a method for automatic, robust and objective detection of the cells to limit user’s biases; (iii) a statistical description of fraction, size, shape and spatial distribution of cells. The study considers 12 samples with densities ranging from about 400 to 600 kg m−3 and pore sizes from a few micrometers to several hundred micrometers. In addition, the database obtained is used to investigate the reliability of 2D measurements to describe the cellular microstructure statistics.

Preparation of nanocapsules of palmitic acid with silica shells and their use as a phase change material within microcellular polyurethane foams

A new nanoencapsulated phase change material (PCM) filled polyurethane microcellular foams is reported in this work. Palmitic acid nanocapsules with silica shells (PA@SiO2) is a well-known phase change material synthesized by the sol-gel process are loaded at selected weight ratios into microcellular polyurethane foam. FT-IR spectra revealed successful PA@SiO2 nanocapsules formation and FE-SEM images showed successful core-shell formation with spherical shapes with a mean diameter approximately 350 nm. TGA thermograms showed superior heat resistivity of prepared PCM in comparison with pristine palmitic acid at the final degradation temperature. DSC thermograms showed the heat storage potential of prepared nanoencapsulated PCM as well as corresponding polyurethane nanocomposites. The polyurethane nanocomposites characterized by FT-IR, TGA, FE-SEM as well as DSC methods and data interpreted in detail in order to evaluate the thermal storage capabilities of newly developed nanocomposites.

Fabrication and Characterization of Microcellular Polyurethane Sisal Biocomposites.

In this study, microcellular polyurethane (PU)-natural fiber (NF) biocomposites were fabricated. Polyurethanes based on castor oil and PMDI were synthesized with varying volume ratios of sisal fiber. The effect of natural fiber treatment using water and alkaline solution (1.5% NaOH) and load effect were investigated. Biocomposites were mechanically and physically investigated using tensile, viscoelasticity, and water absorption tests. The interfacial adhesion between PU and sisal fiber was studied using SEM. Short NF loads (3%) showed a significant improvement in the mechanical properties of the PU-sisal composite such as modulus of elasticity, yield and tensile strength up to 133%, 14.35 % and 36.7% respectively. Viscoelastic measurements showed that the composites exhibit an elastic trend as the real compliance (J’) values were higher than those of the imaginary compliance (J’’). Increasing NF loads resulted in a decrease of J’. Applying variable temperatures (120–80 °C) caused an increase in the stiffness at different frequencies.

Design and numerical analysis of syntactic hybrid foam for superior sound absorption

A microcellular polyurethane (PU) foam is widely used as a sound absorber to eliminate noise by utilizing its complex internal structure. The most intriguing issue for the sound absorbing PU foam is how to reduce density while maintaining or improving the performance. In this study, novel syntactic hybrid foams (SHFs) were designed and suggested by embedding hollow microbeads in the open cell PU foam. Numerical simulation was carried out to predict sound absorbing performance by employing periodic unit cells representing microstructures of a bare foam (BF) and SHFs. It was found from the simulation that the sound damping performance of SHFs was improved significantly by a detoured sound propagating path provoked by the embedded microbeads. The predicted sound absorption performance of SHFs was even superior to that of the bare foam with double density. Furthermore, heat transfer and structural analysis showed that SHFs can provide high thermal insulation and mechanical robustness. It is anticipated that the hybrid microstructure designed in this study will be utilized to develop advanced sound absorbing materials with outstanding sound absorption, thermal insulation, and mechanical stiffness.

Effect of Polyols on the Morphology and Properties of 1,4-Phenylene Diisocyanate-Based Microcellular Polyurethane Elastomers

Effect of Polyols on the Morphology and Properties of 1,4-Phenylene Diisocyanate-Based Microcellular Polyurethane Elastomers

Electroless copper plating on microcellular polyurethane foam

In order to obtain substrates with good conductive foam for high porosity foam metal materials used in the metal electrodes, the technique of electroless copper plating on the microcellular polyurethane foam with pore size of 0.3 mm was investigated. The main factors affecting the deposition rate such as the solution composition, temperature, pH value and adding ultrasonic were explored. The results show that the optimum process conditions are CuSO 4 16 g/L, HCHO 5 mL/L, NaKC 4H 4O 6 30 g/L, Na 2EDTA 20 g/L, K 4Fe(CN) 6 25 mg/L, pH value of 12.5–13.0 and temperature of 40–50 °C. Under these technical conditions, the process has excellent bath stability. Adding ultrasonic on the process can elevate the deposition rate of copper by 20%–30%. The foam metal material with a porosity of 92.2% and a three-dimensional network structure, was fabricated by electro-deposition after the electroless copper plating.

Thermal, Chemical, and Morphological Characterization of Microcellular Polyurethane Elastomers

In this study, three different microcellular polyurethane elastomers (MPUE) based on 4,4'-diphenylmethane diisocyanate with different rigid segment contents are prepared (Formulations 1, 2, and 3 with 32, 35, and 42% of rigid segment content, respectively). The MPUE are obtained through a two-step method using a prepolymer system. The samples are analyzed to determine their thermal, morphological, and chemical properties. The thermogravimetric analysis indicates the presence of two degradation stages, referring to the rigid and flexible phases, respectively. The differential scanning calorimetry tests indicate that for the MPUE there was an increase in the glass transition temperature of the flexible phase with an increase in the percent of the rigid phase. An increase in the quantity of the rigid phase present in the MPUE results in greater values for the crosslink density, which in turn results in an increase in the rigidity of the material. The scanning electron microscopy micrographs indicated a large number of closed cells and that a higher rigid segment content give a better cell homogeneity of the samples.

Efeito da concentração de segmentos rígidos nas propriedades físico-mecânicas, químicas e na morfologia de elastômeros microcelulares de poliuretano

Neste trabalho, foram preparados três diferentes elastômeros microcelulares de poliuretano (EMPU) baseados em 4,4'- diisocianato de difenilmetano (MDI), com diferentes concentrações de fase rígida (Formulações 1, 2 e 3, com 32, 35 e 42% de fase rígida, respectivamente). As amostras foram preparadas através do método de duas etapas, pelo sistema de pré-polímero. As amostras dos EMPU foram caracterizadas através de ensaios físico-mecânicos, químicos e morfológicos. Os resultados dos ensaios mecânicos mostraram que o aumento no percentual da fase rígida levou a um aumento na resistência à tração e na resistência ao rasgo. O alongamento na ruptura não apresentou variação significativa com a modificação do percentual da fase rígida. O ensaio de resistência química demonstrou que os EMPU formulados apresentaram baixos índices de inchamento para solventes industriais comumente utilizados. Entretanto, em acetona, um elevado índice de inchamento foi observado. As análises morfológicas indicaram que o aumento no percentual da fase rígida promoveu a formação de células menores distribuídas de forma mais homogênea no EMPU.

Generation of microcellular polyurethane with supercritical carbon dioxide

AbstractWe examined the formation of microcellular foam in a thermoplastic polyurethane elastomer (TPU) with supercritical carbon dioxide. Measurements of the permeability and impregnation with carbon dioxide suggested that the impregnation of TPU with carbon dioxide was affected by the soft‐segment chain length and soft‐segment concentration in TPU and that carbon dioxide was mainly present in the soft‐segment area. Thus, it seemed likely that the nucleation and growth of the nuclei in the microcells occurred in the soft‐segment area. In addition, scanning electron microscopy of the microcells indicated that the higher the saturation pressure was, the smaller the mean cell diameter was; that is, the higher the cell number density was, the lower the foaming temperature was, the smaller the mean cell diameter was, and the lower the saturation pressure was, the more conspicuous this phenomenon was. These results showed that the saturation pressure and foaming temperature affected the cell structure. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Microfoams based on castor oil polyurethanes and vegetable fibers

AbstractThis work was focused on the production and characterization of microcellular polyurethane (PU) composites reinforced with pine wood‐fibers or with hemp, which can be applied to the manufacture of car interior panels, or acoustic insulation panels for the construction industry. The polymers selected for the study were crosslinked PUs, synthesized from a castor oil‐based polyol, with the formulations adjusted to obtain different foaming levels. Microfoamed composites with preferential orientation were prepared from long hemp fibers. Also, samples with random arrangement of short hemp and wood fibers were obtained. The morphology of the composites was analyzed by scanning electron microscopy. The mechanical performance of the reinforced foams was studied through three point bending and dynamic mechanical tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

The effect of roughness, floor polish, water, oil and ice on underfoot friction:: current safety footwear solings are less slip resistant than microcellular polyurethane

Research over a period of about 18 years has shown that a microcellular polyurethane known as AP66033 is the most slip-resistant safety footwear soling material on oily and wet surfaces. In recent years it has been replaced in commercially available footwear by a dual density polyurethane (DDP) which has a dense outer layer and a soft microcellular backing. This research programme has compared the slip resistance of AP66033 with DDP and some rubber solings. In addition, data were obtained on the effects of soling and floor roughness, and floor polish on slip resistance. Some data were also obtained for walking on ice. The coefficient of friction (CoF) of the solings was measured on 19 water wet surfaces in three conditions: (I) when the solings were new, (II) following abrasion to create maximum roughness and (III) after polishing. The CoF was measured on four oily surfaces after each of 11 abrasion or polishing treatments. The profound effects of the roughening of all soles and of floor roughness on the CoF were demonstrated for both wet and oily surfaces. The superior slip resistance of AP66033 was confirmed for oily and wet conditions; however, some rubbers not suitable for safety footwear achieved higher CoF values on wet floors. All of the floor polishes reduced the CoF of all floors when contaminated with water. The mean CoF of DDP solings was lower than the mean for AP66033 on wet and oily surfaces. No safety footwear soling provided adequate grip on dry ice and the CoF was reduced by water on the ice. A rubber used for rock climbing footwear was one of the most slip-resistant solings on wet surfaces in the laboratory but recorded the lowest CoF on ice. It is concluded that the incidence of occupational injuries caused by slipping could be reduced by the following: (A) returning to safety footwear soled with the microcellular polyurethane AP66033; (B) abrading all new and smooth footwear solings with a belt sanding machine coated with P100 grit; (C) avoiding the use of floor polish; (D) informing the general public about the poor slip resistance of ordinary footwear on ice and the lowering of slip resistance in cold weather.

Surface Roughness of Footwear Soling Materials: Relevance to Slip Resistance

Abstract The slip resistance of commercial safety boot and experimental footwear solings has been studied over a period of 15 years. Shoes, with experimental solings, were worn in a factory, and the coefficient of friction (CoF) measured at intervals, using a walking traction test. These measurements have shown that a microcellular polyurethane, AP66033 (formerly T66/103) gives the greatest slip resistance of any soling material on wet or oily factory floors and laboratory test surfaces. This performance is attributed to the statistically significant relationship between CoF and mean peak to trough roughness (Rtm). The surface structure of soling materials was examined using Scanning Electron Microscopy, and images compared with Rtm measurements. There is now sufficient experimental evidence to confirm that surface roughness is one of the determinants of CoF on lubricated floors. The wear characteristics of the floor/sole combination must be considered: some soling materials may become polished on certain floors. However, AP66033 cannot be polished.

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. I: Phase behavior of polyurethane precursors

AbstractOn investigating the generation of microcellular polyurethane foam via reaction in carbon dioxide, we have observed that common polyurethane precursors are CO2 miscible, whereas typically fluorinated compounds or specially designed surfactants are needed to solubilize polymers in CO2. Both isocyanates and polyols are CO2‐miscible at workable pressures and temperatures and in useful concentrations to allow generation of polyurethane foams in CO2. By characterizing the phase behavior of several series of propylene oxide and ethylene oxide polyols, we have observed that the combined effects of molecular weight and hydroxyl number fix the location of the phase separation pressures. In general, lower molecular weights and lower hydroxyl mole fractions produce phase boundaries at relatively lower pressures in carbon dioxide. It also has been shown that CO2‐soluble compounds may have a com̀patibilizing effect on less CO2‐soluble materials.

Generation of microcellular polyurethane foams via polymerization in carbon dioxide. II: Foam formation and characterization

AbstractMicrocellular polyurethane foams are generated through phase separation, which is induced by reaction‐induced crosslinking or by a pressure quench. The phase separation conditions are shown to impact the microstructure of the foams. Pore growth will occur through two mechanisms: diffusion of CO2 from polymerrich regions into the pores and also through CO2 gas expansion (boiling of liquid CO2 at reduced pressure). Higher CO2 pressures for polymerization (hence, higher fluid density) provide more CO2 molecules for foaming, generate lower interfacial tension and viscosity in the polymer matrix, and thus produce higher cell densities. Increasing the functionality of the polyurethane precursors increases the Tg of the polymer network and leads to smaller cell diameters by raising the vitrification pressure and allowing less time for CO2 gas expansion to play a role in cell growth. Higher reaction temperatures result in an increase in bulk density as the cell density remains invariant and the cell size drops. The use of the more polar fluoroform as a foaming agent results in larger cells, as it is able to plasticize the polymer network and allow for gas expansion during depressurization. A constant composition method of pressure quench results in smaller cell diameters.

Mechanisms of friction and assessment of slip resistance of new and used footwear soles on contaminated floors.

The great number of slipping accidents indicates that footwear providing good slip resistance must be rare. Slip resistance seems to be a purely physical phenomenon, however, more knowledge of the mechanisms of friction is needed to develop slip-resistant footwear and to ensure safer walking in slippery conditions. In the present study the influence of the normal wear of shoe heels and soles on their frictional properties was clarified. The slip resistance of three types of new and used safety shoes on four relatively slippery floor-contaminant combinations, was assessed with a prototype apparatus, which simulates the movements of a human foot and the forces applied to the underfoot surface during an actual slip. The used shoes were collected from 27 workers in a shipbuilding company and classified by sight into four wear classes: Good, satisfactory, poor, and worn-out. The assessed shoe heels and soles were in general more slippery when new compared to used heels and soles. However, footwear must be discarded before the tread pattern is worn-out. Used microcellular polyurethane (PU) heels and soles gave a considerably higher coefficient of kinetic friction (μk) on contaminated floors than used heels and soles made of compact nitrile (NR) and compact styrene rubber (SR). The heel-slide coefficient of kinetic friction (μkl) for used versus new shoes was on average 66% higher for PU (0·216 versus 0·130), 27% higher for SR (0·143 versus 0·113), and 7% lower for NR (0·098 versus 0·105). The fundamental mechanisms of friction between shoe soles and contaminated floors were also discussed, and experiments with seven slabs of sole materials were carried out to assess contact pressure effects from the viewpoint of slipping. Slip resistance particularly seemed to depend on the squeeze film and the contact pressure effects between the soling materials and the floor. An increasing contact pressure dramatically reduced the μk, thus indicating that the slip resistance varies considerably during the normal gait cycle. Hence, average friction readings are probably not at all decisive from the slip resistance point of view. An instantaneous coefficient of friction may be more relevant, because in walking the time available to achieve a sufficient coefficient of friction to avoid a slip is only a few tenths of a second.

The superior slip-resistance of footwear soling compound T66/103

Research over a period of fifteen years consistently revealed that a microcellular polyurethane soling known as T66/103 (T66) is the most slip-resistant soling for use on oily floor surfaces. Many experiments have indicated that T66 is also the most slip-resistant soling available for water contaminated (wet) floors. The walking traction test and a new mobile version of the rig were used in eight new experiments designed to obtain further evidence for the superior slip-resistance of T66 especially on wet floors. The surface roughness of T66 after abrasion is believed to be an important contributor to slip-resistance and this hypothesis led to the examination of some microcellular rubbers (MR) which also become rough when abraded. The T66 soling was compared with five MR samples, a dense Polyurethane (PU) and two dense rubbers and in all the experiments the mean coefficient of friction (cof) of the T66 soling was ranked higher than all other solings on surfaces lubricated with water, or by water and a wetting agent ( p< 0.005). On stainless steel lubricated with two grades of mineral oil T66 was in first place in all four ranks although the ranking was not significant. The slip-resistance of four out of five MR samples was better than that of a dense, commercial rubber previously investigated. There was some evidence that a 6 mm thick sole of T66 showed higher cof values than a 12 mm soling and also that higher concentrations of wetting agent can selectively reduce cof of the MR solings. The MR solings were all 12 mm thick and therefore further work is required to compare the MR materials with T66. The MR solings had poor slip-resistance on oily surfaces. The slip-resistance of the dense PU compound (6 mm thick) was consistently ranked lower than a 6 mm soling of T66 but higher than the dense, commercial rubber ( p< 0.001) and the authors believe that the trend in footwear design towards an outer layer of dense PU is retrograde. It is concluded that T66 is the safest commercial soling found for both oily and wet floors and that the more general use of this soling would reduce the enormous number of injuries caused by slipping accidents. Compound T66 should be used as a standard for the assessment of other solings.

A step towards safe walking

Experiments with a walking traction test (Rig 3) designed in 1987, have continued. It has proved to be a safe, rapid and convincing method of measuring the slip-resistance of solings and floors. A method of preparing flat-slab solings has been refined and can be used to compare the coefficients of friction (cof) of solings and floors by eliminating other variables. Research with Rig 3 has confirmed the findings of work with two earlier rigs, that a microcellular polyurethane compound type T66/103 is the safest soling so far discovered for use on floors subject to contamination by mineral oil. The authors believe that the very large number of injuries caused by slipping on oil could be reduced immediately by the specification of this soling for engineering works and garages.

Optimized Processing of Microcellular Polyurethane Systems Through Catalyst and Surfactant Technology

The paper entitled "Novel Elastomeric Catalysts" presented at last year's SPI meeting in Reno, Nevada demonstrated substantial benefits in demold and ex tended cream for microcellular systems. This paper will review the status of these catalysts and introduce additional processing advantages for shoe soles identified through additives technology. We will demonstrate how improved processing advantages can be achieved with the use of non-silicon surfactants. Several areas will be investigated such as: Improved flow, improved mixing and increased bonding of urethane to urethane. This paper will demonstrate quality and productivity advantages through the use of fast cure catalyst in combination with an organic surfactant.