Integral-skin polyurethane foams

A model describing the expansion of a polyurethane (PU) foam in a closed mold is developed. An energy balance is stated, together with constitutive equations for the vaporization rate of the foaming agent and the polymerization kinetics. A numerical solution is obtained for an experimentally-characterized PU formulation. It is shown that in order to avoid premature gelling or undesirable density distributions, the wall temperature must be close to the initial one. The relative fraction of skin in the foam may be increased by decreasing the part thickness or by adding less catalyst or more blowing agent to the formulation. Factors affecting cream, rise, and process times are discussed.     

Absorption of benzene by open-cell polyurethane foams

The rate of absorption of benzene by open-cell polyurethane foams of varying pore size (30–85 pores per inch) has been shown to be dependent on the size of the foam samples. Mass transport from the bulk vapor to the matrix surface appears to be a significant resistance when compared with the rate of diffusion in the matrix itself. Even though these foams have a large permeability to air at low pressures, pore diffusion appears to be more significant than bulk flow in describing the absorption process, resulting in absorption behavior which is more characterstic of closed-cell foams. A dual resistance model of the obsorption process, has been used to estimate matrix diffusivities and pore mass transfer coefficients. Although the model was inadequate in some regards to describe completely the absorption process, the significance of the unexpected pore diffusion resistance to mass transfer was quantified. The dependence of pore diffusion on foam size reflected the qualitative interpretation that was apparent from the absorption curves. While the reason for this anomalous behavior remains unknown, open-cell foams cannot be considered simply as a high-surface-area thin-walled form of the matrix material in describing the absorption process; the effect of foam size must also be considered.     

Recycling of thermoset polyurethane foams

A new way for recycling polyurethane (PU) foams is shown by scrap pulverization and subsequent compression molding of resulting particles. The compression molding stage is also called “direct molding” to highlight the absence of any linking agent or virgin material. Large disks, 190 mm in diameter, were molded by recycling foam scraps from motorcycle seats. Aluminum alloy molds and a hot parallel press plate press were used: the molding temperature was fixed to 180°C, the molding pressure to 4.2 MPa, and the molding time to 15 min, whereas the weight of the particles to mold was changed so as to obtain disks with different thickness. The final density of molded product was close to 1 g/cm³, resulting in a compacting factor of 14 in comparison with the initial PU foam. Indentation tests and tensile tests showed that final products exhibit good mechanical performances. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

超软质聚氨酯泡沫的制备

概述了超软质聚氯酯泡沫的几种主要制备方法。     

Making polyurethane foams from microemulsions

A remarkable correlation exists between the degree of expansion of polyurethane foams and the structure of the reacting premixes. Polyurethane foams obtained from reacting premixes containing microemulsions are highly expanded. The expansion rate is proportional to the volume fraction of microemulsion in the premix. The stability of premixes with and without microemulsion is completely different suggesting distinct creaming mechanisms. We apply this idea to synthesize polyurethane foams from microemulsions successfully. This approach can be used to rationalize the design of polyurethane formulations leading to highly expanded foams.     

Sustainable rigid polyurethane foams based on recycled polyols from chemical recycling of waste polyurethane foams

The preparation and characteristics of rigid polyurethane foams (RPUFs) based on recycled polyol obtained by glycolysis of waste RPUF scraps from end-of-life refrigerators were investigated. To deactivate the amine adducts derived from isocyanates, the recycled product obtained after depolymerization was chemically modified via addition polymerization of propylene oxide. Two kinds of recycled polyols with different hydroxyl values and viscosity were blended with conventional virgin polyether polyol to prepare the RPUFs. The effects of the recycled polyols on the physical properties of RPUFs such as cell structures, compressive strength, thermal conductivity, and limiting oxygen index were discussed. It was found that the RPUFs from recycled polyols showed superior compressive strength, thermal insulation property, and self-extinguishing property compared with conventional control foam. The results of this study reveal that the recycled polyols could be used as feedstock for RPUFs with superior performance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47916.     

Nanoclay reinforced rigid polyurethane foams

Clay was intercalated and exfoliated by neutralized dimethylol butanoic acid (DMBA) and used to fabricate rigid polyurethane foam (RPUF)/clay nanocomposites. Cream time, gel time, and tack‐free time increased with the addition and increasing amount of clay whereas foam density and compression strength decreased. Cell size, closed cell content, volume change upon heating and cooling, and thermal conductivity of the foam decreased with the addition and increasing amount of clay with a minimum at 2 pphp (parts per 100 polyol by weight). The glass transition and decomposition temperatures increased with increasing clay content due to the restricted motion of chains and barrier property of the clay platelets. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cushioning performance of flexible polyurethane foams

Impact cushioning and deformation of flexible open-cell polyester polyurethane (PU) foams were studied as a function of specimen geometry, including the incorporation of controlled voids. It was shown that cushioning behavior is dependent on sample geometry, which was in trun due to a complex balance of air compression and air flow, which changes with surface area-to-volume ratio of the impact specimen. Deformation studies show that impact compression proceeded initially by crushing the surface layers with little or no deformation of the center layers. As bulk compression was increased, deformation progressively propagated for the collapsed layers tending to a more uniform strain distribution at high bulk compression strains. Local asymmetric strain patterns were exaggerated using square cushions, because of cornr effects which complicated air flow paths. It was concluded that cushion curve determination of open-cell foams would be more accurately performed using circular samples and deflecting air pressure form the top surface of the cushion to more closely simulate practical conditions. When designing at or near the margin, the number of cushions should be kept to a minimum and open surface area to volume ratios minimized by adopting square rather than strip cushions.     

Morphology of water-blown flexible polyurethane foams

A series of four TDI–polypropylene oxide (PO) water-blown flexible polyurethane foams was produced in which the water content was varied from 2 to 5 pph at a constant isocyanate index of 110. A portion of each foam was thermally compression molded into a plaque. The morphology of both the foams and plaques was investigated using dynamic mechanical spectroscopy (DMS), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), swelling, wide angle X-ray scattering (WAXS), and small angle X-ray scattering (SAXS). A high degree of microphase separation occurs in these foams, and its degree is nearly independent of water (hard segment) content. In the foam with the lowest water content the morphology possesses many similarities to that of typical linear segmented urethane elastomers. Small hard segment domains are present with a correlation distance of about 7.0 nm. When the water content is increased a binodal distribution of hard segment material appears. There are the small hard segment domains typical of segmented urethane elastomers as well as larger “hard aggregates” greater than 100 nm in size. The larger domains are thought to be aggregates of rich polyurea that develop by precipitation during the foaming reaction. WAXS patterns of the foams suggest urea and possibly hard segment ordering that may be of a paracrystalline nature but certainly lacking in true 3-dimensional crystallinity.     

Mechanical behavior of reinforced polyurethane foams

The mechanical behavior of three-phase reinforced polyurethane (PU) foam composites was investigated. Chopped-glass fibers, glass beads, and graphite powder were used as reinforcing materials. Emperimental results indicated that chopped-glass fibers enhance the foam mechanical properties in tension, while glass beads and graphite powder tend to improve the mechanical properties in compression. Microscopical observations revealed that the reinforcing filler location is within the cell walls acting as a matrix reinforcement. A modified Kerner equation, based on a model that assumes the superposition of a porous matrix and a rigid particulate filler, was compared with measured elastic moduli of the three-phase composite foams.     

Fracture properties of rigid polyurethane foams

The fracture behavior of rigid polyurethane foams has been investigated and is shown to obey the Griffith criterion for fracture in so far as the predicted behavior of tensile strength on the size of artificially introduced cracks is concerned. The energy for crack propagation (fracture surface energy) has been measured as 91.4J/m². From this result, the intrinsic flaw size of the material is calculated. This value was found to be within the range of cell dimensions of the material.     

Evolved gas analysis of polyurethane foams by time-of-flight mass speetrometry

A time-of-flight mass spectrometer, used for the examination and identification of organic compounds, has been modified for the study of the thermal breakdown of complex organic materials. The development of the apparatus and examination of a range of polyurethane foams is described.     

Degradable polyurethane foams based on disaccharides

New functional elastic polyurethane foams (PUF) degradable under environmental abiotic and biotic factors, retaining all the inherent properties of the conventional foams were synthesized using isocyanate precursors based on disaccharides (DS): lactose, maltose and saccharose. It was shown by the model reactions of monosaccharide glucose, and DS lactose and saccharose, with phenylisocyanate that both the primary and secondary hydroxyls of the carbohydrates reacted to form urethanes. The main properties of DS‐based foams (PUF/DS) were found to be similar to PUF foam (matrix) prepared with conventional polyols. However, the new PUF/DS were found to undergo enhanced acid/alkaline hydrolysis and degradation compared with PUF matrix when incubated in soil. Mass losses of incubated PUF/DSs significantly exceeded the actual carbohydrate content 28.6%, and in 12 months reached 39.58 (PUF‐4), 53.31(PUF‐8), and 47.25 (PUF‐12). In contrast, under the same conditions PUF matrix lost only 2–2.5%, confirming that incorporation of natural compounds into the polymer chain impacted the degradation processes. PUF/DS were characterized by FTIR, ¹H NMR, ebullioscopy, and exclusion chromatography (molecular masses and molecular mass distribution of the oligomeric model), physical and mechanical tests (density, tensile strength, relative elongation, moisture absorption, vapor permeability), morphology, and degradation in the soil. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42131.     

Damage evolution in flexible polyurethane foams

Microcrazing in the struts of flexible polyurethane foams was discovered during compressive deformation and observed directly in the scanning electron microscope. Attributed to this phenomena was the decrease in stress at maximum compression and the intensity of acoustic emission during compressive cycling. The higher content of styrene–acrylonitrile (SAN) copolymer in these foams resulted in higher modulus, more severe microcrazing, an increase in acoustic emission activity, and a decrease in the stress at maximum compression as cycling progressed.     

Water-absorbing polyurethane foams from liquefied starch

Water-absorbing polyurethane foams were prepared from liquefied starch polyols and diphenylmathane diisocyanate (MDI) by using a cell-opening foaming surfactant. The liquefied starch polyols were obtained by the liquefactions of starch in the presence of polyethylene glycol-dominant reaction reagents by using sulfuric acid as a catalyst under either a refluxing condition or a reduced-pressure condition. The influences of the liquefaction conditions on the properties of the liquefied starch polyols were investigated, taking into account the requirements for preparing appropriate polyurethane foam. Feasible formulations for the preparation of the water-absorbing foams were proposed and the properties of the foams obtained were investigated. © 1996 John Wiley & Sons, Inc.     

导电聚氨酯泡沫材料研究进展

从使用不同导电填料（炭黑、碳纳米管、石墨、金属、有机填料等）制备导电聚氨酯泡沫（PUF）材料的角度进行分析,总结了添加不同导电填料的复合泡沫制备方法以及对泡沫材料性能的影响,并论述了导电PUF材料在压阻材料、吸波材料、电磁屏蔽材料以及电极材料等领域的应用。分析表明,通过添加导电填料,可以改善PUF的静电现象,提高防静电、导电等性能并拓宽PUF材料的应用领域。     

Nanofilled polyols for viscoelastic polyurethane foams

The use of polyether polyols is common in polyurethane industry, particularly in soft PU applications. In particular, viscoelastic foams, characterized by slow recovery after compression, are obtained using poly(ethylene oxide) (PEO) polyols. Nanofilled polyols can be used for the production of viscoelastic foams with improved fire resistance properties. The high polarity of polyether polyols is responsible of a poor affinity with the organic modifiers used in commercial organically modified montmorillonite (omMMT). In this work, organically modified montmorillonites were prepared, having an improved affinity with the polyether polyols used for the production of soft PU foams. The montmorillonite was modified by using polyetheramines with different ethyleneoxide/propyleneoxide amounts. A strongly intercalated/exfoliated structure was obtained after mixing the polyol with the omMMT. The viscosity increased by three orders of magnitude and the diffraction angles of the MMT measured by x‐ray analysis decreased to values lower than 1.5°. The intercalated structure was preserved after the curing stage, when the isocyanate was added to the polyol/omMMT. The resulting polyurethane had an irregular open cell structure, and was characterized by a mechanical properties comparable to those of unfilled polyurethane. Copyright © 2009 Society of Chemical Industry