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.     

The preparation and properties of some urethane foams from castor oil and elaidinized castor oil

Summary The preparation and properties of two series of castor oil urethane foams, one from castor oil and the other from elaidinized castor oil, were investigated. The first series of foams was made from prepolymers containing 60% of castor oil prepared at increasing temperature levels to vary the degree of crosslinking in the final foams. These foams had lower tensile strengths than observed for a previously prepared foam of 60% castor oil and did not show significant differences in water resistance as crosslinking varied. They were increased nearly 100% in compressive strength with increased crosslinking and had very good shrinkage characteristics as values of only 1 to 2% were obtained. A second series of foams was prepared from 50, 60, 70, and 80% of elaidinized castor oil to compare with foams from a similar series from castor oil. This series of foams of 50 to 80% elaidinized castor oil contents was similar in density (1.7 to 6.7 lbs./cu. ft.), had improved shrinkage characteristics (11, 1, 3, and 4%, respectively), showed increased compressive and tensile strengths (up to 12.1 p.s.i. at 50% compression modulus and 34.7 p.s.i. ultimate tensile for the 60% foam formulation), and had better water-resistance properties (411 to 155%vs. 515 to 170% water absorption) than the analogous foams from castor oil. In general, humid aging only slightly affected the values obtained for the foams and was significant in only a few instances,e.g., decreased tensile in the elaidinized castor oil series. Thus increasing crosslinks in the foam apparently did not improve water resistance but did improve shrinkage characteristics in addition to some increased strength properties, as would be anticipated. Foams from elaidinized castor oil, while similar in density and foaming characteristics to analogous foams from castor oil, exhibited less shrinkage and improved water-resistance. Presented at the 50th Annual Meeting of the American Oil Chemists' Society, New Orleans, La., April 20–22, 1959. Ono of the laboratories of the Southern Utilization Research and Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Viscoelastic changes and cell opening of reacting polyurethane foams from soy oil

The modulus development of reacting polyurethane foams from modified soy oil (soy polyol) was studied. The reaction and buildup of rheological properties were monitored using vane geometry in a strain‐controlled rheometer. Normal force exerted on the vanes by the expanding foam was measured as a function of time to study the phenomenon of cell opening. The effect of foam ingredients and process parameters on the modulus development was investigated. The morphology of the cured foam was studied using scanning electron microscope (SEM). Experiments were carried out to elucidate the effect of water and addition of petroleum‐based polyol on the modulus development of the reacting foam and the morphology of the cured product. The effect of frequency and thermal history on the modulus development of the reacting foam was also studied. Ozonolysis of soybean oil was carried out to study the effect of adding OH groups on the modulus development during the foaming reaction. Four stages of modulus development, similar to those observed for synthetic polyol (voranol, Aldrich Chemicals) foams, were observed. Increase in water content led to an earlier stiffening of the polymer and a higher modulus. Addition of voranol in soy polyol reduced the liquid foam plateau and significantly reduced the reaction time. Ozonolysis of soy oil led to an earlier phase separation as compared with foams from soy polyol. The temperature at which the foaming reaction takes place dominated the rate of modulus buildup. Higher texture (urea aggregates) and an increase in the cell size were observed with an increase in water content for soy polyol foams. Addition of voranol increased the number of open cells. Polym. Eng. Sci. 44:1977–1986, 2004. © 2004 Society of Plastics Engineers.     

Solvent-blown rigid urethane foams from castor-based polyols

The preparation of trichlorofluoromethane-blown rigid urethane foams using toluenediisocyanate and castor oil-derived polyols was investigated. The castor-based polyols included castor oil, hydroxylated castor oil, technical glycerol-, penta-erythritol-, and sorbitol monoricinoleates, and N,N-bis(2-hydroxyethyl) ricinoleamide. The last of these yielded the best foams when used as the sole polyol component added to the prepolymer. However better foams were obtained by using, as the polyol component, a mixture of a castor oil-derived polyol and a lower-molecular-weight polyol with a higher hydroxyl content. These polyol mixtures yielded more highly cross-linked polymers and hence foams with higher compressive strengths and less tendency to shrink after foaming. The effect of catalyst, silicone surfactant, and trichlorofluoromethane content was also investigated. An empirical relationship between density and compressive strength in a given foam system was derived. Presented at the fall meeting, American Oil Chemists' Society, New York, October 17–19, 1960. A laboratory of the Western Utilization Research and Development Division. Agricultural Research Service, U.S. Department of Agriculture.     

A pre‐polyaddition mediation of castor oil for polyurethane formation

We report a simple, serendipitous, two step mediation that overcomes the polyaddition threshold of castor oil during polyurethane formation. The mediation facilitates formation of polyurethane systems directly from castor oil without triricinolein chain extension or the use of supplementary hydroxyl compounds. The mediation involves refluxing castor oil with n‐Butyl lithium in the presence of a solvent followed by water addition. We demonstrate the effectiveness of this mediation by successfully generating two important polyurethane systems (foam and coating) from castor oil. We identify that the mediation introduces two new compounds in castor oil namely, a lithiated diglyceride and a lithium salt of fatty acid. We characterize the new polyurethane synthesized for their hard‐soft segmented morphology, glass transition temperature, and thermomechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43964.     

Preparation and properties of rigid polyurethane foam based on modified castor oil

Castor oil polyol (COP) having a hydroxyl number of 400?mg?KOH/g was prepared through the transesterification reaction of castor oil with glycerol. The effect of reaction temperature on the composition, hydroxyl number and viscosity of the COP products was studied. A series of rigid polyurethane foams were synthesised using the mixtures comprising COP and a petroleum-based polyol with various proportions as polyol component. It was found that the foaming rate, compressive strength and dimensional stability and morphology of resulting foams were dominated by the foam formulation, in a more accurate way, COP content in the polyol mixtures. The combination of expandable graphite and dimethyl methyl phosphonate exhibited stronger flame retardant function which was ascribed to the synergistic effect associated with the simultaneous presence of the two additives. An improvement in thermal stability was observed due to the inclusion of the flame retardants.     

Physical Properties of Polyurethanes Produced from Polyols from Seed Oils: II. Foams

Rigid polyurethane (PU) foams were prepared using three North American seed oil starting materials. Polyol with terminal primary hydroxyl groups synthesized from canola oil by ozonolysis and hydrogenation based technology, commercially available soybean based polyol and crude castor oil were reacted with aromatic diphenylmethane diisocyanate to prepare the foams. Their physical and thermal properties were studied and compared using dynamic mechanical analysis and thermogravimetric analysis techniques, and their cellular structures were investigated by scanning electron microscope. The chemical diversity of the starting materials allowed the evaluation of the effect of dangling chain on the properties of the foams. The reactivity of soybean oil-derived polyols and of unrefined crude castor oil were found to be lower than that of the canola based polyol as shown by their processing parameters (cream, rising and gel times) and FTIR. Canola-PU foam demonstrated better compressive properties than Soybean-PU foam but less than Castor-PU foam. The differences in performance were found to be related to the differences in the number and position of OH-groups and dangling chains in the starting materials, and to the differences in cellular structure.     

Batch foaming of SAN/clay nanocomposites with scCO2: A very tunable way of controlling the cellular morphology

This paper aims at elucidating some important parameters affecting the cellular morphology of poly(styrene-co-acrylonitrile) (SAN)/clay nanocomposite foams prepared with the supercritical CO₂ technology. Prior to foaming experiments, the SAN/CO₂ system has first been studied. The effect of nanoclay on CO₂ sorption/desorption rate into/from SAN is assessed with a gravimetric method. Ideal saturation conditions are then deduced in view of the foaming process. Nanocomposites foaming has first been performed with the one-step foaming process, also called depressurization foaming. Foams with different cellular morphology have been obtained depending on nanoclay dispersion level and foaming conditions. While foaming at low temperature (40 °C) leads to foams with the highest cell density (∼10¹²-10¹⁴ cells/cm³), the foam expansion is restricted (d∼0.7-0.8 g/cm³). This drawback has been overcome with the use of the two-step foaming process, also called solid-state foaming, where foam expansion occurs during sample dipping in a hot oil bath (d∼0.1-0.5 g/cm³). Different foaming parameters have been varied, and some schemes have been drawn to summarize the characteristics of the foams prepared - cell size, cell density, foam density - depending on both the foaming conditions and nanoclay addition. This result thus illustrates the huge flexibility of the supercritical CO₂ batch foaming process for tuning the foam cellular morphology.     

Elaboration and Characterization of Advanced Biobased Polyurethane Foams Presenting Anisotropic Behavior

Biobased and open cell polyurethane (PU) foams are produced from a synthesized sorbitol‐based polyester polyol. Different formulations are developed with various blowing agent systems (chemical vs physical blowing). Synthetized foams are fully characterized and compared. The cell morphology is carefully investigated by tomography and scanning electron microscopy. The chemical nature of the primary compounds, foaming kinetics, density, thermal behavior, and conductivity are fully studied, with also the main transition materials temperatures. It is shown that blowing agents especially impact the foaming kinetics. In the case of chemically blowing foams, higher foaming rate and temperatures are obtained. The mechanical behavior is particularly analyzed using quasi‐static compression tests, according two main axes compared to the rise direction. A direct relationship is observed between the formulation, foam structure, foam morphology, and corresponding mechanical properties. Results clearly highlight unexpected properties of biobased PU foams with unveil anisotropic mechanical properties.     

Natural Palm Olein Polyol as a Replacement for Polyether Polyols in Viscoelastic Polyurethane Foam

The impact of replacing three polyether polyols with different levels of a single palm olein‐based natural oil polyol (NOP) was systematically correlated with the changes in foaming reactivity, cell structure, physico‐mechanical properties, and morphology of viscoelastic (VE) foams. The data show that replacing the polyether polyols with the NOP slightly increased the rate of the foaming reactivity. Increasing the NOP content resulted in increased cell size and cells remained fully open. Increased NOP content contributed to higher load bearing properties of VE foam, which can be attributed to higher functionality of NOP compared to polyether polyols. Addition of the NOP slightly increased the resilience of the foams, however, the hysteresis which is the measure of energy absorption remained mostly unaffected. Age properties, characterized by dry and humid compression sets, were mostly unaffected by the replacement of the polyether polyol with the NOP. The addition of NOP did not impact the morphology of the VE foam polymer matrix, which appears to retain a low degree of hard and soft segment domain separation. Overall, the results demonstrate a feasibility that the NOP can be used to partially replace the polyether polyols in VE polyurethane foams without significant impact on the functional performance.     

Rigid urethane foams from blown castor oils

Solvent-blown rigid urethane foams prepared from a low-cost polyol mixture composed of raw castor oil and triisopropanolamine have been described. Foams with higher compressive strengths can be obtained by substituting oxidized (blown) castor oil for the raw castor oil in formulations of this type. The properties of rigid foams prepared from several commercial blown castor oils are described. The properties of these foams are correlated with the degree of oxidation of the blown oils used, as indicated by their oxygen content, density, viscosity, and refractive index. Removal of acid from blown oils having high acid values has no significant effect on the compressive strength of foams prepared from these oils. When blown castor oil is used instead of raw castor oil, less isocyanate is required to produce a urethane foam of specified density and compressive strength. Presented at the AOCS meeting in Toronto, Canada, 1962. A laboratory of the W. Utiliz. Res. & Dev. Div., ARS, U.S.D.A.     

溴化蓖麻油多元醇合成及其制备的阻燃聚氨酯硬泡性能

采用可再生的醇解蓖麻油多元醇为原料,与液溴进行加成反应制备溴化蓖麻油多元醇,通过红外光谱证实发生了溴化反应,并测定了产物粘度、羟值、酸值.通过发泡实验和氧指数、烟密度、水平燃烧等测试手段,考察了溴化蓖麻油基聚氨酯硬泡发泡参数和阻燃性质,并与工业级阻燃荆雅保RB-79制备的聚氨酯硬泡进行比较.结果表明,由溴化蓖麻油多元醇...     

Effect of foaming temperature and rubber grades on properties of natural rubber foams

Foaming temperature and grade of dry natural rubber were varied to evaluate their effects on the morphology and mechanical properties of natural rubber (NR) foams. Three different grades of NR were used; namely ENR‐25, SMR‐L, and SMR‐10. NR foams from these grades were produced at three different foaming temperatures, i.e. 140, 150, and 160°C. The study was carried out using formulated compositions containing sodium bicarbonate as the chemical blowing agent and were expanded using conventional compression molding technique via a heat transfer foaming process. The NR foams were characterized with respect to their relative foam density, density of crosslinking, cell size, compression stress, and compression set. Increase in foaming temperature resulted in lower relative density and larger cell size. It was also discovered that the crosslink density slightly decrease with increasing foaming temperature. For mechanical properties, the highest foam density resulted in the highest compression stress. Compression stress at 50% strain increased with increasing foaming temperature and ENR‐25 foam has the highest compression stress among the produced foams. The results showed that the morphology, physical, and mechanical properties of the rubber foams can be controlled closely by the foaming temperature and rubber grades. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Substituting soybean oil-based polyol into polyurethane flexible foams

Polyurethane (PU) flexible foams were synthesized by substituting a portion of base polyether polyol with soybean oil-derived polyol (SBOP) as well as well-known substituent: crosslinker polyol and styrene acrylonitrile (SAN) copolymer-filled polyol. Increases in compression modulus were observed in all substituted foams and the most substantial increase was found in the 30% SBOP-substituted sample. Scanning electron microscopy (SEM) was used to examine cellular structure, in particular cell size. Polymer phase morphology, i.e., interdomain spacing and microphase separation, was studied using small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM). Hydrogen bonding was investigated via Fourier transform infrared (FTIR) spectroscopy. Thermal and mechanical behaviors of foams were examined using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Compression properties were tested and compared via a 65% indentation force deflection (IFD) test. It was found that substituting SAN-filled polyol slightly reduced foam cell size and had no effect on polymer phase morphology. Crosslinker and SBOP polyols, on the other hand, had appreciable influence on polymer phase morphology. Crosslinker polyol disrupted hydrogen bonding between hard segments and was mixed with hard domains. SBOP polyol reduced hard domain size and soft domain fraction, and showed a broad distribution of interdomain spacings. Compression modulus increases in foams correlated well with shear modulus by DMA and could be associated with the polymer phase morphology changes.     

Ultrasound‐induced nucleation in microcellular polymers

In this study, microcellular Acrylonitrile–Butadiene–Styrene foams with high cell density and expansion ratio has been manufactured using ultrasound‐induced nucleation technique in solid‐state batch foaming process. Influence of sonication time, sonication frequency, and ultrasound power were found very crucial in designing of cellular morphology. The initial 10 s of ultrasound exposure was found to influence the foam morphology critically. Longer periods of ultrasound exposure developed foams with lower average cell size as compared to foams developed with lesser ultrasound exposure time. Higher sonication power resulted in foams with uniform morphology and higher cell densities as compared to foams developed with lower sonication intensities. Finally, the ultrasonic frequency was also found to influence the morphology intensely. Low frequency sonication resulted in foams with uniform cell distribution, whereas high frequency sonication developed bimodal microcellular type of microstructure. The results coherently demonstrate that with the advent of ultrasonic waves, the energy barrier for cell nucleation swiftly decreases which enhances the cell density in the final foamed product. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40742.     

Investigation of a strategy for well controlled inducement of microcellular and nanocellular morphologies in polymers

This study is an effort to modify conventional batch processes to be able to produce polymeric foams with high cell density and small cell size, which cannot be reached by conventional batch foaming processes. This has been attained by controlling the foaming temperature and controlled stabilization of the cellular structure. The method was tested for both with and without addition of nanosized particles in polymeric matrix. The desired morphologies were obtained using a novel apparatus with the capability of instantaneous pressure drop and controlling stabilization of the foam structure. The design of the said apparatus was based on the idea that in a foaming process, nucleation is the predominant mechanism that determines the final foam structure. The produced foam products have uniform structures without any unfoamed skin. Results show that the control of the foaming temperature and the cell stabilization are the predominant factors in adjustment of the final foam morphology. A wide range of microcellular structures with cell densities between 10⁷ and 10¹² bubbles/cm³ and average cell sizes of 500 nm–20 μm were produced. Foaming of polystyrene‐nano‐silica nano‐composites with the same method showed that nanoparticles act as nucleating agent and increase the cell density in the final foam products compared with that of neat polystyrene. POLYM. ENG. SCI., 50:1558–1570, 2010. © 2010 Society of Plastics Engineers     

Solvent-blown,rigid urethane foams from low cost castor oil-polyol mixtures

The preparation of solvent-blown rigid urethane foams from low cost castor oil-polyol mixtures was investigated. Solutions of triisopropanolamine, and of mixtures of triisopropanolamine and triethanolamine in castor oil, were used as the polyol component of these foams. Foams were prepared by reacting these polyol mixtures, in the presence of catalyst, surfactant, and trichlorofluoromethane, with prepolymers prepared from toluenediisocyanate and certain polyether polyols or mixtures of these polyether polyols with castor oil. The effect of polyol and prepolymer composition and blowing agent concentration on such foam properties as density and compressive strength was investigated. The properties of the castor oil-based foams were comparable to those of foams obtained from more costly polyols. Presented at the Spring Meeting of the American Oil Chemists' Society, St. Louis, Missouri, May 1–3, 1961. A laboratory of the Western Utilization Researchand Development Division, Agricultural Research Service, U. S. Department of Agriculture.     

Effect of cell structure on oil absorption of highly oil absorptive polyurethane foam for on-site use

This article reports the effect of cell structure on oil absorption of highly oil-absorptive polyurethane foam (ON-PUR), which is suitable for on-site foaming. We have developed ON-PUR as an oil absorbing polyurethane foam using a very reactive recipe. ON-PUR was synthesized by mixing polyol, water, additives, and polymeric diphenylmethane diisocyanate (P-MDI) using a high-pressure foaming machine. Density, airflow, oil absorption of this foam, and cell structure by microscopy were measured. From these results, it was found that the airflow of this foam increased by crushing, and the oil absorption of this foam increased sharply in a narrow airflow range (from 0.1 to 0.8 scfm). This increase is estimated to be due to the decrease of closed cell structures by crushing treatment. Furthermore, we constituted on-site foaming system in bench scale, which was expected to be applicable to on-site preparation of ON-PUR. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 179–186, 1997     

Synthesis and in situ foaming of biodegradable malonic acid ESO polymers

In this study, biodegradable rigid cellular materials were synthesized from the reaction of malonic acid with epoxidized soybean oil. Malonic acid reacts with two epoxy groups to give a network polymer. In the course of this reaction, initially formed malonic acid monoester (MAME) can decarboxylate and produce CO₂, which acts as the blowing agent leading to in situ foaming of the polymer. Epoxide addition and decarboxylation reactions of MAME occur competitively and simultaneously and by controlling their relative rates, foams of controlled density were produced. ¹H NMR spectrum of the synthesized foams showed that increasing the temperature increases the rate of decarboxylation reaction of MAME and decreases crosslink density leading to softer and lower density foams. Addition of 1,4‐diazabicyclo[2.2.2]octane (DABCO) as a catalyst also increases the rate of decarboxylation. Load deflection curves of the cellular materials showed that decreasing the temperature and addition of DABCO increase compressive modulus of samples. Cell morphology was studied by microscopic images of foam samples that showed that foam samples have a closed cell structure and a wide distribution of cell volume. Soil burial test was done to determine rate of biodegradation of foam samples. A half‐life of 815 days showed that foam samples are highly biodegradable. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

One-step foaming method to functional polyurethane absorbents foam

Traditional preparation of superhydrophobic absorbents relies on solvents or further modification with silane. For environmental reasons, it is ideal to find ways that reduce or completely non-solvent. Herein, we show that superhydrophobic sponges can be obtained without solvents by the foaming process. Rough surface morphology and low surface energy were achieved simultaneously during the formation of superhydrophobic foam without further modification. The time required for oil–water separation was shortened significantly, when combined the sponge with a vacuum system. Importantly, the obtained sponge can retain its high oil absorption capacity after several cycles of oil–water separation. The sponge is easy to be scaled up and we have fabricated foams in large scale (37 cm × 30 cm × 22 cm) for making it an ideal candidate for practical application.