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.     

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     

Development of water‐blown bio‐based thermoplastic polyurethane foams using bio‐derived chain extender

Water‐blown bio‐based thermoplastic polyurethane (TPU) formulations were developed to fulfill the requirements of the reactive rotational molding/foaming process. They were prepared using synthetic and bio‐based chain extenders. Foams were prepared by stirring polyether polyol (macrodiol), chain extender (diol), surfactant (silicone oil), chemical blowing agent (distilled water), catalyst, and diisocyanate. The concentration of chain extender, blowing agent, and surfactant were varied and their effects on foaming kinetics, physical, mechanical, and morphological properties of foams were investigated. Density, compressive strength, and modulus of foams decrease with increasing blowing agent concentration and increase with increasing chain extender concentration, but are not significantly affected by changes in surfactant concentration. The foam glass‐transition temperatures increase with increasing blowing agent and chain extender concentrations. The foam cell size slightly increases with increasing blowing agent content and decreases upon surfactant addition (without any dependence on concentration), whereas chain extender concentration has no effect on cell size. Bio‐based 1,3‐propanediol can be used successfully for the preparation TPU foams without sacrificing any properties. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Improved dimensional stability of water-blown polyurethane foam with aluminum hydroxide and magnesium hydroxide

Water is eco-friendly and safe; thus, it used as a blowing agent in the fabrication of water-blown polyurethane (PU) foam. However, water-blown PU foam may experience dimensional instability due to shrinkage of the cells inside the foam. In order to reduce cell shrinkage due to the loss of CO₂ gas, vacuum formation is prevented in the closed-cell foam and the maximum reaction temperature must be raised to increase the degree of curing of the PU foam. In this study, two flame retardants, aluminum trihydrate (ATH) and magnesium dihydrate (MDH), were selected as additives to partially open the cells and increase the maximum reaction temperature. ATH and MDH were both effective for increasing the maximum foam reaction temperature and decreasing dimensional change. Notably, PU foams with 7.5 wt% ATH were the most dimensionally stable at both room temperature and high temperature. Moreover, the compressive strength and flexural strength of such foams were also improved compared to those of the foams without any additive.     

Effects of parameter changes on the structure and properties of low‐density polyethylene foam

Several parameters, such as crosslinking agent concentration, blowing agent concentration, and temperature, were varied to evaluate their effects on the structure and mechanical properties of low‐density polyethylene (LDPE) foams. Dicumyl peroxide (DCP) was used as crosslinking agent, while azodicarbonamide (ADC) was utilized as the blowing agent at different levels. The formulations were prepared by using a thermostatically controlled heated two‐roll mill and foamed by using a compression molding technique via a single‐stage foaming process at three foaming temperatures (165, 175, and 185°C). The resultant LDPE foams were characterized and found to have a closed cell structure. The density and gel content increased proportionally with crosslinking level, whereas density decreased when ADC level and foaming temperature were increased. Another characteristic evaluated was the foam cell size decreased when the crosslinking level and foaming temperature were increased. In contrast, increasing the ADC concentration only gave a maximum cell size increase up to 6 phr that decreased when 8 phr of ADC was used. Results also indicated that compression stress increased proportionally with DCP level and decreased when ADC concentration and foaming temperature were increased. Impact studies on the prepared foams showed that their ability to absorb impact energy decreased with increasing crosslinking level, foaming temperature, and blowing agent concentration. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Modeling of the Dynamics of Water and R-11 blown polyurethane foam formation

Polyurethane foam formation involves both polymerization and expansion processes. The dynamics of the water and R-11 blown foams depend on the rates of chemical and physical blowing processes, along with the rate of viscosity increase of the reacting mixture. Experiments were carried out to study the dynamics of free rising, water and R-11 blown rigid polyurethane foams. The density and temperature change during the foam formation were monitored. A theoretical model was developed to predict the density and temperature variation with time. In the model, the physical blowing agent (R-11) evaporation process is assumed to be heat generation–controlled and the carbon dioxide generation process to be controlled by the rate of the water-isocyanate reaction. The kinetic parameters of the reactions of isocyanate with polyol and water were obtained separately and were asssumed to be independent of each other. The water-isocyanate reaction appears to follow first-order kinetics with respect to concentration of water. The theoretical predictions of the model show good agreement with the experimental data for density variation with time. The model predictions for temperature rise also match experimental data, except at the later stages of foaming when it is found to be slower than the experimental measurements. However, this deviation does not affect the dynamics of density change since it occurs after the completion of the expansion process.     

Effect of dispersion method and process variables on the properties of supercritical CO2 foamed polystyrene/graphite nanocomposite foam

In this study, polystyrene/nanographite nanocomposite foams were made by different compounding methods, such as direct compounding, pulverized sonication compounding, and in situ polymerization, to understand the effect of the process variables on the morphology of the nanocomposites and their foam. The foam was made by batch foaming using CO₂ as the blowing agent. Various foaming pressures and temperatures were studied. The results indicated that the cell size decreased and the cell morphology was improved with the advanced dispersion of the nanoparticles. Among the three methods, the in situ polymerization method provided the best dispersion and the resulting nanocomposite foam had the finest cell size and the highest cell density. In addition, adding nanoparticles as a nucleating agent can make foams of similar cell size and cell density at a much lower foaming pressure. This result can be explained by the classical nucleation theory. This discovery could open up a newroute to produce microcellular foams at a low foaming pressure. POLYM. ENG. SCI., 53:2061–2072, 2013. © 2013 Society of Plastics Engineers     

Foam extrusion characteristics of thermoplastic resin with fluorocarbon blowing agent. II. Polystyrene foam extrusion

The foam extrusion characteristics of three different grades of polystyrene resin were investigated. For the study, cylindrical dies with various values of length-to-diameter ratio, entrance angle, and reservior-to-capillary diameter ratio were used. Fluorocarbon blowing agents were used, and mixtures of citric acid and sodium bicarbonate were used as nucleating agent. It was found that the die temperature, shear rate, the type and concentration of blowing agent, and die geometry affect the quality of the extruded polystyrene foam. Foam density and open cell fraction were used in determining the quality of extruded foams. We have found that the extrudate swell ratio is correlatable to foam density, independent of the die temperature employed. However, the die temperature has been found to be a very sensitive processing variable governing the quality of extruded foams.     

Effect of auxiliary blowing agents on properties of rigid polyurethane foams based on liquefied products from peanut shell

The bio‐based rigid polyurethane (PU) foams were successfully prepared based on liquefied products from peanut shell with water as the blowing agent. The influence of reaction parameters on properties of rigid PU foams was investigated. Rigid PU foams showed excellent compressive strength and low shrinkage ratio, whereas their open‐cell ratio and water absorption were higher. Therefore, rigid PU foams were synthesized with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents and their inner temperature, shrinkage performance, density, compressive strength, water absorption, and open‐cell ratio were determined. The results indicated that above rigid PU foams showed lower compressive strength than the original foam but their water absorption and close‐cell ratio were improved. Compared with the original foam, the highest inner temperature of rigid PU foams with petroleum ether, diethyl ether, and acetone as auxiliary blowing agents was reduced by 11, 19, and 23 °C, respectively. Typically, foams with petroleum ether as auxiliary blowing agent displayed better water absorption and swelling ratio in water and exhibited obvious improvement in close‐cell ratio. These foams were preferable for application in thermal insulation materials because of low thermal conductivity and better corrosion resistance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45582.     

Novel preparation and mechanical properties of rigid polyurethane foam/organoclay nanocomposites

A novel method for preparing rigid polyurethane (PU) foam/organoclay nanocomposites was developed through the direct incorporation of an organoclay into PU foam matrices without the addition of any physical or chemical blowing agent. The resultant foams with an appropriate content of the organoclay had a finer cell structure than the pristine PU foams because the organoclay not only acted as a nucleating agent as expected but also acted as a blowing agent of the PU foams; this could be attributed to the bound water between the interlayers of the organoclay. In addition, the incorporation of the organoclay up to 4 phr resulted in improvements in the tensile and compressive strengths, with the maximum values appearing at 2 phr (110 and 152%, respectively). The significant improvement in the mechanical properties could be attributed to the finer cell structure and the increased internal strength of the materials due to the higher degree of hydrogen bonding. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis of Polyurethane Foam Considering Mixture Blowing Agents for Application to Cryogenic Environments

Polyurethane foams, which are among the most widely used insulating materials, are generally fabricated by the chemical reaction between isocyanate and polyol‐containing chemical additives and blowing agents. Recently, many kinds of blowing agents have been used for the fabrication process of polyurethane foam, such as hydrochlorofluorocarbons (HCFCs) and chlorofluorocarbons (CFCs). However, issues have continuously arisen regarding the destruction of the ozone layer due to these compounds. In the present study, polyurethane foams are manufactured using a mixture of water blowing agents and hydrofluorocarbons (HFC‐365mfc). These samples are subjected to mechanical tests to investigate the effects of the blowing agents on the mechanical properties of the polyurethane foam within a temperature range of 25 to ?163 °C. In addition, thermal and microstructural investigations are conducted depending on the content of the HFC‐365mfc. From the scanning electron microscopy observations, the sizes of the structure cells and the windows are found to decrease with the increase in HFC‐365mfc content. In addition, from the Fourier transform‐infrared spectroscopy observations, the chemical bonds that affect mechanical performance are found to be more distributed with the increase in HFC‐365mfc content.     

Some thermodynamic and kinetic properties of the system PETG-CO2, and morphological characteristics of the CO2-blown PETG foams

The solubility of CO₂ in PETG, a glycol-modified PET, was measured at different temperatures and over a broad pressure range, and diffusion coefficients were derived at the corresponding conditions. The solubility of CO₂ is quits high. For example, almost 15 wt% CO₂ can be dissolved in PETG at 35°C and 6.0 MPa. Consequently, CO₂ is good blowing agent for PETG. Cellular foams in the density range of about 0.04 to 1.2 g/cm³ and diameters in the range of about 10 to 150 µm were produced. The foam density and the cell size were found to depend on the foaming temperature and time, with larger cells obtained at higher temperatures or when the sample was foamed for a longer time. The foam density decreased with an increase in the foaming temperature to about 90°C, beyond which the density tended to increase slightly due to the cell collapse or coalescence. The density reduction also depended on the pressure at which the polymer was saturated with CO₂; the higher the saturating pressure at a given temperature, the greater the density reduction.     

Physical Blowing Agent Residence Conditions Stimulated Morphological Transformations in Extrusion Foaming

In this study, influence of blowing agent residence conditions on foam attributes has been investigated in extrusion foaming process. The blowing agent injection location in the extrusion barrel was found to affect the residence time inside the barrel, which in turn significantly transformed the foam microstructure. The injection location providing higher gas residence time resulted in foams with lower cell size, higher expansion ratio, and enhanced cell density. Further studies were performed to analyze the synergistic influence of residence time variation on foam attributes at different screw rotational speeds, die temperatures, and blowing agent contents.     

Influence of different process and material parameters on chemical foaming of fluorinated ethylene propylene copolymers

In this article, the chemical foaming of fluorinated ethylene propylene copolymers (FEP) is investigated. For the laboratory scale foam extrusion process, a chemical blowing agent adapted to the high melting temperature of FEP had to be found. Foaming experiments were carried out varying process and material parameters. Foam densities as well as cellular structures were analyzed to characterize how the parameters influence the foaming behavior of the FEP melt. An increasing rate of the foam extrusion caused an augmentation of cell numbers at a simultaneous decrease of their diameters. Moreover, a pronounced reduction of the foam density with increasing output rate could be observed. Changing the temperature of the foam extrusion, an optimum in density reduction and homogeneity of the cell size was found. Furthermore, the influence of an appropriate nucleation agent on the resulting geometry and amount of cells was investigated. Though the chemical blowing agent itself can act as an implement for nucleating cell growth, an addition of 10 wt% of calcium fluoride particles showed a significant augmentation in cell quantity. For the chemical foam extrusion process, three FEP with different viscosities were characterized. With decreasing viscosity, a reduction in foam density could be observed for all temperatures. POLYM. ENG. SCI., 47:1740–1749, 2007. © 2007 Society of Plastics Engineers     

Modeling the dynamics of reactive foaming and film thinning in polyurethane foams

Flexible polyurethane foams are widely used in cushioning and packaging applications. A model for the dynamics of formation of polyurethane foams is presented, which includes thinning of foam lamellae. Experimental measurements for water blown flexible foam formulations at different water concentrations are presented to validate the model. Adiabatic temperature rise measurements during foaming are used to obtain the kinetic parameters of the reactions of isocyanate with polyol and water. The variation of foam density during foaming is studied by weight loss and video shooting methods and both are compared to estimate the amount of blowing gas lost during foaming. The average thickness of the foam lamellae of the solid foam is obtained by SEM measurements. The predictions of the model show good agreement with the experimental measurements of temperature and density with time and the final lamellar thickness. The results are important for understanding the cell opening process. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

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

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

辐射交联高密度聚乙烯泡沫塑料交联度的研究

与化学交联方法相比辐射交联的高密度聚乙烯泡沫塑料有光滑、均一的表面,闭孔和树脂的内在性质赋予它良好的机械性能、耐冲击性、绝缘性。研究了加入AC发泡剂、EVA、多官能团单体(SR444)的辐射交联高密度聚乙烯泡沫塑料与交联度相关的性质。测试的参数包括辐射剂量、凝胶含量、泡孔尺寸。高密度聚乙烯树脂中在不同辐照剂量条件下加入5～10份发泡剂及多官能团单体,辐射剂量10～50kGy。在泡孔形成和生长阶段,交联度对于凝胶含量、泡孔结构都有重要影响。     

Polypropylene–nano‐silica nanocomposite foams: mechanisms underlying foamability,and foam microstructure,crystallinity and mechanical properties

We investigate the production and characterization of foams prepared from polypropylene (PP) as well as PP–silica nanocomposites containing different loadings of nano‐silica. This study was carried out to investigate the mechanisms underlying the production of foams with a regular cell structure through the use of nano‐scale fillers. Foaming was carried out in batch mode using an autoclave with CO₂ as the physical blowing agent; high pressures of the order of 14 MPa were achieved through a combination of active pressurization and the use of high foaming temperatures. The resulting PP nanocomposite foams were characterized in detail to quantify the effect of the nano‐silica loading on the foam density and mechanical, morphological and thermal properties. The addition of nano‐silica in PP resulted in the improvement of foam quality – as assessed from the well‐defined and regular cell structures with absence of cell coalescence – as well as an increase in expansion ratio and decrease in foam density. Careful analyses of trends in cell size, cell density and expansion ratio of the foams were correlated with measurements of melt rheology and nano‐filler morphology of the unfoamed specimens in order to identify subtle details regarding the role of silica nanoparticles in improving foam quality. © 2019 Society of Chemical Industry     

Physical and mechanical properties of soy protein-based plastic foams

Flexible plastic foams using soy protein isolate (SPI), soy protein concentrate (SPC), and defatted soy flour (DFS) were produced by interacting proteins with glycerol-propylene oxide polyether triol (polyol), surfactant, triethanolamine (crosslinking agents), tertiary amine (catalyst), and water (blowing agent). The density, compressive stress, resilience, and dimensional stability of foams with SPI, SPC, and DFS increased as the initial concentration of soy protein increased. The foam density increased with increasing weight percentage of SPI, SPC, and DFS. The resilience values of SPI containing foam increased with the increasing addition of SPI up to a maximum 30% SPI addition. An increase in SPI up to 20% caused an increase in the compressive stress (225 kPa) in comparison to control polyurethane foam (187 kPa). The control foam and foam containing 20% DFS had a similar load-deformation relationship. The foam containing 20% SPI and SPC also exhibited a similar shape, but with a higher compressive stress. The compressive stress of all foams was steeply increased after 55% strain, since the foams completely collapsed upon compression.     

Thermosetting foam with a high bio‐based content from acrylated epoxidized soybean oil and carbon dioxide

A resilient, thermosetting foam system with a bio‐based content of 96 wt % (resulting in 81% of C₁₄) was successfully developed. We implemented a pressurized carbon dioxide foaming process that produces polymeric foams from acrylated epoxidized soybean oil (AESO). A study of the cell dynamics of uncured CO₂/ AESO foams proved useful to optimize cure conditions. During collapse, the foam's bulk density increased linearly with time, and the cell size and cell density exhibited power‐law degradation rates. Also, low temperature foaming and cure (i.e. high viscosity) are desirable to minimize foam cell degradation. The AESO was cured with a free‐radical initiator (tert‐butyl peroxy‐2‐ethyl hexanoate, T_i ～ 60°C). Cobalt naphtenate was used as an accelerator to promote quick foam cure at lower temperature (40–50°C). The foam's density was controlled by the carbon dioxide pressure inside the reactor and by the vacuum applied during cure. The viscosity increased linearly during polymerization. The viscosity was proportional to the extent of reaction before gelation, and the cured foam's structure showed a dependence on the time of vacuum application. The average cell size increased and the cell density decreased with foam expansion at a low extent of cure; however, the foam expansion became limited and unhomogeneous with advanced reaction. When vacuum was applied at an intermediate viscosity, samples with densities ～ 0.25 g/cm³ were obtained with small (<1 mm) homogeneous cells. The mechanical properties were promising, with a compressive strength of ～ 1 MPa and a compressive modulus of ～ 20 MPa. The new foams are biocompatible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007