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Flexible Polyurethane Foams
Abstract
Polyurethanes are chemically complex polymers, usually formed by the reactions of liquid isocyanate components with liquid polyol resin components.
... P olyurethanes (PU) are one of the most important classes of synthetic polymers, where availability of a very broad range of starting materials allows polymer scientists and engineers to design and synthesize novel materials with diverse properties and applications [1][2][3][4][5][6][7][8]. ...
... For example, by using difunctional starting materials it is possible to make linear thermoplastic elastomers with a wide range of properties for fiber and film applications. On the other hand, by employing trifunctional reactants it is possible to prepare crosslinked PUs, such as; flexible or rigid foams [8], cast rubbers/elastomers, adhesives and coatings [3][4][5], which are highly desirable for various applications in many different fields. ...
... Urethane R-NH-COOR 0.3 Table 3. Relative reactivities of aromatic isocyanates with different active hydrogen compounds extremely fast reactions rates are required, such as in PU foam formation [8] or in reaction injection molding (RIM) [28,29]. ...
Polyurethanes are one of the most important classes of polymeric materials. This is mainly due to the availability of a very large number of inherently different starting materials that allows the design and synthesis of polyurethane based materials with a wide range of properties for numerous applications. In this short review, important physical and chemical factors and parameters that have a significant effect on the properties of polyurethanes are discussed. Critical contribution of hydrogen bonding on the structure-morphology-property behavior of these materials was emphasized by both experimental data and molecular simulation studies. Influence of the chemical structures, solubility parameters and molecular weights of the soft and hard segments on morphology and properties were discussed. Important issues regarding the reaction chemistry, synthetic method used and thermal history on structure and performance of polyurethanes were explained. We hope this article, which is prepared to celebrate the 100th anniversary of Polymer Science, will be useful to those who are newcomers to the field, but also to the experienced researchers to better understand the structure-property behavior of polyurethanes and tailor-design novel structures for various applications.
... Thus, FPUFs are widely used in many different industries, such as those making cushions for furniture and automobiles, sound-absorbing materials, and packaging materials [4][5][6][7][8][9][10]. PUFs are commonly manufactured according to the following steps: (1) Mixing of polymer components with blowing agents; (2) nucleation and growth of cells; (3) gelation and crosslinking; and (4) cell opening and curing [11][12][13]. The opening of cell windows greatly affects the air permeability of FPUFs and also imparts various physical properties to the FPUFs for a variety of applications. ...
... Cell opening is typically induced through a combination of internal and external parameters. Internal parameters include the viscosity of the liquid resin [14,15], urea precipitation [16,17], catalyst balance [13,18,19], the effect of surfactant on bubble nucleation and or collapse. We investigated the effects of ISB on the air permeability, resilience, and thermal and mechanical properties of FPUFs. ...
... Furthermore, the hydroxyl groups of the short diol, ISB, can approach isocyanate groups more easily than those hydroxyl groups of conventional PPG, leading to a decrease in GT. Density was an important parameter in the physical properties of FPUFs and it strongly depended on the amount of blowing agent [13]. Since the same amount of distilled water was used for the preparation of all FPUFs, all the FPUFs had a similar density (30 ± 1 kg/m 3 ). ...
Isosorbide (ISB), a nontoxic bio-based bicyclic diol composed from two fuzed furans, was incorporated into the preparation of flexible polyurethane foams (FPUFs) for use as a cell opener and to impart antioxidant properties to the resulting foam. A novel method for cell opening was designed based on the anticipated reversibility of the urethane linkages formed by ISB with isocyanate. FPUFs containing various amounts of ISB (up to 5 wt%) were successfully prepared without any noticeable deterioration in the appearance and physical properties of the resulting foams. The air permeability of these resulting FPUFs was increased and this could be further improved by thermal treatment at 160 °C. The urethane units based on ISB enabled cell window opening, as anticipated, through the reversible urethane linkage. The ISB-containing FPUFs also demonstrated better antioxidant activity by impeding discoloration. Thus, ISB, a nontoxic, bio-based diol, can be a valuable raw material (or additive) for eco-friendly FPUFs without seriously compromising the physical properties of these FPUFs.
... Polyurethane (PU) is the most popular and most commonly used polymeric material in acoustic absorption because this material also could be used in thermal insulation and many other technological applications (Defonseka, 2013). PU foam materials come in two forms, namely, flexible PU foams and rigid PU foams. ...
... Open cell flexible PU foams have a higher sound absorption property than rigid PU forms (Ancuţa-Elenaet al. 2014). Flexible PU foams are made with densities ranging from 12 to 50 kg m -3 (Defonseka, 2013). PU foams are generally formed by a chemical reaction between di-or polyisocyanates and polyols (Gwonet al. 2016) and small amounts of blowing agents are added to design low density foams (Jain et al., 2013).Since isocyanates are highly toxic materials, in order to mitigate environmental and health issues, numerous research studies have been carried out to determine how environment-friendly materials could be used to replace these materials and to enhance the sound absorption property of PU materials (Caillolet al. 2012). ...
... PU foams are generally formed by a chemical reaction between di-or polyisocyanates and polyols (Gwonet al. 2016) and small amounts of blowing agents are added to design low density foams (Jain et al., 2013).Since isocyanates are highly toxic materials, in order to mitigate environmental and health issues, numerous research studies have been carried out to determine how environment-friendly materials could be used to replace these materials and to enhance the sound absorption property of PU materials (Caillolet al. 2012). Polyols are petroleum-based materials and continuing research is in progress to use natural products such as soya and other sources to produce ecofriendly polyols to make these foams more cost-effective (Defonseka, 2013). ...
In Sri Lanka, commercial flexible (CF) polyurethane (PU) foams are used for many purposes including sound absorption and noise reduction. The main factors that control sound absorption are thickness, density and flow resistivity of PU foam materials. The primary aim of the study is to experimentally determine frequency-dependant normal incidence acoustic absorption coefficients (NIAACs) of PU foams of densities in the range (12.0 kg m-3 to 21.0 kg m-3) and thicknesses in the range (5.08 cm to10.16 cm) of PU foam materials,using the impedance tube method according to ASTM C384-04 standard. The studied foam materials exhibit excellent acoustic properties with high NIAACs of more than 0.70 in the high frequency range above 1 kHz. For fixed density of these materials, NIAACs increased with increasing foam thickness. However, for fixed thickness of these materials, the NIAACs were found to be independent of the foam density. The air flow resistivity dependency on thickness and density of PU foams were determined based on simulated NIAACs as a function of frequency using the Dunn &Davern model. For fixed thickness of foam materials, the flow resistivity increased with increasing density of foam materials. However, for fixed density of foam materials, the variation between flow resistivity and thickness of foam materials were found to be inconsistent, indicating inhomogeneity / heterogeneity of CFPU foams.
... Polyurethane (PU) is the most popular and most commonly used polymeric material in acoustic absorption because this material also could be used in thermal insulation and many other technological applications (Defonseka, 2013). PU foam materials come in two forms, namely, flexible PU foams and rigid PU foams. ...
... Open cell flexible PU foams have a higher sound absorption property than rigid PU forms (Ancuţa-Elenaet al. 2014). Flexible PU foams are made with densities ranging from 12 to 50 kg m -3 (Defonseka, 2013). PU foams are generally formed by a chemical reaction between di-or polyisocyanates and polyols (Gwonet al. 2016) and small amounts of blowing agents are added to design low density foams (Jain et al., 2013).Since isocyanates are highly toxic materials, in order to mitigate environmental and health issues, numerous research studies have been carried out to determine how environment-friendly materials could be used to replace these materials and to enhance the sound absorption property of PU materials (Caillolet al. 2012). ...
... PU foams are generally formed by a chemical reaction between di-or polyisocyanates and polyols (Gwonet al. 2016) and small amounts of blowing agents are added to design low density foams (Jain et al., 2013).Since isocyanates are highly toxic materials, in order to mitigate environmental and health issues, numerous research studies have been carried out to determine how environment-friendly materials could be used to replace these materials and to enhance the sound absorption property of PU materials (Caillolet al. 2012). Polyols are petroleum-based materials and continuing research is in progress to use natural products such as soya and other sources to produce ecofriendly polyols to make these foams more cost-effective (Defonseka, 2013). ...
In Sri Lanka, commercial flexible (CF) polyurethane (PU) foams are used for many purposes including sound absorption and noise reduction. The main factors that control sound absorption are thickness, density and flow resistivity of PU foam materials. The primary aim of the study is to experimentally determine frequency-dependant normal incidence acoustic absorption coefficients (NIAACs) of PU foams of densities in the range (12.0 kg m-3 to 21.0 kg m-3) and thicknesses in the range (5.08 cm to10.16 cm) of PU foam materials,using the impedance tube method according to ASTM C384-04 standard. The studied foam materials exhibit excellent acoustic properties with high NIAACs of more than 0.70 in the high frequency range above 1 kHz. For fixed density of these materials, NIAACs increased with increasing foam thickness. However, for fixed thickness of these materials, the NIAACs were found to be independent of the foam density. The air flow resistivity dependency on thickness and density of PU foams were determined based on simulated NIAACs as a function of frequency using the Dunn &Davern model. For fixed thickness of foam materials, the flow resistivity increased with increasing density of foam materials. However, for fixed density of foam materials, the variation between flow resistivity and thickness of foam materials were found to be inconsistent, indicating inhomogeneity / heterogeneity of CFPU foams.
... The polyurethane market accounts for around 7% of the global polymer market [4]. Generally, polyurethanes can be classified into flexible foams (Figure 1.a) (50%; furniture, mattresses, automotive seats), rigid foams (Figure 1.b) (30%; insulation and structural materials), as well as coatings, adhesives, sealants and elastomers (20%; paints, binders, lacquers and elastomeric materials) [5,6]. From the chemical point of view, polyurethanes are obtained from a range of different reactions, including reaction between isocyanate (-NCO) and polyol (-OH) which gives 'urethane' groups (-NHCOO). ...
... The catalysts used in the synthesis of polyurethane foams help to precisely control the relative reaction rates of the isocyanate with both polyol and water. The imbalance between them can cause the foam collapse or formation of inappropriate cells that can be closed or opened prematurely [3,5,7,9]. There are mainly two types of catalysts used in polyurethane technology, i.e. amine catalysts and organometallics. ...
... There are mainly two types of catalysts used in polyurethane technology, i.e. amine catalysts and organometallics. Amine catalysts generally catalyze the isocyanate-water reaction better than the isocyanate-polyol reaction, while organometallics are considered as gel catalysts although they additionally influence blowing reactions [3,5]. The amine catalysts, especially tertiary amines, are the most common organic base catalysts in the synthesis of polyurethanes. ...
... Flexible polyurethane foam (FPUF) is a highly adaptable material that is commonly found in a range of products, such as furniture, bedding, packaging, and automotive components. 1,2 The low-density cellular composition of FPUF makes it wellsuited for cushioning purposes, and its flexibility allows for diverse applications. The production of FPUF is a continuous process, involving the pouring of a reactive foam chemical mixture onto a moving conveyor. ...
... The synthesis of FPUF depends on managing equilibrium between two key chemical reactions. [1][2][3] The first reaction involves an isocyanate group (-N=C=O) reacting with water (H 2 O) to generate an amine functionality (-NH 2 ) and carbon dioxide (CO 2 ). The amine that is produced then interacts with a second isocyanate group, forming urea hard segments (-NH-CO-NH-). ...
Flexible polyurethane foams (FPUFs) are versatile materials used in various applications due to their unique properties. Understanding the phase separation behavior in FPUFs is crucial for tailoring their properties to specific applications. In this study, we investigated FPUFs with varying levels of urea phase connectivity using small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), and wide-angle X-ray scattering (WAXS). We explored the effect of water, lithium chloride, and isocyanate structures on the phase separation behavior by employing these methods. An increase in water content in the FPUF formulation resulted in a higher amount of formed urea and larger globular size of urea aggregates. Incorporating LiCl into FPUF formulations demonstrated its ability to prevent hydrogen bond formation, leading to alterations in the urea phase. Moreover, we found that foams prepared with asymmetric diisocyanates showed difficulty in forming the urea phase, while foams prepared with symmetric and aliphatic diisocyanates readily formed the urea phase. Our study sheds light on the morphology of the urea phase, the packaging nature of the hard segment, and the hydrogen bonding behavior of the FPUFs. These findings contribute to a better understanding of phase separation in FPUFs and offer insights into tailoring their properties for specific applications.
... Fixed amounts of surfactants and catalysts were added for all experiments. : Specifications of polyol and PMDI[18]. ...
... Specifications of graphene nanoparticles[18]. ...
The rapid evolution of the nanoparticles in the last two decades has created an interest in combining these materials with common polymers to enhance some properties toward new applications. In this research, nano-graphene was added to polyurethane resin with a goal to improve its endues application for dental-arch models and removable dental appliances. One of the obstacles of adding nanoparticles is the full dispersion of these nanoparticles in the polyol and in the final polymer. Nanographene was found difficult to dispense in the polyurethane resin due to the lack of functional moieties on the surface; however, some property enhancement was observed especially in the mechanical, thermal, and electrical conductivity.
... However, Lee et al. and Herrington et al. demonstrated that there are four roles for silicone surfactant in synthesis of closed cell PUFs. The silicone surfactant roles are improved compatibility of raw materials stabilization, dispersion of inlet gas, stabilization of bubbles and prevention of coalescence [41,42]. On the other hand, silicone surfactant should not have a direct impact on the foam strength and the impact caused by it can be related to the effect of cell size on the foam strength [40][41][42]. ...
... The silicone surfactant roles are improved compatibility of raw materials stabilization, dispersion of inlet gas, stabilization of bubbles and prevention of coalescence [41,42]. On the other hand, silicone surfactant should not have a direct impact on the foam strength and the impact caused by it can be related to the effect of cell size on the foam strength [40][41][42]. ...
In the present study, a new method for the synthesis of the open cell flexible polyurethane foams (PUFS) was developed by using starch powder and the modification of closed cell foam formulation. Starch is the second largest polymeric carbohydrate as a macromolecule on this planet with a large number of glucose units. Copper Oxide Nanoparticles (CuO NPS) were synthesized by thermal degradation method at different temperatures of 400, 600 and 800 °C as antimicrobial agents. The antimicrobial activity of CuO NPS and commercial CuO powder against the main causes of hospital infections were tested. CuO600 was the most effective antimicrobial agent and enhanced polymer matrix tensile strength with starch powder as new polyurethane foams (PUFS) cell opener with high tensile strength. The effects of parameters on tensile strength were optimized using response surface methodology (RSM). CuO NPS and PUF had optimal conditions and were characterized by X-Ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Foam synthesized at the optimal conditions had an open cell structure with high tensile strength and efficient antimicrobial activity that made them suitable to be used as an antimicrobial hospital mattress to control hospital infections.
... Viscosity is considered an important physical property of the polyol. It indicates the degree of oligomerization of the reactants and therefore increases the average molecular weights of the polyols produced which have significant impact in later PU formulations (Herrington et al., 1997). Polyol viscosities are also indicative of product workability especially in mixing big batches in either pilot plant or large-scale production. ...
... Secondary hydroxyl group which composed most of biobased polyols tends to proceed in a slower reaction rate with isocyanate resulting in a weaker polymer network and increased number of open cells. These formed cells are susceptible to air convection and escape of carbon dioxide, both of which contribute to a higher thermal conductivity (Herrington et al., 1997;Szycher, 1999). ...
Polymers derived from plant oils have attracted major commercial interest and significant attention in scientific research because of the availability, biodegradability, and unique properties of triglycerides. Triglycerides rich in unsaturated fatty acids, such as soybean oil (SBO), are particularly susceptible to chemical modification for desired polymeric materials. Soy-based polyols are important industrial prepolymeric materials that use renewable resources; and can be produced or derived through different processing routes. This review paper discusses previous and recent researches about chemical and biochemical polymerization processes to produce soy-based polyols as prepolymers for the production of polyurethane materials in the form of foams (rigid or flexible) and elastomers. The central goal of these research fields is to find effective reaction routes to increase both equivalent weight and hydroxyl functionality of soy-based polyols while taking into consideration the simplicity and economics of these processes.
... Polyurethanes (PUs), polyureas (PUas), and poly(urethaneureas) (PUUs) are amongst an interesting division of polymers with a broad scope of industrial applications [1][2][3][4][5], including coatings [6][7][8], shock-absorbing coatings [9], adhesives [10][11][12][13], foams [14][15][16][17], and elastomers [18,19]. PUas are generally considered as a multi-block copolymer consisting of altering soft segment blocks (typically a polyamine) and hard segment blocks (formed by a reaction between a diisocyanate and a chain extender) [20][21][22][23][24][25]. ...
Polyurea (PUa) elastomers are extensively used in a wide range of applications spanning from biomedical to defense fields due to their enabling mechanical properties. These materials can be further reinforced through the incorporation of nanoparticles to form nanocomposites. This study focuses on an IPDI-based PUa matrix with exfoliated graphene nanoplatelet (xGnP) fillers. We propose a generalized constitutive model by integrating one Fractional Maxwell Model (FMM) and one Fractional Maxwell Gel (FMG) branch in a parallel configuration via introducing a new dimensionless number to bridge between these branches physically and mathematically. Through systematic local-to-global sensitivity analyses, we investigate the behavior of these nanocomposites to facilitate simulation, design, and performance prediction. Consistently, the constructed models share the same most/least influential model parameters. and , the power exponent and the characteristic modulus of the first branch, are found to be the most influential model parameters, while and , the characteristic time-scales of each branch, are recognized as the least influential model parameters. The proposed PU nanocomposite constitutive laws can now make an impact to the design and optimization of coating and shock-absorbing coatings in a range of applications.
... [17][18][19][20] In manufacturing PU foams, reactant A (polyols, blowing agents, catalysts, surfactants, etc.) and reactant B (isocyanates) are mixed at high speed, and the resulting resin mixture is then molded into a desired shape. 21 Due to difficulties in achieving sufficient sound absorption performance in the low-frequency range (less than 500 Hz), low-frequency sound control has received attention. [22][23][24][25][26] Using bulky foams is a solution to this problem, but due to adverse effects including poor mechanical properties, it has limitations for industrial applications, including the construction industry. ...
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 ( ¹ H 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.
... 12 This is owed to the dependency of foam properties on the polyol composition. 13 For vegetable oil based polyols to be viable replacements for petroleum-based polyols, they must meet essential chemical property requirements such as molecular weight, OH number, and functionality. 14 Vegetable oils (VOs) are inherently lowmolecular-weight compounds and possess some degree of acidity due to the presence of free fatty acids. ...
Coconut oil, a low-molecular-weight vegetable oil, is virtually unutilized as a polyol material for flexible polyurethane foam (FPUF) production due to the high-molecular-weight polyol requirement of FPUFs. The saturated chemistry of coconut oil also limits its compatibility with widely used polyol-forming processes, which mostly rely on the unsaturation of vegetable oil for functionalization. Existing studies have only exploited this resource in producing low-molecular-weight polyols for rigid foam synthesis. In this present work, high-molecular-weight polyester polyols were synthesized from coconut monoglycerides (CMG), a coproduct of fatty acid production from coconut oil, via polycondensation at different mass ratios of CMG with 1:5 glycerol:phthalic anhydride. Characterization of the CMG-based polyol (CMGPOL) products showed number-average molecular weights between 1997 and 4275 g/mol, OH numbers between 77 and 142 mg KOH/g, average functionality between 4.8 and 5.8, acid numbers between 4.49 and 23.56 mg KOH/g, and viscosities between 1.27 and 89.57 Pa·s. The polyols were used to synthesize the CMGPOL-modified PU foams (CPFs) at 20 wt % loading. The modification of the foam formulation increased the monodentate and bidentate urea groups, shown using Fourier transform infrared (FTIR) spectroscopy, that promoted microphase separation in the foam matrix, confirmed using atomic force microscopy (AFM) and differential scanning calorimetry (DSC). The implications of the structural change to foam morphology and open cell content were investigated using a scanning electron microscope (SEM) and gas pycnometer. The density of the CPFs decreased, while a significant improvement in their tensile and compressive properties was observed. Also, the CPFs exhibited different resiliency with a correlation to microphase separation. These findings offer a new sustainable polyol raw material that can be used to modify petroleum-based foam and produce flexible foams with varying properties that can be tailored to meet specific requirements.
... Reactions of isocyanates with urethane groups lead to branched and even crosslinked structures (13). Relative reactivities of aromatic diisocyanates with various acidic hydrogen-containing compounds in uncatalyzed reactions at 25°C are summarized in Table 2 (5,14). Influence of various reaction parameters, such as diisocyanate structure, reaction temperature, reaction time, solvent, and catalysts on the kinetics of urethane formation reactions and possible side reactions have been provided in two excellent reviews (5,11). ...
... The loading of the remaining components is kept constant. The initial formulation comes from earlier work [17] however many flexible PU foam formulations exist in literature and could be used as formulation starting points [24,25]. These remaining components are the polyisocyanate, polyols and water that make up the polymer backbone and this DoE studies the effects of the foam structure and morphology at the plant scale rather than the polymer chemistry at the molecular scale. ...
Polyurethane (PU) foams are exceptionally versatile due to the nature of PU bond formation and the large variety of polymeric backbones and formulation components such as catalysts and surfactants. This versatility introduces a challenge, namely a near unlimited number of variables for formulating foams. In addition to this, PU foam development requires expert knowledge, not only in polyurethane chemistry but also in the art of evaluating the resulting foams. In this work, we demonstrate that a rational experimental design framework in conjunction with a design of experiments (DoE) approach reduces both the number of experiments required to understand the formulation space and reduces the need for tacit knowledge from a PU expert. We focus on an in-depth example where a catalyst and two surfactants of a known formulation are set as factors and foam physical properties are set as responses. An iterative DoE approach is used to generate a set of foams with substantially different cell morphology and hydrodynamic behaviour. We demonstrate that with 23 screening formulations and 16 final formulations, foam physical properties can be modelled from catalyst and surfactant loadings. This approach also allows for the exploration of relationships between the cell morphology of PU foam and its hydrodynamic behaviour.
... 65,66 The PU foam market can be grouped under three main topics: flexible PU, rigid PU and spray PU foams. 67 Flexible PU foams are light, durable, comfortable and easy to give a shape. They are also resistant to mildew. ...
In this review article, polyurethane (PU) foam materials are presented in various industrial applications. PU foams have started to replace metals and plastics in various engineering applications by combining the hardness and durability of metal with the flexibility of rubber. PU foams can be synthesized with various isocyanates, polyols, chain extenders and crosslinkers to serve many specific applications, such as bio‐based composite foam, flexible hard/soft PU foam, polymer foam etc. There are different factors to change of hard and soft segments of PUs. These changes form different products, such as urethane, biurets, allophanates and isocyamurates, etc. This review article mostly concentrates on the basic chemistry of the building blocks of PUs and recent developments in industrial applications of PU foams, such as insulator material, sound insulators, refrigerator and freezing insulators, furniture, shoes, automotive materials, coatings and adhesives and other applications. © 2022 Society of Industrial Chemistry.
... However, PEG contains oxygen atoms that are more electronegative than nitrogen atoms inside the PKO-p chemical structure causing the reaction of nucleophilic substitution that occurs in PKO-p. Furthermore, amine has a higher probability of reacting compared to hydroxyl [51]. Amine with high alkalinity reacts with carbon atoms on MDI as proposed by Wong and Badri [41]. ...
Polyurethane (PU) is a unique polymer that has versatile processing methods and mechanical properties upon the inclusion of selected additives. In this study, a freestanding bio-based polyurethane film the screen-printed electrode (SPE) was prepared by the solution casting technique, using acetone as solvent. It was a one-pot synthesis between major reactants, namely, palm kernel oil-based polyol and 4,4-methylene diisocyanate. The PU has strong adhesion on the SPE surface. The synthesized bio-based polyurethane was characterized using thermogravimetry analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy (FTIR), surface area analysis by field emission scanning electron microscope, and cyclic voltammetry. Cyclic voltammetry was employed to study electrocatalytic properties of SPE-polyurethane towards oxidation of PU. Remarkably, SPE-PU exhibited improved anodic peak current as compared to SPE itself using the differential pulse voltammetry method. Furthermore, the formation of urethane linkages (-NHC(O) backbone) after polymerization was analyzed using FTIR and confirmed by the absence of peak at 2241 cm-1 attributed to the sp-hydridized carbons atoms of C≡C bonds. The glass transition temperature of the polyurethane was detected at 78.1°C.
... Besides, polyurethane foam also depends on the degree of cell opening, which is the hole in the flexible foam polyurethane structure surrounded by a polymer membrane or polymer frame after the blowing process is complete. The membrane holes are formed in the cell structure, causing air to be able to enter [17][18][19]. If the cell inserts into the membrane, the polyurethane will be relatively rigid, causing less air to enter the cell. ...
Polyurethane (PU) foams are widely used in the industry, because of the unique physical properties ranging from soft to rigid. The research on polymer using renewables sources urged to be developed, without exception to PU it was supported by enormous resources which possible to replace the decline reserved for petroleum. This work was done by processing 2,4-toluene and 2,6-toluene di Isocyanate isomers to be blended to soy-polyols forming foam formation as a balanced reaction between blowing and gelation. The best catalyst concentration can control the reaction and the synergistic to chain extender can achieve foam stability. It was found the best concentration was 1% (v/v) sulfuric acid at temperature 60 0 C. The method used in this research was a one-shot system. The goals were to determine the best process and production of PU. The chain extender used in this work was ethylene glycol, methanol, and butanol. The sulfuric acid was used for the catalysis and comparison purposes the butanol was catalyzed by bentonite. The morphology of the foam cellular, density, compressive strength was determined to support data.
... Then, the bubbles form a triangular structure called "plateau edges" that form irregular polyhedral cells. After the temperature rise generated by an exothermic reaction, the cells break, and the spherical cells are converted into polyhedral [40,41]. ...
We developed polyurethane foams (PU) filled with eucalyptus charcoal residue (ECR) (5, 10, 20, and 30% by wt) for diesel sorption from seawater. The PU foams were characterized by FTIR, FT-Raman, SEM, density, TGA, contact angle, diesel S500 and S10 sorption, and recyclability. The ECR addition altered PU chemical structure, inducing new chemical bonds and probably altering cross-linking ability of the foams, as indicated by FTIR. FT-Raman spectra of PU-ECR foams showed shifts associated with filler dispersion and interaction with the matrix; besides, its addition decreased the foam pore size and density. The ECR addition did not significantly change the thermal behavior of PU foam and increased hydrophilicity in low ECR content and hydrophobicity in high ECR content samples. Experimental results showed adequate oil sorption capacity, and the optimal amount was 30% (by wt) ECR, which enhanced the diesel sorption from 4.1 and 5.9 g.g−1 to 9.6 and 8.8 g.g−1 for diesel S500 and S10, respectively. The Langmuir sorption isotherm was the best-fitting model to describe oil sorption. Reusability of the PU + 30% ECR was examined through 34 and 39 cycles for diesel S500 and S10, and about 50% of the initial sorption capacity remained at the end. The results indicated the success of developing a sustainable material and demonstrating feasibility in practical applications of PU-ECR foam for spilled oil removal from seawater or treatment of oily effluents.Graphical abstract
... The other reaction appeared in this study with PEG where the oxygen of PEG nucleophile attacks diisocyanate of MDI to form two intermediate complexes A and B. Nevertheless, nucleophilic substitution reaction has greater tendency to polyol compared to PEG owing to the nitrogen atom presence in polyol which is more electropositive than oxygen atom in PEG. Amine has higher possibility to react with isocyanate compared to hydroxyl (Herrington & Hock 1997). The other study stated that amine with a stronger alkalinity has more ability to react with carbon atom of the isocyanate (Wong & Badri 2012). ...
... The properties of polyols, such as hydroxyl number, functionality, and molecular weight, play a signicant role in determining the nal properties of foams. 3 Polyols are characterized by functionality, hydroxyl number, and equivalent weight 4 as well as other properties that may be more specic to application. ...
A sustainable soy-based polyol was synthesis to replace the petroleum-based polyol for producing rigid polyurethane foam. The big challenge in using bio-based polyols was the shrinkage of the foam. The maximum reaction temperature was an indication that can be related to the curing/setting of the foam matrix and eventually reduce foam shrinkage. Two approaches were adopted to increase maximum reaction temperature of the produced foam. The first approach was pre-heating the monomers to increase the initial reaction rate and substantially increase maximum reaction temperature. The second approach was by increasing the hydroxyl number of the polyol which is, in turn, increases the maximum reaction temperature. The experimental results show that the two methods were effective in reducing foam shrinkage and bio-based polyols can effectively use to replace petroleum-based polyols.
... Wide ranges of these panels are made from new lightweight components such as foams. Many types of foams are on the market and the Polyurethane (PU) foams are the most popular types (Defonseka, 2013). The lightweight penalized foam made products are popular because they are light, easy to install and have good thermal and acoustic properties. ...
Foam made panels as efficient building elements are becoming a major role player in modular construction with a variety of applications worldwide. However, construction accuracy, technology, and method can have serious effects on the panels’ behavior. In this study, using a unique pneumatic pressure testing rig, bending tests are conducted on the two types of rigid polyurethane panels. The panels are categorized based on the existence of construction cold joints (seams) as S (Seamless) type and TS (Transverse Seams) type. The S type panels are tested under monotonic uniform loading with a maximum nominal pressure of about 1 atm as the witness specimens. The TS panels are tested under both monotonic and cyclic uniform loading, and the deflections-pressure behavior obtained. The results show that S panels could resist up to 0.77 atm under monotonic uniform loading, while the minimum tensile strength of the foam is 13 MPa. In addition, panels with transverse seams collapsed under monotonic and cyclic loads at an average of 0.46 atm and 0.33 atm respectively but at the same position, located on the seamed section, which represent the same failure mode. Based on the results, the seamed section exhibited a maximum tensile strength of about 33.1% of an intact section under monotonic loading; and 27.9% lower results under cyclic loading.
... This could be due to the presence of water, amines and amino-isocyanates as well as partially polymerized polyurethanes present in the fire smoke, all of which could speed up the degradation of isocyanates (Woolley et al., 1975;Blomqvist et al., 2003). For example, primary aliphatic amines have up to five times faster reaction rate with isocyanates than secondary amines such as the derivatization reagent DBA (Herrington and Hock, 1998). Additionally, other compounds generated in fires, such as water and alcohols can potentially also speed up the rate of degradation of the analysed isocyanates. ...
Inhalation of airborne isocyanates is associated with acute asthma attacks and inflammation in the respiratory tract as well as cancer. These highly reactive compounds are used as monomers in various applications such as foams for insulation materials and upholstery furniture and are therefore commonly found in fire smoke from insulation materials, such as rigid polyisocyanurate (PIR) foams. Consequently, there is an increasing concern regarding the potential adverse health effects they may cause during this type of exposure.
The aim of this study was to investigate the stability of generated isocyanates from aerobic pyrolysis of PIR after sampling in the derivatization solution as well as after sample preparation to establish the optimal storage conditions and rate of degradation. Both airborne and particle-bound isocyanates were collected, using dibutylamine as derivatization agent in a midget impinger and impregnated filter after the impinger. The rapid degradation of the generated isocyanates after sampling emphasizes the need for a prompt sample preparation and analysis, in particular for the collected mono-isocyanates, as the concentration decreased by 50% within 4–8 h.
... Lightweight structural panels are one of the most popular types of mobile and rapidly-assembled structures. Rapidly assembled panels are a form of modular construction, commonly used in residential buildings as well as industrial structures [12][13][14]. A wide range of these panels is made from new lightweight components such as foams. ...
In this paper, the development process of a deployable modular sandwich panelized system for rapid-assembly building construction is presented, and its structural performance under some different action effects is investigated. This system, which includes an innovative sandwich panel and its integrated connections, can be used as structural walls and floors in quickly-assembled postdisaster housing, as well as load-bearing panels for prefabricated modular construction and semipermanent buildings. Panels and connections are composed of a pneumatic fabric formwork, and two 3D high-density polyethylene (HDPE) sheets as the skins, filled with high-density rigid polyurethane (PU) foam as the core. HDPE sheets manufactured with a studded surface considerably enhance stress distribution, buckling performance, and delamination strength of the sandwich panel under various loading conditions. The load-carrying behavior of the system in accordance with some American Society for Testing and Materials (ASTM) standards is presented here. The results show the system satisfies the codes’ criteria regarding semipermanent housing.
... A wide range of these panels are made from new lightweight components such as foams. Many types of foams are on the market and the Polyurethane (PU) foams are the most popular types [12]. ...
In this paper the development process of a deployable modular sandwich panelized system for rapid assembly building construction is presented, and its structural performance under some different action effects is investigated. This system, which includes an innovative sandwich panel and its integrated connections, can be used as structural walls and floors in quickly assembled post-disaster housing, as well as load bearing panels for pre-fabricated modular construction and semi-permanent buildings. Panels and connections are composed of a pneumatic fabric formwork, and two 3-D high-density polyethylene (HDPE) sheets as the skins, filled with high-density rigid Polyurethane (PU) foam as the core. HDPE sheets manufactured with a studded surface considerably enhance the stress distribution, buckling performance and delamination strength of the sandwich panel under various loading conditions. The load-carrying behaviour of the system in accordance with some ASTM standards is presented here. The results show the system satisfies the codes criteria regarding semi-permanent housing.
... The polyurea shells were synthesized by interfacial polymerization in an oil/water emulsion. TEPA as crosslinker was favorable for the formation of polyurea shells with higher crosslink density than traditional polyurethane shells, since the reactivity of amine/NCO was thousands of times higher than that of polyols/NCO [39]. At the surfaces of micro-droplets, TEPA reacted rapidly with both Suprasec 2644 and HMDI [40], while polyols tended to react with more active Suprasec 2644 producing loose polyurethane shells [9]. ...
A new approach was developed to load 4,4′-bis-methylene cyclohexane diisocyanate in microcapsules, with outstanding stability in thermal and chemical environments, and excellent efficiency for both self-healing and self-lubricating uses. Well-dispersed microcapsules with diameter of 80 ± 22 µm and shell thickness of 3.8 ± 0.2 µm were produced with a core fraction of 74 ± 1.3 wt% as determined by titration. In thermal environments, the microcapsules started to lose 5% mass at 230 °C, which was higher than the boiling point of pure HMDI and thermal decomposition temperature of shell material. In chemical environments (hexane, xylene, ethyl acetate and water), the impermeable microcapsules reserved more than 90% of original core material after 20 days immersion. More interestingly, final microcapsules survived successfully in acetone losing only 25% of core material after 24 h. Parameters including microcapsules size, concentrations, immersion durations and solvent polarity were investigated systematically to obtain the stability of microcapsules in organic solvents. The smart coatings (10 wt% microcapsules) showed outstanding self-healing anticorrosion efficiency in sodium chloride solutions, and their friction coefficient decreased by 80% than control samples.
... The critical aspect of fabric formwork for achieving desirable performance is the selection of the fabric itself. Although a wide range of woven fabrics can be used as formwork for fabric formwork, tensile strengths in both warp and weft directions must be sufficient to hold the infill material (which is polyurethane [6] in this research) and a low creep modulus is desirable to limit formwork deformations during casting and curing/hardening. In the literature, to date, there is no known study based on systematic decision making methods for fabric formwork selection. ...
... FT-IR analysis of epoxidized soybean oil and epoxy fusion product of epoxidized soybean oil and bisphenol A the urethane (polyol-isocyanate) reaction in a variety of flexible and rigid foam applications. On the other hand, organometallic catalysts are considered as gel catalysts, which, may have some influence on blowing reaction [26,27]. For the purpose of our experiment, Dabco T9 was chosen, as a representative of organometallics. ...
The paper presents the results of studies on the synthesis and mechanical properties of the fusion product of epoxidized soybean oil with bisphenol A, which are a part of the current research on environmentally friendly raw materials for the preparation and modification of modern polymeric materials. It has been shown that the use of 4,4’-methylene diphenyl diisocyanate in the cross-linking process of the fusion product in the presence of Dabco 33-LV and BYK-A530 or BYK-A525 gives hard materials with interesting mechanical properties.
In this study, effects of di- and trifunctional chain extenders including ethylene glycol (MEG), ethanolamine (MEA), diethanolamine (DEA), and glycerin (GLY) were investigated. 0.3, 0.6, and 0.9 php (parts per hundred parts of polyol mixture) of the chain extenders were added to the polyol formulation. Then, foam parts were produced by molding. The reaction profile, free rise density (FD), and mechanical properties of the specimens were tested regarding ASTM D7487 test methods. First of all, reaction profiles were affected by the chemical nature of the chain extenders. MEA and DEA which have a primary and secondary amine unit, respectively, accelerated both the polymerization and blow reactions and resulted in faster cream (CT), gel (GT), and end-of-rise time (RT) values. On the other hand, MEG also accelerated GT, but retarded CT. Finally, GLY retarded CT, GT, and RT of foam samples. FD of all samples were almost the same with a slight decrease by increasing the amount of chain extenders. Besides, force-to-crush (FTC) as a measure of closed- or open-cell structure, was investigated. Results showed that incorporating di- and trifunctional chain extenders led to a remarkable increase in FTC values. The influence was more profound with amine-based chain extenders. The effects of chain extenders on the mechanical properties were also studied according to the ASTM D3574. In the compression set test, using difunctional chain extenders up to 0.6 php, improved the performance. But higher amounts reversed the trend. On the other hand, trifunctional chain extenders declined the compression set properties of the foam. The addition of chain extenders dwindled the tensile and tear properties of the foams. However, the reduction was less with difunctional chain extenders.
Polymeric foams are a type of lightweight materials that are used for screening
assets against mechanical injuries like shock and vibration.There is much scientific
literature available for the characterization of metals and alloys,and so far, work is
being done in the domain of polymer foams. The polymers have been extensively
used to replace metals and their alloys, and this is becoming increasingly popular.
They prove to be interesting for numerous industrial and home uses because of
their unique properties. On the basis of their shape, they combine the inherent
lightweight nature of porous materials with low electrical and thermal
conductance, along with strong energy adsorption and filtering characteristics.
Polymeric foam properties are complicated, necessitating static and dynamic
experiments for accurate depiction. Polymeric foam’s physical qualities can be
linked to a number of autonomous structural factors. They are frequently
employed in a variety of applications where there is a requirement for insulating
performance. In this chapter, we will briefly cover the numerous techniques
utilized in the manufacture of polymeric foams, as well as the qualities that have
piqued the interest of researchers because of their widespread applications in a
variety of disciplines.
In this study, using a solution casting process, thermoplastic polyurethane elastomer (TPU) composites containing different contents of lead zirconate titanate (PZT) ferroelectric particles were produced. The damping treatment of composites at high volume of fillers was investigated. SEM micrographs showed that PZT particles had a proper distribution in the PU matrix. Differential scanning calorimetry (DSC) thermograms indicates that melting enthalpy decreases by raising PZT filler content. The results of the dynamic mechanical thermal analysis (DMTA) proved that the magnitude of loss factor (tan δ) strongly depends on PZT content, and it decreased from 0.51 to 0.27 as PZT content increased. The value of E0 increases to 0.32 GPa in the composite reinforced with 50 v% of PZT. The role of PZT on the acoustic behavior of TPU was measured using the acoustic absorption coefficient (a). The results showed that as PZT content increased from 0 to 50%, the acoustic absorption coefficient reached 0.25 at 6000 Hz frequency. The composites of PZT/PU with 0–3 connectivity were poled, and the optimal poling conditions that could be applied without sample breakdown were studied. Moreover, we prepared composites containing 70 vol% PZT particles by modifying the particles. Modification of PZT particles caused a decrease in both d33 and g33 constants of the PZT/PU composites.
The versatility of polyurethanes is derived in large part from the wide selection of building blocks available to materials designers. The growth in the use of polyurethanes has been highly dependent on the cheap and available feedstock polyisocyanates, polyols, and chain extender coreactants such as water, alcohols, and amines. This chapter provides an overview of building blocks for conventional polyurethane polymerization. Polyols are the largest volume raw material used in polyurethane applications with weight fractions in applications ranging from 90 wt% in low‐modulus flexible sealants, 70 wt% in flexible foams, and as low as 30 wt% in rigid insulation foams. Isocyanates, especially polyisocyanates, are highly identified with polyurethane chemistry. For any given polyurethane, soft segments and isocyanates may make up more than 95% of the polymer volume. There are a large number of potential chain extenders that can be employed to alter hard‐segment structure, polymerization kinetics, and polymer properties.
Advances in instrumentation coupled with computerization and information technology have greatly advanced our understanding of urethane chemistry and polyurethane materials. Modern technology has developed the means to acquire data at relevant length scales such that many aspects of polyurethane morphology and function can be readily understood. X‐ray analysis has become a standard tool for developing in‐depth understanding of polyurethane microstructure. While x‐ray methods are surely complementary to other less instrumentally demanding techniques (such as calorimetry, IR spectroscopy, AFM, and mechanical analyses), x‐ray analysis, when done with proper care and control, provides a measurement that requires less inductive reasoning than other techniques applied for the same information. However, apart from conventional chemical analyses, its application to polyurethanes and polymer structure has lagged other methods because of the technical difficulties associated with nuclear magnetic resonance spectroscopy of solids.
This chapter covers the mechanism and catalysis to polyurethane structure, the side reactions that can take place, and the results these variances can have on the final product. Also covered are the means of minimizing some routes and maximizing others and the properties achieved in such control. The reaction of isocyanates and water to form urea is essential to many polyurethane industrial applications. Theoretical calculations have also suggested that dielectric strength plays a minor role in urethane formation. It is now thought that the major effect of solvent on urethane formation is the effect of solvent on the hydroxyl phase self‐association and the concentration of free or dimeric alcohol available for reaction. The rate of reaction can decrease with increasing solvent dielectric strength; it can also be strongly affected by the solvent's ability to associate with hydroxyls through polar or hydrogen‐bonding interactions, thereby decreasing the availability of hydroxyl functionality to react with the isocyanate.
Phosphine carboxylate, H2PCO2⁻, has been prepared for the first time both by the reaction of dihydrogen phosphide with carbon dioxide and by hydrolysis of phosphaethynolate, PCO⁻. Acidification of the salt yielded phosphine carboxylic acid that has a surprising kinetic stability compared to carbamic and carbonic acids. The mechanism of phosphaethynolate hydrolysis was investigated.
Abstract
We present a new adduct of carbon dioxide with dihydrogenphosphide, that may be prepared either by direct reaction of NaPH2 with carbon dioxide or by hydrolysis of the phosphaethynolate ion (PCO⁻). In this hydrolysis transformation, a new mechanism is proposed for the electrophilic reactivity of the phosphaethynolate ion. Protonation to form phosphine carboxylic acid (PH2COOH) and functionalization to form esters is shown to increase the strength of the P–C interaction, allowing for comparisons to be drawn between this species and the analogous carbamic (NH2COOH) and carbonic acids (H2CO3). Functionalization of the oxygen atom is found to stabilize the phosphine carboxylate while also allowing solubility in organic solvents whereas phosphorus functionalization is shown to facilitate decarboxylation. Substituent migration occurs in some cases.
We present a new adduct of carbon dioxide with dihydrogenphosphide, that may be prepared either by direct reaction of NaPH2 with carbon dioxide or by hydrolysis of the phosphaethynolate ion (PCO⁻). In this hydrolysis transformation, a new mechanism is proposed for the electrophilic reactivity of the phosphaethynolate ion. Protonation to form phosphine carboxylic acid (PH2COOH) and functionalization to form esters is shown to increase the strength of the P–C interaction, allowing for comparisons to be drawn between this species and the analogous carbamic (NH2COOH) and carbonic acids (H2CO3). Functionalization of the oxygen atom is found to stabilize the phosphine carboxylate while also allowing solubility in organic solvents whereas phosphorus functionalization is shown to facilitate decarboxylation. Substituent migration occurs in some cases.
Enzymatic polymerization is emerging as scalable method to convert sucrose to engineered polysaccharides. Polymer architecture and material properties can be controlled selectively to produce novel differentiated biomaterials. One first example for such an engineered polysaccharide is alpha‐1,3‐polyglucose (alpha‐1,3‐glucan) synthesized using glucosyltransferase (GTF) enzymes. Stable dispersions of alpha‐1,3‐glucan in polyether polyols were prepared with narrow particle size distributions, which are reactive with isocyanate allowing for covalent bonding to the hard segment of the polyurethane polymer matrix. This study further explored the use of alpha‐1,3‐glucan (PS) in the preparation of viscoelastics (VE) polyurethane foams. The introduction of alpha‐1,3‐glucan into the polyurethane polymer matrix was found to increase the load‐bearing properties of VE foams without impacting the density. Other key performance properties of VE foams were effectively unchanged, including resilience, tensile, and tear strength. Cell size and morphology were also unaffected. The glass transition of these VE foams was not impacted; however, the overall thermal dimensional stability was improved as considerable reduction in compression set was observed. The results of this study indicated that alpha‐1,3‐glucan disperses in polyether polyols to improve performance characteristics of the VE foams, as well as other flexible polyurethane foams properties.
Enzymatic polymerization is under development as novel scalable process technology to convert sucrose to engineered polysaccharides. Similar to established monomer‐based polymerization processes, this approach allows for the synthesis of glucose‐based polymers with controlled polymer linkage, structure, and material morphology. Using enzymatic polymerization, alpha‐1,3‐polyglucose (glucan) can now be produced from sugar on scales required for industrial applications. This alpha‐1,3 glucan material, with accessible primary and secondary hydroxyl groups within the overall defined particle morphology, is especially of interest as a partially reactive component in polyurethane chemistry. This study explores the impact of alpha‐1,3‐glucan as additive in a thermoplastic polyurethane model system and the improvement in mechanical properties of these composites. Glucan was effectively first mixed with a polyether polyol diol, forming a stable dispersion with narrow particle size distribution, followed by reaction with diisocyanate and chain extender to form the polyurethane matrix. The analysis of the generated polyurethane matrix indicates that the hydroxyl groups of the dispersed glucan particles directly react with isocyanate. Tetrahydrofuran solubility of the formed polyurethane compound decreased with the addition of glucan, providing evidence of covalent bonding of glucan leading to cross‐linking of the polyurethane matrix. Thermal analysis of this model system suggests that the glucan additive induces hard segment crystallization, resulting in increased hardness and tensile modulus compared with the reference. Based on the observed property enhancements, engineered polysaccharides provide a sustainable performance additive for polyurethane materials.
Fascinating and challenging, the development of repairable materials with long-lasting, sustainable and high-performance properties is a key-parameter to provide new advanced materials. To date, the concept of self-healing includes capsule-based healing systems, vascular healing systems, and intrinsic healing systems. Polyurethanes have emerged as a promising class of polymeric materials in this context due to their ease of synthesis and their outstanding properties. This review thereby focuses on the current research and developments in intrinsic self-healing polyurethanes and related composites. The chronological development of such advanced materials as well as the different strategies employed to confer living-like healing properties are discussed. Particular attention will be paid on chemical reactions utilized for self-healing purposes. Potential applications, challenges and future prospects in self-healing polyurethane fields are also provided.
The detection and location of partial discharge (PD) is of great significance in evaluating the insulation condition of power transformers. This paper presents an active dielectric window (ADW), which is a new concept of combined acoustic emission (AE) and electromagnetic PD detector intended for assembly in a transformer's inspection hatch. The novelty of this design lies in the fact that all structural components of an ultrasonic transducer, i.e., the matching and backing layer, an active piezoelectric element with electrodes, and electrical leads, were built into a dielectric window. Due to the fact that its construction was optimized for work in mineral oil, it is characterized by much higher sensitivity of PD detection than a general-purpose AE sensor mounted outside a transformer tank. Laboratory tests showed that the amplitude of the AE pulses generated by creeping discharges, which were registered by the ADW, was around five times higher on average than the pulses registered by a commonly used contact transducer. A possibility of simultaneous detection of acoustic and electromagnetic pulses (with an integrated ultra-high frequency (UHF) antenna) is an important advantage of the ADW. It allows for an increase in the reliability of PD detection, the accuracy of defect location, and the effectiveness of disturbance identification. This paper describes in detail the applied methods of designing and modeling the ADW components, the manufacturing process of the prototype construction, and the results of preliminary laboratory tests, in which the detector's sensitivity as well as the efficiency of the PD source location were evaluated.
Low-resilience polyurethane foams including several additive constituents were synthesized to improve their vibro-acoustic performances, as well as the thermal insulation. viscoelastic polymer additive can attenuate vibrations and absorb sound energy. the vibro-acoustic properties of two innovative viscoelastic treatments fabricated with polyurethane foams are discussed in this paper using a typical aeronautical panel test setup. Since an aircraft insulation arrangement must provide both noise and thermal insulation for the specified operating conditions and expected thermal comfort of passengers, the thermal conductivity of the samples has been examined assuming a testing range between 20 °C (room temperature) and − 40 °C (cruise altitude). the results highlighted an optimal behavior of the novel viscoelastic foams in terms of both acoustic and thermal performance, offering a very interesting self-embedded solution with a good weight to performance ratio, compared to standard blanket composed by extra viscoelastic treatments.
Striving to utilize sustainable material sources, polyester polyols made via glycolysis and esterification of recycled polyethylene terephthalate (rPET) scrap were used to synthesize flexible polyurethane (PU) foams typically found in automotive interior applications. The objective of this endeavor was to ascertain if a closed-loop model could be established with the discarded PET feedstock. In five separate formulations, up to 50% of the total polyol content (traditionally derived from petroleum-based feedstock) was replaced with the afore-mentioned sustainable recycled polyols. These foams underwent mechanical, thermal, morphological, and physical characterization testing to determine feasibility for use in an automotive interior. Young's modulus, tensile stress at maximum load, tear resistance, and compression modulus all increased by combined averages of 121%, 67%, 32%, and 150% over the control petroleum-based formulation, respectively, in foams possessing 50% rPET polyol content. Thermal stability also increased with sustainable polyol content; thermogravimetric analysis showed that 50% mass loss temperature increased by an average of 20 °C in foams containing 30% recycled polyol. Properties of density and SAG factor remained within 5% of the control petroleum-based reference foams. After comparing these findings to traditional polyols, a compelling argument can be made for the use of post-consumer automotive and industrial feedstocks in developing high-performing interior automotive PU foams.
The selective liquid phase hydrogenation of 2,4-dinitrotoluene (2,4-DNT) to the corresponding 2,4-nitroarylhydroxylamines has been studied over supported Pd, Pt, and Ru catalysts. Pt and Pd samples were found more active and selective than Ru. On the palladium catalysts the influence of metal particle size, temperature and nature of the support on the catalytic activity and selectivity has been also investigated. Both specific activity and selectivity were found to be dependent on the palladium particle size. Larger Pd particles were found more active and selective towards the formation of the nitroarylhydroxylamines The results reported have been interpreted on the basis of a different geometry and strength of adsorption of the substrate on the active sites. The products distribution is influenced also by the acid-base properties of the support used.
Plastic foams are used extensively in architectural (room and building acoustics) and noise control (acoustic insulation and absorption of sound sources) applications. The desired acoustic properties of the foam differ for each application. It goes without saying that the understanding of the relation between the physical parameters of the foam and its acoustic behaviour is of general interest. The study of the acoustic properties of porous materials has occupied scientists since the work of Beranek [1,2], Morse et al. [3] and Zwikker and Kosten [4] in the 1940s. A myriad of models describing sound propagation in porous materials have been published since. An excellent review can be found in [5]. However, most of these models require the introduction of parameters which cannot be measured independently, making them inappropriate for the design of sound absorbing materials. Since 1956, the Biot theory allows in a very general and rigorous way the description of sound propagation in porous materials. This theory has been used amply, including in underwater acoustics and sound propagation through liquid filled rocks. Recently, the Biot theory has been used to calculate the acoustic properties of plastic foams, and it has been proven that in a number of cases the Biot theory is indispensable for explaining the acoustic behaviour of certain foam types.
The kinetics of microphase separation during the processing of flexible polyurethane foam have been investigated. Forced-adiabatic, time-resolved synchrotron SAXS experiments were employed to probe the evolution of structure. Microphase separation was observed to occur at a critical conversion of isocyanate functional groups and shown to follow the kinetics associated with spinodal decomposition. The isocyanate conversion at the microphase separation transition (MST) was in good agreement with our previously reported FT-IR results. From the scattering data, R(q), the amplification rate of the composition fluctuations was determined. The data have been analyzed in terms of a time-dependent Ginzburg-Landau model (TDGL). Plots of R(q)/q2 versus q2 exhibited a maximum at a finite value of scattering vector (q). These observations were in qualitative agreement with the theoretical predictions of the TDGL theory.
The dynamic surface tensions of solutions of various branched and linear polysiloxane polyether block copolymers in a liquid polypropyleneoxide have been measured. These results have been related to the foam-stabilizing effect of such copolymers in polyurethane foam production. It is concluded that an optimum surface elasticity is a necessary but insufficient criterion for successful foam formation.
Pd-Fe/SiO2 bimetallic catalysts with a constant amount of Pd and a different Fe/Pd ratio were prepared by sequential wet impregnation and the hydrogenation of 2,4-dinitrotoluene was carried out at 25°C in a batch reactor. The presence of Fe enhances the Pd catalytic activity. The formation of a dispersed Pd-Fe alloy was evidenced through X-ray powder diffraction and is consistent with the data observed by FTIR analysis, TPR, and chemisorption features. The increase of the Fe total content of the catalysts results in the increase of the dispersion of the metallic phase and in the presence of partially oxidized Fe species. FTIR analysis shows that nitrocompounds chemisorb mainly on the support rather than on the metal surface. It is suggested that the Pd-Fe alloy formation is responsible for the increase of the catalytic activity because of a cooperative effect of Fe in the hydrogen transfer step. 48 refs., 12 figs., 4 tabs.
The formation of urethane, soluble urea and hydrogen-bonded urea species during the fast bulk copolymerization which forms flexible polyurethane foam has been studied using the adiabatic reactor method and forced-adiabatic, time-resolved FT-IR spectroscopy. The evolution of hydrogen-bonded urea is analysed emphasizing the onset of microphase separation of urea hard-segment sequences and their subsequent growth into hydrogen-bonded urea hard-segment domains. FT-IR spectroscopy indicated that the microphase separation transition (MST) occurred at a critical conversion of isocyanate function groups (pNCO = 0·55 ± 0·05) across a wide range of water concentrations. The kinetics of microphase separation during the fast bulk copolymerization of flexible polyurethane foam have also been investigated employing forced-adiabatic, time-resolved synchrotron SAXS experiments. Microphase separation was observed to occur at a critical conversion of isocyanate functional groups (pNCO = 0·54 ± 0·02) and is shown to follow the kinetics associated with spinodal decomposition. The onset of MST was in good agreement with the FT-IR spectroscopy results. Forced-adiabatic rheological measurements have been conducted during the fast bulk copolymerization. Four main regions of rheological development during the formation of polyurethane foam were identified. These were: (i) bubble nucleation, (ii) liquid foam and microphase separation, (iii) physical gelation and (iv) foamed elastomer. Physical gelation of the foamed polymer resulting from vitrification of the hard-segment sequences was observed to occur at pNCO = 0·71 ± 0·01 for a low water concentration foam.
A series of flexible polyurethane slabstock foam samples were prepared with varying water content and studied using transmission electron microscopy (TEM), video-enhanced optical microscopy (VEM), and small-angle X-ray scattering (SAXS). A new TEM sample preparation technique was developed in which the foam is impregnated with water, frozen, and microtomed, and the polyether soft segment is selectively degraded in the electron beam. Structures of two size scales were detected. A texture with grains (“urea aggregates”) 50–200 nm in size was imaged using both VEM and low-magnification TEM for foams with formulations containing more than 2 pphp water. For the first time, images of urea hard segment microdomains in polyurethane foam (approximately 5 nm in size) were obtained using high-magnification TEM. A microdomain spacing of approximately 6–8 nm was estimated from the SAXS scattering profiles. Glycerol was added to one of the formulations in order to modify the urea microphase separation and to give insight into morphology development in molded polyurethane foam systems. No structure was observed in low-magnification TEM images of the glycerol-modified foam, although smaller structures (hard segments) were detected at high magnification and by SAXS. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 573–581, 1998
The rate of nitration of m-nitrotoluene in aqueous sulphuric acid at 25° has been determined as a function of solvent composition over the range 72-87% w/w sulphuric acid. It has been established that a minor product (∼1.4%) of the nitration is 3,5-dinitrotoluene. The relative rates of nitration of the three mononitrotoluenes have been measured by the competitive method. Orientation data for the nitration of the mononitrotoluenes are compared with values predicted by the additivity principle.
The oxypropylation of glycerol in the presence of alkaline catalyst has been studied in a semibatch operation. Initial catalyst concentration was varied from 0.22 to 2.3 weight % KOH, temperature was varied from 220° to 270° F., and agitation speed was varied from 50 to 200 r.p.m. The rate of reaction was shown to increase with increase in all three variables. The most significant variable was catalyst concentration, which gave a fourfold increase in reaction rate.
In this paper, glycolysis of toluenediisocyanate based water-blown polyurethane foam has been examined by high performance liquid chromatography and gel permeation chromatography to determine the product distribution. Glycolysis with diethylene glycol (DEG) yields toluenediamine (TDA), TDA mono- and di- DEG carbamates, a series of urea-linked mono- and di- DEG carbamate TDA oligomers, and polyether triol (polyol). The complexity of the product mixture suggests problems in applying simple glycolysis to the recovery of mixed and/or contaminated polyurethane wastes. A simpler product mixture results when water and a base catalyst are added to the glycolysis reaction (hydroglycolysis). Hydroglycolysis yields TDA and polyol as principal products. Data for the rate of the hydroglycolysis reaction are presented in the temperature range of 150 to 190°C. These results suggest that hydroglycolysis could be used to recover polyols from mixed and/or contaminated water-blown polyurethane wastes.
Cellular solids include engineering honeycombs and foams (which can now be made from polymers, metals, ceramics, and composites) as well as natural materials, such as wood, cork, and cancellous bone. This new edition of a classic work details current understanding of the structure and mechanical behavior of cellular materials, and the ways in which they can be exploited in engineering design. Gibson and Ashby have brought the book completely up to date, including new work on processing of metallic and ceramic foams and on the mechanical, electrical and acoustic properties of cellular solids. Data for commercially available foams are presented on material property charts; two new case studies show how the charts are used for selection of foams in engineering design. Over 150 references appearing in the literature since the publication of the first edition are cited. It will be of interest to graduate students and researchers in materials science and engineering. © Lorna J. Gibson and Michael F. Ashby, 1988 and Lorna J. Gibson and Michael F. Ashby, 1997.
A rapid steady-state technique was developed to measure the effective permeability and diffusion coefficients of closed-cell foam insulation. To test the new technique Nâ data were first obtained by the long-term steady-state technique, and then reproduced ten times faster by the rapid steady-state technique. By using the new technique, reference values of effective diffusion coefficients of Nâ, Oâ, and Fluorocarbon 11 in closed-cell polyurethane foams were obtained at different temperatures. Data for Fluorocarbon 11 were obtained 30 times faster than data could be obtained by long-term steady-state tests. To estimate when steady-state has been achieved, the transient diffusion equation was solved, and the solution was given in the form of a chart. The time needed to achieve steady-state mass flux in a foam sample was found to depend strongly on the ratio of the partial pressures imposed on the surface of a tested sample. By the use of the solution, the value of the foam effective diffusion coefficient can be obtained before steady-state conditions are achieved within the sample.
It has already been asserted, by Mr. Monge and others, that the phenomena of capillary tubes are referable to the cohesive attraction of the superficial particles only of the fluids employed, and that the surfaces must consequently be formed into curves of the nature of lintearias, which are supposed to be the results of a uniform tension of a surface, resisting the pressure of a fluid, either uniform, or varying according to a given law. Segner, who appears to have been the first that maintained a similar opinion, has shown in what manner the principle may be deduced from the doctrine of attraction, but his demonstration is complicated, and not perfectly satisfactory; and in applying the law to the forms of drops, he has neglected to consider the very material effects of the double curvature, which is evidently the cause of the want of a perfect coincidence of some of his experiments with his theory. Since the time of Segner, little has been done in investigating accurately and in detail the various consequences of the principle. It will perhaps be most agreeable to the experimental philosopher, although less consistent with the strict course of logical argument, to proceed in the first place to the comparison of this theory with the phenomena, and to inquire afterwards for its foundation in the ultimate properties of matter. But it is necessary to premise one observation, which appears to be new, and which is equally consistent with theory and with experiment; that is, that for each combination of a solid and a fluid, there is an appropriate angle of contact between the surfaces of the fluid, exposed to the air, and to the solid. This angle, for glass and water, and in all cases where a solid is perfectly wetted by a fluid, is evanescent: for glass and mercury, it is about 140°, in common temperatures, and when the mercury is moderately clean.
This paper reports results of an experimental program which show that the use of various silicone surfactants and amine catalysts strongly influence the processing latitude and physical properties obtained in several flexible foam systems. Selected surfactants and catalysts have been studied in several foam systems. A range of new silicone-oxyalkylene materials have been designed for High Resilience slabstock formulas. High Resilience data is compared in both slabstock and molded systems. The use of several amine catalysts is compared in conventional slabstock foam systems along with hot molded, filled and specialty foams. Extensive test data (including combustibility tests) are included.
The productions of flexible polyurethane foams have been studied by the use of tertiary amines and/or tin compounds as catalysts. The performance of catalysts was evaluated by recording the foam height and the rise rate using a Fluidyne apparatus or ultrasonic equipment.
Two techniques for the study of urethane foam systems have been developed. One method detects cell opening in open-cell foams by measuring gas flow rate when injected at less than 0. 05 psig into the foam via an implanted probe. Cell opening produces a distinct increase in gas flow due to increased permeability. The other method measures foam rate of rise as a decrease in flow through a vertical perforated probe tube as the growing foam progressively obstructs its openings. The methods are non-mechanical and extremely inexpensive.
In recent years urethane foam for seat cushioning has been required to withstand increasing demands throughout its service life with regard to fatigue resistance. The characteristic of a seat relating its performance during use with time is spoken of as its durability. The ultimate durability test is that of actual use in the car over the life of the vehicle; however, practically this test would be shortened to an accelerated schedule. In-car testing can be evaluated two ways - subjectively and objectively. Subjective judgments are based on comfort, feel, and trim. The ability to fatigue test full size seat cushions, in a bench scale accelerated manner, should provide the best possible situation for correlation with in-car testing. The second aspect of car durability is the comfort criteria. Not only must the foam seat cusion maintain its load bearing ability; but also provide the occupant with a comfortable seat. Air flow (breathability) plays an important role in the seating comfort of automobile cushions. Results of an experimental program are presented in which an attempt has been made to define some limits on airflow and corresponding resilience of full foam seat cushions. Also a method of evaluating the resistance of foam seat cushion to load bearing degradation and its relationship to in-car durability performance are examined.
The physical properties of flexible polyurethane foams can be varied to give a wide selection of comfort, support, and durability. The firmness of a foam (as measured by Indentation Force Deflection) can be varied independently of density. However, the support and durability of flexible foam depend upon the foam density. Over the past several years the average density of flexible foam used in residential furniture manufacture has declined by about 20%. The effect of this trend on the quality of the foam used in furniture applications has not been clearly established, although the perceived effect is one of decreased durability. This study confirms and expands upon the preliminary results of several past studies, in which improvements in durability were observed as foam density was increased.
Simple techniques such as swelling and hardness measurements have allowed a comparison of the kinetics of foam formation in hot cure and cold cure of polyurethanes. This study yields only a first approximation of a complete description of what happens in foam molding, but provides a framework to which more detailed observations and further theoretical considerations can be fitted.
Several of the physical, chemical and environmental factors which influence durability characteristics of flexible urethane foams for commercial automotive and furniture cushioning applications have been reviewed. The utility of accelerated aging and fatigue tests for measuring comparative durability responses of flexible foams to changes in composition, processing or application have been described. The reliability of extrapolating service behavior of flexible foams from accelerated test data has been examined. Finally, the significant.
Experimental program is reported in which samples of high resilient (HR) foam, sometimes also referred to as cold foam, as well as of hot foam, produced at a temperature of 150-175 C were prepared and tested in regard to the effect of humidity on their physical properties. It is shown that a major difference in HR foam as compared with hot foam is its greater change in ILD (indentation load deflection), CLD (compression load deflection), and compression set properties with change in humidity conditions. The authors have also discussed possible causes for this difference. Knowing what the problem is constitutes the beginning of its solution. This remains as a major challenge for the urethane industry. Extensive experimental data are presented in tables and curves; they are discussed in terms of theoretical considerations.
A slab stock urethane foam cell ideally resembles an elongated pentagonal dodeca hedron. The faces are bounded by ribs, and membranes stretch across the ribs during the expansion of the foam. The normal formation of the foam does not result in the rupture of all the membranes. Data are presented showing that Air Flow values for flexible polyether and polyester foams are affected profoundly by the membrane population and, to a smaller extent, by density and cell geometry. It is also shown that within a given bun Air Flow values may vary with both position and orientation. Air Flow val ues also vary considerably between different foams. Because variation in Air Flow values is related to cell structure, it can be related to certain physical properties. Examples of this are given for ball rebound, compression load deflection, flex fatigue, and color shad ing. A quantitative definition of operating range based on Air Flow values is demon strated for tin catalyst concentration in a polyether foam. As a result of these findings Air Flow is recommended as a new parame ter for describing flexible urethane foam cell structure.
Thermal density fluctuations within phases and finite interphase widths lead to systematic deviations from Porod's law. The validity of present methods used to analyze these deviations and determine diffuse-boundary widths is determined. In view of the inadequacies found in these methods, a simple yet accurate method is proposed to determine the diffuse-boundary width from direct graphical analysis of slit-smeared intensity data. The diffuse interface is modelled by a sigmoidal-gradient model which is justified on thermodynamic grounds, with the interphase thickness as a function of the Flory–Huggins interaction parameter.
The catalytic hydrogenation of 2,4-DNT over palladium supported on carbon catalysts is reported. The 2-(hydroxyamino)-4-nitrotoluene (2HA4NT) was identified as a reaction intermediate. The characterization of this compound and the reasons for its formation are discussed.
A survey is given of the problems to be solved before catalytic hydrogenation reactors can be applied in a multiproduct plant in which selectivity problems are experienced. Some results are reported on work done on the reaction kinetics of two multistep model reactions and on mathematical modelling and experimental verification of the models. Since hydrogenation reactions are often very exothermic, cooling by solvent evaporation has been applied where appropriate. Sufficient information has been collected and correlated to enable operation of multiproduct catalytic reactors of the slurry or packed bubble column type; interdependence of operating variables is so complex that a mathematical model is indispensable.
Description of the chemical and physical phenomena taking place during foaming is the aim of this work. A technique has been developed to follow the foaming reaction under conditions that resemble actual processing operations. The experimental technique, based on Fourier Transform Infrared spectroscopy (FTIR), is presented, and the results obtained with a typical slabstock system are critically reviewed. Attempts to correlate isocyanate conversion by means of the adiabatic reaction method and infrared measurements during foaming are discussed.
Several relationships have been studied between polymer structure and the physical properties of high resiliency flexible urethane foams. This study revealed that ambient temperature polymer properties are affected primarily by the amount and nature of disubstituted urea sequences. The amount of disubstituted urea sequences can be controlled by the molar amount of water and the molar amount of isocyanate in the urethane formulation. The nature of the disubstituted urea sequences is controlled by the type of isocyanate and by the choice of amine or organometallic catalyst. Polymer properties were also shown to be dependent on crosslink density. Further, it was demonstrated that the modulus of urethane foam polymers can be increased substantially without affecting the glass transition temperature through the addition of the vinyl polymer dispersions contained in polymer-polyols. Extensive experimental data are presented in curves.
The history of the science and technology of polymeric foams is traced from its early beginnings starting in the late 1920s with latex foam. Two major methods evolved for producing the latter, the Dunlop and Talalay processes, both reaching industrial stages in the 1930s. Both natural and synthetic latices, notably SBR, as well as blends were extensively used. With the development of many other synthetic elastomers during the last three decades, many flexible and semiflexible foams were produced from them including polyvinyl chloride, polyolefin, and urethane foams among the major flexible foam categories but which also included specialty foams such as silicone and fluorocarbon-based foams. Among rigid foams, low density foams were first produced from special phenolic resins, and various foaming procedures evolved subsequently for the production of phenolic foams. Urea-formaldehyde foams were developed as early as 1933. The most widely used types of rigid foams today, polystyrene and polyurethane foams, underwent many technological changes. Rigid urethane foams became available as early as the late 1930s. Other rigid foams, including epoxy foams, and more specialized high-temperature-resistant foams were developed in more recent years with urethane-modified isocyanurate foams reaching significant industrial use.
Small-angle X-ray scattering is shown to be an effective technique, complementary to mechanical and thermal methods, for the study of structural ordering in polyurethane elastomers. Wide variations in intensity were found for different sample compositions and are interpreted in terms of the degree of hard segment aggregation. The results support previous conclusions regarding the organization in these samples based on analysis by scanning thermal methods. The polyether polyurethanes studied showed a higher degree of organization than the equivalent polyesters, and longer urethane segments enhance the extent of domain structure. Studies of the temperature dependence of scattering strengthen the previous assignment of a transition at about 150°C to the disordering of domain structure.
Polyether poly(urethaneureas) and polyester poly(urethaneureas) based on 2,4-toluene diisocyanate, ethylenediamine, and poly(tetramethylene oxide) or poly(butylene adipate) were synthesized to study the effect of the urea linkage in the hard segment on the extent of phase segregation, domain structure, and polymer properties. The experimental techniques utilized were differential scanning calorimetry and wide-angle and small-angle X-ray techniques. Phase segregation into the hard segment domains in the soft segment phase was observed in both the polyether and polyester series at all levels of urea content. In both series, the hard segment domains are amorphous with a very high Tg (165-190°C), even in low-urea-content compositions. The Tg of the soft segment phase in the polyether series was found at approximately -55°C for 1000 molecular weight polyether and -75°C for 2000 molecular weight polyether. For the polyester series, the Tg of the soft segment phase was -10 to -30°C for 1000 molecular weight polyester and -40 to -55°C for 2000 molecular weight polyester. Comparison of the thermal transition behavior of poly(urethaneureas) was made with the comparable poly(urethanes) extended with butanediol. In general, the extent of phase segregation is dramatically improved, as is reflected by a much lower Tg of the soft segment phase and by a much higher Tg of the hard segment domain in poly(urethaneureas) extended with ethylenediamine than in poly(urethanes) extended with butanediol.
The thermal transition behavior of two series of polyurethane block copolymers, one based on 2,4-toluene diisocyanate, the other on 2,6-toluene diisocyanate, was studied to determine the influence of an asymmetric diisocyanate structure, such as that represented by 2,4-toluene diisocyanate, on domain organization and polyurethane properties. The 2,4-TDI polyurethanes were transparent and amorphous, and the properties varied progressively with urethane concentration; the 2,6-TDI polyurethanes were opaque, semicrystalline, and hard but tough. In the 2,4-TDI samples the glass transition Tg was a strong function of urethane concentration. Similar behavior was shown by an intermediate temperature transition T2. A higher temperature transition T3 was detected only in the samples of highest urethane content and then only on the initial heating. In the 2,6-TDI samples Tg was generally independent of urethane concentration. No T2 transition was observed. The T3 transition was repeatable and increased with urethane concentration. It is suggested that the T2 transition which occurs in the 2,4-TDI polyurethanes is indicative of weak domain structure and that the increase in Tg with urethane concentration is due to extensive hard segment mixing with the soft segment phase. The absence of a T2 transition in 2,6-TDI is taken to indicate that all domain structure which occurs is highly ordered and, therefore, that hard segment-soft segment mixing is minimal. This is in keeping with the strong T3 transition and observed crystallinity and could account for the invariance of Tg with urethane concentration.
Property-structure relationships in a series of segmented polyurethans (I) have been studied. The structural features of interest - hard segment size, size distribution, and spacing along the chain (i.e., soft segment distribution) - were varied independently by special synthetic techniques. The hard segments are crystalline and have well-defined melting points which increase with segment size. Reciprocal absolute melting temperature is inversely proportional to the number of repeat units in the segment. Degree of crystallinity varies little with size. Cocrystallization of different hard segments is a function of relative size. Narrowing of the hard segment size distribution increases modulus, tensile, and extension set drastically. Narrowing of the soft segment distribution causes a slight increase in modulus, a moderate increase in elongation and tensile, and a large increase in extension set.
Scanning transmission X-ray microscopy (STXM) and atomic force microscopy have been used to study the morphology and chemical composition of macrophase-segregated block copolymers in plaque formulations based on water-blown flexible polyurethane foams. Although there has been a large body of indirect evidence indicating that the observed macrophase-segregated features in water-rich polyurethane foams are due principally to urea components, this work provides the first direct, spatially resolved spectroscopic proof to support this hypothesis. The STXM results are consistent with a segregation model where urea segments segregate, forming enriched phases with the majority of the polyether−polyol and urethane groups at the chain ends of the urea hard segments. Chemical mapping of the urea, urethane, and polyether distribution about the urea-rich segregated phases showed that the urea concentration changes gradually (across several hundred nanometers) in a butylene oxide-based foam. This mapping also showed the urea-rich segregated phases present as a partial network in an ethylene oxide/propylene oxide sample.
As part of our continuing study of the solid-state morphology of poly(urethane urea) segmented block copolymers, we focus in the current paper on the use of atomic force microscopy to visualize the structure of phase-separated microdomains. Free surface and bulk images were obtained from two series of PUU films, for copolymers varying in hard segment content from 14 to 47 wt %. Using a progression of AFM tapping forces, the morphology of the hard domains at the free surfaces was found to be in the form of randomly oriented cylinders with additional spherical domains, both having lateral dimensions on the order of 5−10 nm. At higher tapping forces, phase images of microtomed surfaces of relatively high hard segment content PUU copolymers appear to exhibit hard segment-rich domains at two size scales. However, images of surfaces of specimens freeze-fractured at liquid N2 temperatures (and acquired at relatively low tapping forces) reveal the larger structures to be aggregates of smaller hard microdomains.