Conventional Polyurethane Foam Research Articles

Catalytic polymer self-cleavage for CO2 generation before combustion empowers materials with fire safety

Polymeric materials, rich in carbon, hydrogen, and oxygen elements, present substantial fire hazards to both human life and property due to their intrinsic flammability. Overcoming this challenge in the absence of any flame-retardant elements is a daunting task. Herein, we introduce an innovative strategy employing catalytic polymer auto-pyrolysis before combustion to proactively release CO2, akin to possessing responsive CO2 fire extinguishing mechanisms. We demonstrate that potassium salts with strong nucleophilicity (such as potassium formate/malate) can transform conventional polyurethane foam into materials with fire safety through rearrangement. This transformation results in the rapid generation of a substantial volume of CO2, occurring before the onset of intense decomposition, effectively extinguishing fires. The inclusion of just 1.05 wt% potassium formate can significantly raise the limiting oxygen index of polyurethane foam to 26.5%, increase the time to ignition by 927%, and tremendously reduce smoke toxicity by 95%. The successful application of various potassium salts, combined with a comprehensive examination of the underlying mechanisms, underscores the viability of this strategy. This pioneering catalytic approach paves the way for the efficient and eco-friendly development of polymeric materials with fire safety.

Antimicrobial Nonisocyanate Polyurethane Foam Derived from Lignin for Wound Healing.

Medical dressings, as a cover for wounds, can replace damaged skin in the wound healing process to play a temporary barrier role, avoid or control wound infection, and provide a favorable environment for wound healing. Therefore, there is an urgent need for medical antimicrobial dressings for the treatment of chronic wounds. Although traditional polyurethane foam has been widely used in medical dressings, conventional polyurethane foams are primarily prepared using nonbiocompatible isocyanate-based compounds, which are potentially hazardous for both operators and applications in the medical field. Here, we propose nonisocyanate polyurethane foams naturally derived from lignin by enzymatic lignin alkylation, cyclic carbonation modification, and polymerization with diamine and the addition of a blowing agent. Silver nanoparticle solution was added during foaming to confer antimicrobial properties. This lignin-based nonisocyanate polyurethane/silver composite foam (named NIPU foam-silver) using a green synthesis method has good mechanical properties, which can be used to manufacture polyurethane/silver foams, and thermal and antimicrobial properties. Notably, NIPU foam-Ag showed more than 95% bactericidal efficacy against both Escherichia coli and Staphylococcus aureus within 4 h. Evaluation of in vitro wounds in mice showed that this antimicrobial composite foam rapidly promotes wound healing and repairs damaged tissue. This suggests that this biobased biodegradable antimicrobial foam has significant scope for clinical applications in wound management.

Foam stability and thermo-mechanical properties of micro/nano filler loaded castor oil based flexible polyurethane foam

Use of fillers in polymers is to improve thermo-mechanical properties of the resulting material. Fillers are also used in polymeric foam as cell openers. Flexible polyurethane (PU) foams undergo major loss in structural stability when synthetic polyol is replaced with castor oil in the formulation as an alternate polyol. This study probes the effect of various micro and nano-fillers on PU foams prepared using blend polyol containing castor oil and synthetic polyol at a ratio of 1:1. Physical and cellular properties such as foam height, cell diameter, strut thickness and cell number density were evaluated to probe the structural stability of the foam. All foams prepared were found stable while it was found that the densities of the PU foams synthesized were greater than that of the conventional PU foams. Addition of fillers found to enhance thermal and mechanical properties of the foam. Moreover, all foam samples were found to observe thermal stability over and above 258 °C. Minimum glass transition temperature was recorded for 15% HG samples (i.e., −35.5 °C). Highest tensile strength was observed for 15% Si samples whereas, highest elongation was observed for 10% NC.

Utilization of biomass for energy conservation in agricultural usage

Ensuring food security is a crucial sustainable development goal in developing countries such as India. One of the major challenges is affordable storage infrastructure for food preservation. The high cost of storage facilities is due to expensive insulating materials. In this study, we explored the potential of agricultural biomass, which is often burned, as a low-cost sustainable insulating material for energy conservation in cold storage technologies. We investigated the efficacy of biomass as a heat insulating medium and compared its transmission losses with conventional polyurethane foam (PUF). The biomass characterization results showed that the thermal conductivity of paddy straw biomass was 0.0670 W/m°C, with the lowest conductivity observed for 1–2 mm sized biomass particles. By demonstrating the potential of agricultural biomass as an affordable and sustainable insulating material, this study contributes to the development of cost-effective storage solutions, ultimately benefiting farmers and supporting food security efforts in developing countries.

Recent Progress of Non-Isocyanate Polyurethane Foam and Their Challenges.

Polyurethane foams (PUFs) are a significant group of polymeric foam materials. Thanks to their outstanding mechanical, chemical, and physical properties, they are implemented successfully in a wide range of applications. Conventionally, PUFs are obtained in polyaddition reactions between polyols, diisoycyanate, and water to get a CO2 foaming agent. The toxicity of isocyanate has attracted considerable attention from both scientists and industry professionals to explore cleaner synthesis routes for polyurethanes excluding the use of isocyanate. The polyaddition of cyclic carbonates (CCs) and polyfunctional amines in the presence of an external blowing agent or by self-blowing appears to be the most promising route to substitute the conventional PUFs process and to produce isocyanate-free polyurethane foams (NIPUFs). Especially for polyhydroxyurethane foams (PHUFs), the use of a blowing agent is essential to regenerate the gas responsible for the creation of the cells that are the basis of the foam. In this review, we report on the use of different blowing agents, such as Poly(methylhydrogensiloxane) (PHMS) and liquid fluorohydrocarbons for the preparation of NIPUFs. Furthermore, the preparation of NIPUFs using the self-blowing technique to produce gas without external blowing agents is assessed. Finally, various biologically derived NIPUFs are presented, including self-blown NIPUFs and NIPUFs with an external blowing agent.

Comparison of Satisfaction Levels between Conventional and Silicone-Adhesive Polyurethane Foam Materials in Patients with Skin Wounds

Background: Polyurethane (PU) foam dressing materials have been widely used in commercial wound dressing applications. However, the repeated application of adhesive tapes to keep the foam dressings in place can result in minor injuries to the peri-wound skin. Silicone-adhesive PU foam dressing materials have been developed to prevent such injuries. In this study, the satisfaction levels between conventional and silicone-adhesive PU foams were assessed through a survey of patients and physicians.Methods: A survey study of 140 patients with skin wounds was conducted in a single institution between July 2019 and May 2020. The patients were first treated with either conventional PU foam or silicone-adhesive PU foam, after which they were asked to record their levels of pain, adhesiveness, waterproofness, and satisfaction. At the next visit, dressings of the other material were applied to their wounds, and the same assessment process was repeated at the next dressing change.Results: The silicone-adhesive PU foam dressings demonstrably reduced the levels of dressing-related trauma and pain, compared to that of patients treated with conventional PU foam dressings. The silicone-adhesive PU foam dressings were also associated with substantially higher scores of satisfaction and waterproofness. In comparison, the mean adhesiveness score was superior in the group treated with conventional PU foam dressings, compared to that of the group treated with silicone-adhesive PU foam dressings.Conclusion: Silicone-adhesive PU foam contributed to minimizing pain during dressing change and increasing patient’s comfort. As a result, patients preferred dressing with silicone-adhesive PU foam over conventional PU foam.

Geometrically modified auxetic polyurethane foams and their potential application in impact mitigation of masonry structures

Hollow block masonry buildings constructed alongside busy roads are vulnerable to vehicular impacts resulting in damage to property and harm to the building and vehicle occupants. This paper presents a method for the design and insertion of various forms of geometrically modified auxetic foam structures inside the hollow cores of block masonry walls for mitigating the adverse effects of such impacts. Due to the low tensile strength of masonry, the insertion material should possess high energy absorption characteristics and high strength for impact damage mitigation which can be achieved through auxetic foams with negative Poisson’s ratio. To this end, finite element models of geometrically modified auxetic foams (GMAFs) are developed by inserting thin polyester sheets and hollow acrylonitrile butadiene styrene (ABS) tubes of various geometries into conventional polyurethane foams. The proposed geometrical configurations of inserted tubes and sheets result in auxetic behaviour of the conventional foam with a maximum negative Poisson’s ratio of about −12. These foam models are validated analytically and then employed to model masonry walls with auxetic foam insertions in the hollow cores of blocks. These masonry wall models are then analysed under high-velocity lateral impacts. Results show the beneficial change in the failure mechanism of the masonry walls which altered from severe damage of wall face to the rebound of the impactor without penetration by reducing the displacement by four times, due to the presence of the auxetic foam insertions. This phenomenon occurred due to the significant energy dissipation caused by the combined effects of the re-entrant shaped hollow tubes and thin polyester sheet arrangements in the GMAF. Outcomes of this study will contribute towards safer masonry buildings along busy road fronts.

Eco‐friendly blowing agent, HCFO‐1233zd, for the synthesis of polyurethane foam as cryogenic insulation

AbstractPolyurethane foam is an insulating material, which is adopted in various industrial fields owing to its high compressive strength, low thermal conductivity, and excellent impact resistance. The most important additive in the synthesis process of the polyurethane foam is the blowing agent because it significantly affects the cell structure and density. HFC‐245fa, the most widely used blowing agent, is expected to be terminated under strict environmental regulations owing to its high global warming potential. This study synthesizes a new eco‐friendly polyurethane foam with HCFO‐1223zd in the density range of 90 to 190 kg/m3. After the synthesis process, the microstructural morphology of the HCFO‐1223zd blown polyurethane foam was observed using scanning electron microscopy. Additionally, the insulation performance was compared to conventional polyurethane foam. Furthermore, mechanical characteristics were investigated at 20 and −163°C temperatures. The results show that the HCFO‐1233zd blown polyurethane foam has superior mechanical and thermal properties compared to the conventional blowing agents.

Dynamic Carboxylate Linkage Based Reprocessable and Self-Healable Segmented Polyurethane Vitrimers Displaying Creep Resistance Behavior and Triple Shape Memory Ability

Though conventional polyurethane foams are among the most widely used polymer materials currently, the lack of reprocessability and creep resistance ability restricts their further commercial growt...

Magnetic and Tunable Sound Absorption Properties of an In-Situ Prepared Magnetorheological Foam.

Conventional polyurethane foam has non-tunable sound absorption properties. Here, a magneto-induced foam, called magnetorheological (MR) foam, was fabricated with the feature of being able to tune sound absorption properties, primarily from the middle- to higher-frequency ranges. Three different samples of MR foams were fabricated in situ by varying the concentration of Carbonyl Iron Particles (CIPs) (0, 35, and 75 wt.%). The magnetization properties and tunable sound absorption characteristics were evaluated. From the magnetic saturation properties, the results showed very narrow and small coercivity of hysteresis loops relative to the soft magnetic properties of the CIPs. MR foam with 75 wt.% CIPs showed a higher magnetic saturation at 91.350 emu/g compared to MR foam with 35 wt.% CIPs at 63.896 emu/g. For tunable sound absorption testing, the effect of ‘shifting’ to higher frequency was also observed when the magnetic field was applied, which was ~10 Hz for MR foam with 35 wt.% CIPs and ~130 Hz for MR foam with 75 wt.% CIPs. As the latest evolution of semi-active noise control materials, the results from this study are valuable guidance for the advancement of MR-based devices.

A Green Approach to Modify Surface Properties of Polyurethane Foam for Enhanced Oil Absorption.

The non-selective property of conventional polyurethane (PU) foam tends to lower its oil absorption efficiency. To address this issue, we modified the surface properties of PU foam using a rapid solvent-free surface functionalization approach based on the chemical vapor deposition (CVD) method to establish an extremely thin yet uniform coating layer to improve foam performance. The PU foam was respectively functionalized using different monomers, i.e., perfluorodecyl acrylate (PFDA), 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA), and hexamethyldisiloxane (HMDSO), and the effect of deposition times (1, 5 and 10 min) on the properties of foam was investigated. The results showed that all the modified foams demonstrated a much higher water contact angle (i.e., greater hydrophobicity) and greater absorption capacities compared to the control PU foam. This is due to the presence of specific functional groups, e.g., fluorine (F) and silane (Si) in the modified PU foams. Of all, the PU/PHFBAi foam exhibited the highest absorption capacities, recording 66.68, 58.15, 53.70, and 58.38 g/g for chloroform, acetone, cyclohexane, and edible oil, respectively. These values were 39.19–119.31% higher than that of control foam. The promising performance of the PU/PHFBAi foam is due to the improved surface hydrophobicity attributed to the original perfluoroalkyl moieties of the HFBA monomer. The PU/PHFBAi foam also demonstrated a much more stable absorption performance compared to the control foam when both samples were reused for up to 10 cycles. This clearly indicates the positive impact of the proposed functionalization method in improving PU properties for oil absorption processes.

Stability enhancement of highly loaded nano-clay-based flexible polyurethane foams using hollow glass microspheres

Addition of fillers in polyurethane foams enhances the mechanical properties of polymeric foams. However, fillers can be loaded to a certain extent, as higher percentage of fillers in polymeric foam causes structural instability leading to the collapse of foam. In this article, we report the use of hollow glass microspheres as a possible co-filler which enables higher loading of nano-clay in flexible polyurethane foam. It has been observed that the structural and mechanical properties of nano-clay-loaded foams were found to cause instability at 5 wt% loading of nano-clay. Therefore, upon addition of hollow glass microspheres in 5 wt%, nano-clay-loaded polyurethane foam shows remarkable enhancement in terms of stability and mechanical properties of the resultant foams. A 100-fold increment in tensile strength has been observed for 2 wt% hollow glass microspheres and 5 wt% nano-clay-loaded flexible polyurethane foams as compared to conventional (unloaded) polyurethane foams.

Effect of Air Cushion Seating in Passenger Car on different Road Conditions

Objectives: To improve the ride comfort of the passenger car driver using an air-inflated cushion on top of the conventional polyurethane foam seat. Methodology: The acceleration between the base of the driver and the seat interface in a small passenger car is measured in all the three Cartesian directions for three different drivers each of different weights, on four different types of roads using SV106 Whole Body Vibration (WBV) measurement equipment. The car is driven at different speeds within the range of 20 kmph to 80 kmph on smooth road like highways and a limited maximum speed of 40 kmph on the other roads. The obtained results are used to calculate the percentage Seat Effective Amplitude Transmissibility (%SEAT) to estimate the ride comfort. Findings: The results proved that by using the air-inflated seat cushion placing over the polyurethane seat cushion has decreased the vibration that is transmitted to the driver and the ride comfort is enhanced rather than using only polyurethane foam cushion that is provided by the manufacturer. The air-inflated cushion used is of compartmental celled model which will not get deflated easily assuring comfort for a long period of safe drive. Keywords: Air-celled Cushion, Seat, Transmissibility, Ride-comfort, Whole Body Vibration.

Fabrication and Testing of Auxetic Foams for Rehabilitation Applications

Negative Poisson’s ratio or auxetic foams were fabricated and studied for use in prosthetic applications. A thermomechanical process was used to convert conventional polyurethane (PU) foam into auxetic PU foam. Two types of auxetic PU foams were made using two different volumetric compression ratios, 3.02 and 3.86. Chemical composition analysis showed that chemical structure of the converted auxetic foam remained the same as the conventional PU foam after the thermomechanical process. Compression tests showed that the auxetic foams had higher stiffness than conventional foams, implying that the auxetic foams could be potentially used in seat cushions, shoe soles, and as liners in prosthetic applications. Compression fatigue tests showed that percentage loss in thickness in auxetic foam fabricated using lower compression ratio had loss in thickness that is comparable to conventional foam, whereas auxetic foam fabricated using higher compression ratio had greater loss in thickness. Our study indicates that the auxetic foams made using lower compression ratio need to be further explored for suitability in various rehabilitation applications.

Ultra-Light Reduced Graphene Oxide Based Aerogel/Foam Absorber of Microwave Radiation.

We present the polarization-dependent highly absorptive in Ka-band composition of conventional polyurethane foam filled with in situ synthesized aerogel coated by reduced graphene oxide (rGO). The rGO-based aerogel was in situ prepared into the open-cell polyurethane foam (PUF) skeleton through a bidirectional freeze-drying process. The aerogel is composed of the flat lamellas stacks, possessing the anisotropic structure and unique electromagnetic properties. Further improvement of the electromagnetic shielding ability was possible by the rGO coating introduction as a coupling layer between PUF and rGO-based aerogel. This enhances the overall conductivity of the resulting composites: 1.41 + 3.33i S/m vs. 0.9 + 2.45i S/m for PUF loaded with in situ synthesized aerogel without rGO coating.With this mechanically robust plane easy to process coating one could achieve −20 dB by power with the record light structure (0.0462 g/cm2). That could compete in view of the weight per cm2 even with graphene-based absorbers comprising either dielectric matching elements or back metal reflectors, or both.

Assessing the air filtration efficacy of compressed and uncompressed polyurethane foams

The aim of this work was to assess the change in fungal spore filtration efficacy when conventional polyurethane foams were compressed to different ratios. Ninety PPI polyurethane foam samples of 30- and 50-mm thickness were produced, while different samples of 30-mm thickness were compressed to 5 and 25 mm. Air was drawn through foams in a set-up of manifold ports and spores were trapped onto the membrane filters. Micrographs of the polyurethane foams were also collected. An increase in the thickness of the foams resulted in a higher percentage of filtration efficacy. No observable change in the filtration efficiency of the foam was developed when the foam thickness was increased from 30 up to 50 mm. Compression, by reducing the pore size of the foam, allowed a more sinuous path for the air passing through the foam thus resulting in an increase in its trapping ability. Practical applications Compressed foam filters represent a possible way to control dust and microorganisms which can be dispersed in the air of food storage facilities, thus limiting the risk of product contamination. Such filters may find application, for instance, in postharvest warehouses in order to help producers limit the use of chemical treatments on fruit. Furthermore, a compressed polyurethane foam can be easily uncompressed by heating, so that it can be cleaned from the trapped material and compressed once again to be re-used. This could be of great advantage to cut down the production costs wherever air filters are used and need often to be replaced.

Mechanical properties of a polyurethane hybrid composite with natural lignocellulosic fibers

Several low-cost hybrid composites composed of polyurethane and renewable natural fibers were developed and analyzed for their mechanical and physical properties. Composites were fabricated by replacing up to 20% w/w of the polyethylene glycol present in conventional polyurethane foams with one and the mixture of three natural fibers: sugarcane bagasse, sisal or rice husk. Prior to composite production, fibers were mercerized with sodium hydroxide and hydrogen peroxide to remove lignin and hemicellulose. A simplex-centroid mixture design model was used to evaluate the effects of the added fibers on composite properties such as resilience, elastic modulus and deformation under permanent compression. Obtained hybrid composites demonstrated up to 32% of resilience, 0.1 GPa of elastic modulus, and 7.32% of permanent deformation. In order to optimize these properties, fiber amounts were adjusted using a quadratic mathematical model, indicating that formulations containing only the rice husk or an 82/18 (% w/w) rice husk/sugarcane bagasse mixture will perform best. The obtained composite is a unique low cost material because is environmentally friendly and has a high potential for applications in shock absorption and padding materials, due its proven good resilience and elastic modulus.

Computational fluid dynamics (CFD) simulation of a newly designed passive particle sampler

In this work a series of computational fluid dynamics (CFD) simulations were performed to predict the deposition of particles on a newly designed passive dry deposition (Pas-DD) sampler. The sampler uses a parallel plate design and a conventional polyurethane foam (PUF) disk as the deposition surface. The deposition of particles with sizes between 0.5 and 10 μm was investigated for two different geometries of the Pas-DD sampler for different wind speeds and various angles of attack. To evaluate the mean flow field, the k-ɛ turbulence model was used and turbulent fluctuating velocities were generated using the discrete random walk (DRW) model. The CFD software ANSYS-FLUENT was used for performing the numerical simulations. It was found that the deposition velocity increased with particle size or wind speed. The modeled deposition velocities were in general agreement with the experimental measurements and they increased when flow entered the sampler with a non-zero angle of attack. The particle-size dependent deposition velocity was also dependent on the geometry of the leading edge of the sampler; deposition velocities were more dependent on particle size and wind speeds for the sampler without the bend in the leading edge of the deposition plate, compared to a flat plate design. Foam roughness was also found to have a small impact on particle deposition.

Auxetic composites made of 3D textile structure and polyurethane foam

Auxetic composites have attracted considerable attention in recent years and have demonstrated a high potential of applications in different areas due to their wonderful properties as compared to non‐auxetic composites. In this study, a three‐dimensional (3D) auxetic textile structure previously developed was used as reinforcement to fabricate auxetic composites with conventional polyurethane (PU) foam. Both the deformation behavior and mechanical properties of the auxetic composites under compression were analyzed and compared with those of the pure PU foam and non‐auxetic composites made with the same materials and structural parameters but with different yarn arrangement. The results show that the negative Poisson's ratio of composites can be obtained when suitable yarn arrangement in a 3D textile structure is adopted. The results also show that the auxetic composites and non‐auxetic composites have different mechanical behaviors due to different yarn arrangements in 3D textile structure. While the auxetic composites behave more like damping material with lower compression stress, the non‐auxetic composite behaves more like stiffer material with higher compression stress. It is expected that this study could pave a way to the development of innovative 3D auxetic textile composites for different potential applications such as impact protection.

Preparation and Characterization of Biopolyols and Polyurethane Foams from Liquefied Faba Bean Stalk

In this study, Faba bean stalk was liquefied for the production of biopolyols and polyurethane (PU) foams. The influences of various reaction conditions on biopolyols and PU foams were examined. Furthermore, the property relationships between biopolyols and PU foams were investigated. Biopolyols produced under the liquefaction conditions of 160°C, 90 min, 3% sulfuric acid loading, and 20% Faba bean stalk loading showed promising material properties (i.e. hydroxyl number, 496.1 mg KOH/g, acid number, 17.9 mg KOH/g, and viscosity, 1.1 Pa.s). PU foams produced from promising biopolyols showed compressive strength of 205 kPa and density of 0.035 g/cm3. The results suggested that in addition to density, the compressive strength of PU foams might also be affected by factors such as biomass residues or the chemical structures of biopolyols. The biopolyols and PU foams produced showed material properties comparable to those of conventional PU foams.