Search Results (37)

Polyurethane (PU) foam, renowned for its structural versatility, elasticity, compressibility, and adaptability, has garnered significant attention for its use in flexible strain sensors due to its capability to detect mechanical deformation. This review presents a comprehensive analysis of both the studies and recent advancements in PU foam-based strain sensors, particularly those incorporating conductive materials. The review begins by examining the chemical composition and structural characteristics of PU foam, followed by a discussion of various fabrication methods and their effects on sensor performance. It also explores the sensing mechanisms, including piezoresistive, piezoelectric, and capacitive effects. Moreover, key applications in motion detection, health monitoring, and environmental and industrial sensing are examined. Finally, the review addresses technological advancements, current challenges, and prospects. Full article

This study investigates the impact of polycarbonate diol (PCDL)-modified toluene diisocyanate (TDI)-based polyester polyurethane polishing pads on the chemical mechanical polishing of 4H silicon carbide (4H-SiC) substrates. Employing a unique metho, PCDL alters the ratio of polyurethane soft and hard segments, facilitating the one-step synthesis of a polishing pad via chemical foaming. The extent of the reaction of isocyanate groups was characterized by Fourier transform infrared spectroscopy, while the changes in the glass transition temperature of the material before and after modification were evaluated using differential scanning calorimetry. The mechanical properties and surface morphology of the modified pad have been systematically characterized. The results showed that compared with the polyurethane polishing pad without PCDL, tensile strength was augmented by a factor of 2.1, the elastic modulus surged by a factor of 4.2, the elongation at break improved by a factor 1.6, and the wear index decreased by a factor of 0.5 by 40 wt.% PCDL loading. Furthermore, the modified pad demonstrated a 14.5% increase in material removal rate and a reduction in surface roughness of 4H-SiC from 0.124 nm to 0.067 nm. Additionally, the compact surface pore structure and enhanced chemical stability in the strong oxidizing slurry of the modified pad enabled superior polishing performance, achieving an ultrasmooth 4H-SiC surface. The study highlights the potential of tailored polyurethane formulations in enhancing polishing efficiency and surface finish in semiconductor manufacturing processes. Full article

Arbutus unedo (strawberry tree) is a small Mediterranean tree capable of vigorous regrowth after disturbances like fire. Traditionally used for biomass fuel, its bark and branches hold potential for higher-value products through ecovalorization into liquid mixtures that could replace petroleum-based materials. This study aimed to explore the chemical composition of various components of Arbutus unedo and to produce a liquefied material from its internal (IB) and external bark (EB). Chemical compositions of internal and external bark were determined using TAPPI standards including ash, extractive content, lignin, and cellulose. Metal cations were analyzed by ICP. Liquefaction of bark was optimized in a PARR reactor, evaluating factors such as particle size, temperature, and time, and the best polyols were monitored by FTIR-ATR. Polyurethane foams were made with internal and external bark materials liquefied by polymerization with isocyanate, a catalyst, and water as a blowing agent. Results showed that EB has a higher extractive and lignin content, while IB contains more cellulose. Liquefaction yields were higher for IB (74%) than EB (68%), with IB yielding polyols that produced stronger and more resilient foams with higher compressive strength and modulus of elasticity. Mechanical properties of the foams were influenced by the NCO/OH ratio and catalyst levels. Overall, the internal bark demonstrated superior performance for foam production, highlighting its potential as an eco-friendly alternative to petroleum-derived materials. Full article

Polyurethane foam (PUF) pads are widely used in semiconductor manufacturing, particularly for chemical mechanical polishing (CMP). This study prepares PUF composites with microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC) to improve CMP performance. MCC and NCC were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing average diameters of 129.7 ± 30.9 nm for MCC and 22.2 ± 6.7 nm for NCC, both with high crystallinity (ca. 89%). Prior to preparing composites, the study on the influence of the postbaked step on the PUF was monitored through Fourier-transform infrared spectroscopy (FTIR). After that, PUF was incorporated with MCC/NCC to afford two catalogs of polyurethane foam composites (i.e., PUFC-M and PUFC-N). These PUFCs were examined for their thermal and surface properties using a differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), dynamic mechanical analyzer (DMA), and water contact angle (WCA) measurements. T_gs showed only slight changes but a notable increase in the 10% weight loss temperature (T_d10%) for PUFCs, rising from 277 °C for PUF to about 298 °C for PUFCs. The value of Tan δ dropped by up to 11%, indicating improved elasticity. Afterward, tensile and abrasion tests were conducted, and we acquired significant enhancements in the abrasion performance (e.g., from 1.04 mm/h for the PUF to 0.76 mm/h for a PUFC-N) of the PUFCs. Eventually, we prepared high-performance PUFCs and demonstrated their capability toward the practical CMP process. Full article

This study presents a comprehensive multiscale analysis of sandwich beams with a polyurethane foam (PUF) core, delivering a numerical comparison between finite element methods (FEMs) and a meshless method: the radial point interpolation method (RPIM). This work aims to combine RPIM with homogenisation techniques for multiscale analysis, being divided in two phases. In the first phase, bulk PUF material was modified by incorporating circular holes to create PUFs with varying volume fractions. Then, using a homogenisation technique coupled with FEM and four versions of RPIM, the homogenised mechanical properties of distinct PUF with different volume fractions were determined. It was observed that RPIM formulations, with higher-order integration schemes, are capable of approximating the solution and field smoothness of high-order FEM formulations. However, seeking a comparable field smoothness represents prohibitive computational costs for RPIM formulations. In a second phase, the obtained homogenised mechanical properties were applied to large-scale sandwich beam problems with homogeneous and approximately functionally graded cores, showing RPIM’s capability to closely approximate FEM results. The analysis of stress distributions along the thickness of the beam highlighted RPIM’s tendency to yield lower stress values near domain edges, albeit with convergence towards agreement among different formulations. It was found that RPIM formulations with lower nodal connectivity are very efficient, balancing computational cost and accuracy. Overall, this study shows RPIM’s viability as an alternative to FEM for addressing practical elasticity applications. Full article

Polymeric foams are used in many applications, from packaging to structural applications. While polymeric foams have good mechanical performance in compression, they are brittle in tension and bending; fibre reinforcement can enhance their tension and flexural behaviour. This work reports a novel investigation of the mechanical properties of fibre-reinforced polyurethane (FRPU) foams with natural henequen fibres. Pull-out tests were performed with 10 mm fibres and various foam densities to identify the optimal density of 100 kg/m³. Thus, FRPU foams with this density and fibre contents of 1, 2 and 3 wt% were manufactured for mechanical testing. Compression tests showed an increase in the elastic modulus of the FRPU foam specimens compared to the unreinforced PU foam. The FRPU foams also exhibited higher yield stress, which was attributed to the reinforcing effect of the fibres on the cell walls. A maximum increase of 71% in the compressive yield stress was observed for the FRPU foam specimens with a fibre content of 2%. In addition, FRPU foam specimens absorbed more energy for any given strain than the unreinforced PU foam. Flexural tests showed the FRPU foams exhibited increased flexural strength compared to the unreinforced PU foam. A maximum increase of 40% in the flexural strength was observed for the FRPU foam with a fibre content of 1%. The findings reported here are significant because they suggest that FRPU foams incorporating natural henequen fibre exhibit promising potential as sustainable materials with enhanced mechanical properties. Full article

Measurements of the properties of soft materials are important from the point of view of medical diagnostics of soft tissues as well as testing the quality of food products and many technical materials. One of the frequently used techniques for testing such materials, attractive due to its non-invasive nature, is the indentation technique, which does not puncture the material. The difficulty of testing soft materials, which affects the objectivity of the results, is related to the problems of stable positioning of the studied material in relation to the indentation apparatus, especially with a device held by the operator. This work concerns the comparison of test results using an indentation apparatus mounted on mobile and stationary handles. The tested materials are cylindrical samples of polyurethane foams with three different stiffnesses and the same samples with a 0.5 or 1 mm thick silicone layer. The study presented uses an apparatus with a flat cylindrical indenter, with a surface area of 1 cm², pressed to a depth of 10 mm (so-called deep tests). Based on the recorded force changes over time, five descriptors of the indentation test were determined and compared for both types of handles. The tests performed showed that the elastic properties of foam materials alone and with a silicone layer can be effectively characterized by the maximum forces during recessing and retraction and the slopes of the recessing and retraction curves. In the case of two-layer materials, these descriptors reflect both the characteristics of the foams and the silicone layer. The results show that the above property of the deep indentation method distinguishes it from the shallow indentation method. The repeatability of the tests performed in the mobile and stationary holders were determined to be comparable. Full article

The Elastic Catalytic Foam-bed Reactor (EcFR) technology was used to enhance a model catalytic hydrogenation reaction by improving gas–liquid mass transfer. This advanced technology is based on a column packed with a commercial elastomeric polyurethane open-cell foam, which also acts as a catalyst support. A simple and efficient crankshaft-inspired system applied in situ compression/relaxation movements to the foam bed. For the first time, the catalytic support parameters (i.e., porosity, tortuosity, characteristic length, etc.) underwent cyclic and controlled changes over time. These dynamic cycles have made it possible to intensify the transfer of gas to liquid at a constant energy level. The application chosen was the selective hydrogenation of phenylacetylene to styrene in an alcoholic solution using a palladium-based catalyst under hydrogen bubble conditions. The conversion observed with this EcFR at 1 Hz as cycle frequency was compared with that observed with a conventional Fixed Catalytic Foam-bed Reactor (FcFR). Full article

Thermoplastic polyurethane (TPU) is a versatile polymer with unique characteristics such as flexibility, rigidity, elasticity, and adjustable properties by controlling its soft and hard segments. To properly design and understand the TPU foaming process through supercritical CO₂, a design of experiments approach, the Box–Behnken design (BBD) was adopted using commercial TPU 85A as the model compound. The effect of saturation pressure, saturation temperature, and immersion time on the mean pore size and expansion ratio were investigated. The design space for the production of TPU foam was shown, and the significance of process parameters was confirmed using the analysis of variance (ANOVA). In addition, extrapolation foaming experiments were designed and validated the feasibility of the response surface model developed via BBD. It was found that the pore size of TPU 85A foam could be controlled within 13 to 60 μm, and a stable expansion ratio could be designed up to six. Full article

Fabrication, characterization and testing of protective biomimetic orthopedic footwear advanced insole materials are introduced. The main objective of this material is to preserve and isolate a set of sensors for the Weight-Bearing Monitoring System (WBMS) device. Twenty-one samples of renewably sourced Polyurethane Foam (PUF) composed of poly(trimethylene ether) glycol (PO₃G) and unmodified castor oil (CO) were synthesized and evaluated according to predetermined criteria. Response surface methodology of Box—Behnken design was applied to study the effect of the polyols ratio, isocyanate index (II), and blowing agent ratio on the properties (hardness, density) of PUFs. Results showed that CO/PO₃G/Tolyene Diisocyanate (TDI) PUFs with hardness Shore A 17–22 and density of 0.19–0.25 g/cm³ demonstrate the required characteristics and can potentially be used as a durable and functional insole material. Phase separation studies have found the presence of well-segregated structures in PUFs having polyols ratio of CO:PO₃G 1:3 and low II, which further explains their extraordinary elastic properties (400% elongation). Analysis of cushioning performance of PUF signified that five samples have Cushioning Energy (CE) higher than 70 N·mm and Cushioning Factor (CF) in the range of 4–8, hence are recommended for application in WBMS due to superior weight-bearing and pressure-distributing properties. Moreover, the developed formulation undergoes anaerobic soil bacterial degradation and can be categorized as a “green” bio-based material. Full article

In this study, the uniaxial compression and cyclic loading and unloading experiments were conducted on the non-water reactive foaming polyurethane (NRFP) grouting material with a density of 0.29 g/cm³, and the microstructure was characterized using scanning electron microscope (SEM) method. Based on the uniaxial compression and SEM characterization results and the elastic-brittle-plastic assumption, a compression softening bond (CSB) model describing the mechanical behavior of micro-foam walls under compression was proposed, and it was assigned to the particle units in a particle flow code (PFC) model simulating the NRFP sample. Results show that the NRFP grouting materials are porous mediums consisting of numerous micro-foams, and with the increasing density, the diameter of the micro-foams increases and the micro-foam walls become thicker. Under compression, the micro-foam walls crack, and the cracks are mainly perpendicular to the loading direction. The compressive stress–strain curve of the NRFP sample contains the linear increasing stage, yielding stage, yield plateau stage, and strain hardening stage, and the compressive strength and elastic modulus are 5.72 MPa and 83.2 MPa, respectively. Under the cyclic loading and unloading, when the number of cycles increases, the residual strain increases, and there is little difference between the modulus during the loading and unloading processes. The stress–strain curves of the PFC model under uniaxial compression and cyclic loading and unloading are consistent with the experimental ones, well indicating the feasibility of using the CSB model and PFC simulation method to study the mechanical properties of NRFP grouting materials. The failure of the contact elements in the simulation model causes the yielding of the sample. The yield deformation propagates almost perpendicular to the loading direction and is distributed in the material layer by layer, which ultimately results in the bulging deformation of the sample. This paper provides a new insight into the application of the discrete element numerical method in NRFP grouting materials. Full article

Components for manufacturing polyurethane foams can adversely affect the human body, particularly if they are in contact with it for long periods. In applications where the foam is not placed directly into the body, the study of the product’s effects is often neglected. In the case of human skin, distinguishing the increasingly frequent problems of skin atopy, more attention should be paid to this. This paper presents the influence of the different catalytic systems on cytotoxic and thermomechanical properties in polyurethane foams. Among others, foams were produced with the most popular catalysts on the market, DABCO and a metal-organic tin catalyst. The foams were characterized by thermomechanical properties and were subjected to a cytotoxicity test against human keratinocytes. In biocompatibility tests with skin cells, the results were highly variable. VAB 2 with a catalytic system consisting of commercial Diethanolamine and Addocat^®105 performed the best. However, with such a catalytic system, the mechanical properties have worsened. Full article

Tissue-engineered (TE) scaffolds provide an ‘off-the-shelf’ alternative to autograft procedures and can potentially address their associated complications and limitations. The properties of TE scaffolds do not always match the surrounding bone, often sacrificing porosity for improved compressive strength. Previously, the layer-by-layer (LbL) assembly technique was used to deposit nanoclay containing multilayers capable of improving the mechanical properties of open-cell structures without greatly affecting the porosity. However, the previous coatings studied contained poly(ethylenimine) (PEI), which is known to be cytotoxic due to the presence of amine groups, rendering it unsuitable for use in biomedical applications. In this work, poly(diallydimethylammonium chloride) (PDDA)- and chitosan (CHI)-based polyelectrolyte systems were investigated for the purpose of nanoclay addition as an alternative to PEI-based polyelectrolyte systems. Nanocomposite coatings comprising of PEI, poly(acrylic acid) (PAA), Na+ montmorillonite (NC), PDDA, CHI and sodium alginate (ALG) were fabricated. The coatings were deposited in the following manner: (PEI/PAA/PEI/NC), PEI-(PDDA/PAA/PDDA/NC) and (CHI/ALG/CHI/ALG). Results from scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analyses demonstrated that the nanoclay was successfully incorporated into each polymer bilayer system, creating a nanocomposite coating. Each coating was successful at tailoring the elastic modulus of the open-cell structures, with polyurethane foams exhibiting an increase from 0.15 ± 0.10 MPa when uncoated to 5.51 ± 0.40 MPa, 6.01 ± 0.36 MPa and 2.61 ± 0.41 MPa when coated with (PEI/PAA/PEI/NC), PEI-(PDDA/PAA/PDDA/NC) and (CHI/ALG/CHI/ALG), respectively. Several biological studies were conducted to determine the cytotoxicity of the coatings, including a resazurin reduction assay, scanning electron microscopy and fluorescent staining of the cell-seeded substrates. In this work, the PDDA-based system exhibited equivalent physical and mechanical properties to the PEI-based system and was significantly more biocompatible, making it a much more suitable alternative for biomaterial applications. Full article

In this work, three different polyurethane (PU) foams were prepared by mixing commonly used isocyanate and polyol with different isocyanate indices (1.0:0.8, 1.0:1.0, 1.0:1.1). Then, the prepared polyurethane foam samples were coated by dip-coating with a fixed ratio of nitrogen-doped, bamboo-shaped carbon nanotubes (N-BCNTs) to obtain pressure sensor systems. The effect of the isocyanate index on the initial resistance, pressure sensitivity, gauge factor (GF), and repeatability of the N-BCNT/PU pressure sensor systems was studied. The pore volume was crucial in finetuning the PU-foam-based sensors ability to detect large strain. Furthermore, large pore volume provides suitable spatial pores for elastic deformation. Sensors with large pore volume can detect pressure of less than 3 kPa, which could be related to their sensitivity in the high range. Moreover, by increasing the pore volume, the electrical percolation threshold can be achieved with a minimal addition of nanofillers. On the other hand, PU with a smaller pore volume is more suitable to detect pressure above 3 kPa. The developed sensors have been successfully applied in many applications, such as motion monitoring and vibration detection. Full article

A novel synthesis of polyurethane foam/polyurethane aerogel (PU_F–PU_A) composites is presented. Three different polyurethane reticulated foams which present the same density but different pore sizes (named S for small, M for medium, and L for large) have been used. After the characterization of the reference materials (either, foams, and pure aerogel), the obtained composites have been characterized in order to study the effect of the foam pore size on the final properties, so that density, shrinkage, porous structure, mechanical properties, and thermal conductivity are determined. A clear influence of the pore size on the density and shrinkage was found, and the lowest densities are those obtained from L composites (123 kg/m³). Moreover, the aerogel density and shrinkage have been significantly reduced through the employment of the polyurethane (PU) foam skeleton. Due to the enhanced mechanical properties of polyurethane aerogels, the inclusion of polyurethane aerogel into the foam skeleton helps to increase the elastic modulus of the foams from 0.03 and 0.08 MPa to 0.85 MPa, while keeping great flexibility and recovery ratios. Moreover, the synthesized PU_F–PU_A composites show an excellent insulating performance, reducing the initial thermal conductivity values from 34.1, 40.3, and 50.6 mW/(m K) at 10 °C for the foams S, M, and L, to 15.8, 16.6, and 16.1 mW/(m K), respectively. Additionally, the effect of the different heat transfer mechanisms to the total thermal conductivity is herein analyzed by using a theoretical model as well as the influence of the measurement temperature. Full article