Mechanical Performance of Metallic Bone Screws Evaluated Using Bone Models

To evaluate mechanical performance properties of various types of cortical bone screw, cancellous bone screw, and locking bolt, we conducted torsional breaking and durability tests, screw driving torque tests into bone models, and screw pullout tests (crosshead speed: 10 mm/min) after driving torque tests. The 2° proof and rupture torques of a screw, which were estimated from torque versus rotational angle curves, increased with increasing core diameter of the screw. The durability limit of metallic screws obtained by four-point bending durability tests increased with increasing core diameter. The compressive, tensile, and shear strengths of the bone models used for the mechanical testing of orthopedic devices increased with increasing density of the bone model. The strength and modulus obtained for solid rigid polyurethane foam (SRPF) and cellular rigid polyurethane foam (CRPF) lay on the same straight line. Among the three strengths, the rate of increase in compressive strength with the increase in density was the highest. The maximum torque obtained by screw driving torque tests for up to 8.3 rotations (3000°) into the bone models tended to increase with increasing core diameter. In particular, the maximum torque increased linearly with increasing effective surface area of the screw, as newly defined in this work. The maximum pullout load increased linearly with increasing number of rotations and mechanical strength of the bone model. Screws with low driving torque and high pullout load were considered to have excellent fixation and are a target for development.

Nacre-Mimetic Green Flame Retardant: Ultra-High Nanofiller Content, Thin Nanocomposite as an Effective Flame Retardant

A nacre-mimetic brick-and-mortar structure was used to develop a new flame-retardant technology. A second biomimetic approach was utilized to develop a non-flammable elastomeric benzoxazine for use as a polymer matrix that effectively adheres to the hydrophilic laponite nanofiller. A combination of laponite and benzoxazine is used to apply an ultra-high nanofiller content, thin nanocomposite coating on a polyurethane foam. The technology used is made environmentally friendly by eliminating the need to add any undesirable flame retardants, such as phosphorus additives or halogenated compounds. The very-thin coating on the polyurethane foam (PUF) is obtained through a single dip-coating. The structure of the polymer has been confirmed by proton nuclear magnetic resonance spectroscopy (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The flammability of the polymer and nanocomposite was evaluated by heat release capacity using microscale combustion calorimetry (MCC). A material with heat release capacity (HRC) lower than 100 J/Kg is considered non-ignitable. The nanocomposite developed exhibits HRC of 22 J/Kg, which is well within the classification of a non-ignitable material. The cone calorimeter test was also used to investigate the flame retardancy of the nanocomposite's thin film on polyurethane foam. This test confirms that the second peak of the heat release rate (HRR) decreased 62% or completely disappeared for the coated PUF with different loadings. Compression tests show an increase in the modulus of the PUF by 88% for the 4 wt% coating concentration. Upon repeated modulus tests, the rigidity decreases, approaching the modulus of the uncoated PUF. However, the effect of this repeated mechanical loading does not significantly affect the flame retarding performance.

Experimental Measurements of Mechanical Properties of PUR Foam Used for Testing Medical Devices and Instruments Depending on Temperature, Density and Strain Rate

Rigid polyurethane (PUR) foam is products used as a biomedical material for medical device testing. Thermal stability is a very important parameter for evaluating the feasibility of use for testing surgical instrument load during drilling. This work aimed to perform experimental measurements to determine the dependence of the mechanical properties of a certified PUR on temperature, strain rate and density. Experimental measurements were realised for three types of the PUR samples with different density 10, 25 and 40 pounds per cubic foot. The samples were characterised in terms of their mechanical properties evaluated from tensile and compression tests at temperatures of 25 °C, 90 °C and 155 °C. Furthermore, the structures of the samples were characterised using optical microscope, their thermal properties were characterised by thermogravimetric analysis, and their density and stiffness with the effect of temperature was monitored. The results show that it is optimal not only for mechanical testing but also for testing surgical instruments that generate heat during machining. On the basis of experimental measurements and evaluations of the obtained values, the tested materials are suitable for mechanical testing of medical devices. At the same time, this material is also suitable for testing surgical instruments that generate heat during machining.

Shape Memory Polymer Foams Synthesized Using Glycerol and Hexanetriol for Enhanced Degradation Resistance

Shape memory polymer foams have been used in a wide range of medical applications, including, but not limited to, vessel occlusion and aneurysm treatment. This unique polymer system has been proven to shape-fill a void, which makes it useful for occlusion applications. While the shape memory polymer foam has superior performance and healing outcomes compared to its leading competitors, some device applications may benefit from longer material degradation times, or degradation-resistant formulations with increased fibrous encapsulation. In this study, biostable shape memory polymer foams were synthesized, and their physical and chemical properties were characterized as an initial evaluation of feasibility for vascular occlusion applications. After characterizing their shape memory behavior in an aqueous environment, degradation of this polymer system was studied in vitro using accelerated oxidative and hydrolytic solutions. Results indicated that the foams did not lose mass under oxidative or hydrolytic conditions, and they maintained high shape recovery in aqueous in vitro models. These degradation-resistant systems have potential for use in vascular occlusion and other wound healing applications that benefit from permanent, space-filling shape memory behavior.

Sulfate and metals removal from acid mine drainage in a horizontal anaerobic immobilized biomass (HAIB) reactor

The acid mine drainage (AMD) can causes negative impacts to the environment. Physico-chemical methods to treat AMD can have high operational costs. Through passive biological methods, such as anaerobic reactors, sulfate reduction, and recovery of metals are promoted. This study evaluated the performance of a horizontal anaerobic immobilized biomass (HAIB) reactor for the treatment of synthetic AMD using polyurethane foam as support material, and anaerobic sludge as inoculum. Ethanol was used as an electron donor for sulfate reduction, resulting in an influent chemical oxygen demand (COD) in the range of 500-1,500 mg/L and COD/sulfate ratio at 1. A gradual increase of sulfate and COD concentration was applied that resulted in COD removal efficiencies higher than 78%, and sulfate removal efficiencies of 80%. Higher sulfate and COD concentrations associated with higher hydraulic retention times (36 h) proved to be a better strategy for sulfate removal. The HAIB reactor was able to accommodate an increase in the SLR up to 2.25 g SO₄^2-/L d^-1 which achieved the greatest performance on the entire process. Moreover, the reactor proved a suitable alternative for reaching high levels of metal removal (86.95 for Zn, 98.79% for Fe, and 99.59% for Cu).

The Synergistic Effect of Ionic Liquid-Modified Expandable Graphite and Intumescent Flame-Retardant on Flame-Retardant Rigid Polyurethane Foams

In this study, a nitrogen–phosphorus intumescent flame-retardant 3-(N-diphenyl phosphate) amino propyl triethoxy silane (DPES), the ionic liquid (IL) of 1-butyl-3-methyl-imidazole phosphate, and a phosphorous-containing ionic liquid-modified expandable graphite (IL-EG), were synthesized, and their molecular structures were characterized. The flame-retardant rigid polyurethane foams (RPUFs) were compounded with synergistic flame-retardant IL-EG/DPES to study the effects of the combination IL-EG and DPES on the pore structure, mechanical properties, thermal decomposition behavior and thermal decomposition mechanism of RPUF. The results showed that IL-EG/DPES had good thermal stability, and an excellent expansibility and char yield. The flame-retardant RPUF, modified with IL-EG and DPES at the ratio of 1:1, had a relatively uniform pore size, the highest compressive strength, and an excellent flame-retardant performance due to the form interwoven hydrogen bonds between IL-EG and DPES, as well as the new synergistic flame-retardant coating on the RPUF surface to restrict the transfer of gas or heat into the PU matrix.

Recovery of Flexible Polyurethane Foam Waste for Efficient Reuse in Industrial Formulations

Ester polyurethane (PU) foam waste was reacted at atmospheric pressure in an autoclave and using microwaves with diethylene glycol (DEG) at different PU/DEG ratios in the presence of diethanolamine as a catalyst to find the glycolysis conditions that allow for the improved recovery of the PU foam waste and enable the recycling of the whole glycolysis product in foam formulations suitable for industrial application. The recycled polyol was characterized by dynamic viscosity, hydroxyl number, water content, and density, while thermal stability was assessed using thermogravimetric analysis. In the PU foam formulation, 1% and 5% of the glycolyzed material was reused. The relationship between the reuse level of the recycled polyol and the physical properties of the foam was thoroughly investigated. It was observed that both hardness and air flow decreased with increasing recycled polyol content, particularly for the polyester type foam, while tensile strength and compression strength increased. Depending on the amount of recycled polyol and catalyst used, polyether-based foams could be obtained with a low air permeability, needed in special applications as sealed foams, or with higher air permeability desirable for comfort PU foams. The results open the way for further optimization studies of industrial polyurethane foam formulations using a glycolysis process without any separation stage.

Electrostatic Air Filtration by Multifunctional Dielectric Heterocaking Filters with Ultralow Pressure Drop

In air filtration, for creating healthy indoor air, there is an intrinsic conflict between high filtration efficiency and low wind pressure drop. In this study, we overcame this conflict by developing new dielectric heterocaking (HC) filters, in which high relative dielectric constant (ε_r) materials were heterogeneously loaded on traditional polymer fibers. The dielectric HC filters in an electrostatic polarizing field generate a great amount of charges on their surface, leading to a strong attraction to precharged aerosol particles, and result in high filtration efficiency. Observing via a charged coupled device camera, the migration speed of aerosol smoke particles toward the polarized HC fiber exceeded those toward the unpolarized HC fiber by a factor of 6. We loaded high-ε_r HCs including manganese dioxide (MnO₂), activated carbon, zinc oxide (ZnO), copper oxide (CuO), and barium titanate (BaTiO₃) on polyurethane foams using a fast and large-scale roll-to-roll gel squeezing method. Based on the experimental results, when HCs had a ε_r larger than 5.1, an increased ε_r did not benefit electrostatic filtration efficiency for aerosol particles much, but resulted in a larger net ozone production. We suggested a MnO₂-HC filter for efficient and multifunctional filtration of indoor particles, ambient ozone, and formaldehyde with only 3.8 Pa pressure drop at 1.1 m/s filtration velocity. This efficient and cost-effective dielectric HC filter opens a new avenue for the design of multifunctional filters, which will facilitate its large-scale production and commercial application in the ventilation system for healthy buildings.

Biodegradable shape memory polymer foams with appropriate thermal properties for hemostatic applications

Shape memory polymer (SMP) foams are a promising material for hemostatic dressings due to their biocompatibility, high surface area, excellent shape recovery, and ability to quickly initiate blood clotting. Biodegradable SMP foams could eliminate the need for a secondary removal procedure of hemostatic material from the patients' wound, further facilitating wound healing. In this study, we developed hydrolytically and oxidatively biodegradable SMP foams by reacting polyols (triethanolamine or glycerol) with 6-aminocaproic acid or glycine to generate foaming monomers with degradable ester bonds. These monomers were used in foam synthesis to provide highly crosslinked SMP foam structures. The ester-containing foams showed clinically relevant thermal properties that were comparable to controls and excellent shape recovery within eight min. Triethanolamine-based ester-containing foams showed interconnected porous structure along with increased mechanical strength. Faster hydrolytic and oxidative biodegradation rates were achieved in ester-containing foams in comparison to controls. These biodegradable SMP foams with clinically applicable thermal properties possess great potential as an effective hemostatic device for use in hospitals or on battlefields.

Mica-Based Multilayer Nanocoating as a Highly Effective Flame Retardant and Smoke Suppressant

Highly flammable polyurethane foam (PUF) remains a key risk factor associated with bedding and upholstered furniture, contributing to the yearly destruction of property and loss of lives. In an attempt to tackle this issue and develop a more benign flame retardant for PUF, a mica-based nanocomposite was deposited using layer-by-layer assembly. Chitosan (CH) and poly(acrylic acid) (PAA) were used to stabilize high-aspect-ratio mica. Foam treated with eight bilayers of CH- and PAA-stabilized mica preserves the porous foam structure, prevents melt dripping, and self-extinguishes during a 10 s torch test, while uncoated foam is completely consumed. When exposed to 35 kW/m² heat flux during cone calorimetry, the peak heat release rate is reduced by 54% and less-volatile molecules are released during combustion, resulting in a 76% reduction in the total smoke release. This multilayer coating serves as an environmentally benign template for flame-retarding PUF and various other three-dimensional substrates.

Down-scaling Sample Preparation Using Polyurethane Foam and Colorimetric Technique for the Chromium Assay in Accessories

A simple alternative colorimetric assay of chromium in accessories is proposed. A miniature part of a sample was dissolved by acid digestion. With dithiooxamide (DTO) complexes, metal interferences are retained in polyurethane foam synthesized in the lab, while chromium ions present in the eluate. A 100-μL volume of the eluate was measured for the absorbance using a handy spectrometer. The proposed method was successful for chromium assay and the results obtained agreed with the reference (FAAS) method. The amounts of chromium in accessories were found in the range of 100 to 390 mg g^-1.

Closed Cell Rigid Polyurethane Foams Based on Low Functionality Polyols: Research of Dimensional Stability and Standardised Performance Properties

Currently, polyurethane foam producers come across the several problems when petroleum-based polyols are replaced with low functionality biomass, or waste-based, polyols. In addition, the dilemma is intensified with regulations that require full or partial replacement of blowing agents that can cause high ozone depletion with alternatives like water, which causes the formation of CO₂. Therefore, these gases diffuse out of the foam so quickly that the polymeric cell walls cannot withstand the pressure, consequently causing huge dimensional changes at ambient temperature and humidity. Even though the theoretical stoichiometric balance is correct, the reality shows that it is not enough. Therefore, polyethylene terephthalate waste-based polyol was chosen as a low functionality polyol which was modified with high functionality sucrose-based polyol in order to obtain dimensionally stable polyurethane foams in the density range of 30-40 kg/m³. These more stable foams are characterized by linear changes no higher than 0.5%, short-term water absorption by partial immersion no higher than 0.35 kg/m², and water vapor resistance factors up to 50. In order to obtain thermally efficient polyurethane foams, conventional blowing agents and water systems were implemented, thus, assuring thermal conductivity values in the range of 0.0198-0.0204 W/(m·K) and obtaining products which conform to all the requirements for performance of sprayed and factory-made polyurethane foam standards EN 14315-1 and EN 13165.

Fire Suppression and Thermal Behavior of Biobased Rigid Polyurethane Foam Filled with Biomass Incineration Waste Ash

Currently, there is great demand to implement circular economy principles and motivate producers of building materials to integrate into a closed loop supply chain system and improve sustainability of their end-product. Therefore, it is of great interest to replace conventional raw materials with inorganic or organic waste-based and filler-type additives to promote sustainability and the close loop chain. This article investigates the possibility of bottom waste incineration ash (WA) particles to be used as a flame retardant replacement to increase fire safety and thermal stability under higher temperatures. From 10 wt.% to 50 wt.% WA particles do not significantly deteriorate performance characteristics, such as compressive strength, thermal conductivity, and water absorption after 28 days of immersion, and at 32 °C WA particles improve the thermal stability of resultant PU foams. Furthermore, 50 wt.% WA particles reduce average heat release by 69% and CO₂ and CO yields during fire by 76% and 77%, respectively. Unfortunately, WA particles do not act as a smoke suppressant and do not reduce smoke release rate.

The Influence of Environmentally Friendly Flame Retardants on the Thermal Stability of Phase Change Polyurethane Foams

To improve thermal insulation, microencapsulated phase change materials (micro-PCMs), expandable graphite (EG), and ammonium polyphosphate (APP) were introduced into polyurethane foam (PUF) to enhance the thermal stability and improve the thermal insulation behavior. The morphology of the PUF and micro-PCM was studied using a scanning electronic microscope (SEM), while the thermophysical properties of the PUF were investigated using a hot disk thermal constants analyzer and differential scanning calorimetry (DSC). The thermal stability of the PUF was investigated by thermogravimetric analysis (TGA), and the gas products volatilized from the PUF were analyzed by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA-FTIR). The results revealed that the thermal conductivities of the PUF were reduced because micro-PCM is effective in absorbing energy, showing that the PUF functions not only as a thermal insulation material but also as a heat sink for energy absorption. Moreover, the EG and APP were found to be effective in improving the thermal stabilities of the PUF, and the optimized formulation among EG, APP, and micro-PCMs in the PUF showed a significant synergistic effect.

Numerical Studies of the Viscosity of Reacting Polyurethane Foam with Experimental Validation

Products made of polyurethane foam are manufactured by the chemical reaction of various low-viscosity raw materials and additives. The diversity of different formulations to meet the requirements of the market makes the characterization of their processing and flow properties important for a simple and error-free production. The modeling and simulation of such processes are equally of great importance. This provides additional findings without the expense of real tests and makes it easier to design components. The work described in this paper was carried out against this background. An experimental setup using a rheometer was developed to determine the flow and curing properties of reacting polyurethane foam reproducibly with comparable expansion conditions to industrial processes. The experiment was mathematically modelled to investigate the rheology of reacting polyurethane foams. The mathematical framework consists of coupled, non-linear, partial differential equations for the dynamics and the heat transfer processes in the system. These are solved numerically in 3D using finite volume techniques under adequate physical conditions. The accuracy of two viscosity laws according to the state of the art and their novel combination were investigated in this context. The proposed viscosity model of this study provides accurate results compared to the experiment.

Performance evaluation and substrate removal kinetics in an up-flow anaerobic hybrid membrane bioreactor treating simulated high-strength wastewater

The prime objective of the present study is to evaluate the performance of novel up-flow anaerobic hybrid membrane bioreactor (An-HMBR) treating high-strength wastewater (synthetic) using polyurethane foam as filter media. Treatment efficiency of the entire An-HMBR varied from 88-97% corresponding to 0.67-3.90 d of hydraulic retention time (HRT) with organic loading rate of 6.4-1.06 kg COD m^-3 d^-1. The modified Stover-Kincannon model was the most appropriate model for An-HMBR and anaerobic hybrid bioreactor (excluding membrane). The suspended growth system in An-HMBR could be described by both modified Stover-Kincannon and Grau second order model. The attached growth system in An-HMBR followed conventional Monod's kinetics. A novel combination of suspended, attached and membrane in single reactor increased the solid retention time to as high as 756 d at 3.9 d HRT which not only improved the COD removal efficiency but also enhanced the performance of the membrane.

Anisotropy in Polyurethane Pre-Insulated Pipes

The polyurethane foam in district heating pre-insulated pipes has a critical role to play both as thermal insulation and as load bearing element, as it serves as bond between the medium pipe and the casing. Hence, knowledge on how the foam behaves under multiaxial stresses is of great importance for the design as well as for aging predictions of the network. It is known that cell shape anisotropy in polymeric foams leads to anisotropy in its mechanical properties. In this study, we evaluate and quantify the microstructural anisotropy of PU foam from pre-insulated pipes as well as its mechanical behaviour under compression in the three orthogonal directions. We cover rigid and flexible PU foam, batch and continuous manufacturing, and different pipe diameters. The results were compared with those predicted by available rectangular and Kelvin cell shape models. We have found that PU from pre-insulated pipes is orthotropic and present stronger anisotropy than that typically found in PU slabs. The traditional bonded pipes under consideration behaved in a similar way. However, when comparing the two flexible pipes in this study, despite no significant differences in cell shape anisotropy were found, a significantly different behaviour for the E modulus ratio was observed. This shows that while the manufacturing process exerts the main influence on cell shape anisotropy, to explain the difference in stiffness behaviour other factors need to be taken into consideration, such as cell size and cell size variability.

New Insight on the Study of the Kinetic of Biobased Polyurethanes Synthesis Based on Oleo-Chemistry

Nowadays, polyols are basic chemicals for the synthesis of a large range of polymers, such as polyurethane foams (PUF), which are produced with several other compounds, such as polyisocyanates. During the last decades, the oleo-chemistry has developed several routes from glycerides to polyols for the polyurethanes (PU) industry to replace mainly conventional fossil-based polyols. A large range of biobased polyols can be now obtained by epoxidation of the double bonds and ring-opening (RO) of the subsequent epoxides with different chemical moieties. In preliminary studies, the RO kinetics of an epoxidized model molecule (methyl oleate) with ethanol and acetic acid were investigated. Subsequently, polyols that were derived from unsaturated triglycerides were explored in the frame of e.g., PUF formulations. Different associations were studied with different mono-alcohols derived from epoxidized and ring-opened methyl oleate while using several ring-openers to model such systems and for comparison purposes. Kinetic studies were realized with the pseudo-first-order principle, meaning that hydroxyls are in large excess when compared to the isocyanate groups. The rate of isocyanate consumption was found to be dependent on the moiety located in β-position of the reactive hydroxyl, following this specific order: tertiary amine >> ether > ester. The tertiary amine in β-position of the hydroxyl tremendously increases the reactivity toward isocyanate. Consequently, a biobased reactive polyurethane catalyst was synthesized from unsaturated glycerides. These approaches offer new insights regarding the replacement of current catalysts often harmful, pungent, and volatile used in PU and PUF industry, in order to revisit this chemistry.

3D Carbon Foam Supported Edge-Rich N-Doped MoS2 Nanoflakes for Enhanced Electrocatalytic Hydrogen Evolution

Molybdenum disulfide (MoS₂ ) is one of the most promising alternatives to the Pt-based electrocatalysts for the hydrogen evolution reaction (HER). However, its performance is currently limited by insufficient active edge sites and poor electron transport. Hence, enormous efforts have been devoted to constructing more active edge sites and improving conductivity to obtain enhanced electrocatalytic performance. Herein, the 3D carbon foam (denoted as CF) supported edge-rich N-doped MoS₂ nanoflakes were successfully fabricated by using the commercially available polyurethane foam (PU) as the 3D substrate and PMo₁₂ O₄₀ ^3- clusters (denoted as PMo₁₂ ) as the Mo source through redox polymerization, followed by sulfurization. Owing to the uniform distribution of nanoscale Mo sources and 3D carbon foam substrate, the as-prepared MoS₂ -CF composite possessed well-exposed active edge sites and enhanced electrical conductivity. Systematic investigation demonstrated that the MoS₂ -CF composite showed high HER performance with a low overpotential of 92 mV in 1.0 m KOH and 155 mV in 0.5 m H₂ SO₄ at a current density of 10 mA cm^-2 . This work offers a new pathway for the rational design of MoS₂ -based HER electrocatalysts.

Quantitative Pore Characterization of Polyurethane Foam with Cost-Effective Imaging Tools and Image Analysis: A Proof-Of-Principle Study

This study investigated the pore characterization of polyurethane (PU) foam as a necessary step in water filtration membrane fabrication. Porous material characterization is essential for predicting membrane performance, strength, durability, surface feel, and to understand the transport mechanisms using modeling and simulations. Most existing pore characterization techniques are relatively costly, time-consuming, subjective, and have cumbersome sample preparations. This study focused on using three relatively inexpensive imaging systems: a black box, Canon camera (EOS760D), and LaserJet scanner (M1132 MFP). Two standard, state-of-the-art imaging systems were used for comparison: a stereomicroscope and a scanning electron microscope. Digital images produced by the imaging systems were used with a MATLAB algorithm to determine the surface porosity, pore area, and shape factor of the polyurethane foam in an efficient manner. The results obtained established the compatibility of the image analysis algorithm with the imaging systems. The black box results were found to be more comparable to both the stereomicroscope and SEM systems than those of the Canon camera and scanner imaging systems. Indeed, the current research effort demonstrates the possibility of substrate characterization with inexpensive imaging systems.

Permeable Water-Resistant Heat Insulation Panel Based on Recycled Materials and Its Physical and Mechanical Properties

This paper deals with the development and characteristics of the properties of a permeable water-resistant heat insulation panel based on recycled materials. The insulation panel consists of a thermal insulation core of recycled soft polyurethane foam and winter wheat husk, a layer of geopolymer that gives the entire sandwich composite strength and fire resistance, and a nanofibrous membrane that permits water vapor permeability, but not water in liquid form. The observed properties are the thermal conductivity coefficient, volumetric heat capacity, fire resistance, resistance to long-term exposure of a water column, and the tensile strength perpendicular to the plane of the board. The results showed that while the addition of husk to the thermal insulation core does not significantly impair its thermal insulation properties, the tensile strength perpendicular to the plane of these boards was impaired by the addition of husk. The geopolymer layer increased the fire resistance of the panel for up to 13 min, and the implementation of the nanofibrous membrane resulted in a water flow of 154 cm² in the amount of 486 g of water per 24 h at a water column height of 0.8 m.

Gamma-irradiation-induced micro-structural variations in flame-retardant polyurethane foam using synchrotron X-ray micro-tomography

Flame-retardant polyurethane foams are potential packing materials for the transport casks of highly active nuclear materials for shock absorption and insulation purposes. Exposure of high doses of gamma radiation causes cross-linking and chain sectioning of macromolecules in this polymer foam, which leads to reorganization of their cellular microstructure and thereby variations in physico-mechanical properties. In this study, in-house-developed flame-retardant rigid polyurethane foam samples were exposed to gamma irradiation doses in the 0-20 kGy range and synchrotron radiation X-ray micro-computed tomography (SR-µCT) imaging was employed for the analysis of radiation-induced morphological variations in their cellular microstructure. Qualitative and quantitative analysis of SR-µCT images has revealed significant variations in the average cell size, shape, wall thickness, orientations and spatial anisotropy of the cellular microstructure in polyurethane foam.

Variation of Mechanical Characteristics of Polyurethane Foam: Effect of Test Method

Polyurethane foam (PUF), a representative insulation material, not only prevents heat conduction but can also support a load. Particular interest in rigid PUF proliferated over the past several years in fields where extreme environments are applied. A closed-cell structure which forms the interior of rigid PUF serves to maximize the utilization of these polymeric foams. Rigid PUF is more sensitive to external conditions such as temperature or restraint than other structural materials such as steel. Depending on the market trends in which utilization of a cryogenic environment is expanding, the tendency of material behavior resulting from the binding effect also needs to be investigated. However, most conventional compression test method standards applicable to rigid PUF do not adequately reflect the restraints. Therefore, this study proposes a method for evaluating the mechanical performance of materials in a more reliable manner than that of conventional tests. Experimental observation and analysis validated this compression evaluation method in which constraints are considered. Consequently, the compressive strength of rigid PUF compared to the results of the conventional test showed a difference of up to 0.47 MPa (approximately 23%) at cryogenic temperatures. This result suggests that there are important factors to consider when assessing performance from a material perspective in an environment where rigid PUF insulation is utilized. It is believed that the test methods newly proposed in this study will provide an experimental framework that can be applied to the evaluation criteria of material properties and reflected in structural design.

Facile Fabrication of Conductive Graphene/Polyurethane Foam Composite and Its Application on Flexible Piezo-Resistive Sensors

Flexible pressure sensors have attracted tremendous research interests due to their wide applications in wearable electronics and smart robots. The easy-to-obtain fabrication and stable signal output are meaningful for the practical application of flexible pressure sensors. The graphene/polyurethane foam composites are prepared to develop a convenient method for piezo-resistive devices with simple structure and outstanding sensing performance. Graphene oxide was prepared through the modified Hummers method. Polyurethane foam was kept to soak in the obtained graphene oxide aqueous solution and then dried. After that, reduced graphene oxide/polyurethane composite foam has been fabricated under air phase reduction by hydrazine hydrate vapor. The chemical components and micro morphologies of the prepared samples have been observed by using FT-IR and scanning electron microscopy (SEM). The results predicted that the graphene is tightly adhered to the bare surface of the pores. The pressure sensing performance has been also evaluated by measuring the sensitivity, durability, and response time. The results indicate that the value of sensitivity under the range of 0-6 kPa and 6-25 kPa are 0.17 kPa-1 and 0.005 kPa-1, respectively. Cycling stability test has been performed 30 times under three varying pressures. The signal output just exhibits slight fluctuations, which represents the good cycling stability of the pressure sensor. At the same stage, the response time of loading and unloading of 20 g weight turned out to be about 300 ms. These consequences showed the superiority of graphene/polyurethane composite foam while applied in piezo-resistive devices including wide sensitive pressure range, high sensitivity, outstanding durability, and fast response.

Identification and Quantification of Cell Gas Evolution in Rigid Polyurethane Foams by Novel GCMS Methodology

This paper presents a new methodology based on gas chromatography-mass spectrometry (GCMS) in order to separate and quantify the gases presented inside the cells of rigid polyurethane (RPU) foams. To demonstrate this novel methodology, the gas composition along more than three years of aging is herein determined for two samples: a reference foam and foam with 1.5 wt% of talc. The GCMS method was applied, on one hand, for the accurate determination of C₅H₁₀ and CO₂ cell gases used as blowing agents and, on the other hand, for N₂ and O₂ air gases that diffuse rapidly from the surrounding environment into foam cells. GCMS results showed that CO₂ leaves foam after 2.5 month (from 21% to 0.03% for reference foam and from 17% to 0.03% for foam with 1.5% talc). C₅H₁₀ deviates during 3.5 months (from 28% up to 39% for reference foam and from 29% up to 36% for foam with talc), then it starts to leave the foam and after 3.5 year its content is 13% for reference and 10% for foam with talc. Air diffuses inside the cells faster for one year (from 51% up to 79% for reference and from 54% up to 81% for foam with talc) and then more slowly for 3.5 years (reaching 86% for reference and 90% for foam with talc). Thus, the fast and simple presented methodology provides valuable information to understand the long-term thermal conductivity of the RPU foams.