Rigid Polyurethane Research Articles

Rigid Polyurethane Foam Derived from Renewable Sources: Research Progress, Property Enhancement, and Future Prospects

Rigid polyurethane foam (RPUF) is a widely utilized thermosetting polymer across various industrial applications, valued for its exceptional properties. However, the demand for sustainable alternatives to petroleum-based polymers has grown increasingly urgent due to rising environmental concerns. Despite its widespread use, RPUF faces challenges such as inadequate mechanical strength, limited thermal stability, and high flammability, all of which are crucial considerations in commercial and household applications. Globally, ongoing efforts are focused on developing innovative technologies that convert renewable sources into new monomers and polymers, some of which could serve as alternatives to traditional RPUFs. Several approaches have been explored to improve the thermal stability, mechanical strength, and flame retardancy of RPUFs, including the modification of bio-based polyols and the incorporation of performance-enhancing fillers. This review emphasizes recent advances in RPUFs derived from natural resources, focusing on their preparation, characterization, and properties, and strategies to enhance the mechanical strength and flame safety of bio-based RPUFs. Additionally, it explores the applications of RPUF materials across various fields, addressing the challenges and potential developments in packaging, household items, construction, and automotive applications.

Aluminate coupling agent-based surface modification of BaSO4 and its effects on rigid polyurethane foam grouting material

Aluminate coupling agent-based surface modification of BaSO4 and its effects on rigid polyurethane foam grouting material

Flame‐Retardant Rigid Polyurethane Foam Composites Based on Piperazine Pyrophosphate/Steel Slag: A New Strategy for Utilizing Metallurgical Solid Waste

ABSTRACTIn this work, piperazine pyrophosphate (PAPP) and metallurgical solid steel slag (SS) are used to fabricate flame‐retardant rigid polyurethane foam (RPUF) composites through a one‐step all‐water foaming technology. The thermal stability, combustion properties, and flame retardancy of the PAPP/SS composite were investigated by thermogravimetric (TG) analysis, cone calorimetry, limiting oxygen index testing (LOI), and UL‐94 vertical burn testing. RPUF‐3 showed a char residue of 28.6 wt% at 750°C compared with 24.9 wt% of the pure sample, indicating better thermal stability of the FRPRUF composites. RPUF‐3 possessed an LOI of 21.5 vol% and achieved a V‐0 level in the UL‐94 test. Cone calorimetry displayed the peak heat release rate and fire growth rate index of RPUF‐3 were decreased by 12.66% and 41.6%, respectively, compared with those of pure RPUF. PAPP/SS incorporation led to the formation of compact char layer structures during combustion. Pyrophosphoric acid, generated from the decomposition of PAPP, promotes the formation of esters, ethers, and alcohols, whereas metal oxides in SS enhance the compactness of the char layer. This enhanced structural integrity obstructs mass and heat transmission in the combustion zone, effectively improving condensed‐phase flame retardancy. This approach offers a novel strategy for the fabrication of high‐performance RPUF composites and the high‐value utilization of SS.

Effect of dimethylamine pyrophosphate on the mechanical, thermal decomposition and flame-retardant properties of rigid polyurethane foams

To solve the problem of the insufficient flame retardancy of rigid polyurethane (RPUF), a new flame retardant, dimethylamine pyrophosphate (DMPY), was introduced into rigid polyurethane foam, and one-step foaming technology was used to prepare RPUF/DMPY composites. Furthermore, the thermal stability, flame retardancy, combustion characteristics, and gas-phase products were analyzed via thermogravimetric analysis (TGA), limiting oxygen index (LOI), cone calorimetry (CCT), and thermogravimetric infrared spectroscopy (TG-FTIR). The flame-retardant measurements revealed that when the DMPY amount exceeded 20 parts, the LOI of the RPUF/DMPY composites increased to above 23%, and all the samples reached the UL-94 V-0 level. In addition, the peak heat release rate and total heat release values of the RPUF-3 composites prepared with RPUF/DMPY were 192.6 kW/m2 and 19.98 MJ/m2, respectively, which were 35.0% and 29.1% lower than those of the pure RPUF, respectively, and significantly reduced the heat release of the RPUF composites. The analysis of char residue revealed that DMPY can effectively improve the density and graphitization degree of char residue during the combustion process of RPUF/DMPY composites, thereby endowing them with excellent flame-retardant properties. On this basis, the flame-retardant mechanism of the DMPY-based flame retardant RPUF composite material is proposed. This work provides new ideas for the development of new flame retardant PPUF composites.

Thermal stability, flame retardancy and mechanical properties of casein-based rigid polyurethane foam with starch and sepiolite as fillers

Casein-based rigid polyurethane foam (RPUF) with different ratios of starch and sepiolite were prepared by a one-step process. Thermogravimetric analysis, CONE analysis, scanning electron microscopy analysis, limiting oxygen index (LOI) analysis, vertical combustion analysis, and mechanical property analysis were used to explore the thermal stability, flame retardancy, and compressive properties of the modified RPUFs, respectively. The results showed that the initial decomposition temperature and activation energy (E) of RPUF-C5ST2SE3 (5 g casein, 2 g starch, and 3 g sepiolite) were the highest. Under the condition of radiant flux of 50 kW/m2, the peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), and total smoke release (TSR) were reduced by 35.92%, 10.83%, 36.67%, and 18.20%, respectively, compared with the RPUF without flame retardant. By analyzing the carbon residue, it was found that RPUF-C5ST2SE3 had the highest carbon residue and its carbon residue morphology was relatively intact. In addition, the RPUF-C5ST2SE3 had the highest LOI and a UL-94 rating of V-0. At the same time, it also had the best mechanical property. The present experimental results can provide a useful reference for future RPUF flame retardant studies.

In-situ packing self-intumescent aerogel particles in rigid polyurethane foam towards thermal insulation, flame retardance and smoke suppression

In-situ packing self-intumescent aerogel particles in rigid polyurethane foam towards thermal insulation, flame retardance and smoke suppression

Depolymerization of Rigid Polyurethane Waste by Catalytic Glycolysis with Diethylene Glycol

Depolymerization of Rigid Polyurethane Waste by Catalytic Glycolysis with Diethylene Glycol

Effect of Silicon-Based Surfactant on Compression Strength, Morphology, and Flammability of the Aluminium Hydroxide-Filled Rigid Polyurethane Foam

This study investigates the impact of NiaxTM Silicone L-5440, a silicon-based surfactant, on the foaming behaviors of rigid polyurethane foam (RPUF) filled with aluminium hydroxide (ATH). The aim is to understand the effect of the surfactant on the compression strength, morphology, and flammability of the foam. Various concentrations of the surfactant, ranging from 0.5 to 3 pphp, were incorporated into the RPUF/ATH blend. Five key parameters were examined, including density, closed-cell content, structural characterization using scanning electron microscopy (SEM), compressive strength, and UL-94 rating. The results revealed that adding the silicon surfactant significantly influenced the foam properties. Foam formulations with lower surfactant concentrations resulted in denser foam with a higher percentage of closed cells (86.24%). The morphology of the foams exhibited variation in average pore sizes, initially decreasing and subsequently increasing with increasing surfactant concentration. Notably, the compressive strength of the foam increased when the surfactant concentration reached 1 pphp. Moreover, the inclusion of the surfactant improved the flammability characteristics, as evidenced by a UL-94 rating of V-1 without dripping.

Synergistic Effect of Amino-Modified Co-MOF and APP on Improvement of the Fire Safety of the Rigid Polyurethane Foam.

The combustion of rigid polyurethane foam (RPUF) generates significant amounts of toxic and high-temperature smoke, which restricts its application. Here, an amino-modified Co-MOF (NH2-Co-MOF) was synthesized and it was used in conjunction with ammonium polyphosphate (APP) to decrease the flammability of RPUF. We obtained the expected results: the fire safety of RPUF was greatly enhanced by the addition of NH2-Co-MOF and APP. Compared to neat RPUF, the peak heat release rate (pHRR) and total heat release (THR) values of N-C/A/RPUF decreased by 22.5 and 37.4%, respectively. Based on the analysis of combustion products of the gaseous and condensed phases, it can be seen that the synergistic use of NH2-Co-MOF with APP enhances the barrier effect, dilutes combustible gases, and quenches the combustion chain reaction.

The Complex Valorization of Black Alder Bark Biomass in Compositions of Rigid Polyurethane Foam.

The use of black alder (BA) bark biomass in rigid polyurethane (PUR) foam compositions was the main task of investigation. Extractive compounds isolated from the bark through hot water extraction were used as precursors for bio-polyol synthesis via acid-free liquefaction with the polyether polyol Lupranol 3300 and through oxypropylation with propylene carbonate. The OH functionality and composition of the polyols were analyzed via wet chemistry and FTIR spectroscopy. The solid remaining after the isolation of extractive compounds was also utilized as a natural filler in PUR foams. The effects of replacing commercial polyols with bio-polyols on the foam rising rate and their mechanical properties, morphology, thermal conductivity, and thermal degradation characteristics were examined. The oxypropylated extractive-based PUR compositions demonstrated the most favorable balance between the biomass content and material properties. At an apparent density of 40 kg/m3, the compressive strength of the produced foams was enhanced by 1.4-1.5 times, while the maximum thermal degradation rate in air decreased by 3.8-6.5 times compared to reference materials without adversely affecting the foam morphology. The composition based on liquefied extractives showed lower performance but still improved properties relative to the reference foams. Introducing 3.7-14% of extracted bark into the foam compositions increased the biomass content to 22-24%, although this led to a decrease in the compressive strength and thermal stability. It was shown that partially substituting fossil-derived components with renewable bark biomass in the composition of PUR foams allows for materials with characteristics similar or better to petrochemical-based materials to be obtained. Therefore, the results presented can be considered a contribution to addressing environmental problems and promoting the development of a sustainable economy.

Impact compressive properties of polyurethane foams with 3D continuous fibre reinforcement

Flexible and rigid polyurethane foams are used in applications subjected to impact loads. Integrating a three-dimensional, continuous fibre reinforcement meets high requirements for stiffness and strength. A fundamental comparison of the impact compressive properties was carried out for contributing to a reasonable choice between these variants. A rigid and flexible foam with a bulk density of 85 kg/m3 each was investigated with and without reinforcement by a warp-knitted spacer fabric. The material testing was conducted using a drop weight tester in accordance with a German standard. Three impacts are applied by a hammer with a flat surface larger than the area of the sample plate. Different impact energies were investigated and the deformation behaviour was analysed using a high-speed camera. Much higher energy absorptions at low deformations were found with rigid foam. Peak stresses and decelerations were lower with flexible foam if the load did not densify the material. Reinforcing the foams leads to an anisotropic deformation and improves the impact compressive properties, especially in the case of the flexible variant. The four materials analysed had a similar rebound and largely maintained their performance when subjected to the repeated impact load.

Rigid polyurethane foams co-modified with chicken feather protein and expandable graphite

Rigid polyurethane foam (RPUF) was prepared by synergistic modification using self-made chicken feather protein as well as expandable graphite (EG). The flame retardancy and smoke suppression of the modified RPUFs were analyzed based on the heat release rate (HRR), total heat release (THR), smoke production rate (SPR) and total smoke release (TSR). The HRR, THR, SPR and TSR of RPUF5 with 5g EG were 18.7 kW/m2, 1.35 kW/m2, 0.0028 m2/s, and 21.2 m2/m2, respectively, which showed the best performance at a thermal radiation intensity of 25 kW/m2 and showed a decrease of 42.8%, 35.4%, 66.3%, and 56.3% compared to the pure sample RPUF1. And four methods were used to calculate the activation energy (E) of the modified RPUFs, which showed that RPUF5 had the highest E and the best thermal stability. At the same time, RPUF5 also had good mechanical properties. These results will lay the foundation for the development and application of RPUF in the flame retardant field.

Evaluation of an Innovative Casting Method in the Recovery of Footwear Impressions in Soil

Three-dimensional (3D) shoeprints taken from crime scenes can more accurately depict impressions than photographs, providing a crucial link between the crime scene and the suspect. This paper introduces rigid polyurethane foam as an alternative material for recovering and preserving 3D footwear impressions in soil. The rigid polyurethane is manufactured through gas expansion, solidifying in a foamed state that consists of a dense integral surface and a durable closed-cell structure beneath the skin layer. It is easily molded, lightweight, dimensionally accurate, and exhibits minimal changes in strength when the foam casts are created and stored indoors. In comparison to casts made with plaster of Paris, this method produces impressions on casts that exhibit more identifiable characteristics, serving as a complementary technique for the forensic science community in reproducing 3D footwear impressions found in soil.

Effect of Chemical Structure and Apparent Density of Rigid Polyurethane Foams on the Properties of Their Chemical Recycling Products.

The aim of this work was to synthesize polyurethane foams based on petrochemical polyols and biopolyols with specific apparent densities (40, 60, 80, 100, and 120 kg/m3), test their properties, glycolyze them, and finally analyze each glycolyzed product. The petroleum-based foams, used as reference foams, and the bio-based foams underwent a series of standard tests to define their properties (the content of closed cells 20-95%, compressive strength 73-1323 kPa, thermal conductivity 24-42 mW/m∙K, brittleness 4.6-82.9%, changes in linear dimensions < 1%, and water absorption < 1%). Taking into account the need for recycling, the foams were shredded and then glycolyzed by diethylene glycol, with the addition of a catalyst in the form of potassium hydroxide. The chemolysis products were analyzed through determination, i.e., the amine and the hydroxyl values, viscosity, and molecular weight. The obtained rebiopolyols had hydroxyl numbers ranging from 476 to 511 mg KOH/g. The type of biopolyol used in the PUR foam systems had a significant impact on the amine number and the viscosity of the obtained rebiopolyol.

Effects of Density and Temperature on the Mechanical Shock Mitigation Response of Polymethylene Diisocyanate (PMDI) Based Rigid Polyurethane Foams

Effects of Density and Temperature on the Mechanical Shock Mitigation Response of Polymethylene Diisocyanate (PMDI) Based Rigid Polyurethane Foams

Mechanically Strong and Fast‐Curing Kraft Lignin‐Based Polyurethane Foam

ABSTRACTThe creation of biobased rigid polyurethane from nonfood resources such as lignin has garnered significant interest, especially concerning the biorefinery concept. However, few studies have investigated virgin lignin as a polyol source for polyurethane foam and the effects of single factors, such as the lignin solvent, lignin concentration, and lignin:isocyanate ratio, on the properties of polyurethane. High‐density rigid foam (~500 kg/m3) was successfully formed by all the solvents except sodium hydroxide, which was confirmed via Fourier transform infrared (FTIR) spectroscopy and pyrolysis‐gas chromatography–mass spectrometry (Py‐GCMS). The highest to lowest modulus of elasticity (MOE) and modulus of rupture (MOR) values for the different lignin solvents were as follows: tetrahydrofuran (THF) (402.25 and 13.24 N/mm2) &gt; dimethyl formamide (DMF) (46 and 1.69 N/mm2) &gt; dimethyl sulfoxide (DMSO) (29 and 1.39 N/mm2). DMSO was selected as the optimal solvent because of the considerable curing time (26.67 s) needed to produce rigid foam. A higher lignin concentration resulted in better physical, mechanical, and thermal properties of the foam to some extent. Moreover, the opposite occurred with increasing isocyanate ratio in the system. These findings can serve as a basis for optimizing the utilization of lignin as a bioresource in the manufacture of rigid polyurethane foam with more specific uses.

Three-layer Repair Coating System for Manholes, Pump Stations, and Tanks in Aggressive Sulfate Environment

Advancements in the repair and protection of water and wastewater infrastructure are now focused on using an innovative material called polyurea. Distinguished by its rapid curing time and versatile applications, polyurea is applied using a spray gun with high-pressure pumps. The introduction of new building materials is part of ongoing efforts to meet stringent environmental, health, and performance standards, and polyurea offers significant improvements by eliminating solvents and volatile organic compounds (VOCs). This paper presents a technological protocol starting with inspection and cleaning, followed by drying, and ending with the application of three layers: a moisture-blocking base layer, a rigid polyurethane middle layer for structural reinforcement, and a final sealing and anti-corrosion layer. This innovative method ensures a homogeneous, seamless structure, enhances construction durability, and accelerates the repair process, allowing immediate resumption of operation. Designed specifically for aggressive wastewater environments, this system is characterized by excellent corrosion resistance, making it ideal for water and wastewater infrastructure elements such as reinforced concrete manholes, sewage pumping stations, and tanks. Customizable polyurea properties allow personalization based on environmental aggressiveness, structure size, and abrasion resistance, representing a significant advancement in infrastructure maintenance technology. The paper showcases this modern repair and renovation method, highlighting its applications, benefits, and potential to revolutionize water and wastewater infrastructure maintenance in challenging conditions. The effectiveness of this solution is also compared with traditional methods, demonstrating the superiority of the three-layer system in terms of waterproofing, sulfuric acid resistance, monolithic structure, and application time.

Experimental and numerical investigation on fatigue behavior of PUR (rigid polyurethane) elastomers 90ShA used in automotive engineering

For mechanical automobiles, elastomers are regarded as a common vibration damping material. The most widely used components are made of rubber, mostly because of their cost. PUR (rigid polyurethane) compounds are alternatives. This study presents the findings from studies on polyurethane materials in a specific hardness configuration. The hardness and fatigue tests received the most attention, and more crucially, the impact of the hardness value achieved on fatigue was investigated using both experimental and numerical methods. It was shown how a material with a specific stiffness, defined as 90ShA hardness, behaved significantly. All of the outcomes were contrasted with those of competitive materials, such rubbers, which had comparable hardness. PUR consistently demonstrated substantial fracture toughness.

Optimization Design of Flame-Retardant Rigid Polyurethane Foam Modified by Piperazine pyrophosphate/ Zinc Tailings/ Sodium Ligninsulfonate based on Orthogonal experiment

The flammability of rigid polyurethane foams (RPUF) is a significant concern for application. This study introduces a novel flame-retardant RPUF modified by piperazine pyrophosphate (PAPP), zinc tailings (ZTs), and sodium lignosulfonate (LS). The result of cone calorimeter test reveals that the peak heat release rate (p-HRR) and total heat release (THR) of the RPUF doped with 18wt.% PAPP, 10wt.% ZTs and 2.5wt.% LS decreases by 49.4% and 58.3% respectively. The Fire Resistance Index (FRI) achieved a value of 10.17, and vertical combustion tests indicated V-0 rating, signifying improved flame retardancy. Furthermore, the TG/DTG analysis shows that the decomposition activation energy (Eα) increased from 132.85kJ·mol-1 to 222.12kJ·mol-1 in the main stage of decomposition (249~342 ℃), representing enhanced thermal stability. Subsequently, the orthogonal experiments and regression analysis reveal that LS has the most significant impact on p-HRR, followed by ZTs. The combination of ZTs and LS exerts the most significant synergistic influence on p-HRR, whereas the combination of PAPP and LS has the most insignificant impact. The introduction of LS provides carbon and gas source, and improve the dispersion of PAPP and ZTs in the whole system. The optimal experimental ratio of modified RPUF is obtained through regression optimization. Consequently, the flame-retardant RPUF represents a sustainable bio-based composite material that effectively utilizes industrial and biowaste resources.

Improved thermal insulation, mechanical properties, energy absorption and flame retardancy of bio-based rigid polyurethane foam modified with calcium hydroxystannate

Rigid polyurethane foam (RPUF) is an important energy-saving building material that has attracted much attention. However, it is still a great challenge to effectively prepare RPUF materials with thermal insulation, flame retardant and mechanical properties. In this paper, the non-toxic and halogen-free flame retardant calcium hydroxystannate (CSH) was prepared by a simple and green chemical co-precipitation method, and a low-carbon and environmentally friendly RPUF material was prepared by combining it with RPUF−SO2/Ni3 (10 % wt soybean oil-based polyol and 3 % wt nickel phytate). It was found that SO2/Ni3/CSH4 containing 4 wt% CSH exhibited excellent thermal insulation performance. TG analysis showed that SO2/Ni3/CSH4 had higher initial temperature and activation energy, and its thermal stability was significantly improved. Peak heat release rate (PHRR), total heat release (THR), peak smoke production rate (PSPR), total smoke release (TSR) and Ds were 26.30 %, 17.16 %, 26.67 %, 23.95 % and 11.38 % lower than those of RPUF−SO2/Ni3, respectively. In addition, the compressive strength of SO2/Ni3/CSH4 was increased by 31.10 %, and it also had excellent energy absorption properties. This study provides new ideas for the design of high-performance and multifunctional low-carbon RPUFs, which have potential applications in aerospace and construction.