Fully renewable materials will be a key component of sustainable plastic development and management, and the industrial reliance on petroleum-derived monomers, including aromatic diisocyanates used in polyurethanes (PUs), must be minimized to meet sustainability and production goals. To date, aliphatic diisocyanates have shown great promise as renewable monomers, and scalable production is imminent. This work demonstrates a systematic study and application of aliphatic diisocyanates for the preparation of rigid PU foams. Aliphatic 1,6-hexamethylene diisocyanate (6-HDI) was incorporated with multifunctional renewable polyols and cross-linkers to produce rigid polyurethane-polyisocyanurate foams with high renewable carbon content. Morphological, thermal, and mechanical analyses of these novel foams indicated similar properties and performance to those of commercial rigid foams. The described synthesis of rigid foams without utilization of aromatic diisocyanates broadens the scope of rigid foam formulations possible and serves to advance the understanding of renewable foam and material development.

Rigid polyurethane foams – based composites for sustainable logistics transportation: Synthesis, structure, multifunctional applications, and artificial intelligence integration

Talc modified sodium alginate-based rigid polyurethane foam with enhancing flame retardant, smoke suppression, thermal stability and mechanical properties

Toward sustainable flame-retardant and high-strength rigid polyurethane foams: partial replacement of polyether polyols with CO2-based polyols

Application of waste rigid polyurethane foam for oil removal from water

Suberinic acids (SA) derived from birch outer bark are renewable feedstocks for bio-based polyols suitable for rigid polyurethane (PU) foams. Three SA fractions were prepared under different depolymerization conditions: acidification at pH 1 (SA1), pH 5 (SA2), and FeCl3-assisted treatment (SA3), and their chemical composition was analysed by GC–MS, Py–GC/MS, and GPC–RID. Polyols derived from tall oil fatty acids (TOFA) or epoxidized TOFA with trimethylolpropane were used as the sole polyol components in foam formulations. The SA fractions differed in molecular weight distribution, affecting polyol processability. All foams exhibited similar limiting oxygen index (19–20) and cone calorimetry results, showing no statistically significant differences in flammability. This indicates that variations in depolymerization conditions, including polyphenolic content and removal of higher-molecular-weight fractions during FeCl3 treatment, do not dominate fire performance under the studied conditions. SA3-based polyols showed the lowest viscosity and produced foams with optimal mechanical and thermal properties, while SA1 offered higher yield with comparable performance. These results demonstrate the feasibility of converting SA fractions into functional polyols for rigid PU foams and highlight the FeCl3-treated SA3 fraction and SA1 as the most promising candidates for further development.

Research on reusing industrial and electronic waste in functional composite systems has been spurred by the growing need for sustainable engineering materials. This study used methylene diphenyl diisocyanate (MDI) as a binder to reinforce three recycled fillers: waste rigid polyurethane foam (WRPU), rubber tire waste (RTW), and waste printed circuit boards (WPCB). Response Surface Methodology (RSM) optimization revealed that the optimal composition was 6 wt% WRPU, 3 wt% RTW, and 7.58 wt% WPCB. With a maximum compressive strength of 38.987MPa, this optimized formulation showed significant improvement over the unreinforced matrix (14.128MPa). The mechanical performance was highly precisely validated by numerical simulation using ANSYS Workbench, with a deviation from the experimental results of only 0.75%. FTIR and thermogravimetric analysis (TGA) indicated enhanced interfacial interactions, improved compatibility and thermal stability up to 550°C, while high-resolution scanning electron microscopy (HR-SEM) verified uniform filler distribution. By enhancing interfacial bonding and stress transfer efficiency, the synergistic interaction of WRPU, RTW, and WPCB clarified the structure-property relationship controlling composite performance. These results support a sustainable circular economy by showcasing the potential of recycled polyurethane composites for lightweight, compressive load-bearing applications in automotive non-structural components.

New strategies for reducing flammability and toxic smoke emission in rigid polyurethane foams

Polyurethane foams are widely used polymers. Their end-of-life is largely managed through landfilling and incineration, causing environmental concerns and resource loss. Hydrothermal carbonization and hydrothermal liquefaction have recently emerged as promising thermochemical approaches to valorise polyurethanes waste into value added products. This study presents a systematic investigation of the effects of operating parameters on hydrochars (HCs) yields and properties, using a rigid polyurethane foam as feedstock. Product yields were rationalized using the Severity Value (SV) parameter and the obtained HCs were characterized by ultimate analysis, FTIR, SEM and thermogravimetric analysis. An increase in SV led to a reduction of HCs yields, whereas the effect of the feedstock to solvent ratio exhibited only a minor influence. Ultimate analysis revealed decreased H/C and O/C ratios in all HCs, while the nitrogen content increased in all samples compared to PUR, suggesting their potential application as nitrogen-doped carbon materials. All produced HCs exhibited HHVs higher than that of PUR (27.59 MJ/kg), indicating energy densification. The calculated combustion parameters indicated that HCs exhibit lower reactivity and a slower, more controlled combustion process compared to PUR. These results together with their positioning in the coal-like regions of the Van Krevelen diagram, suggest their potential use as solid fuels. The liquid phases recovered for each test were rich in value-added compounds, including aromatic heterocycles. Overall, these findings offer valuable insights for advancing circular economy strategies in PUR waste management, highlighting the potential of HTC and HTL to simultaneously produce energy-dense solid fuels and value-added platform chemicals. • Hydrothermal treatments were applied to recycle rigid polyurethane foam waste. • The operating parameters strongly influence hydrochar yields and properties • An inverse relationship is observed between severity values and hydrochar yields • Hydrochar has potential applications as nitrogen doped material and solid fuel • Organic phase is rich in compounds with potential applications as chemicals

Valorization of copper tailings: synergistically endowing rigid polyurethane foams with excellent flame retardancy via aluminum hypophosphite

Rigid polyurethane(PU) foams are widely used in engineeringapplications.This is underpinned by their multiscale and hierarchical structure,characterized by a nanometric segmented PU morphology and a closed-poremicrostructure which determine the macroscopic material response.This work correlates the macroscopic behavior of rigid polyurethanefoams derived from castor oil with their nanomorphological (in thecrystalline domains) evolution upon compression. Molecular dynamics(MD) simulations were used to model the behavior of the PU chainsin an ellipsoidal closed-pore structure, as well as the foam’smechanical properties and X-ray diffractogram. Macro-scale experimentaland MD simulation results were correlated using the Nagy model toaccount for strain rate effects. Synchrotron wide-angle X-ray scattering(WAXS) measurements were performed on the foams before and after compression,with the results compared with simulated diffractograms. A shift inthe interplane spacing in the semicrystalline phase of the hard PUsegments was observed upon compression, indicating a change in thenanostructure resulting from macroscopic mechanical loading.

Carbon Nanofiber/Polydopamine/Fe ³⁺ Composite Aerogel Coatings as Gas–Solid Fire Barriers for Rigid Polyurethane Foams

Valorization of Organosolv Lignin into Liquid Polyols for Rigid Polyurethane Foams

A bio‑based chitosan/g‑C3N4 coating for improved fire safety of rigid polyurethane foam

The need to reduce polyurethane (PU) foam waste has encouraged the development of sustainable foam formulations based on recycled raw materials and environmentally friendly additives, addressing both waste management and comparable foam properties to those based on fossil resources. In the present investigation, more sustainable water-blown rigid PU foams were investigated using recycled polyol and halogen-free flame retardants (FRs) for fire-resistant insulation applications. Two series of foam formulations were prepared: a first series with virgin polyol and the inclusion of a halogen-free FR additive (6 wt%) and a second series with recycled polyol (10% added respect to the total polyol) and halogen-free FR additives (6 wt%). Two types of FR were used: FR900, specifically identified as 3,9-Dimethyl-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane-3,9-dioxide, in powder form with 24% phosphorus content and reactive polyol based FR140, an oligomeric ethyl ethylene phosphate, in liquid form with 19% phosphorus content. The density, cellular structure, aged thermal conductivity, dimensional and hydrolytic stability, fire properties, and mechanical properties were characterized for novel foamed systems. Rigid foamed materials with very low densities around 50 kg/m3 were obtained. On the one hand, the inclusion of FR900 into the PU formulation containing virgin polyol generated foam with the lowest thermal conductivity (36.10 mW/mK) due to the smaller open cell content (11.7%) and cell size reduction (433 microns). On the other hand, the inclusion of recycled polyol reduced the foam density by 6 kg/m3 (44.1 kg/m3), increased the cell size average (848 microns) and open cell content (15.1%), maintained thermal conductivity (38.73 mW/mK), slightly improved the fire properties, and worsened the mechanical properties in comparison with the PU reference containing only virgin polyol. The results obtained by the foam containing recycled polyol and 6% FR900 are remarkable, presenting an increase in density (50.3 kg/m3) and in open cell content (73%), but a very high reduction in cell size (465 microns) and thus a low value of thermal conductivity of 37.04 mW/mK with respect to the reference material containing recycled polyol. Moreover, this PU foam containing recycled polyol and FR900 offered improved fire resistance (148.2 kW/m2 of Maximum Average Rate of Heat Emission (MARHE), 179.1 kW/m2 of Maximum Heat Release Rate (HRRmax), and 24.6 MJ/m2 of Total Heat Release (THR)) and mechanical properties (6.97 MPa of Young's modulus and 0.24 MPa of collapsed stress) for the construction sector. The inclusion of FR140 does not improve the properties of the foam system containing recycled polyol, mainly due to the deterioration of the cellular structure (in the open cell content and cell size).

ABSTRACT The adhesive industry is undergoing a transformation towards circularity, seeking sustainable alternatives to fossil-based raw materials. Although bio-based feedstocks have attracted interest, their high cost and limited availability often constrain industrial implementation. As a viable alternative, recycled raw materials derived from polymer waste are being explored to reduce environmental impact while maintaining performance. In this study, a chemically recycled polyol was obtained through glycolysis of post-industrial rigid polyurethane foam waste and used to prepare a hot-melt reactive polyurethane adhesive formulation. The recycled polyol was characterized to evaluate the transfer of additives and residual compounds from the original waste into the adhesive. Particular attention was given to the presence of plasticizers and aromatic amines and their migration into the adhesive due to the antiadherent behavior of the former and the potential toxicity of the latter. The influence of increasing recycled polyol content on adhesive properties was analyzed by FTIR, DSC, TGA, rheology and peel strength of leather/adhesive/SBR joints. Results revealed that glycolysis generated aromatic amines and transferred plasticizers from waste to the adhesive. Nevertheless, the adhesives exhibited good processability and excellent peel strength before and after thermal aging, demonstrating that chemically recycled polyols can serve as high-performance components for adhesive systems.

Rigid polyurethane foams are often manufactured in sealed molds, so knowledge of the density distribution in the molded blocks is essential. A study was conducted with the aim to estimate density distribution within a rigid polyurethane foam block (average core density of ≈96 kg/m3) manufactured in a rectangular sealed mold. The density of 150 rectangular samples was determined experimentally. Characteristic locations of the foams' columns in the block were outlined, having similar foaming conditions. Averaged density in the characteristic columns was calculated for each characteristic location. A mathematical model was developed based on density data of characteristic columns, approximated with second- and third-degree polynomials. Density distribution was calculated, and corresponding color charts with density zones and equidensity lines were constructed for six horizontal and two vertical sections of the block. It was found that the common center of the elliptical equidensity lines is located asymmetrically, ≈17 mm above the geometric center of the untrimmed block. Density gradients were calculated in directions parallel and perpendicular to the foams' rise direction. The developed mathematical model allowed us to estimate density distribution within the rigid polyurethane foam block manufactured in a rectangular sealed mold.

ABSTRACT Rigid polyurethane foam (RPUF) is highly flammable, which severely restricts its practical applications. To address this issue, a phosphorus‐based flame retardant, BDMP (bis(5‐ethyl‐2‐methyl‐2‐oxo‐1,3,2‐dioxaphosphinan‐5‐yl)methyl phosphonic acid methyl ester), was synthesized using the ionic liquid [Bmim]BF 4 as a green catalyst. During synthesis, the ionic liquid [Bmim]BF 4 functioned as a green catalyst and exhibited higher selectivity than γ‐Al 2 O 3 , affording BDMP in a yield of 52.23% within 18 h. BDMP was incorporated into RPUF at loadings ranging from 5 to 25 wt%, with 15 wt% identified as the optimal loading. At this loading, the limiting oxygen index (LOI) increased from 19.0% to 25.1%, and a UL‐94 V‐0 rating was achieved, while the peak heat release rate (PHRR) and total heat release (THR) were reduced by 36.07% and 35.85%, respectively. Scanning electron microscopy further confirmed the good compatibility between BDMP and the RPUF matrix. The enhanced flame retardancy was mainly attributed to the catalytic charring effect of BDMP, which promoted the formation of a stable and protective char layer. Overall, BDMP demonstrates significant potential as a highly efficient and sustainable phosphorus‐based flame retardant for RPUF.

The quest for innovative, eco-friendly materials has spurred the exploration of agricultural biomass waste as a potential resource for polymer composites. The current study examines the impact of untreated oil palm frond (OPF) fiber on the multifunctional and sustainable performance of rigid polyurethane (PU) foam in the oil palm industry, in alignment with Sustainable Development Goals 12 and 13. Using a one-shot polymerization method, OPF foams were fabricated with fiber contents of 0, 5, 10, 20, and 30 (wt%). The foams were tested for density, morphology, compressive strength, and sound absorption performance in accordance with ASTM D1621 and ISO 10534-2. Experimental densities were compared with theoretical values to confirm that the foam production process was consistent. Scanning electron microscopy analysis revealed that OPF contents above 20 wt% disrupted the cellular structure, resulting in non-uniform cell sizes and increased cell wall collapse. These morphological defects contributed to a reduction in compressive strength from 0.1901 N/mm² for neat PU foam to 0.0697 N/mm² at 30 wt% OPF. In contrast, the 30 wt% OPF foam showed greater porosity and a higher proportion of open cells, resulting in superior sound absorption performance in the 1000–2500 Hz frequency range. Overall, the findings reveal a clear trade-off between mechanical strength and acoustic efficiency. PU foams with high OPF content possess eco-sustainable benefits and enhanced sound-absorbing qualities. Despite the reduction in compressive strength, high OPF-loaded PU foams show potential for lightweight, non-structural applications, such as automotive parts and interior building materials.

Mechanism and Life Prediction of Rigid Polyurethane Foams Aging under Coupling Multi-factors