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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Thermal Activation of Zirconium(IV) Acetylacetonate Catalysts to Enhance Polyurethane Synthesis and Reprocessing

Carbamate formation and exchange catalysts enable efficient polyurethane (PU) manufacturing, as well as emerging recycling and reprocessing methods for PU thermosets. Zirconium β-diketonate complexes, such as Zr acetylacetonate [Zr(acac) 4 ], are effective alternatives to toxic organotin catalysts that have been used for PU reprocessing. Here, we report that Zr(acac) 4 undergoes a thermally activated process in the PU network during reprocessing that transforms it into a more active carbamate exchange catalyst. This process is associated with the irreversible loss of acetylacetonate ligands and is not observed for the more sterically hindered Zr 2,2,6,6-tetramethyl-3,5-heptanedione [Zr(tmhd) 4 ] complex. Crossover experiments between PU thermoplastics indicated enhanced carbamate exchange after the thermal activation of Zr(acac) 4 in the presence of one of the PUs, whereas a sample of Zr(acac) 4 activated in the absence of the PU had no catalytic activity. Thermal gravimetric analysis suggested that this process is associated with the loss of one protonated acac ligand. Stress relaxation analysis of PU thermosets indicated a distinct change in the characteristic relaxation time associated with the thermal activation of Zr(acac) 4 at temperatures above 140 °C; no such change was observed for samples reprocessed using Zr(tmhd) 4 . Density functional theory and molecular experiments suggest that irreversible ligand exchange of acac with alkoxide or carbamate reduces the activation energy for urethane formation and reversion. Furthermore, the Zr(acac) 4 catalyst activated in the presence of a PU’s polyol precursor provided more porous and less dense PU foams compared to those made using the unactivated Zr(acac) 4 catalyst. Furthermore, these findings are important for developing improved PU synthesis and recycling processes. Thermally activating a catalyst during reprocessing may provide more nuanced control of the in-use and reprocessing characteristics of PU thermosets.

Alcohols↗
DOE OSTI2024

Source of Processable Vitrimer Viscosities: Swap Frequencies and Steric Factors

Vitrimers exhibit high, processable viscosities, where other polymers do not, and are among the most promising polymers for closed-loop material circularity. We sought to investigate the underlying chemical kinetic factors that result in high viscosities for vitrimers, which are crucial to designing vitrimers with tunable viscosity. To interrogate these factors, we achieved the first simulated predictions of real vitrimer viscosities, using a novel kinetic Monte Carlo molecular dynamics method, overcoming the time and length scale gaps to predict experimental bulk viscosities. The vitrimer architecture investigated is based on poly(dimethylsiloxane) chains and vinylogous urethane bond swaps. We probed the effects of the extent of free swapping groups, %F, the activation energy, E A , and the steric factor, ρ. The steric factor is related to the intrinsic reaction probability for molecules with sufficient energy. All three factors were found to be significant, but the role of ρ was found to be the biggest and also the most underappreciated. The results show that the inclusion of accurate ρ is of critical importance for viscosity predictions, with the evidence suggesting that the typical assumption of ρ = 1 is not valid for vitrimers and that, indeed, very low steric factors are present in bond-swap vitrimers such that values of ρ < 10 –10 may be typical. This greatly influences the bond exchange rates and, ultimately, the viscosities. Recognition of this result is necessary for the prediction of vitrimer viscosities from molecular simulations and to make vitrimers by design from molecular dynamics. We also investigated the effects that E A , ρ, and the number of free swapping groups have upon vitreous range temperatures, TV, with respect to achieving a specific viscosity (η V = 1 × 10 8 Pa·s), as well as for a commonly reported higher viscosity extrapolation (η V = 1 × 10 12 Pa·s). The evidence suggests that vitrimers may follow universal curves for E A vs T V , as a function of ρ. Finally, this study achieves the first of these comparisons of molecular simulations to experiments and reveals critical insights toward creating vitrimers by design, while providing a route for the prediction of T V from kinetic Monte Carlo molecular dynamics simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Molecular Mechanisms Underlying Surfactant-Based Plastics De-Inking

Surfactant-mediated binder removal is critical for de-inking pretreatment in plastics recycling, yet the molecular mechanisms governing surfactant performance remain poorly understood. We used all-atom (AA) and coarse-grained (CG) molecular dynamics (MD) simulations alongside alkaline surfactant washing experiments to investigate interactions between a series of surfactants and a polyether urethane (PEU) binder in solution and on a polyethylene (PE) surface. Experiments reveal a range of de-inking efficiencies, ranging from <25 to >95% depending upon surfactant headgroup charge and tail length. AA simulations reveal that charged surfactants reach stable levels of surfactant coverage, while nonionic surfactants aggregate on the binder. CG umbrella sampling calculations quantify the thermodynamics of binder desorption in water. In ∼0.25 M surfactant solutions, up to a 52% reduction in the free energy barrier is computed, with trends in good agreement (R 2 = 0.92, Pearson’s r = –0.96, Spearman’s ρ = –0.83) with experimental de-inking efficiencies. We find that charged surfactants are more effective than nonionic surfactants for de-inking and propose three regimes of surfactant de-inking processes: good de-inking occurs in surfactants that promote PEU desorption with a low radius of gyration (R g ); moderate de-inking occurs when surfactants stabilize PEU but increase R g ; poor de-inking occurs in surfactants that aggregate on the binder and promote extensive anchoring to the surface. Overall, these molecular-level insights have the potential to guide the design of surfactant formulations for plastics recycling applications.

ink removal↗
DOE OSTI2025

Polyhydroxybutyrate laminated trilayer films with enhanced barrier and mechanical properties for active food packaging

Polysaccharides such as starch and chitosan have been explored for sustainable food packaging films. However, their inherent hydrophilicity and brittleness cause poor water vapor barrier performance and limited mechanical properties. To address these issues, starch was first functionalized with acetoacetate groups and subsequently blended with chitosan. Dynamic cross-linking occurred between the acetoacetate groups and the primary amine groups of chitosan, forming vinylogous urethane linkages that reduced the water solubility of the films while preserving high mechanical strength. With 30 wt% of glycerol as a plasticizer, the resulting films showed a tensile strength of up to 24.68 MPa and an elongation at break of up to 83.96%. To improve the barrier properties, poly(3-hydroxybutyrate) (PHB), plasticized with 5-15 wt% epoxidized vegetable oil, was laminated on top of the chitosan/modified starch films, resulting in a significantly reduced water vapor transmission rate (WVTR) of 66%. Additional components, such as food colors like β-carotene were incorporated into this layer to make UV-protective films. A third layer of PHB without active additives was then coated to further reduce WVTR by 99%. Therefore, this multilayer lamination strategy effectively enhanced the barrier and mechanical properties of the polysaccharide-based packaging films.

Active packaging↗
DOE OSTI2025

Backbone editing and deconstruction of polyethylene by Beckmann rearrangement and hydrogenolysis

Polyethylene is the most widely produced commodity plastic and is used in many applications, including packaging, insulation, and medical devices. However, the inertness of polyethylene makes chemical recycling inefficient and challenging. We report the conversion of oxidized high-density and low-density polyethylene, formed by direct, catalytic oxidation, to polyamides by Beckmann rearrangement of the corresponding oximes. These polyamides have enhanced surface properties over those of unmodified polyethylene, while maintaining the same, favorable mechanical profiles. The amide sites were reductively cleaved by hydrogenolysis with ruthenium-based catalysts to furnish alcohol- and amine-terminated fragments, which were used for the synthesis of polyurea-urethanes with poly(tetrahydrofuran) and methylene diphenyl diisocyanate. These experiments show how to install cleavable moieties into the backbone of polyethylene to facilitate deconstruction and the generation of new materials to affect greater sustainability in polyolefins.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Bioproduction, bioprotection, and biocontainment in multi-kingdom microbial systems with 3D spatial control

Engineered living materials (ELMs) are a class of hybrid materials that include engineered microbes encapsulated by a polymer matrix. The biotic and abiotic components define the ELMs design space and can be altered to improve performance and function. While current synthetic materials in the field display robust biocompatibility with both native and engineered living systems, we have a limited understanding of how to leverage three-dimensional (3D) form factors to spatially organize and control microbial dynamics within the material. Motivated by this knowledge gap, we employed extrusion-based 3D printing to fabricate multi-kingdom hydrogel constructs for the encapsulation of both single and multi-kingdom microbial systems. Core–shell cubic constructs enabled the spatial organization of a constitutive multi-kingdom system of levodopa (L-DOPA)-producing E. coli and betaxanthins (BXN)-producing S. cerevisiae. This spatial organization in 3D materials can introduce precise control over bioproduction, bioprotection, and biocontainment features that are critical to the efficacy of current ELMs. The relative spatial organization of the organisms, as well as the surface area-to-volume ratio were investigated to determine how these design elements impact microbial behavior (metabolite production, growth, expression, and cell distribution) over time. We demonstrated that F127-bis-urethane methacrylate (F127-BUM) core–shell geometries enable the hierarchical 3D printing of multi-kingdom constructs, offering customizable control over bioproduction, bioprotection, and biocontainment. With the optimization of these core–shell structures for continuous bioproduction, these ELMs could be deployed as compact and sustainable bioreactors in remote environments.

additive manufacturing↗
DOE OSTI2025

High-performance reversible adhesive from PET waste for underwater, structural, and pressure-sensitive applications

Developing versatile, tough, and sustainable adhesives that function effectively in both wet and dry environments is a major challenge. Here, we report a bioinspired design for versatile, tough, and reversible adhesives upcycled from consumer poly(ethylene terephthalate) (PET) waste. Our approach uses solvent-free, room-temperature dynamic cross-linking of deconstructed PET macromonomers with a diacetoacetate cross-linker, generating a dynamic, vinylogous urethane–bonded, amphiphilic adhesive. Tunable cross-linker concentration and amphiphilicity yield versatile adhesives suitable for underwater, structural, and pressure-sensitive applications on diverse substrates. Our adhesive exhibits high lap-shear strength and work of debonding under both wet and dry conditions, outperforming common commercial adhesives. The dynamic bonds enable thermal repair, on-demand multicycle debonding/rebonding, facile removal, and chemical recycling. Our strategy of transforming plastic waste into versatile, tough, and reversible adhesives offers a sustainable solution for both plastic waste management and next-generation adhesive design while also providing a commercially viable pathway for valorizing plastic waste.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Water Sorption Study of Various Polymers and Polymeric Composites

In the formulations of many composite materials, polymeric materials are often used as binder materials to enhance processability, functionality, and safety during manufacturing. For instance, poly(ester urethane), such as Estane® 5703, is used in the formulation of PBX 9501, and vinyl copolymer elastomer (VCE) is used in the formulation of VCE/filler compos ites. The stability of these binders directly impacts the overall stability and performance of their composites. Estane and VCE are prone to hydrolytic degradation, with water sorption behavior playing a significant role in their long-term stability and aging behavior. Hence, it is critical to study their water sorption behavior under various humidity and tempera ture conditions. To improve the accuracy and reduce labor-intensive work involved in water sorption experiments, an automated Dynamic Vapor Sorption (DVS) system was employed, which can generate large datasets. To efficiently process and analyze these datasets, Python scripts were developed. These scripts not only streamlined data processing, but also accu rately derived the Arrhenius parameters related to water diffusion and sorption properties for the tested materials. This approach offers a robust framework for evaluating water trans port and sorption processes in polymeric materials and adds valuable capabilities to future water sorption testing efforts.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Oil Filled Flow Shield Performance Evaluation

When hydrophones are used to monitor underwater sound in areas with currents, like rivers or tidal channels, flow noise caused by turbulent flow past a hydrophone can mask low frequency acoustic signals of interest. Flow shields can reduce the impacts of flow noise on hydrophone data. A prior study conducted by PNNL compared three flow shield designs and determined that an oil-filled urethane shield performed better than other designs and was likely sufficiently robust for long-duration marine deployments. However, that study did not assess the high frequency performance of the oil-filled flow shield or conduct long-duration field testing. Further, the prototype flow shield was difficult to assemble. This report details the results of design refinement and testing to address these gaps. Design refinements resulted in a straightforward and repeatable assembly method. Field testing indicated that the flow shields reduce flow noise by over 20 dB below 50 Hz at flow speeds greater than 0.5 m/s and are proven to survive deployments more than 6 months long. Calibration of the same hydrophone with and without a flow shield installed indicated that the shields attenuate propagating sound by no more than 2 dB at frequencies below 30 kHz.

42 ENGINEERING↗
NASA NTRS1966

Grit blasting nozzle fabricated from mild tool steel proves satisfactory

Dry blasting with glass beads through a nozzle assembly descales both the outside and inside surfaces of tubes of Inconel 718 used for the distribution of gaseous oxygen. The inside of the nozzle is coated with polyurethane and the deflector with a commercially available liquid urethane rubber.

Mc Farland, J. E.↗
NASA NTRS1967

Polymer research

Stress-strain distribution in elastomers, and chemical and physical properties of prepolymers, rigid urethane foam, and thermoplastic rubbers for composite solid propellant binders

ELASTOMER↗
NASA NTRS1969

Adhesive for cryogenic temperature applications

Adhesive, which bonds a metal liner to a filament wound composite structure used for cryogenic pressure vessels, prevents the metal liner from buckling under depressurization. The adhesive consists of adducts of urethane and epoxy resins.

Doyle, H. M.↗
NASA NTRS1972

Fire retardant polyisocyanurate foam

Fire retardant properties of low density polymer foam are increased. Foam has pendant nitrile groups which form thermally-stable heterocyclic structures at temperature below degradation temperature of urethane linkages.

Riccitiello, S. R.↗
NASA NTRS1971

Lunar surface engineering properties experiment definition

Research on the mechanics of lunar soils and on developing probes to determine the properties of lunar surface materials is summarized. The areas of investigation include the following: soil simulation, soil property determination using an impact penetrometer, soil stabilization using urethane foam or phenolic resin, effects of rolling boulders down lunar slopes, design of borehole jack and its use in determining failure mechanisms and properties of rocks, and development of a permeability probe for measuring fluid flow through porous lunar surface materials.

Mitchell, J. K.↗
NASA NTRS1973

The GSFC cosmic radiation experiment for the Pioneer F/G Jupiter mission

The extremely lightweight, low power design of the cosmic radiation experiment is obtained by using less than 10 percent of the total weight for the mechanical system. Both the baseplate and the top plate are aluminum honeycomb, the side panels are magnesium trusswork, and the inside circuitry is stacked like a sandwich and interleaved with polyester urethane foam for vibration damping. The flight performance of the experimental hardware is excellent.

Trainor, J. H.↗
NASA NTRS1974

Sound-absorbing slabs and structures based on granular materials (bound and unbound)

Sound absorbing slabs and structures made up of bound or unbound granular materials are considered and how to manufacture these elements at the building site. The raw material is a single grain powder (sand, expanded blast furnace slag, etc.) that imparts to the end products an apparent porosity of 25-45% and an energy dissipation within the structure leading to absorption coefficients that can be compared with those of mineral wool and urethane.

Petre-Lazar, S.↗