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DOE OSTI2025

Corrosion resistant hot melt adhesive to bind metals

Hot melt adhesives (HMAs) play an important role in many industries, and their demand is expected to grow. HMAs don't require any solvents, and their application results in the formation of strong bonds with the substrate upon cooling within seconds. These properties differentiate them from liquid glues and make them preferable for practical application. Currently, commercial HMAs are used in bonding lightweight materials such as paper, polymers, and cartons, and have limited usage in areas necessitating the bonding of heavier objects like metals. Here, in this study, we report a design and testing of versatile platform comprising an ion-coordinating polymer and ionic fillers for performance optimization and understanding of structure–property relationships, enabling the rational design of HMAs with improved adhesion to metal surfaces. All-atom Molecular dynamics (MD) simulations and various characterization methods are used to elucidate the adhesion mechanism in model composite system containing polyethylene oxide mixed with chemically diverse salt particles. The maximum adhesion strength is found in composites with Al(OH) 3 and FeCl 3 fillers. Interestingly, the presence of Al(OH) 3 also provides a multifunctional anticorrosion property as measured electrochemically using the Tafel method. The discovered path to formulations with improved adhesion to metal surfaces constitutes an important step toward advancing HMAs for use in the structural and semi-structural metal work domain.

Adhesive and cohesive forces↗

DOE OSTI2021

Controlling the Morphology of Dynamic Thia-Michael Networks to Target Pressure-Sensitive and Hot Melt Adhesives

A series of multistage (pressure-sensitive/hot melt) adhesives utilizing dynamic thia-Michael bonding motifs are reported. The benzalcyanoacetate Michael acceptors used in this work undergo bond exchange under ambient conditions without external catalysis, facilitating pressure-sensitive adhesion. A key feature of this system is the dynamic reaction-induced phase separation that lends reinforcement to the otherwise weakly bonded materials, enabling weak, repeatable pressure-sensitive adhesion under ambient conditions and strong adhesion when processed as a hot melt adhesive. Furthermore, by using different pairs of benzalcyanoacetate cross-linking units, the phase separation characteristics of the adhesives can be directly manipulated, allowing for a tailored adhesive response.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Strong and recyclable bio-derived poly(ester amide) hot-melt adhesive

Bio-based adhesives offer inherent advantages over conventional petrochemical-derived systems, including renewable sourcing, reduced environmental impact and potential degradability. However, most bio-based adhesives suffer from poor adhesion strength, limited substrate compatibility and a lack of chemical recyclability. Here, in this work, we present a bio-derived multiblock poly(ester amide) adhesive that leverages microphase segregation between different segments to reconcile mechanical robustness with strong interfacial bonding. Notably, this multiblock architecture is accessed through a one-pot, selective acceptorless dehydrogenative polymerization, obviating the need for multistep synthesis. The materials exhibit excellent adhesion across a range of substrates including metals, glass and wet wood surpassing commercial benchmarks, while also demonstrating thermal stability, tunable mechanical properties and closed-loop chemical recyclability even in the presence of other commodity plastics. Furthermore, the adhesive strength of these materials could be tuned for various potential applications through control over the chemical composition of the polymer. By integrating renewable feedstocks, high-performance functionality and efficient chemical circularity within a single platform, this work provides a viable pathway toward more sustainable adhesive technologies and contributes to advancing circular materials manufacturing.

09 BIOMASS FUELS↗

DOE OSTI2025

Chemically Recyclable and Tunable Polyolefin-Like Multiblock Copolymer Adhesives

Adhesives are important in creating multilayer products, such as in packaging and construction. Most current hot-melt adhesives such as poly(ethylene-co-vinyl acetate) (EVA) and polyurethanes lack chemical recyclability and do not easily de-bond, complicating recycling. Here, we achieved tunable adhesive properties of chemically recyclable polyolefin-like multiblock copolymers through regulating the incorporation of crystalline hard blocks, amorphous soft blocks, and ester content highlighted by adhesive strengths up to 6.80 MPa. We further demonstrated applications of these adhesives in multi-layer films and showed that the adhesives can be readily de-bonded, recovered, and chemically recycled. Overall, this study into structure-property relationships, including effects of crystallinity, soft-block incorporation, and ester content of the multiblock copolymers on adhesive properties, has resulted in a modular hot-melt adhesive platform that exhibits chemical recyclability for virgin-quality adhesive re-generation, reprocessability for repeated reuse of the recovered adhesive, and tunability for designing adhesives with a wide range of low to high (up to ~80% stronger than EVA) adhesion strengths.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Chemical Recycling of Plastic Waste to Higher Value Lubricants

The aim of this project was to develop scalable methods to convert plastic waste to petrochemical-equivalent feedstocks and demonstrate their utility in lubricant base oil and wax applications. These objectives were partially accomplished, by scaling up the synthesis of platinum-on-strontium titanate catalysts to twenty gram batches, scaling up the conversion of plastic waste to twenty-five grams of plastic, producing high-melt waxes and characterizing their properties, and demonstrating the purification of high-melt waxes. High-melt waxes are one petrochemical-equivalent feedstock that can be made from plastic waste, consisting of a hard wax with a melt point above 65 C. They are used as ingredients in hot melt adhesives, coatings, and cosmetics. Producing a petrochemical-equivalent feedstock from plastic waste provides an advantage in lower carbon footprint and manufacturing cost, as the waste feedstock costs less than crude oil.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Stereomicrostructure-regulated biodegradable adhesives

Commercial adhesives are petroleum-based thermoset networks or nonbiodegradable thermoplastic hot melts, making them ideal targets for replacement by biodegradable alternatives. Poly(3-hydroxybutyrate) (P3HB) is a biorenewable and biodegradable alternative to conventional plastics, but microbial P3HB, which has a stereoperfect stereomicrostructure, exhibits no adhesion. Here, in this study, by elucidating the fundamental relationship between chemocatalytically engineered P3HB stereomicrostructures and adhesion properties, we found that biodegradable syndio-rich P3HB exhibits high adhesion strength and outperforms common commercial adhesives, whereas syndiotactic, isotactic, or iso-rich P3HB shows no measurable adhesion. The syndio-rich stereomicrostructure brings about desired thermomechanical and viscoelastic properties of P3HB that enable strong adhesion to a range of substrates tested, including aluminum, steel, glass, and wood, and its performance is insensitive to molar mass and reprocessing or reuse.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Environmental barrier coatings on SiC without a silicon bond coating: oxidation resistance, failure modes, and future improvements

Environmental barrier coatings (EBCs) are used to mitigate chemical reactions between SiC ceramic matrix composite (CMC) components and the H 2 O in combustion gas in turbine hot sections. CMCs are currently temperature-limited by the Si-bond coating, which melts at ~ 1414 °C. This work explores EBCs where the bond coating was removed to achieve higher operating temperatures. Various versions of enhanced roughness SiC were utilized to improve EBC adhesion to the substrates prior to 1 h furnace cycle testing in steam at 1250–1425 °C. The enhanced SiC roughness resulted in short coating lifetimes as the roughness was oxidized away with SiO 2 formation. Further, isothermal furnace exposures at 1400–1600 °C showed Yb 2 Si 2 O 7 /Yb 2 SiO 5 EBC microstructural changes, resulting in premature debonding from the substrates. Finally, this work provides baseline requirements for the development of both next-generation EBCs and bond coating strategies to overcome the current limitation of the Si-bond coating melting temperature.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Improved Polypropylene Thermoformability through Polyethylene Layering

Due to its low cost, stiffness, and recyclability, isotactic polypropylene (iPP) is an excellent candidate for packaging applications. However, iPP is notoriously difficult to thermoform due to its low melt strength. The addition of just 10 thin layers of high-molecular-weight, linear low-density polyethylene (LLDPE) into iPP sheets by coextrusion significantly increased extensional viscosity and reduced sag. Both LLDPE and iPP were metallocene-catalyzed with excellent adhesion as measured in our previous work. Here, we performed a series of hot tensile tests and sheet sag measurements to determine the properties of the iPP sheet and the multilayer sheet between 130 and 180 °C. To evaluate the thermoformability of these multilayer sheets, truncated conical cups were positive vacuum formed at different temperatures and heating times, and the crush strength was measured. Cups that released easily from the mold with good shape retention and a crush strength within 80% of the maximum value were used to define a temperature–time thermoformability window. We estimated the maximum stress that occurred during the thermoforming process to be 5 MPa. Layer thicknesses before and after thermoforming were used to estimate an average strain of 0.78. The thin LLDPE layers decreased the yield stress below 5 MPa. This enabled thermoforming at sheet temperatures as low as 150 °C. The immiscible LLDPE interfaces increased extensional viscosity, which decreased sag in the multilayer sheets compared to iPP. This broadened the thermoforming range to temperatures as high as 180 °C and allowed longer heating times. These highly thermoformable, layered sheets may be recycled as iPP since they contain only 8% of LLDPE.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗