Biomanufacturing of Hierarchical Biocomposites for High-Performance Thermal Interface Materials: STTR

OUSD (R&E) critical technology area(s): Biomanufacturing, Biotechnology

Objective: Develop and demonstrate a flexible, polymer-matrix thermal interface material with tunable thermal and mechanical properties, leveraging hierarchical, biocomposite-based microstructures for scalable, sustainable, low-cost thermal management of high-performance electronics and power applications.

Description: This topic addresses the thermal management challenge to dissipate the large amount of heat generated by today’s high-density microelectronics and power storage systems to ensure and maintain performance, reliability, and safety [3, 4, 6] Thermal interface materials (TIMs) are a critical component in this thermal management. TIMs are designed to fill microgaps and surface irregularities between the otherwise bare surfaces between device and cooling system. Without a TIM, if two nominally flat and smooth solid surfaces are joined to form a bare contact, surface microroughness can limit the actual area of contact between the two solids to about 1–2% of the apparent contact area [11]. The solid-to-solid conduction through the contact points and conduction through the air trapped between the area of noncontact are poor thermal conductors and they limit the heat transfer from one surface to another. This thermal contact resistance needs to be reduced by inserting a TIM in the contact interface to eliminate air voids by filling the air gap at the device/cooling system interface.

The general requirements for a good TIM include low interfacial thermal resistance, high thermal conductivity, low elastic modulus, good adhesion, good conformability, long-term stability, and appropriate thermal expansion [7]. This is particularly challenging for mechanically flexible applications because the soft, polymeric materials commonly used as a matrix for TIMs generally have low thermal conductivity (TC) [7, 1], leading to difficulty in handling the thermal management demands. Drones and electric vehicles represent another application classic thermal management challenge arising from high C-rate battery pack discharge/charge cycles during operation. The drone case may be particularly difficult since payload and flight time constraints often dictate passive thermal management approaches such as heat sinks and air cooling [5], with TIMs a critical component for thermal coupling between the heat sink and battery packaging. In addition to thermal conductivity demands, power and high-frequency systems also often require TIMs that pair high heat conduction with electrical insulation, breakdown resistance, low leakage, and geometric conformity [1, 2].

While traditional thermal pastes and greases perform well under certain conditions, they still face challenges such as insufficient thermal conductivity (TC), aging, and poor reliability when applied in high-frequency, high-power density applications. In recent years, significant progress has been made in the material design and synthesis of high-performance TIMs. However, balancing various aspects such as interfacial thermal resistance, TC, and mechanical properties in TIMs continues to pose a significant challenge. Biomanufactured and biocomposite filler-type TIMs with simultaneous high TC and electrical insulation [8, 9] may be ideal materials to address these thermal and electrical requirements, while also offering a lower cost, supply chain sustainable solution compared to cutting-edge fillers such as boron-based semiconductors and carbon nanotubes.

Phase I

This topic is soliciting Direct to Phase II (DP2) proposals only. Feasibility Documentation: The Government expects that the small business has accomplished the following in a Phase I-type feasibility effort and developed a prototype TIM to address, at a minimum, the basic requirements of the stated objective above. For this DP2 STTR, a technical report containing Phase I Feasibility Documentation is required to demonstrate that Phase I feasibility has been met. The Phase I Feasibility Documentation must contain a detailed description of the technical plan, milestones, and data substantiating that the proposer’s technology addresses the Phase I deliverables and thus the proposer’s technology is at an acceptable stage to be funded at the Direct to Phase II level. The proposer must substantiate that feasibility equivalent to Phase I has been met outside of the SBIR/STTR program.

Phase II

Direct to Phase II (DP2): Develop, integrate, and demonstrate the following:

• Scalable (bio)manufacturing and structural control of biocomposite filler-type TIMs. Candidate biocomposite filler-type TIMs must demonstrate a TC exceeding that for state-of-the-art, boron nitride-based, soft polymer composite TIMs, e.g., >23 W/m-K (through-plane) [2024 Bashir]
• Modeling of the processing-structure-property relationship to enable the capability to balance high TC with mechanical flexibility
• Tunable mechanical properties of the biocomposite TIM, while maintaining the desired TC and electrical insulation.
• Candidate biocomposite TIMs must demonstrate tailored flexibility vs TC, with stable TC after 1000 bending cycles at 100% maximum strain.
• TC must be tailorable over the achievable range.
• Sufficient adhesion, e.g., based on a 90° peel test
• Modulus/flexibility comparable to common elastomers

TIM demonstration must be conducted using a prototype system in an operational environment, such as a passively-cooled, lithium-ion battery pack powering a FPV drone or electric vehicle under high C-rate or a state-of-the-art CPU or GPU running at maximum thermal design power (TDP). Thermal management performance will be compared for the high TC biocomposite TIM versus a standard TIM material such as thermal paste with metal or metal oxide, phase change material, or thermal pad with alumina. The goal is to demonstrate that the high TC biocomposite TIM successfully manages the thermal load in situations for which standard TIMs fail, e.g., the high TC biocomposite TIM maintains the maximum pack temperature =35 °C [2016 NREL] regardless of the pack’s discharge C-rate capability and the ambient conditions or maintains the CPU or GPU below the maximum junction temperature even at peak rated TDP. Compared to standard TIMs, high TC biocomposite TIM must deliver a statistically significant reduction in device temperature.

DP2 will also require commercialization and transition planning along with technology development. Throughout the phase, the proposers must collaborate with commercial and military end-users to refine operational requirements and deployment scenarios of their developed solution. Manufacturing and scaling plans for production must also be developed before the end of the Phase including a technoeconomic analysis (TEA). The final report must also include technology transfer documents outlining planned opportunities for commercial and military applications.

The deliverables for DP2 will include the final prototype TIM formulation, a comprehensive testing and validation report outlining the final demonstration, the technology transfer plan with commercialization plans, manufacturing and scaling strategy, and TEA.

DP2 Base milestones for this program should include:

• Month 1: Identify TIM candidate composition(s), biocomposite design, processing/manufacturing method, and design of experiments approach for TIM optimization. Determine target TIM performance metrics.
• Month 3: Initial modeling results for the TIM processing-structure-property relationships. Initial TEA results. Downselect to final TIM candidates.
• Month 6: Initial measurements of the thermal management performance of real-world systems and model validation.
• Month 9: Measurements quantifying TIM thermal and mechanical properties performance, comparing with alternative state-of-the art TIMs. Initial results on long-term TIM stability.
• Month 12: Demonstrations of prototype TIM in an operational environment.

DP2 Base deliverables should include:

• Month 1: TIM candidate(s) selection and design of experiments report.
• Month 3: Modeling and TEA description and results report.
• Month 6: Report describing initial thermal management performance results and model validation.
• Month 9: Prototype TIM demonstration in a laboratory environment. Report on TIM thermal, mechanical, and stability performance.
• Month 12: Final Phase II report documenting final prototype TIM composition, microstructural design, materials processing and scale-up, thermal and stability performance, thermal management results in various operational systems, validated processing-structure-property model, TEA, and commercialization/transition plan.

DP2 Option milestones are:

• Month 15: Scale-up to pilot plant quantities.
• Month 18: High TC TIM integrated into a battery thermal management system.

DP2 Option deliverables are:

• Month 15: Delivery of 20 g of high TC biocomposite TIM. Report documenting pilot plant design and operations and batch-to-batch thermal and mechanical properties uniformity.
• Month 18: Report on high TC TIM integration with a battery thermal management system, and the resulting performance.

Phase III dual use applications

Successful development of a (bio)manufactured, high TC, biocomposite TIM will have significant applications in both military and commercial sectors.

• DoW applications include: military (first person view) FPV drones, soldier-worn power systems, ground vehicle power electronics, and directed-energy thermal management.
• Commercial applications include: commercial delivery drones, EV battery packs, data center GPUs/CPUs, and LED lighting.

References

• [1] Z. Dou et al., “The development of thermal interface materials”, Nature Electronics, 2025.
• [2] A. Bashir et al., “A Novel Thermal Interface Material Composed of Vertically Aligned Boron Nitride and Graphite Films for Ultrahigh Through-Plane Thermal Conductivity”, Small Methods, 2024.
• B. Wei et al., “Thermal interface materials: From fundamental research to applications”, SusMat, 2024.
• Honeywell Application Note, “The Role of Thermal Interface Material in Modern Electronic Devices”, 2024.
• [5] Y.W. Son et al., “Passive battery thermal management system for an unmanned aerial vehicle using a tetrahedral lattice porous plate”, Appl Thermal Eng, 2023.
• [6] W. Xing et al., “Recent Advances in Thermal Interface Materials for Thermal Management of High-Power Electronics”, Nanomaterials, 2022.
• [7] Y. Cui et al., “Flexible thermal interface based on self-assembled boron arsenide for high-performance thermal management”, Nat Comm, 2021.
• [8] A. Khouaja et al., “Dielectric properties and thermal stability of cellulose high-density polyethylene bio-based composites”, Indust Crops & Prod, 2021.
• [9] K. Uetani et al., “Thermal conductivity analysis and applications of nanocellulose materials”, Sci and Technol Adv Mat, 2017.
• [10] A. Pesaran, “Battery Pack Thermal Design”, NREL/PR-5400-66960, 2016.
• [11] R. Prasher, “Thermal Interface Materials: Historical Perspective, Status, and Future Directions”, Proc IEEE, Sept 2006.

Keywords

Thermal interface material, thermal management, thermal conductivity, biocomposite, biomanufacturing, electronics, flexible, battery pack, drone, electric vehicle

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