Solution-processable thermally conductive polymer composite adhesives of benzyl-alcohol-modified boron nitride two-dimensional nanoplates.

Study Summary

Epoxy resins have been extensively used to bond parts in electronic devices and machinery. Recently, owing to the miniaturization, integration, and weight-reduction of products, the resin has been required to dissipate the generated heat. However, the low thermal conductivity (0.2 W/m.K) of the epoxy cannot meet the performance criteria. So many people use a combination of fillers in epoxy called by polymer composite. The hexagonal Boron nitride(h-BN) used as a filler has superior properties including a high thermal conductivity (150-225 W/m.K at 300K) and thermal and chemical stabilities, owing to its unique crystal structure. However, the hydrophobicity of BN hinders its dispersion in a polymer matrix and limits the loading amount in the hydrophilic epoxy matrix, which restricts the heat dissipation. The modification process has proceeded with a NaOH solution, plasma, and oxidation process. These methods were not environment-friendly and cost-effective for mass production.
In order to solve this problem, we utilized ultrasonic wave and benzyl alcohol for facile large-scale synthesis and high performance of the noncovalently functionalized BN (B-BN).

[Fig. 1] Schematic illustration of the BN surface modification process by benzyl alcohol.

The B-BN can result in increasing the content in the epoxy up to 46wt%, being at a similar viscosity of the other 40wt% fillers. Despite just 6 wt& increase, the thermal conductivity of the composite was dramatically improved to be 2.11 W/m.K. The microstructures of the cured epoxy and composites including 40 wt% fillers are observed in the SEM images of the corresponding cross sections. It was confirmed that the affinity between epoxy and BN was improved.

[Fig. 2] Viscosity and thermal conductivity of the free epoxy resin and its composites(BN, S-BN, and B-BN).

[Fig. 3] SEM images of (a) the free epoxy resin and its composites with 40wt% fillers of (b) BN, (c) S-BN, and (d) B-BN. Optical microscope images of (e) the free epoxy resin and its composites with 40wt% fillers of (f) BN, (g) S-BN, and (h) B-BN. Arrow indicates some filler in epoxy matrix.

[Fig. 4 ] 400-MHz 1H nuclear magnetic resonance (NMR) spectra of benzyl alcohol (a) before and (b) after the 10th recycling for the surface modification of BN. (c) thermal conductivities of the composite with 40wt% BN at different numbers of recycling cycles.

Furthermore, 10th recycling tests of the solvent verified the reduction of the manufacturing cost and environmental pollution. We demonstrated a driven synthesis of noncovalently modified BN. We expect that this filler material can not be used as the alternative filler for the conventional NaOH modified-BN but can also be used individually for the heat dissipation in a polvymer composite.