Fabrication of UV-curable polyurethane acrylate composites containing surface-modified boron nitride for underwater sonar encapsulant application

UV-curable polyurethane acrylate (PUA) is currently used as an encapsulant for undersea sonar devices, and new, desirable polymeric materials should have lower swelling ratios when in contact with seawater and paraffin oil, along with better mechanical strength, when compared to PUA after impregnation. We blended PUA with boron nitride (BN) to fabricate these desirable composites for sonar encapsulants. PUA-coated BN was prepared and was found to have better interfacial adhesion between the PUA matrix and the BN filler. The surface-modified filler showed enhanced dispersibility and affinity due to the surface treatment with functional groups that affected the surface free energy and the structural similarity of the doped crystallized diisocyanate molecule in the matrix. Studies of these composites showed that the swelling ratios decreased with increasing BN-PUA content. The tensile strength of the BN-PUA/PUA composite in either seawater or paraffin was higher than that of the BN/PUA composite as the immersion time increased. We conclude that these composites are promising materials for use as sonar encapsulants and can significantly improve both mechanical strength and long term stability.