خصوصیات دینامیکی-مکانیکی و آکوستیکی زیر آب مخلوط الاستومری پلی یورتان/رزین اپوکسی پر شده با دانه های ماکرو منفذ دار پلی (وینیل استات کوتریال-ایزوسیانورات) Dynamic Mechanical and Underwater Acoustic Properties of the Polyurethane/Epoxy Resin Blend Elastomers Filled with Macroporous Poly(vinyl acetate-co-triallyl isocyanurate) Resin Beads

INTRODUCTION Covering a layer of anechoic tiles on a submarine surface is an important method for submarine acoustic stealth.1,2 The key part of the anechoic tiles is the underwater acoustic absorption material matching with the impedance of seawater as much as possible; this material is usually an elastomer or viscoelastic polymer containing various acoustic particles and/ or acoustic structures.3,4 When the incident acoustic wave contacts the material, a part of the incident acoustic wave is reflected by the material surface, and the other enters into the material interior; the entry acoustic wave can be converted into heat energy by changes in the wave mode, scattering, and absorbing due to material damping and structure, except the transmitted acoustic wave.5–۱۲ Polyurethane (PU) elastomer has excellent damping ability and can be used as a damping material and/or underwater acoustic absorption material.13–۱۶ Its damping or underwater acoustic absorption ability can be controlled by molecular design, such as adjustment of the ratio of soft and hard segments,14,17 selection of different sorts of synthetic methods and materials,16,18 and blending with other polymers, such as epoxy resin (EP).19 EP can improve the mechanical and high-temperature damping properties of PU elastomers by the formation of interpenetrating polymer networks or other blend structures.19–۲۳ Therefore, it is possible that PU/EP blends with higher composition ratios of PU to EP could be used as the matrices for underwater acoustic absorption materials. To improve the underwater acoustic absorption properties of elastomeric or viscoelastic matrices, adequate porous fillers (e.g., microballoons, voids, cavities, particles) and acoustic absorption structures are usually introduced into the matrices.3,24–۲۸ Generally, inorganic and rigid fillers can only reflect and scatter sound waves, but porous polymer particles can attenuate sound wave because of their framework high-damping properties, except reflection and scattering.29 Recently, two research groups have discovered that porous polymer particles have good airborne acoustic absorption properties and can also improve the airborne acoustic absorption properties of PU foams, especially at low frequency.30–۳۴ Whether porous polymer particles can improve the underwater acoustic absorption properties of the elastomer matrices or not is worth investigating. In this study, macroporous vinyl acetate (VAc)–triallyl isocyanurate (TAIC) copolymer beads were synthesized and used as acoustic particles for PU/EP blend elastomer matrices, and the dynamic mechanical and underwater acoustic properties were studied. CONCLUSIONS Macroporous P(VAc-co-TAIC) resin beads improved the underwater acoustic absorption properties of PU/EP intercrosslinked elastomer matrices and depended on their amount and diameter size, the composition ratios of PU to EP, the thickness, and the water temperature. The beads with smaller diameters had a better enhancing effect on the underwater acoustic properties of the matrices. In a comparison with the matrix with a 70/30 composition ratio of PU to EP to one without the beads, the composite with 5% beads had higher damping properties, its average acoustic absorption coefficient increased from 0.38 to 0.55, and the peak value increased from 0.42 to 0.65. However, the composites with 10 and 15% beads had lower acoustic absorption coefficients at low frequency and much higher acoustic absorption coefficients at high frequency. The damping properties of the composites depended on the composition ratios of PU to EP.