In this study, carboxyl-terminated poly(butylene adipate) (CTPBA) was synthesized, which was terminated with epoxy and used as a toughening agent to modify the epoxy resin, and the modified epoxy resin was cured at room temperature.

The damping performance and lightweight design requirements of composite sandwich structure core were studied. A series of low density damping cores were prepared by blending epoxy/polyurethane graft copolymer (E-g-U) and epoxy/poly mercaptan block copolymer (E-b-M) with different contents of hollow glass beads (HGM). The damping properties, mechanical properties, density, and interface morphology of the core layer were studied. The damping response and flexure properties of the sandwich composite structure were studied by modal analysis and three-point flexure test. The experimental results show that optimal damping performance of matrix appears at 60% E-b-M ratio, the peak loss factor is 0.88, and the damping temperature range covers À2 $ 52 C. When the HGM content in the core is 10 phr, the density can be comparable to that of the buoyancy material. Under flexural load, the ultimate shear strength and shear modulus of the sandwich structure increase maximum at 15 phr and 10 phr, respectively. Compared with the unfilled HGM sample, the first three modal damping ratios of the sandwich structure are increased by 133.2%, 56.6%, and 56% by 10 phr damping core, respectively. The results are compared with those in other reference. The research shows that the design of lightweight damping core is expected to provide a core material selection for the vibration reduction of sandwich structures.damping core, damping ratio, flexural properties, low density, sandwich structure | INTRODUCTIONComposite materials have developed from rice straw reinforced clay and reinforced concrete used in ancient times to advanced composite materials nowadays. Their bearing capacity and multi-functional characteristics have been developed incisively and vividly. They have been widely studied and applied in aerospace industry, marine structure design, seismic building construction, and sensor detection. [1][2][3][4][5][6] In the face of complex and harsh environment, the theoretical research on the dynamic performance and dynamic stability of composite materials under dynamic load is becoming more and more in-depth. [7][8][9][10] Due to many complex external loads, the composite structure will produce large vibration and noise problems, which will bring security risks such as performance stability to the structure and equipment. This is why the sandwich structure has become the focus of attention due to its high specific strength, sound absorption, vibration reduction, large stiffness, lightweight, and other obvious characteristics. [11][12][13]

To enhance the damping properties of nitrile butadiene rubber (NBR), the elastomer used was blended with chlorinated paraffin 52 (CP52) to prepare NBR/CP52 composites. The results showed that CP52 could significantly enhance the damping properties of NBR and shift the glass transition temperature (Tg) to lower temperatures. Molecular dynamics models of the CP52/NBR system were established, and the damping properties of the CP52-reinforced NBR were investigated using molecular dynamics (MD) simulations. Through the combination of MD simulations and the experimental results, the essential mechanism of the enhanced damping properties of the NBR was methodically expatiated and was ascribed to the Cl-CP-H····NC-NBR (type I) and CP-Cl····H-NBR-CN (type II) analogous hydrogen bonds formed between NBR and CP52. The higher the CP52 content, the higher the analogous hydrogen bond concentration, and the better the damping properties of the CP52/NBR composites. The experimental results were very consistent with the MD simulation results, meaning that the combination method can provide a new means to optimize the design of damping materials and broaden the application range of small polar molecules in the damping modification of polar rubber materials.

A metal-organic framework (MOF) formed between Zn and p-hydroxybenzoic acid (PHBA) is synthesized using a solvothermal method. These Zn-PHBA nanorods, which are inexpensive and suitable for mass production, are added as a flame-retardant into vinyl resin (430 LV, a material used in marine composites). Data from cone calorimetric test demonstrates that adding the Zn-PHBA nanorods to 430 LV significantly improves flame retardation and smoke suppression. At a high Zn-PHBA content of 10.0 wt%, the limiting oxygen index of 430 LV increases from 19.5% to 28.5%, and the material reaches the V-0 rating in vertical burning tests (UL-94). Moreover, the tensile and impact strengths of 430 LV containing 10 wt% Zn-PHBA as flame-retardant do not deteriorate and are even slightly improved. This work demonstrates that this MOF synthesized by a simple and efficient method may be used to produce nanocomposites with excellent flame retardation and mechanical properties, while keeping the material cost sufficiently low for marine applications.