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Study Of Damping And Underwater Acoustic Absorptin Properties Polyurethane Matrix Composites

Posted on:2008-11-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Q GuoFull Text:PDF
GTID:1101360305956339Subject:Materials science
Abstract/Summary:PDF Full Text Request
Polyurethane is an important damping material. To increase its damping property, many polyurethane/filler composites have been studied. In recent years, there is more interesting in the use of nanomaterials for damping. Even though a large amount of work has been carried out on the crystalline, electrical, tribological, and antibacterial properties of ZnO nanoparticles, few reports are found to use ZnO nanoparticles in viscoelastic materials. Tetrapod-shaped ZnO whisker (T-ZnOw) is a unique kind of single crystal that exhibits a needlelike tetrapod-shape. It has four needlelike arms extending from the same center in four directions in three-dimensional space. In this paper, polyurethane (PU)/ZnO nanoparticle or T-ZnOw composites are prepared by in situ suspension polymerization and their properties are studied.The tensile break strength increases dramatically with increment of nano-ZnO content and reaches the maximum (about 1290%) when 2 wt% content. The E′and E" of the composites show no significant change when the temperature is below the Tg, but decrease above the Tg and the decrement reduces with the increment of the ZnO content. The maximum of tanδpeak for the relaxation near Tg obviously increases with the addition of the filler, which with 2 wt% ZnO content is about 120% compared to that of the pure PU.Rigid fillers generally reduce damping of the polymers due to their lower damping relative to that of the polymers, though some rigid fillers increase it owing to new damping mechanisms that don't present in the pure polymers. Whether the filler increases or decreases damping, it will normally increase the loss modulus, since the increase of the storage modulus more than compensates for any decrease in damping. The IR results proved that hydroxy groups of ZnO have reacted with terminal isocyanate groups of linear polyurethane chains, and that linear polyurethane chains have been grafted on the ZnO particle surface. These grafting chains entangle other polyurethane chains. The rigid particles reacted with isocyanate groups are encapsulated by the long linear PU chains so that form the"core-shell"structure. In the case of low particle content, the ZnO particles are encapsulated so entirely that the fillers mostly show the properties of the linear PU when filled in the composites. With the filler content increasing, the properties of ZnO nanoparticles appear and compensate the decrease in E' and E". That results in the progressive decrement in E' and E" and the outstanding increased in tanδ.T-ZnOw increases the mechanical properties and storage modulus of the composites, while it decreases the densities. It is attributed to the high modulus and strength of the whiskers, especially to the tetrapod shape which produces"the pinning effect"to reinforce the matrix in three dimensions. The reason of the decrease of the densities may be the decrease of the regularity of the segment close to the whiskers, and that some segments can not enter into the space near the center of the whiskers. When tetrapod-shaped ZnO are filled in the matrix, acicular particles of whiskers contacting each other can form and stable conducting paths are created. The charge concentrating effect at the pinpoint of the whisker and the tunnel effect may exist and cause the result in lowering electrical resistivity of the composites.As underwater sound absorption materials, polyurethane/ZnO nanoparticles composites have high sound absorption coefficients (α). When the particles are 20nm, the composites with 5 wt% particles have the biggest sound absorption coefficients. The reason maybe is that hydroxy groups of ZnO have reacted with terminal isocyanate groups of linear polyurethane chains, which increase the effect of the interface between matrix and particles. So the particles can vibrate and transfer sound energy to matrix as they take sound wave. Meanwhile, nano-effect can make the particles absorb the polyurethane chains and form the gradient chains.Several methods are utilized to improve the sound absorption coefficient of the composite under press and low frequency, such as increasing internal friction and relaxation. When PPG2000 is 30 wt% of the soft segment, the composites have high sound absorption coefficients overall the experimental presses and frequencies range.
Keywords/Search Tags:polyurethane, nano-ZnO, T-ZnOw, damping, sound absorption coefficient
PDF Full Text Request
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