Low Density Composite With Acoustic Attenuation Property Based On Epoxy Resin

Syntactic foam, which used under water with excellent mechanical and acoustic attenuation properties, based on epoxy resin(EP) filled with hollow microspheres was studied at present thesis. Firstly, on the base resin, highly damping polyurethane(PU) was added into EP, not only toughened the base resin, but also improved the damping properties. Secondly, vinylidene chloride(VDC)/acrylonitrile(AN)/styrene(St) copolymer microsphere with property improvement was carried out, the effect of VDC/AN/St copolymer introduction into base resin on acoustic properties was studied. Finally, syntactic foam with acoustic attenuation property was prepared by using internal hollow glass microspheres and phenolic microspheres, mechanical and acoustic properties of syntactic foam were studied.The modification effects of different PU types based on glycols and isocyanates respectively were compared. PU prepolymers based on PPG-A, PPG-C, HP-A reacted with isophorone diisocyanate(IPDI) was synthesized firstly and then introduced into epoxy network by additive reaction with epoxy and cure reaction of epoxy. It is found that greater toughness and strength were attained by each PU type. PU based on polyether PPG-A owned better toughening effect than that of based on polyester HP-A, with the same molecular weight, while the latter obtained higher strength. As for PU based on polyethers, PU on PPG-C which held smaller molecular chain possessed better modification effect than that of on PPG-A, both on toughness and strength. The addition of 1,4-butanediol(1,4-BD)/trimethylolpropane(TMP) could enhance the tensile and flexural strengthens further. Modification effect can also be attained by hexamethylene diisocyanate(HDI) situ polymerization, but a little worse than that of by preparing prepolymer with IPDI.VDC/AN/St copolymer microsphere with property improvement was performed through increasing divinyl benzene(DVB) amount as cross-linking agent and VDC content in copolymeric monomers. It is found that the increment of DVB amount could heighten the gel fraction. When the dosage of DVB was lower than critical level 0.4%,multi bubble structure microspheres with high bubble density could be obtained on condition that low VDC content was present, the increment of VDC content would resulted in the decrease of bubble density and enlargement of the bubble. Otherwise only single bubble structure with low foaming percentage could be obtained when DVB dosage exceeding the critical level. When the dissolve amount of VDC/AN/St copolymer in EP achieved 5%, the strength and toughness of corresponding curing product would decrease drastically.Filling two types of internal hollow glass microspheres into EP, syntactic foam was prepared and the mechanical property was studied. It was found that the internal hollow glass microspheres led a decline of compressive modulus other than that of from abroad. The compressive strength, compressive modulus and impact strength of syntactic foam on type B microsphere all preceded those on type A. When treating type B microsphere with coupling agent, corresponding compressive strength, compressive modulus and impact strength could be enhanced to some extent. Mechanical property can be improved considerably with the introduction of PU into base resin. Increasing the filling amount of microsphere, syntactic foam with low density of 0.40～0.55g/cm~3 could be prepared but with low compressive strength and modulus.Dynamic mechanical property of PU/EP and acoustic property of syntactic foam were studied. According to the dynamic mechanical analysis, it was shown that the introduction of PU into EP could enhance the damping temperature range and shift the damping peak to lower temperature. Damping peak also appeared a lower temperature shift trend with the decrease of testing frequency. Damping range on master curve of EP storage modulus versus frequency appeared at very low frequency level, the introduction of PU can shift it to higher frequency. Damping property of PU/EP at 16～22 kHz was rather bad, corresponding acoustic attenuation coefficient was low, acoustic velocity increased monotonously with frequency at 2000～3500m/s range. The introduction of 1,4-BD/TMP into base resin could enhance acoustic attenuation considerably and reduce acoustic velocity a little correspondingly. The dissolve of VDC/AN/St copolymer in base resin almost had no effect on acoustic attenuation while resulted in lower acoustic velocity only. VDC/AN/St copolymer introduction could promote the match of acousticimpedance between composite and water as medium. Syntactic foam with the same microsphere volume fraction of type A and type B owned similar acoustic attenuation coefficient, both low than that of pure EP. The acoustic attenuation coefficient can be enhanced greatly when filling phenolic and type A microspheres simultaneously. The acoustic velocity in syntactic foam was higher than that of in pure EP. Hollow microspheres were also useful for the match of acoustic impedance between composite and water. As closed-cell foam, sound absorption coefficient of syntactic foam with phenolic microsphere fluctuated during 0.1-0.25 at 0.2-3.5 kHz.