| Noise pollution is the third biggest public hazard after air pollution and water pollution.People pay more and more attention to its harm,and vibration and noise reduction materials are also developed.Due to the special molecular structure of polymer material,damping coating can reduce vibration and noise by converting mechanical vibration and sound wave vibration into heat energy.Damping coatings can be widely used in automobiles,railway trains,airplanes and various mechanical equipment.In recent years,with the continuous improvement of the quality of life,environmental protection awareness has gradually increased.Traditional solvent-based coatings have gradually been eliminated,and water-based coatings have gradually occupied the dominant position in the market.Viscoelastic polymers are used for attenuating sound and damping the vibrations.Generally,segments of polymer chains can be in full motion near the glass transition temperature(Tg).However,the deformation cannot keep up with the change in the alternating field.Thus,the hysteresis is severe and the damping effect is efficient.In order to meet the demands for damping applications,the mechanical loss tangent(tan ?)of efficient damping materials must be higher than 0.3 for a temperature range of at least 60 ?.Polyurethane(PU)is an important viscoelastic polymer damping material that can undergo glass transition over a wide temperature range.However,traditional PU generally contains a high amount of organic solvents.With increased health and environmental awareness,waterborne polyurethane(WPU)is becoming a popular alternative to traditional polyurethane because its volatile organic solvent is very low or even zeros.WPUs have good physical and mechanical properties,excellent resistance to cold,elasticity,and temperature-dependent hardness.However,WPU has some inherent drawbacks due to the presence of hydrophilic groups,such as poor water resistance,solvent resistance,and weather resistance.Acrylate polymers(PA)have many advantages,including low cost,and good weather ability,and water resistance.Polymerization of waterborne polyurethane-acrylate(WPUA)hybrid emulsions is an important method to combine the advantages of WPU and PA.WPUA hybrid emulsions could have all the advantages of the individual components.At the same time,the composite emulsion was selected as the base emulsion to prepare high-performance water-based damping coatings.To this end,the following investigations were carried out in this thesis:(1)First,the WPU pre-polymer used as seed emulsion was synthesized by stepwise polymerization,and then,the acrylate monomers were added for emulsion polymerization to synthesize a series of WPUA composite emulsions.The influence of the R value,PU/PA ratio,methyl methacrylate(MMA)/butyl acrylate(BA)ratio and the content of divinylbenzene(DVB)on different properties of WPUA hybrid emulsions and films were investigated in detail.Particle size analysis and the appearance of emulsions indicated that a series of WPUA emulsions with controllable particle sizes and a stable appearance were successfully prepared.TEM images showed that the particles size of the WPUA dispersions was in accordance with the DLS results.DMA indicated that the films show good damping properties when the R value is 1.2,the PU/PA ratio is 30/70,MMA/BA ratio is 25/75 and the content of DVB is 0.8%.The maximum value of tan ? was 1.2,and the corresponding temperature range at which tan ? was ?0.3 was approximately 75 ?.It could be used in the application of damping coatings.(2)WPUA composite emulsions with different structures were synthesized respectively by physical blending,graft emulsion polymerization and interpenetrating network(IPN).The effect of the different methods on the properties of WPUA composite emulsions and its latex films was studied.DLS analysis and TEM showed that the grafted WPUA2 composite emulsion had the largest particle size and the blended WPUA1 composite emulsion had the smallest particle size.The grafted WPUA2 film has excellent mechanical properties,good damping properties and thermal stability.This indicates that the chemical bond between PU and PA plays an important role in regulating the properties of WPUA film.The SEM images clearly described that the phase separation of the two phases in the grafted WPUA2 was the least obvious,which proved that PU and PA had good compatibility.The results show that WPUA composite emulsion prepared by graft emulsion polymerization has better comprehensive properties.(3)By designing the molecular structure,three different generations of hydroxyl-terminated hyperbranched polyesters(HBP-OH)were synthesized and used as cross-linking agents to synthesize hyperbranched waterborne polyurethane/acrylate(WHBPUA)composite emulsion.The effects of different generations of HBP-OH on the properties of WHBPUA composite emulsions and films were studied.Fourier transform infrared spectroscopy(FTIR)and nuclear magnetic resonance spectroscopy(NMR)proved that three different generations of HBP-OH with high degree of branching were successfully synthesized,and the molecular structures approximated dendritic structures.With the increase of the generation of HBP-OH,the hydrophobicity,tensile properties,damping properties and thermal stability of the WHBPUA film are all improved.The water contact angle of WHBPUA-3 reached a maximum of 94°,and the tensile strength of the WHBPUA films increased from 10.8 MPa to 13.9 MPa.WHBPUA-3 has the best damping performance,and the effective damping temperature range(tan ? ?0.3)is 84 ?.(4)The previously synthesized WPUA composite emulsion with good damping performance was selected as the base material,and fillers and other additives were added to prepare water-based damping coatings.The effects of the variety,size and amount of filler on adhesion,thixotropy,rheology and damping properties of coatings were investigated.The coatings show obvious "shear thinning" characteristics of pseudoplastic fluids.All samples have good thixotropy and good flow resistance.Comprehensive comparison shows that the damping coating with mica powder as filler has better damping performance.When the number of mica powder is 400 mesh and the ratio of WPUA composite emulsion to mica powder is 70/30,the coating has the best damping performance,the maximum value of tan ? is 0.81,and the effective damping temperature range(tan ? ?0.3)is 106 ?. |
PDF Full Text Request