Preparation Of Sound Absorption Materials Of Polymer Micro-particles And Study On Its Properties And Acoustic Mechanism

Owing to the advantage of low cost, variability and relatively simple assembling, polymer micro-particles are likely to bring a new kind of absorptive materials in many applications, such as in buildings, duct liners and machinery enclosures, which have the possibility to substitute inorganic and metallic particle or other granules materials in many cases. So the preparation and investigation of acoustic materials of polymer micro-particles is a novel and interesting field and strongly desired.Hollow particles with interconnected cavities have been prepared by a simple modified suspension polymerization of acrylate monomers in the incorporation of a phase inversion process and polymerizable emulsifier PUA/IPUA. The morphology of particles has been characterized by scanning electron micrographs (SEM). Detailed information of multi-porous hollow particles (such as surface area) is determined by BET (Brunauer-Emmett-Teller) method. Based on observations using an optical microscope equipped with a digital camera and SEM images of particles obtained under different conditions, the formation mechanisms for multi-porous hollow particles are discussed.Porous/hollow micro-particles of phenolic resin have been prepared by suspension polymerization from the water-soluble phenolic resin in a compound emulsion system (Oil-in-Water-in-Oil). The porous/hollow structure of phenolic resin micro-particle has been characterized by optical microscopy (OM) and scanning electron microscopy (SEM). The experimental results show that the porous/hollow structure is related to the dispersion and curing process of the resol resin. With the increase of Oil content inside, the structures of particle change from porous to hollow.The sound absorption behavior of the micro-spheres materials are tested in an impedance tube. It is shown that the porous structures and low density allows the micro-spheres to embrace more diversified modes to attenuate sound wave energy. Besides the sound energy being dissipated at the interface of air and solid structures of micro-spheres, high absorption coefficient is given rise to by the vibration of the micro-spheres at the resonant frequencies. The micro-particles with intact surface clearly show the primary peak attributable to the excitation of the normal vibration of the polymer particles by the sound wave incidence. Consequently, experimental results demonstrate that the acoustic behavior of the material, and farther the sound absorption ability are apparently been influenced by the multilevel microstructures and properties of polymer micro-particles.Following the contact force model and Newtonian second law, the contact force, velocities and dynamical process analysis of particle under sound are carded out. The numerical simulation model of Discrete Element Method (DEM) for polymer particles is firstly presented to study the sound absorption behavior of the material here. On the basis of the model, a calculation programs using MATLAB have been created and moreover, the evolution of the energy dissipation mechanism for polymer micro-particles have been performed. Based upon thermodynamics—the dissipation characteristics of the systems, the preliminary research on the sound absorption performance of the material and the mechanism are conducted. Theoretical and results analyses indicate that the sound absorption provided by the material mainly consist of two parts: the conventional vsico-thermal mechanism between polymer particles and air and the integrated kinetic loss of particles with motion under external stress.Experimental data from vibration and acoustic tube test have been compared with the data from DEM simulation through the transmission function of vibration acceleration of particles. The result supports the said hypothesis that the integrated kinetic loss of panicles motion under sound wave contribute to the sound absorption characteristic of the panicles material, in addition to the conventional vsico-thermal mechanism between polymer panicles and air.Experimental results show that the sound absorption material of polymer micro-panicles possesses its characteristic frequency band where the average sound absorption coefficient of the material is 0.4 and the maximum is up to 0.92. Compared with pure PU foam, the material needs less thickness for achieving the same effect of sound absorption. Consequently, the results demonstrate that the acoustic behavior of the material, and farther the sound absorption ability are apparently been influenced by the multilevel microstructures and properties of polymer micro-panicles.To solve the problem of the distinct difference of impedance between the micro-panicle and air, a sound absorption material with multi-layered structure has been fabricated by using polymeric micro-particles with low reflection as matching layer and high sound absorption ones as sound energy attenuation layer. To optimize the absorption characters in special frequency regions, a double impedance matching layer have been presented. As the same time, the sound absorption theory of multi-layered material has been used to predict and optimize the sound absorption properties of the multi-layered structure material.With the conception of impedance matching, a novel composite sound absorber has been fabricated, using re-cycled rubber panicles with good attenuation property as sound energy attenuation layer, low characteristic impedance materials such as polymer porous foam or perforated panel as matching layer. Its' attractive characteristics include: low-cost, broad-band sound absorption, thin in thickness and relatively simple processing. Several important influence factors that affect the acoustic absorption of the multi-layer acoustic absorber are discussed. An acoustic transmission analytical model (ATA) is developed and successfully applied to evaluate the sound absorption of the composite absorber.