Abstract: [Objective] In order to obtain new composite material with properties of light, thin and good acoustic insulation performance, the single homogeneous wooden material was composited with the polymer multilayer damping material, and the parameters of wooden damping composites were optimized.[Method] Medium density fiberboard (MDF) and rubber material (R) were composited under the following manufacture conditions: the hot pressing temperature was 100 ℃, the hot pressing pressure was 3 MPa, the hot pressing time was 10min and the coating amount was 64 g. The mechanical properties of wooden damping composites were determined as following: modulus of elastic (MOE) was 3 490 MPa, flexural strength (MOR) was 30.9 MPa and internal bond strength was 1.24 MPa. On the basis of reducing the amount of coating and improving the production efficiency, the mechanical properties of the wooden damping composites were satisfied. Using the all-factor experiment, the impedance tube was applied to investigate the effects of thickness and density of MDF and R on sound insulation performance. The influence extent of each composite parameter on the sound insulation performance was analyzed and determined by SPSS19.0. [Result] MDF thickness showed a significant impact on the sound insulation performance, with the MDF thickness increased from 3 mm to 5 mm, the weighted sound insulation increased from 34 dB to 39 dB, an increase of 5 dB. In the low frequency band, the sound insulation performance of wooden damping composites were controlled by its own stiffness, therefore, the sound insulation performance was influenced by surface density and damping properties to a small extent. With the increase of MDF thickness, the vibration velocity decreased and the sound insulation increased, which attributed to the same frequency incident acoustic excitation. The damping ratio increased from 0.176 to 0.258 with the increase of MDF thickness, an increase of 31.8%. Therefore, the higher damping performance, the greater sound insulation was found. The R thickness showed a significant correlation with the sound insulation performance and the correlation coefficient was 0.979. As the R thickness increased from 0.8 mm to 2 mm, the weighted sound insulation increased from 30 dB to 37 dB, an increase of 7 dB. In the low frequency band, the sound insulation performance was mainly controlled by the stiffness. The slope of sound insulation curve was increased with the increasing stiffness. With the increase of the incident frequency, over the stiffness control area, the resonance effect was gradually disappeared and moved to the quality control area. With the increased of the surface density, the sound insulation performance of the wooden damping composites increased. When the high frequency was reached, the sound insulation performance was mainly controlled by damping performance. The damping ratio of the wooden damping composite increased from 0.065 to 0.201. The higher the damping ratio, the better the damping performance of the composite materials was found. With the increase of the damping performance, the resonance of the plate was suppressed, and the sound insulation at the resonant frequency was improved. The critical frequency moved to high frequency range, which inhibited the anastomosis effects, and the weir valley became shallow and the sound insulation increased. With the R density increased, the weighted sound insulation increased from 36 dB to 37 dB, non-significant effect of R density on sound insulation performance was observed. [Conclusion] The thickness of MDF and R have a great effect on the sound insulation performance of wooden damping composites, and the R density has little effect on the sound insulation performance. The better acoustic damping properties of wooden damping composites were achieved with the following parameters: the MDF thickness was 2 mm, the R thickness was 2 mm and the R density was 2.3 g·cm^-3.

Key words: wooden materials, rubber materials, multi-layer composite, damping performance, sound insulation performance