Improving the sound absorption capacity of wood by microwave treatment

Abstract

Microwave treatment (MW) was used to improve the sound absorption capacity of Pinus sylvestris var. mongolica wood. The effects of the processing parameters such as MW intensity, processing time, and board thickness on the sound absorption of treated wood were investigated. Microstructure changes of the wood after microwave treatment were observed using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). It was found that the microwave treatment significantly enhanced the sound absorption capacity of the wood in the middle frequencies. The optimum microwave treatment parameters for Pinus sylvestris var. mongolica wood to achieve an improved permeability are: MW intensity of 18 Kw, board thickness of 30 mm, and processing time of 80 s. The maximum sound absorption coefficient of treated wood was 0.51. Micro-voids were formed in treated wood due to the destruction of the pit membranes, the wood ray cells, as well as the damage in the intercellular layer of the longitudinal tracheids. The number of micro-voids ranging from 7427.6 nm to 400 um increased, resulting in the increase in the air permeability and in sound absorption by the treated wood.