Improvement And Mechanism Of Acoustic-Vibration Performance Of Wood By Several Physical Treatments

In this research,Picea wood and P.elongata wood are chosen as the main research object for instrument production.Indoor natural aging,artificial accelerated aging,high temperature heating and high-energy rays irradiation are chosen as four physical treatment methods to improve the vibration properties of test wood materials.The paper systematically and comprehensively analyzed the effects of several physical treatment methods on the relevant indexes of several important acoustic vibration properties of test materials,summed up the optimization process parameters,revealed the mechanism of improving the acoustic vibration performance of wood preliminarily.The main research contents and conclusions are as follows:(1)Natural air dry Picea complanata,Picea batfouriana,Picea asperata,Picea purpurea and Picea likiangensis were put indoor for natural aging treatment in 1997.Vibration parameters(such as density,specific Young’s modulus,coefficient of sound-radiation resistance,sound resistance and E/G,etc.)of the five kinds of Picea wood in 1997,2012 and 2015 are tested through FFT,then the rate of change at different period is calculated,respectively.The influence of different ageing time on the vibration performance of wood is discussed.The results show that the acoustic vibration parameters of the five kinds of Picea wood achieve different degrees of improvement through more than ten years of indoor natural aging treatment.The acoustic parameters of indoor natural aging Picea batfouriana have the best improvement,suggesting that the vibration performance of wood can be effectively improved through long-term indoor aging treatment.(2)Picea jezoensis and P.elongata wood are chosen as the research object,on the one hand,the two species of wood are conducted under UV mild accelerated aging treatment in the QUV accelerated aging tester.The most gentle experimental parameters(temperature 45 ℃,ultraviolet irradiation intensity is 0.35 W/m)are chosen to simulate the condition of indoor natural aging,on the other hand,the two species of wood are conducted under UV intense accelerated aging treatment using the ASTMG-154 standard parameters in QUV accelerated aging tester to simulate the condition of outdoor natural drying.The results show that the vibration performance of wood under the two kinds of UV accelerated aging treatment can be effectively improved under suitable aging time.Better treatment time for both Picea jezoensis and P.elongata wood under UV mild accelerated aging treatment is 600h,and for that under UV intense accelerated aging treatment is 100h.It can also be concluded that accelerate aging process can effectively reduce the water absorption and improve the dimension stability which is beneficial to improve the stability of pronunciation effect of wood.Microscopic structure,relative crystallinity and chemical change of the internal structure of the wood under the two different ways of accelerated aging treatment are characterized through SEM,XRD,FTIR techniques.Mechanism of the UV accelerated aging effect on the vibration properties of wood is revealed.The results show that:after accelerated aging treatment,migration of the pit torus occurred and plug up the pits,resulting some formation of aspirated pit.The number of pit may have an impact on the spread of sound energy in wood.The relative crystallinity were significantly increased(including the P.elongata is with a biggest relative crystallinity increase of 5.07%,to 74.38%;Picea jezoensis is with a biggest relative crystallinity increase of 3.46%,to 78.69%)after the two different accelerated aging processes.This is beneficial to the improvement of the efficiency of acoustic vibration of wood and timbre.In the accelerated aging process,dimensional stability of the wood is improved because the reducing of free hydroxyl which is according to the condensation between them,and thus improve the effect of the pronunciation stability of wood.(3)Picea jezoensis and P.elongata wood are heat treated under the temperature of 170 ℃,190 ℃ and 210 ℃,respectively,the heat preservation time is 2h,3h and 4h.The change of various acoustic vibration parameters is analyzed before and after treatment.The results showed that appropriate heat treatment temperature and heat preservation time are effective on achieving a better vibration performance of wood.The vibration performance of Picea jezoensis has the largest improvement under heat treatment at 210 ℃ and heat preservation for 4h;while for the P.elongata,The vibration performance has the largest improvement under heat treatment at 210 ℃ and heat preservation for 2h.Microscopic structure,relative crystallinity and chemical change of the internal structure of the wood under heat treatment are characterized.Mechanism of the high-temperature heat treatment effect on the vibration properties of wood is revealed.The results show that after high temperature heat treatment,migration of the pit torus occurred and plug up the pits,resulting some formation of aspirated pit.The number of pit may have an impact on the spread of sound energy in wood.The relative crystallinity of Picea jezoensis and P.elongata is generally improved under different heating conditions.(The heating condition of heat treatment temperature of 210 ℃,holding time is 4 h for Picea jezoensis is with a highest relative crystallinity of 60.67%,an increase of 9.9%to the control group;the P.elongata wood under heat treatment at a heat treatment temperature 210℃,holding time is 3h,has the highest relative crystallinity of 50.86%,7.4%higher than the control group)This is beneficial to the improvement of the efficiency of acoustic vibration of wood and timbre.Part of the hemicellulose in Picea jezoensis and P.elongata are degraded after different heat treatment process,resulting a reducing of the number of free hydroxyl and carbonyl,and thus improve the effect of the pronunciation stability of wood.(4)Piceajezoensis and P.elongata wood are irradiated under 5kGy～300kGy doses of gamma irradiation.The results showed that when Picea jezoensis and P.elongata wood are irradiated under a dose of 50kGy,there is an ideal improvement on the vibration performance.It can also be concluded that gamma irradiation process can effectively reduce the water absorption and improve the dimension stability which is beneficial to improve the stability of pronunciation effect of wood.Microscopic structure,relative crystallinity and chemical change of the internal structure of the wood under gamma irradiation treatment are characterized.Mechanism of the gamma irradiation heat treatment effect on the vibration properties of wood is revealed.The results showed that after gamma irradiation treatment,migration of the pit torus occurred and plug up the pits,resulted some formation of aspirated pit.The number of pit may have an impact on the spread of sound energy in wood.After gamma irradiation treatment,we can find that the crystallinity of Picea jezoensis wood powder and 1%NaOH processing Picea jezoensis wood powder have a largest increase after a 30kGy irradiation dose treatment.(4.52%,1.94%respectively)While for holocellulose,the largest relative crystallinity increase occurred after 5kGy irradiation treatment.(4.37%)This is beneficial to the improvement of the efficiency of acoustic vibration of wood and timbre.During the radiation process,the radiation resistance ability of cellulose is weak,degradation occurs easily,resulting a reducing of the number of free hydroxyl,and thus improve the effect of the pronunciation stability of wood.(5)Based on the change of vibration parameters of different treated wood,the acoustic vibration performance of wood under indoor natural aging condition can achieve relative optimal improvement,but it requires a long time.And high temperature heat treatment not only has a good effect(being next only to indoor natural aging treatment method),but also with a simple operation and low cost;Artificial accelerated aging treatment can also effectively improve the acoustic performance of wood,and requires shorter time;High-energy rays irradiation treatment can effectively improve the acoustic performance of wood,the ray has a strong penetration ability,thus it can irradiated the wood as a whole uniformly,and the process is easy to control.