Study On The Vibration Characteristics And Mechanism Of Wood Treated With Co⁶⁰ Gamma Rays

The techniques of radiation cross-linking and radiation degradation are important methods for improving properties of polymer materials, which offers new ideas for the acoustic vibration properties modification of wood. The test results showed that the acoustic vibration properties of wood improved remarkably under the treatment of y ray.Taking Picea, jezoensis and Paulownia as research objects, this paper mainly studied the relation between chemical compositions of wood and its acoustic parameters by using some tests in which the plate, wood powder, holocellulose and lignin was radiated using the y-ray of different irradiation dose of 5kGy, lOkGy,30kGy,50kGy, 100kGy,200kGy and 300kGy. The y-ray has key effects on the mechanism of wood performance by analyzing different irradiation dose on the chemical composition content, concentration of free radicals, the micro structure and the influence of physical mechanics of wood. The results showed that:(1) With the increase of irradiation dose, the content of holocellulose content of Picea jezoensis and Paulownia was decreased whereas the content of lignin and the extract content of Picea jezoensis was increased. By contrast, there was no obvious relation between the extract content of Paulownia and irradiation dose. The anti-radiation sequence of three main compositions of the wood was lignin> cellulose> hemicellulose.(2) The chemical content of wood was tested according to GB/T2677.2-2011. The effects of chemical contents on acoustic vibration parameters of wood were analyzed using the one or binary linear regression. The results showed that the vibration parameters of wood reached best when the content of holocellulose is at the 66-68%. Due to the disorder of test results, the relation between lignin content and wood vibration performance need further study. The content of Benzyl alcohol extract had more remarkable influence on the vibration performance of wood than that with 1%NaOH extract content, and the less content of extract was, the better vibration performance of wood was.(3) Based on the results of analyzing the effect of y-ray treatment on wood acoustic parameters, all acoustic parameters improved dramatically at the irradiation dose of 10-50kGy of Paulownia and irradiation dose in 30-100kGy of Picea jezoensis. For the Picea jezoensis, at the irradiation dose is 50kGy, the value of dynamic elastic modulus increased from 7.9 GPa to 9.1 GPa, the ratio of dynamic elastic modulus increased by 15%, and the loss tangent value reduced from 1.63 to 1.37 at 30kGy. For Paulownia, dynamic elastic modulus increased by 5% compared with untreated, the acoustic radiation quality constant increased from 13.97 m3·Pa’1·s-3 to 13.97 m3·Pa-1·s3, and the ratio of dynamic elastic modulus was increased by 23%.(4) The change of molecular structure and chemical bond of Wood powder, holocellulose and lignin under irradiation process was analyzed through infrared spectrum. The results showed that the change of molecular structure of wood powder is minimum, because radiation mainly decreased the hydroxyl and C=O stretching vibration. The concentration of free radicals was measurement at different irradiation dose by ESR. The results showed that radiation did not change the g value, free radical concentration increases with the increase of irradiation dose and the change of the concentration of free radicals mainly comes from the lignin in wood components.(5) The effect of irradiation treatment on the micro structure of wood was characterized using the scanning electron microscopy. The results showed that:the cell wall surface appeared the fine grains and cross section was smooth and plain compared with the untreated wood. This result also showed that the toughness of wood treated by irradiation was reduced while its brittleness was increased. With the increase of irradiation dose, the crystallinity first increased and then decreased. At the irradiation dose of 50kGy, the crystallinity reached largest. At about 100kGy irradiation dose, wood moisture stability was best, which was mainly due to the degradation of cross-linked of hydroxyl groups.(6) The storage modulus and loss modulus were characterized using dynamic thermal mechanical analyzer(DMA). The results showed that:at 100kGy irradiation dose, the storage modulus was reduced minimum, demonstrating that radiation crosslinking was dominating at less than 100kGy irradiation dose. At 300kGy, loss modulus peak both a and P were decreased, implying that the main radiation degradation and reducing the interaction of molecular chains was on the work.