Study On Irradiation Effects And Mechanism In Bamboo Treated With Co⁶⁰Gamma Rays

It has very significant theory and application meaning to research on physical and chemical properties of bamboo irradiated by gamma ray. The Moso bamboo (Phyllostachys pubescens Mazel ex H de Lehaie) was used as experimental materials in this dissertation. it was treated with gamma rays at differerent irradiation dose, such as 10KGy,20KGy, 30KGy, 50KGy, 100KGy, 300KGy, 500KGy, 1000KGy. Through studying Moso bamboo's microstructure and its physical, chemical and mechanical proterties during the process of irradiation, this study initially reveals the irradiation effects mechanism on bamboo treated with gamma rays. Based on which, the applications of gamma ray irradiation on the mildew proof of bamboo have also been researched. And the result could establish an important theoretical foundation for the functional improvement on bamboo with gamma rays. This method was expected to be a new way for bamboo functional improvement, and had some reference meaning for the functional improvement of wood and other biologic materials.Main results were concluded as following:(1) The cross section and microfibril angle of bamboo were characterized by field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD). it can been found that the vascular tissue system and fundamental tissue system were not be injured by gamma rays, the influence on microfibril angle were not obvious, and the cell wall of bamboo were not found shrink and fracture during the process of irradiation. So both microstructure and microfibril angle were not the dominant factors on variation in physical-mechanical properties of bamboo during the process of irradiation.(2) The structure and quality of main chemical composition in cell walls of bamboo were tested by nuclear magnetic resonance spectrometer (NMR), X-ray diffraction (XRD) and traditional means in testing chemical composition content of bamboo. The result indicated that at the beginning of irradiation process, hemicellulose degraded and partial degrading substances polymerized with cellulose, lignin and so on. Which result in hemicelluloses content decreasing, the cellulose and lignin contents increasing, and the bamboo crystallinity also increased. As the irradiation dose was raised to about 100KGy, the main composition in bamboo degraded more quickly, so that the main chemical composition contents and crystallinity in bamboo reduced, and the more irradiation dose, the more reduction.(3)The gamma rays radiation reduced adsorption of bamboo materials through making chemical composition in cell wall interaction, which produced the hydrogen, carbonyl, carboxyl, phenolic etc. The appearance color of the bamboo became darker for lignin degradation, but improved the light stability of color on bamboo surface, and the change rates of them increased with radiation dose growed.(4) At the beginning of irradiation process,the gamma rays radiation enhanced both tangential compressive strength and tensile strength parallel to grain of bamboo, owing to oligomerization of lignin and cellulose. And the degradation of hemicellulose reduced compressive strength parallel to grain of bamboo. As the irradiation dose rose to about 100KGy, both tangential compressive strength and tensile strength parallel to grain of bamboo reduced with degradation reaction comintensifying of main compositions in bamboo. Yet, carbonization of bamboo material enhanced compressive strength parallel to grain of bamboo. In the whole process, modulus of elasticity of bamboo material fluctuated rising tendency. So, the gamma rays radiation intensified stiffness and brashness of bamboo.(5) The dynamic viscoelastic properties of bamboo were tested by dynamic mechanics analyzer (DMA), and the measurements were done in the temperature range of 40℃to 300℃at frequencies of 3Hz. In the initial temperature, temperature of 40℃, the irradiated bamboo had more storage modulus than ordinary bamboo, but with the increase of irradiation dose , the decrease of storage modulus with increasing temperature became more dramatically, because the chain of main components in the cell walls have been cut off, and chain made drasticer reaction during heating process. In addition, irradiation made bamboo glass transition temperature changes. As the irradiation doses was less than 100KGy, the glass transition temperature at 105℃and 220℃fluctuated rising tendency for the oligomerization of lignin and cellulose. And when the radiation dose reached 300KGy, 500KGy and 1000KGy, both glass transition temperatures decreased for the degradation of three main compositions.(6) on the base of study about gamma ray irradiation, the technology of improving the application of bamboo mould-proof performance was researched. The results showed that the mildew proof of bamboo was enhanced after irradiation. Furthermore, the effect was better and better with the irradiation doses increased. At the same time, gamma ray has a side-effect, so the reasonable irradiation technology should be counted on the usefulness of bamboo material.