| The inner adhesive impurities of wood waste are significant problem to wood recycling. Urea-Formaldehyde(UF) is one of the most popular adhesives because of its cheap price, easy preparation and good bonding performance. Therefore, UF adhesive was chosen as the study object, via analyzed and compared the old UF cured system and new UF cured system`s interface morphology, chemical structure and thermal property to understand the effect of old UF cured system to new UF cured system. The bonding strength and peeling ratio of plywood which contained old UF cured powder was tested and the results indicated the grain size and mass ratio range of old UF cured powder affect the reconstitution of wood-based panels. This study provides a theory foundation and application to wood-based panels recycling and reproduction. In order to recycle the wood fiber, two preparation methods have been used to obtain different nanocelluloses: cellulose nanocrystal(CNC) and cellulose nanofibrils(CNF). The technological parameter was optimized by orthogonal experiment, with the purpose to find an effective and efficient preparation method. The yields, composition, thermal property, micro morphology and other physical or chemical properties of the cellulose fibers were compared between those from eucalyptus wood and from waste fiberboard yields. The resulting cellulose fibers from waste wood-based panels were successfully used to prepared high value-added nanocelluloses.The main findings can be concluded as following:(1)The old UF cured system did not fused to the new UF system as indicated by the SEM imaging. By comparing the DSC thermo grams of the UF resins with or without previously cured resin particles, it is concluded that the addition of previously cured resin resulted in more exothermic thermal incidents and an increase of reaction enthalpy. Theshear strength and dip peeling property of the plywood weakened when glued by UF resins containing previously cured resin particles. The higher amount and greater size of the particles resulted in more severe damage to the bonding strength and peeling property of the plywood.(2)During the extraction of cellulose, the yields?FTIR?TGA results indicated that UF adhesive would hydrolyzed in the process, and the hydrolysis reaction mainly happen in alkali treatment. The functional groups included ether link and methylol had been broken.Nevertheless, the hydrolysis reaction did not fully complete, still some UF residue remain in the cellulose product. Cellulose fiber from fiberboard had higher amount of UF residue that from wood powder mixed with UF powder. The UF adhesive would bring forward the cellulose`s initial pyrolysis temperature to 250 degree, and residual char increased to 20%.(3)The orthogonal experiment in sulfuric acid hydrolysis showed the best technological parameter is sulfuric acid concentration of 65%, temperature of 60 degree,reaction time of 30 min. Yields and sulfate content measurement indicated that UF residue was hydrolyzed by sulfuric acid and the resulting CNC had lower sulfonation degree and crystallinity.(4)Different UF adhesive contents in raw materials may not had effect on the yield of to the TEMPO oxidation products. But the yields increased with higher Na Cl O concentration and longer blending time and the optimized production condition was Na Cl O of 5 mmol/g and blender time of 30 min. The higher Na Cl O concentration would increased the degree of cellulose hydroxyl oxidized to carboxyl,while higher UF adhesive impurities would decreased the radio. The micro morphology of nanocelluloses from different sources had distinct difference. CNC and CNF`s fiber width were thinner than those influenced by UF adhesive. |
PDF Full Text Request