| The cellulose of wood was separated by the catalytic ethanol in this paper and the nano crystalline cellulose (NCC) was prepared by acid hydrolysis with the separated cellulose. The silane coupling agent was able to improve the hydrophobic property of NCC. The surface-modified NCC was used to synthesize composites and the mechanism was studied.The new catalyst system containing4-methyl-2-pentanone, dimethyl sulfoxide and formic acid was able to decrease the temperature of separation of cellulose. The maximum temperature of the separation process was130℃and the separation process combined with acid hydrolysis was able to produce the NCC with wood chips continuously. NCC produced with the separated cellulose was characterized by DP, FT-IR, XRD, TG, DSC and TEM, and the results showed that the NCC from larch was more steady and uniform than that from poplar. The NCC modified by silane coupling agent was used to synthesize composites with urea-formaldehyde resin, acrylic resin, waterborne polyurethane and phenolic resin. The improvements of the composites resulted from the silane coupling agents and the contents of NCC were studied and the results were summarized as follows:NCC modified by APTES and MPS was used to synthesize composites with the urea-formaldehyde resin. Compared with the control group, the contact angle between APTES-modified NCC and urea-formaldehyde resin was decreased by26.4%, while the contact angle of MPS-modified NCC was reduced by24.1%. The prominent physical adsorption and chemisorptions of NCC modified by APTES led to a53.2%reduction of the free formaldehyde in plywood, which was more than the reduction resulted from the MPS-modified NCC. The improvements resulted from modified NCC in fibreboard were inconspicuous. With the formation of crosslinked network, the bonding strength of plywood with APTES-modified NCC was improved by23.6%and the improvement led by NCC modified by MPS was7.0%. The bending strength of fibreboard was enhanced by46.1%and35.7%with the additions of APTES and MPS modified NCC, respectively.GPTMS-modified NCC and MPS-modified NCC were synthesized composites with acrylic resin, and the surface-modifcations resulted in the22.8%decrease and19.6%decrease of the contact angles of NCC particles, respectively. The specular gloss of composite with GPTMS-modified NCC was improved by33.3%, which was more obvious than that with NCC modified by MPS. The abrasive resistance of acrylic resin with GPTMS and MPS-modified NCC was enhanced by59.4%and45.3%. The pencil hardness of the composites was affected by the surface modifiers of NCC inconspicuously, and the water absorption rate of the composites was affected by the modified NCC more significantly than the ethanol absorption rate.APTES and GPTMS-modified NCC were used to prepare the composites with waterborne polyurethane. The grafting ratio of APTES-modified NCC was more than that of the NCC modified by GPTMS, and the crystal structure of well-dispersed APTES-modified NCC was destroyed. Taked the case of APTES-modified NCC/waterborne polyurethane composites, the anti-yellowing property of the composites were improved by more than50%and the specular gloss was enhanced by164.8%. Mechanical properties of the composites were improved by the APTES-modified NCC significantly.MCPS and MPS were treated as the modifiers of NCC, and the composites were synthesized with the two kinds of modified NCC and phenolic resin. Compared with MPS, MCPS led to the great improvement of the hydrophobicity of NCC. For the covalent bonds and hydrogen bonds between NCC and phenolic resin, the tensile and bending strengths of composites with MCPS-modified NCC were improved by155.5%and23.8%, which were more than the improvements of composites with NCC modified by MPS. The impact strength of the composites was affected by the modifiers inconspicuously. |
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