Cellulose nanofiber(CNF)was prepared from bleached hardwood pulp fiber(BEP)with the pretreatment using 40％mass fraction of ferric chloride solution combined with high-pressure homogenization.The morphology,size,crystal structure,chemical structure and thermal stability of CNF were characterized by environmental scanning electron microscope(ESEM),atomic force microscope(AFM),X-ray diffraction(XRD)analyzer,Fourier transform infrared spectroscopy(FT-IR)and thermogravimetry(TG)analysis.The results showed that a ferric chloride solution with mass fraction of 40％was highly acidic.The polymerization degree of wood pulp fibers reduced drastically from 1 067 to approximately 160 at a treatment temperature of 110 ℃,and the yield of fiber could rate up to 75.5％after hydrolysis.Combined with high-pressure homogenization treatment,CNF with a height of 25.1-31.8 nm and a length of 1-2 μm could be obtained.Compared with BEP,the hydrolysis process of high concentration ferric chloride effectively broke the amorphous region of the fiber,so that the crystallinity of the prepared CNF increased from 63.7％to 68.7％-71.3％.In addition,the pretreatment with high-concentration ferric chloride had no significant effect on fiber structure.CNF showed high thermal stability,and the maximum weight loss rate temperature of the obtained CNF ranged from 343 to 347 ℃.
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