| Chitin is one of the most abundant,easily obtained and renewable natural polymers,and has been regarded as a 'biomaterial in waiting' in the 21st century. But this polymer is not soluble in usual solvents and for its use,deacetylation is commonly performed.And so the research work on the determination of the degree of deacetylation of chitin/chitosan and the preparation of chitosan from chitin by deacetylation have been carried out.1.Determination of the the degree of deacetylation(DD)of chitosan by UV spectrophotometry using dual standards is investigated.The UV absorbance of a pure chitosan solution is contributed by the N-acetylglucosamine and glucosamine residues,the absorbance divided by the total molar concentration of the residues is linearly related to DD.Using N-acetyl glucosamine and glucosamine hydrochloride as standards in 0.1mol/L hydrochloric acid solutuion, the equation obtained by linear regression is A/ct=-33.651DD+3386.9, R2=0.9958.The result showed that this is a simple,reliable and precise method for determining the DD of chitosan.2.Determination of DD of chitin/chitosan by near infrared spectroscopy was studied.Sixteen chitin and chitosan samples are prepared,and their DD values are analyzed by 13C CP/MAS NMR.A calibration sample set was prepared by adding various amounts of water,protein,sodium hydroxide and sodium acetate.TThe MPLSR model with second derivative spectra in the range of 1100-2000 nm yields the best results,which are ECV=0.7955,(1-VR) =0.9989;SEC=0.3573,Rc2=0.9998。SEP=0.8669,Rp2=0.9986, slope=1.0009。It provides great application potentials to the real-time and on-line inspection for the quality monitoring of deacetylation process for the production of chitosan.3.Ultrafine chitin was prepared using a HMB-701S ultrafine grinder associated a winnower and characterized by IR,SEM,XRD,particle analysis sizer.The diameter of the particles is D(v,50)=2.599μm,the crystallinity decreased to 20.04%from 62.76%,but the molecular weight decresed a few and the reaction activity increased a lot.4.The deacetylation kinetics of ultrafine chitin in NaOH solution was studied.The result showed that the deacetylation of ultrafine chitin followed the first-order kinetics at all time because of the low crystallinity and the small particle size.The activation energy of deacetylation in 40%,50%and 60% solution is 27.73 kJ/mol,22.73 kJ/mol,17.29 kJ/mol,respectively.The results indicated that the deacetylation reaction of chitin at higher concentration proceeded easier.A equation was given from the total experimental data by regression:DD(%)=-142.508+3.400×NaOH(%)+1.209×T(℃)+ 0.745×t(min)-1.694×10-2×NaOH2-2.616×10-3×t2-1.549×10-2×NaOH×T +1.061×10-3×T×t5.A chitosan was prepared by immersing method from ultrafine chitin.Put ultrafine chitin in excessive concentrated NaOH solution,and than filter immediately,meanwhile the chitin/NaOH solution ratio(w/v)of the filter cake is about 1:2,heat the filter cake for a certain hours,a chitosan product with DD almost reach to 90%was obtained.6.Water-soluble chitosan was prepared from ultrafine chitin by slow down the deacetylation rate,the X-ray diffraction showed that the crystallinity of the half-acetylated chitosan obtained from ultrsfine chitin is almost zero.7.The ultrafine chitin is easier to be deacetylated than before,and high DD chitosan can be prepared under mild condition.Deacetylation of ultrafine chitin in 40%NaOH at 100℃for 150min,a chitosan with DD92.6%,Mv16.8×105 was obtained.The experiment result indicated that preparation of chitosan with high molecular weight and high DD from ultrafine chitin is a simple and economical alternative.
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