Research On Functional Modification And Application Of Nanocrystalline Cellulose

Nanocrystalline cellulose(NCC)is derived from the cellulose of huge reserves in the nature and is made by further processing.Due to its good hydrophilicity and high molecular weight,nanocrystalline cellulose can be given some new functions when it is chemically modified.In this paper,based on the characteristics of nanocrystalline cellulose,nanocrystalline cellulose was grafted with saturated fatty acids to prepare modified nanocrystalline cellulose(MNCC)with hydrophobic property.The structure,surface activity and application of MNCC were also studied.MNCC was used as a kind of non-ionic emulsifiers,styrene-acrylic emulsions and O/W soybean oil emulsions were prepared,and their emulsion properties were studied.Microcrystalline cellulose as a raw material was continuously stirred for 2.5 hours and hydrolyzed at 45℃ to prepare a mixture containing NCC.Then the mixture was centrifuged to prepare NCC with an average particle size of 168 nm.The prepared NCC and three fatty acids(lauric acid,palmitic acid and stearic acid)were used as raw materials,and the MNCC were prepared in heterogeneous system by the co-reaction reagent or the initiator.The products of NCC modified by lauric acid,palmitic acid and stearic acid were called MNCC-C12,MNCC-C16 and MNCC-C18,respectively.The co-reaction reagent was trifluoroacetic anhydride,and the initiator was Fe SO4/H2O2 redox system or ammonium cerous sulfate.By changing the reaction temperature,reaction time and the ratio of the reaction materials,MNCC with different degrees of substitution(Ds)was prepared.When trifluoroacetic anhydride was used as co-reaction reagent,the optimal reaction conditions for MNCC-C12 were that the reaction temperature was 50℃,the reaction time was5 h and the feed ratio of anhydroglucost unit(AGU)and trifluoroacetic anhydride was 1:3.The Ds of MNCC-C12 was 0.32.The optimal reaction conditions for MNCC-C16 were that the reaction temperature was 55℃,the reaction time was 6h and the feed ratio of anhydroglucost unit(AGU)and trifluoroacetic anhydride was 1:3.The Ds of MNCC-C16 was0.27.The optimal reaction conditions for MNCC-C18 were that the reaction temperature was55℃,the reaction time was 6h and the feed ratio of anhydroglucost unit(AGU)and trifluoroacetic anhydride was 1:3.The Ds of MNCC-C18 was 0.23.In the preparation of MNCC by grafting copolymerization,two initiation systems were used,namely Fe SO4/H2O2 redox system and ammonium cerous sulfate.Among them,the Fe SO4/H2O2 redox system was better than the ammonium cerous sulfate.In the system,MNCC-C12 was prepared with 0.8%initiator at 50℃ for 8h,and the highest Ds was 0.24.MNCC-C16 was prepared with 1.2%initiator at 55℃ for 20 h,and the highest Ds was 0.16.MNCC-C18 was prepared with 1.2%initiator at 60℃ for 24 h,and the highest Ds was 0.12.The structure of the products was characterized by analyzing the prepared MNCC by infrared spectroscopy,X-ray diffraction,SEM,thermogravimetry and particle size.The test results showed that the carbonyl stretching vibration peak of MNCC appeared at the 1740cm-1wavenumber.It is a characteristic peak of ester bond,which proves that the hydroxyl groups carried by NCC have reacted with the carboxyl groups on higher fatty acids,and ester group is formed.The average particle size of MNCC is in the range of 240-260 nm,and the products have still diffraction peaks at I002,Iam and I004.It proves that MNCC still maintains the basic crystal structure of NCC.In addition,the morphological characteristics of the three modified NCC have not changed significantly.But their thermal stability is different,which decreases with the decrease of the grafted hydrocarbon chain length.The prepared MNCC is used as surfactants and applied in the field of emulsification.The contact angle,HLB value and surface tension were tested to explore their surface activity.The contact angles of MNCC-C12,MNCC-C16 and MNCC-C18 range from 70.0° to 90.0°,and they have a certain degree of hydrophobicity compared with unmodified nanocrystalline cellulose.The HLB value range of the three modified products belongs to the range of surfactant as emulsifier,so they are applied in the emulsifying field.The surface tension of MNCC was tested and the application model of MNCC was constructed.It is found that it has a good effect on reducing the surface tension of water and salt solution.The change of the p H of the test environment does not have a significant impact on the surface tension.Therefore,the modified products does not have harsh requirements for the application environment.It has application prospects and has good emulsification and solubilization effects on the prepared emulsion.