Design,Synthesis And Stabilization Mechanism Of Hydrophobic Water-soluble Nanocrystalline Cellulose Derivatives

The NCC?Nanocrystalline cellulose?is a green,renewable and biodegradable natural macromolecule material with a wide range of sources.The NCC has high chemical reactivity,and its hydrophobic modification can make it have excellent characteristics of wetting,dispersing,emulsifying,decontaminating and penetrating.And the Hydrophobized modified NCC will play an important role in various industries such as washing,textiles,petroleum,construction,coatings,pesticides and medicine.In this paper,NCC prepared by sulfuric acid hydrolysis was modified by lauric acid,palmitic acid and stearic acid.The surface activity of the MNCC?modified nanocrystalline cellulose?was tested,and the styrene-butyl acrylate emulsion was prepared by using the MNCC as an emulsifier.Finally,the basic properties of styrene acrylic emulsion were measured,and the mechanism of MNCC stabilized styrene acrylic emulsion was determined.The specific conclusions were as follows:The effects of reaction temperature,reaction time,initiator type and initiator dosage on the yield of MNCC was investigated.Then the particle size,infrared,XRD,thermal stability and structural morphology of the MNCC was tested.The optimum conditions for grafting modification of NCC with long chain fatty acids were obtained.The yield of L-MNCC?lauric acid modified nanocrystalline cellulose?was 54.2%when the reaction temperature was 50?,the reaction time was 8 h,the initiator was FeSO₄/H₂O₂ and the dosage was 0.8%.The yield of P-MNCC?palmitic acid modified nanocrystalline cellulose?was 20.9% when the reaction temperature was 55?,the reaction time was 20 h,the initiator was FeSO₄/H₂O₂ and the dosage was 1.2%.The yield of S-MNCC?stearic acid modified nanocrystalline cellulose?was 14.5% when the reaction temperature was 60?,the reaction time was 24 h,the initiator was FeSO₄/H₂O₂ or ammonium ceric sulfate,and the dosage was 1.2%.The average particle size of the MNCC was 244-255 nm,and the surface morphology did not change significantly.The thermal stability of the MNCC was also slightly lower than that of the NCC.The crystalline structure and chemical structure of the MNCC obtained by using two kinds of initiators were also different.The stability of the MNCC synthesized by using ammonium ceric sulfate as initiator was better.Hydrophilic and lipophilic properties of MNCC were studied by measuring contact angle,substituting degree,HLB value and surface tension.The contact angles of L-MNCC,P-MNCC and S-MNCC tablets to water were 79.3°,82.5°,and 84.8°,respectively.The optimal substitution degrees of L-MNCC,P-MNCC and S-MNCC were 0.24,0.16 and 0.12,respectively.From this,the HLB values of L-MNCC,P-MNCC and S-MNCC were calculated to be 15.78,16.29,16.81,respectively.The CMC?critical micelle concentration?of MNCC was 12.5 mg/L,and the surface tension of water was the lowest,55.60 mN/m,54.23 mN/m and 53.35 mN/m,respectively.So the MNCC had an excellent hydrophilic and lipophilic ability and could replace the traditional surfactant to play the role of emulsification and solubilization.Styrene acrylic emulsion was prepared by emulsion polymerization with MNCC as emulsifier,styrene and butyl acrylate as monomers,ammonium persulfate as initiator.The emulsifying performance of MNCC was determined by measuring the morphology of emulsion droplets observed by optical microscope and transmission electron microscope,the solid content,emulsification rate,centrifugal stability,particle size,Ca²⁺,pH and dilution stability and Zeta potential of the styrene acrylic emulsion.When the dosage of L-MNCC,P-MNCC and S-MNCC was 0.05%,the solid content of styrene acrylic emulsion was 37%,37.7% and 38.5% respectively,and the emulsification rates were 92.5%,94.2% and 96.3%respectively.The proportion of stable emulsion reached 95.34%,96.36% and 97.22%respectively after centrifugation 10min with 4000 r/min,and styrene acrylic emulsion had good stability for Ca²⁺,pH and dilution.The particle size of styrene acrylic emulsion droplet was about 460 nm.With the increase of MNCC concentration,the absolute value of Zeta potential of styrene acrylic emulsion increased.The MNCC adsorbed on the surface of styrene acrylic emulsion,which encapsulated styrene acrylic emulsion droplets very well,could exert the hydrophilic and hydrophilic ability of MNCC,and styrene acrylic emulsion was stabled.Therefore,the electrostatic repulsion between the MNCC,the hydrophilic and lipophilic property of the MNCC and the space barrier of MNCC adsorption layer could make the styrene acrylic emulsion have good stability.In summary,MNCC could replace the application of surfactants,thus provided an important theoretical basis and practical application value for the conservation and utilization of fossil resources and the prevention of environmental pollution.