Preparation Of Two Distinct Cellulose Nanocrystals From Shells Of Camellia Oleifera Abel And Synergistic Rheological Mechanism Of The Cellulose Nanocrystals To Stabilize Emulsions

Shells of Camellia oleifera Abel（SCOA）are wastes produced in oil processing,containing cellulose,hemicellulose,lignin,tea saponin,etc.However,millions of tons of SCOA are accumulated or incinerated every year,resulting in a resource loss.Cellulose nanocrystals（CNCs）,as a nano-scale fiber segment,are widely used in food emulsification,functional material preparation,drug loading and other fields due to their good biocompatibility and biodegradability.Converting SCOA into CNC significantly increases the added value and realizes resource reuse.The traditional sulfuric acid hydrolysis method has a low utilization rate of cellulose,and the acquired CNC is of a single morphology.To realize the functionalization of CNCs,it is necessary to graft other chemical groups with strong oxidants,which causes environmental pollution.The cellulose of SCOA has low crystallinity and contains a large number of amorphous regions.Therefore,it is of great significance to improve the sulfuric acid hydrolysis method to retain the amorphous regions of cellulose as much as possible for improving the yield of CNC and realizing its functionalization.In this paper,a method of sulfuric acid hydrolysis combined with high-pressure homogenization was proposed to prepare two distinct types of CNCs（CNC1 and CNC2,respectively）from SCOA,and the effect of sulfuric acid hydrolysis time on the physical and chemical properties of the two CNCs was investigated.The morphology evolution mechanism of cellulose in the preparation process was also speculated.Then,we studied the action mode of SCOA-CNC1 and CNC2 at the oil-water interface and compared the properties with the CNCs derived from commercial microcrystalline cellulose.Finally,we investigated the effects of oil-water ratio and CNC concentration on the emulsion properties.Combined with the microstructure and rheological properties of the emulsion,the relationship between CNC interface properties,assembly methods and emulsion stability were discussed.（1）The cellulose was extracted from SCOA by alkali and bleaching processes,and CNC1and CNC2 were prepared with sulfuric acid hydrolysis followed by high-pressure homogeneous degradation.Combined with atomic force microscope,Fourier Transform infrared spectroscopy,X-ray diffractometer,and conductometric titrator,the effect of hydrolysis time on the microscopic morphology,chemical composition,crystallinity,and surface charge density of CNC1 and CNC2 were evaluated.According to the properties,we speculated the evolution mechanism of cellulose morphology during sulfuric acid hydrolysis and high-pressure homogenization treatment.The results show that CNC1 is short rod-like and CNC2 is hair-like.The chemical composition of cellulose does not change significantly after being converted into CNC1 and CNC2,but the crystallinity is greatly improved.With the increase of acidolysis time,the surface of cellulose gradually becomes smooth,and the surface charge densities of both CNCs increase.During the hydrolysis process,sulfuric acid first acts on both ends of the cellulose chain and fractures the cellulose chain longitudinally to obtain CNC1.The middle part of the cellulose chain is fractured horizontally during high-pressure homogenization treatment,so that part of the non-crystalline region is retained at both ends of the CNC,obtaining CNC2for hair features.（2）The interfacial wettability and assembly mode of two kinds of CNCs from SCOA were investigated by static contact angle and dynamic interfacial tension,compared with two kinds of CNCs（M-CNC1,M-CNC2）prepared from commercial microcrystalline cellulose.The CNC suspensions were made into films,and the contact angle between water droplets and CNC film was measured by optical contact angle measuring instrument.The hanging drop image of CNC in soybean oil was captured in real time by high-speed camera,and the dynamic interfacial tension and the variation law of interfacial tension with time were obtained by formula fitting.The results show that the contact angle formed by water droplets on SCOA-CNC1 is greater than the contact angle between water droplets and SCOA-CNC2 and SCOA-CNC1 has strong hydrophobicity and is easy to wet the oil-water interface.The SCOA-CNC1 and CNC2 both reduce the oil-water interfacial tension.The CNC1 makes the interface tension decreases more obviously,and the rate of decreasing the interfacial tension is faster.The static contact angles of the two SCOA-CNCs are larger than those of M-CNCs,and the ability to reduce interfacial tension is higher than that of M-CNCs,which indicates the interfacial wettability and adsorption capacity of SCOA-CNCs are better than M-CNC.The hydrophobicity of CNC facilitates its wetting of the oil phase,making it easier for CNC to adsorb to the oil-water interface to reduce the interfacial tension.（3）The SCOA-CNCs are used as emulsion stabilizers,and oil-in-water emulsions were prepared by high-speed shearing and then high-pressure homogenization.The effect of the CNC assembly method on the emulsion stability was investigated by changing the oil-water ratio and CNC concentration.We investigated the linear rheological behavior of emulsions by steady-state shear and oscillating shear tests.The nonlinear rheological properties of emulsions were studied employing the Lissajous plots and Fourier transform rheology,and the relationship between rheological properties and structural evolution of emulsions was established.The results show that with the increase in the oil-water ratio,the shear viscosity and viscoelastic modulus of CNC1 and CNC2 emulsions increase,but the deformation degree of the Lissajous plots intensifies and the nonlinear characteristic parameters I_3/1 and Q₀ increase,indicating the emulsion nonlinearity increases.The degree of nonlinearity is deepened with the oil-water ratio,and the nonlinear degree of CNC2 emulsion is higher than that of CNC1 emulsion.With the increase of CNC concentration,the shear viscosity and viscoelastic modulus of the emulsion increase,and the deformation degree of the Lissajous plots weaken,the I_3/1 and Q₀ values decrease,which means the nonlinear degree of the emulsion decrease.Besides,the nonlinear degree of the CNC1 emulsion is higher than that of the CNC2 emulsion.The increase in oil-water ratio increases the interface area,and the free CNC needs to be fully adsorbed to the interface.The electrostatic repulsion or steric hindrance between droplets is reduced,leading to the stability of the emulsion being weakened.CNC1 is of high surface charge density and provides enough electrostatic repulsion to disperse droplets,so the nonlinear characteristics of emulsion stabilized by CNC1 are weak.Increasing the CNC concentration enlarges the electrostatic repulsion or steric hindrance between droplets,reducing the chance of droplets colliding with each other,thereby delaying the occurrence of the nonlinear behavior of the emulsion and improving the stability of the emulsion.The CNC2 are connected to form a network structure by the attached amorphous regions,which increases the steric hindrance between droplets,strengthens the structural strength of the emulsion,and improves the ability of the emulsion to resist deformation.