Preparation And Study Of Pickering Emulsion Based On Nanocellulocellulose

The application of cellulosic particles-stabilized Pickering emulsions in food related fields,for instance,immobilization of various bioactive agents,utilization as the fat substitutes,or fabrication of food storage/packaging systems has attracted increasing interest recently,because of nontoxicity,biodegradability,biocompatibility and recoverability of cellulose.To those cellulosic particles-stabilized emulsions,flow and deformation are the most important themes throughout their full life lengths,from preparation to consumption.However.merely limit reports are found in the literatures on the rheological behaviors of this kind of emulsions.Emulsion morphology-viscoelastic responses relationships,which are very useful for the morphology design,preparation and applications of the edible Pickering emulsions,have not yet been well established.This work made a systematical study on the flow and deformation behaviors of the cellulose-stabilized sesame oil-in-water emulsions in different flow fields.Some very interesting results,regarding strain overshoot,scaling flow response,and alteration of thixotropic properties of edible Pickering emulsions were shown,and the relationship between emulsion morphology and viscoelastic responses was then established.This work provides important information also,on the preparation,morphological control,and storage and final applications of food hydrocolloids.Many studies have focused on the effect of fiber lengths on emulsion stability and morphology.This work provides some new and interesting points on the relations between fiber flexibility and emulsion morphology from rheological perspective,which can guide emulsion preparation and morphology control through tailoring aspect ratio of fibers.The main contents and results of this study are listed as follows:1.The Sesame oil can be well emulsified in water using CNF as the emulsifier,forming stable Pickering emulsions.From the perspective of CNF concentration and oil-water ratio,the stability of emulsion,droplet morphology and rheological properties under small amplitude oscillatory shear(SAOS)were explored.A droplet cluster structure forms in those systems due to multicomponent properties of sesame oil and fibrillar structure of CNF.The scaling behavior of the small amplitude oscillatory shear flow response of the emulsion is independent of the oil-water ratio and cellulose concentration The presence of these droplet clusters has little effect on the behavior of SAOS response.2.Using cellulose nanofibers(CNF)as emulsifier to stabilize Pickering emulsion and sesame oil as oil phase,the rheological response behavior of the emulsion was studied in detail from the perspective of CNF concentration and oil-water ratio,and oscillating shear at large amplitude(LAOS),delve into the evolution and relaxation mechanism of its droplet structure.Its deformation and relaxations result in weak strain overshoot behavior in large amplitude oscillatory shear(LAOS)flow,but not affect the scaling behavior of small amplitude oscillatory shear(SAOS)responses.The relaxation time scales can be evaluated by creep of emulsions.This structure can evolve during ramp shear flow,rearranged and oriented at the higher flow rates,which has evident influence on the thixotropic behavior of emulsions.The mechanisms of evolution and relaxations of droplet cluster structure are traced through rheo-optical way.3.Three types of nanocelluloses,including bacterial cellulose(BC),cellulose nanofiber(CNF)and cellulose nanociystal(CNC),were used to prepare oil-in-water Pickering emulsions with the objective to disclose the effect of fiber flexibility on emulsification.The results reveal that nanocelluloses with different aspect ratios show different fiber morphologies during shear flow:the shortest CNC is fully rigid,while the longest BC flexible,which result in large difference in their dilute-to-semi-dilute concentrations,and in their rheological percolation trends.Therefore,three types of nanocelluloses play different roles during emulsification.The flexible BC has no evident emulsifying capacity,whereas the semi-flexible CNF and rigid CNC can be well used to stabilize emulsions.In the subsequent morphological evolution and relaxation stage,however,there is no evident difference in the roles of CNC and CNF.Dynamic rheology provides visible evidence in terms of relaxations of clusters and as-resulted yielding behavior of emulsions.