Preparation Of Nanocellulose Particles And Study On Characteristics Of Emulsions

In this thesis,microcrystalline cellulose was used as raw material.Firstly,the nano cellulose suspension was prepared by hydrolysis of microcrystalline cellulose with mixed acid(a certain proportion of hydrochloric acid and sulfuric acid)and ultrasonic assisted.Then the nano cellulose particles were characterized and the stability of nanometer Cellulose suspension was studied.The experimental results show that as the hydrolysis time increases from 2 h to 10 h,the particle size of cellulose particles decreases from 205 nm to 89 nm,and the cellulose crystallinity increases from 69.90%to 72.31%.Finally,the yield of cellulose particles is maintained at around 70%.As the hydrolysis time increases,the carbon content on the cellulose surface decreases and the oxygen content increases.The oxygen-to-carbon ratio also increased from 0.7582 at 0 h to 0.8611 at 10 h as the hydrolysis time prolonged,and was higher than the theoretical value of 0.83((C6H10O5)n,O/C=0.83).Simultaneous infrared spectroscopy showed that for acid-hydrolyzed nanocellulose,two new bands at 850 and 768 cm-1 exhibited bending vibrations that could be attributed to C-O-S and C-S bonds,respectively.The two peaks represent O-SO3-and C-SO3-,indicating that the sulfuric acid has undergone a sulfonation/esterification reaction with the carbohydrate hydrocarbon/hydroxyl group,and the sulfonic acid group is introduced into the nanocellulose particles.The potential and stability test results of the suspension indicate that the prolongation of the hydrolysis time leads to an increase in the amount of surface negative charge,and the morphology of the cellulose particles becomes more and more regular and becomes an ellipsoid.After one week of the cellulosic suspension,the unhydrolyzed cellulose showed significant delamination,and the hydrolyzed cellulosic suspension showed no significant delamination or change,showing good storage stability.When the cellulosic suspension was heated at 30-90 ℃for 30 min,the suspension did not change significantly,and the particle size also did not change,indicating that the cellulosic suspension had good thermal stability.This is mainly because electrostatic repulsion plays an important role in the stability of the cellulose suspension.Based on the research of nanocellulose particles,the cellulose emulsion system was constructed by using nanocellulose as emulsifier.The stability of emulsion which was stored in the storage environment(time,pH value and salt ion)was observed by investigating the average particle size,surface charge,microstructure and interface adsorption characteristics of the emulsion.The result showed that when the cellulose concentration was 0.9%and the sunflower oil was 1%,the prepared emulsion droplets were 400 nm,and the surface had more negative charges.The dispersibility between the emulsion droplets was good,and no flocculation occurred.In addition,the cellulose particles increase the stability of the emulsion to environmental stresses such as storage time,pH,:and salt concentration.By observing the emulsion,the particle size increased by 20-30 nm after one week of storage,indicating that the emulsion has good stability to storage time.Because the cellulose particles form a relatively thick interfacial layer on the surface of the oil droplets,which inhibits the Ostwald ripening of the oil droplets.At different pH and salt concentrations,there was no significant change in the particle size and potential of the emulsion,indicating that the electrostatic force is not the only major force to maintain the stability of the emulsion.Finally,the embedding effect of thyme oil with cellulose emulsion as carrier system was studied.The storage stability,embedding rate,retention rate and antioxidant properties of the emulsion were analyzed.The results showed that thyme oil could be well embedded by cellulose emulsion.The embedding rate reached 80%and the prepared thyme oil emulsion droplet size is about 400 nm,When the emulsion is placed under different environmental conditions,the particle size of the emulsion increases with the extension of the time,the particle size increases slightly,The potential has a slight decrease with the extension of the standing time.After the emulsion is placed under different conditions for 7 days,the retention rate of thyme oil decreases,it drops to 75-80%at 4 and 25 degrees.,and the retention rate dropped to about 60%under the condition of 37 degrees.It is indicated that the use of cellulose to prepare emulsion to stabilize thyme oil can increase the dispersibility of thyme oil and improve the stability of hydrophobic active substances.