Preparation,Characterization And Rheological Behaviors Of Calcium Alginate Nanocapsules

Nanocapsulation is technology that the sensitive elements is embedded by the coating or wall material (usually polymer) to protect them from the surrounding medium physical chemistry. The liquid essence is embedded in capsules or membrane, which can separate them from the external environment. Nanocapsulation technology can solve effectively the high volatile and chemical instability that caused by oxidation of liquid essence. Sodium alginate (SA) is extracted from natural seaweed, a kind of natural polysaccharide source is widespread, has good biocompatibility, and its gel process is gentle, which makes the SA is used widely in wall material of microcapsules which embeds drug, protein and of cell.In this paper, on the base of using sodium alginate (SA) and calcium chloride as wall materials, the nanoparticles encapsulating citrus fragrance were prepared in o/w emulsion using the ionic polymeric method. The effects of sodium alginate concentration, calcium chloride concentration, emulsification types, emulsification amount, emulsification ways, emulsification time, fragrance amount, calcium chloride stirring rate, sodium alginate drip rate and reaction temperature on the size and size distribution were investigated in detail. The size, morphological properties, molecular structure and thermal stability fragrance were characterized using dynamic light scattering (DLC), transmission electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR) and Thermogravimetric analysis (TGA). The steady and dynamic rheological behaviors of nanocapsules emulsion under different sodium alginate concentration, fragrance amount, emulsifier amount, emulsification ways and reaction temperature were also studied systematically.Results indicated that the size and particle of dispersion index (PDI) of CANs were strongly dependent on various preparation conditions. The optimal preparation conditions were obtained:SAmass concentration of 0.02%, Cacl2 mass concentration of 0.080%, AEO9 as emulsifier, emulsifier of 1/30 (w/w) based on fragrance amount, ultrasonic emulsification for 10 min, oil/water matio of 1:1, fragrance amount of 0.6%, stirring rate of 1000 r/min, SA drip rate of 0.5d/s and reaction temperature of 45 ℃. Under the optimal preparation conditions, CANs exhibited irregularity sphericity in shape and the average particle size was about 110.2 nm, the polydispersity (PDI) was 0.062. In addition, FTIR spectras of SA, CANs and fragrance showed that fragrance had encased into the wall. In the preparing process of CANs, sodium alginate and calcium chloride formed "egg cell" structure, which promoted the embedding of fragrance. Thermogravimetry diagrams of CANs, fragrance and blank nanoparticles showed the thermostability of fragrance encapsulated in nanoparticles was improved.The thermal stability of nanocapsules emulsion was 98.6% and the placed stability was 94.8%. The result of dynamic rheological measurements demonstrated that the linear viscoelasticregion is 0.1%-10%, nanocapsules emulsion from viscous (G">G’) at low oscillation frequency to elastic (G’> G") at high oscillation frequency. The result of Static rheological measurements demonstrated that 20～40 °C is the safety temperature range of the sample, nanocapsules emulsion is non-Newtonian, it is Newtonian only for shear rate of 0.001-10s-1 and its apparent viscosity had remain unchanged for shear rateof 10-1000s-1.The steady and dynamic rheological behaviors of nanocapsules emulsion under different sodium alginate mass concentration, fragrance amount, emulsifier amount, emulsification ways and reaction temperature were also studied systematically. The result of dynamic rheological measurements demonstrated that loss modulus of nanocapsules emulsion was greater than storage modulus (G">G’) at low oscillation frequency, showed the viscosity characteristics. When oscillation frequency increased gradually, storage modulus increased gradually, storage modulus of nanocapsules emulsion was greater than loss modulus (G’> G") at high oscillation frequency, showed the elasticity characteristics. Different preparation conditions leaded that the size of nanocapsules is different, the turning point shift to the lower frequency with the increase of particle size.The result of Static rheological measurements demonstrated that anocapsules emulsion is non-Newtonian, it is Newtonian only for shear rate of 0.001-10s-1 and its apparent viscosity had remain unchanged for shear rateof 10-1000s-1. Different preparation conditions leaded that the size of nanocapsules is different, the decreasing trend of apparent viscosity and descending slop with the rise in particle size were observed.