| Fragrance polydopamine microspheres?fragrance@PDA NPs?and polydopamine fragrance microcapsules?PDA@fragrance microcapsules?were prepared from DA as raw material with phenethyl alcohol,citronellol,phenylacetaldehyde,citronellal,phenethyl acetate and citronellyl acetate as the model fragrances.The preparation,properties and application in fragrance sustained-release systems were studied by Fourier infrared spectroscopy?FT-IR?,UV-visible absorption spectrum?UV-vis?,scanning electron microscopy?SEM?,dynamic laser light scattering?DLS?,X-ray diffraction analysis?XRD?,gas chromatography?GC?,thermogravimetric Analysis?TGA?and other methods.1.The spherical PDA NPs with uniform particle size distribution was prepared by the oxidation and self polymerization of DA in the Tris-HCl buffer solution.The results showed that the particle size of PDA NPs decreased with the increase of pH and the decrease of DA initial concentration,which turns from 644 to 144 nm.Up to 800?,PDA can still retain more than 50%and a diffuse peak is present near 20°at 2?,show that PDA NPs has better thermal stability and amorphous structure as a material.Zeta potential and UV-vis spectrum analysis show PDA NPs have excellent dispersibility and UV shielding.With the decrease of the particle size,the absolute value of the Zeta potential becomes-61.98 mV to-7.29 mV,the dispersion becomes better.When the concentration of PDA NPs with 144 nm exceeds 0.10.1mg·mL-1,all the UV light can be shielded.2.Polydopamine fragrance microspheres?fragrance@PDA NPs?loaded with fragrances maintained spherical morphology.The particle size was increased and surface was relatively adhesive after loading.The loading capacity of phenethyl alcohol,citronellol,phenylacetaldehyde,citronellal,phenethyl acetate and citronellyl acetate was 49.8%,47.3%,19%,20.5%,31.7%and 35.8%respectively.The retention amount of fragrances was improved from 3.4%,6.6%,4.5%,2.7%,8.3%and 16.7%to 30.3%,20.6%,37.6%,34%,40.6%and 28.1%days after 45 days.All fragrance@PDA NPs had relative better sustained release compared to fragrances alone.3.In order to study the loading mechanism of fragrances onto PDA NPs,the influence factors,adsorption kinetics,adsorption equilibrium isothermal line and thermodynamic parameters of PDA NPs adsorbed with phenethyl acetate were studied.It was found that the adsorption amount increased initially,then slowed down with the contact time,and tended to balance finally.With volume fraction became larger,adsorption capacity increased.The adsorption kinetic process was more consistent with Pseudo-second order model equation.The adsorption equilibrium isotherm is suitable for Freundlich model fitting.The thermodynamic parameter is calculated,as?H>0 means a endothermic reaction,??H?<40kJ mol-11 means a physical adsorption,?S>0 means a entropy increasing process,and?G<0means a spontaneous process.4.PDA fragrane microcapsules?PDA@fragrances?were prepared by coating PDA layers onto fragrance emulsion droplets.The effects of fragrance concentration,emulsifier dosage,pH value,ultrasonic amplitude and DA concentration on the formation of fragrances emulsion,formation of microcapsules and loading capacity of fragrances were studied.The results showed that phenylacetaldehyde and citronellal could not be encapsulated into PDA microcapsules because of the Maillard reaction with dopamine?DA?.Phenethyl alcohol,citronellol,phenethyl acetate and citronellyl acetate could be encapsulated into PDA microcapsules.Polydopamine fragrance microcapsules were basically spherical with a uniform size distribution.Varieties of fragrances had great influence on the size and changed from 88 nm?citronellyl acetate?to 556 nm?phenethyl alcohol?.Zeta potential of PDA@phenethyl alcohol to PDA@citronellyl acetate was-13.88,-33.23,-47.12 and-102.46m V.All PDA fragrance microcapsules have good dispersion in water except PDA@phenethyl alcohol less.UV-vis spectrum analysis showed with the larger microcapsules concentration and smaller size,the region of shielded ultraviolet ray can be expanded.The encapsulating amount of citronellol is the highest,which can reach 19.8%.The relative amount of fragrances remained can reach over 69.39%at normal temperature for 50 days that showed PDA fragrance microcapsules had good sustained release performance.Thesecharacteristicsindicatethathydrophilic,UV-shielding,biodegradable fragrance@PDA NPs and PDA@fragrance microcapsules with good physiological compatibility,controllable particle size,and excellent sustained release performance,provide the possibility for the application of photosensitive or phototoxic fragrance and perfume sustained release system. |
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