Preparation,Structure Control And Release Properties Of Melamine Resin Fragrance Microcapsules

Microencapsulation is widely used in many fields due to its excellent functional properties.Because of their low cost,stable performance and strong adaptability,melamine resin based microcapsules become one of the most important microcapsule types.In this work,we prepared microcapsules with different ionic system by in-situ polymerization method,using methanol-modified melamine-formaldehyde(MMF)as the shell material and fragrance oil as the core material.The related techniques and theories have been studied and the main contents include:(1)The fabrication,optimization and scale-up study of the microencapsulation process in non-ionic system.The chemical structure,micro-morphology,particle size and size distribution of the prepared microcapsules were characterized,and the microencapsulation mechanism in non-ionic system and its influence on preparation were studied.The synergistic effect of emulsifiers and protective colloids was found to be the key to microencapsulation.At the reaction scale of 100 g,the morphology and particle size distribution of the prepared microcapsules were optimal when the amount of TO-7 was 2 wt%and PVA-1799 was 0.05 wt%.In the scaled-up reaction,the microencapsulation is deteriorated due to changes in fluid flow conditions.This problem can be effectively improved by adding a baffle or using the scrapping paddle-dispersion paddle dual agitators system.(2)The non-ionic microcapsules were immersed into the fabric substracts,and the solid phase microextraction-gas chromatography-mass spectrometry(SPME-GC-MS)was introduced to analyzed the sustained and broken release properties of the microcapsules in the fabrics qualitatively and quantitatively.It was found that the prepared microcapsules have a long-lasting sustained release characteristic,and the release rates of different substances in core material are different.The sustained release curve of microcapsules in more than 2400 hours was tested by weighing calculation method,the change trend followed the Peppas model(fitting result:y=100-2.30t^0.3213),and the predicted release half-life was 1.65 years.In addition,the broken release characteristic of microcapsules under external force are well recognized and characterized,and the release intensity is positively correlated with the times of external force action.The samples can be broken released under external force after a period of sustained release,and its release intensity decreases slightly,indicating that the microcapsule finished fabrics has the potential of sustained release and broken release for a long time.The release characteristics of microcapsules are close to fragrance oil,which is better than traditional application methods.(3)The anion system microcapsules were prepared,and the particle size control strategy was proposed.By adjusting the stirring speed,reaction scale and the stirring equipment(orifice paddle),different reaction fluid flow conditions were formed to achieve the controlling of microcapsule size and size distribution.The CFD numerical simulation was introduced to further study the fluid flow velocity field,turbulent flow energy and shear force distribution in microencapsulation process.The relationship between experimental data and simulation results was built to support and improve the proposed strategy.It was found the simulated average flow velocity showed a good negative linear correlation with the average particle size of the prepared microcapsules(y=-2.166x+42.626).Moreover,it was verified by SPME-GC-MS analysis that the broken release characteristics of microcapsules in two ionic systems were very similar.The structure-property relationship between the microcapsules size and the fragrance fabric finishing property was established,and the maximum broken release intensity of non-additives finished fabric can be achieved when the microcapsules size was 25-30?m.(4)9 different fragrance oils were selected as core materials,and melamine resin microcapsules were prepared by a uniform process.The morphology was characterized by optical microscopy,the encapsulation efficiency,particle size and size distribution were tested.All these was correlated with the interfacial tension,relative permittivity,viscosity,density and refractive index of the core materials.The influence of core materials characteristics on microencapsulation was studied.It was found that the interfacial tension of core material can be preliminarily decided whether it is suitable for microencapsulation,and the other parameters also have different degrees of influence.Finally,a“dimensionless microencapsulation number(x)”was tentatively proposed:x=[F^0.25·?(n-n_H2O)]/(?^0.25·?^0.5),and further fitted with the corresponding encapsulation efficiency(y=87.06-296.95·e^-128.99·x),which can be as a semi-empirical formula for practical work.