Preparation And Properties Of Single/Double Wall Microcapsules Encapsulated With Benzoyl Peroxied

Microencapsulation technology is widely used in monomer/initiator binder systems.The early polymerization reaction caused by the pre-activation of initiator will limit the storage time of products.Microencapsulation can significantly improve product stability and shelf life.By encapsulating active substances such as initiators and separating them from monomers,polymerization can only take place when microcapsules are broken and encapsulating materials are released.In this paper,a general method for preparing high stability double-wall microcapsules is proposed.Benzoyl peroxide(BPO)is selected as a suitable free radical initiator,and embedded in a two-step simple method through a composite coagulation method and an in-situ polymerization method.Benzoyl peroxide(BPO)is selected as a suitable free radical initiator,and embedded in a two-step simple method through a composite coagulation method and an in-situ polymerization method.The single-wall and double-wall microcapsules successfully prepared were characterized and analyzed,and their release and stability were studied.This paper mainly studies the following three aspects:1.Preparation of Single-Wall Benzoyl Peroxide Microcapsules by Complex CoagulationGelatin(Gel)and sodium alginate(SA)were used as composite wall materials and benzoyl peroxide(BPO)dispersed in dibutyl pHthalate(DBP)was used as core materials.The preparation of BPO microcapsule by composite coagulation method can start from the following single factor conditions:wall material composition,core-shell ratio,wall material concentration,ph,mixing speed and emulsification rate.The experimental conditions of BPO single-wall microcapsules were optimized through parallel experiments and orthogonal experiments.The optimal conditions were obtained as follows:m(gelatin):m(sodium alginate)is 1:1,core-shell ratio is 1:1,the concentration of wall gelatin and sodium alginate are both 1.0%,stirring speed is 500 rpm,pH value is 3.6,and homogenization emulsification speed is 11000 rpm.Under this technological condition,the encapsulation efficiency of microcapsules was 77.6%and the loading amount was 58.3%.2.Study on physicochemical properties of single-wall benzoyl peroxide microcapsulesThe characterization and analysis BPO single-wall microcapsule prepared under the best technological conditions were carried out.According to the optical microscope(OM)and scanning electron microscope(SEM)images,it was observed that the morphology of the microcapsule was regular and spherical,with smooth surface and no depression,and its particle size was mainly distributed at(95.6 ± 3.8)?m.The characteristic peaks of BPO can be seen from Fourier transform infrared spectroscopy(FTIR)of microcapsules.By comparing the characteristic peaks in the infrared spectrum,it is confirmed that the core material BPO has been successfully encapsulated.According to the experimental data of differential scanning calorimetry(DSC)and thermogravimetry(TGA),the glass transition temperature of the microcapsule increased to 71.8?,and the decomposition rate of the core material slowed down after microencapsulation,and the thermal stability was improved.Research on the release performance of microcapsules shows that low-temperature storage is more conducive to slowing down the release rate of microcapsules and thus reducing the loss of microcapsules.The release process of microcapsules at 4? and 25? conforms to the first-order release kinetics,while at 80?,its release kinetics conforms to Higuchi equation.In addition,it was found that the retention rate of microencapsulated BPO in low humidity and oxygen-free environment was significantly higher than that in high humidity and oxygen-free environment,indicating that the core material is easier to preserve in low humidity and oxygen-free environment after microencapsulation.3.Preparation of double-walled benzoyl peroxide microcapsules and study of its propertiesGelatin-sodium alginate/polyurea-formaldehyde double-wall microcapsules with BPO dispersed in DBP as the core were prepared by in-situ polymerization between urea-formaldehyde prepolymer and Gel-SA layer.Microcapsules prepared by SEM,OM and FTIR were characterized.The obtained microcapsule showed a spherical structure,its particle size was mainly distributed in 104-130 ?m,and the wall thickness was between 0.35-0.7 ?m.It is concluded that the microcapsules prepared at different mixing speeds have a high loading capacity of 83-89%.DSC and rheometer results show that BPO is not affected by microencapsulation process and its activity is maintained.In addition,the stability of double-walled microcapsules is higher,and there is no leakage of core materials in acrylate-based resin and toluene organic solvent.The obtained microcapsules have great potential for use in industries such as self-healing systems and structural adhesives.