| Leather finishing is regarded as one of the most crucial processes in leather manufacturing.It can endow leather products with waterproof,mildew proof,antibacterial performance.However,the moisture permeability of the coating will reduce.In addition,water resistance of the coating is affected by polymer polar groups and the gravity of water droplets in the finishing agent when water droplets gradually penetrate into the interior of the coating.These problems lead to the poor comfort and hygienic performance of leather products.Therefore,it is significant to develop leather coating materials with good moisture permeability and hydrophobic antifouling properties.Mesoporous hollow SiO2 microspheres show potential advantages in stabilizing emulsion and constructing functional coatings since they possess large specific surface area,low density,high load and easy selective surface modification.Based on this,in this dissertation,mesoporous hollow SiO2 microspheres with unique mesoporous hollow structure instead of traditional surfactants were used to stabilize acrylate monomer/water Pickering emulsion.Subsequently,the polyacrylate Pickering latex was prepared after polymerization.Finally,the leather coating with waterproof moisturepermeability was obtained.In this way,the moisturepermeability of leather coating was improved by the unique mesoporous hollow structure of SiO2 microspheres.Meanwhile,the water resistance of leather coating was improved by the avoidance of surfactants.In addition,amphiphilic reactive SiO2 Janus microcapsules were prepared by grafting hydrophobic monomer and hydrophilic monomer on the both sides of mesoporous hollow SiO2 microspheres,respectively,further encapsulating the low surface energy substances in the microspheres.Thereinto,the hydrophobic antifouling performance of leather coating came from the solid particle effect of amphiphilic reactive SiO2 Janus microcapsules,their reactive hydrophilic chain segment,their low surface energy of hydrophobic chain segment and controllable release to hydrophobic core material.The main results were as follows:(1)The stable acrylate monomer/water Pickering emulsion was prepared by using the mesoporous hollow SiO2 microspheres as stabilizer.The stability mechanism of Pickering emulsion was revealed by exploring the effects of different stabilizers,hollow size,wall thickness,wettability,dosage of mesoporous hollow SiO2 microspheres,and oil/water ratio on the stability of Pickering emulsion.The results confirmed that the stability of acrylate monomer/water Pickering emulsion stabilized by mesoporous hollow SiO2 microspheres was better than that of traditional surfactant sodium dodecyl sulfate(SDS)and solid SiO2 microspheres.The stability of Pickering emulsion was the best when the cavity diameter of mesoporous hollow SiO2 microspheres was about 30 nm,its wall thickness was about 6.5 nm,its water contact angle was about 88°,its dosage was 1.50 wt%,and its oil/water ratio was 5:5.It revealed that solid particles with smaller density could improve the stability of Pickering emulsion.According to the theoretical calculation,the stability of Pickering emulsion was determined by the total stress of the particles in the liquid and the energy required to remove the particles from the oil-water interface.(2)On the basis of Pickering emulsion,polyacrylate Pickering latex stabilized by mesoporous hollow SiO2 microspheres instead of SDS was prepared by the further polymerization.The effects of different stabilizers,hollow size,wall thickness,wettability,dosage of mesoporous hollow SiO2 microspheres and the dosage of initiator on the stability of Pickering latex and the waterproof moisturepermeability of film were investigated.Then,the relationship between the structure of mesoporous hollow SiO2 microspheres and the moisture permeability of film was revealed.Finally,the film formation mechanism was further studied.Compared with SDS and solid SiO2 microspheres,mesoporous hollow SiO2 microspheres could improve the stability of Pickering latex and the waterproof moisturepermeability of film simultaneously.It was concluded that Pickering latex had the excellent stability,and the film had the outstanding waterproof moisturepermeability when the dosage of hexamethyldiazosilane was 5 wt%,the dosage of initiator was 2.8 wt%,soft/hard monomer mass ratio was 13:10,hollow size of mesoporous hollow SiO2 microspheres was about 60 nm,their wall thickness was about 9 nm,and their dosage was 0.3 wt%.Combined with theoretical calculation,mesoporous hollow SiO2 microspheres with moderate hollow size,wall thickness and dosage could effectively improve the moisture permeability of film.Finally,the film-forming process of polyacrylate Pickering latex was mainly divided into four stages:Dispersed suspension of latex particles,concentrated suspension of latex particles in contact with each other,orderly arranged and deformed latex particles,and continuous uniform film.It was not conducive to the uniform distribution of mesoporous hollow SiO2 microspheres in the film when the adsorption layer of mesoporous hollow SiO2 microspheres on the latex surface was too thick.(3)Taking mesoporous hollow SiO2 microspheres as raw materials,the amphiphilic reactive SiO2 Janus microspheres were successfully prepared by grafting the hydrophobic monomers dodecyl mercaptan and hydrophilic monomer mercaptoethylamine to both sides of the y-(methacryloxypropyl)trimethoxy silane modified mesoporous hollow SiO2 microspheres by thiol-ene click reaction at Pickering emulsion interface.Amphiphilic SiO2 Janus microcapsules were further prepared by impregnation method.Specifically,the amphiphilic reactive SiO2 Janus microspheres were used as wall materials and the low surface energy materials as core materials.Finally,superhydrophobic leather coating with wear resistance and self repair properties was obtained by spraying amphiphilic SiO2 Janus microcapsules on the leather surface pretreated with polyurethane using layer-by-layer(LBL)spraying method.The results showed that dodecyl mercaptan and mercaptoethylamine have been successfully grafted onto the both sides of mesoporous hollow SiO2 microspheres.The obtained amphiphilic reactive SiO2 Janus microspheres showed obvious asymmetric structure and good amphiphilicity.Furthermore,amphiphilic SiO2 Janus microcapsules were fabricated by loading hydrophobic core materials successfully when the impregnation time was 9 h,the hydrophobic core material was polydimethylsiloxane,and the particle size of mesoporous hollow SiO2 Janus microspheres was about 30 nm.The coating based on amphiphilic SiO2 Janus microcapsules displayed excellent superhydrophobicity with the water contact angle of 168° and rolling angle of 2.3°.Compared with the coating constructed by amphiphilic reactive SiO2 Janus microspheres,the coating based on amphiphilic SiO2 Janus microcapsules showed more excellent wear resistance and self repair performance.The coating still showed super-hydrophobicity after 220 times of friction.It was attributed to the cross-linking reaction between the hydrophilic groups of amphiphilic SiO2 Janus microcapsules and polyurethane,and the slow release of low surface energy substances.(4)Taking the polyacrylate Pickering latex stabilized by mesoporous hollow SiO2 microspheres as the bottom layer,polyurethane as the middle layer and amphiphilic reactive SiO2 Janus microcapsules as the top layer,Pickering latex/Janus microcapsules composite leather coating was obtained by the combination of Pickering latex and amphiphilic SiO2 Janus microcapsules using LBL spraying method.The obtained composite leather coating showed excellent waterproof moisturepermeability and hydrophobic antifouling property.The results demonstrated that,compared with leather treated by traditional polyacrylate latex,the water vapor permeability of Pickering latex/Janus microcapsules composite leather coating was improved by 43.0%,its air permeability was improved by 38.3%,its water resistance was improved by 20%,its water contact angle of coating was 170.2° and its rolling angle was 1.8°.Its water contact angle was still greater than 150° and rolling angle was less than 10°after 240 times of friction,which possessed excellent antifouling self-cleaning performance.These results illustrated that the waterproof moisturepermeability and hydrophobic antifouling property of leather coating could be synchronously improved by the combination of polyacrylate Pickering latex and amphiphilic Janus microcapsules. |
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