| Due to environmental legislation constraints,the emission of volatile organic compounds(VOC)in the field of coatings,adhesives,and inks has been greatly restricted in recent years.The development of new coatings with low or zero VOC emissions,as well as their preparation technologies,such as those for waterborne coatings,is currently a vital problem of coatings research.However,hydrophilic components such as functional monomers and common small molecule surfactants are added to aqueous polymer emulsion systems,to ensure that the latex is stable in the aqueous phase medium.When latexes form a film,their hydrophilic components reduce the barrier properties of the coating,limiting the use of latex polymers in protective coatings.As a result,the development of polymeric latex films with high water-barrier properties to replace traditional solvent-based coatings has received a lot of attention.A series of composite latexes of polyacrylate modified with barrier domain,organicfluorine and organicsilicon were prepared via soap-free reversible addition-fragmentation chain transfer(RAFT)miniemulsion polymerization.The effects and rules of barrier domain,organicfluorine,and organicsilicon on the barrier properties of the polyacrylate latex were investigated,as well as the synergistic barrier effect of the composite latexes containing barrier domain,organicfluorine,and organicsilicon.By studying the surface and bulk microstructure of the latex films,the relationship between the surface and bulk microstructure and the barrier properties was established,and the high-efficiency barrier mechanism of the waterborne polyacrylate films was obtained.(1)Preparation and barrier properties of barrier domain type polyacrylate composite latex:the current study describes the synthesis and characterization of two macro-RAFT reagents,namely,poly(methyl methacrylate-b-poly(methacrylic acid)(p MMA12-b-p MAA10)and polystyrene-b-poly(methacrylic acid)(p St47-b-p MAA9),as a replacement for conventional small molecule surfactants.These reagents were used in RAFT-mediated soap-free miniemulsion polymerization with ethylene glycol dimethacrylate(EGDMA),3-(trimethoxysilyl)propyl methacrylate(MPS)-modified Si O2 nanoparticles(with an average particle size of 30 nm),and crystalline monomer stearyl methacrylate(SMA)as barrier components.The composite latex films were characterized for their surface and bulk microstructures using atomic force microscopy(AFM)and section transmission electron microscopy(TEM),respectively,to determine the size and distribution of the barrier domains.The barrier performance of the latex films was assessed,and it was found that the presence of barrier domains significantly improved the water barrier performance.The optimal amount of barrier domains was identified as 4%EGDMA,0.5%Si O2,and 7%SMA,which increased the water absorption rate by 17.09%,6.51%,and 10.29%,respectively,compared to conventional polyacrylate latex.(2)Preparation and barrier properties of short-chain perfluoropolyether polyacrylate latex:short fluorinated chain methyl methacrylate end-capped perfluoropolyether monomer(PFPE-MMA)that does not produce perfluorooctane sulfonate(PFOS)and perfluorooctanoic acid(PFOA)was designed and synthesized.The monomer was copolymerized with butyl acrylate(BA)and methyl methacrylate(MMA)using surfactant-free RAFT emulsion polymerization to obtain a series of copolymer latexes with PFPE-MMA content ranging from 1%to 25%.Calculation of contact angle and surface energy showed that the addition of 25%PFPE-MMA resulted in a copolymer film with a water contact angle of 119.8°and a surface energy of 12.36 m N/m.The morphology of the PFPE-polyacrylate copolymer latex film showed that an increase in PFPE content promoted the movement of PFPE chains towards the air/film interface,thereby reducing the wettability of water molecules at the interface of the latex film.Different degrees of micro-phase separation occurred between the PFPE and polyacrylate matrices,resulting in the formation of hydrophobic regions of PFPE with a size ranging from 37 nm to 84 nm in the copolymer latex film.This led to an increase in the barrier properties of the copolymer latex film,with the impedance value of 25%PFPE copolymer polyacrylate latex film increasing nearly one order of magnitude compared to that of the polyacrylate latex film.(3)Preparation and barrier properties of polyacrylate copolymer latex with organic silicon grafts:we synthesized a series of silicone grafted polyacrylate copolymer latexes,employing the soap-free RAFT miniemulsion macromonomer approach,with methacrylate-capped polysiloxane(PDMS-MA)as the copolymer monomer.The PDMS-MA content varied between 10%and 50%.The water contact angle and water absorption rate were investigated,and it was observed that the water contact angle of the 50%PDMS-MA copolymer latex film was 117°,while the water absorption rate was 10.9%.These values represented a 29%and 55%enhancement,respectively,compared to the polyacrylate latex film.The surface and bulk microstructure analysis of the latex film indicated that the silicone side chains migrated to and completely covered the surface of the latex film,while the bulk structure gradually transitioned from a spherical to a bicontinuous phase structure.The electrochemical impedance spectroscopy(EIS)test results revealed that the impedance value of the 50%PDMS-MA copolymer latex film increased by 3 orders of magnitude when compared to the polyacrylate latex film,which highlighted its excellent water barrier performance.(4)Preparation and synergistic barrier effect study of polyacrylate copolymer latex with barrier domain,organic fluorine,organic silicon,and cooperative barrier domain:to further enhance the barrier and mechanical properties of polyacrylate composite latex film,crystalline SMA monomer was introduced into the organofluorine polyacrylate composite system,and cross-linker EGDMA and MPS-modified Si O2nanoparticles were introduced into the silicone grafted polyacrylate composite system to create a synergistic barrier effect with organofluorine and organosilicon.The study of water absorption,surface ontology microstructure,and mechanical properties of the latex film revealed that the barrier domain demonstrated excellent synergistic performance.The introduction of SMA crystalline monomer into the organofluorine polyacrylate composite system restricted the reconstruction of fluorine on the surface of the composite latex film,which further enhanced the surface properties of the composite latex film,resulting in a water contact angle of 119.8°and a surface energy of 12.36 m N/m.Additionally,SMA formed a crystalline barrier domain within the bulk of the latex film,creating a more convoluted path for the diffusion of water molecules and augmenting the barrier properties.This resulted in improved barrier performance.Furthermore,when EGDMA and MPS-modified Si O2 were used as composite barrier domains in the silicone-grafted polyacrylate composite latex,the EIS test results exhibited an 80-fold increase in impedance to 1.1×10~6 and a 75.3%increase in tensile strength to 7.72 MPa,compared to the 50%PDMS-MA grafted polyacrylate composite latex film.This indicated that the presence of barrier domains in the latex film achieved a synergistic effect of both barrier and mechanical properties.(5)Barrier mechanism and application performance comparison of polyacrylate composite latex films:by comparing the surface and bulk microstructure of the latex films modified with organicfluorine,organicsilicon,and barrier domain,the diffusion process of polymer chains during film formation was inferred,and a synergistic barrier enhancement mechanism of the low surface energy barrier at the surface and the tortuous diffusion pathway of the bulk barrier domain was proposed.Electrochemical impedance spectroscopy(EIS)results showed that the composite latex films of polyacrylate prepared in this study had a 4-order-of-magnitude higher impedance than traditional polyacrylate latex films,and were in the same order of magnitude as the impedance of a commercial solvent-based polymer(product number:FX-2050)thin film.Furthermore,the prepared composite latexes were applied to leather coating and printing coatings,and the results showed that the leather coatings did not blister or peel after being immersed in water for 12 hours,and the wet rubbing color fastness of the printed fabric reached above level 4,which was comparable to that of commercial solvent-based coatings,suggesting the potential of replacing solvent-based polymer coatings.In this study,a soap-free RAFT miniemulsion polymerization was used to create a polyacrylate composite latex with synergistic barrier enhancement of organofluorine,silicone,and barrier domains.The microstructure of the surface and bulk of the polyacrylate composite latex film was studied,as well as the structure of the composite latex.The surface and bulk microstructures were found to be related to the water barrier effect.Furthermore,a synergistic barrier enhancement mechanism involving a low surface energy barrier on the surface of the latex film and a zigzag diffusion path of the barrier domain in the bulk was proposed.This study lays the theoretical groundwork for replacing traditional solvent-based coatings with high-performance water-based coatings with excellent barrier properties. |
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