Preparation And Properties Of Transparent Wear-resistant Hydrophobic Coating

Transparent plastics such as plexiglass have been widely used in the fields ofoptical instrument, automotive, aviation, construction and so on due to its advantageswhich include low density, excellent toughness, solvent-resistance, low cost and easymolding. However, the transparent plastics have defect of poor performance of wearresistant and scratch resistant. To overcome this problem, organic-inorgaic hybrid SiO2coating was universally adopted during in the past decades. But the disadvantage ofsuch a coating is that it will be easily fouled, leading to the loss of transparency. Hence,enhancement of stain-resistant properties of the coating is an important project as wellas enhancement of abrasion resistance of PMMA and PC. In this paper, a series offluorocarbon-SiO2hybrid coatings were prepared with nano-SiO2as an intensifier,which was modified to improve its hydrophobic and compatible characteristics. Theproperties such as wear resistance, transparency and foul resistance were examinedwith the aim to develop a new type of transparent coating which bears wear resistanceand self-cleaning performance. The main content and results are shown as follows:(1) SiO2nanoparticles were prepared by sol-gel method and microwave methodrespectively. Its structure and morphologies were characterized with XRD and TEM.The results indicate that the nanoparticles obtained via either approach are amorphous,but the ones prepared by microwave method exhibit a more regular morphology,smaller diameter, and uniform distribution of particle size.(2) SiO2nanoparticles were modified by silane coupling agent DMDCS and KH570,successively, and fluorocarbon hybrid coating were further prepared. The effect ofmodification conditions on the content of hydroxyl group on SiO2surface wasinvestigated and the nanoparticles were characterized with Fourier Transform Infrared(FTIR) and Thermo Gravimetric Analyzer (TGA). The effect of the loading of nanoSiO2particles on the coating performance was also studied. The results indicate that,for modification of the nanoparticles, the optimum amount of DMDCS, H2O were25%,4%respectively. The graft rate of DMDCS on the surface of nanoparticles was5.07%,while that of KH570was3.88%. The addition of modified SiO2has little effect on thetransparency of the fluorocarbon coating. The contact angle between H2O and hybridfluorocarbon coating increases as the addition of nano-SiO2increases. When thecontent of nano-SiO2is6%, the contact angle of the hybrid coating increases from79° to127°, indicating the coating had a good hydrophobicity. But the wear resistance andhardness of the fluorocarbon coating decrease slightly. The results showed that theoptimum content of nano-SiO2is5%.(3) In order to obtain nano-SiO2particles with its surface bearing C=C bond,surface modification of nano-SiO2was conducted first by reaction with silane couplingagent KH-590, followed by thiol-ene Michael addition reaction to introduce DAP ontothe surface of nano-SiO2.The modified nanoparticles were added into fluorocarboncoating and the resulted hybrid coating was characterized by FTIR, TGA, ultravioletspectrophotometer and interfacial tension tester. The results show that the silanecoupling agent KH-590and DAP were grafted onto the nano-SiO2surface successfully,and the grafting ratio was13.02%and14.71%respectively. The contact angle of thehybrid coating increases with the increasing of the modified SiO2content, and themaximum contact angle is104°. The wear resistance of the hybrid coatingwasimproved when increasing the content of the modified SiO2, while its transparencycould be keep at above85%.(4) Benzyl trithiocarbonate acid was attached onto the surface of nano-SiO2bycoupling reaction and the reaction products were used as chain transfer agent to initiatethe RAFT polymerization of MMA to obtain the macro chain transfer agent, which wasfurther used to initiate the copolymerization of styrene and malic anhydride to prepareSiO2-g-PMMA-b-Poly(St-r-MA)hybrids, the structure and composition of which werecharacterized by FTIR, TG,1H-NMR, GPC. The results of FTIR, TG,1H-NMR indicatethat PMMA-b-Poly(St-r-MA)was successfully grafted onto the surface of nano-SiO2.The graft ration of PMMA and Poly(St-r-MA)was31%and24.6%respectively. TheGPC result reveals that the graft reaction is a living polymerization. Fluorocarbonhybrid coating was further obtained by addition of SiO2-g-PMMA-b-Poly(St-r-MA)hybrids, and the effect of the loading of the filler was studied. It was found that, withthe increasing of nano-SiO2content, the contact angle of the hybrid coating increasesand reaches135°when the content of nano-SiO2is6%. The hardness and wearresistance are improved by addition of the nano-SiO2hybrids.