Study On Modification Of Super-hydrophobic Surface Of Polypropylene

Super-hydrophobic surface of polypropylene sheet is successfully prepared via acombination of micro-molding method and photo-grafting method. In this method, PPsheets with a roughness surface were firstly prepared by micro-molding, and thenphoto grafting method was employed to prepare a low energy layer on the roughsurface. With the advantages of roughness and low-energy layer, the modified PPsurface became super-hydrophobic, and the contact angle (CA) was 170o.To prepare a PP surface with roughness, a stainless steel sheet corroded by FeCl3solution is used as the template. Because of the well- distribution of micro-scale pit onthe metal surface, the topography of surface of PP sheet is shaped as a kind of roughstructure which consists of abundant of micro-convex. The metallographicmicroscope was used to observe the template surface, scanning electron microscope(SEM) was used to observe the PP surface, WAC measurement instrument was usedto characterized the hydrophobicity of PP surface. The results indicated that extendingthe etching time and rising the etching temperature could contribute to increase theroughness of PP surface and the WAC arrived at 135 o.UV-induced photo-grafting polymerization was employed to make one kind offluorinated acrylate monomer graft on to the rough surface of PP substrate. Thehydrophobicity of the surface before and after modified was investigated by watercontact angle measurement. SEM was used to observe the microstructure ofsurface．The existence of a fluorinated polymer layer and its linkage with the PPsubstrate through chemical bonds were confirmed by FT-IR, surface elementalanalysis (EDS) and DSC measurements on the extracted grafted films. The influenceof experimental factors on the grafting yield (GY) was studied systematically whichwas including plasma treatment conditions, the concentration of initiator and monomer, and UV-grafting conditions. The results show that GY could be promotedby increasing the power and extending the time of plasma treatment, increasing theconcentration of initiator and monomer and raising the temperature of graftingreaction. In this study, the WAC of prepared PP surface is 155 o under optimalconditions.Finally, the micro-molding method and UV-induced photo-grafting were combinedto modify PP surface. Fluorinated groups were grafted onto the rough PP surface,which result in many micro- and nano- scale binary convexities distributed on thesurface. SEM, X-ray photoelectron spectroscopy (XPS) and WAC measurements wereused to characterize the effect of modification. The results indicated that this kind ofcomposite structure and low surface energy together endowed the surface excellentsuper-hydrophobic ability.