Environmentally Friendly Functional Paper With Superhydrophobic Surface And Moisture Resistance

Cellulosic paper is applicated in more and more areas as one kind of green andenvironmently friendly materials. However, troditional hydrophobiczation-sizing-cannot meetthe demands of moistrue and water resistance. Nowadays composite materials of paper-plastic/metal are usually ustilized to retard water vapor, which enhace the water vapor barrierevidently. The inherent advatanges of paper is no longer preserved in the meantime. Thesuperhydrophobization of paper rises recently years and there are few of studies in domesticand international reports. In this paper, a systematic study about the superhydrophobization ofpaper for enhaced moistrue and water resistance and its mechanisam, was carried out throughwet-end, surface coating and cellulose modification.The effects of beeswax aditive methods (wet-end aditive, surface coating, dip coating) andpost treatments (heat treatment, polishing) on water and moisture resistance were investigated.The results showed that water with pore structure had almost no barrier properties to watervapor. According to the thermodynamics and kinetics of water vapor through materials, thesurface coating film could be effective shield against the moisture in the condition of lowsolubility diffusion coefficient of the material. The roughness of hydrophobic material couldimprove its hydrophobicity according to the contact model analysis.The results of chitosan-beeswax bilayer coated paper showed that the WVTR was reducedas the chitosan concentration increased. However, the beeswax coating weight decreased dueto the good film forming of chitosan based on the microstructure observation. Besides, theinterface effect between beeswax and chitosan layers made the water vapor barrier of compositefilm better than pure beeswax. In the experiment of beeswax-chitosan emulsion coating, themicrostructure showed that the beeswax particles melted and re-agglomerated during heattreatment, and the creaming process of beeswax-chitosan emulsion magnified at highertemperature, both of which resulted in an improved moisture barrier property of the coatedpaper.The effort of surface morphology played a larger part than surface free energy did on thesuperhydrophobicity. Wax mixture, composed of beeswax and carnauba wax, was emulsified and coated at paper surface. At proper temperature, the beeswax part in the wax particles wasin "liquid state", while the carnauba wax part in "solid state", resulting mass of bowl-shape orfold structure at the surface of wax particles during phase seperation process. The hierarchicalsubmicro-/-micro-structure greatly reduced the contact area between wax miture and water,thus producing superhydrophobic surface.Compared with TMCS and DMDCS, MTCS had three Si-Cl bonds and showed the mostactive chemical reaction and thus best hydrophobization property. First, the MTCS condensedwith the hydroxyl group at the fire surface, resulting in the formation of self-assemblymonolayer (SAM) of polymethylsilane with a thickness of less than10nm; then, the MTCSpolymerised within its molecular to form filaments in a diameter of20-50nm at the SAMsurface. The formation of hierachical nano-/micro-structure composed of hydrophobic fibre andfilaments enssrured the production of superhydrophobic surface. In the process of silanizationof fibre, the hydrogen bonds, which provided the mechanical strength of paper, decreaseddramatically due to the condensation reaction and the strengh of papre was reduced. In order tocontrol the reaction sites just at the paper surface, the paper was treated with partially-dissolution and precipitation to obtain the dense cellulosic cellulosic flake. The modifiedcellulosic flake had a superhydrophobic surface and the mechancial strength was also preserved.