Surface Modification And Functionalization Of Silk Fabric Based On Layer Assembly Technology

Silk is a natural protein filament.This material is known as the“queen of fibers”for its inherently light and soft,smooth texture,elegant sheen,and excellent mechanical strength.Howover,the protein nature of silk also yields inherent disavantages,such as photo-induced aging and yellowing and microbe adherence.Currently,the textile industry has developed to the extent that it requires not only functional textile products with basic comfort,but also materials with added features to broaden the application of silk.Firstly,silk fabric was successfully modified by nanoscale titania coatings prepared by atomic layer deposition（ALD）.Fourier transform infrared spectroscopy（FTIR）,X-Ray Diffraction（XRD）,X-Ray photoelectron spectroscopy（XPS）,Scanning electron microscopy（SEM）,and Transmission electron microscopy（TEM）results showed the deposition of titania will not destroy the molecular structure of silk fabricand the uniform and conformal titania coatings can be deposited onto the silk fiber.The results of thermal properties showed that the thermal stability was slightly higher than the uncoated one and the ALD process yields typical ALD growth behavior.While the ALD treatment process will not affect the fine permeability properties of silk fabric.TiO₂-coated silk fabric convert the super hydrophilic state of raw silk to a stable hydrophobic state with a contact angle of 134 degree.The anti-UV properties of TiO₂-coated silk fabric were superior than the control silk fabric through higher UPF value,lower transmittance of UVA and UVB.The anti-UV properties increase with the increase of ALD cycle number.Zinc oxide thin films with different cycles were deposited on silk fabric by ALD technique.The basic structure and properties of the films were characterized by FTIR,XRD,XPS,SEM,TEM,tensile and gas permeability test methods and the results show that the deposition of ZnO will not destroy the white color,smooth surface and molecular structure of silk fabric.On the surface of silk fabric,there is a uniform and conformal ZnO film with hexagonal wurtzite structure.While the ALD treatment process will not affect the fine permeability and mechanical properties of silk fabric.ZnO coated silk fabric convert the super hydrophilic state of raw silk to a stable hydrophobic state with a contact angle of 135～140 degree and 10 min with 0 mm core suction height.The anti-UV properties of ZnO-coated silk fabric were superior than the control silk fabric through higher UPF value,lower transmittance of UVA and UVB.The UV protection capability of silk fabrics followed the order:400-cycle ZnO>800-cycle ZnO>100-cycle ZnO>pristine silk fabric.However,crystalline ZnO coated silk fabric has good antibacterial effect to both Escherichia coli and Staphylococcus aureus with a maximum inhibition zone diameter of 18.1±0.1 mm,while silk fabrics can still exhibit long-lasting antibacterial effect with prolonging of incubation time to 72 h after treatment.This paper used the mass fraction of polyurethane solution 15%to form film on part of silk fabric by wet method,and then the TiO₂ layer was deposited on the modified silk fabric by ALD technique,subsequently,the fabric was soaked in N,N dimethyl formamide（DMF）.Thus,the polyurethane film and the ALD layer of the polyurethane coated fabric was removed,and the ALD layer of the uncoated polyurethane silk fabric was preserved.The former part of silk fabric is hydrophilic and the latter part of silk fabric is hydrophobic.Area-selective hydrophobic fabric was formed eventually.At last,the millimeter scale rare earth metal-organic frameworks（MOFs）bulk crystal materials are loaded on the surface of silk fabric by layer by layer self-assembly method,which are inconvenient to be used in the literature.By adding sodium oxalate and sodium acetate,respectively,the particle size of Eu-MOFs was reduced to the micro-nanometer level while a new yellow-green fluorescence was produced for the silk fabric which showed blue fluorescence under ultraviolet.In addition,the ALD technique was used to deposit different cycles of TiO₂ on the surface of silk fabric,and then self-assembled layer by layer to synthesize Eu-MOFs.The size of Eu-MOFs particles prepared by this method is smaller than that of directly loaded Eu-MOFs particles while the film formation of Eu-MOFs is better and more uniform than that of Eu-MOFs loaded directly,and the amount of MOFs loaded on silk fabric increases and the fluorescence intensity increases with the increase of ALD cycle number.The fluorescence intensity decreases with the increase of temperature in the temperature range of 100 K～300 K,which can be used to detect the low temperature.Due to the essential characteristics of self-limiting reaction of ALD technology,it can be used to fabricate homogeneous,conformal and easily controlled thin films,which can be used to modify the surface interface of many kinds of materials.The method of obtaining fluorescence color and changing temperature fluorescence property by using rare earth MOFs loading on fabric is expected to be applied to intelligent color control,anti-counterfeiting,temperature detection and so on,which provides a new idea for the application of rare earth MOFs and the modification of silk fabric.