Preparation,Properties And Application Of Polypropylene Dual-wavelength Fluorescent Anti-counterfeiting Fibers

The fluorescent anti-counterfeiting fibers have wide applications in the field of anti-counterfeiting because of the distinctive photochromic capabilities.The traditional fluorescent fibers are generally single-wavelength anti-counterfeiting fibers which only emit one color of light under the excitation of a special light.However,the single-wavelength fluorescent fibers cannot meet the increasingly needs of anti-counterfeiting security technologies with the development of the society and technology.The dual-wavelength fluorescent anti-counterfeiting(DWFA)fibers,which can emit two different colors of light under the excitation of two different wavelength lights,are the upgraded products with higher anti-counterfeiting security.In this thesis,the polypropylene(PP)was selected as the matrix because of its high transparency and many excellent properties,and three kinds of DWFA fibers including Infrared/UV short-wavelength,Infrared/UV long-wavelength and UV short-wavelength/UV long-wavelength excitable DWFA fibers were spun by the traditional melt spinning process using three kinds of rare earth fluorescent powders as luminescent materials,and the influences of fluorescent powder content on the structure and properties of DWFA fibers were discussed.In addition,DWFA fibers with skin-core structure were spun,and the fluorescent properties of DWFA fibers with and without skin-core structure were compared.Then,the environmental resistance of DWFA fibers was investigated,and finally,the application of DWFA fibers in anti-counterfeiting paper was preliminarily explored.Firstly,three kinds of fluorescent powders(Infrared,UV short-wavelength,UV long-wavelength)were selected and treated with coupling agent,and fluorescent powder/PP pellets were prepared and then three kinds of DWFA fibers mentioned above were spun through the melt spinning process,and the effects of fluorescent powder content on the structure and properties of DWFA fibers were investigated.The results showed that each of the three kinds of DWFA fibers can emit two kinds visible lights under the excitation of two different wavelength lights,which shows double anti-counterfeiting functions.The fluorescence spectra showed that the fluorescence intensity of all three kinds DWFA fibers increased with the increase of fluorescent powder content.DSC data showed that fluorescent powder promoted the crystallization property of DWFA fibers in order of UV long-wavelength fluorescent powder > UV short-wavelength fluorescent powder > Infrared fluorescent powder.The mechanical properties analysis showed that the tensile strength and elongation of DWFA fibers declined with the increase of fluorescent powder content.The fluorescent microscope and SEM photos revealed that the agglomeration of fluorescent powder in fibers matrix was more obvious and the rougher surfaces of fibers could be observed with the increase of fluorescent powder content.In order to improve the luminous efficiency of fluorescent powder in fibers matrix,three kinds of DWFA fibers with skin-core structure were spun by the melt spinning process using fluorescent powder/PP pellets as the skin material and pure PP as core material.Take UV short-wavelength/UV long-wavelength DWFA fibers for example,the influence of skin-core ratio on the structure and properties of fibers were investigated.The 3D simulation of fluorescent powder in fibers matrix by confocal laser scanning microscope and fluorescent microscope photos indicated that the fluorescent powders were basically distributed in the skin layer of fibers.The fluorescence spectra showed that DWFA fibers with skin-core structure exhibited higher luminous efficiency than DWFA fibers without skin-core structure under the same fluorescent powder content.DSC data and mechanical properties analysis showed that the crystallinity and tensile strength of UV short-wavelength/UV long-wavelength DWFA fibers with skin-core structure decreased firstly and then increased,whereas elongation continued to increase with the decrease of skin-core ratio.In order to research the anti-counterfeiting stability and the application conditions,the effects of p H value,temperature,solvents,washing and UV radiation on the structure and properties of Infrared/ UV short-wavelength DWFA fibers were investigated,respectively.The results demonstrated that the DWFA fibers showed stable mechanical properties in acid and alkali resistance,whereas the fluorescence properties of fibers decreased with the increase of relative strength of acids & bases and processing time.With the extension of high temperature treatment time,the mechanical properties of fibers decreased slightly and tended to be stable,while the fluorescence performance of fibers decreased gradually with the increase of temperature and processing time.The influences of different organic solvents on the properties of fluorescent fibers were different,and the fibers showed relatively good solvent resistance.Moreover,DWFA fibers exhibited good washing resistance and poor UV radiation resistance,the mechanical properties and fluorescence properties of fibers continued to decrease with the extension of UV radiation time.Finally,in order to explore the application of DWFA fibers in anti-counterfeiting papers,Infrared/ UV short-wavelength DWFA papers were prepared using polyethylene oxide(PEO)as the dispersant to improve the dispersion of fibers in the papers.The results revealed that DWFA papers showed dual-wavelength anti-counterfeiting features,and the addition of PEO could improve the dispersion of fluorescent fibers in papers compared to those without adding PEO.The thickness of anti-counterfeiting papers increased and the density decreased,and the retention rate of DWFA fibers was improved by adding PEO.The mechanical properties of DWFA papers decreased,and the addition of PEO showed little effect on the mechanical properties of anti-counterfeiting papers.Moreover,the optical properties results showed that the opacity of DWFA papers decreased slightly,and the brightness increased slightly,whereas PEO had no obvious influence on the optical properties of papers.