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The Deformation Mechanism Of Fibers During Laser Radiation-Drawing And Their Characterizations

Posted on:2004-09-18Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y J LiFull Text:PDF
GTID:1101360095453660Subject:Materials science
Abstract/Summary:PDF Full Text Request
It was the aim of this work to apply CO2 laser radiation as new type energy of unique properties to fibers drawing in order to find their deformation mechanism and to characterize the structure and properties of obtained fibers. The main deformation was occurred in the micro-zone of high energy density and was quite different from that in the classical fiber drawing process. With poly(ethylene terephthalate) fiber as an example, the characteristics of properties of fibers prepared by this new technology were illustrated. The unique properties were explained in terms of structure of fiber, therefore the primary relations of process-structure-properties were suggested for the new technology. The Dissertation was divided into 6 sectors as following:1) The general relationship of tenacity, modulus and toughness of fiber and its structure, the methods of producing fibers with specific properties and the application of structure models in constructing the relations of structure and properties were discussed. It was concluded that the following three items of improving fiber structure must be done in order to get high tenacity and high modulus fiber: (a) to perfect the structure of crystalline and to increase the physical crosslinkage of molecule chains in amorphous region; (b) to reduce the number of end chains and loop chains to increase the number of chains forforce applied, and (c) to reduce the difference in chain length in amorphous region to make a more homogeneous stress distribution. Then the main methods (such as solution spinning, swelling-drawing, vibrating drawing and zone drawing) producing fiber of high tenacity and modulus were summarized. Particular attention was paid to zone drawing process and its technical potential and the significance for further study were pointed out. The idea of performing more small zone drawing combined with laser radiation was introduced.2) In order to show why CO2 laser was selected for fiber drawing, the dependence of laser's wavelength and power on processing methods (cutting, welding, ablating, etc.) was discussed. The basic principles of CO2 laser, its properties and its effect on polymers were briefly introduced. The main characteristics of CO2 laser were high monochromatic, interferential, directional and great brightness. When it was applied to polymer, coupling various vibrations between the electric magnetic wave of CO2 laser and atoms or groups of polymer occurred. Due to the viscosity of polymer, the vibration would cause friction, and transfer the electric magnetic energy to heat consequently the temperature of polymers would rise rapidly. CO2 laser has the wavelength of 10.6um, and its photon energy was 0.176eV, which was much lower than the ionization energy of compounds, therefore it would not directly cause the degradation of polymers. When laser is irradiated on polymers, the phenomena of nonlinear optics (such as self-focus) and elastic stress appeared. The radius of fibers had the effect on the coefficiency of laser energy transfer. When fiber radius was less than 1/10 of laser's wavelength, there would appear Mie's scattering, which would greatly increase the fiber absorption of laser radiation. The effenciency of absorption also depended on the orientation, crystalline, structure and temperature of fibers. The practical adjustable parameters were also introduced here. The power and the waist of laser in this work were 30-70W and 2rnm, respectively, and Rayleigh distance was 1184mm, which was bigger than the distance between fiber and laserfocus.3) The principles of methods for structure analysis (density gradient, DSC, WAXD, sonic velocity, FTIR, etc.), their physical meaning and the limitations were discussed. The experimental conditions of all the mentioned methods used in the work were listed. The obtained data constituted the foundation for building the relations of process-structure-properties.4) The fiber deformation model during laser-drawing process was suggested. Firstly, laser energy transition, strain, strain ra...
Keywords/Search Tags:laser radiation, PET fiber, drawing, orientation, crystallization
PDF Full Text Request
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