| Polymer surface modification has long been the focus of polymer scientific research due to its significance in polymer industry. Poly (ethylene terephthalate) (PET) has become one of the most widely used polymers because of its excellent properties and versatile performance. However, the surface properties of PET materials sometimes do not meet the various requirements, thus affect their applications. Therefore, surface modification of PET material is necessary and crucial. Being a relatively new hi-tech, laser technique has been applied to polymer surface treatment for around twenty years. In this dissertation, XeCl excimer laser was applied to conduct the surface graft modification of PET with certain monomer in order to improve the surface hydrophilicity and the related performances.The origin, development and current research situation of the excimer laser-induced surface treatment of polymers were introduced here firstly, following with the changes of surface morphology, chemical structure and surface properties found in previous researches. On the basis of the previous research results, the mechanism of the laser-induced ablative photodegradation (APD) on polymer surfaces and a few mechanisms of the laser-induced periodic surface structure (LIPSS) were summarized and integrated, which were the theoretical background of the research herein.Several methods of the laser-induced graft modification were designed and 4 of them were proved to be effective in improving the surface hydrophilicity of PET material by measurements of contact angle of a water drop on PET film and the time of water drop permeation on PET fabric. The one-step method of irradiation-graft in solution was chosen to be applied in successive research. With the precise measurement of film sample weights, it was discovered that the effect of laser ablative on the weight change of samples could not be omitted. Therefore, a new equation to calculate the graft degree was proposed, which is more applicable for laser treatment. The surface lubricating abilities of the ablated and grafted films were measured, the results showed that the lubricating abilities in "watery" and "non watery" environment were quite different between the ablated and grafted surfaces, indicating some potential applications.The changes of surface morphologies, of surface chemical structures and compositions, and surface thermodynamic properties of the ablated and grafted PET materials were studied systematically and intensely. The reasons and mechanisms of hydrophilicity improvement of the ablated and grafted surfaces were explained in several aspects. The SEM observation, the measurement of surface tension, and the determinations of ATR-FT-IR, XPS, and DSC spectrums led to further understandings. The surfaces became rougher after ablation and graft, and the morphologies of the control, ablated and grafted samples were also different. Polar groups were newly formed in the ablated surface, and more formed in the grafted surface, resulting in a markedly increase of polar component of the surface tension; the breakage of ester bonds occurred both in the ablated surface and in the grafted surface. The amorphous region of both kinds of film was increased. In addition, it was also found that the ether bonds were presented in the grafted surface. A nitrogen peak appearing in XPS spectrum of the grafted film proved the existence of the grafted acrylamide. The percentage of the monomer which was grafted in the surface was reckoned accordingly. The fusion enthalpy and crystallinity percentage of ablated and grafted films were measured and calculated. They decreased in the order of the ablated one and the grafted one.Elements distribution in-depth of the grafted film was investigated by the angle-resolved XPS analysis. The results showed that the monomer molecules in the fused surface diffused into deeper layers.The effects of different factors on the laser-induced graft polymerization on the PET surface were analyzed, and the mechanisms were discussed. The factors were: 1) Monomers with smaller molecules resulted in better modification than polymeric monomers. Acrylamide monomer was chosen as hydrophilic modifier finally; 2) Higher concentration of the monomer solution favored the graft reaction; 3) With the increasing laser fluence, the surface hydrophilicity of PET films increased at first, then decreased. More laser pulses led to a more hydrophilic surface; 4) Benzophenone as a photosensitizer hindered the graft polymerization; 5) The homopolymer retardant of ammonium iron ( II ) sulfate hexahydrate in a proper concentration retarded the formation of homopolymers and promotes the graft copolymerization; 6) The solvent of monomer solution also affected the graft reaction. Different solvents functioned in different ways. Ethanol can promote the graft reaction because of the activity of hydrogen in its structure; 7) pH value of the monomer solution affects the polymerization rate, and a lower pH value was favorable to the graft reaction.It was analyzed and deduced that the laser-induced graft polymerization modification was a radical polymerization in terms of the chemical structure and property of the monomer, the source of radicals and the function of retardant. It was estimated that there were a few sources of radical initiating polymerization, conducing the complexity of reaction system. On the basis of the findings in the research, the laser-induced graft reaction processes and the changes of PET surface occurred during irradiation and graft were described systematically.The staining of Eosin B, a biological reagent, on the grafted PET fabric confirmed the existence of amide groups in the grafted surface. The dyeing properties of the ablated and grafted PET fabrics were also studied, indicating the significant improvements of dyeing properties of disperse dyes and cationic dyes on the grafted fabric. The two major contributions to the dyeing property of disperse dyes were considered to be the increase of surface roughness and amorphous regions. However, for cationic dyes, besides these two contributions, the electrostatic attraction between dye cations and negative polar groups of the fiber also promoted dyeing. The water layer brought by the hydrophilic groups in the surface promoted the dissolution, absorption and diffusion of dye molecules as well. The improvements of dyeing properties of the grafted fabric with disperse dyes and cationic dyes were of great significance in application. The dyeing performance of direct dyes in either the ablated or the grafted fabric was improved little due to the larger dye molecules, the little diffusion ability into fibers, and the electrostatic repellence between dye anions and polar groups of fiber.The major originalities included in this dissertation are listed as follows:1) 4 effective treatment methods for the laser-induced graft modification were designed in conformity with the characteristics of laser irradiation;2) It was discovered that the influence of the laser-induced ablation on the weight change of the treated sample could not be ignored, and a new calculation method of graft degree was proposed, which was more applicable for laser treatment. 3) The changes of surface morphologies, surface chemical structures and compositions, and surface thermodynamic properties of ablated and grafted PET materials were studied systematically. The origins and mechanisms of the improved hydrophilicity of the ablated and grafted surfaces were explained in different aspects. Therefore, the laser-induced graft processes and the changes in the treated surface were discovered.4) The effects and theories of influencing on the laser-induced graft polymerization on PET surface were studied, and it was found that laser-induced graft polymerization differed from the UV light-induced graft polymerization. The type of the laser-induced graft reaction was determined.5) The dyeing properties of the ablated and grafted PET fabrics with disperse dyes and cationic dyes were improved significantly. The reasons and the mechanisms for the improvement were analyzed.
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