Surface modification of poly (ethylene terephthalate) (PET) by laser irradiation

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Surface modification of poly (ethylene terephthalate) (PET) by laser irradiation

 

Author: Wong, Chi-chung Wilson
Title: Surface modification of poly (ethylene terephthalate) (PET) by laser irradiation
Degree: Ph.D.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Polyethylene terephthalate
Materials -- Testing
Irradiation
Department: Institute of Textiles and Clothing
Pages: xxii, 249 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1667768
URI: http://theses.lib.polyu.edu.hk/handle/200/3682
Abstract: The thesis is aimed to study the surface morphological modification of poly (ethylene terephthalate) (PET) by pulsed UV laser irradiation. A study on the physical and chemical properties of the irradiated PET was reported. Laser irradiated surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC) and some other traditional physical methods. The resulting properties and the potential industrial application of the irradiated PET were studied. Polymers have been widely used across most industrial sectors due to their excellent physical and chemical properties. Besides, they are inexpensive and easy to process. However, when polymers are required for high value market or high performance products, the demand made upon these polymers can often not be satisfactorily fulfilled. The not always satisfactory performance of polymers has led to the consideration of introducing new finishing technologies. Besides, due to ever-increasing demands in designing new functional fibres for high value added products, new finishing / modification technology is essential. In recent years, there has been great interest for simple but efficient, dry and physical methods for surface modification of polymers. This is partly because of traditional wet chemical finishing processes involve the use of solvents, which are environmentally unfriendly. One of the most studied technologies is UV laser irradiation of polymer surfaces. It was known that polymer surfaces often developed a periodic roughness or ripple in the range of micron size by UV laser irradiation at fluence (laser energy, unit = mJ/cm2) above the ablation threshold i.e. high fluence irradiation. However, ripple could be reduced to sub-micron level by an irradiation energy below the ablation threshold with a polarized beam i.e. low fluence irradiation. The development of the high fluence ripple is believed to be due to an extremely high absorption coefficient of the polymer to the laser radiation, releasing the frozen-in tension fields, resulting in a self-organizing of material by convection. The low fluence ripple is believed to be induced by repeated periodic interference of the scattered and incoming waves created by a polarized beam. UV laser irradiation of polymers involves not only photothermal processes but also photochemical processes. In general, a chemical modification of the polymer by UV irradiation takes place in a limited thickness to the top several hundreds of nanometres or less and does not affect the bulk properties. It was observed the PET modified by high fluence would normally result in the deposition of debris on the treated surface. These debris are ionized and carbon rich materials which finally condense forming higher aggregates, resulting in a reduction of the O/C ratio. Conversely, modification of PET surface by low fluence irradiation led to oxidation and almost no ablation was detected. The increase of oxygen concentration on low fluence modified surfaces was probably due to a subsequent reaction with atmospheric O2 during irradiation. Polar oxidized groups like carboxyls were induced, together with the increased oxygen content, which has given a more hydrophilic character to low fluence irradiated surface. Modifications in textile properties due to laser irradiation were studied. Properties included fibre weight and diameter, tensile strength and elongation, yarn abrasion, bending, surface lustre, wetting, whiteness and air permeability. Some properties were observed to be advantageous to the material, while some would have adverse effects. Potential application of the laser treatment on polymer was conducted based on the study of the dyeing and adhesion properties.

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