Kai Shui Lau

Low temperature plasma-treated nylon fabrics

Abstract Nylon 6 fabrics were treated with low temperature plasma (LTP) with three non-polymerizing gases: (i) oxygen, (ii) argon and (iii) tetrafluoromethane. After plasma treatment, the properties of the fabric, including surface morphology, low-stress mechanical properties, air permeability and thermal properties, were investigated. The nylon fabrics treated with different plasma gases exhibited different morphological changes. Low-stress mechanical properties obtained by means of the Kawabata evaluation system fabric (KES-F) revealed that the surface friction, tensile, shearing, bending and compression properties altered after the treatments. The changes in these properties are believed to be related closely to the inter-fiber/inter-yarn frictional force induced by the LTP treatment. A slightly decrease in the air permeability of the treated fabrics was found which is probably due to plasma action effecting on increase in the fabric thickness and a change in the fabric surface morphology. The change in the thermal properties of the treated fabrics was in good agreement with the above findings and can be attributed to the amount of air trapped between the yarns. This experimental work suggests that the changed properties induced by LTP can effect an improvement in certain textile products.

Chemical Modification of Poly(ethylene Terephthalate) Induced by Laser Treatment

Poly(ethylene terephthalate) (PET) is modified by a 248 nm KrF excimer laser with high (above ablation threshold) and low (below ablation threshold) energy irradiation. The PET surface develops a well-oriented periodic structure of hills and grooves or a “ripple structure” with high energy treatment. However, the ripple size can be reduced to submicron level by irradiation of the sample below the ablation threshold. Chemical surface changes of the material are characterized by x-ray photoelectron spectroscopy (XPS) and contact angles, PET modified by high energy will normally exhibit the deposition of some yellow to black ionized, carbon-rich debris on the treated surface, resulting in a reduction of the O/C ratio. In contrast, a PET surface modified by low energy leads to oxidation and almost no ablation. The increased oxygen concentration on low energy modified surfaces is probably due to a subsequent reaction with atmospheric O2 during irradiation. Polar oxidized groups like carboxyls are also induced. Contact angle measurements are in good agreement with these findings.

Study on the surface chemical properties of UV excimer laser irradiated polyamide by XPS, ToF-SIMS and CFM

Abstract Polyamide (nylon 6) was irradiated by a pulsed ultraviolet (UV) excimer laser with a fluence below its ablation threshold. Chemical modifications on laser treated nylon were studied by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (Tof-SIMS) and chemical force microscopy (CFM). XPS study provides information about changes in chemical composition and the chemical-state of atom types on the fiber surface. The high sensitivity of ToF-SIMS to the topmost layers was used to detect crosslinking after the laser treatment. Gold-coated AFM tips modified with COOH terminated self-assembled alkanethiol monolayers (SAMs) were used to measure adhesion forces on the untreated and laser treated samples. XPS results revealed that the irradiated samples have higher oxygen content than prior to laser irradiation. Tof-SIMS analysis illustrated that carbonyl groups in nylon 6 decrease significantly but hydroxyl groups increase after low-fluence laser irradiation. The adhesion force measurements by CFM showed spatial distribution of hydroxyl groups on nylon 6 after the laser treatment.

Surface properties of polyester fabrics induced by excimer laser processing

Abstract Induced properties of polyester fabric due to irradiation of excimer laser, including surface luster, wettability, dyeability and stability of the resulting micro-structures in the fibre surface are investigated. After excimer laser treatment, the irradiated polyester fabric samples exhibit better hydrophobicity at room temperature and the dyeability of the fabric is improved. The study on surface reflectance shows that excimer laser treatment results in a reduction and a more uniform distribution of fabric glossiness: the treated polyester fabric samples have a silk-like appearance. Scanning electron microscope (SEM) observation reveals that the resulting structures on the fibre surface is virtually unaffected by hot air and hot water and is chemically as stable as its untreated counterpart.

Surface structuring of poly(ethylene terephthalate) fibres with a UV excimer laser and low temperature plasma

Abstract There has been great interest recently in applying energetic beams, notably excimer lasers and low temperature plasma (LTP), on polymers for the modification of their surface properties. The interaction produces the characteristic ripple/roll-like structures and changes in physical and chemical properties, resulting in better dyeability and adhesion to coatings, etc. Poly(ethylene terephthalate) (PET) fibres of different draw ratios were selected to investigate the effects of these sources on the surface modification. The effect of laser treatments on LTP irradiated fibres was also studied. It is observed that although the morphological modification features on the PET fibre surface developed under laser and LTP treatments are not identical, they have great similarity. The doubly treated surfaces also reveal some interesting results.

Chemical surface modification of poly (ethylene terephthalate) by excimer irradiation of high and low intensities

Abstract Poly (ethylene terephthalate) (PET) was modified by a KrF 248 nm excimer laser with high- (above ablation threshold) and low- (below ablation threshold) fluence. The PET surface develops usually a periodic roughness or ripples with high fluence. The roughness size is in the micron range and the surface shows signs of global melting. However, the ripple size can be reduced to sub-micron level by an irradiation of the sample below the ablation threshold with a polarized beam. The morphology of the irradiated surfaces was examined by scanning electron microscopy (SEM). Chemical surface changes of the materials were characterized by X-ray photoelectron spectroscopy (XPS). The PET modification by high fluence will normally results in the deposition of some yellow to black materials (debris), on the treated surface. The debris are ionized and from carbon rich materials which finally condense forming higher aggregates, resulting in a reduction of O/C ratio. By contrast, modification of PET surfaces by low fluence leads to an oxidation and almost no ablation is detected. The increase of oxygen concentration on low fluence modified surfaces is probably due to a subsequent reaction with atmospheric O2 during irradiation. Our work suggests that a careful selection of laser parameters for the surface modification of polymer is of primary importance.

Study of plasma-etched and laser-irradiated polyamide materials

Abstract.Surface morphological structures of the Low Temperature Plasma (LTP) and UV Excimer Laser treated polyamide materials were investigated. The effects of different parameters were studied by using Scanning Electron Microscope (SEM). For LTP treatment, different non-polymerizing gases (oxygen, argon), discharge power and exposure time were selected as treatment parameters. For Laser treatment, high-fluence (above ablation threshold), low-fluence (below ablation threshold) and number of pulses were studied. High-fluence laser treatment gives the most distinct ripple-like structures on the surface of polyamide and these structures are more obvious when the number of pulses increases. Low-fluence treated polyamide develops some stripes of sub-micron size within a narrow fluence window. On the other hand, oxygen and argon plasma also gives ripple-like structures but with smaller dimensions than those due to high-fluence laser treatment. Although the morphological modification features on the polyamide fiber surface developed under laser and LTP treatments are not identical, they have certain similarity.

Surface Modification of Polyamides Materials with Low Temperature Plasma

The surface properties of materials are often the important determinants of their usefulness, and many of the chemical treatments now in use are aimed at modifying these properties. The important properties of polymer materials such as adhesion, friction, wetting, penetrability and biological compatibility are strongly influenced by their surface characteristics. Low Temperature Plasma (LTP) is a technology which can produce not only interesting morphological modification on the surface of the polymers, but also can replace less environmental-friendly finishing processes. In this paper, four non-polymerizing plasma gases: oxygen, argon, tetrafluoromethane and 75%/25% nitrogen/hydrogen mixture were used to modify Nylon 6 filaments and fabrics. The results of SEM study reveals that interesting morphological changes on the surface of treated samples. Besides, with the appropriate LTP treatment, the fabric properties, such as the hydrophobicity of polyamides, surface luster, etc. can be greatly modified.

Comprehensive study of pulsed UV-laser modified polyamide fibers

Abstract. Polyamide fibers (nylon 6) are modified by UV-radiation using a pulsed excimer laser with different treatment parameters. The treated samples are characterized by using a scanning electron microscopy (SEM), tapping mode atomic force microscopy (TM-AFM), x-ray photoelectron spectroscopy (XPS), and chemical force microscopy (CFM). Depending on the conditions during the irradiation, different surface modifications are obtained which can generally be distinguished as high-fluence (above the ablation threshold) and low-fluence (below the ablation threshold). Topographical results indicate that ripple-like structures of micrometer size are developed under high-fluence laser irradiation. On the contrary, smaller sub-micron structures are formed by low-fluence treatment. XPS results show that bond scission occurs on the polymer surface under the action of high-fluence while low-fluence modifies the sample by an oxidative process. Changes in surface chemical properties of the laser-irradiated polyamide are supported by chemical force microscopy experiments with gold-coated AFM tips modified with -COOH terminated self-assembled alkanethiol monolayers (SAMs).

A Potential Textile Application of UV Excimer Laser Irradiation on Polyester Fabrics

UV Excimer laser treatment can be used to produce a modification of surface morphology on polymer. The interaction produces the characteristic ripple/roll like structures and changes in physical and chemical properties. Possible textile application of this non-contacting physical technique on polyester microfibre fabric was systematically studied. Two commercially available high temperature dyes of red and blue were used in this study and results revealed that dyeing rate of both dyes on polyester increased remarkably after laser treatment.