**1. Introduction**

Polyester fabrics made from PET poly(ethylene terephtalate) account for almost 50% of all fiber materials. PET fibers have high uniformity, mechanical strength or resistance against chemicals or abrasion. However, high hydrophobicity, the build-up of static charge, stain retention during laundering and being difficult to finish are undesirable properties of PET.

Enhancement of the hydrophilicity of PET fibers is a key requirement for many applications, ranging from textile production to applications in the biomedical field. In the textile field, increased hydrophilic properties improves comfort in wear with a better moisture management due to increased wettabilility, wicking, adhesion to other materials (i.e. coating), and dyeing (Pastore M, 2001). Several strategies can be adopted to increase the surface energy and hence the hydrophilicity of PET fibers such as by chemical finishing or grafting, chemical surface treatment with NaOH (Collins, 1991, Haghighatkish, 1992), biochemical treatment with enzymes (Vertommen, 2005) or physical surface treatment using plasma. Treatment with NaOH is environmentally unfriendly and causes drastic weight and strength losses (Collins, 1991), while certain plasma treatments would be of interest from an environmental point of view.

Atomic Force Microscopy – For Investigating Surface Treatment of Textile Fibers 245

discharge (DBD) is created between two metal electrodes covered with insulating layers (ceramic and polycarbonate). Under specific conditions, the DBD can produce the so-called atmospheric pressure glow (APG) discharge, which can also be effectively used for the

Studies show that the highly reactive species in the discharge regime of DBDs can interact with the surfaces of materials and induce some physical and chemical changes (oxidation, polymerization, cross-linking, etching etc) and thus improve their surface properties such as

Ageing of surface-modified polymers can be detrimental to the performance of a device. Therefore an improved understanding of the ageing of modified surfaces during storage is required to optimize the processing conditions leading to interfacial properties that are controlled and predictable at the time of use. It has been shown that as a result of ageing, the surface properties, acquired after a plasma treatment, disappear (Krump, 2005). Moreover, ageing survey data (Borcia, 2004) show that materials never fully return to their untreated surface state. The ageing effects observed depend on the nature of the polymeric materials, structure, crystallinity, (Novak, 2004) porosity etc. Additionally, it has been reported (Leroux, 2006), that the fabric porosity which depends on the fabric structure (e.g. woven, nonwoven, knitted) influences the ageing of air-atmospheric plasma treated fabrics subjected to aqueous conditions at room temperature and pressure. It was also shown that for a low porosity-(high density) woven fabrics, oxidised species formed at the fabric surface

wettability, printability, adhesion and conductivity (Oktem, 2000, Fang, 2004).

are more easily removed by simple washing than for high porosity textile structure.

plasma treatment of PET fabrics for specific dyeing conditions.

uptake, and XPS (X-Ray Photoemission Spectroscopy).

**2. Experimental work 2.1 Sample preparation** 

**2.1.1 Woven polyester fabric** 

The work presented here demonstrates the potential use of Atomic Force Microscopy to optimize the atmospheric plasma process parameters (speed treatment and electrical power) on the treatment of a particular woven PET fabric. The effect of ageing during normal use conditions (i.e room temperature and pressure in absence and presence of day light) and in conditions used for dyeing polyester fabrics, has equally been studied. PET fabrics are dyed with disperse dye and need high temperature (130°C) and pressure for maximum dye uptake. Dyeing at 90°C would be more environmentally friendly because of reduced energy requirements, but dye uptake would be reduced. One of the strategies to increase dye uptake at 90°C is to activate the PET fabric surface by plasma treatment so as to increase its hydrophilicity. It is therefore necessary to check the permanence of the air-atmospheric

In the final part, the effect of immobilizing a hydrophilic oligomer PEG -poly(ethylene glycol) 1500 immediately after plasma treatment is shown. AFM results are also compared to other fabric surface characterization methods such as water contact angle, capillary

A 100 % Polyester (PET) woven fabric of density 284 g/m² with a thickness of 0.56 mm and 63.5% porosity was used for the study. The PET woven fabric was cleaned to be free from surface impurities and spinning oil. The cleanliness of the PET samples was checked by

surface treatment (Borcia, 2003, Fang, 2004).

Plasma techniques have been used in materials science since 1960s, for the activation and modification of different materials. Plasma processes have been utilized to improve the surface properties of fibers for various textile applications: sterilization, desizing, wettability or hydrophobicity improvement, anti-shrinking finishing, dyeability enhancement and adhesion promotion (Hocker 2002, Jasso, 2006, Leroux, 2006, Oktem, 2000). The fibers that can be modified by plasma processing include almost all kinds of fibers such as natural and man-made, metallic fibers, glass fibers, carbon fibers and organic fibers (Höcker, 2002, Borcia, 2003). Low-pressure plasma methods have been investigated, but they are difficult to apply in industry since they require vacuum and consume a considerable amount of energy. Moreover, these treatments can be carried out only in a batch process which increases the treatment time. New methods based on atmospheric plasma treatments seem to be quite attractive for the textile industry. These treatments have the advantage of being applied online without vacuum, and allow continuous plasma processing (Leroux, 2006). Atmospheric plasma treatments are used to modify polymer surfaces using plasma gases made up of a mixture of charged particles (electrons and ions), excited atoms (free radicals, meta-stable molecules) and photons. In order to create a plasma field, the gases are brought through two charged electrodes of different potentials. During plasma treatment, the polymer to be treated is exposed to the plasma which interacts and modifies the polymer surface. Surface modifications vary with the nature of the substrate and the chemistry of plasma gases, as well as the treatment operating parameters (Borcia, 2004, Leroux, 2006,)].

Fig. 11. Plasma treatment under atmospheric pressure by means of dielectric barrier discharge, using "Coating Star" plasma machine manufactured by the Ahlbrandt System Company

Among various atmospheric pressure non-thermal plasmas, the dielectric barrier discharge (DBD) process is studied mostly for the easy formation of stable plasmas and its scalability. Numerous studies of surface modified materials using DBDs under atmospheric pressure have been undertaken mainly for treatment of polymers and metals. The dielectric barrier

Plasma techniques have been used in materials science since 1960s, for the activation and modification of different materials. Plasma processes have been utilized to improve the surface properties of fibers for various textile applications: sterilization, desizing, wettability or hydrophobicity improvement, anti-shrinking finishing, dyeability enhancement and adhesion promotion (Hocker 2002, Jasso, 2006, Leroux, 2006, Oktem, 2000). The fibers that can be modified by plasma processing include almost all kinds of fibers such as natural and man-made, metallic fibers, glass fibers, carbon fibers and organic fibers (Höcker, 2002, Borcia, 2003). Low-pressure plasma methods have been investigated, but they are difficult to apply in industry since they require vacuum and consume a considerable amount of energy. Moreover, these treatments can be carried out only in a batch process which increases the treatment time. New methods based on atmospheric plasma treatments seem to be quite attractive for the textile industry. These treatments have the advantage of being applied online without vacuum, and allow continuous plasma processing (Leroux, 2006). Atmospheric plasma treatments are used to modify polymer surfaces using plasma gases made up of a mixture of charged particles (electrons and ions), excited atoms (free radicals, meta-stable molecules) and photons. In order to create a plasma field, the gases are brought through two charged electrodes of different potentials. During plasma treatment, the polymer to be treated is exposed to the plasma which interacts and modifies the polymer surface. Surface modifications vary with the nature of the substrate and the chemistry of plasma gases, as

well as the treatment operating parameters (Borcia, 2004, Leroux, 2006,)].

Fig. 11. Plasma treatment under atmospheric pressure by means of dielectric barrier discharge, using "Coating Star" plasma machine manufactured by the Ahlbrandt System Company

Among various atmospheric pressure non-thermal plasmas, the dielectric barrier discharge (DBD) process is studied mostly for the easy formation of stable plasmas and its scalability. Numerous studies of surface modified materials using DBDs under atmospheric pressure have been undertaken mainly for treatment of polymers and metals. The dielectric barrier discharge (DBD) is created between two metal electrodes covered with insulating layers (ceramic and polycarbonate). Under specific conditions, the DBD can produce the so-called atmospheric pressure glow (APG) discharge, which can also be effectively used for the surface treatment (Borcia, 2003, Fang, 2004).

Studies show that the highly reactive species in the discharge regime of DBDs can interact with the surfaces of materials and induce some physical and chemical changes (oxidation, polymerization, cross-linking, etching etc) and thus improve their surface properties such as wettability, printability, adhesion and conductivity (Oktem, 2000, Fang, 2004).

Ageing of surface-modified polymers can be detrimental to the performance of a device. Therefore an improved understanding of the ageing of modified surfaces during storage is required to optimize the processing conditions leading to interfacial properties that are controlled and predictable at the time of use. It has been shown that as a result of ageing, the surface properties, acquired after a plasma treatment, disappear (Krump, 2005). Moreover, ageing survey data (Borcia, 2004) show that materials never fully return to their untreated surface state. The ageing effects observed depend on the nature of the polymeric materials, structure, crystallinity, (Novak, 2004) porosity etc. Additionally, it has been reported (Leroux, 2006), that the fabric porosity which depends on the fabric structure (e.g. woven, nonwoven, knitted) influences the ageing of air-atmospheric plasma treated fabrics subjected to aqueous conditions at room temperature and pressure. It was also shown that for a low porosity-(high density) woven fabrics, oxidised species formed at the fabric surface are more easily removed by simple washing than for high porosity textile structure.

The work presented here demonstrates the potential use of Atomic Force Microscopy to optimize the atmospheric plasma process parameters (speed treatment and electrical power) on the treatment of a particular woven PET fabric. The effect of ageing during normal use conditions (i.e room temperature and pressure in absence and presence of day light) and in conditions used for dyeing polyester fabrics, has equally been studied. PET fabrics are dyed with disperse dye and need high temperature (130°C) and pressure for maximum dye uptake. Dyeing at 90°C would be more environmentally friendly because of reduced energy requirements, but dye uptake would be reduced. One of the strategies to increase dye uptake at 90°C is to activate the PET fabric surface by plasma treatment so as to increase its hydrophilicity. It is therefore necessary to check the permanence of the air-atmospheric plasma treatment of PET fabrics for specific dyeing conditions.

In the final part, the effect of immobilizing a hydrophilic oligomer PEG -poly(ethylene glycol) 1500 immediately after plasma treatment is shown. AFM results are also compared to other fabric surface characterization methods such as water contact angle, capillary uptake, and XPS (X-Ray Photoemission Spectroscopy).
