*1.2.1. Plasma grafting*

Surface properties of polymer materials such as nonwovens can be tailored by wet chemical treatments or physical techniques such as glow discharge plasma treatment [2, 3, 4, 5].

Grafting is a method to modify and functionalize fibrous surfaces and it leads to a thin film coating on the substrates (Fig. 2). In surface grafting, a second polymer is attached to the polymer backbone of the fibrous surface through covalent bonding. Properties of the surface, such as wettability, hydrophobicity, adhesion, and friction, can be dramatically changed by this method [2, 3].

**Figure 2.** Schematic of surface grafting of a polymer on a substrate [2]

Plasma glow discharge is a method used for surface grafting reaction, where radio frequency energy is applied to an electrode (Fig. 3) pair in order to excite a gas such as oxygen, air, helium, or argon at low pressure (0.1 - 1.0 torr). Free radicals are generated at high energy levels through stripping of electrons from the gas particles. Then polymerization starts with the introduction of one or more types of monomer gases such as acrylic acid, carboxyl and amino groups into the plasma treatment chamber where the radicals react with monomer gases [2, 3, 6].

**Figure 3.** Schematic of plasma treatment reactor for surface modification and deposition [3]

Plasma conditions are controlled by plasma parameters such as plasma power, frequency, duration, carrier gas, gas pressure, flow rate, and monomer types [3].

Corona discharge is commonly used for surface treatment of polyethylene and polypropylene having low surface energy. In this method, an electrode at a high electric potential (of 15 kV at 20 kHz) ionizes the surrounding gas which generates a corona discharge (Fig. 4). While the fabric passes between the high-potential electrode and a grounded electrode, chemical reactions occur between some of the ionized gas particles and the surface of the substrate. During this process, surface roughening and addition of functional groups such as carbonyls, hydroxyls, carboxylic acids, and unsaturated bonds to the fabric surface take place. Oxidation of the substrate surface occurs when corona discharge is performed at atmospheric pressure in air, which oxidizes the surface [6].

#### *1.2.2. Thin film deposition*

Plasma polymerization includes the formation and deposition of thin polymeric films on the surface of substrates with the influence of plasma generated by some kind of electrical discharge [6].

Plasma polymerization process includes fragmentation of vapor-type organic, organosilicone, or organometallic monomer molecules, the formation of reactive radicals, and recombination of the activated fragments in which the treatment time influences the thickness of the applied coatings [6].

Thin films of metals and metal oxides have been applied to nonwoven substrates using different thin film deposition techniques such as ionized gas treatments, plasma treatment,

**Figure 4.** Schematic of corona discharge treatment process [6]

**Figure 3.** Schematic of plasma treatment reactor for surface modification and deposition [3]

duration, carrier gas, gas pressure, flow rate, and monomer types [3].

in air, which oxidizes the surface [6].

*1.2.2. Thin film deposition*

discharge [6].

218 Non-woven Fabrics

coatings [6].

Plasma conditions are controlled by plasma parameters such as plasma power, frequency,

Corona discharge is commonly used for surface treatment of polyethylene and polypropylene having low surface energy. In this method, an electrode at a high electric potential (of 15 kV at 20 kHz) ionizes the surrounding gas which generates a corona discharge (Fig. 4). While the fabric passes between the high-potential electrode and a grounded electrode, chemical reactions occur between some of the ionized gas particles and the surface of the substrate. During this process, surface roughening and addition of functional groups such as carbonyls, hydroxyls, carboxylic acids, and unsaturated bonds to the fabric surface take place. Oxidation of the substrate surface occurs when corona discharge is performed at atmospheric pressure

Plasma polymerization includes the formation and deposition of thin polymeric films on the surface of substrates with the influence of plasma generated by some kind of electrical

Plasma polymerization process includes fragmentation of vapor-type organic, organosilicone, or organometallic monomer molecules, the formation of reactive radicals, and recombination of the activated fragments in which the treatment time influences the thickness of the applied

Thin films of metals and metal oxides have been applied to nonwoven substrates using different thin film deposition techniques such as ionized gas treatments, plasma treatment,

chemical vapor deposition (CVD), physical vapor deposition (PVD), surface grafting, and layer-by-layer deposition [2, 7, 8, 9, 10, 11, 12, 13].

In physical vapor deposition (PVD), vaporized material is deposited on the substrate surface uniformly as a thin film in a vacuum environment where the use of different coating materials is possible [14]. Coatings on polymeric materials by PVD methods have been found to improve the surface properties without altering the bulk properties [15, 16, 17, 18]. PVD techniques offer advantages over conventional textile coating [10, 12, 16, 19, 20, 21], since it is an environmen‐ tally friendly, solvent-free process without any need to dispose of any liquid waste. Moreover, a strong bonding is achieved between the fibrous substrate and coating layer.

PVD techniques are commonly used for coating very thin metallic or ceramic films on different substrates. Sputtering is a PVD technology in which atoms are ejected from a solid target material through bombarding the target by energetic ions in a plasma confinement. These atoms condense on the substrate and form a thin film. Sputtering techniques include direct current (DC) sputtering, radio frequency (RF) sputtering, reactive sputtering, and magnetron sputtering [12].

Wei et al. [22] studied the interfacial bonding between polypropylene (PP) fibrous nonwoven substrate and sputter-coated copper. Adhesion of the coating layer to the PP fibrous substrate was found to be affected from plasma treatment and heat during the sputtering process. PP nonwoven showed the lowest abrasion resistance among the tested materials, whereas the sputtered copper coating significantly improved its abrasion resistance further.

Deposition of layers onto the substrates by chemical vapor deposition (CVD) is achieved by chemical reactions in a gaseous medium [23]. A thin film is deposited on the substrate surface through decomposing and/or reacting one or more volatile precursor materials using plasma energy [2]. Different monomers such as methane, hexamethyldisiloxane, tetramethylsilane, hexafluoropropylene ethylene, butadiene, hydroxyethylmethacrylate, and *N*-vinylpyrroli‐ done have been used in plasma-enhanced chemical vapor deposition processes to obtain surface coatings with different functionalities such as oleophobic, hydrophobic, and corrosionresistant [24].
