**4. Microwave applications in textile industry**

Microwaves comprise electromagnetic radiation in the frequency range of 300 MHz–300 GHz. As the polar or charged particles in a reaction medium fail to align themselves as fast as the direction of the electric field of microwaves changes, friction is created to heat the medium [18].

They can penetrate into a material and heat the deep layers of the material strongly when they release their energy. Microwave irradiation offers a number of advantages over conventional heating methods, including using less energy, offering a higher heating rate, and offering the ability to more quickly start and stop heating.

Sulfonating a PET fabric by dilute sulfuric acid and microwave irradiation has been found to produce a super-hydrophilic PET fabric, and the fibers sustained minimal damage.

PET fabric has been immersed in H2SO4 solutions with different concentrations at room temperature for 5 min.

PET fabric samples were then dried at 50°C for 30 min and then irradiated with microwaves at 2450 MHz using a commercial 700 W microwave oven for 4 min. The SEM images of both untreated and treated PET are shown in **Figure 4**. The surfaces of the original and the modified PET fibers are all smooth.

**Figure 4.** SEM images (×1500 and × 5000) of (a, b) the original PET fibers; (c, d) PET fibers modified by 10 g/L H2SO4; (e, f) PET fibers modified by 20 g/L H2SO4; and (g, h) PET fibers modified by 25 g/L [19].

Microwave modification process is quick and inexpensive. Therefore, the modification process could be used in a wide range of applications [19].

Polyamide 66 (PA 66) is one of the most abundantly used fabric in many areas attributed to its low cost, resistance to shrinkage, abrasion, etc. However, its combustibility and serious dripping produced during combustion cannot meet industrial and civil requirements in many cases. Zhao et al. researched the efforts on surface modification of PA 66 fabric by microwaveinduced grafting with 2-hydroxyethyl methacrylate (HEMA). The grafting reaction was undertaken in water solution to decrease the damage of fabric. The hydrophilicity, dripping tendency, and mechanical properties of grafted samples have been significantly improved. However, the slight change of limiting oxygen index (LOI) values and high damaged length during burning cannot meet the flame retardant requirements in many fields [20].

Microwave (MW) energy which is used in dying of various types of textile staple and fixation processes has brought positive results. Microwave irradiation increases the diffusion of dye molecules in dyeing process when applied to both synthetic and natural fibers. It is also used in prefinishing of silk yarns. In addition MW energy is accepted as more efficient than conventional methods for cotton fabric finishing, drying, and curing processes, durable press finishing, incombustibility, water and oil repellent finishing [21].
