**2.5. Microfluidics process**

ca particles generates core-shell structures with an average size comparable to the parent

As an environmental and efficient approach, ultrasonic energy was firstly reported to assist various textile processes by Sokolov and Tumansky in 1941 [32]. Sound is transmitted through a medium by inducing vibrational motion of the molecules through which it is trav‐ elling. Power ultrasound induces cavitations in liquids, which is the origin of the sound ef‐ fect in cleaning and in chemical processes [33]. Ultrasound has been widely applied in textiles, for example, preparing nano-scale pigments, fabric pretreatment, dyeing and finish‐

Power ultrasound can enhance a wide variety of chemical and physical processes, mainly due to the phenomenon known as cavitation in a liquid medium, which is the growth and explosive collapse of microscopic bubbles. Sudden and explosive collapse of these bub‐ bles can generate hot spots, i.e. local high temperature, high pressure, shock waves, and severe shear force capable of breaking chemical bonds. Dispersion of UMPs involves the application of shear forces to the agglomerates so that they break down into primary par‐ ticles [34]. If a proper amount of Ultramarine is added to water and stirred briskly, the ag‐ glomerates will simply be carried within the flow and hardly change their nature. Ultrafine modified pigment blue FFG was mixed with dispersant and dispersed with an ultrasonic homogenizer for 30 min, and the particle size was reduced to 91 nm from the

Encapsulating UMP with various polymers is a promising approach for improving the qual‐ ity of the UMP dispersion. In the last decade, many techniques have been developed for en‐ capsulating UMP [36]. It must be noted that a successful encapsulation technique should not impair the original color appearance of UMP but enhance their dispersion stabilities. Poly‐ meric resins in encapsulation work basically as an adsorbed surface layer around UMP par‐ ticles and also a fixing agent upon being colored on a substrate. The microencapsulated UMP supplies dispersion stability, and the surface-modified UMP gives fixing on a hydro‐

The whole encapsulation process probably divides into four steps below [37]. Organic UMP are dispersed into solution of polymeric dispersant leading to the polymeric dispersant ab‐ sorbing onto the UMP. The absorption auxiliary is added slowly and the copolymers precip‐ itate and encapsulate onto the UMP surface by van der Waals forces. After the precipitate is filtered and dried, the copolymer is tightly encapsulated onto the UMP surface. The copoly‐ mer onto the encapsulated UMP is hydrolyzed, and then the UMP is dispersed uniformly in

Dispersion is controlled by attractive force between the UMP and the hydrophobic part of the polymer, and the stability of the particles is made both by electrostatic repulsive force

silica particles (20 nm) [5].

82 Eco-Friendly Textile Dyeing and Finishing

ing processes.

original size 220 nm [35].

aqueous media.

**2.4. Microencapsulated process**

philic body, such as the fiber in textiles [20].

**2.3. Ultrasonic wave process**

Microfluidics with excellent dispersing and smashing effects is in favor of leading particles in liquid to reducing particle size to a submicron level to create pure and stable nano-emul‐ sions and suspensions [38]. With this process, the effectiveness of high-performance materi‐ als increases, because particles are more uniformly and stably dispersed. Through microfluidizer high shear fluid processors, the fabrics with UMP easily achieve high K/S val‐ ue and gloss, and the amount of volatile organic compounds by increasing water content is declined. Microfluidizer high shear fluid processors are frequently used to reduce particle size to less than 150 nm.

For example, Pigment Red CI 22 was stirred with an aqueous solution of an anionic poly‐ meric dispersant for 30 min at 10,000 rpm, and the average particle diameter of the obtained UMP dispersion was 1, 500 nm. Whereas, the average particle diameter of 128 nm was avail‐ able as the dispersion was converted to modified dispersion in a microfluidizer at pressure 22,000 Pa for 2.5 h [13]. Also, a UMP suspension system was prepared by adding the Gemini dispersant and water. Then it was mixed and dissolved and the deformer was added in the mixing process. The Pigment Red CI 22 was added into the above dispersant solution stir‐ ring at 600 rpm for 10 min and 9000 rpm for 30 min. The UMP system was treated using a microfluidizer at 172, 368 kPa for 50 min to prepare UMP suspension system. And particle size of the UMPs was the 211.9 nm, the Zeta potential was 32.4 mV and the viscosity was 1.33 Pa∙s [16].

#### **2.6. Combined process**

It is exceedingly difficult to handle a dry powder comprising of UMP particles as the UMP is in the form of larger soft agglomerates. These agglomerates must be broken down into the medium in a process called dispersion. The UMP dispersion can be stabilized by dispersing agents in order to prevent the formation of uncontrolled flocculates. Combining two or more dispersing methods, for example, grinding/ultrasonic wave, microencapsulation/ grinding and dispersant/microfluidizer, the homogeneity of making UMP dispersion along with the use of organic dispersants for viscosity control and the prevention of particle from further agglomeration can be realized [8].

Dispersions are usually prepared by ball grinding a mixture of the pigment, dispersant and solvent. This is a simple combined process in which grinding process is used together with dispersant. The ultrasonic process can also disperse the UMP and this method can endow a high-throughput approach. The methacrylic copolymer was used to disperse carbon black in water using both ball mill and ultrasonic approaches. The particle size distribution was de‐ termined by laser diffraction. After 16 min both ultrasonification and ball grinding achieve the same particle size distribution (Figure 1). The ultrasonic approach could be used to ob‐ tain much smaller sample volumes than the ball mill approach [39].

UMP particle size and its distribution are greatly influenced by the dosage of dispersants. The particle size decreases at first and then increases with the enhancement of the disper‐ sant, and the particle size reaches its minimum when the ratio is about 10% for phase sepa‐ ration method. The smaller the particle size is, the larger the UMP surface is, thus the more amount of dispersant is needed. However, excessive dispersants, higher than 10%, will dis‐ solve in media instead of attaching onto UMP surface, resulting in increasing viscosity of dispersing media and poor wetting performance in that excess dispersants (Figure 2) [30].

Preparation, Characterization and Application of Ultra-Fine Modified Pigment in Textile Dyeing

http://dx.doi.org/10.5772/53489

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**Figure 2.** Particle size distribution of treated and untreated pigment red 170. (I) 1wt%pigment, 0 wt% dispersant; (II) 1wt% pigment, 0.01wt% dispersant; (III) 1wt% pigment, 0.02wt% dispersant; (IV) 1wt% pigment, 0.1wt% dispersant;

The -COOH group of copolymers encapsulated onto the surface of UMPs would form a pol‐ ymeric shell around the particles and also increase the surface charges of UMP particles. The interaction between UMP particles is weakened due to the existence of these charges and polymeric layer on the UMP particle surface, so that the UMP particles can be finely dis‐ persed in aqueous media [37]. With the dosage of siloxane dispersant descending, the per‐ centage of big particle ascends at first. However, while the dispersant is greatly excessive (10

Initial experiments, using dilute aqueous dispersions of carbon black of known average-parti‐ cle size distribution, were performed using both a standard UV/Vis spectrometer and a digital camera to estimate light-transmission/attenuance. The results, summarized in Figure 3(A) and

(V) 1wt% pigment,10wt% dispersant.

wt%), the particle size increases.

**Figure 1.** (A) Particle size distribution data from ball grinding; (B) Particle size distribution data from ultrasonication
