**2. Yarn and fabric characterizations**

Yarn and fabric properties can be measured using theoretical calculation and classical test standards as well as the X-ray micro-computed tomographic 3D images of the fabrics. This section will discuss the measurement methods in details. The fabrics which will be used for comparison included four plain and four satin woven fabrics made from 100% cotton ring-spun yarns (40 and 60Ne linear density) [12, 13]. The fabrics varied in thread density, and were grouped into 'low density' and 'high density' fabrics for respective weave designs and yarn counts. **Table 1** below represents the fabrics.

*Non-destructive Characterizations of Natural Yarns and Fabrics DOI: http://dx.doi.org/10.5772/intechopen.102587*


**Table 1.**

*Woven fabrics were coded for easy identification where the 1st letter indicated weave design (P = plain and S = satin), the middle two-digit numbers indicated yarn count or linear density (40 for 40Ne, and 60 for 60Ne), and the 4th letter indicate fabric thread density (L = low and H = high). For example, P40L stands for low-density plain-woven fabric made of 40Ne yarn [12, 13].*

### **2.1 Theoretical evaluation and classical test methods**

**Yarn Diameter**: Given the yarn count (yarn linear density), yarn diameter can be theoretically calculated using the Eq. (1) below [12, 13, 26]. In the development of the equation, the yarns were assumed to be uniform round cylinders and the diameters were expressed in terms of yarn count (tex system).

$$d = \frac{1}{280.2} \sqrt{\frac{N\_t}{\mathfrak{D}\rho\_f}}\tag{1}$$

Specification and Unit:

*d* = yarn diameter (cm).

*Nt* = yarn count (tex, expressed in g/km);

14.76 tex (for 40Ne), and 9.84 tex (for 60Ne)

∅ = yarn packing factor (constant, and varies with spinning type).

0.6 For ring-spun yarns

*ρ <sup>f</sup>* = fiber density (g/cm<sup>3</sup> ); 1.52 g/cm<sup>3</sup> for cotton fiber.

For example, the calculated yarn diameters were 0.014 and 0.012 cm for 40 and 60Ne yarns respectively. The diameter units were then converted to other units (such as to mm) as needed for further analysis [12, 13].

**Yarn Packing Factor or Packing Density**: Yarn packing factor can be theoretically calculated using the Eq. (2) below [12, 13, 27, 28].

$$\text{Packing factor} = \frac{\text{Fiber Area}}{\text{Yarn Area}} = \frac{\frac{\text{Yarn count (in denier)}}{\text{Volumetric density of fiber}, \rho\_f}}{\text{Yarn area}, \ (\pi r^2)}\tag{2}$$

The calculated counts (in denier) for 40 and 60Ne yarns were 132.87 denier and 88.58 denier respectively, and yarn area was calculated using the theoretical yarn diameters discussed earlier.

**Yarn Twists**: Yarn twists can be measured by untwist-retwist method (revolution/ 20 inch) following the ASTM D1422–99(2008) test standard which satisfactorily

determines the approximate twist in all ring-spun yarns and 100% cotton open-end spun yarns [29]. **Figure 1**. shows a RU-493 power-driven Twist Tester. In this method, 25 yarns are extracted from each fabric and the twist direction is identified. One end of a 10″ yarn sample is pulled through the stationary clamp (then immediately closed), and the other end is fastened to the rotational clamp (**Figure 1**) ensuring the marker (or pointer) is in the zero position. Twist direction is then selected on the tester to let the untwisting/rotation of yarn in the same twist direction. The motor is turned on, allowing yarns to untwist and elongate by releasing the yarn tension, and then retwist back in the opposite direction. When the marker returns to zero position, the motor is stopped. Number of turns is recorded from the reading dial and yarn twists (in TPI value that stands for Twists per Inch) can be calculated using Eq. (3). In the equation, the value 2 implies untwisting and retwisting. Twist multiplier (TM) can be then calculated using Eq. (4), and the entire process is repeated for the remaining 24 yarn samples extracted from fabrics [27–29].

$$\text{TPI} = \frac{R}{2L} \tag{3}$$

$$\text{TPM} = \frac{\text{TPI}}{\sqrt{\text{Ne}}} \tag{4}$$

**Yarn Crimp**: ASTM D3883, 'Standard Test Method for Yarn Crimp and Yarn Take-Up in Woven Fabrics' is usually followed for yarn crimp measurements [14]. In both warp and weft directions on fabrics, marks are made 10″ apart, and yarns are unraveled for measurements. Following option, A of ASTM D3883, a yarn is stretched to the point of no crimp, and the distance between yarn markings in its stretched state is measured. The process is repeated 10 times for both warp (also known as ends) and weft (also known as picks or filling yarns) yarns of each fabric.

$$\text{Yarn Crimp\%} = 100 \times \frac{\text{(Straightened yaran length -- marked yaran length in fabric)}}{\text{marked yaran length in fabric}} \tag{5}$$

Yarn crimp (%) can be then calculated using Eq. (5). Note 2 of ASTM D3883 states that Option A may lead to variation from the possible inconsistency during stretching of yarns by hand since the stretch force is unknown.

**Figure 1.** *RU-493 power-driven twist tester for yarn twists measurements [27].*

*Non-destructive Characterizations of Natural Yarns and Fabrics DOI: http://dx.doi.org/10.5772/intechopen.102587*

**Fabric Thread Density**: Fabric thread density are determined following the ASTM 3775, Standard Test Method for End (warp) and Pick (weft/filling) Count of Woven Fabrics [30]. 1-inch marks are made on fabrics in both the warp and weft directions. Fabrics are then cut cautiously near a mark to unravel before the mark. Using a handheld pick, yarns are pulled out of the fabric while counting, and the total number of yarns within the 1-inch marks is reported as ends/inch (EPI) and picks/inch (PPI).

**Fabric Basis Weight**: Basis weight of the fabrics (g/m<sup>2</sup> or gsm) can be measured following the ASTM D3776, standard test methods for mass per unit area (weight) of fabric [31]. Samples are cut into 6″ � <sup>6</sup>″ size, and weighed (g) in a high precision electronic balance. The values are then recorded in g/m<sup>2</sup> and the process is repeated 5 times for each fabric.

**Fabric Thickness**: Thickness of the fabrics can be measured in a thickness gauge (Ames Digital Comparator; model #3-P1500; displayed in **Figure 2**) following the ASTM D1777–96(2002) Standard Test Method for Thickness of Textile Materials (table option 1; 4.14 � 0.21 KPa) [12, 13, 27, 28, 32]. A sample is placed (technical face up) on the base of the instrument called anvil, and a weighted pressure foot is lowered. Pressure is applied for at least 5–6 s. Thickness (mm) is determined by the distance between anvil and pressure foot and recorded. The process is repeated at least 10 times for each fabric.

**Fabric Cover Factor**: Fabric Cover factor is expressed as percentage (%), and refers to the area of the fabric which is actually covered by fibers and yarns. It is defined as the ratio of surface area covered by yarns to total fabric surface area. Fabric cover factor can be calculated using Eqs. (6)–(8) [12, 13].

$$\mathbf{C}\_f = (\mathbf{C}\_1 + \mathbf{C}\_2 - \mathbf{C}\_1 \mathbf{C}\_2) \times \mathbf{100} \tag{6}$$

$$\mathbf{C}\_1 = p\_1 \times d\_1 \tag{7}$$

$$C\_2 = p\_2 \times d\_2 \tag{8}$$

Specification and Unit: *Cf* = fabric cover factor (%). *C*<sup>1</sup> = warp cover factor. *C*<sup>2</sup> = weft cover factor.

**Figure 2.** *Ames digital thickness gauge (model #3-P1500) [27].*

*p*1, and *p*<sup>2</sup> = fabric thread density; warp or ends per inch (EPI), and weft or picks per inch (PPI) respectively (measured following ASTM 3775).

*d*1, and *d*<sup>2</sup> = warp and weft yarn diameters (inch) respectively (theoretically calculated).

### **2.2 X-ray micro-computed tomographic 3D image analysis**

Recent research [12] demonstrated the use of an Xradia 510 Versa 3D X-ray microscope (XRM) (Zeiss, Germany) (**Figure 3**) for imaging the fabric samples. Fabrics were mounted on the sample holder maintaining warp in the vertical direction to ensure accuracy and consistency in the test method. The high-resolution images (pixel size: 1.31 μm) were obtained at 50 kV and 10 W using the 4X objective lens, and from a projection number set to 1601. The source-to-fabric and detector-to-fabric distances were maintained constant for all fabrics to ensure same resolution at the same magnification. The images were then imported to the XMReconstructor software for post-reconstruction into 8-bit TIFF files with a size of 9801008990 (width, height, and depth) [12, 13].

The reconstructed TIFF images were then imported into the Dragonfly Pro software (ORS, Montreal, Canada). Window leveling, contrast and intensity space were adjusted for both the 3D (**Figure 4a**) and 2D images (**Figure 4b**), and image segments were created for a more meaningful visualization as well as for different sets of measurements. New segmented regions of interest (ROIs) were created which highlighted the fibers (**Figure 4c**), noise was removed (**Figure 4d**), and then the images were converted to binary scale (**Figure 4e**) for analysis. The 2D planes were then adjusted to be as perpendicular to each other as possible (**Figure 5**) where *X*, *Y* and *Z*-axis indicated thickness, warp and weft directions respectively. In the images, the black color represented air while the white represented the fibers in the fabrics [12, 13].

**Yarn Diameter**: Yarn diameters (μm) were measured from the 2D images using the scales in the Dragonfly Pro software (**Figure 6a**). Warp and weft yarn diameters were measured using the 2D XZ and XY images respectively (as depicted in **Figure 5**). Fifty measurements (μm) were taken and averaged for yarn diameters for both warp and weft yarns, and then converted into cm [12, 13].

*Non-destructive Characterizations of Natural Yarns and Fabrics DOI: http://dx.doi.org/10.5772/intechopen.102587*

#### **Figure 4.**

*3D and 2D views of P40H fabric, obtained from Xradia 510 versa 3D X-ray microscope (XRM): (a) 3D image, (b) 2D view, original image, (c) 2D view of image segment with noise, (d) 2D view of image segment after noise removal, and (e) 2D binary image of the segment highlighting the fibers for computation [12, 13].*

#### **Figure 5.**

*2D views of P40H fabric where each dimension is perpendicular to each other. X, Y and Z-axis indicated to the thickness, warp and weft directions respectively [12, 13].*

#### **Figure 6.**

*Measurements of (a) yarn diameter and crimp% (requires the straight length and curved length), and (b) fabric thickness defining the two surfaces [12, 13].*

**Yarn Crimp**: Yarn crimp (%) was calculated using the Eq. (9) below. Ten measurements of both straight length and curved length (as depicted in **Figure 6a**) were taken to calculate the respective warp crimp% (from XY images) and weft crimp% (from XZ images) [12, 13].

$$\text{Yarn crimp\%} = \frac{\text{Curved length} - \text{Straight length}}{\text{Straight length}} \times 100\tag{9}$$

**Yarn Packing Factor**: Yarn packing factor was calculated using the yarn diameters obtained from the CT measurements (units converted as required) in Eq. (2) as discussed in Section 2.1 [12, 13].

**Fabric Thickness**: CT fabric thickness (μm) was defined and measured by the distance between the two surfaces (technical face and technical back) as depicted in **Figure 6b**. A total of fifty measurements were taken from different cross-sections of each fabric. The values were then averaged and converted to mm [12, 13].

**Fabric Cover Factor**: CT fabric cover factor was calculated using the CT yarn diameters for the respective fabrics, and following the Eqs. (6)–(8) [12, 13].
