Non-destructive Characterizations of Natural Yarns and Fabrics

Abstract

Textiles, next to skin, are an integral part of our lives, govern the skin microclimate, and contribute to our comfort and health. Over the years, natural and synthetic textiles have dominated the industry in diverse application areas. However, when it comes to the sustainability of the raw materials or products, processes, and the environment, the natural polymers or fibers will always dominate the preference. One of the many natural fibers, cotton fiber is the most popular and widely used one, leading to many fundamental researches in the fields of polymers, fibers, fabrics, their manufacturing processes and finishing, as well as in product characterizations and performance evaluations. To-date, most textile-characterization techniques involve processes which compromise the morphology of the textiles being tested, and are mostly destructive. In this chapter, a few novel non-destructive characterizations of textiles, made from natural fibers (specifically cotton), will be discussed which involve X-ray micro-computed tomographic (XRM-CT) three-dimensional (3D) image analysis. Tomographic characterizations allow the investigation of both the surface profiles and the inner construction of the textiles without compromising the morphology. The findings discussed in this chapter will assist in non-destructive characterizations and performance evaluations of other diverse material classes as well.

1. Introduction

Textiles are complex porous structures, composed of fibers, yarns and fabrics. It refers to a vast and diverse application areas, and are an integral part of our lives used in many routine applications such as apparel, shoes, accessories and home furnishings. The functionality and performance of different textile products depends on their physical, mechanical, and thermal properties, as well as, air and moisture (and/or liquid) transport properties. Hence, in order to optimize and improve the performance of the textiles in diverse application areas, characterization of the textiles and an understanding of their structure–property relationships are imperative. For instance, textiles next to skin regulate the skin micro-climate, and skin-textile friction (measured by friction force or friction coefficient) play a vital role in skin comfort and health in different conditions [1]. The frictional properties of textiles can become an important issue when it expedites the development of skin injuries. For example, excessive and repetitive friction from moist textiles (due to absorption of skin sweat) were reported to expedite tissue deformation and skin damage, friction blisters, pressure ulcers (also known as decubitus ulcers), and even more severe unwanted problems in athletes, military, and in people with compromised skin conditions and immobility [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]. Therefore, to optimize the fabric frictional properties, depending on applications, it is essential to have an understanding of the structural characteristics of the fibers, yarns and fabrics, and their effects on respective physical and mechanical properties in different micro-climatic conditions. These understanding can provide valuable insights on how to engineer and design textiles to lower the friction force when in contact with the skin [12, 13].

Textile characterization is also a broad topic which involves the study of polymers, fibers, yarns, and fabrics as well as their end products in diverse applications. Over the years, there has been a significant number of studies by scientists to develop theories and systematic test methods, and standardize these methods to ensure consistency in textile characterization (methods) all around the world. However, most characterization methods are destructive in nature, and/or compromise the structure during tests which may compromise the resultant data. For instance, measurement of yarn crimp% in fabrics following the ASTM D3883 (option A) test method involves the extraction of the yarns from the fabrics which may influence the measurements by releasing the tension acting on the yarns [12, 14]. In addition, natural fibers (for example, cotton) tend to be hairy on the surface. The hairiness on the fabric surfaces makes the characterization of natural fibers, yarns and fabrics more challenging. This is why there is a growing interest in nondestructive characterization of textiles. Literature reveals the use of the X-ray micro-computed tomography (XRM-CT or X-ray CT) systems for nondestructive characterization of fibers [15, 16, 17], yarns [12, 18] and fabrics [12, 19, 20, 21, 22]. The X-ray CT system has also been well-known for nondestructive analysis and its diverse applications in biological and medical science [23], material science [24], and in the analysis of membranes [25]. The nondestructive analysis reported in these studies [12, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25] involved acquiring high resolution 3D images of the test samples using the X-ray CT system. CT images are reconstructed and then imported to processing software for advanced analysis of both the 2D and 3D images [12]. CT images can also be analyzed to represent different fibers with different densities using gradients of gray levels or intensities. In this chapter, a few non-destructive yarn and fabric characterization methods using the X-ray CT system and image analysis tools will be discussed. In addition, the characterized properties will be compared with those obtained from the existing classical test standards. It is to be noted that the chapter will focus on the interpretation of the test results of cotton-made yarns and fabrics.

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.

Sample code	Yarn linear density (Ne)	Weave design	Fabric density
P40L	40	Plain	Low
P40H	40	Plain	High
S40L	40	5-H Satin	Low
S40H	40	5-H Satin	High
P60L	60	Plain	Low
P60H	60	Plain	High
S60L	60	5-H Satin	Low
S60H	60	5-H Satin	High

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).

$$d=\frac{1}{280.2}\sqrt{\frac{N_t}{\varnothing {\rho }_f}}$$E1

Specification and Unit:

$d$ = yarn diameter (cm).

$N_t$ = yarn count (tex, expressed in g/km);

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

$\varnothing$ = yarn packing factor (constant, and varies with spinning type).

0.6 For ring-spun yarns

${\rho }_f$ = fiber density (g/cm³); 1.52 g/cm³ 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].

$$\text{Packing factor}=\frac{\text{Fiber Area}}{\text{Yarn Area}}=\frac{\frac{\text{Yarn count}\left(\text{in denier}\right)}{\text{Volumetric density of fiber},{\rho }_f}}{\text{Yarn area},\left(\pi r^2\right)}$$E2

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, 28, 29].

Figure 1.

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

$$\mathrm{TPI}=\frac{R}{2L}$$E3

$$\mathrm{TM}=\frac{\mathrm{TPI}}{\sqrt{\mathrm{Ne}}}$$E4

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.

$$\text{Yarn Crimp}\%=100\times \frac{\left(\text{Straightened yarn length}-\text{marked yarn length in fabric}\right)}{\text{marked yarn length in fabric}}$$E5

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.

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/m²or 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″ × 6″ size, and weighed (g) in a high precision electronic balance. The values are then recorded in g/m² 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.

Figure 2.

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

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].

$$C_f=\left(C_1+C_2-C_1{C}_2\right)\times 100$$E6

$$C_1=p_1\times d_1$$E7

$$C_2=p_2\times d_2$$E8

Specification and Unit:

$C_f$ = fabric cover factor (%).

$C_1$ = warp cover factor.

$C_2$ = weft cover factor.

$p_1$, and $p_2$ = fabric thread density; warp or ends per inch (EPI), and weft or picks per inch (PPI) respectively (measured following ASTM 3775).

$d_1$, and $d_2$ = 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 980$\times$1008$\times 990$ (width, height, and depth) [12, 13].

Figure 3.

Zeiss Xradia 510 versa 3D X-ray tomography system (inside view) [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].

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].

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].

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].

$$\text{Yarn crimp}\%=\frac{\text{Curved length}-\text{Straight length}}{\text{Straight length}}\times 100$$E9

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].

3. Comparison of yarn and fabric properties (non-destructive versus theoretical and classical standards)

This section will provide an understanding of the cotton-made yarn and fabric properties and how realistic the nondestructive measurements from the XRMCT images are.

The yarn and fabric characteristics obtained from the classical test standards are displayed in Table 2. In addition, Figures 7 and 8 depict the comparison between theoretical calculation and experimental measurements obtained from CT images and classical test standards.

Fabric code	Yarn twist (TPI ± Std. Dev.)	Twist multiplier, ${TM}=\frac{{TPI}}{\sqrt{{Ne}}}$	Yarn crimp% ± Std. Dev.		Fabric thread density		Basis weight (gsm) ± Std. Dev.	Fabric thickness (mm) ± Std. Dev.	Calculated volumetric density (g/cm^3)
			Warp crimp%	Weft crimp%	EPI	PPI
P40L	28.15 ± 1.57	4.45 ± 0.25	11.00 ± 0.03	10.50 ± 0.03	151	84	128.63 ± 0.64	0.26 ± 0.00	0.49
P40H	26.64 ± 2.08	4.21 ± 0.33	13.13 ± 0.03	11.88 ± 0.05	141	116	140.81 ± 1.34	0.24 ± 0.00	0.59
S40L	28.10 ± 0.84	4.44 ± 0.13	13.00 ± 0.04	6.88 ± 0.03	144	78	129.16 ± 0.46	0.42 ± 0.00	0.31
S40H	25.58 ± 0.81	4.04 ± 0.13	7.75 ± 0.04	4.00 ± 0.03	187	74	147.88 ± 0.30	0.34 ± 0.00	0.43
P60L	35.22 ± 2.03	4.55 ± 0.23	15.25 ± 0.05	7.50 ± 0.05	156	100	99.01 ± 1.75	0.2 ± 0.00	0.50
P60H	35.89 ± 0.98	4.63 ± 0.13	4.00 ± 0.03	15.25 ± 0.05	185	144	117.79 ± 0.95	0.28 ± 0.00	0.42
S60L	29.16 ± 1.92	3.76 ± 0.25	5.88 ± 0.03	3.00 ± 0.03	220	96	109.64 ± 0.74	0.24 ± 0.00	0.46
S60H	36.51 ± 2.10	4.71 ± 0.27	13.00 ± 0.03	4.75 ± 0.03	219	132	128.47 ± 0.50	0.28 ± 0.00	0.46

Table 2.

Structural characteristics of the yarns and fabrics used in the study [12, 13].

Figure 7.

Yarn characteristics obtained from ASTM test standards and XRM-CT methods. (a) Yarn diameter, (b) yarn packing factor (PF), and (c) yarn crimp% [12, 13].

Figure 8.

Fabric characteristics obtained from ASTM test standards, theoretical values and XRM-CT method. (a) Fabric thickness, (b) fabric volumetric density calculated using ASTM thickness and CT thickness, and (c) fabric cover factor calculated using theoretical yarn diameters and CT yarn diameters [12, 13].

Yarn Diameter: Results showed that both the theoretical warp and weft yarn diameters [calculated from Eq. (1)] were statistically different (P-value <0.05) than the respective CT yarn diameters (Figure 7a). Irrespective of weave design, the calculated theoretical diameters were constant for the same count yarn as well as for both warp and weft yarns. Experimental CT measurements showed that the same count yarns resulted in different diameters of the warp and weft yarns in both plain and satin woven fabrics. Diameter in 40Ne yarns was higher than 60Ne yarns. In addition, given the same yarn count, higher yarn diameters were observed in satin fabrics than the plain-woven fabrics [12, 13].

Different weave designs and thread densities attributed to the distortion of the yarns as they interlaced with each other during weaving. Such distortion resulted in the differences in the warp and weft yarn diameters which can be understood from Figure 9.

Figure 9.

X-ray micro-computed tomographic 2D images of the fabrics studied. (a) P40L, (b) P40H, (c) S40L, (d) S40H, (e) P60L, (f) P60H, (g) S60L, and (h) S60H [12, 13].

Plain woven fabrics contained high number of interlacements. In contrast, satin fabrics had more floats or weft yarns which allowed more freedom to the yarns to move around and resulted in larger yarn diameters (Figure 9). The authors suggested that the CT images were capable of providing more realistic yarn diameters in the fabrics than the theoretical values [12, 13].

Yarn Packing Factor: Figure 7b shows that the different diameter yarns obtained from the CT measurements resulted in a variation in the yarn packing factors while the theoretical yarn packing factor was constant (0.6 for ring-spun yarns). Given the same yarn count, an increase in yarn diameter decreases the yarn packing factor which was not reflected from the theoretical values but from the CT measurements [12, 13].

Yarn Crimp: Yarn crimp% obtained from ASTM D3883 (option A) test method (Table 2) and CT method were compared (Figure 7c). For both warp and weft yarns, results from a two-sample t-test at 95% confidence interval showed that the measurements from the two methods were not statistically different (P-value of 0.43 and a higher R²). Given the same yarn count and weave design, a further analysis of the CT data showed that warp crimp% was significantly higher than the weft crimp% (P-value <0.05). In addition, yarns in the plain-woven fabrics exhibited higher crimp% than the satin fabrics. The ASTM method of yarn crimp measurement involved extraction of yarns while the CT method was nondestructive. Therefore, the CT method can be reliably used to measure yarn crimp without compromising the structure [12, 13].

Fabric Thickness: Fabric thicknesses obtained from ASTM D1777–96(2002) method and CT method were compared. Results depicted in Table 2 and Figure 8a suggested that the measurements from the two methods were not statistically different (P-value 0.21, and R² = 0.97). It was also observed that the satin fabrics exhibited higher thickness than the plain-woven fabrics. In the satin fabrics, the presence of more floats or weft yarns which extended across multiple yarns (Figure 9) attributed to overriding of yarns and looser fabric construction, and therefore, greater fabric volume and thickness than the plain-woven fabrics. In addition, 60Ne yarn-made satin fabrics had lower thickness than the 40Ne yarn-made fabrics. The smaller diameter 60Ne yarns contained higher twists (TPI) which compressed the fibers and increased yarn tightness (Table 2), and therefore, attributed to lower fabric thickness. However, despite the different twists in different count-yarns in the fabrics, twist multiplier were nearly the same suggesting the same internal structure (helix angle) of the yarns [12, 13].

With increasing fabric density (thread density), thickness decreased in 40Ne yarn-made fabrics, and increased in 60Ne yarn-made fabrics (Figure 9). With increasing fabric density, less twisted and larger diameter 40Ne yarns compressed within the structure, and filled up the voids. This resulted in a closer fiber and yarn packing, and reduced thickness in the 40Ne yarn-made fabrics (Figures 7b and 9). In contrast, finer, tighter (with more twists) and smaller diameter 60Ne yarns had less voids (as discussed above in yarn packing factor). Hence, in the presence of low voids in the 60Ne yarns, the yarns expanded in the thickness direction with increasing fabric density (Figures 7b and 9) [12, 13].

Fabric Volumetric Density: Both the ASTM thickness and CT thickness were used to calculate fabric volumetric density (g/cm³) for further comparison (Figure 8b), and were obtained by multiplying fabric basis weight (gsm) with thickness. The methods did not exhibit any statistical differences in the measurements (P-value 0.51) [12, 13].

Fabric Cover Factor: Fabric cover factor obtained from the theoretical values and the CT method (using CT yarn diameter) were compared and depicted in Figure 8c. A further statistical analysis showed that there was no significant difference between the measurements obtained from the two methods (P-value 0.62), and satin fabrics exhibited higher fabric cover factor. Irrespective of weave design, no significant difference was observed between 40 and 60Ne yarn-made fabrics [12, 13].

Therefore, unlike other classical test methods, the CT method are nondestructive and capable of providing realistic measurements from both the 2D and 3D images. Apart from the structural properties discussed in this Chapter, the CT method can be used for a more advanced analysis of the fabrics such as fiber area distribution [12, 13], porosity analysis [22], surface profile analysis [1] etc. Such in-depth analysis and understanding of the cotton-made yarn and fabric structures will help engineers and scientists optimize the structure and improve the performance of the textiles for diverse applications and end-uses.

4. Conclusion

In this chapter, a nondestructive characterization method using an X-ray microscope was discussed. The method involves acquiring a high-resolution tomographic 3D images of the cotton fabrics, and is capable of providing reliable quantitative measurements. Yarn diameter, packing factor, yarn crimp, fabric thickness, volumetric density and fabric cover factor were measured and discussed. The measurements were also compared with those obtained from existing theory and classical test methods. The findings on cotton-based yarns and fabrics discussed in this chapter will also assist in non-destructive characterizations and performance evaluations of other natural and synthetic fibers, yarns and fabrics as well as other material classes.

Acknowledgments

We sincerely appreciate the supports from the Analytical Instrumentation Facility (AIF) and the Wilson College of Textiles, North Carolina State University, USA. We acknowledge the technical advice from Anton Jansson (Ex-Postdoctoral Research Scholar, AIF). This work was performed in part at the Analytical Instrumentation Facility (AIF) at North Carolina State University, which is supported by the State of North Carolina and the National Science Foundation (award number ECCS-1542015). The AIF is a member of the North Carolina Research Triangle Nanotechnology Network (RTNN), a site in the National Nanotechnology Coordinated Infrastructure (NNCI).

Conflict of interest

The authors declare no conflict of interest.