Structural and dimensional behavior of flax double weft knitted fabrics after washing

Abstract

This study investigated the influence of fabric variant and fabric state on the structural and dimensional behavior of flax double weft knitted fabrics. Two fabric variants were examined: variant I, an unbalanced structure with a 1 × 1 rib with a single miss stitch; and variant II, a balanced structure with a 1 × 1 rib with a 1 × 2 rib. Key structural characteristics, including stitch density, stitch length, weight, and thickness, were analyzed in dry-relaxed (DR) and wet-relaxed (WR) states. Additionally, the dimensional changes following washing were studied. Results showed that variant I had higher stitch density on the back, longer average stitch length, and greater weight and thickness than variant II. These differences reflect the effect of single miss stitches on fabric structure versus the 1 × 2 rib in fabric variant II. Washing caused structural relaxation and partial recovery in both variants, with variant I showing smaller dimensional changes and greater overall stability. Both fabrics shrank in length and expanded in width; variant I demonstrated notably reduced widthwise expansion. Statistical analysis confirmed that the fabric variant significantly influenced stitch formation, dimensional changes, and overall stability. These findings suggest that the structure with a 1 × 1 rib with single miss stitches (variant I) provides enhanced dimensional control and predictable performance during following washing, making it especially suitable for applications requiring high fabric stability.

Introduction

Flax (Linum usitatissimum) is among the most ancient and adaptable bio-based fibers cultivated for textile applications. Historically, flax has been extracted, spun, knitted, and woven into fabrics ranging from coarse linens to fine-quality textiles, demonstrating its enduring relevance in both traditional and modern manufacturing processes.^1,2 As a renewable natural resource, flax exhibits favorable mechanical and physical properties, including high tensile strength, specific stiffness, durability, and excellent moisture-regulating breathability.^3–6 Moreover, flax is inherently environmentally friendly, with a benign life cycle, making flax a sustainable alternative to synthetic fibers. ⁷ Consequently, growing environmental awareness and increasing stringent regulations have driven demand for sustainable textiles. This trend is reflected in the flax fiber market, which is projected to grow at a compound annual growth rate (CAGR) of 9.1% through 2033. ⁸

Furthermore, beyond conventional textile applications, flax is increasingly used in automotive, construction, and composite materials, where its combination of strength, lightness, and low environmental impact provides a clear competitive advantage. ⁹ The mechanical properties of natural flax fiber are comparable to those of certain synthetic fibers, making them suitable for sports, marine, and even aerospace applications. However, fiber performance varies considerably due to differences in plant origin, growth conditions, maturity, stem position, extraction methods, and irregularities. A key limitation of flax is its high moisture absorption, which can lead to swelling, softening, and reduced mechanical strength. ¹⁰ Nevertheless, flax-containing yarns gained increasing importance in knitted textile production owing to their sustainability, durability, and distinctive comfort-related attributes.

Knitted fabrics can be engineered to exhibit a wide range of physical and mechanical characteristics through variations in stitch types – such as knit, miss (float), and tuck stitches – and their structural configurations.^11,12 Numerous studies have shown that each stitch type confers unique characteristics to the resulting fabric, and that structural selection must be aligned with the intended application and performance requirements. ¹³ In this context, understanding the influence of stitch geometry on fabric behavior is essential for the design of knitted textiles with optimized functionality and quality. Fabric structure and performance are strongly influenced by both the fiber composition and the knit stitch type. Previous research shows that fiber composition strongly influences the properties of double-jersey weft knitted fabrics. For example, 100% flax fabrics behave differently from cotton/flax (70/30) and PAN/flax (70/30) blends, with key structural parameters, such as wale and course density, stitch density, weight, and thickness, being governed by yarn type, yarn properties, and loop length. Most dimensional changes occur during the first washing cycles, while non-creasing and air permeability depend mainly on yarn composition, fabric density, and loop structure. ¹⁴ Hundred percent flax yarn offers high strength but limited elasticity and high torsional stiffness, which can restrict widthwise extensibility and increase residual deformation. Therefore, blending flax with fibers such as cotton or PAN improves yarn flexibility, loop formation, and fabric uniformity, resulting in more stable and better-performing knitted structures. ¹⁵ Single-jersey and pique knits from flax yarn showed the best mechanical and comfort properties, while rib knits were less suitable. ¹⁶

In addition, fabric mass significantly influences performance characteristics. Lighter flax knitted fabrics have higher compressibility, air permeability, and thickness reduction but lower resistance to compression, bursting strength, and elongation. Thus, they offer better breathability but less durability and recovery. ¹⁷ Flax yarn provides high strength but lower elongation and evenness compared to cotton. However, blending flax with cotton enhances processability and overall performance, with a 20% flax content offering the best balance between strength, elasticity, and fabric quality. ¹⁸ Regarding comfort performance, flax fiber provides efficient moisture management and thermal conduction in knitted fabrics. Sensorial comfort tests revealed that 100% flax knitted fabrics demonstrated higher tensile resilience and better compression linearity, whereas 50/50 cotton-flax blends showed increased compressional energy and resilience. ¹⁹ Similarly, stitch configuration plays a crucial role in dimensional behavior. The incorporation of the single miss stitches significantly affected the structure, dimensions, and stretch of double weft cotton/flax (70/30) fabrics. Increasing the number of miss stitches decreased widthwise shrinkage and stretch, with lengthwise changes remaining larger. Fabrics with similar miss-stitch levels behave similarly, underscoring the importance of stitch type in optimizing fabric performance for fashion and technical uses. ²⁰ The rib set-out repeat also significantly influences the structural, dimensional, and mechanical properties of double weft cotton/flax (70/30) knitted fabrics. Increasing the number of float loops leads to greater shrinkage, higher density, thickness, and weight. Fabrics with the same percentage of inactive needles (50%) show minimal variation, highlighting the importance of rib set-out design in optimizing dimensional stability for high-quality cotton-flax knitted fabrics. Moreover, the first wash has a significant impact on the dimensional stability of falx-containing double weft fabrics. ²¹ The width repeat of miss stitches, defined by the arrangement and proportions of knit and miss loops, is an important structural parameter that influences the dimensional stability and overall structure of double knitted fabrics. In contrast, the effect of the number of washing cycles on structural properties is generally less.^20–22

In general, the type of knit stitch and its combinations greatly influence the mechanical and physical properties of weft knitted fabrics. The plain stitch offers the most excellent flexibility but lacks fullness and stability. The rib stitch exhibits significant elongation in one direction, leading to dimensional instability during wear. In contrast, a combination of plain and rib stitches, such as half Milano rib or Milano rib, demonstrates more balanced mechanical properties, providing better shape retention, thickness, and structural stability. ²³

Therefore, this study focuses on pure flax double weft knitted fabrics produced by alternating two courses: 1 × 1 rib stitch with single miss stitches and 1 × 1 rib stitch with 1 × 2 rib stitches. Since fabric condition significantly influences its ability to recover from stresses and maintain intended dimensions, both dry-relaxed and wet-relaxed states were examined. The primary objective is to address existing knowledge gaps by exploring how variations in knit stitch structure, particularly the use of single miss stitch or 1 × 2 rib stitch in combination with 1 × 1 rib stitch, and fabric conditions affect structural characteristics and dimensional stability. Ultimately, understanding these relationships is essential for developing high-quality double weft knitted fabrics that achieve an optimal balance of durability, comfort, and aesthetic performance, thus satisfying consumer expectations.

Materials and Methods

Materials

The combination of single and double stitches, and of double and double stitches, significantly influences the structure and properties of knitted fabrics.^20–22 Incorporating different structural elements, such as knit loops and float loops, and their various combinations, allows the creation of knitted fabrics with tailored dimensional stability and optimized performance.

The research investigates two variants of double weft knitted fabrics produced from commercially used 100% flax yarn Nm14. Fabric variant I was constructed with two courses: a 1 × 1 rib structure knitted by the first yarn feeder, and a single miss-stitch structure knitted by the second yarn feeder (Figure 1(a)). Fabric variant II also comprised two courses: a 1 × 1 rib structure by the first yarn feeder and a 1 × 2 rib structure by the second yarn feeder (Figure 2(a)). Both variants of the double weft knitted structure exhibit distinct technical face (front) and back (reverse) sides.

Figure 1.

Graphical notation (a), visual representation of the technical face (b), and back (c) sides with X–X and Y–Y cross-sections; corresponding photos of the face and back sides of knitted fabric variant I in states: (d, e) DR, (f, g) after WR1, and (h, i) after WR4, respectively.

Figure 2.

Graphical notation (a), visual representation of the technical face (b), and back (c) sides with X–X and Y–Y cross-sections; corresponding photos of the face and back sides of knitted fabric variant II in states: (d, e) DR, (f, g) after WR1, and (h, i) after WR4, respectively.

All fabrics were knitted on a CMS 340.6L double-needle flat V-bed knitting machine (Stoll, Germany) with a gauge of E12. During the knitting process, the main knitting parameters on the knitting machines, such as stitch cam position, yarn input tension, and fabric take-down rate, were maintained constant to ensure uniform knitting conditions and minimize structural variability.

Knitted fabric variant I represents an unbalanced structure with two courses (1 × 1 rib and single miss stitch) on the technical face and one course of 1 × 1 rib on the technical back. The technical face consists of knit loops from the 1 × 1 rib (including conventional and extended, i.e. held loops) and single miss stitch formed by conventional knit loops and float loops (Figure 1(b) and (d)). The extended knit loops of the 1 × 1 rib (held loops) are positioned in the same wales where the float loops are produced by the subsequent yarn feeder. In contrast, the technical back side of the fabric variant consists solely of the knit loops of the 1 × 1 rib structure, which is extended (Figure 1(c) and (e)).

Knitted fabric variant II represents a balanced double structure composed of two courses on both the technical face and back sides. The technical face consists of knit loops from the 1 × 1 rib (including conventional and extended, i.e. held loops) and from the 1 × 2 rib structure (Figure 2(b) and (d)). The extended knit loops of the 1 × 1 rib (held loops) are located in the same wales where the inactive needles are positioned during the formation of the 1 × 2 rib by the subsequent yarn feeder. In contrast, the technical back side of the fabric is composed of knit loops belonging to both the 1 × 1 and 1 × 2 rib structures, resulting in a more uniform and structurally balanced configuration (Figure 2(c) and (e)).

Methods

Structural Characteristics

The structural characteristics of the double knitted fabrics were assessed in dry-relaxed (DR) and wet-relaxed (WR) states. Before testing, all knitted fabric samples were conditioned in accordance with ISO 139:2005 under standard atmospheric conditions. ²⁴

The stitch density was determined as the number of wales (W) and courses (C) per centimeter, which was measured on each side of the fabrics (technical face W_f, C_f, and technical back W_b, C_b) in accordance with EN 14971:2006. ²⁵ Each value shown is the average of 10 separate measurements on each side of the fabric, taken at different sample points. Using the measured wales (W) and courses (C) per centimeter, the stitch density (S) of the fabric was calculated for each side (technical face S_f and technical back S_b), based on the following equation:

$$\mathrm{S}=\mathrm{W}.\mathrm{C}(\mathrm{loops}/\mathrm{c}{\mathrm{m}}^2)$$

(1)

The stitch length in both variants of the knitted fabric was measured for each type of the knit stitch in the height repeat and expressed as the average yarn length per stitch, following EN 14970:2006 ²⁶ and GOST 8846-87. ²⁷ Measurements covered an area with 50 wales. Each value shown is the average of ten measurements for both stitch lengths (the stitch length for the knit stitch produced first yarn feeder l₁ and second yarn feeder l₂). The average stitch length (l_a) was then calculated from the individual stitch lengths using the equation:

$${\mathrm{l}}_{\mathrm{a}}=\frac{{\mathrm{l}}_1+{\mathrm{l}}_2}{2}\left(\mathrm{mm}\right)$$

(2)

The fabric’s weight or mass per unit area (W) was measured according to EN 12127:1997. ²⁸ Results are averaged from five measurements per fabric variant.

Fabric thickness (t) was determined in accordance with ISO 5084:1996 ²⁹ using an SM-124 thickness. The measurement was conducted under a pressure of 2.5 N/cm² (25 kPa) over a 1 cm² area. Each value is the average of ten measurements taken at different locations on each sample.

Dimensional Changes of the Knitted Fabrics After Washing

Before testing, all knitted fabric samples were conditioned under standard atmospheric conditions for 48 h of dry relaxation in accordance with ISO 139:2005. ²³ After a dry relaxation, all fabrics were washed following the procedure outlined in ISO 6330:2021. ³⁰ The washing process included four complete cycles.

After each washing cycle, the samples were laid flat and allowed to dry under controlled environmental conditions for at least 24 h. For each fabric variant, nine measurements were taken in both the length and width directions, and the results are reported as average values.

To assess the stability of the knitted fabrics, the lengthwise (DC_l) and widthwise (DC_w) dimensional changes were measured in accordance with ISO 5077:2007. ³¹ These changes were then calculated using the following equation, allowing for a quantitative evaluation of fabric shrinkage (“−”) or expansion (“+”) after washing:

$$\mathrm{DC}=\frac{\mathrm{FM}-\mathrm{OM}}{\mathrm{OM}}.100[\%]$$

(3)

where DC – dimensional changes of the knitted fabrics (%); FM – final measurement (mm); OM – original measurement before first washing (mm; OM = 200 mm).

Based on the experimental data, the calculated theoretical dimensional change (DC _t ) during washing cycles.^20,21 The theoretical dimensional change (DC _t ) is determined using the equation:

$$\mathrm{D}{\mathrm{C}}_t=\frac{\mathrm{k}}{\mathrm{a}+\mathrm{b}.\mathrm{k}}[\%]$$

(4)

where k – the number of washing cycles; a and b – the material-specific constants.

As k → ∞, the potential total dimensional change approaches the limiting value 1/b.

Statistical Analysis

The statistical analysis used the Student’s t-test:

• For the independent sample was determined by applying the equation:

$$\mathrm{t}=\frac{|\overline{{\mathrm{x}}_1}-\overline{{\mathrm{x}}_2}|}{\sqrt{\frac{{\sigma }_1^2.({\mathrm{n}}_1-1)+{\sigma }_2^2.({\mathrm{n}}_2-1)}{{\mathrm{n}}_1+{\mathrm{n}}_2-2}.\frac{{\mathrm{n}}_1+{\mathrm{n}}_2}{{\mathrm{n}}_1.{\mathrm{n}}_2}}}$$

(5)

• For the dependent sample, it was calculated using the equation:

$$t=\frac{\overline{\left|d\right|}}{\frac{{\sigma }_d}{\sqrt{n}}}$$

(6)

where ${\overline{x}}_1$ and ${\overline{x}}_2$ are the samples’ mean values of the determined characteristic; ${\sigma }_1$ and ${\sigma }_2$ are the samples’ standard deviation of the determined characteristic; n₁ and n₂ are their corresponding sample sizes (n₁ = n₂); $\overline{d}$ is the sample mean value of the differences of the determined characteristic of the knitted fabrics in dry-relaxed and wet-relaxed states; ${\sigma }_d$ is the sample standard deviation of the differences, while n is the sample size (n = 10 for the number of wales W and courses C; the length of yarn l₁, l₂, and l_a; the fabric thickness t; n = 5 for the weight W).

Results and Discussion

The Structural Characteristics

The Number of Wales and Courses, and Stitch Density

As noted earlier, the width repeat of double weft knitted fabrics with float loops is a key structural parameter that strongly influences the fabric’s structural characteristics.^21,22 In contrast, the number of washing cycles does not appear to have a significant effect on the dimensional changes of double weft knitted fabrics with float loops. Therefore, in this study, the structural characteristics were primarily evaluated after the first washing (WR1), as this stage is known to be critical, while four washing cycles (WR4) were selected for comparative analysis.

The results showed that both the relaxation state of the knitted fabrics, whether dry-relaxed (DR) or wet-relaxed (WR), and the fabric variant significantly affected the structural features (Figure 3).

Figure 3.

The number of wales (W_f, W_b) and courses per centimeter (C_f, C_b), fabric stitch density (S_f, S_b) for the technical face: (a) and back (b) side of the knitted fabrics, respectively, including the different states of fabrics.

The structure of the knitted variants influenced differences in the structural characteristics between the face and back sides in several ways (Figure 3). The number of wales on the face side (W_f) was generally lower for both fabric variants and fabric states, varying by up to 6.4% compared with the back side (W_b). The extent of these changes was dependent on the fabric variant. Specifically, for variant I, the number of wales decreased by 6.4% on the face (W_f) and 2.3% on the back (W_b). In variant II, the decrease was more significant, with wales reducing by 11.3% on the face (W_f) and 18.1% on the back (W_b). A more noticeable effect was observed in the number of courses, which can be attributed to the specific arrangement of the knit stitches: variant I has an unbalanced stitch (two rows on the face and one on the back). In comparison, variant II has a balanced stitch (two rows on both the face and back sides). For variant I, the number of courses on the face side (C_f) was 26.6% lower in the dry-relaxed state (DR) and 22.0% lower after washing (WR1 and WR4) than on the back side (C_b). Conversely, variant II showed the opposite trend, with the number of courses on the face side (C_f) being higher in the dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states than on the back side (C_b). This trend was reflected in the fabric stitch density, which decreased for variant I in dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states on the face side (S_f) compared with the back side (S_b). In contrast, for variant II, the fabric stitch density on the face side (S_f) was higher in the dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states than on the back side (S_b).

The observed variations in the number of wales and courses on both sides of the examined knitted fabric variants exerted a significant influence on the fabric stitch density (S_f and S_b), as illustrated in Figure 3. For variant I, the stitch density on the face (S_f) and back (S_b) sides increased by 7.9% and 19.9%, respectively, after the first washing (WR1) compared with the dry-relaxed state (DR). During the subsequent washing (WR4), the stitch density of the face side (S_f) remained practically unchanged, whereas that of the back side (S_b) increased by an additional 6.0% relative to its value after the first washing (WR1). In contrast, the stitch density of the face side (S_f) of variant II remained stable, while that of the back side (S_b) decreased by 6.2% compared with the dry-relaxed fabric (DR). In the wet-relaxed state (WR4), the stitch density on the back side (S_b) of variant II increased by 5.0% compared with that of the fabrics after the first washing (WR1).

The comparison of the fabric stitch densities for variants I and II revealed distinct differences between the face and the back sides. The fabric density on the face (S_f), variant I, exhibited a 13.3% in stitch density in the dry-relaxed state (DR) and a 19.6% decrease after the first washing (WR1). In contrast, the stitch density of the back side (S_b) showed the opposite trend. The fabric stitch density on the face (S_b) in variant I was higher by 67.2% and 30.8% than that in variant II in the dry-relaxed (DR) and wet-relaxed (WR1) states, respectively. These differences can be attributed to the approximately double number of courses per centimeter on the back side of variant II compared with variant I.

The Stitch Length

The stitch length varied depending on the fabric variant and the state of the knitted fabrics (Figure 4).

Figure 4.

The stitch lengths (l₁, l₂, l_a) of the knitted fabrics, including both variants and states.

The fabric variant significantly influenced stitch length, which is determined by the type of knit stitches in each variant’s repeat. The presence of single missed stitches in the repeat of variant I significantly increased the stitch length in the missed stitches by 50.2% compared with the stitch length of the 1 × 2 rib of variant II (both types of knit stitches produced by the second yarn feeder). These differences can be attributed to variations in the knit structure (single miss stitch and 1 × 2 rib stitch) and the methodology used to determine stitch length. In single miss stitches, the stitch length comprises both knit and miss loops, whereas in the 1 × 2 rib, it consists solely of knit loops. This structural difference has a pronounced effect on the measured stitch length of the knit stitch.

The state of the knitted fabrics depends on the stitch length. After the first washing (WR1), the stitch length of all knit stitches increased. For variant I, the 1 × 1 rib stitch length (l₁) increased by 40.1% after the first washing (WR1) and by 6.7% after the fourth washing (WR4); for variant II, this increase was 10.7% after the first washing (WR1) compared with the dry-relaxed state (DR) and then remained relatively stable with subsequent washings.

The variations in stitch length per knit stitches (l₁, l₂) in the examined fabric variants significantly affected the average stitch length (l_a), as shown in Figure 4.

The Weight and Thickness

The weight (W) and thickness (t) of the examined fabrics were influenced by both fabric variant and the state of the knitted fabrics (Figure 5).

Figure 5.

The weight (W) and thickness (t) of the knitted fabrics, including both variants and states.

For variant I, the fabric weight (W) in the dry-relaxed state (DR) increased by 13.8% compared to after the first washing (WR1), followed by a 8.2% reduction after the fourth washing (WR4) relative to after the first washing (WR1). The thickness (t) exhibited a similar trend, increasing by 12.7% after the first washing and then slightly decreasing (2.0%) after the fourth washing (WR4). A comparable trend was observed for variant II, where the fabric weight (W) increased by 6.6% after the first washing (WR1), and subsequently decreased by 8.1% after the fourth washing (WR4) relative to the first washing (WR1). The thickness (t) increased after the first washing (WR1) and remained constant thereafter, up to the fourth washing (WR4).

When comparing the two variants, variant I remained on average 7.5% heavier and 13.0% thicker than variant II across all washing stages. This difference can be attributed to the more compact, structurally complex combination of 1 × 1 rib and single miss stitches in variant I, which results in higher weight (W) and greater fabric bulk than the 1 × 1 and 1 × 2 rib structures of variant II.

The overall behavior suggests that initial washing induces structural relaxation and compaction, resulting in increased fabric density and thickness. Subsequent washing, however, causes partial structural recovery and stabilization, as the yarns reposition and internal stresses are released. These findings highlight the influence of fabric structure on dimensional stability and the different responses of rib-based knitted structures to repeated washing.

Statistical Analysis (t-Test) of the Structural Characteristics

The statistical results for determining the structural characteristics of knitted fabrics in the dry-relaxed (DR) and wet-relaxed (WR1, WR4) states, using a t-test for independent samples (Table 1) and for dependent samples (Table 2), are shown.

Table 1.

Statistical analysis (t-test) of the structural characteristics of knitted fabrics for DR and WR (WR1, WR4) states for independent samples.

	Values of the parameter tI/II (df = n1 + n2 − 2 = 18 for Wf, Cf, Sf, Wb, Cb, Sb, l1, l2, la, t and df = n1 + n2 − 2 = 8 for W)
Fabric state	Wf	Cf	Sf	Wa	Ca	Sa	la	W	t
DR	0.3 -	12.9 a	5.5 a	3.7 b	24.9 a	18.9 a	136 a	1.9 -	3.7 b
WR1	2.4 c	13.6 a	10.2 a	4.4 a	10.5 a	6.3 a	347 a	6.7 a	4.9 b
WR4	3.7 b	13.0 a	8.1 a	5.3 a	23.4 a	11.4 a	226 a	4.8 b	5.7 a

DR: dry-relaxed state; WR1: first washing; WR4: fourth washing; I and II: variant of fabrics; d_f: degree of freedom; WR: wet-relaxed.

-

No statistically significant difference.

a

Level of significance 0.001.

b

Level of significance 0.01.

c

Level of significance 0.05.

Table 2.

Statistical analysis (t-test) of the structural characteristics of knitted fabrics after DR and WR (WR1, WR4) states for dependent samples.

	Values of the parameter t (df = n − 1 = 9 for Wf, Cf, Sf, Wb, Cb, Sb, l1, l2, la, t and df = n − 1 = 4 for W)
	Variant I			Variant II
Tested parameter	t I-DR/I-WR1	t I-DR/I-WR4	t I-WR1/I-WR4	t II-DR/II-WR1	t II-DR/II-WR4	t II-WR1/II-WR4
Wf	3.0 c	2.5 c	0.3 -	8.0 a	7.7 a	2.3 c
Cf	12.6 a	17.8 a	1.3 -	10.2 a	14.2 a	3.3 b
Sf	3.3 b	2.5 c	0.4 -	0.1 -	0.5 -	0.6 -
W-	0.9 -	0.9 -	3.0 c	10.2 a	6.8 a	1.2 -
C-	4.7 b	11.4 a	0.4 -	6.5 a	10.9 a	0.8 -
S-	3.3 b	8.5 a	1.4 -	5.1 a	0.5 -	1.8 -
lc	258.6 a	322.0 a	63.4 a	47.4 a	65.3 a	17.9 a
W	4.5 b	1.3 -	6.9 a	1.6 -	0.4 -	2.5 c
t	8.7 a	3.7 b	0.9 -	4.4 b	4.0 b	0.2 -

DR: dry-relaxed state; WR1: first washing; WR4: fourth washing; I and II: variant of fabrics; d_f: degree of freedom; WR: wet-relaxed.

-

No statistically significant difference.

a

Level of significance 0.001.

b

Level of significance 0.01.

c

Level of significance 0.05.

The results of the t-test (Table 1) show statistically significant differences in the number of courses between the face (C_f) and the back (C_b) sides. These differences led to corresponding variations in stitch density (S_f and S_b) on both sides, with all comparisons across the dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states demonstrating high significance at the 0.001 level. The number of wales on the back side (W_b) varied significantly across all states, with significance levels of 0.01 in the dry-relaxed (DR) state and 0.001 in the wet-relaxed states (WR1, WR4). This result shows that the structural difference between the face and back sides significantly affects how stitches form and are distributed. The continued presence of statistically significant differences across all washing stages confirms that fabric structure has a substantial, consistent impact on stitch density, even as washing induces dimensional changes.

The statistical analysis also showed significant differences in the weight (W) and thickness (t) of the investigated knitted fabrics. In the case of fabric thickness (t), significant differences were detected in the dry-relaxed (DR) and wet-relaxed (WR1) states, with a significance level of 0.01 in both the dry-relaxed state (DR) and after first washing (WR1), and a higher significance level of 0.001 after the fourth washing (WR4). These results indicate that both structural parameters (wales and courses) and dimensional characteristics (weight and thickness) are strongly influenced by washing, especially in the later stages, where fabric compaction and yarn rearrangement become more pronounced.

The t-test results for the structural characteristics of knitted fabrics in the dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states (Table 2) showed statistically significant changes in most parameters, confirming that the washing process significantly impacts the fabric structure and dimensional behavior. For both fabric variants, significant changes were observed mainly between the dry-relaxed (DR) and wet-relaxed (WR1 and WR4) states.

The Dimensional Changes

The results of the dimensional change measurements after successive washing cycles (WR1–WR4) are presented in Table 3. Based on the received results, the values of the a and b constants, along with the potential total dimensional change widthwise, expressed as 1/b, for knitted fabrics, are presented in Table 4. Figure 6 shows the experimental (ex) and theoretical (t) dependencies of the lengthwise (DC_l) and widthwise (DC_w) dimensional changes on the number of washing cycles (k) for fabric variants I and II.

Table 3.

The experimental dimensional changes of the double knitted fabrics.

		The values of the dimensional changes of the knitted fabrics after four washing cycles (%)
The direction of the changes	Fabric variants	WR1	WR2	WR3	WR4
Lengthwise DCl	I	−14.06 ± 1.84	−15.06 ± 2.07	−15.44 ± 1.65	−14.50 ± 2.52
	II	−11.61 ± 2.46	−10.44 ± 2.82	−11.33 ± 2.98	−10.17 ± 2.67
Widthwise DCw	I	6.44 ± 1.81	10.17 ± 2.96	10.39 ± 2.46	11.17 ± 1.54
	II	24.11 ± 5.24	26.06 ± 4.45	28.28 ± 5.76	34.56 ± 7.38

Table 4.

The calculated values of a and b constants, the potential total dimensional change widthwise 1/b for knitted fabrics.

	Constant
Fabric variant	a	b	Potential total dimensional change, 1/b	Dependence
I	−0.004	−0.066	−15.23	$\mathrm{D}{\mathrm{C}}_{\mathrm{l}}=\mathrm{k}/(-0.004-0.066.\mathrm{k})$
	0.074	0.072	13.97	$\mathrm{D}{\mathrm{C}}_{\mathrm{w}}=\mathrm{k}/(0.074+0.072.\mathrm{k})$
II	0.005	−0.095	−10.55	$\mathrm{D}{\mathrm{C}}_{\mathrm{l}}=\mathrm{k}/(-0.005-0.095.\mathrm{k})$
	0.017	0.027	36.70	$\mathrm{D}{\mathrm{C}}_{\mathrm{w}}=\mathrm{k}/(0.017+0.027.\mathrm{k})$

Figure 6.

Ex and t dependence of DC_l and DC_w on the number of washing cycles (k) for fabric variants I and II: (a) DC_l and (b) DC_w.

As shown in Figure 6, it demonstrates that both fabric variants (I and II) experienced significant shrinkage in the length direction (DC_l) and expansion in the width direction (DC_w).

In the length direction (DC_l), both fabrics showed a negative dimensional change, indicating shrinkage. Variant I exhibited greater shrinkage than variant II across all washing stages, suggesting that its structure or yarn composition was more prone to relaxation shrinkage. The results indicate that, as expected, the knitted fabrics of both variants tend to shrink significantly in length during the first two washing cycles (WR1, WR2). This result is consistent with previous findings for double weft knitted fabrics produced from flax-containing yarns. ¹⁴

In the width direction (DC_w), both variants showed positive dimensional changes, indicating fabric widening with repeated washing. The knitted fabrics of both variants (I and II) tend to expand significantly in width during the first two wash cycles (WR1, WR2). The same trend is mentioned in the papers.^21,22 Overall, the data suggest that fabric variant I was more dimensionally stable, exhibiting moderate shrinkage and limited width expansion, while variant II experienced more pronounced deformation, especially in the width direction. This behavior indicates differences in structural compactness or fiber relaxation properties between the two fabric variants. This trend suggests that a single miss stitch, combined with a 1 × 1 rib structure, in variant I has a greater impact on dimensional stability than the 1 × 2 rib and 1 × 1 rib configurations used in variant II. This can be explained by the presence of knit loops with longer float loops in the single miss stitch (variant I) compared to fabric variant II with 1 × 2 rib stitches. The widthwise dimensional changes in variant I after all washing cycles were approximately three times smaller than those observed in variant II. However, the lengthwise dimensional changes in variant I were about 1.3 times higher than those measured for variant II across all four washing cycles. The same trends were observed for the potential total dimensional change in both directions, presented in Table 4.

Statistical Analysis (t-Test) of the Dimensional Changes

The statistical results for determining the dimensional changes of knitted fabrics, using a t-test for independent and dependent samples, are shown in Table 5.

Table 5.

The statistical results for determining the dimensional changes after four washings for independent samples using the t-test.

	Value of parameter (tI/II) between fabric variants I and II (df = n1 + n2 − 2 = 16)
Tested parameter	WR1	WR2	WR3	WR4
DCl	2.4 c	4.0 b	3.6 b	3.5 b
DCw	9.6 a	8.9 a	8.6 a	9.3 a

WR1, WR2, WR3, and WR: first, second, third, and fourth washing, respectively; I and II: variant of fabrics; d_f: degree of freedom.

a

Level of significance 0.001.

b

Level of significance 0.01.

c

Level of significance 0.05.

The results of the t-test for independent samples (Table 5) showed statistically significant differences in both lengthwise (DC_l) and widthwise (DC_w) dimensional changes between fabric variants I and II after each washing cycle. In the length direction (DC_l), significant differences were observed across all washing cycles, with p values of 0.05 after the first wash and 0.01 after the second, third, and fourth washes. In the width direction (DC_w), even more noticeable differences were observed at the 0.001 significance level across all four washes, indicating a greater structural sensitivity of the fabrics to widthwise deformation during washing. These results suggest that variant I exhibited greater dimensional stability in width, while variant II showed a higher tendency for lateral expansion, likely due to differences in loop configuration and stitch density between the two fabric variants.

Conclusion

Structural differences among fabric variants significantly affect the dimensional stability of 100% flax double weft knitted fabrics. Variant I, combining a 1 × 1 rib with a single miss stitch, forms an unbalanced structure characterized by fewer courses per centimeter on the face, higher stitch density on the back, longer average stitch lengths in the float loops, and greater weight and thickness. In contrast, variant II, combining a 1 × 1 rib with a 1 × 2 rib, creates a more balanced structure with lower stitch density, shorter stitch lengths, and reduced weight and thickness. These differences in stitch configuration directly affect stitch geometry and dimensional stability, underscoring the critical role of structural design in optimizing knitted fabric performance.

Washing induced notable changes in both knitted fabric variants. The first wash led to structural relaxation and compaction, accompanied by an increase in stitch length, whereas subsequent washings resulted in partial recovery and minor adjustments. Variant I exhibited relatively stability, characterized by reduced widthwise expansion and more predictable lengthwise shrinkage. In contrast, variant II showed greater structural variability and a greater tendency toward lateral expansion.

These results indicate that the combination of a single miss stitch with a 1 × 1 rib structure in variant I exerts a stronger stabilizing effect on dimensional behavior than the 1 × 2 rib with a 1 × 1 rib configuration used in variant II. After all washing cycles, widthwise dimensional changes in variant I were approximately three times smaller than those observed in variant II. Conversely, the lengthwise dimensional changes in variant I were about 1.3 times greater than in variant II across all subsequent washing cycles. Similar patterns were observed for the total dimensional change in both directions.

Statistical analysis confirmed significant differences in both structural parameters (wales and courses) and dimensional characteristics (weight, thickness, and dimensional changes) across all washing cycles, emphasizing the critical role of stitch structure and loop configuration in fabric behavior.

For applications requiring high-dimensional stability, such as garments subject to repeated washing, fabrics with unbalanced rib-miss combinations, as in variant I, are recommended. This configuration provides improved widthwise stability and controlled lengthwise shrinkage while maintaining consistent structural performance.