Comprehensive Assessment of the Properties of Cotton Single Jersey Knitted Fabrics Produced From Different Lycra States

2.1 Materials

To investigate the effect of using the Lycra state on the properties of the SJKF, four different SJKF were produced using 100% cotton, cotton with additional Lycra (full-plated), core-spun, and DCS yarns, at the same loop length (3 mm) on KEUMYONG KM-3WVP circular knitting machine with Gauge 28, 30-inch diameter, and 90 feeders. The cotton yarn count is 24 Ne (Giza 86, combed, twist multiplier is 3.8 α_e), and the specifications of core and DCS yarns are listed in Table 1. All fabric samples were washed for three consecutive washing cycles at 60°C using laboratory laundering machine. Figure 1 presents the macroscopic images of all SJKF at two extension levels 20 and 40%.

Figure 1

The macroscopic images of evaluated knitted samples.

2.2 Methods

The fabric recovery was evaluated by calculating the permanent set using a method similar to the ASTM D3107 for denim fabrics [12] but using a constant rate of elongation instead of the constant rate of loading [11]. Knitted samples (30 x 5 cm²) were subjected to tension by using TENSOLAP tester with a gauge length 20 cm and applying five levels of extension, namely 15, 30, 45, 60, and 75% for 30 min. Later, the length of new samples was measured directly. Then the samples were kept at the standard conditions (20 ± 2°C and 65 ± 5% relative humidity) for 2 h before measuring its new length again. The permanent set before and after relaxation was calculated according to Eq. (1).

where L is the sample length after unloading and relaxation, and L_o is the original sample length.

The fabric thickness was measured according to ASTM D1777. The fabric bulk density was calculated using the following formula [13]:

where W is the fabric weight per unit area (g/m²), and t is the fabric thickness (mm).

Thermal comfort properties were measured for all fabric samples. Alambeta instrument was used to measure the dry thermal resistivity according to ISO EN 31092-1994, and relative water vapor permeability (RWVP) was tested by Permetest according to ISO 11092. Air permeability was measured by FX 3300-20 according to EN ISO 9237, and OMMC was measured by M 290 MMT according to ISO 9073-8. The fabric bursting strength was tested using Tinius Olsen material testing machine 500 according to ASTM D3787-2001. Total hand value (THV) was measured and calculated using Kawabata evaluation system (KES). The statistical analysis of variance (ANOVA) tests was applied using SPSS software to determine the significance levels of the Lycra state on all tested properties.

3.1 Geometrical properties

The geometrical properties of all samples (thickness, weight, bulk density, and stitch density) are shown in Table 2. The fabric thickness of full-plated samples and samples produced from core and DCS yarns increased by 9, 15, and 11%, respectively, compared to 100% cotton sample because the additional Lycra leads to stitch overlapping which increases the fabric thickness. The fabric linear density (g/m²) of elastic fabric is higher than 100% cotton fabric due to the higher stitch density.

3.2 Permanent set percentage

Figure 2 shows the relationship between the extension percentage and the permanent set percentage of the four knitted fabrics after relaxation in the standard conditions for 2 h. The 100% cotton fabric sample had the lowest dimensional stability. The permanent set percentage ranged from 2.5 to 21.5% and the extension percentage ranged from 15 to 75%, respectively, and this is the main disadvantage of knitted fabrics especially the SJKF. The permanent set of knitted fabrics decreased when the Lycra yarn was added for any Lycra state (full-plated, core, and DCS yarns). The permanent set of full-plated samples was within the acceptable level (<5%) but it reached 10% at the maximum extension 75%. Moreover, it is also noted that the permanent set of dual-core samples dropped to 0% at four levels of extension of 15, 30, 45, and 60%, and recorded only 2% at 75%. This is may be due to the polyester fibers proportion in the dual-core yarn construction, which in turn increases the yarn elongation, as previously illustrated in Table 1.

Figure 2

Effect of extension percentage and yarn type on permanent set percentage for single jersey knitted fabrics after relaxation.

The lowest number of stops was recorded during fabric production with DCS yarns compared to core-spun yarns because of the presence of 33.86% polyester fibers. However, this ratio of polyester might negatively affect the other knitted fabric properties. The statistical analysis confirmed that the effect of extension percentage and yarn type is significant, as shown in Table 3.

3.3 Bursting strength

Figure 3 shows the bursting test for the four different fabrics. The ball reached its maximum distance down but it did not penetrate all samples except the 100% cotton sample because of the high extensibility of Lycra. All samples had a good resistance to the bursting strength, but the stretched knitted fabric had a higher extension compared to 100% cotton samples. The produced samples from core-spun and DCS yarns had the highest elongation at the same strength which gives high extensibility and comfort. This may be due to the Lycra existence in the yarn core.

Figure 3

The relation between bursting strength and displacement for single jersey knitted fabrics.

3.4 Water vapor permeability

Water vapor permeability is the ability to transmit vapor out of the body [14]. Figure 4 illustrates the RWVP of all samples. It is noticed that the 100% cotton sample had the highest RWVP (65%) than the full-plated samples (53%) because of hydrophilic property of cotton fibers compared to Lycra and polyester fibers (moisture regain values are 8.5, 0.4, and 0.1% for cotton, polyester, and Lycra, respectively), and because they had the lowest stitch density as listed in Table 2. So, there are higher pore sizes that enable the water vapor to transmit compared to the samples produced from core-spun and DCS yarns. Therefore, if these fabrics (produced from core and DCS yarns) are used for underwear or summer t-shirts, it might give a discomfort feeling. This is a negative impact, and the statistical analysis showed that the Lycra state has a significant effect on the RWVP.

Figure 4

Effect of Lycra state on relative water vapor permeability percentage for single jersey knitted fabrics.

3.5 Thermal resistance and thermal absorptivity

Due to increase in the thickness of the produced samples by the core-spun yarn, as illustrated in Table 2, the thermal resistance increased as shown in Figure 5 according to Eq. (3).

where R is the thermal resistance (K.m².W⁻¹), λ is the thermal conductivity (W.m⁻¹.K⁻¹), and t is the fabric thickness (m).

Figure 5

Effect of Lycra state on thermal resistance of single jersey knitted fabrics.

If the thermal resistance of clothing is low, heat energy will tend to gradually decrease, giving rise to a cool feeling [15]. So, if these fabrics are used as winter clothes, they will retain the temperature of the human body and give a warm feeling due to their higher thermal resistance [16].

Thermal absorptivity is the objective measurement of the warm–cool feeling of fabrics at the first touch [17]. When the thermal absorptivity increases, it gives a cool feeling. Figure 6 displays the thermal absorptivity of the four SJKF. The thermal absorptivity increased by 20% for the full-plated samples and 27% for the samples produced from core and DCS yarns compared to 100% cotton sample. This may be because the cotton samples had the lowest stitch density, as shown in Table 3, according to Eq. (4) [18].

where b is the thermal absorptivity (W.S^1/2.m⁻².K⁻¹), λ is the thermal conductivity, ρ is the fabric density (kg/m³), and c is the specific heat capacity (J.kg⁻¹.K⁻¹).

Figure 6

Effect of Lycra state on thermal absorptivity of single jersey knitted fabrics.

So, these fabrics will give cool feeling more than 100% cotton fabric. The statistical analysis confirmed that the effect of Lycra state on thermal resistance and absorptivity is significant.

3.6 Air permeability

Figure 7 shows the air permeability of fabric samples with different Lycra state. The air permeability reduced by 96% in case of the produced samples from core-spun yarn and by 80% in the full-platted samples compared to 100% cotton sample due to the higher fabric density and stitch density. So, the spacing and pores between the loops (stitches) and each other decreased. The statistical analysis showed that the effect of Lycra state on the air permeability is significant.

Figure 7

Effect of Lycra state on air permeability for single jersey knitted fabrics.

3.7 Moisture management parameters

The results of moisture management parameters were summarized in Table 4. Figure 8 displays the accumulative one-way transport capacity (OWTC) of samples with different Lycra states. The OWTC is defined as the difference in the accumulative moisture content between the top and bottom layers of the fabric in the unit of testing time period [19]. The full-plated and 100% cotton samples had the largest OWTC, and this may be due to decrease in the stitch density which achieves more possibility of water penetration in voids and the higher cotton fibers volume fraction compared to the produced samples from core and DCS yarns, so it absorbs much water. Therefore, the fabric can transmit the sweat from the body surface to the fabric surface quickly. The 100% cotton sample had the highest OWTC than the full-plated sample. The OWTC of the sample produced from DCS yarns is higher than the sample produced from core-spun yarn. So, the sweat will transfer much faster in case of the sample produced from DCS yarns compared to core-spun yarns.

Figure 8

Effect of Lycra state on one-way transport capacity single jersey knitted fabrics.

The overall moisture management capacity (OMMC) is a term that indicates how the fabric is capable of managing the moisture transfer. It can be measured and calculated as follows [19, 20, 21]:

where C₁ = 0.25, C₂ = 0.5, and C₃ = 0.25 are the weights of bottom absorption rate (BAR), OWTC, and bottom spreading speed (BSS), respectively.

It is known that the higher the OMMC, the higher the overall moisture management ability of that fabric. Figure 9 displays the effect of Lycra state on the OMMC. It can be concluded that OMMC of the 100% cotton and full-plated samples are higher than the produced samples from core and DCS yarns because they had higher values of BAR, OWTC, and BSS due to the higher water absorption of cotton fibers. So, the ability of managing the moisture transfer of the 100% cotton and full-plated fabrics is better than the produced samples from core and DCS yarns. The effect of the Lycra state on the overall moisture management is significant as demonstrated in the statistical analysis (see Table 3).

Figure 9

Effect of Lycra state on overall moisture management capacity for single jersey knitted fabrics.

3.8 Total hand value

The primary HV and THV of all samples were determined by KES where 16 properties were measured. The system uses multivariate regression to relate the subjective assessment results completed by the Japanese experts to the objectively measured data on the KES-F instruments and to formulate the equations for HV calculation. The primary hand properties depend on the end use of the fabric. Those samples are used as winter lady thin wear, so the primary hand properties are Koshi (stiffness), Numeri (smoothness), and Fukurami (fullness and softness). Primary HV is ranked from 0 to 10 corresponding to the intensity of feeling whereas the large number corresponds to the strong feeling of hand. THV was standardized using a scale of 0–5 from unacceptable to excellent [22]. Figure 10 shows the HV and THV of different samples of Lycra state. THV of fabric sample produced from 100% cotton yarn was the highest. This value decreased with sample produced from additional Lycra, core-spun, and DCS yarns by 17, 38, and 45%, respectively. This is may be due to the structural properties of each yarn.

Figure 10

Primary hand value and total hand value of different Lycra state,