Knitted fabrics are characterized by comfort compared to woven fabrics due to their high extensibility, air permeability, and heat retention, but they have low-dimensional stability, especially single jersey knitted fabrics (SJKF), after repeated washing. Therefore, the additional Lycra (elastane) yarns are used to maintain the dimensions of knitted fabrics during use and after repeated stresses.
Recently, the core and dual-core-spun (DCS) yarns are commonly used in stretched denim woven fabrics and there are some researches that evaluated the properties of denim fabrics produced from these yarns. The effect of linear density, twist multiplier, stretch percentage, and applied load on tenacity and elastic performance of cotton/Lycra core-spun denim yarn was investigated . Due to its lower linear density, stretch, and twist multiplier, the cotton/Lycra core-spun yarn has better elastic performance. The weight, size, elasticity, tensile strength, and cost properties of the denim fabrics woven with the dual-core weft yarn with different densities were evaluated .
In stretched knitted fabric, the additional Lycra (full- and half-plated) and core-spun yarn are used, and there are many researches that evaluated the geometrical and mechanical properties of these fabrics. Dimensional characteristics of core-spun cotton/Lycra interlock structures with high, medium, and low tightness factors were studied under dry, wet, and full relaxation conditions . The effect of knitting yarn feeding load on the alteration in the mechanical properties of plated plain knitted fabrics was studied . The relation between Lycra consumption and fabric dimensional and elastic behavior was investigated . The dimensional and physical properties of cotton/spandex SJKF were investigated [6,7,8,9] and the effect of extension percentage of bare Lycra yarns during loop formation on the geometrical, physical, and mechanical properties of plain jersey fabrics was studied . According to the previous research, the elastane fibers had a significant effect on the geometrical properties of elastic knitted fabric. As the fabric weight, thickness, and stitch density increased, the air permeability and spirality decreased compared to 100% cotton fabric.
Limited research discussed the effect of dual-core yarns on the properties of knitted fabrics. The properties of the weft knitted fabrics with different structures (single jersey, rib 1 × 1, and full cardigan) produced from core and DCS yarns at different levels of loop length were compared . Results showed that the yarn type had a significant effect on fabric recovery, elasticity, and shrinkage. However, it had insignificant effects on drapability, thermal resistivity, and air permeability. So, more research is required to investigate the properties of stretchable knitted fabric produced from DCS yarns compared to other Lycra states.
This research aims to investigate the geometrical and thermal properties of stretched knitted fabrics produced from cotton yarns with additional Lycra (full-plated), cotton/Lycra core-spun, and DCS yarns and then compare the results with the 100% cotton fabric samples.
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 αe), 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%.
The knitted yarns characteristics
|Yarn types||Dual core||Core|
|Yarn composition||Cotton 24.1 Ne (52.5%)/polyester 33.86%/elastane 13.64% (117 dTex)||Cotton 24.2 Ne (85.02%)/elastane 14.98% (117 dTex)|
|Linear density (Ne)||24.1||24.2|
|Yarn twist (TPI)||22.58||22.63|
|Irregularity, C.V. (%)||10.16||11.5|
|Mean elongation at break (%)||10.9||5.08|
|Minimum elongation at break (%)||9.97||4.72|
|Mean tenacity (cN/Tex)||12.06||10.07|
|Minimum tenacity (cN/Tex)||11.35||9.47|
|Mean breaking force (cN)||295.4||245.7|
The fabric recovery was evaluated by calculating the permanent set using a method similar to the ASTM D3107 for denim fabrics  but using a constant rate of elongation instead of the constant rate of loading . 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).
The fabric thickness was measured according to ASTM D1777. The fabric bulk density was calculated using the following formula :
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 Results and discussion
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.
The dimensional properties of fabric samples
|Yarn types||Fabric thickness (mm)||Fabric weight (g/m2)||Bulk density (kg/m3)||Stitch density (cm−2)|
|Dual core spun||0.99||385.1||376||502|
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.
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.
The results of variance analysis (P value at 95% confidence interval)
|Permanent set||Lycra state||0.001|
|Water vapor permeability||0.016|
|Overall moisture management capacity||0.015|
|Total hand value||0.014|
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.
3.4 Water vapor permeability
Water vapor permeability is the ability to transmit vapor out of the body . 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.
3.5 Thermal resistance and thermal absorptivity
If the thermal resistance of clothing is low, heat energy will tend to gradually decrease, giving rise to a cool feeling . 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 .
Thermal absorptivity is the objective measurement of the warm–cool feeling of fabrics at the first touch . 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) .
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.
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 . 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.
Fabric moisture management parameters
|Parameters||Symbols||100% cotton yarn||Full-plated yarn||Core-spun yarn||Dual-core-spun yarn|
|Wetting time top (s)||WTT||15.99||15.28||6.44||8.71|
|Wetting time bottom (s)||WTB||6.31||9.86||17.49||16.68|
|Top absorption rate (%/s)||TAR||39.29||33.41||38.88||42.29|
|Bottom absorption rate (%/s)||BAR||83.60||87.60||31.32||34.41|
|Top max wetted radius (mm)||MWRT||17||14||16||13.75|
|Bottom max wetted radius (mm)||MWRB||18||16||17||16.25|
|Top spreading speed (mm/s)||TSS||0.99||1.12||1.11||0.86|
|Bottom spreading speed (mm/s)||BSS||1.43||1.27||0.81||0.72|
|Accumulative one-way transport capacity||OWTC||382.89||276.67||−63.77||30.10|
|Overall moisture management capacity||OMMC||0.655||0.597||0.086||0.160|
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).
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 . 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.
Four different SJKF (100% cotton, cotton with full-platted Lycra, core, and DCS yarns) were produced to estimate the properties of cotton SJKF produced by different Lycra states. The thermal comfort properties, fabric recovery, THV, moisture management parameters, and air permeability were measured.
The results showed that the use of DCS yarns in the SJKF improves the fabric recovery by 100% at various tensile levels compared to sample produced from 100% cotton yarn, and by 55% compared to the full-plated fabric sample. The produced samples from core-spun and DCS yarns had the highest elongation at the same strength which gives extensibility and comfort. Thermal absorptivity of core and DCS samples increased by 27% and the water vapor permeability decreased by 18% compared to 100% cotton sample. Overall moisture management of dual sample decreased by 75% and air permeability dropped to 96% compared to 100% cotton samples, which gives discomfort feeling. The THV of dual sample reduced to 34% compared to full-plated fabric samples.
In general, the production process of knitted fabrics produced from core and DCS yarns is much easier than additional Lycra with cotton yarns in production because special Lycra feeders are needed. Also, the use of DCS yarns is better than the core-spun yarns, where the number of breaks and stops are lower, so the quality and productivity could improve.
This work is supported under Student Grant Scheme (SGS 21316) by Technical University of Liberec, Czech Republic.
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