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Thermal Resistance of Gray Modal and Micromodal Socks

  • Zenun Skenderi EMAIL logo , Lubos Hes , Beti Rogina-Car and Dora Hranilović
Published/Copyright: October 1, 2022
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AUTEX Research Journal
From the journal AUTEX Research Journal Volume 23 Issue 3

Abstract

Men's socks were produced on a Lonati circular knitting machine in 18 different combinations in multi-plated plain jersey from basic modal and basic micro modal yarn with the addition of cotton or PA multifilament yarn and elastane yarn in the sock cuff. The modal and micromodal yarns were ring-spun, rotor-spun and air-spun; they consist of 38 mm long staple fibres with a fineness of 1.3 and 1.0 dtex respectively. Thermal resistance was determined by use of the thermal foot. The thermal resistance values for all socks samples range from 0.0091 to 0.01586 m2 °C W−1. The highest thermal resistance per groups of basic modal fibres was obtained in the samples made of air-jet spun yarn of 0.0132 m2 °C W−1 and the lowest in samples of rotor yarn of 0.0109 m2 °C W−1. The highest thermal resistance in all groups of basic micromodal samples made of ring yarn (0.0132 m2 °C W−1) and the lowest in the samples made of air-spun yarn (0.0099 m2 °C W−1). At low levels of thermal resistance, as the thickness of the sample of basic modal and micro modal fibres of ring and rotor yarns increases, the thermal resistance of socks increases with a correlation coefficient of 0.711. The tested sock samples have low thermal resistance, i.e. they can conduct heat better than the sock leg, thus achieving cooling and comfort, which is important for wearing socks in warm weather.

Keywords: socks; modal; thermal resistance; thermal foot; comfort

1. Introduction

Socks, in dependence on environmental exposures (neutral/cold/warm) and level of activity (rest, walk, exercise, run, recovery) are primarily worn to provide: 1) insulation in order to maintain foot skin temperature for comfort and cold-related injury 2) to reduce frictional forces as a major determinant of blister formation, and 3) to mediate buil-up moisture within the layers (air and textile) between the skin and footwear [1]. Socks used in everyday life that adhere to the skin are made of knitted fabrics, as their specific structure and stretchability allow them to adapt well to the body and provide a high level of wearer comfort. The properties and structure of socks are predominantly defined by: type of raw material and its parameters (cotton, modal, blends, Polyamide, elastane), type of yarn (ring, rotor, air jet, filament, etc.), yarn fineness and socks pattern. Textile fibres as polymeric materials are widely used in various engineering fields from the field of clothing (including socks) to the technical field such as fibre-reinforced composites [2]. Today, cotton is the predominant fibre used to it make socks. Cotton fibre production will not be sufficient in the future to meet the needs of the earth's population growth due to limited cotton acreage. Therefore, regenerated cellulose fibres such as modal, viscose and Lyocell are used to meet people's needs in garment production. The share of regenerated cellulose fibres in global fibre consumption increased to more than 7 million tonnes (more than 6%) in 2019 compared to the previous year [3]. Modal fibres (CMD) are obtained using a viscous technological process of spinning from a solution, but from higher quality wood pulp and with different process parameters [4]. Compared to viscose fibres, modal fibers are characterised by a higher dry and wet strength and a lower elongation at break. The most common products made of modal fibres are underwear, pyjamas, socks and household linen. As modal fibres are expensive than cotton, they are often blended with cotton in the form of fibres or in the manufacture of garments in the form of yarn. Socks made of modal fibres have a stronger lustre, feel soft and are more expensive than products of the same structure made of cotton or viscose fibres.

One of the properties of socks is certainly thermal comfort, which is also determined by the amount of thermal resistance. The thermal resistance of socks, to a certain level of human load and certain environmental conditions depends largely on the type of raw material, the structure of the knitted fabric and sewing patterns. The wearing comfort of socks, is determined by objective and/or subjective methods [5]. Thermal and water-vapour resistance of textile fabrics is usually determined on the basis of the sweating guarded hotplate test according to ISO 11092 [6], while thermal and water-vapour resistance of garments, resp. socks is determined using the so-called Thermal manikins, resp. the Thermal Foot”. More specifically, Kuklane [7] states that the thermal foot method is more advanced compared to the existing prEN-344 1999 standard (withdrawn from 08.11.2004.).

There are several published papers dealing with the wearing comfort of knitted fabrics and garments that do or do not adhere directly to the skin, while the number of published papers dealing with the wearing comfort of socks is nevertheless smaller. Kuklane [8] investigated the thermal resistance of boots (without socks) made of different materials using the thermal foot as well as the subjective well-being of test persons. He states, among other things, that the physiological parameters of the human being and the insulation values of shoes and socks are decisive in certain activities and environmental conditions in order to achieve a balance between the heat generated by the blood circulation and heat loss. Kuklane [9] also studied the comfort of footwear combined with socks in a cold environment. I Insulation (thermal resistance) values were determined with the thermal foot models (F2 and F3) placed on a copper/zinc alloy plate. He found that thick socks add overall foot thermal resistance compared to thin ones (by 5 to 11%). Vasanth Kumar and Raja [10] investigated the thermal comfort of socks knitted in single jersey structure from PES, cotton and their blends. They used the Alambeta Textile Tester (Sensora Instruments, Czech Republic). They concluded that polyester (recycled) fibre socks achieve higher thermal resistance than cotton socks. Özdil [11] investigated the thermal comfort of socks made of different raw materials (wool, PAN, Cotton, PA, some blends), by measuring the thermal resistance with the Alambeta instrument. They concluded, among others, that socks containing PA fibers give high values of thermal conductivity and heat absorption. Chiukas et al., in their papers [12, 13], investigated the thermal comfort properties (air permeability, thermal conductivity coefficient and thermal resistance) of platted knitted fabrics with different basic materials with the addition of textured PA and elastane (Lycra). Thermal conductivity was measured with a measuring device which operating pripciple was described in their first paper. They concluded, among others, that using two or three yarns in the knit allows to control air permeability, the thermal conductivity coeffiecient and thermal resistance. Cimili and Özdemir [14] investigated the thermal properties of socks made of different types of fibers (Cotton, Modal, Viscose, Micro modal, Bamboo, Chitosan and Soybean), and used a “special experimental setup” for measuring thermal resistance. They concluded that the fiber type seems to markedly affect the comfort properties. Van Amber and et al.[15] state that the most thermal and moisture transfer properties of sock are affected by fabric variables via two different mechanisms: fabric thickness, and the density and arrangement of fiber and yarns. Rogina-Car et al [16, 17] investigated the thermal resistance of socks made of viscose (ring) and tencel (ring, rotor and air-jet) base yarn with the addition of PA multifilament yarn or cotton yarn of the same knitted structure, using a thermal foot.

As socks today are mainly made of cotton yarn with a small addition of multifilament polyamide yarn and elastane, this paper will investigate the thermal resistance of socks containing modal / micromodal yarn (as a basic yarn) of the same fineness with the addition of PA. multifilament yarn of different fineness and coarser cotton yarn, using a thermal foot [8, 19]. By selecting a larger number of basic modal and micromodal yarns, which is less common for commercial sock samples, the aim of this paper is to investigate the influence of modal fibers and their fineness (1.3 dtex and 1 dtex) as well as the type of basic yarn (ring, rotor, air-jet) on thermal resistance of socks.

2. Experimental

1.1. Materials

20 tex modal and micromodal ring spun yarns (tricot) were produced on a Zinser 351 ring spinning machine with a ring diameter of 42 mm, 20 tex modal and micromodal rotor spun yarns (tricot) were made on a Schlafhorst A8 rotor spinning machine with a rotor diameter of 33 mm, whereas 20 tex modal and micromodal air-jet spun yarns (tricot) were made on a Rieter J20 air-jet spinning machine with an inner spindle diameter of 1.2 mm. A 25 tex cotton ring-spun yarn (tricot) was made using the combing process and was commercially purchased. A 156 dtex and 220 dtex multifilament PA yarn was also commercially purchased. A 500 dtex elastane yarn was inserted into the sock cuff.

The size of the socks is adjusted to the size of the thermal. The size of the thermal foot is adjusted to fit in shoes of the standard 42 EU size [18]. Samples of sock size 42 (EU size) were made on a Lonati automatic sock knitting machine with a cylinder diameter of 95 mm with 108 needles. The designations of the sock and yarn as well as mass, thickness and square mass (GSM) of all samples are given in Table 1 and the structure of the sock samples is shown in Figure 1.

Table 1.

Designation and description of the sock patterns and the yarns used; 4 yarns per course were used, plus an elastane yarn in the cuff

Sock group Sock combination Yarns Yarn label Mass (g/sock) p = 0.05 Thickenss (mm) p = 0.05 GSM (g/m2)
MR MR_A Modal and polyamide yarns M 20 tex × 3 + PA 6.6 156 dtex f68 19.0 ± 0.0 1.24 ± 0.01 215.4
MR_B M 20 tex × 3 + PA 6.6 220 dtex f68 21.4 ± 0.0 1.29 ± 0.01 242.7
MR_C Modal, cotton and polyamide yarns M 20 tex × 2 + Cot 25 tex + PA 6.6 220 f68 dtex 23.0 ± 0.0 1.40 ± 0.02 260.8
MR Average 21,1 1.31 239.3
MRO MRO_A Modal and polyamide yarns M 20 tex × 3 + PA 6.6 156 dtex f68 19.2 ± 0.0 1.21 ± 0.01 217.7
MRO_B M 20 tex × 3 + PA 6.6 220 dtex f68 21.4 ± 0.0 1.30 ± 0.01 242.7
MRO_C Modal, cotton and polyamide yarns M 20 tex × 2 + Cot 25 tex + PA 6.6 220 dtex f68 22.8 ± 0.0 1.41 ± 0.01 258.5
MRO Average 21.1 1.31 239.3
MAJ MAJ_A Modal and polyamide yarns M 20 tex × 3 + PA 6.6 156 dtex f68 19.4 ± 0.0 1.25 ± 0.01 220.0
MAJ_B M 20 tex × 3 + PA 6.6 220 dtex f68 21.7 ± 0.0 1.36 ± 0.02 246.1
MAJ_C Modal, cotton and polyamide yarns M 20 tex × 2 + Cot 25 tex + PA 6.6 220 dtex f68 23.0 ± 0.1 1.44 ± 0.02 260.8
MAJ Average 21.4 1.35 242.7
MMR MMR_A Micromodal and polyamide yarns MM 20 tex × 3 + PA 6.6 156 dtex f68 19.0 ± 0.0 1.25 ± 0.01 215.4
MMR_B MM 20 tex × 3 + PA 6.6 220 dtex f68 21.3 ± 0.0 1.30 ± 0.02 241.5
MMR_C Micromodal, cotton and polyamide yarns MM 20 tex × 2 + Cot 25 tex + PA 6.6 220 dtex f68 22.9 ± 0.0 1.39 ± 0.01 259.7
MMR Average 21.1 1.31 239.3
MMRO MMRO_A Micromodal and polyamide yarns MM 20 tex × 3 + PA 6.6 156 dtex f68 19.2 ± 0.3 1.20 ± 0.02 217.7
MMRO_B MM 20 tex × 3 + PA 6.6 220 dtex f68 21.7 ± 0.0 1.31 ± 0.01 246.1
MMRO_C Micromodal, cotton and polyamide yarns MM 20 tex ×2 + Cot 25 tex + PA 6.6 220 dtex f68 23.1 ± 0.1 1.42 ± 0.02 261.9
MMRO Average 21.3 1.31 241.5
MMAJ MMAJ_A Micromodal and polyamide yarns MM 20 tex × 3 + PA 6.6 156 dtex f68 19.4 ± 0.0 1.23 ± 0.01 220.0
MMAJ_B MM 20 tex × 3 + PA 6.6 220 dtex f68 21.6 ± 0.0 1.32 ± 0.02 244.9
MMAJ_C Micromodal, cotton and polyamide yarns MM 20 tex × 2 + Cot 25 tex + PA 6.6 220 dtex f68 22.9 ± 0.0 1.39 ± 0.03 259.7
MMAJ Average 21.3 1.31 241.5
Overall Average 21.2 1.32 240.4

  1. M – Modal; MM – Micromodal; Cot – cotton, R - ring spun yarn; RO - rotor spun yarn; AJ – air-jet spun yarn; PA – polyamide; A, B, C combinations of different types of yarn in the structure of knitted fabric

Figure 1. Sock structure of leg and cuff
Figure 1.

Sock structure of leg and cuff

The main physical-mechanical parameters of the basic modal and basic micro modal yarns (linear density, unevenness, faults, hairiness, and spectrograms) are provided in the earlier published paper [20]. Nominal values were used for the linear density of cotton yarn, PA yarn and elastane. The surface mass of the sock is determined from the ratio of the mass of the sock and the measuring surface of the thermal foot. The total area of the thermal foot is 96,450 mm2, and as the 2 upper upper segments were excluded from the measurement, the total measuring area on the thermal foot was 88,190 mm2. Dividing the mass of a sock by the measuring surface provides the real surface mass of the sock in the wear simulation. Therefore, the surface mass of unstretched socks was not determined.

1.2. Methods

Dimensions of the unstretched socks, mass and thickness

The following dimensions of unstretched socks were determined: sock leg length Ll, foot length Lf, half foot circumference B1, half circumference of sock leg length B2 and half circumference of cuff width B3 (Fig. 2). The dimensions of the socks were determined using a flexible length meter with a reading accuracy of 1 mm. Five test specimens (socks) were used for each combination of 18 samples, and the average value was determined.

Figure 2. Sock shape and main dimensions [17]
Figure 2.

Sock shape and main dimensions [17]

The dimensions of the unstretched sock samples (according to Fig. 1) are given in Tab. 2. The range of mean deviations was determined with 95% confidence.

Table 2.

Dimensions of unstretched sock samples

Sock group Sock abbreviation Leg length Ll (mm) Foot length Lf (mm) B1 (mm) B2 (mm) B3 (mm)
MR MR_A 242 ± 4 275 ± 2 90 ± 1 85 ± 1 84 ± 1
MR_B 245 ± 3 279 ± 2 93 ± 1 89 ± 1 85 ± 1
MR_C 249 ± 1 278 ± 2 95 ± 1 90 ± 0 86 ± 1
MR Average 245 277 93 88 85
MRO MRO_A 249 ± 3 270 ± 60 93 ± 1 87 ± 1 84 ± 0
MRO_B 250 ± 4 273 ± 3 94 ± 1 89 ± 1 85 ± 1
MRO_C 249 ± 2 274 ± 2 95 ± 1 90 ± 2 86 ± 1
MRO Average 249 272 94 89 85
MAJ MAJ_A 255 ± 3 280 ± 5 92 ± 1 89 ± 1 85 ± 1
MAJ_B 251 ± 2 275 ± 7 94 ± 1 90 ± 1 85 ± 0
MAJ_C 250 ± 3 277 ± 3 94 ± 2 91 ± 1 86 ± 1
MAJ Average 252 277 90 85
MMR MMR_A 239 ± 1 272 ± 2 91 ± 1 85 ± 0 83 ± 1
MMR_B 241 ± 2 270 ± 4 93 ± 1 88 ± 1 85 ± 1
MMR_C 246 ± 2 272 ± 1 94 ± 1 89 ± 1 85 ± 0
MMR Average 242 271 93 87 84
MMRO MMRO_A 249 ± 3 276 ± 3 91 ± 1 88 ± 1 84 ± 1
MMRO_B 253 ± 1 279 ± 5 93 ± 2 90 ± 1 85 ± 1
MMRO_C 249 ± 2 275 ± 2 93 ± 1 93 ± 1 86 ± 1
MMRO Average 250 277 92 90 85
MMAJ MMAJ_A 248 ± 3 276 ± 2 91 ± 1 87 ± 1 84 ± 1
MMAJ_B 250 ± 1 277 ± 3 92 ± 2 89 ± 1 84 ± 1
MMAJ_C 249 ± 1 273 ± 6 93 ± 1 90 ± 1 85 ± 0
MMAJ Average 249 275 92 89 84

The mass of the socks was determined using the analytical balance. One mass measurement of each sample combination was carried out on 5 different test specimens. Sock thickness was measured at 10 different points of each test specimen on a HESS model 2000-U thickness measuring gauge according to standard ISO 9073-2.

The results for the mass and thickness of the unstretched socks are shown in Table 1. The range of deviation from the mean value was determined with 95 % confidence.

The procedure for determining the dimensions of stretched socks

The shape of the stretched sock after placement on the thermal foot is shown in Figure 3.

Figure 3. Dimensions of the unstretched and stretched sock along the curve on thermal foot [17]
Figure 3.

Dimensions of the unstretched and stretched sock along the curve on thermal foot [17]

The elongation of the socks in the wale direction εl (%) in the sock leg after placement on the thermal foot was determined by the equation:

(1) εl=L1l−L0lL0l⋅100=ΔLlLol⋅100

The elongation of the socks in the wale direction in the section of the foot εf after placement on the thermal foot (%) was determined by the equation:

(2) εf=L1f−L0fL0f⋅100=ΔLfLof⋅100

where: L1l, L1f values measured along the thermal foot curve (mm), L0l, L0f the actual length of the part of the unstretched sock of the unstretched sock (L0l = 150 mm, L0f = 200 mm), ΔLl, ΔLf elongation of the sock in the the actual length of the part of the unstretched sock leg or foot (mm).

Stretching the actual length of the part of unstretched sock on the Thermal Foot was determined according to equations 1 and 2, and it is shown in Table 3.

Table 3.

Stretching the actual length of the part of socks on the Thermal Foot

Sock group Sock abbreviation L1l (mm) SD (mm) CV (%) Ɛl (%) L1f (mm) SD (mm) CV (%) Ɛf (%)
MR MR_A 153.7 0.78 5.05 2.47 209.7 0.25 1.20 4.85
MR_B 158.7 0.23 1.46 5.80 213.7 0.35 1.64 6.85
MR_C 149.7 0.92 6.17 0.1 195.7 0.49 2.52 0.5
Average 154.0 0.64 4.23 2.79 206.4 0.36 1.80 4.07
MRO MRO_A 150.7 0.51 3.41 0.47 208.7 0.64 3.04 4.35
MRO_B 153.7 0.72 4.71 2.47 202.3 0.25 1.24 1.15
MRO_C 152.3 0.25 1.65 1.53 199.3 0.23 1.16 0.2
Average 152.2 0.49 3.26 1.49 203.4 0.37 1.81 1.90
MAJ MAJ_A 157.3 0.46 2.94 4.87 205.0 0.56 2.72 2.50
MAJ_B 156.0 0.36 2.31 4.00 200.7 0.25 1.25 0.35
MAJ_C 156.3 0.32 2.06 4.20 205.3 0.15 0.74 2.65
Average 156.5 0.38 2.44 4.36 203.7 0.32 1.57 1.83
MMR MMR_A 154.3 0.12 0.75 2.87 209.0 0.36 1.73 4.50
MMR_B 155.3 0.25 1.62 3.53 206.3 0.32 1.56 3.15
MMR_C 152.3 0.40 2.65 1.53 205.7 0.60 2.93 2.85
Average 154.0 0.26 1.67 2.64 207.0 0.43 2.07 3.50
MMRO MMRO_A 154.7 0.25 1.63 3.13 214.3 0.40 1.89 7.15
MMRO_B 154.7 0.25 1.63 3.13 206.3 0.40 1.96 3.15
MMRO_C 156.7 0.51 3.28 4.47 201.0 0.53 2.63 0.50
Average 155.4 0.34 2.18 3.58 207.2 0.44 2.16 3.60
MMAJ MMAJ_A 153.7 0.21 1.35 2.47 201.0 0.17 0.86 0.50
MMAJ_B 148.3 0.29 1.95 0.1 205.3 0.45 2.20 2.65
MMAJ_C 153.0 0.82 5.35 2.00 201.3 0.15 0.03 0.65
Average 151.7 0.44 2.88 1.52 202.5 0.26 1.03 1.27

Thermal resistance measurement procedure on thermal foot

The thermal foot (Fig. 4a) consists of 13 segments of different surface, each of which can be heated separately at different temperatures or switched off [18]. In order to place the sock samples as evenly as possible on the thermal foot relating to their partially different heights, for the purpose of this work the upper segments No. 9 and 13 of the thermal foot were switched off (Figs. 4a, 4b). On the bare foot, a basic cotton sock was used in this work, which is placed on the thermal foot when measuring the values of Rct0 and Rct. When measuring the Rct0 value, a certain period of system stabilization was required, and the start of measurement was determined at the moment when the power of the heater (W) was constant (steady state), which was observed at the interface of the control unit (Fig. 4c). Measuring the Rct0 value takes 20 minutes. Upon completing the measurement of Rct0 the sock test specimen is placed on the thermal foot with the basic sock. System stabilisation is restored and the state of equilibrium is expected. Measuring the total resistance Rct of the thermal foot with the basic sock and the sock test specimen also takes 20 minutes (Fig. 4b). The value of thermal resistance Rct0 was determined by one measurement per sock test specimen. The measurement conditions were: thermal foot temperature 35 ºC, ambient temperature 20 ± 2 ºC, relative humidity 65 ± 5% and air flow rate 0.2 – 0.3 m/s (natural convection). For each sample combination, three thermal resistance measurements were made with the thermal foot.

Figure 4. Termal Foot and elements of interface of control unit
Figure 4.

Termal Foot and elements of interface of control unit

The general equation according to which the thermal foot measures thermal resistance has the following form [18]:

(3) Rct=Am(Tm−Ta)P

where: Rct thermal resistance (m2 °C W−1), Am measuring surface of the thermal foot (m2), Tm ttemperature of the measuring surface of the thermal foot (ºC), Ta ambient temperature (20 ± 2ºC); P total heater power of all thermal foot segments (W).

The thermal resistance of the thermal foot Rct is determined in this paper by the equation (Fig. 4) [18]:

(4) Rct=(∑TinTa)∑Ai∑Pi

where: Ti average temperature of the i-th segment (°C), n number of segments switched on, Ai total measuring surface of the switched-on segments (m2), Pi total power of the switched-on segments (W).

The thermal resistance of the sample is determined by the equation:

(5) Rcts=Rct−Rct0

where: Rcts thermal resistance of the sock sample (m2 °C W−1), Rct total thermal resistance of the thermal foot + basic sock + sock sample (m2 °C W−1), Rct0 thermal resistance of the thermal foot + basic sock (m2 °C W−1).

The thermal resistance of the sock depends on the sample thickness d (mm) and the thermal conductivity of the material of which the sample is made λ (W °C m−1), and it can be determined by the following equation if the thermal conductivity of the material and its thickness are known:

(6) Rct=dλ

3. Results and discussion

Dimensions of unstretched socks

The length of the sock leg Ll of all sample combinations ranges from 239 mm (sample MMR_A) to 255 mm (sample MAJ_A) (Fig. 5, Tab. 2,). The difference is 16 mm, i.e. 6.7 %. The length of the sock leg Ll in the samples knitted from basic modal yarns (245, 249, 252 mm) is not significantly different from the samples knitted from micromodal yarns (242, 250, 249 mm). Moreover, samples of basic modal ring and basic micro modal ring yarns have a slightly shorter average leg length (245, 242 mm) than basic modal and micro modal rotor yarns (249, 250 mm) and air-jet spun basic modal and micro modal yarns (252, 249 mm). Differences in the leg length Ll per sample groups are nevertheless small and can be attributed to differences in the structure of the ring, rotor and air-jet spun yarn and the difference in the fineness of the added yarns in the samples under equal knitting conditions. The values for the foot length Lf of all sample combinations range from 270 mm (sample MRO_A) to 280 mm (sample MAJ_A), and the difference is 10 mm, i.e. 3.7 %, which is still probable marginal. Furthermore, no significant difference was found between samples of basic modal and basic micromodal yarns.

Figure 5. Dimensions of unstretched socks
Figure 5.

Dimensions of unstretched socks

Although the largest differences in the leg length of the samples Ll (16 mm) and the foot length Lf (10 mm) are small, they can be significant for complete and uniform covering of the measuring surface of the thermal foot. When measuring unstretched and stretched socks on the thermal foot, the unavoidable subjective error is also taken into account to a lesser extent due to straightening the socks.

Mass, thickness and GSM of socks

The mass of all sample combinations ranges from 19.0 g/sock to 23.1 g/sock (Fig. 6, Table 1,). The greatest mass difference among all samples was 21.6 %. As expected, the use of coarser PA and cotton yarns also increases the mass of the socks in each sample group (samples marked B and C). Although the sock masses of each group ranged from 21.1 g/sock to 21.4 g/sock, which makes a difference of 1.4%, it was necessary to consider each sample combination separately.

Figure 6. Mass and thickness of unstretched socks
Figure 6.

Mass and thickness of unstretched socks

The thickness of the socks of all sample combinations ranges from 1.21 to 1.44 mm, which gives a maximum difference of 19.0% and is significant in percentage terms. By using coarser PA and cotton yarn, the sock thickness is expected to increase. Furthermore, the mean thickness values of individual groups range from 1.31 to 1.35, which makes a difference of 3.1%. This was also the reason for a more detailed analysis of all sample combinations.

Sock foot dimensions and stretching

Stretching socks on the Thermal Foot was determined according to equations 1 and 2, and it is shown in Figs. 7 and 8 (from Tab. 3). The stretching of samples of all sample combinations in the wale direction on the selected segments of the leg and foot (150 and 200 mm, resp.) ranges from 0.1 % to 7.15 %. The leg of the sample has a stretch of 0.1 to 5.8 %, while the foot stretches between 0.2 and 7.15 %. The average stretch values in the wale direction on both selected segments of the sample of individual groups lie below 4.07 %, which is relatively low and shows that the socks are well uniformly placed on the surface of the entire basic sock and foot with the upper segments 9 and 13 disconnected (Fig. 4b). The average values of the two stretches (Ɛl and Ɛf) of the basic modal and micromodal samples amount to 2.9 % and 2.6 % and 2.7 % and 2.8 % respectively. This suggests that the percentage differences are still low.

Figure 7. Stretching the sock leg (εl) and foot (εf) of socks of basic modal yarn
Figure 7.

Stretching the sock leg (εl) and foot (εf) of socks of basic modal yarn

Figure 8. Stretching the sock leg (εl) and foot (εf) of socks of basic micromodal yarn
Figure 8.

Stretching the sock leg (εl) and foot (εf) of socks of basic micromodal yarn

Thermal resistance

Prior to measurement, the samples were kept for 24 hours at standard conditions of 20 ± 2 °C and 65 ± 5 %. The measurement results are shown in Tab. 4 and in Figures 9 to 12.

Table 4.

Thermal resistance of the socks (Rct)

Sock group Sock samle abbreviation Rct (m2 °C W−1) CV (%)
MR MR_A 0.0125 8.1
MR_B 0.01260 3.4
MR_C 0.0138 6.9
MR Average 0.0130 6.1
MRO MRO_A 0.0091 14.3
MRO_B 0.0116 4.7
MRO_C 0.0122 14.7
MRO Average 0.0109 11.2
MAJ MAJ_A 0.0128 4.9
MAJ_B 0.0119 12.9
MAJ_C 0.0148 9.3
MAJ average 0.0132 9.0
M Average 0.0124 8,8
MMR MMR_A 0.0119 14.7
MMR_B 0.0129 4.8
MMR_C 0.0148 12.6
MMR Average 0.0132 10.7
MMRO MMRO_A 0.0105 28.6
MMRO_B 0.0130 16.1
MMRO_C 0.0156 4.3
MMRO Average 0.0130 16.3
MMAJ MMAJ_A 0.0104 22.3
MMAJ_B 0.0102 21.5
MMAJ_C 0.0092 15.4
MMAJ Average 0.0099 19.7
MM Average 0.0121 15,6
M and MM Overall Average 0.0122 12.2
Figure 9. Thermal resistance Rct of basic modal socks
Figure 9.

Thermal resistance Rct of basic modal socks

Figure 10. Thermal resistance Rct of basic micromodal socks
Figure 10.

Thermal resistance Rct of basic micromodal socks

Figure 11. Relation between thermal resistance and square mass (GSM) of stretched samples
Figure 11.

Relation between thermal resistance and square mass (GSM) of stretched samples

Figure 12. Thermal resistance of sock samples group according to type of yarn: ring, rotor and air-jet
Figure 12.

Thermal resistance of sock samples group according to type of yarn: ring, rotor and air-jet

As no significant differences were obtained between unstretched socks in the foot length (Ll) and foot length (Lf) parameters (Table 2), no significant differences were obtained in stretching (Ɛl and Ɛf).) (Table 3), the discussion of thermal resistance results was carried out as a function of the thickness of the unstretched sock and the surface mass of the stretched sock on the thermal foot.

Thermal resistance values for all samples range from 0.0091 to 0.01586 m2 °C W−1 (Tab. 4). The thermal resistance values of all sample combinations of modal basic fibres range between 0.0091 (sample MRO_A) and 0.0148 m2 °C W−1 (sample MAJ_C) (Fig. 9), while the values of thermal resistance of all sample combinations of basic micro modal fibres range from 0.0092 (sample MMAJ_C) to 0, 0156 m2 °C W−1 (sample MMRO_C) (Fig. 10). The trend of increasing thermal resistance was observed by decreasing the fineness of the additional yarns for both basic types of raw materials in ring and rotor yarn samples (consequently an increase in fabric surface mass) and is more significant in micro-modal yarn samples with a high correlation coefficient of 0.711 (Fig. 11). The highest thermal resistance per groups of basic modal fibres was achieved in samples of the airjet spun yarn with 0.0132 m2 °C W−1 (group MAJ) and the lowest in samples of the rotor yarn with 0.0109 m2 °C W− (group MRO). This is due to the higher sample thickness of the air-spun yarn (1.35 mm) with an average low stretch of the samples on the thermal foot (below 4.07 %). The highest thermal resistance per groups for the basic micro-modal fibres in the group of samples was found in the ring yarn (0.0132 m2 °C W−1, group of samples MMR) and the lowest in the samples of the air-jet spun yarn (group of samples MMAJ, 0.0092 m2 °C W−1). The reason for the lower thermal resistance may be a greater compactness of the air-spun yarn structure of finer micromodal fibres and consequently less air in the space between the yarn in knitted fabric structure. Since modal and other cellulose fibres (e.g. cotton) have a thermal conductivity many times higher than air, the thermal resistance of such samples is consequently lower. In addition, the thickness of this group of samples is lower (MMAJ, 1.31 mm) than the thickness of the sample group of the basic modal fibres (MAJ, 1.35 mm), which further reduces thermal resistance (Eq. 6). Comparing the individual samples of basic modal fibres, low thermal resistance was found for the samples of rotor yarn (0.0109 m2 °C W−1 compared to the samples of ring yarn (0.0130 m2 °C W−1) by 16.1%, with the same average sock thickness of 1.31 mm, which may be due to differences in the structures of rotor and ring yarns. For micromodal base samples, the difference in thermal resistance between rotor and ring yarns is very small (0.0002 m2 °C W−1) and practically negligible. Comparing the average value of the thermal resistance of all sample combinations of the basic modal yarn (0.0124 m2 °C W−1) with the average value of all sample combinations of the micromodal yarn (0.0121 m2 °C W−1), it is obvious that the differences are small (0.0003 m2 °C W−1) (Table 4). Since these are samples of high uniformity of basic modal yarns and uniform structure of the knitted fabric with a low production speed on the knitting machine, the influence of the fineness of modal fibres on thermal resistance is not clearly found.

The influence of different yarn types in the samples on thermal resistance should be considered taking into account both the thickness of the samples and the fineness of the modal fibres. Thus, the highest thermal resistance per sample group was found in the samples made of ring yarn (0.0132 m2 °C W−1 of the MMR and MAJ sample groups) and the lowest in the samples made of air-spun yarn (0.0099 m2 °C W−1, of the MMAJ) (Tab. 4, Fig. 12).. The thermal resistance of the sample groups of ring and rotor yarns is 24.4 % and 21.1 % higher, respectively, than the thermal resistance of the group of air-spun yarns. The reason for the lower thermal resistance of the air-jet spun yarns is also due to the higher average thickness of the MAJ sample group (1.35 mm).

As the yarns used for the sock samples were predominantly made of cellulose fibres (cotton, modal and micro modal with the addition of the usual percentage of PA multifilament yarns), whose thermal conductivity values vary relatively slightly (cotton 0.461 W/(m °C), viscose 0.289 W/(m °C)), the average thermal resistance value of 0.0122 m2 °C W−1 determined on the thermal foot for all sample combinations is comparable to the thermal resistance values of similar sock samples published in other papers. Moreover, thermal comfort, characterised by numerical values of thermal resistance, is high. The sock samples tested have low thermal resistance, which means they conduct heat well, resulting in cooling, which is especially important for wearing in warmer weather. The thickness of the sock and the volume of air held usually determine the thermal resistance under static test conditions, and the effect of the fiber itself is reduced [15]. Thicker socks made of modal and micro modal basic ring and rotor yarns, which contain coarser other added yarns, have a higher thermal resistance as a result of the different compactness of the structure. Furthermore, the greater thickness of the basic modal/micromodal sock samples used allows for better moisture transport from the sock leg, which further increases comfort, especially during heavier sweating.

4. CONCLUSIONS

Based on the results obtained, the following conclusions can be drawn:

  1. The length of the selected section of the leg of the sample Ll of all sample combinations ranges from 239 mm to 255 mm (difference of 16 mm i.e. 6.7 %). The length Ll in samples knitted from basic modal yarns is not significantly different from samples knitted from basic micromodal yarns.

  2. The length of the selected foot section Lf is between 270 mm and 280 mm for all sample combinations (difference of 10 mm, i.e. 3.7 %) and is nevertheless small.

  3. No significant difference was found between the lengths Lt and Lf between samples of basic modal and basic micromodal yarns.

  4. The mass of all samples ranges from 19.0 g/sock to 23.1 g/sock. When using coarser additional yarns (cotton and PA multifilament), the mass of the socks in each sample group also increases.

  5. The thickness of the socks of all samples ranges from 1.21 to 1.44 mm, which gives the largest difference of 19.0 %, and the percentage is significant. The mean thickness values of the individual groups range between 1.31 and 1.35 mm.

  6. The stretching of the selected section of the sock leg and foot in the wale direction of all sock sample combinations ranges from 0.1 % to 7.15 %, is less than 4.07 % per group.

  7. The thermal resistance values for all samples range from 0.0091 to 0.01586 m2 °C W−1. An increasing trend of thermal resistance was observed by decreasing the fineness of the additional yarns for both basic types of raw materials in samples of ring and rotor yarns, and it is more prominent in samples of micromodal yarn with a correlation coefficient of 0.711.

  8. The highest thermal resistance per groups of basic modal fibres was obtained in the samples made of air-jet spun yarn of 0.0132 m2 °C W−1 and the lowest in samples of rotor yarn of 0.0109 m2 °C W−1.

  9. The highest thermal resistance in all groups of basic micromodal samples made of ring yarn (0.0132 m2 °C W−1) and the lowest in the samples made of air-spun yarn (0.0099 m2 °C W−1).

  10. The tested sock samples have low thermal resistance, i.e. they can conduct heat well, thus achieving cooling, which is important for wearing socks in warm weather.

  11. The greater thickness of the basic modal/micromodal sock samples used allows for better moisture transport from the sock leg, further increasing comfort, especially during heavier sweating.

  1. Funding

    This work was funded by the Croatian Science Foundation based on Project IP-2016-06-5278.

ACKNOWLEDGEMENTS

This work has been fully supported by the Croatian Science Foundation under project No. IP-2016-06-5278.

While submitting the manuscript to ARJ author is obliged to send all figures included in the work in separate source files. This requirement is dictated by the attention to quality of published work.

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Published Online: 2022-10-01

© 2022 Zenun Skenderi et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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https://doi.org/10.2478/aut-2022-0022
Keywords for this article
socks; modal; thermal resistance; thermal foot; comfort
Creative Commons
BY 4.0

Articles in the same Issue

  1. The Effects of Sensory Marketing on Clothing-Buying Behavior
  2. Washing Characterization of Compression Socks
  3. Polyaniline Electrospun Composite Nanofibers Reinforced with Carbon Nanotubes
  4. Review on 3D Fabrication at Nanoscale
  5. Investigation of the Performance of Cotton/Polyester Blend in Different Yarn Structures
  6. Transport of Moisture in Car Seat Covers
  7. Investigating the Effect of Recycled Cotton Included Fabrics on the Thermal Behaviour by Using a Female Thermal Manikin
  8. Application of Spectral Analysis in Spinning Measurements
  9. Wearable Design for Occupational Safety of Pb2+ Water Pollution Monitoring Based on Fluorescent CDs
  10. Investigation of Surface Geometry of Seersucker Woven Fabrics
  11. Current Development and Future Prospects of Designing Sustainable Fashion
  12. Design of Clothing with Encrypted Information of Lost Children Information Based on Chaotic System and DNA Theory
  13. Thermal Resistance of Gray Modal and Micromodal Socks
  14. Study on Process Optimization and Wetting Performance of Ultrasonic-Oxidized Wool Fiber
  15. Liquid Moisture Transport in Stretched Knitted Fabrics
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