clothing and textiles research journal 2014 stankovic 202 14

Article

Effect of Yarn Folding onComfort Properties ofHemp Knitted Fabrics

Snezana B. Stankovic1 and Matejka Bizjak2

AbstractThe operation of folding provides a complex yarn differing to an appreciable degree from singlecomponents. Although the characteristics of folded yarns have been the subject of many investi-gations, there is a serious lack of study concerned with the influence of yarn folding on comfortproperties of clothing materials. Therefore, this study focused on the effect of yarn folding on boththermal and tactile comfort of plain knitted fabrics. In addition to the structural characteristics of theyarns and knitted fabrics, the transport properties, deformation behavior and surface properties ofthe knitted fabrics were investigated. The results obtained indicated that the influence of yarn foldingon thermal and tactile comfort properties of clothing materials is mainly positive. These effects werecaused by the modification of yarn packing density which further influenced the air volume distri-bution as well as the fiber and yarn mobility within the fabric.

Keywordstextiles, textile performance, comfort, knit, yarn

Modern consumers are interested in clothing with good aesthetic performance, comfort-related prop-

erties, and durability. While aesthetic and utility performances are desirable in clothing, comfort is

the intrinsic and essential performance requirement in clothing materials. Therefore, research on

clothing comfort is of great importance for an improvement in the quality of peoples lifestyles.

Generally, comfort is defined as a state of satisfaction indicating physiological, psychological, and

physical balance among the person, his or her clothing, and his or her environment (Slater, 1985).

The science of comfort categorizes it into three broad categories: psychological, thermal, and tactile

comfort. Psychological comfort is mainly based on subjective feelings and fashion trends and bears

little relation to the properties of fabrics. Thermal comfort relates to the ability of the clothing mate-

rials to support the thermoregulation system of the body in order to keep its temperature at the mean

value even if the atmospheric conditions or physical activities change. The governing properties of

1 University of Belgrade, Faculty of Technology and Metallurgy, Textile Engineering Department, Belgrade, Serbia2 University of Ljubljana, Department of Textiles, Faculty of Natural Science and Engineering, Ljubljana, Slovenia

Corresponding Author:

Snezana B. Stankovic, University of Belgrade, Faculty of Technology and Metallurgy, Textile Engineering Department,

Karnegijeva 4, 11120 Belgrade, Serbia.

Email: [email protected]

Clothing and TextilesResearch Journal2014, Vol. 32(3) 202-214 The Author(s) 2014Reprints and permission:sagepub.com/journalsPermissions.navDOI: 10.1177/0887302X14537114ctr.sagepub.com

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clothing materials by which they influence the thermal balance of a wearer are thermal properties,

water vapor permeability, and air permeability, which are known as transport properties. Tactile

comfort relates to the mechanical interaction between clothing material and human body. A dressed

human body is always subjected to a complex mechanical load arising from the weight of the gar-

ment or the load accompanying deformation of clothing material. Thus, the deformation behavior of

textile materials during their stretching, bending, shearing, compression, and so on, is responsible for

tactile sensations. Since the load transmits to the body at skin-fabric contact areas, the surface char-

acteristics of clothing materials are also very important for tactile sensory perception.

Folded yarn is a complex yarn composed of two or more component yarns arranged parallel and

twisted together to make a new quality yarn. Generally, the operation of folding or plying modi-

fies and improves existing single yarns to an appreciable degree by combining them together.

Among the properties improved by yarn folding, those of the greatest importance for the perfor-

mance of textile materials are yarn evenness (uniform diameter), strength (and strength variation),

liveliness (the reduction of residual torque), and yarns surface characteristics (hairiness). The char-

acteristics of folded yarns have drawn the attention of many scientists from the 1950s to today

(Bennett & Postle, 1979; Honold & Grant, 1961; Milosavljevic, Tadic, & Stankovic, 1998; Park

& Oh, 2003; Skau, Honold, & Boudreau, 1958; Xia, Xu, &Wang, 2012). However, there is a serious

lack of study about the effects of folded yarns on the properties of textile materials, especially those

concerned with comfort properties. Bearing in mind the growing popularity of clothing comfort, this

lack of investigations is surprising, and the knowledge of the effects of folding operation on comfort

properties seems requisite. For instance, folding operation will certainly improve the strength and

evenness of a yarn, but it does not mean that comfort properties of textile fabric made of folded yarn

will always be improved. Pac, Bueno, and Renner (2001) and Behera andMishra (2007) investigated

the thermal properties of knitted and woven fabrics produced from folded cotton and wool/silk

yarns, respectively. The complex relations between the thermal properties and air permeability of

rib-knitted fabrics and folding density of the yarns used were confirmed by Stankovic, Popovic, and

Poparic (2012). The investigation of handle properties of woven fabrics produced from various

folded (ring, rotor, and vortex) yarns indicated the importance of spinning technique and both twist

and folding direction (Unal, 2010). In the investigation conducted by Stankovic (2008), the folding

technique was used to produce staple/filament hybrid yarns from which the rib-knitted fabrics with

different compression properties were produced. Bueno, Renner, and Pac (2002) compared surface

properties of knitted fabrics produced from two-folded cotton yarns with their counterparts.

For our research, the idea was to evaluate the effect of yarn folding on both thermal and tactile

comfort of the knitted fabrics. Since the structure of knitted fabric and constituent yarn could be

changed by physical or chemical treatment, the knitted fabrics were in the virgin state during com-

fort investigation. In such a way, the effect of yarn folding on comfort properties becomes more dis-

tinct. In our research eco-friendly hemp yarn was chosen to fold and produce knitted fabrics.

Specific characteristics, such as excellent hygienic, antielectrostatic, and ultraviolet radiationresis-

tant properties, make hemp fabrics physiological-friendly textiles. However, hemp fibers have some

limitations concerned with tactile comfort, because hemp by nature is coarse and does not have

much elasticity. Therefore, the main task was to improve the tactile comfort properties of hemp

knitted fabrics without deteriorating their good thermal comfort properties. The results presented

in this article are the part of the project aiming to introduce hemp to the area of high-quality comfort

clothing.

Materials and Methods

In the present study, 100% hemp yarn (Linificio Canapificio Nazionale, Italy) with the nominal lin-ear density of 50 tex and nominal twist level of 400 turns per meter (Z direction) was used. By

Stankovic and Bizjak 203


folding two single hemp components, the folded hemp yarn (hemp/hemp) with the nominal linear

density of 100 tex and nominal folding twist level of 310 turns per meter (S direction) was pro-

duced. The folded hemp yarn was produced on a Saurer Allma ring twister having 12 spindles

and ring dimensions of 160 mm 16.7 mm. After folding, the yarn was subjected to treatmentsfollowing the standard routines applied at St. George Company (Serbia): steaming 20 min at 80C in an autoclave and storage for at least 72 hr in a conditioned room (65% relative humidity+2% and 20 C + 2 C) in order to reduce residual torque. The properties of the yarns used,which could influence the comfort properties of the knitted fabrics, are given in Table 1. Factual

values of linear density of the yarns used were determined in accordance with ISO 2060:1994

(TextilesYarns from PackagesDetermination of Linear Density [mass per unit length] by

Skein Method). Factual twist of the yarns was determined according to ISO 2061:1995 (Tex-

tilesDetermination of Twist in YarnsDirect Counting Method). Diameter of the yarns was

determined using a Nikon SMZ800 microscope. After 50 readings for both yarns, the average

diameters were calculated. The diameter and linear density of the yarns were used to calculate

their bulk density. Packing factor of the yarns was calculated by dividing bulk density of the

yarns by fiber density. Hairiness of the yarns was measured using the Shirley Hairiness Monitor.

The hairiness was registered on traveling yarn samples in 5-sec intervals and later was reduced to

1 m of yarn length. Thirty hairiness tests per yarn were performed, so the hairiness of both single

and two-folded yarns presented in Table 1 was the average of these 30 tests.

From these yarns, two variants of plain knitted fabrics, one having single hemp yarn and the sec-

ond consisting of two-folded hemp yarn, were produced on a 20 gauge and 3000 diameter Fouquetcircular double jersey knitting machine with positive storage, 36 feeders, and 1,885 needles. The

knitting process was completed for both knitted fabrics with constant machine settings (known to

the company) according to the production standards of the industry. Therefore, as much as possible,

identical structure of the knitted fabrics was obtained. In addition, the variant of knit consisting of

the single hemp yarn was produced by feeding two single yarns simultaneously, side by side,

Table 1. Characteristics of the Yarns.

Parameter, Unit Hemp Hemp/Hemp

Linear density, tex 47.8 95.6Twist, m1 370 297Diameter, mm .22 .41Bulk density, gcm3 1.258 .721Packing factor .84 .48Hairiness, m1 3.4 6.7

Table 2. Construction Characteristics of the Plain Hemp Knitted Fabrics.

Parameter, Unit Hemp hempa, 2Cs Hemp/Hempb, FCsStitch density Course, cm1 13.7 12.0

Wale, cm1 5.5 5.5Surface, cm2 75.4 66.0

Loop length, mm 5.0 5.3Thickness, mm .916 .948Mass per unit area, gm2 360.4 334.4aTwo assembled hemp yarn.bTwo-folded hemp yarn.

204 Clothing and Textiles Research Journal 32(3)


through the same hole in each feeder. This was an attempt to ensure both knitted fabrics were pro-

duced from the yarns with the same linear density. The samples were kept without tension on a flat

surface in a conditioned room (65% relative humidity+ 2% and 20 C+ 2 C) for the relaxationbefore testing. These commercially produced knitted fabrics in their existing state after last commer-

cial treatment (i.e., virgin state) were used for all tests. Stitch density, loop length, and mass per unit

area of the knitted fabrics were determined according to procedures described in the literature

(Koblyakov, 1989). Thickness of the knits was measured in accordance with ISO 5084:1996 (Tex-

tilesDetermination of thickness of textiles and textile products). Construction characteristics of

the plain hemp knitted fabrics are presented in Table 2.

Among the secondary parameters describing the structure of knitted fabric, porosity, open poros-

ity, stitch moduli (planar and volume), cover factor, and structural tightness factor were determined.

Porosity of the knitted fabrics P (%), defined as the portion of all air spaces in knitted fabric bothbetween yarns and inside them, was calculated using the equation given subsequently:

P 100 rk=rf 100: 1

where rf (g/cm3) is the fiber density and rk (g/cm

3) is the bulk density of the knitted fabrics calcu-

lated by dividing their surface density (mass per unit area) by thickness.

Open porosity O (%) expressing the portion of air spaces between yarns was calculated by thefollowing equation:

O 100 rk=ry100: 2

where ry (g/cm3) is the bulk density of the yarn.

Planar stitch modulus, presenting the relationship between the area of a stitch and the area

occupied by the yarn within the stitch, and volume stitch modulus, showing the relationship

between the volume of a rectangular solid outlining a stitch and the volume occupied by the yarn

within the stitch, were estimated by the relations described in the literature (Koblyakov, 1989).

Cover factor CF (tex1/2 cm1), indicating the extent to which the area of the knitted fabric is cov-ered with the yarn, was calculated as the ratio between the square root of the yarns linear density,

and loop length. Knowing the cover factor of the knitted fabrics, the structure tightness factor

(STF; tex1/2 cm1) was calculated by multiplying cover factor by stitch density constant (Knapton,Ingenthron, & Fong, 1968).

Air permeability of the knitted fabrics, defined as the volume of air measured in cubic meters

passed per minute through a square meter of fabric at a constant pressure (m3/m2 min), was mea-

sured according to standard procedure (ISO 9273:1995, TextilesDetermination of the perme-

ability of fabrics to air). A Textest FX-3300 air permeability tester was used. The air pressure

differential between the two surfaces of a sample was 100 Pa. Five tests per each knitted fabric

were conducted. Water vapor permeability and thermal properties of the knitted fabrics were mea-

sured using the Permetest. The testing procedure was somewhat different from the standard ISO

11092 (TextilesPhysiological effectsMeasurement of the thermal and water-vapor resis-

tance). Measurements are made at 2022 C isothermal laboratory temperature (instead of 35C) and relative humidity of 6065% (instead of 40%), which should match the ambient condi-tions. Water vapor permeability for each knit was investigated by making five separate tests. The

capability of the knitted fabrics to transfer water vapor was indicated by measuring the absolute

vapor resistance and calculating the relative water vapor permeability (the ratio of heat loss from

the measuring head with knitted fabric and without it). The capability of transferring heat was

determined by measuring thermal resistance of the knitted fabrics. During determination of ther-

mal resistance, the measuring head was dry and the temperature was maintained at 32 C. Fivetests were conducted on different portions of the knits.



The mechanical and surface properties of the knitted fabrics were determined using the Kawabata

Evaluation System for fabric (KES-FB). The KES measures 16 mechanical parameters correspond-

ing to the fundamental deformation mechanisms (tensile, shear bending, and compression), surface

coefficient of friction, and geometrical roughness. Many contributions have been published on the

topic of this expert system, and there is thus no necessity to precisely describe the system. Three

replicate specimens were prepared from each fabric. Each of the specimens was subjected to testing

following the prescribed order: surface, compression, shear, and tensile. Due to edge curling of the

plain knitted fabrics investigated, we were unable to perform the bending test. Data were collected

for both the wale and course direction for each tested specimen, except compression for which there

is no direction (normal to specimens plain). The main values of KES parameters for all three speci-

mens (for wale, course, and their averages) were calculated.

Two-sample students t-test procedure is used to compare the means of the results obtained for

the knitted fabrics. Generally, when the probability value (p) is less than .05, the evidence to reject

the null hypothesis of equal means is provided. The standard deviation (SD) at a 95% confidenceinterval for tested parameters of each knitted fabric was also calculated.

Results and Discussion

Structure of the Yarns and Knitted Fabrics

The packing density of a staple yarn generally falls in the range of .3 to .7 depending on the fiber

cross-sectional shape, twist level, and crimp density, whereas the ideal packing density of .907 is

difficult to obtain. The packing density of the single hemp yarn of .84 indicates its quite compact

structure, and the value of hairiness (Table 1) indicates its smooth surface. It could be explained by

lower elasticity and flexibility of hemp fiber. The reduced deformability of hemp fibers impeded

their mobility during yarn formation, resulting in the more compact core and reduced hairiness of

the yarn as can be seen in Figure 1a. The complex yarn formed by folding two single components

was expected to have the new quality structure because of the inevitable changes in fiber orien-

tation in the folded yarn. As a result, the diameter of the folded hemp yarn was doubled with a

reduction of 57% in its bulk density and packing factor. It can be seen from the scanning electronmicrographs (Figure 1) that the fibers orientation was altered by twisting together two single

hemp components. Due to introduction of the secondary twist (folded yarn twist) in the opposite

direction to the primary twist (single yarn twist), the hemp fibers in the folded yarn were partially

untwisted. The micrograph of the folded hemp yarn (Figure 1b) illustrates some fibers (indicated

in the picture with black arrows) almost parallel to the yarn axis. Even though the hairiness of the

Figure 1. (a). Geometry of the single hemp yarn. (b). Geometry of the two-folded hemp yarn.



two-folded hemp yarn was doubled in value (Table 1), we would describe both single and folded

hemp yarns as smooth.

In order to obtain constructions as similar as possible, the knitted fabrics were produced under

controlled machine settings. Nevertheless, some slight differences in structural characteristics of the

knits were found (Table 2) as a consequence of differences in internal structure of the yarns. The

knitted fabric having two-folded hemp yarn as a component was characterized by lower stitch den-

sity which in turn was influenced by its lower course density. Since the knitted fabrics were knitted

under the same knitting conditions, their different course densities must have resulted from the dif-

ference in loop configuration coming from the bending rigidity of the yarns. Bending rigidity of the

two-folded hemp yarn was assumed to be lower than that of the single or two assembled hemp yarn

due to the twist reduction in each single component. By losing a part of the single components twist,

the fiber mobility inside the two-folded yarn was increased, leading to a reduction in bending rigid-

ity. A different loop configuration manifested itself in the slightly greater stitch height (.83 mm) of

FCs (two-folded hemp) knit in relation to that of 2Cs (two assembled hemp) knit (.73 mm), while the

stitch width was the same for both knits (1.82 mm).

In addition to the primary parameters of the knitted fabrics, the yarns used influenced their sec-

ondary parameters given in Table 3. The knitted fabric produced from two assembled hemp yarns

(hemp hemp, 2Cs) was characterized by higher bulk density and lower porosity as a conse-quence of the yarn aggregation into a highly packed (higher stitch density) knitted structure.

Although having lower total porosity, 2Cs knitted fabric was characterized by higher open poros-

itythe parameter known for governing transport properties. The different pore distributions in

these two knitted fabrics were qualitatively confirmed by scanning electron microscope (SEM)

Table 3. Secondary Structural Parameters of the Plain Hemp Knitted Fabrics.

Parameter, Unit Hemp Hemp, 2Cs Hemp/Hemp, FCsBulk density, gcm3 .398 .353Porosity, % 74.0 76.5Open porosity, % 68.4 51.0Cover factor, tex1/2 cm1 19.6 18.4Structural cover factor, tex1/2 cm1 369.4 341.7Planar stitch modulus .48 .49Volume stitch modulus 1.60 2.06Area of a stitch, mm2 1.33 1.52

Figure 2. (a). Geometry of the knitted fabric made from two assembled hemp yarn (2Cs). (b). Geometry of theknitted fabric made from two-folded hemp yarn (FCs).



micrographs (Figure 2). The more open structure of 2Cs knitted fabric seems clearly visible

(Figure 2a). On the other hand, calculated cover factor and structural cover factor showed that

the area of knit covered with the yarn was higher in 2Cs knit (Table 3) as a result of the differences

in loop length and course density between the knits. In addition, the planar stitch modulus of

the knitted fabrics confirmed the more compact structure of 2Cs knit since the lower value of

2Cs planar stitch modulus expresses the reduced size of the interstitial pores (Table 3). This was

also confirmed by the volume stitch modulus, since the higher volume stitch modulus of FCs

knitted fabric indicated the structure had less volume in one stitch filled with yarn; this further

indicates the larger volume of interstitial pores.

Transport Properties of the Knitted Fabrics

Open porosity is known to be a governing factor influencing the transport properties of a fabric, such

as water and air permeability, and heat transfer properties. Bearing in mind that the knitted fabrics

produced from single and two-folded hemp yarn were characterized by some differences not only in

construction characteristics but also in porosity distribution, some differences in transport properties

could be expected. According to the results of air permeability (Table 4), the knitted fabric produced

from the two-folded hemp yarn was more permeable, which is confirmed by a two-sample students

t-test (p value, Table 4). Many studies of structural factors influencing the air permeability of fabrics

confirmed that airflow takes place through open pores (interstices between yarns). Additionally,

Goodings (1964) shows that the increased number of the pores per unit area would reduce the airflow

of the pores with reduced size. Taking these facts into consideration, we concluded that the higher air

permeability of the FCs knit was due to its reduced stitch density or larger area of a stitch. Even

though the spacing of the folded hemp yarn seems higher (Figure 2), the larger stitch spacing (the

area of a stitch; Table 3) in FCs knit resulted in the larger size of open pores between wales, leading

to increased air permeability.

Water vapor permeability of textile materials is defined as the quantity of water vapor passing

through a unit area of the fabric in a definite period of time due to a pressure gradient between inner

and outer surfaces of the fabric. Water vapor resistance is inversely proportional to water vapor per-

meability and describes the resistance to evaporative transport through the material. Various studies

implicated water vapor diffusion as a dominant mechanism for moisture transport under steady-state

conditions. The diffusion mechanism of water vapor transfer includes diffusion through the inter-

yarn pores and interfiber spaces and through the fiber substance itself as well as the migration of

absorbed water vapor along the fiber surface. Since the vapor diffusion through the air spaces of the

fabric is far faster than diffusion through the fiber due to lower moisture diffusivity of textile fibers,

the transfer of water vapor is considered to be dependent on the fabric geometry and especially on

the inter-yarn pores (open pores). The differences in geometry between the knitted fabrics resulted in

reduced water vapor resistance and increased relative water vapor permeability of FCs knitted fabric

(Table 4). Although 2Cs knit was characterized by higher open porosity (Table 3), the reduced size

Table 4. Transport Properties of the Plain Hemp Knitted Fabrics.

Parameter, Unit Hemp Hemp, 2Cs Hemp/Hemp, FCs p Value (a .05)Air permeability, m3 m2 min1 (SD) 71.2 (2.5) 74.0 (2.1) .031*Thermal resistance, m2 K W1 (SD) .024 (.002) .026 (.002) .444Water vapor resistance, m2 Pa W1 (SD) 1.787 (.143) 1.717 (.105) .036*Relative water vapor permeability, % (SD) 53.0 (2.7) 56.9 (1.6) .001*

*Statistically significant (p < .05).



of its interstitial pores, which was previously confirmed by its lower air permeability, decreased

water vapor permeability due to higher resistance to water vapor flow of the pores with reduced size.

It also may be assumed in the case of FCs knitted fabric that due to lower bulk density and packing

density of the two-folded hemp yarn, the migration of absorbed water vapor along the fiber surface

was hastened. The students t-test results confirmed the significant difference between the knitted

fabrics with respect to water vapor resistance and water vapor permeability (p values, Table 4).

Heat transfer through textile materials generally involves all three mechanisms: conduction, con-

vection, and radiation. However, it is generally accepted that heat transfer by conduction is more

significant than others. Since the thermal conductivity of air is lower than that of fibers, the thermal

conductivity of fibers is a major contributor to the heat transfer process. However, the air entrapped

in the fabric structure is also of considerable importance to the thermal behavior of the fabric, since

air behaves as an insulating medium. Thermal resistance of textile materials is determined by the

thermal conductivity of the fiber and fabric thickness. With the increase of the fabric thickness

and/or decrease of the fabric thermal conductivity, its thermal resistance increases. Since the FCs

knitted fabric was slightly thicker than 2Cs knit (Table 2), it could be expected FCs knit to increase

its thermal resistance. In addition, it could be expected that the air immobilized in the loose structure

of the two-folded yarn would reduce thermal conductivity of the FCs knit, whereas more intimate

contact between fibers in the single yarn, manifesting itself in higher bulk density and packing fac-

tor, should contribute to the conduction of thermal energy through 2Cs knit. Although thermal resis-

tance of the knitted fabric produced from two-folded hemp yarn was slightly higher in relation to that

of 2Cs knit (Table 4), the statistical analysis did not confirm the significance of the differences.

Therefore, it could be noted that there is no significant deterioration of thermal properties of the

knitted fabrics.

Concerning transport properties of the knitted fabrics, SD values showing how much dispersion

from the mean exists indicated better uniformity of air and water vapor permeability properties for

the knitted fabric produced from two-folded hemp yarn (Table 4).

Deformation and Surface Properties of the Knitted Fabrics

There is no unique optimal solution for the mechanical and surface properties of textile clothing

materials. However, there are still some universal design guidelines to maximize the tactile comfort

of textile materials. In addition to the extensibility of fabric, which should be maximized even at the

expense of tensile resilience, shear hysteresis and bending rigidity should be minimized so as to

obtain extensible and flexible textile materials. In order to produce soft and smooth textile fabric,

compressibility and compressional resilience (RC) should be maximized, while the surface coeffi-

cient of friction, variation of coefficient of friction, and surface geometrical roughness should all be

Table 5. Compression and Tensile Properties of the Plain Hemp Knitted Fabrics.

Parameter, Unit Hemp Hemp, 2Cs Hemp/Hemp, FCs p Value (a .05)Compression WC, Nm/m2 (SD) .505 (.031) .608 (.021) .008*

EMC, % (SD) .462 (.043) .488 (.054) .016*RC, % (SD) 31.48 (6.68) 32.29 (6.67) .889LC (SD) .310 (.08) .280 (.06) .755

Tensile WT, Nm/m2 (SD) 15.29 (2.85) 15.39 (1.82) .971EMT, % (SD) 9.51 (.40) 10.07 (.14) .656RT, % (SD) 31.75 (6.15) 30.59 (4.57) .836LT (SD) .656 (.001) .624 (.001) .000*

*Statistically significant (p < .05).



minimized. According to various investigations, the deformation behavior of clothing materials in

compression, tension, bending, and shear is dependent on fiber type and both yarn and fabric struc-

ture. Since only one fiber type was used in this investigation, and knitted fabrics were produced

under controlled settings, the influence of yarn structure and properties on tactile comfort could

be evaluated.

Compression behavior of textile materials is a determining factor in wearing comfort, since it is

closely related to their smoothness and softness. Four indices can be used as a measure of compres-

sion behavior: compressibility (EMC, relative compressibility calculated as a percentage of original

fabric thickness), compression energy (WC), compression linearity (LC), and compression resili-

ence (RC). Higher softness is reflected by higher values of EMC and WC and lower values of

LC (the compression load-thickness curve exhibits higher deviations from linearity). According

to the parameters EMC, WC, and LC (presented in Table 5), the knitted fabric produced from

two-folded hemp yarn was characterized by higher softness in relation to the knitted fabric produced

from single hemp yarn. Having lower bending rigidity, as well as fiber-packing density and conse-

quently, higher fiber mobility, the two-folded hemp yarn contributed to the higher compressibility of

FCs knit. Difference in compression behavior could also have resulted from fabric stitch density.

The previous results have shown that the increase of stitch density (i.e., the increase of the number

of yarn contact points) reduces the inter-yarn and interfiber mobility, leading to the reduction of

knits compressibility (Choi & Ashdown, 2000; Stankovic, 2008). However, it should be noted that

in this investigation the variation of stitch density resulted from the structure of the yarns used. An

easier movement, the slippage of two-folded yarn into knit, and hemp fibers into this yarn due to

lower stitch density of FCs knit enable its more compressible structure in relation to 2Cs knit. The

improvement in compressibility of the FCs knitted fabric was statistically confirmed for EMC and

WC parameters (p values, Table 5). Regarding RC, the greater the RC values, the better the retention

ability of the fabric after compression. Better retention ability of FCs knit (Table 5) can be explained

by the increased friction between single components into two-folded yarn caused by introduced sec-

ondary twist. Although better RC of the FCs knit was not statistically confirmed (p values, Table 5),

we believe that folding technique can provide an improvement in retention ability of fabrics under

compression.

Besides better compression, knitted fabrics have greater elasticity and ability of relaxation com-

pared with woven fabrics. For this reason, a knitted fabric substantially contributes to increased

comfort with elasticity of the clothes because of the reduced pressure on the skin, allowing the body

movement to be free. In general, there are three factors contributing to the stretching of a plain

knitted fabric: friction resistance to relative displacement of yarns at the interlacing points, bending

deformation of the loops, and the yarn extension. Since clothing material is rarely stretched to a point

when the yarn is stretched, the most important yarn parameters responsible for the stretching of a

knit are considered to be the inter-yarn friction and yarn bending behavior. Extensibility (EMT) has

a good correlation with fabric comfort. A higher EMT value signifies greater tactile comfort. The

FCs knitted fabric was characterized by higher course extensibility (EMTcourse 8.93) in relationto that of 2Cs knit (EMTcourse 7.12), which is confirmed by a students t-test (p .0004). Thehigher course extensibility of FCs knit is attributed to the lower bending rigidity of two-folded hemp

yarn. In addition, the lower friction resistance to yarn movement in course direction due to lower

course density of FCs knitted fabric and consequently less number of interlacing points contributes

to the course extensibility of FCs knit. However, the knitted fabrics exhibited similar wale extensi-

bility (11.20 and 11.90 for FCs and 2Cs, respectively) and therefore similar averaged extensibility

(Table 5). The lower value of the linearity of load-extension curve (LT) for FCs knitted fabric (Table

5) means higher extensibility in the initial strain range and thus better comfort, which is confirmed

by a students t-test (p value, Table 5). LT is almost the same in the course and wale direction for

both knitted fabrics. Tensile resilience (RT) measures the recovery from tensile deformation and



indicates dimensional stability of textile material. In the course stretching of 2Cs knit, the lowest

EMT was followed by the highest RT (37.61%), which is significantly different (p .013) from thatof the FCs knit (34.9%). Being more resilient to tensile deformation in course direction due toincreased inter-yarn and interfiber frictional forces, 2Cs knit was characterized by better recovery.

However, higher averaged resilience of 2Cs knitted fabric (Table 5) was not statistically proven as a

consequence of similar RT values in wale direction (25.9 and 26.3 for 2Cs and FCs, respectively).

Better uniformity of the measured tensile parameters for the knitted fabric produced from two-folded

hemp yarn was confirmed by calculated SD.

Shear deformation is very common during the wearing process since fabric needs to be stretched

or sheared to a greater or lesser degree to conform to new body movement. Shear rigidity provides a

measure of the resistance to rotational movement of the threads within a material subjected to low

shear deformation. The lower the value, the more readily the material conforms to the intended

shape. As can be seen from Table 6, the knitted fabrics were different in shear rigidity (G). The shear

rigidity of FCs knit was quite uniform in both (wale and course) direction, whereas the shear rigidity

of 2Cs knit was much higher in course direction than wale direction. In addition, during shear defor-

mation in course direction, the shear rigidity of 2Cs knit was higher than that of FCs knit due to the

increased course density of the former, which in turn increased the resistance to slippage between the

yarn intersections. When comparing the values of shear rigidity in wale direction, the reduced value

for 2Cs knit was supposed to be a consequence of both the lower inter-yarn and intra-yarn frictional

forces in wale direction. Unlike the two-folded hemp yarn composed of two single components

twisted together in order to obtain new linear structure, in the assembled yarn, two single yarns

have been brought together immediately before knitting. Therefore, their inter-cohesion is mainly

determined by the number of interlacing points in 2Cs knit, which causes greater yarn slippage in

wale direction in relation to that of the two-folded yarn. In a two-folded yarn, even though fibers

Table 6. Shear and Surface Properties of the Plain Hemp Knitted Fabrics.

Parameter, Unit Hemp Hemp 2Cs Hemp/Hemp FCs p Value (a .05)Shear G, N/m. (SD) Wa 1.14 (.18) 1.56 (.05) .030*

Cb 1.73 (.15) 1.45 (.15) .040*Ac 1.43 (.16) 1.50 (.09) .554

2HG, N/m (SD) W 4.36 (.74) 6.25 (1.02) .024*C 6.76 (1.03) 5.56 (.86) .253A 5.56 (.86) 5.90 (.91) .672

2HG5, N/m (SD) W 4.83 (.22) 6.81 (1.03) .042*C 7.55 (.84) 6.05 (.52) .030*A 6.19 (.31) 6.43 (.77) .643

Surface properties MIU (SD) W .192 (.011) .189 (.009) .769C .255 (.037) .232 (.011) .360A .224 (.024) .211 (.009) .427

MMD (SD) W .0137 (.001) .0145 (.003) .680C .0469 (.005) .0336 (.006) .027*A .0303 (.003) .0240 (.004) .032*

SMD, mm (SD) W 5.501 (.533) 7.404 (.926) .037*C 27.956 (1.682) 27.976 (1.683) .989A 16.728 (1.022) 17.690 (.542) .223

Note. MIU surface coefficient of friction; MMD mean deviation of MIU; SMD geometric roughness of fabric surface.aWale.bCourse.cAverage.*Statistically significant (p < .05).



are partially untwisted with increased mobility inside the yarn, the slippage of the yarn is reduced

due to well-integrated fiber assembly in its structure enabled by secondary twist. Additionally, due

to the higher covering power of the two-folded yarn, the areas of frictional contact inside the stitches

were increased which caused the slippage of the yarn to decrease. As can be seen in Figure 2, the

areas of frictional contact between yarn segments forming a loop are lower in 2Cs knitted fabric,

thus providing reduced resistance to shear deformation in wale direction. The differences in wale

and course shear rigidity between the two knits were statistically confirmed (p values, Table 6);

however, there is no difference in averaged shear rigidity between the knits due to the compensating

effect of directional (wale and course) rigidity. Shear hysteresis is defined as the friction force occur-

ring among interlacing points of the treads when they are moving over each other measured at+.5

shear angle (2HG) and+5 shear angle (2HG5). The lower the 2HG and 2HG5, the better the recov-ery from shear deformation. Similar to shear rigidity, the knitted fabrics were characterized by dif-

ferent 2HG and 2HG5 parameters. The ability of FCs knit to recover from wale- and course-

directional shear deformation was converged, whereas the values of 2HG and 2HG5 parameters for

2Cs knit were lower in wale than those in course direction (Table 6). According to the parameters

similar profiles of the knitted fabrics regarding shear behavior, it can be concluded that the stitch

density of the knits and friction between fibers and yarns, which in turn resulted from yarn charac-

teristics, are responsible for directional shear hysteresis (as confirmed by statistical analysis). But,

again, there is no statistically proven difference in averaged shear hysteresis parameters. An

improvement in course-directional shear deformation of the FCs knitted fabric was followed by

an improvement in uniformity of the measured KES parameters, which is indicated by the calculated

SD (Table 6).

Generally, the knit surface has a number of ridges formed by yarns and, in the case of a staple

yarn, is covered with a large number of fibers protruding out of the yarn bulk. Since the skin-

fabric contact areas as well as surface fibers act as the transmitting media of the mechanical load,

the surface properties of textile materials are considered to be an important determinant of tactile

comfort. Surface properties are represented by the surface coefficient of friction, the mean deviation

of coefficient of friction (MMD), and geometrical roughness of the fabric surface (SMD). A lower

value of MIU, MMD, and SMD indicates the smoother surface of the knit. According to the results

presented in Table 6, MIU and MMD for the knitted fabric produced from two-folded hemp yarn

were less than that of the knit produced from two-assembled yarn. However, it should be noted that

the t-test results did not confirm this for the MIU. Nevertheless, SD indicated improved uniformity

of FCs knit with regard to the MIU (Table 6). This is also confirmed by the MMD, especially in

course direction, which can be explained by improved uniformity of two-folded yarn. Namely, the

diameter of the two-folded hemp yarn was expected to be more regular than that of the single yarn,

since the irregularities of both single components were partially compensated. The results of surface

roughness indicated quite different values of the parameter SMD in wale and course directions

(Table 6). This directional difference resulted from stitch formations in the weft-knit structure.

Roughness is generally greater in course direction since stitches are connected in the wale direction.

Having the same wale density (i.e., the density in horizontal direction; Table 2), the knitted fabrics

were characterized by the same roughness. However, in wale direction, FCs knit was rougher than

2Cs knit probably due to higher packing density of single yarn. The higher packing density of single

yarn together with the closer aggregation of yarn in a vertical direction (higher course density of 2Cs

knit) seems to cause more regular contours in the wale direction at least as it was recorded by KES-

FB4 unit. Although the t-test results verified these comments (p values, Table 6), we believe that the

difference in SMD value of the knitted fabrics in course direction was not as large as measured by

the KES-FB4 unit, thanks to the compensating effect of yarn spacing. The lower packing density of

the two-folded hemp yarn, as well as the slightly higher loop length of FCs knit, made this yarn even

bulkier since it was not stressed in compression. Due to this relaxation of the yarn, which can be seen



in Figure 2, FCs knitted fabric has higher softness (compressibility, Table 5) and larger real contact

area than the one made of single yarn. During the measurement of surface roughness using the KES-

FB4 unit, a contact between the probe (steel wire) and the surface exists which causes the yarn to be

stressed and not relaxed as is the real case.

Conclusion

In the scope of this study, the knitted fabrics composed of single or two-folded hemp yarn were com-

pared from the aspect of comfort properties in order to bring to light the potential of yarn folding for

clothing comfort. On the basis of the results obtained, some conclusions can be drawn. The operation

of yarn folding influences both primary and secondary parameters of the knitted fabric structure

through the effectiveness of fiber aggregation, which manifests itself in packing density and bulk

density of the complex yarn. Moreover, the new quality structure of the two-folded hemp yarn,

with the new properties coming from the changes in fiber orientation in the first place, was proved to

have a great influence on comfort properties of the knitted fabrics. The results indicated an improve-

ment in air permeability and water vapor permeability of the knits produced from two-folded hemp

yarn, whereas the increase of thermal resistance was not proved. The results concerning deformation

behavior indicated a mainly positive effect of yarn folding on compression behavior and course-

directional tensile and shear deformations. An improvement in transport and deformation properties

was followed by an improvement in uniformity of the measured parameters. As a consequence of

reduced two-folded yarn mobility in wale direction, higher resistance to shear deformation of the

knit was noticed. This mainly positive influence on comfort properties was reflected through the air

volume distribution within the fabric as well as the intra- and inter-yarn mobility which are highly

related to the transport properties, deformation behavior, and surface properties of clothing

materials.

Since the deformation properties of the knitted fabric composed of two-folded hemp yarn are

improved (with the exception of the resistance to shear deformation in wale direction) without seri-

ous deterioration of its transport and surface properties, the folding operation merits further consid-

eration as an effective means for improving tactile comfort properties of hemp textile materials.

Although the results obtained cannot be explicitly extrapolated to clothing materials other than

those tested in this study, it could be said with certainty that the influence of yarn folding on fabric

comfort cannot be neglected. Further investigations including various fiber types, textile materials

with a wide variety of structures, and yarns with a wide range of folding density are needed in order

to ascertain the general guidelines for design of clothing materials with satisfactory comfort

properties.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or

publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publica-

tion of this article: This research was funded by the Ministry of Education, Science and Technological Devel-

opment of the Republic of Serbia by the Project OI-171029.

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Author Biographies

Snezana B. Stankovic, PhD, is an assistant professor in the Textile Engineering Department at Faculty of

Technology and Metallurgy, University of Belgrade (Serbia). Her research interests are in the area of clothing

comfort: thermal and tactile comfort, as well as the structure and properties of textile materials.

Matejka Bizjak, PhD, is an associate professor in the Department of Textiles at Faculty of Natural Science and

Engineering, University of Ljubljana (Slovenia). Her research interests are in the area of clothing comfort,

structure, and properties of textile materials as well as structure of historical textiles (Coptic weaving and

woven structures).



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