Moisture management of underwear fabrics and

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Moisture management of underwear fabrics and linings of firefighter protective clothing assemblies ab

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Stojanka Petrusic , Elena Onofrei , Gauthier Bedek , Cezar Codau , Daniel Dupont & Damien Soulat

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ENSAIT, GEMTEX, Roubaix, France

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University Lille Nord de France, Lille, France

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Catholic University of Lille, HEI, GEMTEX, Lille, France

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Technical University “Gheorghe Asachi” of Iasi, Faculty of Textiles-Leather and Industrial Management, Iasi, Romania Published online: 02 Jan 2015.

Click for updates To cite this article: Stojanka Petrusic, Elena Onofrei, Gauthier Bedek, Cezar Codau, Daniel Dupont & Damien Soulat (2015): Moisture management of underwear fabrics and linings of firefighter protective clothing assemblies, The Journal of The Textile Institute, DOI: 10.1080/00405000.2014.995457 To link to this article: http://dx.doi.org/10.1080/00405000.2014.995457

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The Journal of The Textile Institute, 2014 http://dx.doi.org/10.1080/00405000.2014.995457

Moisture management of underwear fabrics and linings of firefighter protective clothing assemblies Stojanka Petrusica,b*, Elena Onofreic,d, Gauthier Bedekc, Cezar Codauc, Daniel Dupontc and Damien Soulata,b a

ENSAIT, GEMTEX, Roubaix, France; bUniversity Lille Nord de France, Lille, France; cCatholic University of Lille, HEI, GEMTEX, Lille, France; dTechnical University “Gheorghe Asachi” of Iasi, Faculty of Textiles-Leather and Industrial Management, Iasi, Romania

Downloaded by [Bibliotheque Universitaire D'Orleans] at 07:42 12 May 2015

(Received 15 October 2014; accepted 13 November 2014) Thermal comfort of firefighters is strongly dependent on moisture management of clothing layers closest to the skin. This study centers on liquid moisture and moisture vapor transfer across various types of underwear fabrics and innermost layers of the firefighter intervention jacket (linings). Importance of the underwear neighboring layer in liquid moisture and moisture vapor transfer and hence, in thermal comfort of a firefighter is underlined and discussed. Moisture management tester is employed as an efficient tool in evaluating a transfer of liquid moisture not only through individual underwear fabric but also through bi-layers underwear lining. Moisture vapor transfer properties of mono- and bi-layer fabrics were investigated by evaporative dish method. The results show that moisture management performances of tested mono- and bi-layer fabrics are related to their composition and the general physical properties. Composition of both underwear and lining has a crucial impact on liquid moisture transfer through bi-layers. Transfer of moisture vapor is mainly governed by fabric physical properties. Combination of natural and synthetic fibers results in best performing fabrics with regard to the moisture management. Keywords: thermal comfort; moisture transfer; firefighter protective clothing; underwear fabrics; moisture management tester

Introduction Apart from the primary role of firefighter protective clothing to provide protection against environmental impacts, it should also provide a certain level of comfort to a wearer. According to Rossi, four aspects of clothing comfort can be distinguished: sensorial, body movement, psychological, and thermal comfort (Rossi, 2005). Sensorial comfort refers to the induction of various sensations when a fabric comes in contact with skin. Body movement comfort concerns person’s freedom of movement inside the clothes, decreased burden or load on the body and body shaping (Ibrahim & Genedy, 2012). Psychological comfort associates with the esthetics and the suitability of the clothing for the occasion (Rossi, 2005). Finally, thermal or thermophysiological comfort is related to the transport of heat and moisture through a fabric. This aspect of clothing comfort is regarded as highly influential on performances of firefighters, in addition to their safety (Onofrei et al., 2014). A state of thermal comfort refers to a state of body heat balance. Design and properties of the protective clothing directly impact certain processes that lead to body heat gains and losses, such as radiation, conduction, convection, and evaporation of perspiration (ASHRAE, 2010). When the environmental temperature is high and/or a person is involved in intensive physical *Corresponding author. Email: [email protected] © 2014 The Textile Institute

activities, intensive perspiration occurs. When a transfer of moisture (and heat) away from the body through the clothing layers is not efficient enough, a feeling of discomfort appears due to skin wetness (Gerrett, 2012). If the sweat cannot be efficiently evaporated and a cooling effect is impaired, a risk of heat stress increases. Moreover, heat protection properties of the overall garment alter with change in moisture content (Keiser, Becker, & Rossi, 2008). Hence, an important aspect of thermal comfort of firefighters refers to the liquid moisture and moisture vapor management of their clothing, in particular, of the layers that are closest to the skin (Hu, Li, Yeung, Wong, & Xu, 2005). A standard firefighter intervention jacket contains four fabric layers: an outer shell, a moisture barrier, a thermal insulation, and a lining. Main role of the outer shell is to protect a wearer from the direct flame and physical hazards. Moisture barrier provides safety from the external source of water but also allows passage of water vapor from body toward the outside. Layer of thermal insulation is characterized by low thermal conductivity and thus is the most responsible for lowering heat transfer from the environment to a wearer. The last, innermost layer (lining or face cloth), acts as a mechanical support for the thermal insulation and comes in direct contact with the underwear. It is proved that lining significantly affects distribution of the perspiration


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and the ultimate skin feeling (Keiser et al., 2008). Studies on moisture distribution in firefighter protective clothing assemblies indicate that more than 75% of the perspiration accumulates in the inner two or three clothing layers (Keiser et al., 2008; Mäkinen, Smolander, & Vuorinen, 1988). Hence, it is of high importance to understand the parameters of moisture transfer from the underwear fabric into the innermost layer of the firefighter protective garment. This paper centers on detailed moisture management behavior of various types of underwear fabrics (UW) specially developed for firefighters and linings of firefighter intervention jackets. Beside UW of pure natural (cotton) fibers, that were the topic of relevant studies on moisture absorption in firefighter multi-layer protective clothing (Keiser et al., 2008; Mäkinen et al., 1988), this study also reports on performances of knitted UW based on combination of natural and synthetic fibers, as increasingly popular underwear fabric types in European firefighter protective clothing market. Moisture management tester (MMT) was used as a main tool for evaluating liquid moisture management of selected mono- and bi-layer fabrics. The MMT, developed almost a decade ago (Yao, Li, Hu, Kwok, & Yeung, 2006) has been aimed at testing of single fabrics and not the multi-layers (AATCC, 2010). This study highlights the applicability and utility of the MMT in analysis of liquid moisture transfer through complex bi-layer fabric structures, and not only through mono-layers intended for firefighter protective garments. Analysis of moisture vapor transfer through mono- and bi-layer fabric structures was performed according to evaporative dish method (BS 7209, 1990). The impact of knit structures of individual fabrics composed of cotton and cotton/ polyester on their breathability using evaporative dish method was reported by several researchers (Chen, Fan, Sarkar, & Jiang, 2010; Kanakaraj, Dasaradan, & Ramachandran, 2013). However, there has not been enough research focus on moisture vapor transfer properties of underwear and protective clothing intended for firefighters, in particular, not on bi-layer structures. The present study discusses vapor and liquid transfer properties of various types of individual firefighter UW as well as their bi-layer combination with linings of firefighter intervention jacket. The role of fabric fiber composition and general physical properties in transfer of moisture is examined using standardized and accessible experimental methods. Materials and methods Fabric materials Firefighter underwear fabrics (UW) of three fiber compositions (aramid/viscose, cotton, and cotton/

Protex®) were selected for characterization, each of them in two knitted structures (interlock and jersey pique). The UW fabrics were also tested in combination with three types of woven linings (L). Summary of fabric name codes along with general description of their structures and compositions is given in Table 1. Determination of general physical properties Thickness of fabrics was measured under a pressure of 1 ± 0.01 kPa, according to the standard ISO 5084. Values of fabric surface weight were determined gravimetrically, as an average of 10 measurements. Density was calculated from the values of fabric thickness and surface weight. The same procedures were applied for characterization of fabric bi-layers. Air permeability of the fabric samples was determined using an air permeability meter FX 3300 under a pressure drop of 100 Pa, in compliance with the standard ISO 9237 (1995). Air permeability was obtained as the volume of air in liters which is passed through a defined surface of the fabric in cm² in one second at a predetermined pressure difference. An average of 10 readings was taken for each fabric type. Cover factor of knitted fabrics was determined according to Cioară (2011), while that of woven fabrics using the relationship given in Spencer (2001). Determination of fabrics moisture regain was performed in accordance with the French standard for the methods of chemical analysis of fibers, yarns and fabrics NF G 06-006 (AFNOR, 1988). The weight of samples in equilibrium with standard atmospheric conditions was measured after conditioning period of 24 h in a climatic chamber at 20°C and 65% RH. Dry weight of the samples was determined after 4 h-drying at 105°C followed by 2 h-cooling in a desiccator at room temperature. Moisture management tester Moisture management properties of the selected UW fabrics, L fabrics, and bi-layers UW/L were measured using a MMT, conforming to AATCC Test Method 195 “Liquid Moisture Management Properties of Textile Fabrics” (AATCC, 2010). The tests were performed by dropping a predetermined amount of artificial sweat solution onto the center of upward-facing surface of a sample that is placed between two horizontal electrical sensors, each with seven concentric pins. Scheme of the MMT experimental setup is given in Figure 1. A number of MMT indices are determined for grading the liquid moisture management properties of fabric that are based on a transfer of liquid in three directions: radial spreading on the top surface, movement from the top to the bottom surface, and radial spreading

The Journal of The Textile Institute Table 1.

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General description of tested fabric types.

Fabric name code

Function

Structure

Composition

AV_P C_P CP_P AV_I C_I CP_I L1 L2 L3

Underwear

Knitted – jersey pique

Aramid/viscose Cotton Cotton/Protex®a Aramid/viscose Cotton Cotton/Protex®a Aramid Aramid/antistatic P140 Aramid/viscose/antistatic P140

Knitted – interlock Lining

Woven – honeycomb weave Woven – ripstop plain weave Woven – ripstop plain weave

Protex® is a registered trademark of specialized modacrylic fiber (Kaneka Americas Holding Inc., 2014).


a

Figure 1.

Scheme of the MMT setup.

on the bottom surface of the fabric (AATCC, 2010). Apart from the indices, such as wetting time, absorption rate, maximum wetted radius, and spreading speed, for comparison of fabric performances, accumulative one-way transport capability (AOWT) and overall moisture management capability (OMMC) were analyzed as well. AOWT denotes the difference between the area of the liquid moisture content curves of the top and bottom surface of a specimen with respect to time. OMMC is a measure of the overall capability of a fabric to transport liquid moisture and is calculated by combining three other indices: absorption rate on the bottom surface, AOWT, and spreading speed on the bottom surface (AATCC, 2010). Each mono-layer and bi-layer type was tested five times and the corresponding indices and percentages of water content are presented as average values. All fabrics were subjected to five washing cycles at 40°C (followed by air drying) prior to MMT measurements. Distribution of liquid remained in the upper (UW) and the lower (L) fabrics of bi-layers was determined gravimetrically by weighing fabrics immediately before and after the MMT tests. Percentage of the total amount of liquid remained in each of the layers was calculated as a ratio of liquid weight in a layer and the overall weight of liquid in both layers. Evaporative dish method tester Moisture vapor transfer properties of the fabric monoand bi-layers were analyzed by evaporative dish method,

using an experimental setup defined by the standard BS 7209 (1990). Testing procedure implied sealing the test sample over the open mouth of a test dish that contains predetermined quantity of water to give a 10 ± 1 mm deep layer of air between the surface of the water and the bottom surface of the sample. In each test run, 100% woven polyester satin fabric was used as a reference. Assembled dishes were placed on a turntable and rotated uniformly to avoid formation of still air layers above the test dishes (Figure 2). Difference in partial vapor pressure on both sides of a fabric is a driving force for water vapor transfer. The dishes were weighed before and after a 16 h-conditioning period in a controlled atmosphere with temperature variation of ±2°C and relative humidity variation of ±3%. Water vapor permeability (WVP) in g m−2/day of a specimen was calculated from the weight loss of the assembled dish over the predetermined time according to the Equation (1) (BS 7209, 1990): WVP ¼

24 M ; At

(1)

where M (in g) is the loss in mass of the assembled dish over the time period t (in h), A is the area of exposed test specimen equal to the internal area of the test dish (0.0054106 m²). To compare the behavior among the samples, a WVP index I (%) was used. It was determined as a ratio of WVP of the fabric under test (WVP)test and WVP of the reference fabric (WVP)ref, as

Figure 2.

Scheme of the evaporative dish method setup.

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shown by Equation (2). Each value of I was obtained as an average of three measurements. I¼

ðWVPÞtest 100: ðWVPÞref

(2)


Pearson’s correlation coefficient The strength of linear correlation between two variables, a value of general physical property (thickness, surface weight, and density) and a value of WVP index of bi-layers UW/L, was evaluated through values of Pearson’s correlation coefficient (as well as graphically). Pearson’s coefficient can take value between +1 (total positive correlation) and −1 (total negative correlation), where 0 signifies the absence of correlation. Results and discussion General physical properties Measured average values of general physical properties of washed UW and L fabrics are given in Table 2. The thickest UW fabric is aramid/viscose pique knit sample, which also features the lowest bulk density. Interlock knit UW samples are thinner, less air permeable, and of lower cover factor in comparison with their pique knit counterparts of the same fiber composition (except for cotton/Protex® composition). In comparison to similar moisture regain values of cotton and aramid/viscose fabrics, fabrics of cotton/Protex® composition have significantly lower moisture regain, primarily due to low moisture regain of synthetic Protex® fibers (modacrylic). Chosen linings are of similar densities and have slight differences in thickness, with pure aramid lining being the thickest one. Liquid moisture transfer properties Transfer of moisture through fabrics occurs via two main processes, wicking and absorption. Good wicking abilities imply efficient moving of liquid from the skin

Table 2.

General physical properties of washed fabrics.

Thickness Sample (±SD), mm AV_P AV_I C_P C_I CP_P CP_I L1 L2 L3

surface to the outside surface of the fabric. On the other hand, absorption refers to the uptake of moisture by individual fibers from the surface of skin. Natural fibers like cotton and regenerated cellulose fibers like viscose show much higher absorption abilities in comparison with synthetic ones (e.g. aramid, acrylic). These properties affect the ultimate values of a number of MMT indices. Measured average values of wetting time, maximum wetted radius, absorption rate, and spreading speed of all six individual UW fabrics are plotted (Figure 3). Similar top and bottom wetting time was registered for AV_I, AV_P, C_I, and CP_P and higher bottom wetting than top wetting time for C_P and CP_I. Therefore, moisture does not remain longer at the top of fabric surface, i.e. near the skin, but is transferred faster to the bottom surface. The longest time to get wetted requires cotton pique-knitted UW, notably higher than its interlock knit counterpart (Figure 3(a)). The reason for that can be found in lower cover factor of C_I, i.e. its more open structure, which is in accordance with findings in literature (Venkatesh & Ninge Gowda, 2013). The maximum wetted radii on top and bottom surfaces are of high grade (AATCC, 2010), and almost the same for all fabrics except for AV_P (Figure 3(b)). This result implies that liquid moisture is spreading in a large radius and thus, increases the probabilities for faster evaporation of sweat from fabrics away from the skin. The smallest maximum wetted radius was recorded for the sample C_P, which, followed by C_I, as a consequence of the strong absorption of liquid by cotton fibers. All the fabrics have higher bottom than top absorption rate. These findings would lead to the conclusion that the bottom surface of the fabrics has greater ability to absorb moisture than the top surface, but this can be attributed also to the horizontal position of the samples and to the gravity force. No appreciable differences in absorption rate are detected among the analyzed fabric types (Figure 3(c)). In other words, only the initial changes of water content at start of solution injection period were similar for all samples (according

1.34 ± 0.01 1.18 ± 0.02 1.22 ± 0.01 1.04 ± 0.02 0.90 ± 0.01 0.88 ± 0.01 0.48 ± 0.01 0.33 ± 0.00 0.40 ± 0.01

Surface weight (±SD), g m−2 260 ± 5 248 ± 3 262 ± 5 276 ± 5 254 ± 4 220 ± 5 150 ± 1 109 ± 1 127 ± 2

Bulk density (±SD), kg m−3 194 ± 3 210 ± 4 215 ± 3 265 ± 4 281 ± 5 250 ± 7 316 ± 6 330 ± 4 322 ± 8

Cover factor 1.71 1.24 1.58 1.37 1.85 1.28 99.0% 84.8% 76.6%

Air permeability (±SD), l m−² s−1 1898 ± 46 1481 ± 25 888 ± 15 354 ± 12 687 ± 9 948 ± 41 282 ± 11 1367 ± 54 1163 ± 26

Moisture regain (±SD), (%) 7.2 ± 0.2 6.5 ± 0.1 6.6 ± 0.1 6.2 ± 0.2 2.7 ± 0.1 2.7 ± 0.1 5.5 ± 0.2 4.7 ± 0.2 7.6 ± 0.1


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Figure 3. Selected MMT indices of individual UW fabrics: wetting time (a), maximum wetted radius (b), absorption rate (c), and spreading speed (d).

to definition of absorption rate by AATCC, (2010)). On the other hand, spreading speed values indicate that highest wicking abilities on both surfaces have aramid/ viscose interlock-knitted fabric AV_I and cotton/protex® pique-knitted fabric CP_P (Figure 3(d)). It can be concluded that these two fabrics, composed of combination of natural and synthetic fibers, provide the best skin feeling since high maximum wetted radius along with good spreading speed increases the possibilities of more efficient evaporation of perspiration, i.e. quick drying. Indices of AOWT of six UW fabrics range from −10 to 65%. These results imply that all UW types belong to the same grading group that refers to the fabrics of fair ability to transfer liquid away from the skin (AATCC, 2010). According to overall moisture management capacity (OMMC) values (Figure 4), the least performing fabric is cotton pique-knitted one (C_P). Table 3 summarizes the average values of 10 MMT indices obtained for three lining fabrics. Fabrics L2 and L3 are designated as water penetration fabrics due to excellent values of AOWT index. These results could be explained by small thickness of lining L2 and good ratio of absorption and wicking abilities of lining L3 that is composed of aramid and viscose. On the other hand, pure aramid lining L1 is characterized as good

Figure 4. Overall moisture management capacity of individual UW fabrics.

absorption and quick drying fabric, but of overall lower moisture management capability in comparison with other two samples. After analysis of liquid moisture transport through individual fabrics, we combined the two types of clothing layers, UW and L. MMT tests on bi-layers were performed by placing UW fabric on top, so as to be in a direct contact with the injection solution. According to the report of constructors of MMT instrument, the values of MMT indices were initially established on a basis of tests performed only on mono-layer fabrics (Yao et al.,

4.10 (0.22) 6.46 (1.39) 10.73 (0.78)

Top

4.53 (0.31) 6.22 (1.07) 9.33 (0.99)

Bottom

Wetting time (s) Top 62.48 (4.82) 67.14 (8.11) 80.42 (9.61)

Bottom

Absorption rate (%/s)

50.50 (5.15) 8.42 (1.38) 6.47 (0.85)

MMT indices of individual L fabrics.

Note: Standard deviation values are given in parenthesis.

L1 L2 L3

Sample

Table 3.

26 (2.24) 12.5 (3) 10 (0)

Top 25 (0) 12.5 (5) 10 (0)

Bottom

Max wetted radius (mm)

4.27 (0.32) 1.43 (0.35) 0.74 (0.08)

Top

4.05 (0.23) 1.40 (0.39) 0.81 (0.02)

Bottom

Spreading speed (mm/s)


47.28 (38.75) 687.21 (65.34) 759.81 (38.00)

AOWT index (%)

0.50 (0.03) 0.69 (0.03) 0.70 (0.03)

OMMC

6 S. Petrusic et al.


The Journal of The Textile Institute 2006). Hence, MMT indices obtained for UW/L bi-layers in this study are not presented nor discussed. Nevertheless, water content curves obtained for bi-layers were taken in consideration and as a valid reference for comparison of liquid transfer within the complex structure and liquid distribution between the layers. Water content profiles registered for top and bottom surfaces of UW/L bi-layers are presented in Figures 5 and 6. Figure 5 refers to bi-layers of pique knit UW and L, while Figure 6 displays result of bi-layers of interlock knit UW and L fabrics. Among bi-layers with pique knit UW, the highest water content on top surface of UW was detected for bi-layer C_P/L1 (Figure 5(a)), as the combination of mono-layers with individually weakest ability of liquid management. Water content profiles on bottom surface of bi-layers can give us information on time necessary for liquid to be transferred from UW fabric to the bottom surface of L fabric. Figure 5(b) indicates that the

Figure 5.

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shortest time necessary for bottom layer to get wetted is registered for the combination of pique knit UW of aramid/viscose composition and lining L2. In other words, transfer of liquid away from the skin is fastest for bi-layers AV_P/L2. This result can be explained by the fact that AV_P possesses the best wicking abilities, while L2 is the thinnest and least dense among the linings (Table 2). On the other hand, according to MMT water content curves, at the end of measuring period more liquid is transferred to L3 when it is combined with AV_P and C_P. This is the consequence of hydrophilic nature of L3 due to viscose presence, as opposed to L1 and L2, which is also depicted in their moisture regain values (Table 2). Finally, the least liquid is transferred from top to bottom in case of bi-layers cotton/Protex® pique knit UW (CP_P) and pure aramid lining (L1). According to the water content profiles obtained for bi-layers containing interlock knit UW fabric (Figure 6(b)), the most efficient liquid transfer occurs

MMT curves of water content at top surface (a) and bottom surface (b) of bi-layers pique knitted UW/L.


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Figure 6.

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MMT curves of water content at top surface (a) and bottom surface (b) of bi-layers interlock knitted UW/L.

from CP_I to L3 and from CP_I to L2, even though AV_I (aramid/viscose) combined with L2 and L3 provides quicker wetting of the bottom surface. Both Figures 5 and 6 show that linings L2 and L3 provide almost the same liquid moisture management behavior when they are combined with same type of UW fabric. It can be also observed that individual AV_I sample that feature almost as much as good liquid management properties as CP_I, does not manage liquid as good when it is in a bi-layer. Hence, moisture accumulated in the underwear depends not only on the material of the underwear, but also on the interaction with the neighboring layer and the ability of water to evaporate. From the aspect of fiber composition, correlations among MMT curves of bi-layers with pique knit UW are not the same as those of bi-layers with interlock knit UW fabrics. To understand those results, one should take into consideration the fact that differences in physical properties among AV_P, C_P, and CP_P are not the

same as those among AV_I, C_I, and CP_I. Geometrical factors like loop length and threads density (yarns/cm)

Figure 7. Weight fraction distribution of liquid in UW and L fabrics at the end of MMT test on bi-layers.

The Journal of The Textile Institute


Table 4.

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WVP index and corresponding standard deviation values of individual UW and L fabrics.

Sample

AV_P

AV_I

C_P

C_I

CP_P

CP_I

L1

L2

L3

I, % SD, %

98.01 2.18

98.51 1.11

98.56 1.70

99.46 0.66

101.01 2.13

98.83 2.29

98.23 1.38

101.78 1.23

101.67 0.10

that determine the cover factor and inter-yarn spaces might have a significant role in liquid transfer through fabrics (Zhu & Takatera, 2013). Gravimetrical determination of the weight fraction of liquid remained in each fabric of UW/L bi-layer at the end of MMT tests was conducted to verify the conclusion withdrawn from MMT water content curves. Weight fraction distributions of liquid in UW and L fabrics are shown in Figure 7. The higher is the liquid fraction in the lining, the better is the thermal comfort since perspiration is more efficiently removed from the skin surface. Gravimetrical measurements confirm that the best performing bi-layers in terms of liquid management are CP_I-L3, followed by AV_I-L2 and AV_I-L3. Likewise, the least desirable combinations are cotton/Protex® pique knit UW (CP_P) and cotton interlock knit UW (C_I) with pure aramid L (L1). The reasons for lower liquid moisture management performances of bi-layers with cotton UW than the aramid/viscose ones could be partly related to weaker wicking abilities of cotton textile structures and their higher water retention capacity that retards transfer of liquid to the neighboring layer. Differences among behavior of bi-layers of same UW and linings L2 and L3 are slight (with a minor advantage of L3) and altogether much better than of bi-layers with L1. Fabric L3 is more hydrophilic than L1 due to viscose presence and hence, absorbs liquid from the neighboring layer more efficiently. Good performances of L2 than L1 could be found in its smaller thickness and lower bulk density. Above given results are in accordance with the study of Keiser et al. who found that the moisture accumulated in the underwear depends not only on the material of the underwear, but also on the interaction with the neighboring layer and the ability of water to evaporate (Keiser et al., 2008).

Table 5.

Figure 8. bi-layers.

Water vapor permeability indices of UW/L

Moisture vapor transfer properties Apart from liquid moisture, another aspect of moisture transfer phenomena through fabric is a transfer of moisture vapor. This transfer determines a level of fabric breathability. Both mono- and bi-layer fabrics were tested by evaporative dish method. Values of WVP index (I) for all mono-layers are given in Table 4. WVP indices of all six UW fabric types have similar values. Transfer of water vapor through majority of fabrics is carried out via diffusion through air spaces within the fabric. Hence, water vapor transfer properties of fabrics depend on a number of geometrical variables (e.g. the yarn structure) that are not taken into account in this study. A general dependence of water vapor diffusion on air permeability of fabrics (Table 2) cannot be withdrawn. Even though certain authors support the claim that there is a correlation between WVP and air permeability of the fabric (Das, Das, Kothari, Fanguiero, & Araujo, 2007), the others reported that the correlation

Pearson’s correlation coefficient between general physical properties and WVP index of bi-layers UW/L. Water vapor permeability index

Physical property Thickness Surface weight Bulk density

All bi-layers

Bi-layers with pique UW

Bi-layers with interlock UW

−0.63 −0.80 0.25

−0.26 −0.92 −0.04

−0.96 −0.76 0.47

S. Petrusic et al.


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Figure 9. Graphical correlation of WVP indices of UW/L bi-layers with: thickness (a), surface density (b), and bulk density (c) of the bi-layers.


The Journal of The Textile Institute between WVP and air permeability, in case of double-layered knitted fabrics does not exist (Bivainyte & Mikucioniene, 2011). Figure 8 presents average I values obtained for bi-layers UW/L. As opposed to mono-layers, differences in breathability among bi-layers are notable. The addition of L layer to UW layer reduces rate of water vapor transfer from around 5% to 8%, in comparison with an individual UW. The least breathable bi-layers are those of pique-knitted UW fabrics in combination with pure aramid lining L1, the thickest among the linings. Although AV_P, C_P, and CP_P feature different physical properties, when they are combined with the same lining, they give bi-layers of more or less similar breathability. One could ascribe this behavior to the fact that pique knit structures are characterized by a rough fabric face that is in contact with a neighboring layer, a liner. Depending on the roughness of the fabric face, different quantity of air will be entrapped between tested pique UW samples and the corresponding L fabric. Hence, the water vapor diffusion might be affected. When evaluating the impact of the L fabrics on breathability of bi-layers with the same UW fabric, it is without exception clear that the most preferable lining is L2, followed by L3 and L1. If a comparison of bi-layers of interlock-knitted UW and same L fabric is undertaken, rising trend of WVP index with increase in UW sample thickness is observed. This conclusion is supported by high Pearson’s correlation coefficients between the thickness of the bi-layers that contain interlock-knitted UW fabrics and their I value (Table 5). The results in Table 5 show that the physical factors of bi-layers breathability determined by evaporative dish method are not the same for bi-layers with pique-knitted UW and for bi-layers with interlock-knitted UW. Graphical correlation between the general physical properties and the WVP index of bi-layers is given in Figure 9. Figure 9(a) confirms earlier indication that the transfer of moisture vapor through bi-layers with piqueknitted UW is not well correlated with the thickness of the system, as opposed to bi-layers with interlock-knitted UW that are characterized by more controllable and uniform contact of mono-layers. Marked bi-layer groups in Figure 9 show linear dependence between WVP index and thickness/surface weight/bulk density of bi-layers with same UW. Physical properties of the second layer, i.e. lining show notable impact on breathability of bi-layer structures. When considering all bi-layers, the highest breathability exhibited the combination of cotton/ Protex® interlock-knitted UW sample CP_I and the lining L2. This result can be related to general physical properties of the CP_I fabric as the thinnest and the least dense among all six underwear types. Thinner fabrics provide easier and faster diffusion of moisture vapor through their structure. Moisture vapor transmission

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through fabrics is assumed to be controlled mainly by constructional variables that determine fabric thickness and porosity, especially in low-density open textile structures (Onofrei, Rocha, & Catarino, 2011; Prahsarn, Barker, & Gupta, 2005). Therefore, results obtained in this study indicate the importance of transversal diffusion path length of moisture vapor through fabrics. Conclusions Liquid moisture and moisture vapor transfer phenomena within UW and innermost layers (linings) of firefighter protective clothing assemblies were investigated using MMT and evaporative dish method. The impact of fabric structure, their composition, and physical properties in managing the moisture transfer away from the skin was analyzed. Tests of liquid moisture transfer showed that UW composed of combination of natural and synthetic fibers transfer liquid moisture away from next-to-skin surface faster and more efficiently than those based on cotton, regardless of the knit type. Fabric bi-layers with aramid/viscose lining showed the most satisfying absorption and wicking abilities required for the efficient transfer of liquid moisture and moisture vapor. This study underlines the importance of the composition of underwear neighboring layer in liquid moisture transfer and hence, in thermal comfort of a wearer. MMT was proved to be useful tool in characterization of liquid moisture transfer properties of complex textile structures such as bi-layers. Management of moisture vapor by bi-layers underwear lining is mainly affected by construction variables of materials and less by their chemical composition. Design for firefighters as well as layers of firefighter protective garment demands consideration of both physical and chemical parameters in order to provide a high level of thermal comfort to a wearer. Further studies of liquid moisture distribution within the underwear and innermost layers of firefighter intervention jacket might include the analysis of pressure exercised upon tested samples via modification of the MMT, which would bring closer the bi-layer configuration to real conditions. Acknowledgments This study was financially supported by the French Region Nord-Pas-De-Calais and the European Regional Development Fund.

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