Scholarly article on topic 'Fabric Selection for the Reference Clothing Destined for Ergonomics Test of Protective Clothing: Physiological Comfort Point of View'

Fabric Selection for the Reference Clothing Destined for Ergonomics Test of Protective Clothing: Physiological Comfort Point of View Academic research paper on "Earth and related environmental sciences"

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Academic research paper on topic "Fabric Selection for the Reference Clothing Destined for Ergonomics Test of Protective Clothing: Physiological Comfort Point of View"

DE GRUYTER

FABRIC SELECTION FOR THE REFERENCE CLOTHING DESTINED FOR ERGONOMICS TEST OF PROTECTIVE CLOTHING: PHYSIOLOGICAL COMFORT POINT OF VIEW

Grazyna Bartkowiak1, Iwona Frydrych12, Agnieszka Greszta1

'Department of Personal Protective Equipment, Central Institute for Labour Protection - National

Research Institute, Lodz, Poland, 2Faculty of Material Technologies and Textile Design, Lodz University of Technology, Lodz, Poland

E-mail: grbar@ciop.lodz.pl

Abstract:

The currently used methods of ergonomic assessment of protective clothing depend on the subjective feeling of research participants and don't take into consideration all aspects of its use. Therefore, more amount of work is undertaken toward the development of new research tools for the ergonomic assessment of protective clothing. Research was carried out at the Central Institute for Labour Protection - National Research Institute in Lodz. A new methodology will take into consideration a variant of reference clothing, which is related to the results of ergonomics research of protective clothing. Preparation of the reference clothing initiated by picking the appropriate fabric is based on the results of parameters influencing the physiological comfort and sensorial comfort. In the current part, results of different fabric parameters are presented, which are related to physiological comfort, i.e., the thermal resistance, water vapor resistance, hygroscopicity, and air permeability. In the next part of research, we will focus on the parameters related to objective sensorial feelings, i.e., total hand value and its components. Seven fabrics, including six cotton/polyester fabrics, diverse in terms of constituent fiber content and structure parameters (weave, thread density per 1 dm, thread linear density, mass per square meter, thickness), and Tencel/polyester fabric were tested. The best in terms of thermal resistance, water vapor resistance, and air permeability was the cotton/ polyester fabric (35% cotton/ 65% PES) with the smallest mass per square meter. This fabric also exhibits the high hygroscopicity of 7.5%, which puts it into the fourth position.

Keywords:

Physiological comfort, reference clothing, protective clothing, ergonomics

1. Introduction

Protective clothing allows workers across many sectors of the economy to work safely, even in conditions where conditions dangerous to health and human life exist. Sometimes, however, the use of the protective clothing can cause a restriction of the movement in professional activities, resulting from too large mass of clothing, reduced discharge of sweat, too much rigidity, or too small flexibility in the materials used, which entails the reluctance or even total abandonment of workers from the protection application [26]. According to the Directive 89/686/EEC, the personal protective equipment, including the protective clothing should be so designed as to preclude risks and other nuisance factors in foreseen conditions of use [5]. Therefore, the protective clothing is tested not only in terms of protective properties, but it is also subjected to an ergonomic analysis.

The currently used methods of ergonomics assessment of protective clothing are based on assumptions contained in the relevant standards: EN ISO 13688: 2013 (the standard on the general requirements for the protective clothing) [22] and EN 469: 2014 (the standard presented the requirements for the

protective clothing for the use by firefighters during the action fire) [6]. However, these methods are not the best research tools, because they didn't take into consideration all aspects of the use of protective clothing and ergonomics assessment of protective clothing. They depend only on the subjective feelings of one, rarely a few participants in tests. Therefore, there were found new research tools that would allow for the objective ergonomic assessment of protective clothing [1, 18, 15, 16]. Work in this direction was carried out at the Central Institute for Labour Protection - National Research Institute in Lodz. A new methodology of ergonomics research will take into consideration a variant of reference clothing, which should be related to the results of ergonomics research of protective clothing. It is assumed that clothing has no protective properties, but designed to allow freedom of movement, but made of fabric, which is characterized by a small mass per square meter and thickness and very good biophysical and sensory parameters.

The first step toward the preparation of reference clothing was selection of appropriate fabric based on the results of parameters influencing the physiological comfort and sensorial comfort. The results of such research are presented in this publication.

Physiological comfort is defined as the state providing the human being with suitable microclimate in layers of the skin during his physical activities in various climatic conditions, while maintaining complete physical and mental efficiency [27]. Figure 1 shows the body's thermoregulatory mechanism, which protects from overheating or cooling down the body.

rain • * *

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T=const

environment T=const

Figure 1. The body's thermoregulatory mechanism

Physiological comfort is largely dependent on the used clothing, its construction as well as the properties of used materials such as the thermal resistance, water vapor resistance, hygroscopicity, and air permeability, which are called the biophysical properties [10, 28].

The most important factors influencing the thermal resistance of fabric is the thickness, cover factor, surface roughness, and a kind of finishing [3]. Numerous studies show that the thicker fabrics, made from the yarn of the higher linear density exhibit the greater thermal resistance than the thinner fabric [21, 22, 29]. In addition, research conducted by Frydrych, Dziworska, and Bilska [11] have shown that the thermal resistance of fabric depends also on a kind of raw material, from which it is made. Cotton fabrics, regardless the kind of weave, is characterized by the higher thermal resistance than the fabrics made of Tencel yarn.

The moisture transmission through textiles plays a very important role in maintaining physiological comfort[3, 4, 28]. The fabrics, of which the clothing is made, should allow the drainage of perspiration from the skin to the environment in order to cool the body and reduce the degradation of thermal insulation of the fabric caused by moisture buildup [2, 3, 10, 11, 12]. For this to happen, fabrics should be characterized by low water vapor resistance. Research conducted by Das et al. [4], and Nyak et al. [24] have shown that an increase of polyester content leads to the increase of the fabric water vapor resistance. Gericke and Van der Pol [12] investigated the properties related to physiological comfort of knitted cotton, bamboo, and viscose fabrics of similar structure, mass and finishing treatment, and found no significant differences in their "breathability".

Physiological comfort is also determined by hygroscopicity of

the clothing materials, or the ability to absorb moisture from the skin surface [10, 21]. Numerous studies show that this feature depends mainly on the properties of fibers, of which the product was made [19, 20, 28, 31]. The natural fibers are characterized by the good hygroscopicity [30]. Wool fibers are able to absorb up to 50% of the moisture without a feeling of wetness on touch. However, when it comes to synthetic fibers, their ability to absorb moisture is very low [19]. The amount of absorbed water depends also on the fabric weave, as well as its cover factor, and it has been demonstrated that fabrics with a loose, porous structure absorb significantly more moisture as compared to the fabric packed densely [3, 10].

An important impact on the feeling of physiological comfort comes from the air permeability of fabric. This parameter determines the hygienic property of clothing, because it allows for a drainage of carbon dioxide from the human body to the environment and at the same time it ensures providing fresh air [21, 28]. Several studies have shown that the air permeability is closely related to the structure of the fabric. Fabrics with the loose, porous structure exhibit the greatest air permeability [14, 23, 30].

As rightly stated, Kobiela-Mendrek [18], "a human residing in the physiological comfort reaches its maximum intellectual and manual possibilities".

The main aim of this paper is to study the influence of constituent fiber content and fabric structure parameters on their biophysical properties and selecting the fabric ensuring the highest level of physiological comfort.

2. Experimental

2.1. Materials

For research, seven fabrics of different raw material content and different structures were chosen. The fabrics were designated by letters from A to G (Table 1). In six cases, these are cotton/ polyester fabrics, wherein three of them, i.e., fabrics D, E, and G were characterized by the identical weave and the content of constituent fibers (35% cotton/65% PES), while the remaining structure parameters, i.e., the warp and weft density, warp and weft linear density, mass per square meter, and thickness were different. A viscose/polyester fabric with a preponderance of polyester fibers was also tested.

The selection criterion was the low mass per square meter and appropriate raw materials, i.e., the contents of both the hydrophilic fiber (cotton or viscose) and hydrophobic fiber (polyester). The participation of both kinds of fiber can provide satisfactory biophysical and biomechanical properties.

2.2. Methods

The selected fabrics were tested in terms of the following parameters of physiological comfort:

• Thermal resistance

• Water vapor resistance

AUTEX Research Journal, Vol. 16, No 4, December 2016, DOI: 10.1515/aut-2016-0037 © AUTEX Table. 1. Fabric characteristics

Symbol Raw materials Linear density [tex] Weave Number of threads per 1 dm [dm-1] Mass per square meter [g/m2] Thickness [mm]

Warp Weft Warp Weft

A Tencel 30% PES 70% 32.0±0.56 29.2±0.63 twill 2/1 S 389±1.30 241±0.84 196.9±1.51 0.29±0.005

B cotton 65% PES 35% 28.3±0.72 27.4±0.77 twill 2/1 S 370±1.67 238±0.71 190.0±1.24 0.38±0.007

C cotton 50% PES 50% 20.8±0.66 19.5±0.59 satin 4/1(2) 545±1.64 325±1.34 184.9±0.93 0.36±0.005

D cotton 35% PES 65% 31.1±0.65 32.1±0.65 twill 2/1 S 382±1.73 244±1.48 212.7±0.56 0.37±0.000

E cotton 35% PES 65% 29.8±0.52 30.0±0.67 twill 2/1 S 401±1.10 237±1.67 207.4±0.72 0.40±0.0005

F cotton 85% PES 15% 19.6±0.61 18.6±0.65 reinforced twill 2/2 S 572±2.05 320±1.48 196.6±1.69 0.38±0.003

G cotton 35% PES 65% 18.4±0.45 24.1±0.58 twill 2/1 S 521±1.41 238±1.87 176.4±0.54 0.35±0.000

Table 2. Methodology of fabric measurements

Parameter Unit Test method

Thermal resistance m2K/W EN ISO 11092:2014[8]

Water vapour resistance m2Pa/W EN ISO 11092:2014 [8]

Hygroscopicity % PN-P-04635:1980 [25]

Air permeability mm/s EN ISO 9237:1995 [7]

• Hygroscopicity

• Air permeability.

The measurements of above parameters were carried out according to the methods described in the appropriate standards (Table 2).

The measurements of thermal resistance and water vapor resistance were performed on the selected fabrics with the use of "skin model." This device simulates processes of emitting heat and moisture, which appear on the human skin.

The measurements of fabric air permeability were carried out on an air-permeability instrument at the pressure difference of 100 Pa between the inside and outside of the fabric.

All measurements were conducted in the Central Institute for Labour Protection - National Research Institute in Lodz.

3. Results and discussion

The results of measurement of individual fabrics are presented graphically in the bar graphs (Figures 2-5). In the bar graphs, for all parameters, standard deviation values are shown.

3.1. Thermal resistance

In the case of the reference clothing, it will be more advantageous if it will be made of fabric characterized by lower thermal resistance, which is tantamount to a greater ability to heat exchange between the human body, clothing, and environment.

Among the selected fabric, the fabric designated by letter G indicated the lowest value of thermal resistance, which is understandable, because this fabric is characterized by the lowest mass per square meter and relatively small thickness. Comparing the value of thermal resistance of fabrics with the identical raw materials (fabrics D, E and G), it is clear that this parameter increases with the increase of mass per square meter. A high content of polyester fibers in relation to the cotton fibers certainly influenced on the low value of thermal resistance of fabric G. It is known from the literature [10] that the polyester fibers indicate much lower thermal insulation than the cotton fibers.

The impact of raw materials on the value of fabric's thermal resistance can be seen, especially in the case of fabrics B and E with the identical weave, but having different contents of cotton and polyester fibers. On the basis of Fig. 2, it is clear that the fabric B with the higher content of cotton fibers indicates the higher thermal resistance.

Aside from fabric G, the fabric F is also characterized by the low value of thermal resistance, despite the high content of cotton fibers. It can result from the kind of used weave, because this fabric has a reinforced twill weave, which is characterized by the smaller number of interlaces than the twill weave used in the case of other fabrics (an exception is fabric C). In turn, the smaller number of interlaces in fabric influences the higher ability to heat exchange, which confirmed these results.

In turn, the highest value of thermal resistance, aside from fabric D (with the highest mass per square meter), was observed also in the case of fabric A. The reason for this may be the relatively high mass per square meter and also the content of viscose fibers (Tencel).

3.2. Water vapor resistance

Figure 2. Comparison of thermal resistance of examined fabrics (in the figure there are showed SD).

A high level of physiological comfort decided, among the others, the low value of water vapor resistance, which in real conditions of use is the ability of the fabric to allow for the discharge of sweat from the skin surface. The research results indicated that the lowest value of water vapor resistance is displayed by fabric G, as illustrated in the bar graph 2 (Figure 3). Low value of this parameter (except the low mass per square meter and small thickness) can be influenced by the appropriate raw materials. The best effect was reached for cotton/polyester fabrics with the highest content of polyester fibers. Polyester fibers, as hydrophobic materials, practically do not absorb moisture, but they are able to transmit it by diffusion to hydrophilic fibers, such as for example cotton, so that the moisture is drained from the skin surface, giving the user the feeling of comfort.

Moreover, analyzing the graph in Figure 3, we can see that the water vapor resistance of viscose/polyester fabric A is significantly higher in comparison to other fabrics made on the basis of cotton and polyester fibers. The cotton/polyester fabric denoted by the letter D, with a similar content of polyester fibers as fabric A, identical weave, and similar warp and weft densities, exhibits more than twice less water vapor resistance than viscose/polyester fabric A. Therefore, we can suppose that in the analyzed cases, the decisive influence on the value of Ret has a kind of hydrophilic fibers. The use of natural cotton fibers in the fabric structure turned out to be more advantageous from the viewpoint of water vapor resistance than the use of artificial cellulose fibers, Tencel.

The classification of clothing materials in terms of water vapor resistance was proposed by the Hohenstein Institute, a leading German research institute [17]. This classification is based on numerous studies carried out in this institute:

• Ret < 5 m2Pa/W (materials with very good water vapor resistance)

• 5 m2Pa/W < Ret < 20 m2Pa/W (materials with good water vapor resistance)

• 20 m2Pa/W < Ret < 35 m2Pa/W (materials with acceptable water vapor resistance),

• Ret > 35 m2Pa/W (materials with insufficient water vapor resistance).

Given the classification criterion of clothing materials listed, it

Figure 3. Comparison of water vapor resistance of examined fabrics (in the figure there are showed SD).

can be concluded that all the fabrics, except fabrics A and B, meet the requirements for materials with the very good water vapor resistance. Fabrics A and B may be put in the category of materials with the good water vapor resistance. However, they will not be able to provide the highest level of physiological comfort to users.

3.3. Hygroscopicity

The other important property influencing the feeling of physiological comfort in the case of outerwear is the hygroscopicity. Research has shown that the cotton/polyester fabric B was characterized by the highest hygroscopicity (Figure 4). This is mainly due to the high content of cotton fibers, because they constitute as much as 65% of the overall raw material of fabric. The fabric F has somewhat less hygroscopicity than the fabric B despite the higher content of hydrophilic fibers (cotton fibers) that have the ability to absorb moisture. This is probably due to the significantly higher warp density in the structure of fabric F, which directly affects the decrease of fabric porosity and thereby the limitation of the ability to absorb moisture.

The polyester/viscose fabric A also displays high hygroscopicity, mainly due to the content of viscose fibers (Tencel), which

are known as highly absorbent fibers. In spite of the high hygroscopicity, this fabric exhibits the very low water vapor resistance compared with the other fabrics. In turn, the fabric G has both the high capacity to absorb moisture (the hygroscopicity less only approximately 1% of hygroscopicity of fabric B) and very low water vapor resistance, which, in fact, allows for evaporation of secreted sweat.

3.4. Air permeability

The last tested property of fabrics was air permeability. Research showed that fabric G has the highest value of air permeability (Figure 5). The high value of the air permeability of this fabric was undoubtedly due to its small thickness, because it is one of the thinnest fabrics that were tested. In addition, this fabric has the smallest mass per square meter and it is also characterized by relatively small weft density (Table 1). Although the warp yarn occur in a large number in the fabric, their linear density is significantly less than the linear density of warp in other fabrics. These factors endow the structure of fabric G with free spaces (pores), leading to the high air permeability of this fabric.

The air permeability of other fabrics include a wide range of 60.1-158.5 mm/s. The lowest value of less than 70 mm/s was achieved for the fabrics D and E, which were characterized by the highest mass per square meter of all the tested fabrics.

4. Conclusions

For performing the selection of fabric to the reference clothing, there were a need to analyze the impact of various fabric parameters on the user's physiological comfort.

Research showed that the fabric designated by letter G is the best in terms of the thermal resistance. This is mainly due to its low mass per square meter and relatively small thickness. The low value of thermal resistance of this fabric also results from the highest content of polyester fibers, which are known to have low thermal insulation.

Fabric G is characterized also by lowest water vapor resistance. Small thickness and the lowest mass per square meter contribute an improvement of the water vapor resistance of this fabric. According to the classification proposed by the German Institute Hohenstein, fabric G can be classified as the fabric with very good water vapor resistance.

In terms of hygroscopicity, fabrics A, B and F were better than fabric G, which may be due to the high content of Tencel fibres or cotton fibers having a higher ability to absorb moisture.

However, the highest air permeability, at levels more than 200 mm/s, is guaranteed by fabric G. The high value of this parameter results from the high porosity of this fabric.

Thus, the analysis of biophysical parameters of fabrics shows that fabric G the highest level of physiological comfort for reference clothing and is made up of the following raw materials: 35% cotton/65% PES.

A B C D E F G

Figure 4. Comparison of hygroscopicity of examined fabrics (in the figure there are showed SD).

A B C D E F G

Figure 5. Comparison of air permeability of examined fabrics (in the figure there are showed SD).

Acknowledgments

The publication has been based on the results of Phase III of the National Programme "Safety and working conditions improvement", funded in the years 2014-2016 in the area of tasks related to services for the State by the Ministry of Family, Labour and Social Policy (The Programme coordinator: Central Institute for Labour Protection - National Research Institute).

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