Effect of the Imperfection of Open-End Yarn (Thin, Thick, and Nep Place) on Air Permeability of Plain Woven Fabric

Abstract

Wearing clothes is an intermediate channel by exchange of air released from human bodies and environments to bring breathing stability and to control body temperature. Air permeability is an expression describing the properties of a fabric that permit the passage of air through the fabric’s interstices. It has been found that there are many factors that can affect the air permeability of a fabric comfort. Several early studies of air permeability of different materials showed that different factors affect air permeability and breathability of fabrics, and some of them are imperfections of yarns (thick, thin, and nep place) which are introduced on the surface of the fabric that originated from the appearance of the yarn. In this experiment, the yarn and fabric samples are collected from five different spinning mills which have an identical warp yarn linear density of 20 Ne regardless of the weft linear density, and the fabric was constructed from those selected yarns by using the thread set of 28 ends per centimeter and 20 picks per centimeter. The experiment was conducted by measuring the imperfection of each code of yarn on USTER statistics and air permeability of the fabric with respect to the thin, thick, and nep place/km of the yarn and fabric cover. The impacts of each factor were analyzed, and the relationships of each parameter were stated on the graph. The results were discussed by using the design of the experiment by quadratic and linear models to the response of air permeability and fabric cover, respectively, and the results showed that there is a direct impact of thin, thick, and neps of the yarn on the ability of the fabric to permeate air.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

Clothes are used to maintain and protect body temperature. In order to balance high heat that surrounds the body, garment permits sweat to evaporate (cooling off by perspiration). When humans are under high temperatures or do physical exercises, the fluctuation of fabric during movement creates air streams, which increase perspiration and cooling off. Body temperature is kept cold by the fabric layer that provides insulation a little. For these reasons, clothing comfort is of great importance from the point of a user. Clothing comfort can be examined in three different categories such as psychological, handle, and thermal comfort. Psychological comfort can be explained with the user influenced by the fashion and culture. Fabric handle is defined basically as the feeling when the thumb and index finger touch the fabric. Thermal comfort is a phenomenon, which is close to thermal and liquid or air permeability properties of fabrics [1]. The human body produces moisture in the form of perspiration; it should be removed from to the surface of the skin and from the inside of the fabric surface. The fabrics should allow moisture in the form of sensible and insensible preparations to be transmitted from the body to the atmosphere in order to cool the body. After the body has stopped the sweating, the textile fabric should release in the atmosphere. There are different research works which are carried out to improve the transportation properties of fabrics such as air, water, or thermal [2].

Air permeability is an important factor in the performance of textile materials such as gas filter, fabrics for air bags, clothing, mosquito netting, parachutes, sails, tentage, and vacuum cleaners. It can also be used to provide an indication of the breathability of weather-resistant and rainproof fabrics. The end-use and performance requirements of woven fabrics are strongly related to their cover factors (CFs) or, in opposite terms, to their porosity and permeability [3–5]. The air permeability of the fabric is influenced by different factors, such as the number of warp and weft per centimeter or inch, fabric design, fabric structure, yarn twist, yarn appearance, imperfection, the size of yarn, yarn structure, and fabric finishing. Therefore, to investigate the relationship of all fabric parameters with air permeability is difficult.

In this paper, those parameters are limited to show the effect of imperfections (thin place, thick place, and neps) on the fabric air permeability based on the properties of the yarn which include the irregularity (U%), coefficient of mass variation (CVm%), number of thin places/km (−50%), thick places/km (+50%), and neps/km (+280%) drawn from five spinning mills with similar yarn linear density.

1.1. Air Permeability

The void volume in woven textile fabrics causes air permeability. The air permeability of the textile is determined by the rate of air flow through the material under a differential pressure between the two fabric surfaces [6, 7].

1.2. Cover Factor of the Fabric

Cover factor (CF) is defined as the area of yarn in the solid unit cell rectangle [8]. The coefficient of CF is the characterization of the degree of area covered by the threads in the fabric [9]. It can be written as$$\begin{array}{}\text{(1)}& \text{cover\hspace{0.17em}factor}\text{CF}=\frac{\text{area\hspace{0.17em}covered\hspace{0.17em}by\hspace{0.17em}yarn}}{\text{whole\hspace{0.17em}fabric\hspace{0.17em}area}}.\end{array}$$

The cover factor of the fabric is the sum of the coverage of the warp and weft yarns. According to different literature studies, the total fabric cover (TFC) has to be$$\begin{array}{}\text{(2)}& \text{TFC}=\text{D}1\text{N}1+\text{D}2\text{N}2-\text{D}1\text{N}1\times \text{D}2\text{N}2,\end{array}$$where TFC is the total fabric cover, D₁ is the warp yarn diameter in cm, D₂ is the weft yarn diameter in cm, N₁ is the warp yarn density (threads/cm), and N₂ is the weft yarn density (threads/cm) as illustrated in Figure 1.

[figure omitted; refer to PDF]

The diameter of the yarn is estimated based on the linear density of the yarn and its fiber density as follows:$$\begin{array}{}\text{(3)}& D=4.44\times {10}^{-3}\frac{\sqrt{T_{tex}}}{\rho },\end{array}$$where D is the diameter of the yarn in cm, T_ex is the linear density of the yarn, and $\rho$ is the fiber density in g/cm³. The density of the cotton fiber is 1.54 g/cm³.

1.3. Thin and Thick Places

Together with the impairment of the optical appearance of the textile surface, the number of thin and thick places is important information on the condition of the raw material and/or manufacturing process. An increase in the number of thin places does not necessarily mean that the number of machine standstills increases accordingly during weaving and knitting with this yarn: in many cases, thin places indicate larger yarn twists. This means that the yarn tensile strength must not necessarily decrease proportional to the reduction in the fiber count [10].

1.4. Neps

Apart from the strong influence on the optical appearance of textile surface structures, neps from a certain size upwards also lead to problems in the knitting machine sector. Not only the size but also the number of neps are decisive criteria as to whether the yarn is useable or not. Neps in the raw material are mainly foreign bodies such as, for example, shell or plant residues, whereas neps in production are created during the spinning process through unsuitable machine settings and a bad ambient climate [11].

2. Materials and Methods

2.1. Materials

The woven fabric is constructed from the rotor yarn which has the warp density of 28 ends/cm, and the weft density is 20 picks/cm. The fabric is produced from different codes of yarn (Codes A, B, C, D, and E) with a similar linear density and thread set. Figure 2 shows that a fabric which is constructed from 100% cotton open-end yarn and drawn from five spinning mills has a similar number of warp and weft densities in centimeter and also has a similar linear density of warp yarn 20 Ne regardless of weft yarn counts and its imperfection. Both samples which are yarn and fabric were used, and the tests were conducted based on the selected properties of both samples; in fact, these cause highly influential impacts on the ability of fabric air permeability. The reasons for testing of the yarn properties are direct impact on the porosity and coverage of the fabric. To test the imperfection of the yarn is very important to identify the passage of air through the surface of the fabric.

[figure omitted; refer to PDF]

The lack-of-fit F-value of 27.76 implies the lack of fit is significant. There is only a 0.15% chance that a lack-of-fit F-value this large could occur. Significant lack of fit is bad and needs to change the model, but in this regard conceder only the selected parameters and it need to check the other properties of yarn and fabric. There are a lot of factors which affect the air permeability of fabrics.

Table 5 shows that the model F-value of 15.44 implies the model is significant. There is only a 0.06% chance that an F-value this large could occur, and $P$ values less than 0.0500 indicate model terms are significant. In this case, neps are a significant model term. Values greater than 0.1000 indicate the model terms are not significant. In this regard, the number of neps has a direct impact on the fabric cover, but the thick places on the surface of the yarn is not change or a direct impact on the fabric cover as shown in the model, in this situation it needs to see other parameters related to yarn properties and fabric cover unless otherwise if there is a thick place on the yarn strand it leads to reduce the space between the two consecutive warp and weft yarns by regardless of twist and others.

On the normal probability plot, we are looking to see if the observations follow the given line. This tells us that the distribution of residuals is approximately normal as shown in Figure 6. Positive values for the residual (on the y-axis) mean the prediction was too low, and negative values mean the prediction was too high; 0 means the guess was exactly correct.

[figure omitted; refer to PDF]

Figure 7 shows the linear regression model of the fabric cover within the factors of the number of neps and thick places. This model is significant meaning that there is an impact of factors on the response and the thick place and the number of neps accumulation are leads to a great contribute the coverage of yarn on the surface of the fabric with its porosity because those two imperfections are a thicker diameter of yarn with compare to the standard diameter. Always, the neps and thick places are higher in diameter than the normal cross section of the yarn.

[figure omitted; refer to PDF]

4. Conclusion

In this experiment, the impacts of the imperfections (thin place −50%, thick place +50%, and neps +280%) on the air permeability of the fabric and fabric cover are discussed. In this paper, two approaches were used to know the significance of two levels of factors with respect to air permeability of the fabric and fabric cover. These are neps (+280%) and thick places (+50%) as presented two levels of factors and fabric air permeability (m³/m²/min@100 Pa) as presented a response and used the quadratic model for fabric air permeability and linear model for fabric cover. The values of the factors which are the number of neps and thick places increase the fabric air permeability which is high. In fact, during the interlacement of two systems of yarns with high number of neps, thick and thin place are leads to construct open fabric due to the occurrence of porosity between the two consecutive yarns regardless of the level of twist. Both regression models showed that all values are significant which means there is a direct impact of the two factors on the response regardless of some parameters.

Acknowledgments

The author would like to express their sincere gratitude to EiTEX (Ethiopian Institute of Textile and Fashion Technology) for providing the chance and funding to carry out this research work in laboratories under the Textile Production Research Center (TRIC).

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