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Journal of Engineered Fibers and Fabrics 39 http://www.jeffjournal.org Volume 8, Issue 1 – 2013

Ultrasonic Washing Effect on Thermo Physiological Properties of Natural Based Fabrics

Muhammet Uzun

University of Bolton, Bolton Lancashire UNITED KINGDOM

Correspondence to:

Muhammet Uzun email: [email protected] ABSTRACT Ultrasonic technology is widely used to assist many industrial and domestic applications. However, the effect of ultrasonic washing on the thermo-physiological properties of natural based fabrics has not been studied yet. This study aims to examine the relationship between unwashed, ultrasonically washed, and conventionally washed fabrics in terms of their abrasion behavior, flexural rigidity, and comfort properties (thermo physiological). Five specimens of 100% natural based fabrics: linen, bamboo, organic cotton, cotton and wool, were washed using both ultrasonic and conventional methods under a 40ºC degree washing temperature. All fabrics were washed ten times for 15, 30, 45 and 60 minutes. No direct correlation between the unwashed and washed fabric abrasion and flexural rigidity properties was observed. Fabric thermal conductivities were changed after the washing processes and in most cases; the ultrasonically washed fabrics had higher conductivity values. It was also observed that lower washing times (15 and 30 min) using the ultrasonic method decreased the thermal resistance of the fabrics. Furthermore, it was also clear, according to the thermal absorptivity results, that the ultrasonic washing method benefited the natural fiber based fabrics. Conventionally washed fabrics were found to have superior water vapor permeability compared to ultrasonically washed fabrics. The ultrasonically washed fabrics have considerably higher heat loss values than the conventionally washed fabrics. Keywords: ultrasonic energy, conventional washing, thermo physiological properties, abrasion, flexural rigidity, natural fabrics INTRODUCTION The thermal comfort properties of textile fabrics are desirable characteristics for garment usage and thus have scientific importance and concern to textile specialists [1-3]. Thermo physical comfort has been described as the garment’s ability to keep the wearer dry while maintaining body temperature even when

the wearer is subject to varying surrounding temperatures and humidities. Comfort has been defined by many; the most popular definitions are “the absence of displeasure or discomfort” and “a neutral state compared to the more active state of pleasure”. The comfort of a garment mainly depends on its thermal properties, water vapor permeability and air permeability [4, 5]. Garment comfort characteristics are based on fiber type (natural, synthetic), yarn production method (ring, open-end) and properties (count, twist), fabric structure (woven, knitted, nonwoven) and physical features (thickness, warp-weft number) and also textile finishing process (bleaching, dyeing) [6-8]. The vast majority of natural based clothes produced commercially are comprised of linen, cotton and wool fibers – that is, they exhibit a wide range of application advantages. In addition to these, there are two emerging fibers: organic cotton which is farmed differently in comparison to traditional cotton and a regenerated cellulosic bamboo fiber. Bamboo fiber is a recent addition to the textile market and it has certain superior characteristics, such as higher absorption rate, antimicrobial characteristics, softness and breathability [9, 10]. All the textile products are subjected to a variety of finishing process including industrial washing, and they are also subjected to domestic washing. The cleaning process of laundry is synergistic actions between the mechanical energy, chemical energy, thermal energy and time. Conventional apparel washing techniques require a large amount of water and chemical consumption. Studies carried out on the ultrasonic washing method have shown that the ultrasonic washing method has many advantages including; superior cleaning properties, reduction in process time, energy and chemical and also ultrasonic agitation produces less fiber migrations when compared to the conventional washing method. Ultrasonic energy generates millions of bubbles or cavities into the liquid with very high frequency


which constantly strike at the target material surface and as a result, remove dirt off the fibers. One of the most important parameters for the ultrasound mechanism is the power of ultrasonic cavitations in liquids [11-15]. In this paper, natural fiber based plain woven fabrics were washed with both ultrasonic and conventional methods. The fabric dimensional properties were determined prior to the washing processes. Unwashed (control), ultrasonically and conventionally washed fabrics were tested and analyzed in terms of abrasive testing (Martindale abrasion tester), flexural rigidity testing (Shirley stiffness tester), thermo physiological (Alambeta and Permetest instruments) testing including; thermal conductivity, thermal resistance, thermal absorptivity, water vapor permeability, and heat loss. MATERIALS AND METHODS Materials 100% natural fiber based unbleached and undyed plain woven fabrics; linen, bamboo, organic cotton, cotton and wool fabrics were purchased from different suppliers in the UK market. The plain weave, being the fundamental weave, was chosen as the fabric structure where each filling yarn passes successively over and under each warp yarn, alternating each row (Figure 1). The fundamental properties of the fabric, which included density, thickness, bulk density, warp and weft yarn count were determined. The test results showing the dimensional properties are given in the Results and Discussion section of the study. A standard powder type commercial detergent was employed with a 1g/L ratio. The brand name of detergent used in this study is DAZ (manufactured by Procter Gamble Ltd) and the ingredients of the detergent are:

5-15 % anionic surfactants which oxygen-based bleaching agents;

<5% non-ionic surfactants, phoshonates, polycarboxylates, zeolites;

Optical brighteners, enzymes, perfumes, butylphenyl methylpropional, hexyl cinnamal, geraniol.

FIGURE 1. Plain woven fabric structure. Methods Washing Processes The five specimens were ultrasonically and conventionally washed at 40ºC degree washing temperature with four different washing times, 15, 30, 45 and 60 minutes. For the ultrasonic washing method, the ultrasonic bath (Branson 2200, 220 volt and 205 watt) was employed using 20 kHz frequency. The conventional washing was performed using Roaches model-MB lab type HT dyeing machine. The fabric specimen sizes were prepared 20cm ×20cm. A 1g of detergent and 1L of deionized water was pre prepared as a mixture and poured into the ultrasonic bath for each specimen. The fabric specimens were washed using both ultrasonic and conventional methods and each fabric washing was repeated 10 times and after the washing process, the specimens were rinsed three times in deionized water. Finally, the specimens were left to dry at room temperature for 24 hours [15]. Fabric Dimensional Properties Fabric area density (gm-2), thickness (mm) and the number of weft and warp yarn per cm were determined in accordance with BS EN 12127:1998 [16], BS EN ISO 9073-2:1997 [17], and ISO 4602:2010 [18], respectively. The density of five specimens of each fabric was measured individually and the mean mass per unit area of the specimens was calculated. The specimen sizes were prepared 5cm ×5cm for determination of mass and these were converted to gm-2. The thicknesses of specimens were determined using Shirley thickness tester.


Abrasive Testing Prior to all the testing, the fabric specimens were conditioned for 48 hours in 65% relative humidity and 20oC atmosphere [19]. The abrasion test was performed with Martindale Abrasion Tester, using the established standard Martindale abrasion method. The abrasive wear testing determines the resistance to abrasion of textile fabrics. The measurement of the resistance to abrasion of textile fabrics relies on several parameters such as the mechanical properties of the fibers, the dimensions of the fibers, the structure of the yarns, the construction of the fabrics, the type and kind of finishing material etc. The abrasion test specimens were prepared with press cutters; the fabric specimens were cut into circular specimens of 38mm diameter and placed on the specimen holder. The test was performed while applying a pressure of 9kPa, and the machine speed was maintained at 50 rubs per minute for 5000 rubs, which equates to 10 minutes per the specimen cycle. After performing every 1000 rubs, the specimens were inspected for abrasion. The endpoint was determined by a specified number of cycles or the appearance of a hole in the specimen’s test area. Flexural Rigidity Testing The stiffness depending on bending length and flexural rigidity of fabrics were carried out using Shirley stiffness test, in accordance with BS 3356:1961 [20]. Three specimens of warps and three wefts were tested and the mean values were calculated. The test specimens were both in 25mm width and 200mm length. Thermo Physiological Testing The thermo physiological properties of the woven fabrics were determined using an Alambeta instrument (Sensora Instruments, Czech Republic). The Alambeta instrument provides values for thermal conductivity, thermal resistance (insulation) and thermal absorptivity (warmth-to-touch), fabric thickness and thermal diffusion. The test instrument was used to determine the transient and steady state thermo physical properties of the fabrics. The

specimen’s size of 20cm ×20cm were prepared and placed in between two plates. With the two plates the heat flow through the fabric due to the different temperature of the bottom measuring plate (at ambient temperature) and the top measuring plate which is heated to 40ºC. The thermal absorptivity of the textile structure is a measure of the amount of heat conducted away from structure surface per unit time [21-23]. The test was performed on dry specimens and on wet specimens which were wetted with 0.2mL of water on the center of the fabrics and allowed 4 minutes to thermal recovery of the fabric. For each side (back and front side of fabric) of the unwashed and washed fabrics 20 measurements were made, and the average values of the measured parameters were calculated. Water vapor permeability and the resistance to evaporative heat loss of the fabrics were tested using the Permetest instrument (Sensora Instruments, Czech Republic). This instrument is based on a skin model, which simulates dry and wet human skin in terms of its thermal feeling [1]. The instrument uses the same principle as specified in ISO 11092 developed by Hohenstein Institute whereby a heated porous membrane is used to simulate sweating skin. The heat required for the water to evaporate from the membrane, with and without a fabric covering, is measured [21]. RESULTS AND DISCUSSION Fabric Dimensional Properties To determine the dimensional properties of selected fabrics, it is important to compare the thermo physical properties. The Alambeta and Permetest instruments operate based on the fabric area density, thickness and bulk density. The fabric area density, thickness and the number of weft and warp yarn per cm and bulk density values are given in Table I. These results show that the dimensional properties of fabrics were fairly similar. The thickness of the bamboo fabric was lower in comparison to the other fabrics tested. Although the bamboo based fabric is

TABLE I. Dimensional property of woven fabrics.

Area density (gm-2)

Thickness (mm)

Bulk density (gm-3)

Warp no. (in cm)

Weft no. (in cm)

Linen 140 0.5 0.280 30 19 Bamboo 170 0.4 0.425 45 22 Organic C. 160 0.5 0.320 36 13 Cotton 168 0.5 0.335 30 20 Wool 171 0.5 0.343 28 19


thinner, it has the highest bulk density (0.425g/m3). The area density of the linen fabric is slightly lower compared to the other fabrics; however, the difference is not noteworthy. The dimensional property differences of the fabrics are negligible for this experimental work since the main purpose of this study was to highlight the washing methods influence on the physical and thermal comfort properties of fabrics. Abrasive Test Results The linen, bamboo, organic cotton, cotton and wool based woven fabric resistances to abrasion were tested and compared as unwashed and washed fabrics for a total of 45 fabrics (5 control, 20 ultrasonically washed and 20 conventionally washed fabrics). The abrasion results are given in Table II. Each specimen was inspected to analyze its abrasion behavior after every 1000 rubs. After the initial 15000 rubs, none of the fabrics exhibited any sign of damage or wear. This result indicates that all the fabrics were not subject to significant abrasion after 15000 rubs; however, the linen based fabric did show some minor weak points. The unwashed linen fabric, after 23000 rubs, and the washed linen fabric, after 22000 rubs, showed signs of deterioration for both ultrasonic and conventional washing methods, whereas the other fabrics; bamboo, organic cotton, cotton and wool, maintained their abrasion resistance properties when they were washed. After 30000 rubs, the unwashed bamboo fabric was damaged. After 3200 and 35000 rubs, the organic cotton and cotton fabrics showed some weak points respectively. After 50000 rubs wool had formed a hole through the fabric thus ending its abrasion resistance.

TABLE II. Abrasion test results of woven fabrics (rubs).

The relationship between the wear resistance and washing is found not to be critical at this laundering set up and under controlled conditions. As mentioned before the resistance to abrasion of textile fabrics depends on fiber, yarn, fabric structure, finishing and so on. The fabrics which are mostly used for apparel manufacturing are expected to keep their structural properties even if when they are washed frequently. There were no significant differences found between

the unwashed and washed fabrics due to the fabrics higher abrasion and wear resistance. The only notable difference was that both the linen and bamboo based fabric’s abrasion were slightly decreased when washed using both methods. This study shows that there is no difference between the ultrasonic and conventional washing methods according to the abrasion behavior. These test results illustrate that the wool has superior abrasion characteristics in comparison with the other tested fabrics. It was to be expected that the abrasion characteristic of the fabrics were not affected after washing ten times. It may be worth to consider the abrasion properties of fabrics with the increased number of washing times. Flexural Rigidity Testing The flexural rigidity is the ratio of the small change in bending moment per unit width of the material to the corresponding small change in curvature as determined by:: Flexural rigidity;

G = M X C3 X 9.807 X 10-6 in µNm (1) where: C = bending length (mm); M = fabric mass per unit area (g/m2). Table III shows the flexural rigidity values of the unwashed and the washed fabrics. The washed fabrics had lower flexural rigidity values compared to the unwashed fabrics. The reason of this is the unwashed raw fabrics have close structure due to the looming tension while weaving the fabrics. The washing process can open the yarn and fabric structures and the fabric become softer than their raw fabric forms. A lowering of flexural rigidity for washed natural fabrics is known phenomena, however; there is no experimental study which demonstrates the interaction between ultrasonically and conventionally washing and flexural rigidity. For all the experimental combinations, the differences between flexural rigidities for bamboo and other tested fabrics are considerable, and in all cases, bamboo based fabric have substantially lower flexural rigidity than the tested fabrics. The softness of bamboo fiber is commercially advertised as one of important features of bamboo based fabrics and in this study, the flexural rigidity test results confirm the assumption. The higher flexural rigidity of fabric can be caused by the compactness of the structures which affects the freedom of movement during bending, which is an undesirable property for clothing. Lower flexural rigidity value is preferred for textile fabrics


[24]. It was found that the fabrics washed using the ultrasonic method have slightly lower flexural rigidity values as compared with the conventionally washed fabrics. This could be attributed to the decrease in fiber migrations as seen with ultrasonic washing. Fiber migration can influence the rigidity of the fabric. The washing times did not have a significant effect on the flexural rigidity of fabrics. TABLE III. Average values of weft and warp flexural rigidity of woven (µNm).

Thermal Conductivity of Woven Fabrics in Dry and Wet State The thermal conductivity of the fabrics was measured using an Alambeta instrument. It basically gives the amount of heat, which passes from 1 m2 area of tested structure through the distance 1 m within 1 s and create the temperature difference 1 K. The thermal conductivity can be calculated by using the following expression, [25, 26] λ = Q/ Fτ×ΔT/σ in Wm-1 K-1 (2) where: Q = amount of conducted heat, F = area through which the heat is conducted, τ = time of heat conducting ΔT = drop of temperature, σ = fabric thickness Both the dry and wet states fabrics were investigated separately due to the importance of fabric application areas. The thermal conductivity results are presented in Table IV and Figure 2 for dry state and Table V and Figure 3 for wet state. The linen fabric obtained had the highest thermal conductivity values in its dry and wet states for all the test combinations. The thermal conductivity ranged from 31.3 to 36.1W/mK×10-3 in its dry state and 44.7 to 57.7 W/mK×10-3 in its wet state. Both the washing methods increase the linen fabric’s thermal conductivity appreciably. The ultrasonically washed linen fabric had a slightly higher thermal conductivity

in comparison with the conventionally washed linen fabric. The washing times were did not have a noteworthy effect on this measured property for linen fabric. There are three fundamental ways by which heat energy can be transferred through porous materials such as woven fabrics conduction, convection, and radiation. Depending on the fiber’s specific thermal conductivities, the size and configuration of the space between the fibers in the woven specimen, heat transfer mechanisms - conductive, radioactive, and convective – will provide very different contributions to the overall heat transfer throughout the specimens. Very complex interactions and contributions of various heat transfer mechanisms in the overall thermal properties of woven fabrics makes the direct instrumental measurement of the thermal conductivity [29]. It is evident that the fabric’s thermal conductivities were altered after washing with ultrasonic and conventional methods. In the dry state, the fabrics resulted in reduced conductivity for all washing combinations. The only exception to this was the linen fabric which showed increased conductivity after washing. In wet state the fabric behavior exhibited different direction than dry state, the conductivity of washed fabric increased when they were tested after 4 min wetting with 0.2ml water. The conductivity of the fabrics is higher in the wet state due to excess amount of water content on the fabric surface. Most of the fabrics which were washed with the ultrasonic method had higher thermal conductivity compared to the conventionally washed fabrics. This may be due to decreased fiber damage and migration as seen with ultrasonic washing. The action of conventional washing was, however, deteriorative for most of the natural fiber based fabrics. It is also highlighted in this study that the washing times do not have any considerable effect on the fabric conductivity however for some of the cases, like linen fabric, washing times increased the conductivity. where; UW: ultrasonically washed CW: conventionally washed


TABLE IV. Thermal conductivity (λ) of woven fabrics in dry state (W/mK×10-3).

FIGURE 2. Thermal conductivity (λ) of woven fabrics in dry state (W/mK×10-3).

TABLE V. Thermal conductivity (λ) of woven fabrics in wet state (W/mK×10-3).

FIGURE 3. Thermal conductivity (λ) of woven fabrics in wet state (W/mK×10-3).


The results of this study showed that the area density of the fabrics do not have a prior effect on fabric conductivity. According to previous work on thermal conductivity, the conductivity was explained by area density changes; however, in this study it has been found that the fiber structures have significant influence on the conductivity. For instance the wool fabric, which has the highest area density, has the lowest thermal conductivity for all cases [27]. Thermal Resistance of Woven Fabrics in Dry and Wet State The fabrics analyzed in this study are mostly used for summer clothes manufacturing. The most important characteristic for summer clothing is to keep the wearer drier and cooler and, due to this, the fabrics used to make the garments should have a relatively low thermal resistance. A higher thermal resistance will cause the wearer to become uncomfortable and extremely warm. The thermal resistance property of the structures depends on the fabric thickness and thermal conductivity value. The resistance is expressed by the following relationship. R (m2kW-1) = h(m)/λ in W-1K m2×10-3 (3)

where: h = fabric thickness λ = thermal conductivity Table VI and Figure 4 in dry state and Table VII and Figure 5 in wet state show the results for the tests performed on Alambeta in terms of the fabrics thermal resistance. The resistance of the unwashed fabrics ranged from 35.9 to 72.2W-1K m2×10-3 for the dry state and from 24.8 to 58.0W-1K m2×10-3 for the wet state which is both significantly higher values when compared to the washed fabrics. In the wet state, the washed fabrics, using both washing methods, had up to five times lower values of thermal resistance than the unwashed fabric’s thermal resistance.

The differences between the unwashed and washed are considerable. The washing times affected the thermal resistance of the fabrics in variable directions however in general there was no correlation in terms of thermal resistance and washing times. Ultrasonic washing reduces the thermal resistance of the linen fabric for all the washing combination, particularly in the wet state. The ultrasonic washed linen fabric showed five times lower value than the unwashed linen fabric. The differences between the unwashed and washed linen fabrics are significant. The bamboo fabric which is washed using the ultrasonic method has a slightly lower thermal resistance value. The difference is not noticeable yet for the 15 and 30 min washing times. Conventional washed organic cotton, cotton and wool based fabrics had lower values in terms of their thermal resistance in comparison with the ultrasonic washed fabrics. These results are similar with the bamboo fabric, which result in 15 and 30 min washing. The wool fiber based fabric had the lowest thermal resistance value out of all the tested fabrics which is unexpected as it is generally thought that wool is winter clothing. Only few have performed similar research, Mao and Russell being two of them who have demonstrated that when a wool fiber is integrated on the structure surface, the thermal conductivity is reduced by 50% [28]. All the washed fabrics (Table VII), using both ultrasonic and conventional methods, felt relatively drier and cooler when in contact with the skin as compared to the unwashed fabrics. The ultrasonically washed fabrics have better thermal resistance at lower washing times (15 and 30minutes). At 45 and 60 minutes, linen and bamboo fabrics which are washed with ultrasonic method have preferable values. Organic cotton, cotton and wool fabrics which are washed using conventional methods have lower thermal resistance at 45 and 60 minutes.

TABLE VI. Thermal resistance (r) of woven fabrics in dry state (W-1K m2×10-3).


FIGURE 4. Thermal resistance (r) of woven fabrics in dry state (W-1K m2×10-3).

TABLE VII. Thermal resistance (r) of woven fabrics in wet state (W-1K m2×10-3).

FIGURE 5. Thermal resistance (r) of woven fabrics in wet state (W-1K m2×10-3).

The percentage recoveries of the fabrics after 4 min of wetting are presented in Table VIII. Any fabrics which have a 75% recovery are assumed to dry quickly. The unwashed fabrics have a higher percentage recovery value after 4 min of wetting. The reason for this could be hydrophobic nature of the unwashed fabrics. As a result of high conductivity in wet state, the recovery also shows an increase. Only washed wool fabric had a higher percentage recovery

values in comparison to the unwashed wool fabric for all washing times. For 15 and 30 min washing times, the ultrasonic washed fabrics had a higher % recovery compared to the conventional washed fabrics. Moreover 45 and 60 min washing time the conventional washed fabrics had better recovery after 4 min wetting.


TABLE VIII. % recovery after 4 min wetting (%).

Time Unwashed 15 minutes 30 minutes 45 minutes 60 minutes Washing types UW CW UW CW UW CW UW CW Linen 80.5 42.5 34.9 44.1 39.4 34.3 42.8 40.3 50.3 Bamboo 80.3 79.9 35.1 64.3 41.0 53.9 62.9 66.0 66.5 O. Cotton 67.6 55.2 87.4 53.3 69.2 55.2 55.1 53.7 40.2 Cotton 82.1 65.9 43.3 69.3 48.1 58.6 59.1 66.2 57.4 Wool 69.1 85.7 89.1 72.7 55.3 51.3 60.1 50.0 65.0

Thermal Absorptivity of Woven Fabrics in Dry and Wet State ‘Warm-cool’ feeling (thermal absorptivity) of fabric is one of prior characteristics for textile garments and this feature is first sensation that is felt when any customer touches the garments, this is a kind of heat transfer between the skin and the fabric surface. Pure fabric ‘warm-cool’ characteristic can be modified during the textile finishing processes. Lower thermal absorptivity causes a warm feeling and a diametrically higher thermal absorptivity value tends to give a cooler feeling. The thermal absorptivity can be measured by an Alambeta instrument and the value and is calculated by the following equation:

b =√ λ×ρ×c in Ws1/2 m-2 K-1 (4)

where: λ = thermal conductivity; ρ = fabric density; c = specific heat of the fabric. The significant differences in thermal absorptivity of the fabrics were detected when the specimens were washed both conventionally and ultrasonically (Table IX and X and Figures 6 and 7). The washed fabrics had at least twice as high thermal absorption values however the cotton fabric’s absorptivity only increased 0.1 times when it was washed. The thermal absorptivity values of fabrics in their wet states are considerably higher than the dry state fabrics. The bamboo fabric had the lowest absorptivity values for the all washing combinations. It is possible that its thinner fabric thickness causes its lower absorptivity compared to the rest of the fabrics. It is observed that the washing processes added a critical amount of thermal absorptivity on the tested fabrics.

TABLE IX. Thermal absorptivity (b) of woven fabrics in dry state (W m-2 s 0.5 K -1).

FIGURE 6. Thermal absorptivity (b) of woven fabrics in dry state (W m-2 s 0.5 K -1).


TABLE X. Thermal absorptivity (b) of woven fabrics in wet state (W m-2 s 0.5 K -1).

FIGURE 7. Thermal absorptivity (b) of woven fabrics in wet state (W m-2 s 0.5 K -1).

The results clearly show that the ultrasonically washed fabrics have higher thermal absorptivity values than the conventionally washed fabrics. This difference is considerable. According to the results of the thermal absorptivity analysis, it is beneficial to clean summer fabrics using the ultrasonic washing method, which is due to the higher absorptivity which results in cooler feeling which is preferred in summer seasons.

Percentage loss in warmth to touch feeling from dry to 4 min wetting was determined using the following equation: % loss = (the absorptivity value of wetted fabric

– the absorptivity value of dry fabric (5) / the absorptivity value of dry fabric) × 100

TABLE XI. % loss in warmth-to-touch feeling from dry to 4 min wetting.

Water Vapor Permeability and Resistance to Evaporative Heat Loss (Permetest) The Water Vapor Permeability (WVP) depends on the water vapor resistance which indicates the amount of resistance against the transport of water through the fabric structure. The amount of water present in a garment (which has crucial importance in

the degree of comfort) must to be a minimum. The relative WVP is expressed using the following formula. WVR=Qs(Wm-2) / Q0 (Wm-2)×100 in % (6)


where; Qs = the heat flow with the fabric specimen Q0 = the heat flow without the fabric specimen The WVP and resistance to evaporative heat loss results are summarized in Table XII and XIII. The study of WVP was performed by using Permetest instrument. According to the results there are no noticeable differences between unwashed and washed fabrics, all the tested fabrics have more than 50%

WVP value. It is clear that the conventionally washed fabrics have enhanced WVP values compared to the ultrasonically washed fabrics. The physical effect of conventional washing can cause more open structure than ultrasonic washing method therefore the permeability of conventionally washed fabric is higher. The washing times did not have any detrimental effect on the WVP property of the fabrics.

TABLE XII. Water vapor permeability (%).

The resistance to evaporative heat loss has to be lower due to the WVP of fabric. As seen Table XIII, only the washed linen fabric’s heat loss value is lower than the unwashed linen fabric and also the

ultrasonically washed linen fabric. The rest of the fabric heat loss values increased with both washing methods. The ultrasonic washing has a noticeably higher WVP values. The washing times do not have any significant effect on the fabric heat loss values.

TABLE XIII. Resistance to evaporative heat loss (m2 Pa W-1).

CONCLUSION The laundering of apparel has always been an important matter for mankind even in the early stages of the world history. The main aim of the developments for laundering is better cleaning with lower damage to the textile fabrics. Natural fiber based fabrics has to be washed as gently as possible. In this case, ultrasonic energy can offer a good cleaning with a lower effect on the fabrics properties. Keeping this in mind, the physical and thermal comfort properties of ultrasonically washed fabrics were determined and compared with the unwashed and conventionally washed counterparts. The results proved that the difference between unwashed, ultrasonically and conventionally washed fabrics is important for most of the tested parameters and the variation is highly critical.

Due to the nature of abrasion resistance of tested fabrics, there were no considerable changes after ten times washing processes. The linen and bamboo fabrics showed slightly lower abrasion properties after the washing with both methods. This may be due to the fibers poorer tensile strength and breaking elongation properties. It was also observed that the wool fabrics had the highest wear resistance in comparison with rest of the fabrics. The washing processes reduced the flexural rigidity of tested fabrics and the changes were found to be considerable. Ultrasonically washed fabrics had lower flexural rigidity than conventionally washed fabrics. As explained previously, the washing process positively affects the close structure of newly loomed fabrics. The fabrics which were ultrasonically washed had better flexural rigidity values because of lower


physical effect on the fabrics. Conversely, the fabrics which were washed conventionally can lose their yarn and fabric formations hence had higher flexural rigidity. The twist and regularity changes after washing need to be investigated with in depth microscopic methods. The bamboo based fabric has a significantly lower flexural rigidity in all cases, which is an acceptable performance. Due to the physical and surface changes of the fabrics after washing processes, certain amount of decreases and/or increases were observed of the thermal comfort values. The thermal properties of fabrics are dependent on the fiber’s specific thermal conductivities, size and configuration of the space between the fibers in the woven specimen and fabric structures. In this study, most of the fabrics which were washed ultrasonically had higher thermal conductivities in comparison with conventionally washed fabric. The only linen fabrics conductivity increased by both washing methods. It can be considered due to highly absorbent and good conductor of heat properties of linen fiber. The washing times did not influence the conductivity significantly. The laundering process of fabrics was found to provide relatively drier and cooler feelings when the fabrics in contact with the skin as compared to the unwashed fabrics. In lower washing times (15 and 30 min), the ultrasonically washed fabric have improved thermal resistance. Due to their outstanding close structure and lower wettability the unwashed fabrics had a greater percentage of recovery after 4 min of wetting when compare to the washed fabrics. For 15 and 30 min, the ultrasonically washed fabrics showed a more desirable percentage recovery. Besides its superior advantages such as better cleaning, reducing process times, lower chemical and energy consumption, the ultrasonic washing method would be beneficial for summer clothes cleaning since it increases the thermal absorptivity values of the natural fabrics. In wet states of fabrics, the thermal absorptivity is considerably higher than in a dry state due to the higher absorptive properties of water. According to the Permetest results, the differences between the unwashed and the washed fabrics are inconsiderable. Heat loss increases when the fabrics are washed with both ultrasonic and conventional washing methods, furthermore; the ultrasonically washed fabrics have considerably higher heat loss value than the conventionally washed fabrics.

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AUTHORS’ ADDRESSES Muhammet Uzun University of Bolton Deane Road Bolton Lancashire BL3 5AB UNITED KINGDOM

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