Washing efficiency and fabric damage by beating and rubbing movements in comparison with a front-loading washer

Abstract

The objective of this study was to evaluate washing performance by beating and rubbing movements that simulate traditional washing methods. By comparing washing performance between these washing methods and a front-loading washer, we examined the potential of the new washing technique and proposed an efficient washing system. In this study, the new rubbing movement, that mimics a washboard, shows low fabric damage with high washing efficiency. The rubbing movement provides high mechanical force, which allowed easy transfer between soil and the detergent solution on the fabric surface. Thus, efficient washing can be accomplished by rubbing movements which minimize fabric damage and achieve high washing efficiency. A beating movement that copies a laundry bat gave the lowest damage and washing performance, so may be used for delicate textiles. In addition, location changes through flexing enhanced washing efficiency and showed better performance than strong force in a fixed location.

Keywords

flexing fabric rubbing fabric beating washing efficiency fabric damage

The washing of clothing using water, detergent, and a washer is influenced by physicochemical and mechanical actions.¹ The physicochemical action plays a role in separating soil from clothes and stably dispersing it into the detergent solution. The mechanical action functions to separate soil by inducing flexing and friction between fabrics, moving loosened soil to the detergent solution, and delivering fresh detergent solution to the textile surfaces.^2,3 Therefore, an understanding of both the physicochemical and the mechanical actions is necessary to precisely determine the washing mechanism and improve washing performance.^4,5

The mechanical actions of washing are categorized as large-scale, small-scale, and molecular scale, based on their effects.^6,7 The large-scale effect is to uniformly maintain the concentrations of detergent and soil through the movement of fabrics and detergent solution. The small-scale effect is the mass transfer that facilitates detergent solution penetration into textiles, and the dispersion of soil separated from the textiles. The molecular scale effect is operative at less than 1 µm distances, in the form of van der Waals forces or zeta potential, but it has a low influence on washing performance, as compared to the physicochemical action of detergents.

Based on this classification, fabric movements in a washer are large-scale and small-scale effect, and affect textiles in terms of tensile strength and shearing stress by textile flexing and detergent flux.^8–11 The control of these forces in a washer is primarily regulated by the main parameters of wash spin-speed, on/off time of motor, washing time, and water amount.¹² Controlling these parameters leads to diverse fabric movements in a washer, and subsequently influences the washing performance.^13,14 The fabric movements in a front-loading washer can be divided into sliding, falling, and rotating, and the falling movement is the most efficient for washing, due to the magnitude of force imparted to the textiles, the number of flexings, and opportunities for exposure to detergent solution.^15,16

Two simulators were designed to mimic the rubbing movement of washboards and the beating movement of laundry bats that were used in traditional washing methods, in order to investigate the effect of these newly-introduced mechanical actions on washing performance. By comparing washing performance between these new washing methods and a front-loading washer, we examined the potential of the new washing technique and proposed an efficient washing system.

Experimental details

Specimens

EMPA 106, cotton fabric soiled with carbon black and mineral oil, was used to evaluate washing efficiency. To examine the fabric damage, EMPA 306 was used, which is “Poka Dot” Type A cotton test fabric for mechanical action. EMPA 106 and EMPA 306 were purchased from Testfabrics Inc. (West Pittston, PA, USA). Cotton fabric and polyester fabric were used as the dummy load. The characteristics of the dummy load are shown in Table 1, and C1 was used as the base fabric for the washboard simulator and the laundry bat simulator. The fabric size for the dummy load was 40 × 80 cm.

Table 1.

Characteristics of dummy loads

	P1	C1	C2
Fiber content	Polyester 100%	Cotton 100%	Cotton 100%
Weave type	Plain	Dobby	Oxford
Weight (g/m²)	38.7	237.0	289.1
Water contents (%)	59.2	203.8	63.6
Thickness (mm)	0.065	0.923	0.700

Washer and simulator

Washer

A front-loading washer (Samsung Electronics, WW-HF135UV; maximum capacity 13 kg) was used to investigate the washing efficiency and fabric damage caused by the movements involved in a front-loading washer, such as sliding, falling, and rotating. Wash spin-speed was 46 or 60 r/min, and the reversing rhythm was 30 s on/4 s off.

Washboard simulator

For equipment to simulate washing by rubbing on a washboard, three pieces of soiled fabrics were attached to the base fabric, and textile or a washboard were used as the rubbing surface. The rubbing speed was 10–30 to-and-fro motions per minute, and the simulator was designed to control the magnitude of frictional force by changing spring heights between 0 mm and 5 mm. The schematic diagram of the washboard simulator is shown in Figure 1, and videos of the movement is given in supplementary files.

Figure 1.

Schematic diagrams of (a) washboard simulator and (b) laundry bat simulator.

Laundry bat simulator

This is equipment to simulate washing by beating with a laundry bat, and two pieces of soiled fabrics can be attached to the base fabric. It was designed to control fabric movements at the point of beating for different types and numbers of base fabrics. The beating speed is regulated between 50 and 180 times per minute, and the lower plate can rotate six times per minute, to continuously change the beaten location. Figure 1 also shows the schematic diagram of the laundry bat simulator.

Washing conditions

Tap water at 15℃ was used in set amounts for full immersion of the soiled fabric in each equipment. The amount of water for a front-loading washer was 6.5 L, for the washboard simulator 1.5 L, and for laundry bat simulator 12 L. IEC 60456 reference detergent A* was used according to the recommended amount (2 g/L). The washing time of washer and simulators was 30 minutes.

Evaluation of washing performance

Measurement of reflectance and Y value

A spectrophotometer (CM-2600d, Minolta) was used to measure the reflectance and Y value among CIE Tristimulus to examine the washing efficiency and the fabric damage, and Spectra Magic (Minolta) software was utilized for analysis.

Evaluation of washing efficiency

The reflectance by spectrophotometer was converted into K/S values by equation (1), and then the washing efficiency was calculated using equation (2)¹⁷

K / S = \frac{(1 - R)^{2}}{2 R}

(1)

where K is the absorption coefficient, S is the scattering coefficient, and R is reflectance

D = \frac{(K / S)_{s} - (K / S)_{w}}{(K / S)_{s} - (K / S)_{o}} \times 100

(2)

where D is washing efficiency, (K/S) _s is the K/S value of the soiled strip, (K/S) _w is the K/S value of the washed strip, and (K/S) _o is the K/S value of the original strip.

Evaluation of fabric damage

Fabric damage using EMPA 306 was measured by Y value difference (ΔY) before and after washing.¹⁸

Results and discussion

Washing efficiency of rubbing movement

The washing efficiency was examined by varying the spring height, fabric condition (immersing or wetting), and rubbing surface in the washboard simulator. The experimental conditions are described in Table 2, and Figure 2 shows the results of washing efficiency. The plastic washboard was a commercial one, whose shape was similar to the traditional washboard, as shown in Figure 3.

Figure 2.

Washing efficiency of rubbing movement according to the experimental conditions.

Figure 3.

Shape of a traditional washboard.

Table 2.

Rubbing conditions

	Compressed height of spring (mm)	Fabric condition	Rubbing surface	Rubbing speed (cycles/min)
A	5	Immersed	Cotton fabric	21
B	0	Immersed	Cotton fabric
C	5	Immersed	Plastic washboard
D	0	Wet	Cotton fabric

The height of the spring pushing against the rubbing surface was varied to control the compression force on the textiles. The difference in washing efficiency with changing forces was obtained by comparison of experiments A and B. The results indicated that higher compression force delivered to the fabric made it easier to remove soil, as expected. The comparison of experiments A and C was conducted for material difference of rubbing surface. Force calculated by the equation shown in Table 4 in experiment A was 11.7 N, and 9.9 N in experiment C, according to the different rubbing surfaces. The difference of washing efficiency due to force magnitude was partially offset because textiles can have movements similar to flexing, according to the shape of washboard, in experiment C. The effect of fabric immersion was investigated by comparing experiments B and D. It is expected that while the frictional force was reduced under the immersing condition, experiment B exhibited higher washing efficiency, because the immersing condition was favorable to the transfer the separated soil and the supply fresh detergent solution.

Washing efficiency of beating movement

The washing efficiency of the beating movement was evaluated by changing the number of base fabrics and the fabric conditions (immersing or wetting) in the laundry bat simulator. The experimental conditions are described in Table 3, and Figure 4 shows the results of this washing efficiency.

Figure 4.

Washing efficiency of beating movement by test conditions.

Table 3.

Beating conditions

	No. of base fabric	Fabric condition	Beating speed (strokes/min)
A	1	Immersed	180
B	4	Immersed
C	1	Wet

Table 4.

Comparison of applied force for three movements

	Falling	Rubbing	Beating
Schematic diagram
Equation related	$F = \frac{m \sqrt{(R ω \sin θ)^{2} + 2 gH}}{Δ t}$	$F = μ PS$	$F = \frac{mv}{Δ t}$
Abbreviations	m: mass (kg) R: radius of drum (m) ω: angular velocity (rad/s) θ: angle moved (rad) g: gravitational acceleration (9.8 m/s²) H: height (m) t: time (s)	μ: friction coefficient P: pressure (kg/m²) S: area (m²)	m: mass (kg) v: velocity (m/s) t: time (s)
Force (N)	4.8	11.7	2.4

Comparison of experiments A and B indicated that experiment B, with many base fabrics, showed higher washing efficiency. Fabric movements, like flexing, were easily observed in experiment B, with four base fabrics, when force was delivered to soiled fabrics in the simulator. The effect of fabric immersion, through comparing experiments A and C, indicated that immersion resulted in higher washing efficiency than wetting. This might be because the soil removed from the textiles under immersion is easily transferred, and fresh detergent solution is continuously supplied to the textile surface. This result was in accordance with the washing efficiency of the washboard simulator.

Comparison of forces by movements

The magnitude of mechanical forces from each movement was compared, before comparing the washing performance by the various motions. Among three fabric motions involved in a front-loading washer, the falling motion with the highest washing efficiency was compared.^13,15 Schematic diagrams, related equations, and forces for the three movements are shown in Table 4.

The three forces were calculated under the conditions used in the following “Comparison of washing performance” section, using the mean values of three measurements. The falling force was calculated as 4.8 N by analyzing fabric movement from the washing process when wash spin-speed was 46 r/min and mass of wet fabric was 0.184 kg. The rubbing force was 11.7 N when the compressed height of the spring was 5 mm, the fabric was immersed, cotton fabric was used for rubbing, and the rubbing speed was 21 cycles/min. The beating force was calculated as 2.4 N by analyzing mass (0.67 kg) and acceleration (3.55 m/s²), with a beating speed of 180 strokes/min. The force by the rubbing simulator was the largest, so it was expected that the rubbing movement could be a candidate for an efficient washing method.

Comparison of washing performance

Washing efficiency and fabric damage of the new test methods were compared with movements of sliding, falling, and rotation involved in a front-loading washer. Conceptual diagrams for the three movements are shown in Figure 5, and represented by varying the wash spin-speed and the types of fabric that were used in previous studies.^13–16 Sliding is the behavior of the fabric moving backward through sliding over the lifter when rotating counter-clockwise; falling refers to the movement when the fabric spins and then falls down due to gravity upon hitting the lifter; and rotation is the movement that moves along the drum wall of the washer.¹⁵ The optimum wash spin–speed for sliding and falling was 46 r/min, and 60 r/min for rotation, since the major movement occurring at each spin speed was different. Five types of movements were compared under the condition that each piece of equipment consumed same electric energy for 30 min of washing time. The speed of each movement type was controlled so as to consume the same energy of 13.1 watt-hour, which is the amount of electricity consumed by a front-loading washer. For the other simulators to consume this amount of energy throughout the washing time, the rubbing speed was set to 21 cycles/min and the beating speed to 180 strokes/min.

Figure 5.

Conceptual diagrams for various fabric movements in a front-loading washer.¹⁵

Washing efficiency

The test results of washing efficiency for the five movements are shown in Figure 6. The rubbing movement simulating the washboard showed the second highest washing efficiency after the falling movement, which exhibited the highest efficiency among the motions of the front-loading washer. This was because the rubbing movement had the largest force, and the soiled fabric consistently faced the rubbing surface, while the falling or beating force was applied to the soiled fabric in a shorter time. However, the beating movement by the laundry bat simulator showed the lowest performance of the five movements, because it had the smallest force, and the soiled fabrics could experience the energy only at the moments of beating. These results suggest that if flexing is maximized in the movements of rubbing and beating, simulators will represent higher washing efficiency.

Figure 6.

Washing efficiency of five movements.

Fabric damage

Figure 7 and 8 show the results of fabric damage from the five movements. The beating and rubbing of the simulator represented lower damage, as compared with the three movements of the front-loading washer. Especially, the rubbing movement showed less damage with higher washing efficiency than the sliding or rotating movements. In the case of sliding and rotating movements, the mechanical force is focused on several positions of the fabric, and thus results in more severe fabric damage. However, in case of the rubbing movement, the position of the fabric where force is applied changes continuously, thus the mechanical force is distributed over all positions. Thus, the force applied by the rubbing movement is efficiently transferred to the soil, minimizing fabric damage. Therefore, the rubbing movement is a good potential candidate for a new washing method in the future.

Figure 7.

Fabric damage of five movements.

Figure 8.

Photos of EMPA 306: (a) unwashed; (b) falling; (c) beating.

Conclusions

Simulators mimicking a washboard and a laundry bat were designed for a new washing system, and their washing efficiency and fabric damage were compared with movements such as sliding, falling, and rotation in a front-loading washer. The rubbing movement that simulated a washboard represented a lower level of fabric damage and higher washing efficiency than sliding or rotating. This was due to the large force of the rubbing movement and the easy exchange of soil and detergent solution at the fabric surface; in addition, it resulted in efficient washing and minimized damage to the textiles. The beating movement simulating the laundry bat showed the lowest damage and washing efficiency, so it may be used for washing delicate fabrics such as silk and wool. In addition, changes in location receiving a force, through textile bending or stretching, were better for washing than a strong force continuously in a fixed location. Furthermore, forcing movement under immersion conditions of textiles confirmed that it is important for washing efficiency to remove soil separated from clothes and supply fresh detergent solution on the fabric surface.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by Samsung Electronics Co., Ltd (grant number 350-20130030), the National Research Foundation of Korea (NRF) grant, funded by the Korea government (MSIP) (grant number 2015R1A2A2A03002760), and the BK21 Plus project of the National Research Foundation of Korea Grant, funded by the Korean Government

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