Measurement of the relationship between shade (%), reflectance (%) and color strength (K/S)

Md. Shak Sadi (1), Md. Jakir Hossain (2)   Department of Textile Engineering, Southeast University, Tejgaon I/A, Dhaka-1208, Bangladesh.  Email: saditex43@gmail.com (1) 
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Abstract:

The research was carried out at H.R. Textile Mills Limited located at 4 Karnapara, Savar, Dhaka, Bangladesh. In this study dyeing of 100% cotton knit fabrics were performed by using reactive dye at different shade percentages (0.5%, 1%, 1.5% & 2%). Exhaust dyeing method was applied in the experiments for 100% cotton knitted fabrics. Three types of knitted fabric samples (single Jersey, 1×1 rib & Pique) were taken for this experiment. Scouring & bleaching was carried out at 98oC for 45 minutes while dyeing was carried out at 60oC for 60 minutes. Reflectance (%) of the dyed fabric samples were measured after dyeing. The color strength of a dyed fabric is usually expressed by its K/S value. The color strength (K/S) of the dyed samples were also measured from the reflectance (%).

Key Words: Dyeing, Shade (%), Reflectance (%), Color Strength (K/S).

  1. Introduction:

Dyeing is a distribution process from one medium (dye liquor) to another medium (substrate). Dyeing of textiles has been practiced for thousands of years with the first written record of the use of dyestuff dated at 2600 BC in China (Rita, 2012). Reactive dyes are the most suitable dyestuff for the dyeing of cellulosic fibers (cotton, viscose, lyocell etc.) considering it’s fastness properties since this dye make strong covalent bond with cellulose. Shade means the depth of color on the weight of the fabric. 2% shade means 100kg of fabric contain 2 kg dyestuffs. Shade (%) influence the reflectance (%) of the dyed fabrics. Reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at an interface. It is known to us that when reflectance is more, absorbance is less and when reflectance is less, absorbance is more. The color strength of a dye is a measure of its ability to impart color to other materials. This property is characterized by the absorption in the visible region of the spectrum and can be expressed as a color strength value (Werener et al., 1987). Color strength (K/S) is most important parameter to test the quality measurement of a sample in terms of depth of the color dyed fabric. The aim of this research is to find out the relationship among shade (%), reflectance (%) & color strength (K/S) of single jersey, 1×1 rib & pique 100% cotton knitted fabric dyed with reactive dyes (Bezaktive Red SMARTRIX, Germany) at different shade (%).

  1. Materials and methods

2.1 Materials:

This investigation has been carried out with single jersey, 1×1 rib & pique 100% cotton knitted fabric. The well scoured & bleached single jersey, 1×1 rib & pique fabrics were collected from Fong’s machine-1 of dyeing floor of HR Textile Mills Limited.

The machine capacity was about 1200kg with a temperature range of 0°C to 140°C and the number of nozzle was 4. All the required dyes & chemicals were taken from the dyes & chemicals store.

2.2 Methods:

2.2.1 Dyeing of RFD (Ready For Dyed) fabrics

A rapid sample dyeing machine of “ROACHES” made in England was used for dyeing. Dyeing of single jersey, 1×1 rib & pique 100% cotton knitted fabric was done by using following recipe;

 

Bezaktive Red SMARTRIX (Germany)        = X%

Salt (Na2SO4)                                          = X%

Soda (Na2CO3)                                        = X%

Anticreasing agent (Knitlub)                      = 1g/l

Antifoaming agent (Rustol ASA)                = 0.10 g/l

Detergent (Felosan NOF)                          = 0.80g/l

Sample weight                                          = 5gm

Time                                                        = 60 min

Temperature                                             = 60°C

M:L                                                          = 1:7

PH                                                            = 10.5-11

Table 1: Usage of Salt & Soda.

Usage of Salt & Soda according to shade percentage
Shade (%) Salt (g/L) Soda (g/L)
0.5 20 10
1 30 12
1.5 40 15
2 50 18

 

Figure 1: Dyeing curve of single jersey, 1×1 rib & pique fabrics.
Figure 1: Dyeing curve of single jersey, 1×1 rib & pique fabrics.

2.2.2 After-treatment:

After dyeing cold wash is performed for 2/3 times and normal hot wash is performed for 2/3 times followed by neutralization with acetic acid & rinsing. After hydro dyed samples were dried at “Rapid” hydro machine for 3 minute & the maximum temperature of the machine was 140°C.

2.2.3 Measurement of reflectance (%) & color strength (K/S)

Reflectance (%) of the dyed fabric samples were measured by using Data color 650 TM spectrophotometer. Strength of any colorant (dyestuff / pigment) is related to absorption property. Kubelka–Munk theory gives us the following relation between reflectance and absorbance:

K/S = [{(1-R) 2 / 2R}]

Where R is the reflectance, K is absorbance and S is the scattering. By using the above equation color strength of different samples were measured.

  1. Results and discussion

3.1 Evaluation of reflectance (%) & color strength (K/S) of single jersey fabrics:

The reflectance (%) of single jersey dyed fabric samples were evaluated. The following table shows the reflectance (%) and color strength (K/S) values of single jersey fabric samples for different shade (%). For 0.5% shade (%) the reflectance (%) was 82.65% and the color strength (K/S) value was 40.33. For higher shade (%) i.e. 2%, the reflectance (%) and color strength (K/S) was lower i.e. 80.81% and 39.41 respectively.

Table 1: Analysis of reflectance (%) & color strength (K/S) of S/J fabric

 Fabric Type Shade (%) Reflectance (%) Color Strength (K/S)
Single Jersey 0.5 % 82.65 40.33
Single Jersey 1 % 82.26 40.13
Single Jersey 1.5% 81.16 39.58
Single Jersey 2% 80.81 39.41

The following figure (Figure 2) shows that reflectance (%) & color strength (K/S) are decreasing with the increase of shade (%). Single Jersey fabric samples have shown greater reflectance (%) & color strength (K/S) than 1×1 rib & pique fabric samples.

Figure 2: Shade (%) VS. Reflectance (%) & Color Strength (K/S) for Single Jersey Fabric.
Figure 2: Shade (%) VS. Reflectance (%) & Color Strength (K/S) for Single Jersey Fabric.

3.2 Evaluation of reflectance (%) & color strength (K/S) of 1×1 Rib fabrics:

The reflectance (%) of 1×1 rib dyed fabric samples were also evaluated. The following table shows the reflectance (%) and color strength (K/S) values of 1×1 rib fabric samples for different shade (%). For 0.5% shade (%), the reflectance (%) was 80.38% and the color strength (K/S) value was 39.19. For 2% shade (%),the reflectance (%) was 74.56% and the color strength (K/S) value was 36.28.

Table 2: Analysis of reflectance (%) & color strength (K/S) of 1×1 rib fabric

Fabric Type Shade (%) Reflectance (%) Color Strength (K/S)
1×1 Rib 0.5 %  80.38 39.19
1×1 Rib 1 % 78.49 38.25
1×1 Rib 1.5%  75.07 36.54
1×1 Rib 2%  74.56 36.28

 The following figure (Figure 3) shows that reflectance (%) & color strength (K/S) are decreasing with the increase of shade (%). 1×1 rib fabric samples have shown lower  reflectance (%) & color strength (K/S) than single jersey& pique fabric samples.

Figure 3: Shade (%) vs. reflectance (%) & color strength (K/S) for 1×1 rib fabric.
Figure 3: Shade (%) vs. reflectance (%) & color strength (K/S) for 1×1 rib fabric.

3.3 Evaluation of reflectance (%) & color Strength (K/S) of pique fabrics:

The reflectance (%) of pique dyed fabric samples were evaluated. The following table shows the reflectance (%) and color strength (K/S) values of pique fabric samples for different shade (%). For lower shade (%) i.e. 0.5%, the reflectance (%) was 82.16% and the color strength (K/S) value was 40.08. For higher shade (%) i.e. 2%, the reflectance (%) and color strength (K/S) was lower i.e. 79.64% & 38.83 respectively.

Table 3: Analysis of reflectance (%) & color strength (K/S) of pique fabric

Fabric Type Shade (%) Reflectance (%) Color Strength (K/S)
Pique 0.5 %  82.16 40.08
Pique 1 %  81.44 39.73
Pique 1.5%  80.22 39.11
Pique 2%  79.64 38.83

The following figure (Figure 4) shows that reflectance (%) & color strength (K/S) are decreasing with the increase of shade (%). Pique fabric samples have shown moderate reflectance (%) & color strength (K/S).

Figure 4: Shade (%) vs. reflectance (%) & color strength (K/S) for Pique Fabric.
Figure 4: Shade (%) vs. reflectance (%) & color strength (K/S) for Pique Fabric.

Conclusion:

Reflectance (%) of a dyed fabric is greatly influenced by shade (%) of that dyed fabric. At the same time reflectance (%) also influenced by the absorption properties of a dyed fabric. When shade (%) is higher, the absorption of dye by the substrate is also higher which results in lower reflectance (%) value. At the same time when shade (%) is lower, the absorption of dye by the substrate is also lower which results in higher reflectance (%) value. Color strength (K/S) of the dyed fabric also influenced by the increase of reflectance (%) value. In this research a relation was found among shade (%) & reflectance (%) & Color Strength (K/S).When shade (%) increase, reflectance (%) & color strength (K/S) decrease. At the same time reflectance (%) & color strength (K/S) increase with the decrease of shade (%).

References:

Werner Baumann (Sandoz Chemical Corpn), Bengt-Thomas Groebel (Hoechst AG), Markus Krayer (Ciba-Geigy AG), Hans-Peter Oesch (Sandoz AG), Rolf brossman (Bayer AG), Norbert Kleinemeier (BASF AG) and A T Leaver (ICI plc), Determination of relative colour strength and residual colour difference by means of reflectance measurements, Journal of the Society of Dyers and Colourists, Volume 103, February 1987.

Salima Sultana Shimo, ShamimaAkterSmriti, Color co-ordinates and relative color strength of reactive dye influenced by fabric gsm and dye concentration, International Journal of Research in Engineering and Technology, eISSN: 2319-1163, pISSN: 2321-7308.

Rita Kant, Textile dyeing industry an environmental hazard, Natural Science, Vol.4, No.1, 22-26 (2012).

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