Objective of study
- The main objective of this study is to focuses on the effect of different concentration of hydrogen peroxide (an oxidizing bleaching agent) on 100% single jersey cotton knit fabric. Five different concentrations (25%, 30%, 35%, 40% and 45%) of hydrogen peroxide solution (5% stock solution) were adopted for this experiment. For each individual concentration, bleaching was performed in three different quantities (6gm/L, 8gm/L and 10gm/L) at the same temperature (100˚C) and same time (60 minute) cycle. 5gm samples were taken where 1:10 material and liquor ratio was maintained in each operation. Spectrophotometer (data color 650) was used to test the reflectance of all bleached samples, and their bursting strengths were measured by an Auto burst instrument following ISO 13938-1 method. The effects of hydrogen peroxide concentration on various physical properties such as weight loss, absorbency, GSM, bursting strength, and whiteness was studied to minimize the cost of bleaching process by optimizing the concentration of hydrogen peroxide.
What is Bleaching
Bleaching is the process of removing natural color from textile substrate, which yields a permanent white color of fibre, yarn or fabric. Thus, the results of coloring would be better. It is the process of destroying
natural coloring matter from the textile materials to achieve a clean white end product. This is also called as some times Ready for dyeing (RFD). This is a second step of pretreatment of textile materials as well as wet processing technology. Owing to the presence of protoplasmic residues of the protein and flavones pigments of cotton flowers, it possesses its natural grey color . As a consequence, it needs to pre-treat the cotton to produce a perfect white surface that is suitable for dyeing or any other wet process treatment. Hydrogen peroxide is the most commonly used bleaching agent among all others, since it can bleach both cellulosic and protein fibers successfully .
It is a slightly more viscous and colorless liquid whose chemical formula is H2O2, with high sensitivity to metal ions. It is primarily used as an oxidizer, bleaching agent, and disinfectant. Although there is no exact evidence in the case of the nature of bleaching action of hydrogen peroxide, it is believed that the per-hydroxyl ion is the active group. Formation of this ion happened when hydrogen peroxide cleaves into the following manner .
In the absence of any kind of hue,
high luminous color of material gives an aspect of whiteness index . White is a monochromic color, and it is categorized by constant absorption from 400 to 700 nm wave length.
Material and Methods
Substrate
Fabric Type: Single jersey Fabric Construction Composition- 100% cotton CPI- 42;WPI-60
Yarn count- 28 Ne, Loop length-2.4mm GSM-160
Color: Grey
Recipe of bleaching
Sample weight 20gm
Wetting agent 2gm/L
Sequestering agent 2 cc/L
Detergent 3 cc/L
Caustic soda 6 cc/L
Hydrogen per oxide (25/30/35/40/45)%———– 10/8/6 cc/L
Stabilizer (Sodium silicate)————-2 cc/L
Temperature (90-100)0C Time 60 minutes
pH 11
M: L 1:10
Bleaching Procedure
Bleaching of grey fabric was done in a closed vessel for 1 hour at 100°C keeping the material to liquor ratio at 1:10 with hydrogen peroxide (6- 10 cc/l), sodium hydroxide (6 cc/l), sodium silicate (2 cc/l), and none ionic detergent (3 gm/L). The pH of the bath was maintained at 11. Then it was rinsed thoroughly with hot and cold water and subsequently dried in oven at 80 deg c
Type of Test Conducted
Measurement of Whiteness Index (WI)
The cotton bleached fabrics were tested through a spectrophotometer (data color 650, USA) in order to determine the whiteness index at D65 illuminant and 10° observer setting.
Weight Loss Measurement
Percentage of weight loss occurred in the cotton knit fabric due to bleaching which was evaluated by oven dry-weight basis. Usually, it is calculated from the following equation which shows the difference of pretreated and treated sample weight. It is also measured in percentage of pretreated weight of the of the sample.
Absorbency Test
The absorbency test of bleached sample was performed by drop test and wicking test according to the established procedure.
v Drop Test
In a pipet, water is taken and water drops are dropped on the scoured fabric. Then the absorption of the water drop is observed visually.
v Wicking Test
In a beaker, 1% direct dye Blue color is taken and a sample (18cm x 5 cm) is cut from bleached fabric which is hung from a wood stick. This is supported by immersing that 1cm portion of fabric in the dye liquor. Then the point is measured up to which the colored solution is absorbed by the sample in 5 min time.
Bursting Strength
All the samples were tested through a bursting strength testing instrument (Auto burst, SDL Atlas, England) followed by ISO13938-1 method. Each specimen was placed beneath the ball. It must also be flat and free from creases and any kind of distortions. Then the two clamp buttons were pressed. After that, the standard flow rate was selected. It measures the speed
at which the ball will inflate. Then start button was pressed and the diaphragm was automatically inflated until the specimen bursts. The reading was then collected from the instrument as KPa unit
Result and Discussions
Whiteness Index of Bleached
Sample
Greater value of “STD CIE WI” indicates that sample is whiter. It is observed
that the sample bleached with hydrogen peroxide
at 25% concentration has higher value of STD CIE WI, while less tint
variation is achieved during
bleaching of hydrogen peroxide for 30% concentration. On the other hand, STD CIE WI is 162.5 for 30% concentration of
hydrogen peroxide bleaching which is
near to 25% concentration. Therefore, it can be said that bleaching of hydrogen peroxide at 30% concentration for 10cc/L comparatively yields
the best whiteness result.
Variation in GSM
Enormous GSM variation has been observed for bleaching of hydrogen peroxide at 45%, 40%, and 35% respectively. This is not appreciated because it means that fabric is over bleached. On the other hand, GSM loss of hydrogen peroxide bleaching is 1.1 and 1.2 for 25% and 30% concentration.
Thus, GSM fabric bleached
with 25% and 30% concentration of H2O2 is
better.
Absorbency Test
v Drop Test
From the drop test results, it has been observed that
fabric bleached with hydrogen
peroxide at 25% concentration takes
more time to absorb the droplet. At
30% and 35% concentration, 4 sec is required to absorb the drop, while 3 sec is needed for 40% and 45%
hydrogen peroxide concentration of bleached fabric.
Table 1. Test result
of drop test of all bleaching samples
v Spot Test
The surface area of the absorption of all sample bleached with hydrogen
peroxide shows the good scouring effect at 30%, 40%, and 45% concentration. This is according to its
spot observation of dye solution as its spot are nearly round shape.
Table 2. Pictorial view of spot test of all bleaching samples
v
Wicking Test
The absorbed length of 45% concentration of peroxide bleached
sample is 55 mm. This sample shows the over bleaching than other concentration of peroxide bleached sample.
On
the other hand, fabric
bleached at 35% and 45% shows very good results as they wick 43
mm and 48 mm dye solution. In addition, 30% concentrated hydrogen
peroxide gives good
bleaching effect as it can wick 37 mm dye solution
after passing through
wicking test.
Table 3. Wicking test results of bleached samples
Bursting Strength
After analyzing the bursting test of cotton bleached fabric
properly, it has been seen that
fabric bleached with 40% hydrogen peroxide shows the lower bursting strength. On the contrary, 25% concentrated
bleaching agents yield high bursting
results which is more than 410 Kpa. However, 407 kPa strength is noticed in the case of 30% and 35% concentration of
hydrogen peroxide as bleaching
agents which is acceptable.
