*3.2.3. Whiteness and whiteness after bleaching with H2O2*

0

25 50 75 Marseille soap

**Esperase 8.0L and Papain Activities (Units/ gfabric)**

Papain Esperase 8.0L Marseille soap **(b)**

fabric showed adequate water absorbency (<1 sec). On the other

g-1 fabric).

20

40

60

**Degummng Efficiency (%)**

**Figure 2.** a) weight loss of silk fabrics treated with different types of proteases at enzyme dosages ranged from 25 to

The amount of sericin in raw silk measured in terms of weight loss varies between 17and 38%. Some of the good Chinese and Japanese varieties show about 17 to 17.5%, while yellow

Wettability was a function of both enzyme dosage and type of protease. Silk fabrics treated

hand silk fabrics treated with papain showed higher wetting times namely more hydropho‐ bic fabrics. Although the implementation of higher papain activities formed silk fabrics with lower wetting times (Table 7) these values were higher than 1 sec, which is the maximum wetting time required for efficient dyeing and finishing. The lowest wetting time achieved

**Treatment Wetting time (sec) Crystallinity Index (%)**

25 6.12 ± 0.25 61.73 ± 1.48 50 4.16 ± 0.16 62.27 ± 0.98 75 3.65 ± 0.19 63.90 ± 0.89

25 1.80 ± 0.20 63.90 ± 1.30 50 1.36 ± 0.15 66.61 ± 1.10 75 <1 66.72 ± 1.20 Marseille soap <1 66.48 ± 1.35 No enzyme 6.85 ± 0.20 63.90 ± 1.27

**Table 7.** Wetting time and Crystallinity Index of silk fabrics treated conventionally (Marseille soap) or enzymatically.

Italian silk has about 23% sericin and some Thai varieties have as high as 38% [27].

0

*3.2.2. Wettability and crystallinity*

with Esperase® 8.0L at 75 U.

25 50 75 Marseille soap

**Esperase 8.0L and Papain Activities (Units/ gfabric)**

g-1fabric and (b) degumming efficiency of the enzymatic process

g-1

using papain was 3.65 sec at the highest papain activity (75 U.

Papain Esperase 8.0L Marseille soap **(a)**

5

10

**Weight Loss (%)**

74 U.

Papain (U.

Esperase®

g-1 fabric)

8.0L (U.

g-1 fabric)

15

20

25

246 Eco-Friendly Textile Dyeing and Finishing

80

100

Natural coloring matters present in silk are associated mainly with sericin and hence are eliminated during degumming. The natural colouring matter of silk can be roughly divided into yellow, green and brown pigments. However the residual pigments are adsorbed by fi‐ broin and hence silk fabrics made from yellow raw silk after degumming are not white but have a cream colour [65]. Lustre is one of the most important properties of silk, hence the method of degumming is significant.

A slight increase in whiteness was observed after treatment with the two different proteases compared to the fabric treated in the absence of enzyme. Esperase® 8.0L exhibited better re‐ sults compared to papain. However, whiteness of silk fabrics treated with Marseille soap was superior to that of enzymatically treated fabrics (Figure 3a).

The results are in contrast to those reported by Chopra et al., [49] who demonstrated that enzyme treated samples rate marginally better than the soap-treated samples.

Bleaching of silk is for white and pastel shades only. Degummed silk fabrics present a slight‐ ly off-white in colour, because of some sericin, which is stubbornly stuck to the fibrin [65]. After enzymatic and conventional degumming the silk fabrics were bleached with H2O2. The results indicated that the whiteness after bleaching of all Esperase® 8.0L treated fabrics were the highest (Figure 3b).

**Figure 3.** a) Whiteness Index and (b) Whiteness Index after bleaching with Η2Ο2 of degummed silk fabrics using Mar‐ seille soap (conventional treatment) or papain and Esperase® 8.0L at different loadings.
