**2.3. Enzyme activities**

The proteolytic activity was assayed spectrophotometrically with azocasein as a substrate [57]. One unit of activity was defined as the amount of enzyme required to produce a 0.1 increase in absorbance at 440 nm under the assay conditions (50o C and pH 8.0).

**2.7. Weight loss and degumming efficiency determination**

105o

ment [51].

following equation (Eq. (2)):

**2.8. Wettability: Drop test**

performed in triplicate.

**2.10. Crystallinity index (CrI)**

**2.9. Whiteness**

applying Eq. (3)

Fabric weight loss was recorded as dried sample weight loss. The drying conditions were

tor. The following equation (Eq. (1)) was used to calculate the weight loss (wt%):

1 2 % ( ) 100 <sup>1</sup> *W W Wt W*

where, *W1* and *W2* are the weights of the fabric before and after treatment, respectively [59]. The efficiency of the degumming was calculated through a comparison of the enzyme proc‐ ess for silk fabrics with the standard method (degumming using Marseille soap), using the

> *E MST*

where, *DegumEff* is the Degumming Efficiency (%), *WE* is the percentage of weight loss by the enzyme treatment and *WMTS* is the percentage of weight loss by the Marseille soap treat‐

Wettability of the fabric was measured, by means of the ''drop test" before and after the de‐ gumming process. The dried samples at room temperature were tested using AATCC Test Method 39-1980 (evaluation of wettability) [60]. The time period (in sec) between the contact of the water drop with the fabric and the disappearance of the water drop into the fabric was counted as the wetting time. The time of drop disappearance was averaged from meas‐ urements in different points of the fabric sample. Wetting times equal or less than 1 sec were considered as indication of adequate absorbency of the fabrics [61]. All measurements were

The whiteness index (Berger degree) of the fabrics was determined using a reflectance meas‐ uring Datacolor apparatus at standard illuminant D65 (LAV/Spec. Excl.,d/8, D65/10o) [62].

An X-ray diffractometer (Siemens D5000), was used in order to determine the Crystallini‐

Crystallinity Index was determined according to the empirical method of Segal et al. [63]

ty Index, using copper Ka radiation. The angles scanned were 10–30o at 0.01o

The degumming with Marseilles soap was taken as the standard 100% weight loss.

C in an air-circulated oven for 1 h. The samples were weighed, after cooling in a desicca‐

Physichochemical and Low Stress Mechanical Properties of Silk Fabrics Degummed by Enzymes


http://dx.doi.org/10.5772/53730

243

*<sup>W</sup> DegumEff <sup>W</sup>*<sup>=</sup> (2)

/s. The

Lipase activity was determined against p-nitrophenyl- propionate (pNPP) at pH 7.0 and 25°C [58]. The release of p*-*nitrophenol was monitored spectrophotometrically at 410 nm with the aid of a microplate reader (Molecular Devices Corporation, Sunnuvale, USA). The reaction was initiated by adding 10 μL of properly diluted enzyme to 190 μL of substrate solution (0.4 mM). Control reactions with inactivated lipase were used to correct nonenzy‐ matic pNPP hydrolysis. One unit of activity was defined as the amount of enzyme which released 1 μmol of product per minute under the conditions described.
