was determined after reference to the respective calibration
curve of the lac dye using LamberteBeer law.
2.5. Nitrogen percentage
Nitrogen was determined by the Cole and Parks modification
of the semimicro Kjeldahl method [22].
2.6. Fastness testing
The dyed samples were tested according to ISO standard
methods. The specific tests were ISO 105-X12 (1987), colour
fastness to rubbing; ISO 105-C02 (1989), colour fastness to
washing and ISO 105-E04 (1989), colour fastness to
perspiration.