The bulk and surface elemental compositions of the silk sericin and chitosan powders were determined by elemental analyzer and X-ray photoelectron spectroscopy and the results are summarized in Table 1.
Sericin constitutes roughly up to a third of the raw cocoon silk and consists of three polypeptides with molecular masses of 400, 250 and 150 kDa.
It composes of 18 different amino acids including serine (30–40%), aspartic acid (10–20%)
and glutamic acid (3–15%) that have high content of hydroxyl groups.Wu et al. reported that sericin recovered from silk wastewater contains 92% protein, 1% sugar and 4% ash with a total
nitrogen content of 14.6%.
Vaithanomsat and Kitpreechavanich also reported the nitrogen content of sericin to be within 12–14%.
Table 1 shows that our sericin powder had total nitrogen and sulphur
contents of 11.9 and 5.0%, respectively.
The XPS data in the table indicates that the surface and bulk nitrogen contents are comparable,
but most of the sulphur was located in the bulk instead Fig. 2.
Fourier transformed infrared spectra of silk sericin and chitosan biosorbents.
of the surface. The chitosan powder contained less nitrogen (i.e.,7.3%) and significantly lower sulphur contents (i.e., 0.1%) than the silk sericin, but a greater proportion of nitrogen groups are present on the surface.