The Degumming of Silk Fabrics: A Preliminary near Infrared Spectroscopy Study

Abstract

The silk fi lament spun by the silkworm (Bombyx mori) is composed of two fi broin fi laments held together by a cementing layer of sericin. Fibroin and sericin account for about 75 w% and 25 w% of the raw silk, respectively. The degumming process involves removing the sericin layer prior to dyeing. Generally, it makes use of a solution containing soap, synthetic detergents or proteolytic enzymes. A set of 50 protease degummed silk fabrics (crêpe) with different weight losses were analysed by means of near infrared (NIR) spectroscopy. A correlation between degumming loss (SE = 0.312%) and NIR spectra was obtained using the principal component regression (PCR) algorithm. The correlation obtained had a coeffi cient of determination (R 2 ) of 0.97 and a standard error of calibration (SEC) of 1.6% for a mean value of 14.6%. In the second part of the study, NIR spectroscopy was used to determine the concentration of sericin in solution. A set of sericin aqueous solutions ranging from 20 g L -1 to 200 g L -1 was prepared and the spectra were acquired in transfl ectance mode between 10000-3700 cm -1 and correlated with corresponding sericin concentration values. The correlation obtained between specifi ed sericin concentration values and values estimated by NIR spectra had the statistics R 2 of 0.99 and SEC of 4.9 g L -1 for an average sericin concentration of 103.8 g L -1 . The assignment of characteristic NIR spectral bands of sericin and fi broin was made.

Polymeric materials based on silk proteins

“…Once the cocoon is complete, silk farmers kill the caterpillar via exposure to hot water/steam, and the silk can be harvested. The crude silk needs both degumming [49][50][51][52][53] (from the glue-like sericin) and processing before it can be dyed and sold.…”

Historical Silk: A Novel Method to Evaluate Degumming with Non-Invasive Infrared Spectroscopy and Spectral Deconvolution

“…The main assignments are described in Table 4. Significant changes in intensities occur in this region; while the water band at 5170 cm −1 (O-H combination) increases in hard silk, amides bands at 4850, 4620, and 4520 cm −1 (hydrogen bonded N-H and C=O vibration) are more prominent in soft silk, as experienced by Mossotti et al [48]. Mo et al's study [76] showed that NIR bands are sensitive to conformational changes, so higher intensities in soft silk are probably due to the dominant conformation of fibroin, which is β-sheet.…”

“…The NIR range (7000-4000 cm −1 ) of the spectrum of hard and soft silk references HS1 and SS1 is shown in Figure 7, while Figure S3 shows the same range for all of the references. The literature [47,48,[75][76][77] about silk reports overtone and combination bands arising from OH (water and serine), NH (peptides), and CH (peptides, alanine, serine, etc.). The main assignments are described in Table 4.…”

“…On the contrary, NIR spectroscopy is a well-known method to measure dampness in the textile industry [45]. Finally, Mossotti et al [48] first used NIR data associated with chemometrics to detect sericin on textiles, considering water as an interferent for the analyses.…”

Studies on structural and functional properties of sericin recovered from silk degumming liquor by membrane technology

“…Sericin is easily degraded by heat or chemical treatment, during its separation from fibroin threads. Depending on the method used, sericin removal from the fibroin is a combination of dispersion/solubilization and hydrolysis process, which produces a wide range of the soluble sericin polypeptides 22. The recovery of sericin from the degumming liquor thus affects its structural and functional properties.…”