Biosorption study of copper and zinc by particles produced from silk sericin – alginate blend: evaluation of blend proportion and thermal cross-linking process in particles production

Abstract

Sericin is a protein present in the cocoon of silkworm silk (Bombyx mori), usually discarded in the effluent from the spinning process, and alginate is a linear natural polysaccharide, extracted mainly from brown algae. Both biomaterials have been attracting attention due to their properties. Sericin isolated present weak structural properties, but its strongly polar side groups enable easy cross-linking, polymerization and blending. The use of blends provides an improvement in the physical characteristics of the materials produced with the protein, and the use of alginate has an advantage because it has affinity for a variety of cations. The aim of this paper is to evaluate the particles produced from the blend between sericin and alginate and its properties. The gelation technique, dripping blends in aqueous and alcoholic solutions of CaCl2, was applied to produce particles with 1%, 2% and 3% w/V of alginate in sericin solution (2.5% w/V). Posteriorly, the thermal cross-linking process at 40, 100, 125 and 150 °C was performed in sericin-alginate particles and the biosorption processes of these particles for zinc and copper metals were investigated. The evaluation of the data was carried out through the measurement of water solubility, Scanning Electron Microscopy (SEM) images, Fourier Transform Infrared Spectrometry (FTIR) spectra and adsorption capacity. Water solubility of particles decreased when they were produced in alcoholic solution, which is probably related to the formation of β-sheet structure confirmed by FTIT analyses. Also, it was observed that adsorption capacity increased when the particles were produced in alcohol solution. The thermal cross-linking process increased the adsorption capacity until 100 °C, with values around 75% and 65% of reduction of Cu2+ and Zn2+, respectively. From temperature 100 °C all particles got higher degree of browning with an increase of solubility and decrease of adsorption capacity by particles because of the degradation of protein/polysaccharide.