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Stability toward alkaline hydrolysis of B . mori silk fibroin grafted with methacrylamide
Author(s) -
Taddei Paola,
Pavoni Eleonora,
Tsukada Masuhiro
Publication year - 2016
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.4892
Subject(s) - fibroin , methacrylamide , bombyx mori , silk , raman spectroscopy , hydrolysis , chemistry , infrared spectroscopy , polymer chemistry , alkaline hydrolysis , hydrogen bond , polymer , chemical engineering , materials science , organic chemistry , molecule , monomer , composite material , biochemistry , acrylamide , gene , physics , optics , engineering
Bombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B . mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH 2 groups into COOH and COO − groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β‐sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH − attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high‐performing silk‐based materials. The A 731 / A 1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain ( R 2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd.