Wool keratin and silk fibroin are excellent biopolymers with outstanding properties that make them extremely valuable for biomedical and biotechnological applications. As proteins, fibroin and wool can be chemically modified at side chain groups of constituent amino acids, thus improving their properties according to the desired function. Among the chemical modifications techniques, graft copolymerization of vinyl monomers has been considered a powerful method to substantially improve some intrinsic fibre properties. Grafted fibres represent an interesting model for studying the possible structural changes induced by grafting and the interactions between the fibre matrix and the grafted polymer chains. In this study, wool and Bombyx mori and Anthaerea pernyi (Tussah) silk fibres were grafted with methacrylamide (MAA) and styrene (St) and were analysed by Raman spectroscopy to comparatively assess the reactivity of vinyl monomers towards silk fibroins and wool and to elucidate the interactions between fibres and polymers as well as the possible conformational changes caused by grafting. Upon grafting with both MAA and St, new bands (indicated with an asterisk, Figure 1) appeared with increasing intensity at increasing grafting yield. For B. mori and Tussah silk fibroin grafted with MAA, experimental and calculated spectra of the samples with the highest weight gains (97.6 and 71.4%, respectively) appeared different in several ranges, suggesting that silk fibroin and poly-MAA should be thermodynamically compatible rather than phase separated: intermolecular interactions seem to prevail and the changes in the niNH range indicated different H-bond interactions in the grafted samples. B. mori silk fibroin showed a conformational rearrangement towards a more disordered state. Conformational rearrangements seemed to involve poly-MAA as well, as suggested by the wavenumber shifts of some bands (indicated with a circle). Wool fibres showed less significant spectral changes, according to the lower grafting yield. With regards to grafting with St, experimental and calculated spectra showed less significant differences than after grafting with poly-MAA. No changes were observed in the niNH stretching range, suggesting the occurrence of interactions different from those observed with poly-MAA, probably of hydrophobic nature. The reactivity towards MAA and St was higher for B. mori and Tussah silk fibroin than for wool. Spectral changes reflected weight gain data. The spectroscopic marker that appeared the most useful to predict the MAA grafting yield was the I730/I644 intensity ratio; it was found to increase linearly with weight gain (R2 = 0.9). Analogous results were obtained for the I1602/I644 and I1002/I644 intensity ratios (St-grafting). Different interactions appeared to occur between the fibres and the two polymers.
Raman study on the structural modifications of silk and wool fibres upon grafting with methacrylamide and styrene
TOZZI, SILVIA;TADDEI, PAOLA;
2014
Abstract
Wool keratin and silk fibroin are excellent biopolymers with outstanding properties that make them extremely valuable for biomedical and biotechnological applications. As proteins, fibroin and wool can be chemically modified at side chain groups of constituent amino acids, thus improving their properties according to the desired function. Among the chemical modifications techniques, graft copolymerization of vinyl monomers has been considered a powerful method to substantially improve some intrinsic fibre properties. Grafted fibres represent an interesting model for studying the possible structural changes induced by grafting and the interactions between the fibre matrix and the grafted polymer chains. In this study, wool and Bombyx mori and Anthaerea pernyi (Tussah) silk fibres were grafted with methacrylamide (MAA) and styrene (St) and were analysed by Raman spectroscopy to comparatively assess the reactivity of vinyl monomers towards silk fibroins and wool and to elucidate the interactions between fibres and polymers as well as the possible conformational changes caused by grafting. Upon grafting with both MAA and St, new bands (indicated with an asterisk, Figure 1) appeared with increasing intensity at increasing grafting yield. For B. mori and Tussah silk fibroin grafted with MAA, experimental and calculated spectra of the samples with the highest weight gains (97.6 and 71.4%, respectively) appeared different in several ranges, suggesting that silk fibroin and poly-MAA should be thermodynamically compatible rather than phase separated: intermolecular interactions seem to prevail and the changes in the niNH range indicated different H-bond interactions in the grafted samples. B. mori silk fibroin showed a conformational rearrangement towards a more disordered state. Conformational rearrangements seemed to involve poly-MAA as well, as suggested by the wavenumber shifts of some bands (indicated with a circle). Wool fibres showed less significant spectral changes, according to the lower grafting yield. With regards to grafting with St, experimental and calculated spectra showed less significant differences than after grafting with poly-MAA. No changes were observed in the niNH stretching range, suggesting the occurrence of interactions different from those observed with poly-MAA, probably of hydrophobic nature. The reactivity towards MAA and St was higher for B. mori and Tussah silk fibroin than for wool. Spectral changes reflected weight gain data. The spectroscopic marker that appeared the most useful to predict the MAA grafting yield was the I730/I644 intensity ratio; it was found to increase linearly with weight gain (R2 = 0.9). Analogous results were obtained for the I1602/I644 and I1002/I644 intensity ratios (St-grafting). Different interactions appeared to occur between the fibres and the two polymers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
