Structural analysis of methacrylamide‐grafted silk fibers

Abstract

SYNOPSISThe structural changes and the thermal behavior of silk fibers grafted with methacrylamide (MAA) were investigated as a function of the weight gain. The refractive index parallel to the fiber axis decreased with increasing weight gain, whereas that perpendicular remained almost unchanged. Accordingly, birefringence decreased with a steeper slope in the weight gain range 0-80%, suggesting a lower degree of average molecular orientation. Only small changes in the isotropic refractive index were detected, suggesting that the crystallinity of the fibers remained essentially unaffected by MAA grafting, as confirmed by the X-ray diffraction data. The molecular orientation in the crystalline regions remained unchanged in the weight gain range 0-60%, then sharply decreased. The strength and the initial tensile resistance of grafted silk fibers decreased both in the dry and wet states, while elongation at break increased in the dry state and remained almost constant in the wet state. The results of the thermal behavior, investigated by differential scanning calorimetry, thermomechanical and thermogravimetric analysis, and dynamic mechanical measurements, were consistent with an increased thermal stability conferred on silk fibers by MAA grafting. The cross-sectional area of MAA-grafted silk fibers increased. Moreover, ion-etched cross sections of the grafted silk fiber showed the presence of fibrils with a diameter larger than that of the untreated control. 0 1993 John Wiley & Sons, Inc.

Silk grafting with methacrylic monomers: Process optimization and comparison

“…[8][9][10] Many works on silk grafting have been developed using various vinyl monomers: styrene, 11 acrylamide, 2 methacrylamide, 3,4,10,[12][13][14][15][16][17][18][19][20] N(nbutoxymethyl)methacrylamide, 21,22 methacrylonitrile, 23,24 vinyltrimethoxysilane 25 and several methacrylates: methyl-, [4][5][6][7][8]20,24,[26][27][28][29] ethyl-, 24 isopropyl-, 10 n-butyl-, 30 benzyl-, 31 glycidyl-, 2 2-hydroxyethyl-, 3,4,9,10,18,19,32 ethoxyethyl-methacrylate. 33 Methacrylamide (MAA), however, is the monomer most used in industry because it gives products with soft hand, crease recovery (up to 30% weighting), and increased hygroscopicity.…”

Structure and properties of tussah silk fibers graft-copolymerized with methacrylamide and 2-hydroxyethyl methacrylate

“…12,13 On increasing the weight gain, the decomposition peak of silk fibroin in the grafted samples showed a tendency to move downwards. However, these changes were too small to be considered indicative of a selective modification of the thermal behavior of Figure 3 shows the DSC curves of untreated and grafted silk fibers with increasing weight gain.…”

“…This feature the upper limit of polymer loading for most textile applications of grafted silk fibers, because higher may be related to the strengthening effect brought about by the loaded polymer, which filled the weight gains may entail some negative consequences on fiber properties. 2 However, it is intervoids within the fiber and increased the cohesion between the fibroin chains, thus balancing the efesting to note that the experimental conditions adopted permitted to raise the weight gain until fect of chemical degradation. Similar results have been reported for mulberry silk.…”

“…These results are consistent with those reported for mulberry silk. 12,13 The viscoelastic properties of silk may be significantly influenced by grafting, the changes being closely dependent on the kind of monomer used, as well as on the weight gain attained. The tendency to induce broadening and shifting to lower temperature of the dynamic loss modulus peak is shared by HEMA and other vinyl monomers.…”

“…In this work, tussah silk fibers were grafted with MAA and HEMA, and characterized for their physicomechanical, therExtensive studies have been conducted on Bombyx mori silk fibers (mulberry silk). 1,2 Varimal, and morphological properties. The changes induced by grafting in fiber fine structure were ous kinds of vinyl monomers have been used, and the properties of the resulting grafted fibers have studied by Raman spectroscopy.…”