PHYSICAL CHARACTERISTICS OF SILK FIBERS MODIFIED WITH DIBASIC ACID ANHYDRIDES

The objective of this study was to investigate the physical properties of silk fibers modified with dibasic acid anhydrides. These are poten tially attractive modifying agents to reduce the rate of photoyellowin g of silk during and following UV irradiation. Several analytical tech niques were employed, which included the measurement of the basic mech anical properties (tensile strength and elongation at break), equilibr ium regain, amino acid analysis, dynamic viscoelastic measurements, X- ray diffractometry, and scanning electron microscopy (SEM). The succin ylated silk fibers, which have been conditioned under different relati ve humidity atmospheres, always exhibited slightly higher equilibrium repin values than those of equivalently conditioned glutarylated silks . The amount of the basic amino acid residues slightly decreased follo wing modification with both succinic and glutaric anhydrides. The bire fringence values and the isotropic refractive indices decreased only s lightly, which suggests that the fine structure of the treated silk fi bers was not significantly altered. The X-ray diffraction curves demon strated that no changes in the crystalline structure were induced by r eaction with dibasic acid anhydrides. The tensile properties of the mo dified silks remained more or less unchanged. Only the initial tensile resistance of glutarylated silks in the dry state significantly decre ased. The dynamic viscoelastic behavior of modified silk fibers was ch aracterized by a reduced thermal stability. In fact, the onset tempera ture of the prominent E' peak corresponding to the molecular movement shifted to lower values. The surfaces of modified silk fibers were as smooth as that of the untreated control sample. (C) 1994 John Wiley & Sons, Inc.