Studies On Modification Of Silk Using Acrylate Monomers Containing Fluorine

Silk fibers were chemically modified by grafting copolymerization with acrylate series monomers containing fluorine such as trifluoroethyl methacrylate(G01), hexafluorobutyl methacryate(G02), hexafluorobutyl acrylate(G03), dodecafluoroheptyl methacrylate(G06), dodecafluoroheptyl acrylate(G07). In addition, we synthesized octafluoropentyl meth- acrylate (G04) and octafluoropentyl acrylate (G05) for modification of silk fibers and examined the reactivity of these above seven grafting agents toward silk fibers. Mean while, we investigated the structure and properties of these grafted silk fibers in relation to the graft yield on the basis of the results of mechanics properties as well as thermal properties, dyeing properties, X-ray diffraction, IR, Raman spectrum, birefringence(△n), SEM, NMR, XPS, amino acid, wrinkle recovery, whiteness, surface contact angle, and so on analyses.Using toluene and p-toluene sulphonic acid as solvent and catalyst respectively, Methacrylic acd or acrylic acd and octafluoropentanol were esterified respectively to produce G04 and G05. Under the optimum synthesis conditions the yields of G04 and G05 are 42.5% and 50% respectively. The chemical structures of these products were analyzed by IR, NMR, gas chromatography and elementary analysis so that good results were obtained.The grafting of acrylate monomers containing fluorine onto silk fibers in composite emulsified liquid system using potassium persulfate(KPS) as initiator was investigated. The formulation of the pre-emulsification was optimized by studying three stabilities of different pre-emulsification liquid, namely, fluorocarbon surfactant FSO 12% (owm), DF-10 8% (owm), Tween 80 30%(owm). Effects of grafting conditions, such as concentrations of monomers, initiators, pH, temperature and time, on the graft yield were determined. The optimum graft conditions were found (Monomer 100-150%(owm), KPS 1-3.5%(owm), pH 3, 75-80℃, 100-120min). The activation energy of grafting at 50~80℃was found to be 8.99 kJ/mol for G01, 13.97 kJ/mol for G02, 15.28 kJ/mol for G03, 11.96 kJ/mol for G04, 14.21kJ/mol for G05, 15.66 kJ/mol for G06, 23.8 kJ/mol for G07.Grafting equations also were counted. The moisture regain of silk fibers grafted with acrylate monomers containing fluorine decreased linearly as the graft yield, while the size of the silk fibers increased linearly as the graft yield. The grafted silk fabrics showed greatly improved wrinkle recovery behavior, especially in wet state and resistance to alkaline according to the solubility of the silk fibers in NaOH aqueous solution. The grafting of silk fabric caused a little reduction of acid and reactive dye uptakes as well as whiteness. By treating silk fabric with KPS, in the absence of a monomer the whiteness values decreased linearly with increasing both initiator concentration and treatment temperature, indicating that the initiator plays a specific role in decreasing silk whiteness through macro-free radical formation. At the same time, after the grafting treatment with fluoride monomers, the breaking strength, elongation at break and air permeability of grafted silk fibers all decreased. The DSC and TG results showed that the position of decomposition peak of grafted silk fibers shifted to higher temperatures, suggesting the more thermal stability. The cross-linkage between the molecule of silk fibers and fluoride monomers may limit macromolecular motion in silk fibers, so, the peak of loss modulus(E'') determined by dynamic viscoelastic measurements become lower and the initial position of this peak shifted to higher temperature, when the silk fibers graft yield increased. The amion acid analysis indicated fluoride monomers were inclined to graft with TYR, ARG and GLU of silk fibers which had some reactive groups, i.e., the hydroxyl, amido and imine groups acting as the center of reactive activities. X-ray diffraction patterns and Birefringence(△n) of silk fibers suggested that the grafting of fluoride monomers does not affect directly the crystalline regions, but causes a decrease of macro-molecular average orientation in the amorphous regions. The IR of the grafted silk fibers had overlapped absorption bands due to the molecular conformation of this fiber and monomer polymers, giving evidence that the monomer grafting occurred inside the amorphous areas of silk fibers. When the graft yields are more than 35%, the surface of silk fibers showed the presence of several granules, consisting of monomer polymers, and the cross-sectional area of silk fibers showed the appearance of separating fiber.Moreover, the NMR spectrum(19F)of grafted fibers indicated the chemical shifts of -78.16ppm, -215.71ppm and -122.51ppm represented the structures of–CF3,–CF2– and–CFH– of macromolecules of grafted fibers respectively. Furthermore, the XPS spectrum(19F)of grafted fibers also showed the binding energy positions of 688.92ev, 284ev, 289ev, 291ev and 294ev belonged to C–F, C–H, CFH, CF2 and CF3 structures respectively, which gave evidence that acrylate monomers containing fluorine had grafted with silk fibers and side chain structures containing fluorine had been covered or distributed on the surface of fabrics. With the increase of graft yields gradually, the surface contact angle of fabrics increased correspondingly and showed the trend of a gradual slowdown. When the grafting yield reached a certain value, if it is further increased, the contact angle will decrease. Besides, the contact angles of monomers with methyl structure are bigger than those of non- methyl monomers under the condition of similar graft yields. With the growth of fluorocarbon chain, the higher contact angle of fabric is, the lower grafting yield is needed. After washing many times, the grafted silk fibers still took on higher contact angle and with the growth of fluorocarbon chain of monomer, the washing fastness was improved. In a word, through the syntheses of G04 and G05 and the study of seven acrylate monomers containing fluorine reacting to silk as well as the research of structure and properties of grafted silk, the paper provides a basis for chemical modification and finishing of silk.