Flame Resistance Finishing On Silk Fabric With Organophosphorus Compounds

The flame resistance finishing of silk fabric is still a challenge for chemical treatments available are not able to ensure sufficient laundering durability and some treatments are based on carcinogenic formaldehyde.To solve this problem, in this paper, two kinds of different environment friendly flame resistance finishing systems were applied to treat silk fabric.One method is copolymerization of vinyl phosphate and silk fabric. Two vinyl phosphate monomers were synthesized using a new synthesis route in our lab: diethyl methacryloyloxyethyl phosphate (DEMEP) and dimethyl methacryloyloxyethyl phosphate (DMMEP), the schemes are as follows:The structure of DEMEP and DMMEP were confirmed by ¹H NMR, ¹³C NMR and IR spectra of the two compounds. DEMEP can not dissolve in water, and it must be pre-emulsified before copolymerization. The suitable emulsifier is the combination of Tween 80 / Span 80 on the ratio of 65.9 %/34.1 % (w/w). DMMEP can dissolve in water well and it can be applied in water directly. Adding 10% of the complex emulsifier can disperse DEMEP well in water and the emulsion is stable.By investigating the reaction parameters, an optimized copolymerization was obtainedas follows: the amount of DEMEP or DMMEP is 60-120 % (on the weight of fibers, owf); the initiator potassium persulfate 0.9 ¹.0% (on the weight of monomer, o.w.m.). The pH of thermal decomposition of control and flame retarded silk fabric was studied and showed that the apparent activation energy (E) of flame retarded silk fabric was lower than that of the control silk fabric, which showed that flame retarded silk fabric decomposed more easily than control silk fabric. The pyrolysis experiments showed that after grafted with DEMEP, silk fabric changed the pyrolysis model and decomposed at lower temperature. By all this measurement, the possible flame retardancy mechanism of DEMEP and DMMEP can be speculated that these two flame retardants work in condensed phase; they can promote silk fabric dehydration and char formation, reduce the flammable gas volatiles.The other method is chemical crosslinking of silk fabric with flame retardant by a crosslinking agent 1, 2, 3,4- butanetetracarboxylic acid (BTCA). The flame retardant here used is a hydroxyl-functional organophosphorus oligomer (HFPO):The optimized flame resistance finishing formula is: BTCA 15-30 %( w/w), the molar ratio of BTCA and HFPO is 1:1.75, catalyst sodium phosphate is 80%(on the weight of BTCA), the pH value of finishing solution should be adjusted to 2.5 by HC1 or NaOH, two dips, two nips, the wet pick up is 100%, then dry at 90℃for2min, cured at 160℃for 2 min, and wash, dry. Adding 25% triethanolamine (TEA, on the weight of BTCA ) can improve the fixation of HFPO onto silk fabric and improve the laundering durability.The paper explored the crosslinking mechanism of silk fabric and BTCA, HFPO and TEA. Much BTCA can not bond much HFPO because of the competitive reaction of BTCA-silk, silk-BTCA-HFPO and BTCA-HFPO. And the reaction of BTCA with both HFPO and silk which results in the bonding of HFPO onto the silk through a BTCA "bridge", which is hoped to happen. The mechanism was studied by measuring the wrinkle recovery angle, phosphorus content, carbonyl band intensity in the infrared spectra and the stiffness of the treated silk fabric. The amount of triethanolamine can not be high because of the competitive reaction between TEA-BTCA and HFPO-BTCA, and too much triethanolamine is not good for handle and flame retardancy.The LOI of silk fabric is higher than 27% after adding 15-30%HFPO and can pass vertical flammability test. But this treatment can cause the whiteness and tensile strength loss for silk fabric. And the most negative effect is the stiffness of silk fabric. This treatment can withstand 15 laundering cycles.Thermal gravimetric analysis showed that after treated with HFPO/BTCA/TEA system, the initial decomposition temperature is lowered about 50℃compared with control silk fabric and at the end of the decomposition; The char residue is increase by 14 perentage points, which showed that HFPO HFPO/BTCA/TEA system worked in condensed phase. It still give silk fabric flame retardancy by promote char formation.