Study On The Color Fixation Of Naturally Colored Domestic Silk With Tetrakis (Hydroxymethyl) Phosphonium Sulfate Reagent

Naturally colored domestic silks(NCSs)are referred to silk fibers with natural lustre and colour,which are harmless and even healthy.The NCSs exhibit brilliant colors and need not to be dyed.And the pigments of NCSs endow the silk fibers with some ecological properties like UV-shielding,antibacterial and antioxidant properties,which make the NCSs suitable for weaved into underwear or summer clothing.The color and properties of NCSs are mainly from the intrinsic biological pigments in the silk fibers,such as carotenoids and flavonoids,the structures of which are not stable.And the color of NCSs completely lost after degumming,attributing to the accumulation of pigments in the sericin.So the developments of NCSs are restricted in a certain extent.In this paper,the color stability and oxidation resistance of NCSs were studied,as well as studying the effect of color fixation with tetrakis(hydroxymethyl)phosphonium sulfate(THPS)on the color stability of naturally yellow-colored domestic silk(NYCS).Finally,the structure and properties of NCSs before and after color fixation were studied.The main results of this study are as follows.The antioxidant properties of NCSs were studied by using 1,1-diphenyl-2-picryl-hydrazyl(DPPH)and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(ABTS)methods.The results showed that the NCSs(pink,yellow,green)had excellent antioxidant properties,especially the green type,owning much remarkable antioxidant capacity than naturally green cotton,which has been found to be the highest known antioxidant-active natural fiber.However,the scavenging capacities of NCSs toward DPPH and ABTS free radicals decreased 40~80% after the first washing.With the increase of washing cycles,the antioxidant capacities of NCSs showed a good retention in 15 cycles.In view of the output and color stability,NYCS is most likely to first appear in the market.In order to clarify the influence of conventional fabric processing and daily use on the color of NYCS,this paper studied the effects of heat,p H,oxidant,reductant,home laundering and sunlight on the color changes of NYCS.The results showed that NYCS began to fade at 105 ? when under dry heat treatment,and at 120 ? during wet heat treatment.At the same temperature,the degree of fading of NYCS during wet heat treatment was higher than that during dry heat treatment.At room temperature,the color change of NYCS treated in acid was not obvious,while the alkali treatment deepened the color significantly.Both the oxidant and reductant dipping could make the NYCS darker and yellower.NYCS was apt to fade during home laundering and sunlight exposure,under which the color stability was poorer,the sunlight fastness was only one level.Under the conditions of heat,acid and alkali,oxidant and reductant treatment in this experiment,the color changes of NYCS could not be differentiated by the naked eye obviously.The effect of repeated home laundering and short-time sunlight exposure treatment on the color of NYCS was obvious and could be easily distinguished by naked eye.The color of NYCS had poor resistance to home laundering,especially to sunlight exposure.In order to improve the color stability of NCS,THPS reagent was used to fixate the sericin as the pigments existed in the sericin.Sericin degumming loss percentage was used to express the fixation effect to explore the color fixation conditions.The results showed that the factors of pH,THPS concentration,fixation time and temperature had great influences on fixing performance,the optimum conditions were as follows,pH of sulutions was 7.0,THPS concentration was 0.3%,reaction time and temperature were 6 h and 40 ?,respectively.Fourier transform infrared(FT-IR)spectrogram revealed that fixation by THPS resulted in the change of sericin from random coil structure to crystalline structure.Color fixation treatment had little effect on the color stability of NCYS after heat or acid/ alkali treatment.However,the color stability of color fixation silk was improved after treated in oxidant or reductant,leading to less yellowing of the fiber.Also,the fading degree of color fixation silk was less than NCYS after repeated home laundering and sunlight exposure,indicating that color fixation could improve color stability to home laundering and sunlight exposure.The structures and properties of NCYS and color fixation silk were studied by scanning electron microscopy(SEM),thermogravimetric analysis(TG),differential scanning calorimetry(DSC)and tensile testing machine.The results showed that the smoothness of color fixation silk decreased,as the surface of that was occurred etching.And color fixation treatment could improve the thermal stability of NCYS,as well as the breaking strength,indicating that color fixation could increase the interaction between silk protein molecular chains.Also found that the antioxidant capacity of color fixation silk decreased,while the UV-shielding performance improved.