| With the rapid development of society,people’s demand of living rises ceaselessly and the resources that we can use are on the decrease,looking for new rich resources become a hot social concern.Natural biopolymer as a kind of biodegradable abundant resource has been the focus of research fields.Wool,consisting of approximately 95 wt% pure keratin containing more than 20 amino acids,is a natural polymer,and extensively used in the textile and pharmaceutical industry because of its excellent properties,such as biocompatible,biodegradable and bioactive.Wool keratin is difficult to dissolve in conventional solvents,due to the tight packing of the secondary structures in the polypeptide,as well as the inter-and intra-molecular strong hydrogen bonds and disulfide bonds.Ionic liquids(ILs),as a new class of devisable green solvents,can dissolve a large number of biopolymers,for instance,feathers,cellulose,lignin with high efficiency,due to their unique properties like high thermal stability,tunable properties,and good dissolving ability.Promising results of keratin dissolution in ILs have been obtained.However,the mechanism that how the structure of anions and cations of ILs can influence the dissolution performance of ILs is still a challenge,and the study of ionic liquid/keratin solution spinning are still less.In this study,a series of 1,5-diazabicyclo [4.3.o]-non-5-ene(DBN)-based and imidazole-based ionic liquids were designed and employed for the dissolution of wool keratin.The effects of ILs anion and cation structures on the dissolution capability for keratin were systematically studied,and the optimal IL with high dissolution capability for goat wool was finally obtained by overall taking the time for complete dissolution and properties of the regenerated keratins into account.In addition,the strength of the keratin fibers was enhanced by glutaraldehyde crosslinking with keratin molecules.Specific content is as follows:(1)The influence of ILs anion and cation structures on the dissolution time of keratin.A series of 1,5-diazabicyclo [4.3.o]-non-5-ene(DBN)-based and imidazole-based ionic liquids have been designed and synthesized.All of the ILs were employed for the dissolution of wool keratin under the conditions of 130 ℃ and the weight fraction of keratin in the experiments is 8 wt%.The effects of the anion and cation structures on the dissolution capability for keratin were systematically studied.It is found that the dissolution capability of anions follow the decreasing order of [OAc]-> [DEP]-> [DMP]-,and the cations follow the order of [Emim]+ > [DBN]+.In a word,structures of the ILs play an important role in the dissolution process of goat wool,by modulating polarity and hydrogen bond basicity of ILs.The stronger the polarity and hydrogen bond basicity,the greater dissolution capability could be obtained.That result would play an important role in the design and synthesis of new functional ILs for wool dissolution.(2)The influence of ILs anion and cation structures on the structures and properties of regenerated keratin.Keratin was regenerated from the ionic liquid/keratin liquid by using ethanol as a regenerant.The yields of the keratin regenerated from different IL / keratin solutions were also studied.The results show that the shorter the completely dissolution time,the lower the yield.The yields of keratin regenerated from the [DBNE]DEP solution is 0.4471 g/g,which was higher than that from other IL solutions.The structure and properties of regenerated keratin were also analyzed.We found that the shorter the time needed for wool keratin completely dissolved,the lower the regenerated keratin crystallinity and α-helix content in the secondary structure,and the more serious damage disulfide bond were suffered.Thermal stability of regenerated keratin is similar.In particular,dissolution time of [DBNE]DEP was 3 h,and the disulfide bonds break ratio and contents of α-helix were 53.46%,57.88%,respectively,which means that [DBNE]DEP is the best IL to dissolve wool keratin by overall taking the time for complete dissolution and properties of the regenerated keratins into account.(3)The rheological property of IL/keratin solutions.The rheological property of IL/keratin solutions using DEP based ILs were studied.Values of non-Newtonian index(n),which increases first and then slightly decreases,are all about 0.8,indicating excellent potential for spinning.Moreover,the best spinning temperature range of the [Emim]DEP IL/keratin solution at 8 wt% is 343-353 K,while that of the [DBNE]DEP IL/keratin solution at 8 wt% is 323-333 K,indicating less energy consumption.In addition,the [DBNE]DEP IL showed excellent performance for recycling.(4)Glutaraldehyde as crosslinking agent to enhance keratin fiber strength.The strength of pure keratin fibers can be enhanced through crosslinking reaction between crosslinking agent and keratin molecular.With glutaraldehyde as crosslinking agent,the influence of glutaraldehyde concentration and crosslinking reaction temperature on the ionic liquid/keratin liquid spinning and the structure and properties of keratin silk were examined.The results indicated that the concentration of glutaraldehyde crosslinking reaction has important influence on the crosslinking reaction.When the concentration of glutaraldehyde between 0.45% and 0.8 %,the IL / keratin solution has a good spinning performance and the keratin fibers have higher content of secondary structure.Crosslinking reaction temperature is also an important parameter.Under the condition of 333 K and 0.5 % glutaraldehyde concentration,ionic liquid / keratin solution has good spinning performance and high content of α-helix structure in secondary structure,the cysteine of keratin molecules were suffering lighter destroy. |
