Effects of textile refining enzymes on the process conditions and performance of silk degumming
Silk,as a natural protein fiber,has a soft touch and bright color.The main body of silk fibers is fibroin,with a proportion of from 70% to 80%,and the outer layer is wrapped with sericin with a proportion of from 20% to 30%,which plays a protective role for the fibroin.Nevertheless,an excessive presence of sericin will affect the luster and softness of the silk,which is detrimental to the processing and production of silk products.Therefore,it is essential to perform degumming treatment on the silkworm cocoons.Traditional methods for degumming silk primarily include alkaline degumming,soap degumming,and acid degumming.However,these degumming methods commonly result in issues such as a rough texture,poor mechanical properties,susceptibility to yellowing,and the presence of residual chemical substances with irritating odors in the silk after degumming.In recent years,a new type of silkworm cocoon degumming method—enzyme degumming,has been widely applied in the field of silk degumming due to its advantages such as environmental friendliness,non-toxicity,mild reaction conditions,high catalytic efficiency,easy degradation,and strong specificity.The use of enzyme preparations for the degumming of silkworm cocoons primarily relies on the biological characteristics of enzymes.Silk proteins undergo hydrolysis by proteolytic enzymes,causing the cleavage of peptide bonds and the formation of bioactive peptides.Therefore,biological enzyme preparations(proteases)have been increasingly used to replace other chemical refining agents in the refining and processing of silk.This represents a promising and prospective research area.In this paper,alkaline protease(NP-TEE)and textile refining enzyme(AP-TRE)were used to degum silkworm cocoons.The degumming rate,single-fiber tensile breaking strength,and whiteness were used as the indexes to examine silk properties.An orthogonal test was conducted to determine the optimal process for the enzymatic degumming of cocoons.The experimental results show that the two enzyme degumming processes have an effect on the degumming effect of cocoons,and the performance of silk after degumming with textile refining enzyme is better compared with that of alkaline protease degumming.The optimal degumming process conditions of cocoons by textile refining enzyme are as follows:a degumming temperature of 55℃,a degumming time of 60 min,and an enzyme concentration of 5 mL/L.The degumming rate of cocoons is 17.07%,with an average breaking strength of single silk fiber of 12.20 cN/dtex,and whiteness of cocoons of 66.04% which is higher than the original cocoons of 58.78%.The infrared spectra show that there is no significant difference in the structure between cocoons treated with the textile refining enzyme method and the original silkworm cocoons.Under scanning electron microscopy,it is observed that the surface of silk fibers treated with textile refining enzyme appears smoother and more even compared to the original silk fibers.TGA analysis shows that there is no significant change in the thermal stability of silk fibers after degumming with textile refining enzymes.This approach provides a new choice for cocoon degumming process,and it will contribute to subsequent industrial production.
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