Preparation of tea stem catechins and their staining and functional modification of silk fabrics
As a major tea-producing country,China produces a huge amount of tea stems every year.In order to improve the current situation of tea stems being abandoned,increase the utilization of tea stems,and solve the waste of resources caused by discarded tea stems,the paper investigated the dyeing and function of tea stem pigments.In this paper,catechins were extracted from Tieguanyin tea stems,and LC-MS,UV-visible spectrophotometer,Fourier transform infrared and other instruments were used to identify and analyze the structure of the tea stem extract.Then,the extract was used to dye silk.The dyeing pH value,dyeing temperature and dyeing time were used as variables,and the Integ value of silk was used as an indicator to explore the optimal dyeing process.Finally,by using the best process for direct dyeing and Al3+as a pre-mordant dyeing method,the Tieguanyin tea stem extract,Tieguanyin extract and Alpine green tea extract were used as dyes to compare the differences in color fastness and functional finishing for dyeing silk between the tea stem extract and tea leaf extracts.The results indicate that LC-MS characterization shows that the Tieguanyin tea stem extract has the same retention time and fragment ion peak as the catechin standard monomer.At the same time,the UV absorption spectrum shows that the extract has strong absorption at 280 nm and has structure of flavanols.The Fourier transform infrared spectrum also shows that the extract contains the same function group as catechins.Therefore,the main component of the Tieguanyin tea stem extract has been determined to be catechins.Under the condition that the catechins dye dosage is 10%(o.w.f)and the liquor ratio is 1∶50,the dyeing time is 70 minutes,the dyeing temperature is 80℃,and the dyeing pH value is 7.5,the Integ value of the silk can reach over 21.The color fastness of silk dyed with Tieguanyin tea stem catechins are the same as those dyed with Tieguanyin catechins and Alpine green tea catechins,which can meet the basic requirements of clothing.The UPF values of the silk directly dyed with the three dyes extracted from different sources are 168.84,150.58,and 150.20 respectively.The UPF values of the silk after mordant dyeing are all more than 230.The Tieguanyin tea stem catechins are slightly higher than the other two catechins extracted from tea.After direct dyeing,the antioxidant properties of the three catechins are 67%,64%,and 77%respectively.The Alpine green tea catechins are higher than the Tieguanyin tea stem catechins and Tieguanyin catechins,and they are still demonstrated to have the highest antioxidant property after mordant dyeing.In conclusion,although the Tieguanyin tea stem catechin don't have the best antioxidant properties,they have satisfactory dyeing effect and functional results as a natural pigment obtained from tea wastes,so they have good application value.
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