Extraction Of Natural Vegetable Dyes

In recent years, as people healthy and green environmental protection requirements continue to increase, people welcome natural dyes more and more. According to the British Association of Dyes and dyeing, they give the definition of "natural dyes" that from plant, animal, or mineral resources obtained, with little or no dye through chemical processing. Vegetable dyes are the most important class of natural dyes, with its wide source, less pollution, no poison, insect sterilization and other excellent features help save unique. General plant leaves, bark, flowers and roots contain a certain amount of pigment. Currently, the extraction of natural dyes in the dye, there are many areas worthy of further study, they are broken up filtration, conventional flooding method, organic solvent extraction, ultrasonic extraction, microwave extraction, enzymatic and supercritical CO2and other methods, these methods are associated with the development of related technologies applied to the dye extracted, the application has not yet form a more perfect system, especially the newer method is rarely used in actual production into large-scale. In this paper, optimization of extraction of natural dyes more starting to gall extract and other natural dyes, for example, to explore the various factors on the conventional immersion, ultrasonic extraction, microwave extraction and supercritical CO2extraction method effects, and optimize design the best extraction process, discuss the advantages and disadvantages of each method, in order to obtain a practical, efficient and economic extraction process.Extraction of the dye in the gall, the immersion’s time is the highest(120min), temperature requirement is also the maximum one(90℃).Corresponding to the solid-liquid, it’s ratio requirements are relatively large, the acidity (refers to the changes in relative value before adjustment) requirements relatively low, but the extraction efficiency is low. Relative to the immersion, ultrasonic’s time (60min) significantly decreased, the temperature (50℃) is also much lower, solid-liquid ratio and acidity are basically the same, extraction is efficiency, microwave uses the least time, slightly larger changes in acidity, decreases in solid-liquid ratio, extraction is efficiency. By supercritical CO2, time (105min) longer, low temperature and medium pressure requirements, high extraction efficiency, in the dyeing of gall extracting dye, the light fastness resistance of the fabric dyeing by immersion extraction is better, but it’s rubbing fastness and washing fastness is general. The fabric dyeing by ultrasonic extraction has superior rubbing fastness, better light fastness and wash fastness. The fabric dyeing by microwave extraction has better rubbing fastness. The fabric dyeing by supercritical CO2extraction has better light fastness, but it’s abrasion fastness is poor.In the extraction of vegetable dyes, the immersion’s equipment requirements is low, but consums time and energy; although the ultrasonic’s equipment are special, but due to time and temperature requirements are lower, it significantly can save time and resources; time efficiency of microwave is high, relatively speaking, you can save water, but when dealing with security issues need more attention; supercritical CO2is the most green one, has environmental protection, and extraction efficiency, but needs the high cost of their equipment, demanding conditions.