Study On Identification Methods Of Naturally Colored Cotton And Dyed Cotton

Naturally colored cotton that gets its color at the opening of boll is cultivated form the original wild colored cotton by using modern biotechnology. The only two types of naturally colored cotton used in textiles industry currently are brown cotton and green cotton. Naturally colored cotton needs not to be processed because of its natural born color that can eliminate the environmental pollution caused by using dye, and leave no chemical toxins in its products. Due to its unique "ecology", "green" and "environmental" quality, the naturally colored cotton is one of the most development potential products in international textile market in the 21st century. The world’s major cotton producing countries are committed to the naturally colored cotton research while it is relatively late in China. There haven’t been effective methods to identify naturally colored cotton or dyed cotton. In order to sell at a high price, some companies dyed ordinary white cotton close to the color of naturally colored cotton deliberately to deceived consumers. Considering the development of naturally colored cotton in the future, the structure and properties of the naturally colored cotton should be analyzed and the special reactions of the naturally colored cotton pigment need to be evaluated to propose effective identification methods.The differences between naturally colored cotton and dyed cotton products in chemical composition, morphology, qualities of fibers and the special reactions of the naturally colored cotton pigment were studied. Chemical analysis and elemental analysis testing methods were used to research the chemical components of cotton fibers. Fourier Transform Infrared Raman （FTIR-Raman） spectroscopy, X-ray Diffraction, Cross Polarization Magic Angle Spinning Nuclear Magnetic Resonance （CP/MAS-NMR）, Gas Chromatography Mass Spectrometry （GC-MS） were used to observe the structure of cotton fibers. Fineness, strength, Young’s modulus of cotton fibers were measured to characterize the qualities of fibers. The naturally colored cotton pigment was effectively extracted in order to research the special reactions of the pigment.The results of these tests showed that the significant difference in content of N elements in Elemental analysis could be a qualitative indicator in judging whether cotton products contain naturally colored cotton. The peak at 2850cm^-1 of IR spectroscopy, the chemical shifts at 33ppm of CP/MAS-NMR and the retention time at 27.7min～29.4min of GC-MS were distinctions between naturally green cotton and ordinary white cotton .The reversible color change of pigment extraction in different pH environment could identify the naturally colored cotton or dyed cotton fibers. The pigment of naturally colored cotton is one kind of flavones, so we could identify the naturally colored cotton by special reactions of flavone.