Identification of cashmere and fine wool

The identification of cashmere and fine wool is a difficult point in the detection work. Because cashmere and fine sheep wool are relatively close in appearance and morphology, it is not easy to distinguish the two fibers using ordinary optical microscopes, so scanning electron microscopes are generally used in combination for identification. The instrument operation for SEM identification is divided into two steps: sample spray plating and on-machine inspection. The first step: sample spray plating. First cut the representative yarn sample into short segments of 0.5-1mm, then stick the sample evenly on the conductive adhesive, place the conductive adhesive on the sample stage, cover the sample chamber, turn on the power switch of the ion sputtering instrument, and confirm the voltage mode and set the spraying time (generally set to 1.5-2min, the longer the time, the greater the thickness of the film. Generally, when observing at low magnification, the plated film is thicker; when observing at high magnification, the plated film is thinner), Turn the vacuum adjustment knob to adjust the pressure to 7Pa. After confirming that the instrument is ready (ready light is on), turn on the discharge switch to start spraying, and the time indicator starts to count down. After the end, remove the sample and prepare for on-board testing. The second step; on-board detection. Turn on the main power switch of the scanning electron microscope and the power switch of the circulating water machine, fix the prepared sample on the sample holder, and adjust each handle of the sample stage to the standard position. Turn on“AIR”Switch on and off the pre-pumping chamber and load the sample after the aerated gas. Push the pre-extraction door tightly, press“EVAC"vacuum, then turn on the“DISPLAY POWER”Power, enter the corresponding software operating system. Finally, add high voltage (HV) to the system, select the scanning speed, and adjust the magnification, focal length, pixels and other parameters until the image is clear. Use scanning electron microscope to identify difficult cashmere and wool, mainly observe and make judgments from the thickness, density, aspect ratio, scale shape, etc. of fiber scales (Figure 1) Scale density refers to the number of scales per unit length , the density of cashmere scales is about 60 pieces/mm, and the density of sheep wool scales is about 90 pieces/mm. The aspect ratio refers to the ratio of the diameter of the fiber to the scale spacing (or height). The scale spacing and diameter of cashmere are close, and the thicker the fiber, the greater the ratio of the diameter to height; the thickness of the cashmere scales is 0.35μAbout m, the thickness of the scales of sheep wool is about 0.8μThe thickness of m cashmere scales increases with the increase of fiber diameter, but it is not obvious. The shape of the scales of cashmere mainly presents the characteristic of ring-like uniform covering of the hair shaft, but the difficult fibers observed by scanning electron microscope generally do not show the typical characteristics of ring-like covering. The edge of the scale of this fiber is serrated, similar to the scale characteristics of coarse wool, but the scales are thinner, and the other is irregular scales, no ring features, thick scales, high density, obvious bright lines on the surface of the scales, scale shape Also close to wool fibers. When encountering the above-mentioned fibers suspected of wool, a variety of characteristics must be combined to judge. The morphological characteristics of cashmere and wool scales are shown in Table 1.

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