During the processing of textiles from fiber to dyeing, they are subject to mechanical, chemical and thermal function, resulting in fiber damage. Every quality defect caused by damage will have a great impact on the quality of the product. These quality defects are often not easy to find during the production process, and are reflected in the final dyeing process, at which time the quality defects can no longer be compensated. Using microscopic technology to observe fiber damage, combined with practical production experience, we can make accurate judgments on the causes of quality defects, which can clarify many difficult product quality issues, trace the production process of quality defects, and control product quality defects.
Foreword
Easy to use and Effective methods to detect the quality of textiles and infer the main causes of quality defects through analysis of test results have always been an important means for manufacturing companies to control product quality, commercial companies to clarify responsibilities for quality disputes, and scientific research institutions to overcome quality difficulties.
During the production and use of textiles, if not handled properly, chemical, mechanical, thermal or microbial damage may occur, and each damage will have a great impact on the quality of the product.
For example, due to acidic or alkaline damage to wool, uneven dyeing of tops occurs;
Due to mechanical damage, light marks appear after dyeing and stains;
The fibers are squeezed to cause dark spots on the fabric;
The fibers are scratched and cracked. Stripes appear on dyed black fabrics;
Silk fabrics partially turn gray or form light-colored markings due to fiber cracking;
Nylon fabrics Due to the antistatic finishing, the fibers melt to form hard lumps and so on. Under normal circumstances, such damage is not easy to find during the production process, but is reflected in the final dyeing process. At this time, the quality defects can no longer be compensated, causing irreparable losses to the production company, and can easily cause commercial quality disputes.
In the process from fiber raw materials to yarn, gray cloth and dyeing, the fibers are subjected to repeated effects of mechanical external forces, heat and chemical reagents. The fiber damage caused in this process can be It is classified into three categories: mechanical damage, thermal damage and chemical damage.
Microscopic analysis of dyeing defects caused by mechanical damage
Figure 1 Mechanical damage of wool fibers in nylon and wool (bottom) blended fabrics Mechanical damage of textiles during the entire processing process It is often caused by wear and tear, and often only shows up in the finishing stage of the fabric, resulting in dyeing defects such as gray marks and light marks that cannot be compensated. Natural fibers and regenerated cellulose fibers are more susceptible to mechanical wear than synthetic fibers. The reason is that the wear resistance of synthetic fibers is generally better than that of natural fibers and regenerated cellulose fibers. As shown in Figure 1, in fabrics made of nylon and wool blends , took out the wool and nylon, observed it under a microscope at 100 times magnification, and found that many wools were cracked, while the nylon was intact.
1. Mechanical damage to wool fibers
The mechanical damage to wool fibers comes from shearing, Processing processes such as scouring and carding, as well as insect infestation, cause the fibers to crack and expose spindle-shaped cells or hair bundles [1], as shown in Figures 2 and 3.
Figure 2 Cracks formed by shearing to expose spindle-shaped cells Figure 3 Cracks formed by washing and spinning During the scouring process of raw wool, due to defects in the conveying equipment between the washing tanks, the wool fibers may be felted or torn, resulting in mechanical damage. This kind of damage is not easy to detect on the finished fabric, but is more obvious due to mechanical damage during wool spinning or brush-like cracking in recycled wool.
Wool fibers are easily eaten away by fabric moths, fur beetles and carpet beetles. Crescent-shaped gaps appear on the edges of the fibers, and in most cases, one end of the fiber will be bitten off. [2], as shown in Figure 4 and Figure 5.
Figure 3 Wool is bitten by insects into a crescent shape Figure 4 The head end of wool is bitten by insects The cracks of wool fibers are prone to light marks and stains after being dyed into dark colors. Figures 6 and 7 respectively show the appearance of bright streaks and stains after dyeing fabrics with cracked wool fibers.
Figure 6 Wool cracking causes bright lines in the warp direction of polyester/wool fabric Figure 7 Wool cracking Cause stains to appear on dyed wool fabrics
2. Fiber abrasion of silk fabrics
Natural mulberry silk and tussah silk are very sensitive to mechanical effects such as extrusion and friction in the entire production process from degumming to dyeing and finishing, especially in the wet state of dyeing and degumming, which are more susceptible to wear and tear. .
The fiber wear of silk fabrics causes local graying (also known as whitening) or the formation of light-colored spots. The reason is that after the fibers are scratched or cracked, the fabric becomes indented.Concentrated hydrochloric acid, and then slowly drop into the sodium nitrite solution (1 g sodium nitrite added to 2 mL of distilled water) and allow it to slowly diazotize (10 to 15 min) to obtain diazo p-aminobenzene sulfonic acid. Filter nitrogen-para-aminobenzene sulfonic acid with a glass filter, add 50 mL of 10% sodium carbonate solution, and when it is completely dissolved, add 50 mL of water and ice cubes. Since the diazo compound solution is unstable, the solution temperature cannot exceed 5°C, and the solution must be used immediately after preparation. The distilled water, sodium nitrite solution and sodium carbonate solution used to prepare the diazo compound should be refrigerated.
Figure 21 Pauly reaction characteristics of silk fabrics Operation points of wool and Pauly reagent reaction: wool sample It must be kept moist. The sample is immersed in distilled water before the reaction. After centrifugal dehydration or extrusion dehydration, the sample is placed in a refrigerated diazo compound for 10 minutes, rinsed with refrigerated distilled water, and then dehydrated by centrifugation or extrusion. After dehydration, dry it in the air or in a drying oven at 60°C.
Key points for the reaction between silk and Pauly reagent: basically the same as those for wool fiber, but the reaction time should not be longer than 1 to 2 minutes. This is because silk is different from wool. It has no scale layer and only a thin silk protein layer. If the reaction time is longer, especially if the temperature is too high, the reagent will penetrate the surface layer and enter the inner layer of the fiber.
If you are not experienced enough, in order to ensure that the results are correct, you can use known intact fiber and damaged fiber samples to conduct parallel tests. To prepare damaged wool, the wool can be boiled in a carbonic acid solution of 1 to 2 g/L; to prepare damaged degummed silk, raw silk can be degummed in a soap solution with a pH value greater than 10.
Editor’s Note
Dynamic and accumulated damage and structural unevenness during the processing of textiles , hidden quality defects caused by microscopy technology and microscopy + chemical color development technology can be used to transform hidden quality defects into explicit structural features. The yarns and fibers are taken out from actual defects to analyze their structure and production process, and the relationship between defects and structural characteristics is established, so that hidden quality defects can be controlled before irreparable defects are formed in the fabric. It should be noted that in actual production, quality defects are caused by many reasons. While using microscopy technology, analysts also need to have a thorough understanding of the raw material properties, structure and production process and rich testing experience. There are even times when inspiration needs to be analyzed.
Using microscopic technology to observe defects in fiber structure, combined with practical production experience, to make accurate judgments on the causes of quality defects can clarify many difficult product quality issues. The use of microscopy technology to identify the causes of quality defects has four significances: first, the operation method is accurate and convenient, the cost of instruments and equipment is low, and the generalizability is strong; second, the analysis of the causes of hidden defects is irreplaceable; third, It makes it possible to trace multi-process textile production quality defects and resolve commercial quality corrections; fourth, it can excavate and extract typical quality defect cases in enterprise production, and provide engineering and technical personnel and quality control professionals in textile production and trade with Technical Support.
References:
[1] Written by Karl Mahall, translated by Zhang Jiahong. Textile quality defects and Cause Analysis – Microscopic Technique [M]. Beijing: China Textile Press, 2008: 26./2008: 27./2008: 31. /2008: 34./ 2008: 37.< /p
