Suede is woven from island-type ultra-fine polyester silk, and then undergoes desizing, scouring, relaxing, pre-shaped fiber opening, sanding and dyeing to obtain a suede fabric. It has a soft hand, good drape and style. Elegant; smooth and shiny to the touch Soft, strong suede feel, good “writing effect”; good breathability and moisture permeability, good wearing comfort; although the absolute strength of the monofilament is low, its relative strength is high, and the total strength of the filament can meet the use requirements , good wear resistance. In addition, it also has the characteristics of dimensional stability and washability that are common to chemical fiber fabrics. Therefore, suede products are deeply favored by consumers.
The key to obtaining a good style of suede fabric is the dyeing and finishing of the fabric, in which pre-treatment is particularly important. The main purposes of the pre-treatment process are: 1) to wash away the oil on the gray fabric to prevent color flowers from being produced during dyeing and affecting the finishing; 2) to fully open the island-type polyester microfiber and reduce its weight, so as to facilitate subsequent sanding. , and make the fabric have good drape and feel; 3) make the fabric fully shrink, so that the pile is dense, has an excellent “writing effect”, and fully reflects the product style. This article discusses the pre-treatment process of suede fabric in order to provide a reference for developing new suede products and formulating a reasonable dyeing and finishing process.
1.1 Effect of temperature and NaOH concentration on weight loss rate
Under the same holding temperature, as the mass concentration of NaOH increases, the weight loss rate increases. This is mainly because the greater the NaOH mass concentration, the higher the contact probability between fiber and caustic soda, which increases the probability of OH- attacking the ester bond, so the weight loss rate increases. At the same time, under the same NaOH mass concentration, the weight loss rate increases with the increase of the holding temperature. The main reasons are: First, the alkali hydrolysis of polyester is a double diffusion reaction process, that is, the reactants in the solution diffuse to the fiber surface, amorphous area, and the edge of the crystalline area, and the hydrolysis products diffuse from the inside of the fiber into the solution. As the temperature rises, double diffusion occurs. As the coefficient increases, the double diffusion rate increases and the reduction rate increases. Secondly, according to the free volume theory, as the temperature increases, the free volume fraction of polyester increases, that is, the activity space of the chain segments increases, the number of active units of the fiber molecular chain increases, the density of the fiber decreases, and the carbonyl group contacts OH- As the frequency of the reaction increases, the weight loss rate also increases, so the increase in temperature is conducive to the occurrence of the fiber alkali hydrolysis reaction.
1.2 Effect of temperature and NaOH concentration on fabric shrinkage
As the NaOH mass concentration increases, the warp and weft shrinkage of the fabric increases, but as the concentration further increases, the degree of increase in shrinkage becomes smaller; As the temperature increases, the warp and weft shrinkage of the fabric also increases, but as the temperature further increases, the degree of increase in shrinkage decreases. The main reason for this change in the warp shrinkage of the fabric may be that as the mass concentration of NaOH increases and the temperature rises, the weight loss rate of the fabric increases, the space for high shrinkage yarns to move increases, and the shrinkage rate decreases. However, as the concentration and temperature further increase, its shrinkage basically reaches a maximum value, so the degree of increase in shrinkage decreases. Another reason for the increase in fabric shrinkage is that the high shrinkage yarn has low crystallinity and high temperature.The higher the degree, the smaller the binding force on the movement of macromolecular segments, making it easier for highly oriented macromolecules in the amorphous region to deorient, resulting in greater macroscopic shrinkage of the fiber.
1.3 Reasons for the difference in warp and weft shrinkage of fabrics
The warp shrinkage is much greater than the weft shrinkage, about 2.1 times the weft shrinkage. This is determined by the island-type multifilament used.
After the multifilament is opened, there are still thick fibers. These thick fibers are the high shrinkage yarns in the multifilament. High shrinkage polyester fiber has the characteristics of low crystallinity and high orientation supramolecular structure. At a certain temperature, due to its low crystallinity and small binding force on the movement of macromolecular segments, the highly oriented macromolecules in the amorphous region are deoriented, resulting in high macroscopic fiber shrinkage. Island silk is generally used in combination with this high-shrinkage yarn through a network to make the fabric fully shrink during dyeing and finishing, thus reflecting the style of the product.
1.4 Effect of treatment time on weight loss rate
When suede fabric is treated with alkali weight reduction, when the concentration and temperature are determined, time is the decisive factor in controlling the weight loss rate. As the reduction treatment time increases, the reduction rate increases, but when the time increases to a certain value (20 min), the reduction rate increases gradually. This is because as the treatment time increases, the reaction between NaOH and polyester becomes more complete, and the utilization rate of NaOH also increases accordingly, so the weight reduction rate increases; at the same time, because the OH- concentration in the system decreases as the reaction proceeds, the hydrolysis reaction The speed slows down and the reaction reaches equilibrium after a certain period of time.
1.5 The impact of weight loss rate on fabric properties
For ordinary polyester fabrics, as the weight loss rate increases, the bending stiffness, breaking strength and thickness in the warp and weft directions should gradually decrease, and the air permeability should gradually increase. . The reason why the performance of suede fabric changes with the weight loss rate is different from that of ordinary polyester fabric is mainly caused by the fact that the warp yarn of suede fabric is a mixed fiber of sea island yarn and high shrinkage yarn. The weight reduction reduces the bending stiffness, breaking strength and thickness, and increases the air permeability, while the shrinkage of the mixed fiber in the warp direction causes these properties to change in the opposite direction. The abnormal change points are the result of the dominance of performance changes caused by the shrinkage of the mixed fiber yarn. For small pattern suede fabrics, when the weight reduction rate is in the range of 18.9% to 21.76%, the performance of the fabric is better.
2 Conclusion
1) Under the same holding temperature, as the mass concentration of NaOH increases, the weight loss rate increases; under the same NaOH mass concentration, the weight loss rate increases as the holding temperature increases. big.
2) As the NaOH mass concentration increases, the warp shrinkage of the suede fabric increases, but as the concentration further increases, the increase in shrinkage becomes smaller; as the temperature increases, the suede fabric The warp shrinkage of the fabric also increases, but as the temperature further increases, the increase in shrinkage decreases.
3) The warp shrinkage of suede fabric is much larger than the weft shrinkage, which is about 2.1 times of the weft shrinkage.
4) As the processing time increases, the reduction rate increases, but the time increases to a certainvalue (about 20 min), the reduction rate gradually increases with the extension of treatment time.
5) The optimal weight reduction rate to obtain a more ideal suede fabric style effect is 18.9% ~ 21.76%.
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