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Pretreatment process for small pattern suede fabric
- Jul 19, 2018 -

The suede is made of sea-island type ultra-fine polyester yarn, which is then desizing, scouring, slackening, pre-formed fiber-opening, sanding and dyeing to obtain a suede fabric with soft handfeel and good drape. Elegant; smooth handfeel, soft luster, strong suede, good "writing effect"; good ventilation, moisture permeability, good wearing comfort; low absolute strength of monofilament, but relatively strong, silk The total strength can meet the requirements of use and wear resistance is good. In addition, it has the characteristics of dimensional stability and washability that are common to chemical fiber fabrics. Therefore, suede products are favored by consumers. The key to good style of suede fabrics is the dyeing and finishing of fabrics, of which pretreatment is particularly important.


    The purpose of the pretreatment process is mainly: 1) washing off the oil agent of the grey cloth to prevent coloring and affecting finishing after dyeing; 2) making the island-type polyester microfiber fiber fully opened and reduced, which is convenient for the subsequent grinding And make the fabric have good drapability and feel; 3) make the fabric fully shrink, so that the fluff is dense, with excellent "writing effect", fully reflecting the product style.


    1.1 Effect of temperature and NaOH concentration on the reduction rate At the same holding temperature, as the NaOH mass concentration increases, the reduction rate increases. This is mainly because the higher the concentration of NaOH, the higher the probability of contact between the fiber and the caustic soda, and the increased probability of OH-attacking the ester bond, so the reduction rate increases. At the same time, at the same NaOH mass concentration, the reduction rate increases with the increase of the holding temperature. The main reason: First, the alkali hydrolysis of polyester is a double-diffusion reaction process, that is, the reactants in the solution diffuse toward the fiber surface, the amorphous region, and the edge of the crystallization zone, and the hydrolyzed product diffuses from the fiber to the solution, the temperature rises, and the double diffusion The coefficient increases, the double diffusion rate increases, and the reduction rate increases. Secondly, the free volume theory shows that the temperature increases, the free volume fraction of the polyester increases, that is, the active space of the segment increases, and the number of active units of the fiber molecular chain increases. When the fiber density decreases, the frequency of the carbonyl-OH-contact reaction increases, and the reduction rate also increases, so the increase in temperature is favorable for the occurrence of the fiber alkali hydrolysis reaction.


    1.2 Influence of temperature and NaOH concentration on fabric shrinkage With the increase of NaOH mass concentration, the warp and weft shrinkage of fabric increases, but with the further increase of concentration, the degree of shrinkage increases; as the temperature increases, the fabric The latitude and longitude shrinkage rate also increases, but as the temperature increases further, the degree of increase in shrinkage decreases. The main reason for the change of the warp shrinkage rate of the fabric may be that as the mass concentration of NaOH increases, the temperature increases, the fabric reduction rate increases, and the space for high shrinkage filaments increases, and the final shrinkage rate increases. The larger, but as the concentration and temperature further increase, the shrinkage rate reaches a maximum, so the degree of increase in shrinkage decreases. Another reason for the increase in fabric shrinkage is that the high shrinkage yarn has a low crystallinity, and the higher the temperature, the smaller the binding force to the movement of the macromolecular segment, so that the highly oriented macromolecule in the amorphous region is more easily dissociated, thereby producing The greater the macroscopic contraction of the fiber.


    1.3 Reasons for the difference between the warp and weft shrinkage of the fabric The warp shrinkage rate is much larger than the latitudinal shrinkage rate, which is about 2.1 times of the latitudinal shrinkage rate. This is determined by the island-type multifilament used. After the multifilament is opened, there are also coarse fibers, which are high shrinkage filaments in the multifilament. The high shrinkage polyester fiber has the characteristics of low crystal structure and high orientation of supramolecular structure. At a certain temperature, due to its low crystallinity, the binding force to the movement of macromolecular segments is small, so that the highly oriented macromolecules in the amorphous region are de-oriented, thereby producing macroscopic high fiber shrinkage. The island silk is generally used in combination with such a high-shrinkage thread to make the fabric shrink sufficiently during the dyeing and finishing process, thereby reflecting the style of the product.


    1.4 The effect of treatment time on the reduction rate When the suede fabric is treated with alkali reduction, when the concentration and temperature are determined, the time is the decisive factor for controlling the reduction rate. As the reduction processing time is extended, 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 is more sufficient, and the utilization rate of NaOH is correspondingly increased, so the reduction rate is increased. At the same time, the hydrolysis reaction is caused by the decrease of the OH-concentration in the system as the reaction progresses. The speed slows down and the reaction tends to balance after a certain period of time.


    1.5 Effect of reduction rate on fabric properties For ordinary polyester fabrics, as the reduction rate increases, the warp and weft bending stiffness, breaking strength and thickness should be gradually reduced, and the gas permeability is gradually increased. The reason why the performance of the suede fabric changes with the reduction rate is different from that of the ordinary polyester fabric mainly because the warp yarn of the suede fabric is caused by the mixed yarn of the island silk and the high shrinkage yarn. The reduction reduces the bending stiffness, breaking strength and thickness, and the gas permeability increases, while the shrinkage of the warp yarns causes these properties to change in opposite directions. The abnormal point of variation is the result of a change in performance due to the shrinkage of the mixed filament. For small-pattern suede fabrics, the fabric performance is better when the reduction ratio is in the range of 18.9% to 21.76%.


    2 Conclusion


    1) At the same holding temperature, with the increase of NaOH mass concentration, the reduction rate increases; at the same NaOH mass concentration, the reduction rate increases with the increase of the holding temperature.


    2) With the increase of NaOH mass concentration, the warp shrinkage rate of the suede fabric increases, but with the further increase of the concentration, the degree of increase of the shrinkage rate becomes smaller; as the temperature increases, the warp of the suede fabric The rate of shrinkage also increases, but as the temperature rises further



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