Introduction To Invented Mercerizing Cotton And Mercerizing Technology

1、 Preface:

Mercer first invented mercerized cotton, which is used to treat cotton fabrics with strong caustic soda under no tension, with the main purpose of increasing the strength of cotton fibers and affinity for dyes. It was not until half a century later that tension was applied to cotton fabrics during alkaline treatment, thus producing shiny fabrics.

Mercerizing process, whether under tension or not, will increase the chemical reactivity of cotton fabric, making the fiber easier to absorb dyes and adapt to various chemical finishing. Recently, we found that in some cases, the main purpose of mercerizing cotton fabrics is to improve their affinity and chemical activity to dyes. For some fabrics, the improvement caused by mercerizing engineering can only improve the affinity of dyes and the chemical activity of cotton, which has little impact on the general appearance of fabrics.

Careful control of mercerizing engineering can establish a certain degree of stability. In many cases, this stability is almost as important as increasing affinity for dyes. Increasing stability can make the fabric have better yield after shrink proof treatment. Therefore, mercerization engineering is a necessary process to obtain proper stability.

In a word, mercerizing works are currently carried out for the following purposes:

1. Increase the affinity for dyes.

2. Increase chemical activity.

3. Increase stability.

4. Increase tensile strength.

5. Gloss.

6. Fabric smoothness.

As mercerizing engineering is applied to both cloth and yarn, many of the same principles and technologies are also applied to mercerizing engineering of cloth and yarn. We will first discuss the mercerizing engineering of cloth, and then discuss some basic differences between the two processes in depth.

2、 Mercerizing of cloth:

The first decision that must be made in the mercerizing project of cloth is to select the fabric to be mercerized when it is in the state of original embryo or has been pretreated or partially pretreated. Since none of the methods can be used for the three states mentioned above, the fabric can be mercerized without any treatment in the case of the original embryo, whether it is pre desizing or scouring or after scouring and bleaching.

The choice of whether materials need pretreatment before mercerizing depends on the type of materials, special plant equipment, and the demand for finished mercerized fabrics. In theory, for most factories, if it is to mercerize the proembryo, the operation should be the simplest, because drying or special pretreatment can be omitted. However, as a large number of impurities are brought into the lye, these impurities will hinder the mercerizing engineering or the recovery of the lye. However, in an ideal situation, after mercerizing, the proembryo will show satisfactory luster and affinity for dyes, and enhance toughness and other excellent properties. Therefore, in order to obtain satisfactory results in the mercerizing engineering of proembryo, it is necessary to add strong penetrant into the lye.

The mercerizing of proembryo, or the desizing of proembryo or the mercerizing of refined cotton, their respective gloss, toughness, chemical activity and affinity for dyes cannot help us to choose between good and bad. This decision can only be made after strict evaluation of the convenience of manufacturing machines, the effectiveness of alkali recovery equipment and drying equipment. Before mercerizing, materials may have been completely refined and bleached, and there are many manufacturing machines to cooperate with this equipment. Generally speaking, assuming that all mercerizing processes are controlled under the best conditions, the materials that undergo mercerizing engineering after scouring and bleaching will have a better gloss and smooth appearance than the materials that only have bleaching before mercerizing engineering.

One possible disadvantage of mercerizing of bleached materials is that the adverse effects of excessive bleaching will not show up under normal conditions, but will show up after mercerizing. Any over bleached fiber will be dissolved slightly in alkali liquor, and the tensile strength will be damaged to a certain extent.

Generally speaking, different mercerizing pre-treatment will not cause great differences between products. If the main purpose of mercerizing is excellent gloss and smoothness, then the whole set of bleaching pretreatment is of course the best. If the maximum tensile strength must be maintained, bleaching should be carried out after mercerizing.

All cotton, whether dry or wet, proembryo or bleached, should be unfolded to smoothly feed into the mercerizing lye. Wrinkles, especially on thick cotton fabrics, will show traces on the dyed products later. Therefore, before the cotton is put into the lye, some tension should be applied to prevent wrinkling. If wet cotton needs mercerizing, it should be sent to Mangle first to make the moisture content more uniform. Generally, the less the moisture content, the better. To obtain the best mercerizing effect, the cotton should be dried before entering the lye.

When considering which equipment is most suitable for caustic soda impregnation and mercerizing, we should pay attention to the reaction between cotton and lye. When the cotton is very dry and can be used as an absorbent, the sodium hydroxide will be sucked into each fiber after it contacts with caustic soda, and then the fiber will swell due to the absorption of sodium hydroxide. The swollen cotton fiber becomes plastic and can change its shape at will. Mercerization occurs instantaneously. Mercerization has a time factor, which cannot be ignored even if it is very small. It is not enough for a small amount of lye to be squeezed into the fiber. Caustic soda must really react with cotton fiber. If the fiber is an absorbent, extrusion or pressure will not accelerate the reaction. If the cotton does not enter the lye in the dry state, the mercerizing will take a long time, because the real mercerizing will not occur until some of the moisture in the cotton is replaced by the lye.

Obviously, the selection of impregnation equipment takes a lot of time. We know that when the cotton is completely filled with lye, mercerization will occur, and cotton will no longer be immersed in lye. Therefore, we only need to have a storage tank long enough to make the cotton be filled with lye. If the cotton is in a completely dry absorbent state, and there is enough time after the yarn rack is installed and before the washing, there is a very simple pressure suction operation, that is, one time immersion in the alkali bath. However, if the cotton contains water, the lye will be diluted by water due to this alkali soaking operation, and the real concentration of lye is only one half to one third of the original concentration. Therefore, if the cotton enters the mercerizing alkali tank with water content, the impregnating equipment must be long or deep enough so that the cotton leaving the alkali liquor can be fully saturated, and the alkalinity is the same as that in the alkali bath. Under normal circumstances, wet cotton should be mercerized, and its impregnation tank should be designed with several inlets that allow cotton to reach the alkali liquor, and inject strong alkali from its opposite side. The correct time of contact between cotton and lye is unknown, about 30 seconds. Although a longer contact time or a longer storage tank will not be harmful, it is unfavorable in terms of economy and protection.

3、 Mercerizing pressure:

The extrusion amount of cotton after leaving the alkali dipping equipment is very important. Lack of understanding of this factor is one of the main reasons why all the advantages of mercerization cannot be obtained. Generally speaking, most factory operations are that when cotton leaves mercerizing lye, the less the amount of lye, the better; In some cases, it is often necessary to set a heavy pressure suction roller and adjust it to reduce the alkali content in cotton to 60%. Factory managers believe that high grouting pressure is conducive to saving the consumption of alkali liquor and improving the benefits of cotton cleaning on the Tenstrum later. Low alkali content does mean less alkali consumption and easy cleaning, but in many cases, it also indicates that incomplete mercerization, insufficient stability, poor gloss, or all three may result.

When the alkali treated cotton exists in a plastic state, there must be a certain amount of lye near each fiber to provide proper lubrication when the fiber changes shape. I have visited many factories. When their cotton leaves the lye, it will bring out a very small amount of sodium hydroxide, so you don't have to worry about cracks in the process of widening. We do not know the proper alkali content of the cotton that will leave the alkali liquor. Usually, this content is at least 100% of the cotton weight. For many lightweight fabrics with good operation and gloss requirements, cotton must be wetted by alkali liquor when leaving the alkali bath. By trial and error, adjust the pressure on the cotton that is about to leave the lye, which can be connected with the operation of the frame, so that the best mercerizing effect can be obtained. When this operation method is implemented in every factory, a series of materials must be tested first.

4、 Alkali concentration:

The photochemical treatment of most pieces of cloth is carried out within the concentration of 28~31 Be. Although some are operated under 19~22 Be `, the purpose is only to improve the affinity for dyes Our experience is that the range of 28~31 Be 'is most suitable for most situations. Alkalinity higher than 31 Be' will not increase gloss or improve other characteristics, while alkalinity lower than 28 Be 'will reduce gloss and cause poor appearance. The reason why the range of 28~31 Be ` is particularly good is that when there is temperature change or impurities in the lye, this range can still provide good results, unless the temperature change is too large or there are too many impurities, the finished product will be affected. In general, we recommend that the factory set the alkalinity within the range of 29~30 Be. From the perspective of control technology and finished product effect, this standard is satisfactory. If any factory adopts this standard range, as long as the Twaddel is raised or lowered according to this standard, there will be no difference in the final results. In addition, the temperature change caused by climate does not affect the mercerizing effect of operations within this alkalinity range.

5、 Temperature effect:

For many years, the temperature effect of lye has been deeply misunderstood. Many factories attach great importance to the temperature control of lye. In fact, from the perspective of cost or quality, it is improper. In fact, the lye in many mercerizing plants is only equipped with a cooling system. Only in recent years have many factories abandoned cooling equipment. In fact, if a factory uses lye within the range of 28~31 Be ', large temperature changes will not cause any variation in the final product of mercerization. The research conducted under actual operation and proper control shows that there is no difference in the temperature change of 70~100 ℉ (21~38 ℃) for the lye within the range of 28~31 Be `. Once the temperature exceeds 110 ℉ (43 ℃), the gloss of the mercerized product is obviously poor. When the temperature drops below 70 ℉ (21 ℃), there is no obvious improvement. Therefore, it is undoubtedly a waste to provide cooling equipment for a large amount of lye. However, for low concentration lye, its temperature effect deserves special attention. If a 19 Be alkaline solution is used, a slight temperature change will cause a significant difference between the fabric appearance and the affinity for dyes. The alkali liquor of 25-27 Be 'is also in the range of low alkali liquor and high alkali liquor, so the allowable variation of temperature is also in the range.

Perhaps the misunderstanding of temperature in mercerizing originates from the concept pointed out in Massey's earliest book, that is, weak caustic soda must be cooled to obtain satisfactory mercerizing. At present, the lye bath in many factories is designed not to raise the temperature of lye too high. In some special cases, materials are mercerized in a small bath of lye, and the temperature will exceed 100 ℉ (38 ℃). If the material is dried, or the large bath lye is used, or the newly prepared lye is completely cooled, either method can solve the problem of excessive temperature. The so-called hot filament photochemical treatment is very interesting. It is to heat the cloth soaked with alkali liquor above the boiling point under pressure. Because the cotton to be mercerized will not change its physical and chemical properties when it comes into contact with the alkali liquor in the process of heating up. The physical and chemical properties of the cotton will not be changed until the fabric is removed from the pressure supply, cooled, and entered the mercerizing process of Fu Tong. Therefore, hot filament polishing is just mercerizing before alkali liquor refining. Another advantage of this treatment is that the amount of lye permeated into cotton increases due to the increase of lye temperature. However, the same effect can be achieved by adding chemical penetrant to the lye at room temperature.

6、 Mercerizing tension:

This procedure is the most difficult step in the mercerizing process. No matter how perfect the cotton pretreatment is, or how complete the lye permeates in the cotton, the mercerizing effect cannot be guaranteed, unless the cotton is properly handled in the fabric spreader and washed evenly and thoroughly on the stenter, Only then can obtain the satisfactory mercerizing effect. In other words, improper operation and cleaning process of the cloth spreader is the main reason for poor mercerizing effect. When the cotton is mercerized, it is semi plastic in the state of the cloth spreader. Unless the cotton is shaped to the correct width by the treatment of the cloth spreader and cleaned properly after leaving the cloth spreader, it will cause poor gloss and poor shrinkage, It may even lead to uneven dyeing.

In theory, in the operation of the cloth spreader, the cotton should be pulled to the predetermined width as soon as possible before cleaning. The actual operation must be compromised, that is, the cotton is gradually pulled to the specified width. The exact information about the length of time or how long the cotton can be pulled to the predetermined width cannot be provided here. However, they are related to the length of the cloth spreader and the subsequent cleaning process. The compromise made previously is also due to unsatisfactory cleaning volume. The width of cotton on the loom is also a controversial issue. Generally, for most operations requiring excellent gloss and shrinkage, the cotton should be pulled to the width of the original embryo, and if possible, an additional 1 inch should be pulled. If the width of the stretched cotton is less than the width of the proembryo, the gloss of the finished product will be lost and the shrinkage and stability will be reduced. Many factories are afraid of pulling the cotton to the width of the proembryo. In fact, cracks appear after the cotton is stretched because the cotton is too dry. This disadvantage can be remedied by taking some lye away from the cotton before leaving the lye.

Another factor that sometimes hinders the factory from stretching the cotton is the effect of ginning caused by the increased tension on the cloth clamp and the machine. This effect can be offset by the lubrication effect of slowly dropping lye on the clip, and also has the effect of preventing knotting.

It is almost unnecessary to apply extra tension along the warp. Generally speaking, the tenter should move at the same speed as the alkali hydraulic suction, so that the cotton will not stretch along the warp and will not shrink. When we want glossy warp, the spreader operates at a speed higher than that of alkali hydraulic suction, so that the warp can be stretched extra. Usually, the maximum difference between the speed of cloth tensioning and alkali hydraulic suction is 5%.

7、 Cleaning:

When the cotton is pulled to the proper width, the lye must be removed from the cotton immediately, so as to obtain the best effect. Once the cotton leaves the spreader, any washing or stretching will not affect the mercerizing effect in the fabric. We know that under normal temperature, cotton will wrinkle in 3.5 Be 'lye, which means that before leaving, the content of lye in each cotton fiber should be reduced to less than 3.5 Be'. If there is a large amount of lye in the fiber, the cotton will wrinkle after leaving the cloth spreader, which will also cause poor gloss and stability.

There is a common mistake that people think that when washing the material at the end of the cloth washer, the washing down can be expressed as the real alkali content of the fiber; But in fact, the washing water may only contain 5% alkali. Some measurements of the cleaning efficiency of the spreader can be converted by measuring the width of the cotton removed from the end of the spreader immediately. If there is a lot of cleaning, the width of the cotton will only slightly decrease after it comes down from the stenter clip.

8、 Mercerization of raw billet:

When the raw material (Greige) is mercerized, it is very important to add a strong penetrant in the alkali hydraulic suction to make caustic soda enter the cotton fiber and react with it. When the pretreatment of cotton before mercerizing has been completed, including bleaching, the cotton can reach saturation without the effect of penetrant. Most of the early mercerizing penetrants on the market are used to help lye penetrate into the proembryo. They are generally designed to be within the range of 28~30 Be ` and are very effective penetrants. However, they often lose their penetration at low alkalinity.

Recently, mercerizing penetrants have new development. mercerizing penetrants can be used as penetrants in the mercerizing alkalinity range, but they can be used as interfacial active agents in low alkalinity. The use of mercerizing penetrants or interfacial active agents that can act in a wide range of alkalinity, i.e. auxiliaries, will affect the cleaning work on the spreader. The auxiliaries can help to remove the lye in cotton during cloth spreading, and because of their interfacial active agent effect, cotton can be refined on the cloth spreading machine.

9、 Mercerizing of polyester cotton blend:

Now we are going to discuss some special problems of mercerization related to cotton blending. Remember that mercerizing is used in blending to improve some properties of fibers other than cotton. Polyester and cotton are two kinds of fibers with completely different properties. Cotton is a water sensitive fiber, while polyester is just the opposite, and can only be affected by soaking in high concentration alkali liquor for a long time under high temperature. Fortunately, the best condition for mercerizing effect is to dip in strong alkali at low temperature for a short time.

Therefore, in mercerizing treatment, the risk of polyester damage is not great, and the normal mercerizing of cotton can also meet the needs of cotton and polyester blends. On the contrary, the cotton fiber in the cotton polyester blend often does not exist in the form of absorbent, because the pre scouring and bleaching of all cotton fabrics are not exactly the same. Therefore, it is necessary to add special penetrant into mercerizing lye.

Since the mercerizing of cotton and polyester combination has no special improvement, and because the mercerizing operation of this blend and the finished product are almost similar to the mercerizing results of cotton, we will continue to discuss the blend of cotton and viscose rayon without repeating.

10、 Mercerizing of cotton viscose blend:

The mercerization blending project of Viscose Rayon and cotton with high moisture modulus (High Wet Modulus) and mercerization blending products of cotton and ordinary viscose rayon have brought us some special problems. In the mercerizing process, we hope to improve the properties of cotton without affecting the viscosity. This problem involves both theoretical and practical aspects, because all viscose rayons will swell in the soaking of caustic soda. When we make another kind of viscose rayon with high humidity modulus that is not easy to expand in alkali liquor, they will be more sensitive than cotton in some cases. Therefore, unless the operation is appropriate, the blended product after mercerizing may have many shortcomings such as hardness, brittleness, low tensile strength or the effect of wool papering.

Fortunately, the alkalinity of viscose rayon is not the same as that of cotton. For a long time, people have known that the lower the temperature of lye, the better the expansion effect of cotton. However, temperature has a great influence on viscosity, and in some cases, rayon will dissolve in caustic soda. For cotton, the time factor of alkali dipping is also different from viscose rayon. For cotton, most mercerizing effects start at the beginning of alkali dipping, and soon reach a balanced expansion state. However, for viscose rayon, it will take a long time for alkali liquor to reach a balance. Therefore, we know that the time factor of alkali dipping is not very important for cotton, but it is very important for viscose rayon. Finally, since viscose rayon fibers can absorb more than cotton, some methods must be used to promote the penetration of lye into cotton.

Based on the above discussion, we know that the following points must be considered in the mercerization of cotton and viscose rayon blends:

1. Alkali concentration.

2. Alkali temperature.

3. Contact with alkali liquor.

4. The penetration of alkali liquor.

5. Cleaning method.

We once suggested that mercerizing of all cotton fabrics should be carried out in the range of 28~31 Be ` alkali concentration, which can not only increase luster, promote affinity and stability to dyes, but also improve other properties. At the same time, this range has the least adverse effect on viscose rayon. Therefore, if the luster of cotton, affinity for dyes and stability are our goals for improvement, then the alkali bath of 28~31 Be 'can really achieve good results in the mercerizing treatment of cotton blended with viscose rayon.

We have also recommended the use of mercerizing equipment without cooling system, but the temperature of lye should not be higher than 110 ℉ (43 ℃). We also give the same advice on mercerizing cotton/rayon rayon rayon blends. However, if the alkali bath temperature can be maintained below 110 ℉ (43 ℃) for several degrees, the good effect of minimizing the expansion of rayon can be achieved. Since cotton fiber is the main place where the reaction takes place, and rayon rayon has a strong absorption effect, it is very important to improve the rate of alkali penetration into cotton and promote the reaction of cotton after contact with alkali as soon as possible. The use of some newly developed and marketed additives can help us meet this requirement. Since extending the contact time between cotton and alkali liquor is not a big problem, sometimes it is beneficial. Therefore, for those cotton fabrics, we often recommend two alkali dipping operations, just like the operation of air oxidation, in order to give sufficient time so that the reaction between alkali and cotton is complete. However, long-term immersion in lye will have a negative impact on viscose rayon. Therefore, a compromise must be envisaged in the mercerizing technology of cotton and viscose rayon blends. Air oxidation and alkali bath twice are not applicable now, but cotton must pass through alkali liquor quickly. It is usually enough to simply modify the standard mercerizing machine. Using special auxiliaries in mercerizing lye can also make the reaction between alkali and cotton occur quickly. If the improvement of gloss is not considered, as long as the affinity of cotton fabric to dyes is improved, the operation method in many factories is to design the lye within the range of 16~22 Be `. Unfortunately, the concentration of lye that is most likely to have adverse effects on viscose rayon blended with cotton is near this range. On the other hand, some experienced mercerizing technicians also operate at the same concentration range, but keep the temperature of lye near 100 ℉ to allow cotton to pass through the lye quickly, and finally, carry out the cleaning step with special care. Generally speaking, we still think that it is better to operate in the range of 28~31 Be ` than in the sensitive range of 16~22 Be `.

For blending, if special alkali dipping equipment other than standard equipment cannot be provided, it must be specially adjusted when cotton leaves alkali dipping, which is important for adjusting cotton pressure absorption. For all cotton goods, we suggest to leave some lye in the cotton for lubrication when stretching after the frame. In theory, this suggestion can also be used for the blending of cotton and viscose rayon. If there is no proper cleaning equipment, it is unnecessary to consider this point. If the cleaning during spreading is not ideal, it is better to apply maximum pressure suction when the cotton leaves the lye.

Or, it is also beneficial to apply the maximum tension to the cotton in a gentle way during the stretching of the tensioning machine. The field operator must keep these details in mind so that the cotton can be pulled to the predetermined width or wider after spreading, leaving some lye in the cotton to lubricate the spreading. On the other hand, alkali must be washed out from the rayon fiber as soon as possible, otherwise it will cause friability or tensile strength loss.

In the mercerizing of cotton or cotton/polyester fabrics, the ideal arrangement after alkali dipping is to allow the spreader to operate for a long time, so that the cotton can be slowly pulled to the desired width, and then the spreader can be cleaned with a large amount of cold or lukewarm water. However, the blending with viscose rayon must be treated in the opposite way. Now it is not only necessary to wash out the alkali as soon as possible, but also to use a large amount of extremely hot water to clean at the same time as the operation of the cloth spreader starts.

As mentioned earlier, viscose rayon is quite sensitive to weak alkali from 12 to 19 Be. Specifically, cotton/viscose rayon blends must pass through alkali liquor quickly and be washed with very large amount of water. Secondly, the alkali content of these cleaning water is low. In the counter current washing equipment used in mercerizing of cotton fabrics, the washing water contains quite high alkali content, which is quite dangerous, especially when it is not hot enough. Fortunately, high temperature helps the influence of alkali liquor on rayon. In other words, Lei is between 18 and 30. TW cold or tepid lye is more suitable for expansion than lye with the same concentration but temperature higher than 180 ℉ (82 ℃). Therefore, a large amount of washing water is used to make the alkali content in the washing water as low as possible, and the water temperature should preferably exceed 180 ℉ (82 ℃) to achieve satisfactory results.

Finally, adding appropriate mercerizing additives in the original alkali bath can also promote the rate of alkali washing out from viscose rayon.

The latest mercerizing auxiliaries have the effect of both penetrant and interfacial active agent, and can function in a wide range of alkalinity. They are very important for the mercerizing of cotton/rayon blends, because even if cotton is in absorption state, it can also promote the alkali to penetrate into cotton quickly. At the same time, they will also accelerate the reaction between cotton and alkali. Another important thing is that they can function even when washed because they can remain active in any alkalinity. With their existence, the lye can be quickly removed. Their high activity prevents the possible damage caused by the lye, and also makes the washing water quickly distributed to each part of the fiber.

11、 Yarn mercerizing:

Warp Mercerizing is indispensable to the discussion of mercerizing. As many of the items we discussed in the silk polishing, such as alkali bath concentration and cleaning parameters, can be applied to the silk polishing of warp yarns. Therefore, we will only discuss the categories of different or other special technologies.

The question is, why can the mercerization of warp yarn achieve the maximum benefit we require and become the first choice to replace the mercerization of cloth? There are many answers, most of which can be directly observed. First, yarn can be used for knitting. Obviously, it is almost impossible to mercerize the fabric completely unless there are special circumstances. Moreover, cotton thread is often knitted with silk, wool, rayon and other fibers. There are also technical difficulties in processing this kind of fabric. Therefore, in order to achieve the significant development of mercerized cotton products, yarn mercerization is the only reasonable method. In the same way, fiber can also apply to the above statement.

The answer that yarn is used for weaving is easy to be confused. From the beginning, it is learned that the mercerization of fabric is faster and more economical than that of yarn, which is the most reasonable way to obtain good results. However, the mercerizing of yarn is not only flexible in operation, but also has the development potential in toughness and other characteristics compared with mercerizing of cloth woven from the same yarn. Even by mercerizing a weak yarn, it can improve its toughness and increase the benefits of knitting.

If the yarn to be woven into cotton cloth is mercerized, the finished product can have many special effects. For example, warp yarns can be mercerized and woven into a fabric with yarns made of other fibers. Finally, with regard to the maximum toughness and the best gloss, the yarn can usually replace the mercerizing of the finished product to obtain the best results.

Warp treatment has many advantages in mercerizing the yarn when twisting. First, it allows continuous mercerizing of yarns over 6000 yards long, and can process thousands of yarns simultaneously, which is quite economical. This mercerizing method is the most convenient in management, because the yarn will be automatically transferred from the yarn frame to the spherical warp, continuously mercerized and dried, and then wound onto the bobbin or bobbin. Finally, the warp process itself has a feature that the chemicals used in this process will not be consumed. In addition, since counter current water washing is allowed for warp treatment, alkali liquor can be recycled. If the amount of yarn used for mercerization is large, it is better to treat it by warp method.

As early practitioners of the silk polishing of warp yarns, they tied several warp yarns into a single yarn and loosely tied them into a bundle with clues or original yarns, which is named Water Ribbon. Recently, some operators abandoned the single yarn system and mercerized the yarn in a free state, thus obtaining a similar continuous warp sheeting.

In the process of yarn mercerization, whether the yarn should be bleached before or after mercerization is also the same question as the answer in the discussion of fabric, which need not be considered. For all mercerizers who mercerize with virgin yarn, if the yarn has been refined or soaked, we must control the yarn under the best conditions in order to get good results in mercerizing. The problem between wet mercerizing and dry mercerizing is a topic centered on this. First, because this is the earliest technology in the earliest and original manufacturing process, of course, there are people who support it. When Mercer first discovered the mercerizing process, he found that in order to make alkali react with cotton, cotton must be thoroughly soaked.

Mather's knew how to let alkali penetrate by itself, so early mercerizers first thoroughly boiled their yarns, then extracted excess water, and then mercerized them. Many of today's warp mercerizers still adhere to the old process, but there are also improvements.

The bitter experience of foam generation in the lye evaporator is caused by some poor mercerizing penetrants in the early stage and some ineffective penetrants. They make many operators refuse to use dry mercerizing. In most cases, wet mercerizing has more disadvantages than dry mercerizing, which mainly soaks yarn directly in lye. Wet mercerizing has few advantages and is not important, so it is often ignored by people. One of its small advantages is that the pre soaking process before alkali dipping filters out some impurities in the yarn, thus preventing the pollution of alkali liquor. If the yarn is exposed to the air for a long time, the impurities contained in it will be considerable.

Kiering before mercerizing has long been an outdated and expensive treatment. It may have been the earliest method of immersion. In fact, it has long been abandoned by practitioners. Today, the so-called "wet type" is different from "dry type", that is, one is the way to pre soak the yarn on the mercerizing machine before alkali treatment, and the other is the way to directly soak the yarn into the alkali solution with a special penetrant added. If the soaking treatment only boils the yarn in hot water without adding any chemicals, the only cost is steam. However, if the soaking treatment is uniform and complete, it is almost impossible to boil the yarn without an extremely long working line. In this method, the cost of steam is quite large. However, the operators who use this method usually add two devices to the mercerizing apparatus before alkali impregnation to ensure that the yarn is completely saturated by wetting agent. In this method, the cost of chemicals is also considerable. In addition, in order to provide a uniform and constant soaking force, the Wetting Bath should be carefully controlled.

One disadvantage of the soaking process is that there is insoluble wax on the cotton, which will cause considerable accumulation and float on the alkali bath. These waxes are also taken away by some yarns, occasionally leaving Resist Spots or causing uneven dyeing. However, the biggest disadvantage of soaking treatment is the considerable amount of water brought into the alkali liquor by the yarn, which is about 70~140% of the yarn weight, which means that if the mercerization must be carried out under a fixed alkalinity, such as 29Be, then high alkalinity alkali liquor must be often added to the alkali bath to compensate for the dilution caused by the yarn. At the same time, the effect of the wet yarn immersed in the alkali bath on the alkali can only be produced after the alkali liquor displaces some water. It means that the soaking tank used for wet treatment is longer and slower than that used for dry treatment.

The new mercerizing penetrants and auxiliaries used in dry treatment can bring us many advantages that make wet treatment more inferior.

First, the use of penetrant not only makes the alkali liquor wet the yarn of the proembryo quickly, but also has the catalytic effect of accelerating the mercerization reaction. The addition of penetrant also makes the alkali liquor washed into the recovery system without foam. In addition, by immersing the yarn in an alkali bath with appropriate penetrant, the mercerization can start to work immediately, and the whole yarn can work at the same time. Therefore, the uneven infiltration produced in the wet method cannot occur in the dry method.

Second: Because the yarn will not bring water into the alkali bath, the alkalinity in the alkali bath is easy to control. At the same time, because the maintenance of alkalinity in the alkali liquor bath only needs to add a small amount of high alkalinity alkali liquor, in other words, the alkalinity change of the alkali liquor bath is very small, so in the washing water recovery system, the recovery of low alkalinity can be simplified, and it is not necessary to evaporate high concentration alkali liquor like the washing water of wet method. In the dry method, since the yarn carries some impurities into the lye without being washed, these impurities can be easily removed by the circulating filter of the equipment in the factory that usually does wet mercerizing. As far as the dry process is concerned, the cost of good auxiliaries for mercerization is no more than that of wetting agent, steam supply and evaporation in the wet process.

Finally, the quality of the finished yarn after mercerization should be mentioned. The finished product of dry mercerization can accept more tension, and because there is no different water content along the length of a special end of the yarn, the reaction with alkali liquor is quite average. Therefore, the dry method is more likely to produce evenly dyed yarns than the wet method. It must be assumed that other factors remain unchanged.

Tension is the basic factor in the glossing of warp yarns. Therefore, the control of tension is also very important. Strictly speaking, the term "tension" has been misused in the industry. Tension is a force acting on the yarn. In the machine of warp silk polishing, we can only control the tension by the expansion ability of stretching, shrinking or penetrating the alkali solution. If the alkali liquor maintains a constant alkalinity, the tension in the mercerizing machine will be controlled by the relative speed of the Squeeze Roll in the alkali bath and the phenomenon of yarn slippage in the pressure suction drum.

Therefore, from the point of view of mercerization, we are more concerned about the shrinkage or extension of the yarn when the yarn enters into mercerization lye until some lye in the yarn is washed out. From the point of view of general quality and efficiency, we are concerned about boiling, washing, scouring, and even stretching or shrinking when drying. In all these steps, stretching and shrinking will affect the yarn quality in all aspects. However, we will first discuss the extension or contraction in the lye. For most yarns, it is a simple and common practical operation to keep the yarn flat and not shrink during alkali treatment and pre cleaning. Under these conditions, satisfactory gloss, shrinkage and affinity for dyes can be developed. However, some special properties of mercerized yarns will be improved with increasing stretching, while others will be weakened.

If the yarn is not allowed to shrink before washing, the gloss is directly related to stretching during alkali treatment. Even if the stretching degree is as high as 10 ℃, the previous conclusion is true. However, in the same case, the increase of extensibility must lead to the decrease of affinity for dyes and the decrease of flexibility. According to the nature of the yarn, during alkali treatment, the breaking strength of the finished yarn will be increased to a certain extent by increasing the stretch, and then the breaking strength will be weakened by increasing the stretch. For yarns with standard mercerized twist, the twist range is from 20s/z to 90s/z, which is equivalent to 4% of the stretch during alkali treatment. You don't need to worry about reducing the stretch of the finished yarn, so you can use it with confidence. Moreover, the gloss will be greatly increased, and the tensile strength will also be improved. For single yarn, any extra stretch will bring danger, so it is better to avoid shrinkage of single yarn.

For special dyeing effects, such as high affinity for dyes, the yarn can be allowed to shrink by up to 10% during alkali treatment. If the yarn is stretched or shrunk during this process, the total number of finished yarns will not equal the total number of original yarns used. Under normal circumstances, due to the natural loss of some gum and impurities in the yarn during mercerizing, there will be one or two total yarns. However, the main reason for the change of the total number of yarns is large shrinkage or extension.

During mercerizing, any difference in extension or shrinkage will cause uneven dyeing of finished yarns, although we cannot see any change in gloss and strength caused by them. In order to control these tensions, the most important thing is to have a precise method to control the speed of the suction roller when entering and exiting the alkali liquor, and when leaving the final cleaning process. It is very important that these pressure suction rollers maintain a true and average density so that the ends of the warp can achieve the same effect. It is obvious that the control of the uniformity of the tension in the warp is also important in the manufacture of warp yarns. When tension is applied at both ends of the yarn, if there are slight differences, we will not see obvious differences in gloss and strength, but will perceive differences in affinity for dyes. Therefore, in order to obtain the maximum evenness of the warping yarn, the tension or stretch at both ends of the yarn must be very similar.

If the scouring or soaking system is used before mercerizing, and no tension is applied to the yarn during the soaking treatment, it will usually result in a shrinkage of 2-4%. If you want the best gloss, you'd better make the yarn shrink a little when soaked, and then stretch it when soaked in lye to make up for the loss.

If the yarn is slightly slack when soaked, the penetration will be more complete, and the yarn will also be thoroughly soaked. How to choose to soak under tension and maintain the same stretching degree during mercerizing, or allow a little shrinkage during wetting, and then stretch during lye treatment, depends on the existing equipment.

Finally, in the cleaning process, when a certain amount of lye is removed, the yarn will tend to increase its length. At this moment, it is better to accelerate the drum that is about to leave the lotion, so as to leave the least amount of slack in the yarn. Too much slack will break the end of the yarn and cause some trouble in the final winding process.

From the latest development of some mercerizing in recent years discussed above, it is obvious that good mercerizing is still based on the basic practices disclosed in the process first developed by Mather.