Method for bleaching and removing burlap from original color yarn and linen fabrics

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Flax fiber contains a lot of impurities. Some of these impurities are removed during fiber degumming, chemical processing of flax roving, and fabric pre-treatment. Some of them are still present in the linen fabric after dyeing and finishing. Therefore, flax spinning is generally called bundled fiber yarn, and linen fabric is also bundled fiber yarn fabric. In the textile and chemical processing of linen fabrics, the processing of linen fibers and fabrics has always been an “impurity removal” process. During the fabric pre-treatment process, some impurities are needed and must be removed, and some impurities are best retained. to maintain the style of the linen fabric, but part of it had to be removed during processing. During the chemical processing of fibers, rovings, and fabrics, the main things that need to be removed are the removable part of pectin I (pectin I and pectin II exist in flax bundle fibers), all lignin, etc., and impurities that have to be removed. Or called flax fiber companions, they mainly include hemicellulose, some pectin I, ester wax substances, etc.

In order to successfully remove the impurities that must be removed from linen fabrics and minimize the removal of flax fiber companions that need to be retained, it is necessary to analyze and study the flax fiber impurities to select targeted process technologies to maintain the strength of linen fabrics and ensure the quality of linen fabrics. linen style.

Linen fabrics from different sources (raw yarn linen fabric, fully bleached linen fabric, dry-spun linen cotton fabric) were pre-processed in the same bath to verify the ease of bleaching and the degree of bleaching removal of linen bark. On this basis, a pretreatment process test was conducted on linen-cotton fabrics containing serious flax skin. (The scouring experiment and chlorine bleaching experiment process are omitted…)

The characteristics of flax fiber bundles into yarn bring unique processing processes to flax spinning, dyeing and finishing. For example, flax fiber spinning has a unique needle combing and carding process, chemical processing of roving, wet spinning of spun yarn, etc.; Unique process conditions for fabric dyeing and finishing. Among them, the initial processing of flax fiber is the process of making flax fiber from the original flax stem, which requires the removal of part of the gum and the fiber from the flax stem; the carding of flax fiber is to increase the splitting degree (fiber fineness) of flax fiber. The scouring and bleaching of rovings are mainly to remove lignin and improve the spinnability of the fiber; the dyeing and finishing of linen fabrics are also to remove impurities such as lignin, part of pectin, hemicellulose, etc., so as to achieve the required bleaching and processing of fabrics. Exterior. The important issues that plague the research on flax textile dyeing and finishing are the need to clarify the structural composition and definition of flax fiber lignin, seek methods for bleaching or removing flax bark, and solve how to reduce the weight loss rate of linen fabrics and reduce the weight loss of linen fabrics in the dyeing and finishing process. Strong loss to maintain the linen style of linen fabrics.

(linen knitted fabric)

[Popular definition of flax fiber impurities]

Flax fibers and fabrics contain a lot of impurities. The main thing that needs to be removed from linen fabrics is the lignin in the flax bark, and lignin is the main obstacle to the bleaching of flax bark. However, the chemical structure of lignin is not yet very clear, and the structures of lignin obtained using different methods and channels vary greatly. In addition to lignin, flax fibers also contain impurities such as hemicellulose, pectin, and ester waxes. Most of these impurities are not expected to be removed, but they have to be partially removed for fabric pretreatment. With the removal of fiber impurities, there is a weight loss in the processing process. The greater the weight loss, the greater the strength loss of the fiber, yarn or fabric.

From the experience of planting and harvesting flax fiber, we know that the original stems of flax fiber harvested in the yellow ripening stage have the highest cellulose content, less lignin content, and lower hemicellulose content. The later the harvest period of flax raw stems is, the higher the lignin content will be, the hemicellulose content will decrease, and the cellulose content will also decrease. In this sense, flax lignin can be generally defined as aged flax cellulose. If the harvest period is advanced, the cellulose content decreases, the lignin content also decreases, and the hemicellulose content increases. In this sense, flax hemicellulose can be defined as immature flax cellulose.

(linen woven fabric)

[How to remove pockmarks by bleaching]

Flax skin can be bleached and removed through a variety of ways and methods. Looking at the development process of linen fabric pre-treatment technology and the currently used process methods, it can be summarized into three categories: First, the use of enhanced scouring process methods, which use aggravated scouring. The scouring process mainly includes aggravating the scouring conditions, such as long-term scouring at high temperature and high pressure, or increasing the concentration of scouring chemicals; the second is to use the pickling process, which includes pickling and chlorine cleaning before desizing. Pickling after bleaching can reduce the weight loss rate of linen pre-treatment; the third is to improve the sodium hypochlorite bleaching process and bleach the flax skin through chlorination and pickling after chlorination.

The scouring test shows that the cost of increasing the scouring method is a high weight loss rate and a serious reduction in fabric strength. At the same time, it is also easy to cause excessive degumming of the flax fiber, leading to cotton fiberization, making the linen fabric lose its flax style, and should not be used. Solving the problem of bleaching or removing linen bark through acid washing or chlorine bleaching process adjustment is currently a commonly used process method. For original color yarn and linen fabrics, it is advisable to use a combination of the two methods, that is, pickling and adjusting the chlorine bleaching process conditions, so as to minimize the reduction in the strength of the fabric and the easiest way to remove the linen bark.

(linen curtain cloth)

[The significance of retaining flax fiber companions]

The significance of retaining flax fiber companions in pre-treatment of linen fabrics is to maintain the strength of linen fabrics, maintain the style of linen fabrics, and maintain the health care properties of linen fabrics.

The main removal of cellulose companions in linen fabrics includes pectin, lignin, hemicellulose, ester wax substances, etc. Its weight loss is reflected as weight loss rate. The higher the weight loss rate, the higher the fiber splitting degree of the yarn, the weaker the bonding force between fibers, and the lower the fabric strength. In this sense, the pre-treatment of linen fabrics will inevitably reduce the strength of the fabric. Some companies have stipulated the maximum limit index for strength reduction when formulating the process. The style of linen fabric is mainly reflected in the roughness and stiffness caused by bundled fiber yarns. The dyeing and finishing process is not allowed to reduce this style. However, excessive removal of impurities in linen fabric will lead to the “cottonization” of the fiber. Lose the style of the fabric. The health-care properties of linen fabrics mainly refer to hygroscopicity and antibacterial properties. These properties come from impurities such as pectin and hemicellulose remaining in the fiber.

Before dyeing and finishing linen fabrics, it is necessary to retain pectin, hemicellulose, ester wax substances, etc. in the fibers as much as possible, and the pre-treatment process conditions need to be targeted and relatively “soft”.