Hemp is a natural bast cellulose fiber, primarily including fibers from flax, ramie, cannabis, jute, linseed, abaca, sisal, kenaf, banana fiber, and pineapple fiber. Currently, the main types of hemp fibers that can be widely used in the textile industry—either in pure spinning or blended yarns—are flax, ramie, cannabis, linseed, and abaca.
During the processes of retting, carding, degumming, spinning, weaving, dyeing, and finishing of hemp fiber products, the varying properties of different types of hemp fibers dictate distinct approaches to pre-spinning degumming, differences in spinning methods, and unique weaving techniques. Consequently, the pretreatment methods, specific process technologies, and operational measures for hemp-based knitted fabrics are significantly more complex compared to those used for other cellulosic cotton fibers. It is essential to first understand the exact steps involved—both before and during the spinning process—before determining the appropriate pretreatment techniques for hemp knitted fabrics. This section provides an overview of the dyeing and finishing process flow for hemp knitted fabric materials as follows:
1. Natural-colored hemp fibers and blended products:
(1). Greige fabric → Singeing → Overflow machine (scouring → hydrogen peroxide bleaching → oxygen bleaching) → Setting → Mercerization → Post-finishing → Finished product
(2). Greige fabric → Singeing → Desizing machine (scouring → hydrogen peroxide bleaching → oxygen bleaching) → Setting → Mercerization → Dyeing → Post-treatment
2. Bleached linen fabrics and blended products: (1) Greige fabric → Singeing → Overflow machine (desizing → oxygen bleaching) → Setting & mercerization → Post-finishing → Finished product; (2) Greige fabric → Singeing → Clarifying machine (desizing → oxygen bleaching) → Setting → Mercerization → Dyeing → Post-finishing → Finished
3 Songhuai Diti Colored Cotton Fiber and Colored Blended Products:
(1). Raw fabric → Singeing → Overflow machine (desizing) → Setting → Mercerization → Post-finishing → Finished product

1. Singeing
The singeing process is a method used to remove the surface fuzz from linen fiber fabrics, minimizing defects that may occur during subsequent processing—such as fiber shedding or uneven dyeing—thereby enhancing the fabric’s smoothness and overall appearance quality. Currently, when it comes to the production and processing of linen-based knitted fabrics, especially flax-based ones, improper handling can easily lead to batch-wise defective products (e.g., holes), given that the fibers themselves are bundled for spinning. As a result, there are relatively few enterprises capable of mass-producing these fabrics on a large scale. Therefore, this discussion provides only general guidance; specific technical details should be determined based on each company’s unique production experience. (Note: At present, there is no complete industrial chain of circular singeing machines available in the market for printing and dyeing equipment. Hence, the following explanation will focus on flat-width knitted fabric singeing machines as an example.)

II. Boiling and Scouring
The retting process for hemp is equivalent to the degumming process for hemp. Since the bast fibers of hemp plants contain not only cellulose but also various gummy impurities—primarily hemicellulose, pectin substances, and lignin—efficiently removing these gummy components through a highly clean biochemical method can effectively eliminate surface gums and contaminants from the hemp fibers, thereby enhancing their strength, flexibility, and durability. Moreover, degummed hemp fibers become more receptive to dyes and chemical additives, resulting in brighter, more vibrant colors while simultaneously reducing costs associated with dyeing and post-treatment processes—and ultimately improving product quality. The following example illustrates the complete process of natural-color dyeing for hemp.

3. Bleaching
Through the bleaching process, impurities and residual gums on the surface of hemp fibers can be removed, enhancing the fiber's purity and making its color appear whiter. This also improves the dyeing uptake rate and the overall appearance quality of the fabric. Additionally, the process can partially refine the fiber's physical properties, increasing its looseness and softness.

IV. Shaping
Overflow dyeing machine: boiling & scouring → dehydration & setting

5. Mercerization
Linen knitted fabrics are typically mercerized using a caustic soda solution at a concentration of 160–180 g/L, a process also referred to as semi-mercerization. Because linen fibers have both high crystallinity and high orientation—resulting in significantly lower dye absorption capacity compared to cotton—semi-mercerization can markedly enhance the fiber's ability to take up dye, thereby improving the dye uptake rate. However, if full mercerization is carried out instead, the permeability of linen fibers will increase dramatically, allowing dyes to penetrate deep into the fabric. While this boosts color penetration on the fabric surface, it often leads to reduced color depth overall and weaker fabric strength, resulting in a coarser, stiffer hand feel. Therefore, semi-mercerization is generally preferred for linen fabrics.

Key techniques and precautions
(1) Fabric treatment time with strong alkali: Typically, standard fabrics require about 50 seconds, while high-density, thick fabrics or unscoured greige fabrics should be treated for approximately 60 seconds.
(2) Alkali solution temperature: Lower temperatures (15°C) are beneficial for enhancing the mercerization effect, but in actual production, the temperature is typically maintained between 15°C and 22°C.
(3) Tensioning for Width Expansion: During the mercerization process, the fabric is passed through a cylindrical width-expanding device to increase both lateral and longitudinal tension. This step plays a crucial role in enhancing the fabric's luster and ensuring consistent density throughout—both across the width and along its length. Therefore, it’s essential to maintain a steady level of tension throughout the process. Specifically, the circumference of the first cylindrical spreading plate should be controlled at approximately twice the fabric’s original width multiplied by 0.93, while the longitudinal tension should generally match the fabric’s original length; otherwise, the hand feel may become stiff.
(4) Alkali Removal: During hot-water washing for alkali removal, the temperature is typically maintained at 70–75°C. It’s crucial to thoroughly rinse away any residual alkali from the fabric immediately after mercerization—especially important when the raw fabric remains under tension during the process.
(5) Before mercerization, the fabric must be uniformly moist throughout—otherwise, the mercerization effect will vary, leading to uneven color distribution during subsequent dyeing processes.
(6) During the mercerizing process, it is essential to keep the fabric width perfectly flat to prevent wrinkles and other defects; additionally, the seam edges between the greige fabrics must be aligned neatly.
(7) After hot washing, the concentration of the alkali used for descaling should be measured regularly and adjusted promptly as needed.
(8) The pH value of the mercerized and washed fabric should be checked regularly, typically maintained between 7 and 8.