The main component of flax fiber is cellulose, with a content of 70-80% and a white color. In addition to cellulose, it also contains hemicellulose (12-15%), pectic substances (1.4-5.7%), lignin (2.5-5%), nitrogen-containing compounds (0.3-0.6%), and fatty waxes (1.2 -1.8%). These impurities directly affect the physical and mechanical properties of flax fiber, reduce the wettability of the yarn, and make the hand feel rough and the color yellow. The impurity content in flax fiber is significantly higher than that in cotton fiber, which increases the difficulty of the bleaching process of linen fabric and makes the dyed linen fabric less bright in color and poor in dye fastness.
- The influence of physical and chemical properties of flax fiber on dyeing and finishing process
Effect of pectin and hemicellulose
Dyeing uptake rate
In linen fabrics, the pectin content is inversely proportional to the dyeing rate, that is, the more pectin content, the lower the dyeing rate.
color fastness
There is an inverse relationship between pectin content and color fastness.
Hemicellulose
Hemicellulose content is directly proportional to dye fastness and dye uptake rate.
Lignin content
The lignin content has a great influence on the dye uptake rate. The higher the lignin content, the lower the dye uptake rate.
color fastness
The influence of lignin content on dye fastness is inversely proportional. The higher the lignin content, the lower the dye fastness.
- The impact of different retting methods of raw flax stems on the dyeing and finishing process
Both warm water retting and rain degumming are biological degumming. The different retting methods of flax raw stems only affect the dyeing performance of its yarn and fabric, but the general trend is consistent. Here we discuss the dyeing issues of flax fibers using different retting methods in the raw material stage.
The dyeing rate of warm water hemp is higher than that of rain dew hemp, with dark colors being 9.3% higher and light colors being 2.1% higher. Excluding the influence of lignin content, warm water hemp is very close to rain dew hemp due to its lignin content. The dyeing rate of warm water hemp is significantly higher than that of rain dew hemp (the pectin content of warm water hemp is 3.53% and that of rain dew hemp is 5.5%).
At present, under the same fineness and specifications, the price of long linen yarn and long linen fabrics is much higher than that of short linen yarn and short linen fabrics. The residual glue content of short linen fabrics is 3 times lower than that of long linen fabrics. Therefore, the dyeing and finishing process effect of short linen fabrics is much better than that of long linen fabrics of the same specifications. Taking reactive dyes with dual reactive groups as an example, in the light color range of long linen fabrics, for every 0.1% increase in residual glue content, the dye uptake rate decreases by 0.9% to 1.25%; in the dark color range, the dye uptake rate decreases by 1.4% to 1.6%.
Therefore, to solve the problems of long linen fabrics with high residual glue content and poor dyeing and finishing effects, other technical aspects should be studied.
- The impact of the chemical degumming process of flax roving on the dyeing and finishing process
Whether the chemical degumming process is long linen or short linen roving, the best results in the dyeing rate experiment and color fastness experiment are the scouring-oxygen bleaching process and the hydrogen peroxide bleaching process. Since there is no alkali boiling process pretreatment before, As a result, the pectin content is higher. The degree of decrease in dyeing effect caused by high pectin content is much greater than the increase in dyeing effect caused by increased oxidized cellulose.
Light sub-bleaching and heavy oxygen bleaching: For long linen, the dyeing effect is almost similar to the best scouring oxygen bleaching process, but for short linen, there is a big difference.
Scouring and bleaching: the effects of long and short flax are poor.
- The influence of flax fiber polymerization degree on dyeing and finishing process
Fiber polymerization degree: According to relevant research, in each process of the long linen production line and short linen production line, the scouring and bleaching of gray fabric is the main link that causes the fiber polymerization degree to decrease significantly. After scouring and bleaching, the polymerization degree of the long linen fabric decreases. More than 30%, short linen dropped by more than 50%.
The basic process of bleaching: water washing – alkali boiling – water washing – sodium hypochlorite bleaching – water washing – hydrogen peroxide bleaching – water washing – drying
The significant decrease in fabric polymerization occurs in the two process steps of sodium hypochlorite bleaching (the largest step) and hydrogen peroxide bleaching.
- Effect of chemical reaction properties of flax fiber on dyeing and finishing process
The destructive effect of sodium hypochlorite on the degree of fiber polymerization directly causes the breakage of the cellulose macromolecular chain, which is a reduction in the degree of fiber polymerization. Although it does not directly cause a decrease in the degree of polymerization of the fiber, it does cause potential oxidative damage to the fiber that cannot resist acid or alkali treatment. Chemical reaction performance, the effect of acid treatment, the effect of alkali treatment, the effect of oxidant treatment.
The effect of sulfuric acid on the strength and other physical indicators of linen yarn will not cause major changes in the strength and other physical indicators when it fluctuates within a wide range based on the current process conditions.
The role of sodium chlorite: Due to the bonding effect of the remaining pectin in the flax yarn on the fibers, the ability of sodium chlorite to shorten and thin the fibers is effectively curbed, and the selectivity of sodium chlorite to flax fibers is The oxidation effect greatly increases the carboxyl fibers in the fiber, thereby significantly improving the strength of the linen yarn.
Effect of hydrogen peroxide: Hydrogen peroxide does not cause major changes in physical indicators such as flax fiber strength.
Sodium hypochlorite: The non-selective oxidation effect of sodium hypochlorite on flax fiber greatly increases the amount of oxidized cellulose in the flax fiber, thereby causing the single yarn strength to decrease.
- The influence of the mechanical and physical properties of flax fiber on the dyeing and finishing process
Hygroscopic swelling: The polar groups on the fiber macromolecules rely on hydrogen bonds to complex with water molecules to form hydrates – the reason for water absorption. The cellulose content in flax fiber is less than 70%, but the non-cellulose components absorb more moisture than cellulose.
Strong elongation properties: Flax fiber has very high elongation properties. The higher elongation properties provide the possibility to adjust its dyeing and finishing process within a wide range.
Microstructure: Flax fiber has high crystallinity, high orientation, and small inclination angle. This is the main internal reason for the poor comprehensive performance of flax fiber dyeing and finishing. It is manifested in poor hygroscopicity of the fabric, difficulty in dye penetration, and low dye uptake rate.