Extraction Process
Dissolution of hemicellulose fractions from plant cell walls occurs when raw cellulose is treated with strong alkaline solutions. This xylan solubilization releases pentosan polymers into the mercerizing bath, which increases the viscosity and organic load of the process water over time. These dissolved polymers must be continuously removed to maintain the effectiveness of the treatment bath.
Chemical Mechanism
Sodium hydroxide breaks the hydrogen bonds that hold the hemicelluloses within the crystalline matrix of the cotton fibers. Once these bonds are disrupted, xylan solubilization proceeds rapidly as the deprotonated hydroxyl groups of the sugar chains become highly soluble in water. The rate of this process increases with temperature and alkali concentration.
Industrial Effect
High levels of dissolved pentosans in the recycled lye bath can coat the yarn during subsequent drying stages, which creates a stiff hand feel and reduces the dye affinity of the finished fabric. By monitoring the extent of xylan solubilization, the mill can determine when the extraction bath has reached its contamination limit and requires purification. This monitoring prevents the accumulation of residues that can cause patchy dyeing in later stages of production.
Control Method
Utilizing specialized membrane filtration allows the mill to extract the dissolved xylans while reclaiming the sodium hydroxide solution. Efficient control of xylan solubilization reduces both chemical waste and production costs.
