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The concentration of caustic soda in the pine-heap mercerization process: The purpose of mercerizing cotton yarns or fabrics is to convert natural cellulose I into cellulose II, thereby endowing the cellulose with various favorable properties that enhance its suitability for dyeing and finishing processes. The true degree of mercerization refers primarily to the amount of natural fiber (cellulose I) that is converted into cellulose II; the greater this amount, the higher the degree of mercerization, which is manifested in improved absorption capacity and reactivity. A prerequisite for this conversion is that the NaOH hydrate can penetrate into the cellulose microcells and cause swelling within them, thereby altering the structure of the fibers. Cellulose fibers are linear polymers formed by glucose residues connected through 1–4 glycosidic bonds. The glycosidic bonds in the long molecular chains of cellulose can rotate freely, and the intermolecular forces cause these long chains to come close together and aggregate into bundles. The hydroxyl groups on the long molecular chains form hydrogen bonds, allowing them to arrange in an orderly and compact manner; this enables the formation of crystals ； A more relaxed arrangement with relatively low orientation can result in amorphous regions that are more easily swelled. The crystal regions are generally very small; they are called micelles and belong to the sub-microscopic scale. Therefore, cellulose fibers are composed of alternating arrangements of crystalline regions parallel to the fiber axis and amorphous areas. Water or caustic soda solutions can penetrate between the long-chain molecules of cellulose fibers, expanding the space between them and causing swelling without any chemical damage. During the mercerization process, all parts of the fiber have the opportunity to swell, but the ease and likelihood of this occurring vary; more importantly, external conditions also play a role in this process. This is related to the process conditions for mercerization, such as temperature, concentration, impurities in soda ash, and especially the fabric tension during swelling. Swelling can be divided into infinite swelling and finite swelling; in the mercerization process, caustic soda is used as the swelling agent. Generally, swelling is kept within the range of finite swelling. At 80 g/L, weakly alkaline solutions and water can generally only penetrate the amorphous regions of the fibers, not their crystalline regions; this phenomenon is known as intermicrocellular swelling ； If an alkaline solution can enter the microcells and cause the crystals to swell, increasing the distance between molecules until the crystal structure of the microcells is altered, this is known as intramicrocellular swelling. This intramicrocellular swelling is precisely what is necessary for the mercerization process to denature cellulose fibers, and it depends on whether the NaOH hydrate can enter the cellulose microcells. This is related to the diameter of the NaOH hydrate, which in turn depends on the concentration of the caustic soda solution; this concentration represents the ratio of the number of NaOH molecules to the number of H2O molecules. The diameter of the hydrate that can enter the cellulose microcells is 1 FNm (1 OA). At a mass concentration of NaOH of 126 g/L, the composition of the hydrate is NaOH·12H2O, and its diameter is much larger than 1 nm. At a mass concentration of 154 g/L, it is NaOH·10H2O, belonging to the type of solvated dipolar hydrate; its diameter is large enough to allow it to enter the highly ordered crystal regions. However, its diameter is on the higher side ； At 180 g/L, it is NaOH·8.6H2O; its diameter is smaller than that of NaOH·10H2O, thereby increasing the safety factor of the process. The concentration of the alkali solution in the calendering tanks in conventional tight-ness mercerizing processes varies depending on the product, ranging from 240 g/L to 11260 g/L. In the compact mercerization process, since the residence time of caustic soda on the fabric is short, the diameter of the NaOH hydrate should be reduced to the range of 0.6–0.7 nm in order to improve the diffusion and swelling of the alkali solution in the fabric. The pine pile mercerization process allows for sufficient time for stacking after dipping in the alkaline solution, which facilitates the penetration of caustic soda into the cellulose microcells. As a result, a concentration of 180 g/L in the alkaline bath is sufficient. This not only increases the proportion of cellulose II ； Increase dyeing color load and evenness of coloring ； Reduce the shrinkage rate of fabrics ； It also saves alkali usage and reduces the alkali evaporation load.