Diacetate fiber tow is a kind of precision filtration material. It is made of natural wood pulp (sometimes natural cellulose such as cotton pulp is also used) as raw material, which is processed into diacetate cellulose sheets through acetification, and then processed through dissolution, filtration, spinning, curling, drying and other production processes to form a regenerated cellulose fiber. This material has the advantages of non-toxic and tasteless, excellent filtration effect, good air permeability, good adsorption, good thermal stability, and quick drying. Therefore, it is widely used in the production of cigarette filters. It is also used in textiles, clothing, medical filter materials and other fields. Diacetate fiber tow can be divided into filament tow and staple fiber tow according to its morphology, textile tow, filtration tow and industrial tow according to its use, and antibacterial tow, flame retardant yarn, conductive tow, etc. according to functional modification.
As an important textile and filtration material, diacetate fiber tow has been widely used in many fields in recent years. Its production process is complex and technically demanding, but after continuous technological innovation and optimization, a relatively mature and stable production process has been formed. The diacetate fiber tow is mainly divided into the steps of raw material preparation, acetylation reaction, spinning process, post-processing process, quality control points, etc.
1. Raw material preparation
The raw materials mainly include high-purity cellulose (derived from wood pulp or cotton linters), acetic anhydride, acetic acid, catalysts (such as sulfuric acid), etc. The cellulose needs to be crushed and treated with alkali (to remove impurities such as lignin and hemicellulose) to obtain α-cellulose (purity>95%), and dried to control the water content (usually <5%) to avoid hydrolysis side reactions in the acetylation reaction.
2. Acetylation reaction
Cellulose and acetic anhydride react with esterification under the action of catalyst to generate diacetate cellulose ester. The reaction temperature is controlled at 40-50℃ (to avoid high temperature causing cellulose degradation); sulfuric acid (dosage 0.5-2%) is used as the catalyst, which needs to be precisely controlled to prevent excessive hydrolysis; at the same time, the degree of substitution is controlled between DS=2.2-2.7, which is adjusted by reaction time and the ratio of acetic anhydride to cellulose. After the reaction, the catalyst is neutralized, precipitated, washed, and dried to obtain cellulose diacetate sheets (substitution degree and molecular weight distribution need to be tested).
3. Spinning process
First, a solution needs to be prepared to dissolve cellulose diacetate in acetone (concentration 20-30%) to form a uniform spinning solution. Filtering and degassing are required to ensure the uniformity of the solution. The spinning methods are mainly divided into dry spinning (mainstream process) and wet spinning. In dry spinning, the spinning solution is extruded through a spinneret (aperture 50-100μm) and enters a high-temperature channel (80-120℃). Acetone evaporates, the fiber solidifies, and is stretched (3-5 times) to enhance orientation and strength. The advantage of this method is that the fiber surface is smooth and the strength is high, while the disadvantage is that the solvent recovery cost is high. In wet spinning, the spinning solution is squeezed into a water or alcohol coagulation bath, and the fiber is formed after the solvent diffuses. The advantage is that the solvent is easy to recover, while the disadvantage is that the fiber cross section is irregular and the strength is low.
4. Post-processing process
The post-processing process mainly includes three steps: stretching and heat setting, curling processing, and cutting and packaging. Among them, stretching and heat setting are secondary stretching (wet heat or dry heat) to improve crystallinity and optimize mechanical properties. Curling processing is mechanical or chemical curling to increase the cohesion between fibers, which is convenient for subsequent production of filter tips or textiles. Cutting and packaging are cut into specific lengths according to application requirements (such as cigarette filters commonly use 3.0-8.0 deniers and lengths of 38-40mm).
5. Key points of quality control
Esterification uniformity is ensured by titration or NMR detection. Its fiber performance indicators are fineness (denier), breaking strength (≥1.5 cN/dtex), and whiteness (＞85%). Residual solvents (acetone <500 ppm) and heavy metal content (in line with FDA standards). Its environmental protection indicators are solvent recovery rate (dry spinning requires ＞90%) and wastewater COD control (＜100 mg/L).
