1. Raw Material Pretreatment
• Polyester Chip Drying: Polyester has extremely low hygroscopicity, but excessive moisture content (>0.02%) can easily hydrolyze and break during spinning. Drying is performed in a vacuum drum dryer at 120-140°C for 4-6 hours to keep the moisture content below 50 ppm.
• Viscose Fiber Preparation: Viscose undergoes aging, yellowing, and dissolution to create a spinning solution (a viscous solution containing alkali cellulose). Filtration and degassing are then performed to remove impurities and bubbles to ensure spinnability. Viscose fiber is typically blended in the form of staple fibers (such as viscose staple fibers), with a length of 38-51 mm and a fineness of 1.67-2.22 dtex.
2. Spinning Process
Blended yarns are produced primarily through two methods:
• Ring Spinning: Polyester staple fiber and viscose staple fiber are mixed uniformly (using manual premixing or a disc blender). The blended yarn is then processed through opening, carding, drawing, roving, and spinning. This method achieves highly uniform fiber blending and is suitable for conventional fabrics, but with lower production efficiency.
• Siro Spinning/Compact Spinning Optimization: By feeding two rovings (one polyester yarn and one viscose yarn) and combining them for twisting, yarn strength and yarn uniformity are improved, while reducing hairiness, making it more suitable for high-end fabrics.
3. Weaving Process
Blended yarns can be woven or knitted depending on the target fabric type:
• Woven Fabrics: Woven fabrics utilize plain, twill, or satin weaves, with both the warp and weft yarns being a polyester/viscose blend (e.g., a 65/35 ratio). During weaving, attention should be paid to static electricity in the viscose fibers (which can be alleviated by waxing or increasing the humidity in the workshop to 60-70%).
• Knitted fabrics: Commonly produced on weft-knitted circular or flat knitting machines, such as jersey and rib, viscose fibers utilize their softness to enhance the wearer's fit, while polyester fibers ensure loop stability.
4. Key Finishing Steps
• Desizing and Scouring: If the fabric contains sizing (for woven fabrics), desizing enzymes or alkali agents are used to remove natural impurities and spinning auxiliaries. During this stage, the alkali concentration for viscose fibers should be controlled (≤5g/L) to avoid excessive damage.
• Softening and Setting: Padding softeners (such as silicones) are used to enhance the hand feel, while high-temperature setting (180-200°C for 20-30 seconds) stabilizes the polyester's dimensional stability and prevents excessive shrinkage of the viscose fiber (the heat shrinkage rate for viscose is approximately 5-8%, while that for polyester is only 0.4-0.8%).
• Dyeing process: Because polyester requires high temperature and high pressure disperse dyeing (around 130°C), while viscose fiber is suitable for reactive dyeing at room temperature and normal pressure (60-80°C), the two-bath method of "dying viscose first and then polyester" is usually adopted, or the process is optimized through the "one-bath two-step method" (dying viscose at low temperature first and then dyeing polyester at higher temperature).
