China processes more than half of the world's textile fibers, and with rising per capita fiber consumption, the volume of waste textiles generated each year is enormous. Promoting their recycling is not only an important way to supplement textile raw material supply, but also a key part of reducing pollution and carbon emissions and building a green, low-carbon circular economy. However, due to the lack of systematic technology for recycled fiber recovery, problems such as scattered, disordered, slow, and poor production have long existed, causing severe fiber damage and poor yarn quality, which restricts the industry's scaled development.

Recycled Fiber Varieties and Trends

Waste textiles mainly come from three sources: waste silk and scraps from production, discarded clothing and home textiles after consumption, and waste plastics such as polyester bottles. Recycling methods include mechanical, physical, chemical, and energy recovery methods. At present, the mechanical method is the most widely used—processing waste fabrics into short fibers or yarns through opening, cutting, and other processes. The main fibers separated by the mechanical method are cotton and polyester, and some blended fibers can also be processed.

Recycled fibers are mainly used to produce nonwovens, low-count rotor-spun yarns (5-10 English counts), and low-count ring-spun yarns with lower quality requirements. Their applications are expanding from traditional glove yarn and car-wiping cloth to workwear fabric, canvas, denim, and even apparel fabrics. This trend will force the continuous upgrading of recycled fiber spinning systems.

Pain Points of Systematic Carding

The typical recycling process for waste textiles is: sorting → decomposition → pre-opening → fiber carding → spinning. Because the industry started late, early stages lacked specialized equipment, technical standards, and process specifications, and mostly borrowed card clothing and card bar opening equipment for simple processing, which could only spin low-end yarns. Although recycling technology has improved in recent years, the core opening and decomposition stage is still at a preliminary level and faces multiple problems: low-end equipment and low safety factors; harsh production environments and unstable quality; low recovery efficiency and severe fiber damage, leading to subsequent yarn breakage and wrapping around the cylinder and carding roller; short card clothing life and frequent bent teeth and needles, resulting in high maintenance investment; and recycled fibers have short length and high short-fiber content, leading to poor spinnability.

Opening and Decomposition: Card Clothing Configuration and Challenges

The role of opening and decomposition equipment is to use card needles or card bars to break fabric pieces and scraps into smaller fabric pieces or fiber bundles, creating conditions for subsequent single-fiber separation. Main equipment includes L-bar openers, needle-board openers, carding machines, and modified cotton cards. In terms of card clothing configuration, the number of opening points must be set according to fabric structure, and opening card bar or card needle beaters should be selected.

Opening uses two methods: beating and tearing. Beating uses free-state striking and oscillation to loosen fiber blocks, while tearing uses held splitting to reduce large pieces into smaller ones. Because the carding force on fabric pieces is extremely large, opening equipment mostly uses card needles and large-size card bars, and rollers are often made of wood or aluminum. However, in actual operation, when the main cylinder or roller speed exceeds 800 r/min, card clothing damage becomes severe, with bent needles, twisted teeth, and skewed teeth. If the raw material contains large amounts of impurities, foreign fibers, spandex filaments, or filaments, it is even more likely to cause winding and wrapping, increasing short fibers and neps, lowering recovery efficiency, shortening card clothing replacement cycles, and making it difficult to improve production efficiency.

Solutions and Development Directions

In response to the above problems, the industry is exploring several improvement paths: increasing the hardness of L-shaped card bar clothing to extend service life and simplify replacement; promoting card needle rollers because they cause less fiber damage and transfer well, but needle implantation firmness must be strengthened to reduce replacement costs; improving card needle boards by increasing angles and tooth density to enhance fiber control and holding and avoid insufficient opening. In the long run, unified machinery, unified special parts, and unified processes are an inevitable trend for waste textile opening and decomposition and the foundation for scaled production. At the same time, standardizing opening and carding card clothing models and extending service life have become industry consensus.

For the waste textile recycling industry, technical breakthroughs in the opening and decomposition stage directly determine the quality and spinnability of recycled fibers. Only by solving chronic problems such as card clothing damage and high short-fiber content can recycled fibers penetrate from low-end filling materials into higher value-added fields such as workwear, denim, and apparel fabrics, truly opening the path for high-value recycling of waste textiles.

Source: Technology | Typical Problems and Solutions in Systematic Carding of Recycled Fibers from Waste Textiles (Part 1) · Originally published 2023-04-10