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Why is it said that composite spun fibers have good elasticity

source：pypaly.cn  |  Release time：2025-05-28
     The good elasticity of composite spun fibers is closely related to their special fiber structure design, material combination characteristics, and processing technology. The following analysis is conducted from the perspectives of technical principles and practical applications:
1、 The structural advantages of composite spun fibers
     Composite spinning fibers are fibers formed by synchronously extruding two or more polymer melts or solutions with different properties through special spinning components (such as composite spinning nozzles), resulting in microstructures such as parallel, skin core, sea island, and orange petal shapes. This structural design endows it with a unique elastic mechanism:
1. Two component stress difference drives elasticity
     Principle: Two types of high polymers (such as high elastic components and rigid components) form a stress imbalance state in composite fibers. For example:
     Parallel structure: One side is a high elastic polymer (such as polyurethane PU, polyether ester PEE), and the other side is a rigid polymer (such as polyester PET, polyamide PA). When fibers are stretched by external forces, the rigid component restricts excessive elongation, while the elastic component stores energy; After the external force is released, the elastic component shrinks and drives the fibers to return to their original state.
     Leather core structure: The core layer is made of elastic material (such as spandex), and the outer layer is made of wrapping material (such as nylon). The cortex constrains excessive deformation of the core layer, while transmitting stress through interfacial adhesion, forming an elastic system similar to a "spring shell".
     Case: Nylon/spandex composite fibers (such as 80% nylon+20% spandex) are commonly used in sportswear, with a stretch recovery rate of over 90%, which is superior to single nylon fibers (about 85%).
2. Dynamic response mechanism of microstructure
     The interface region of composite fibers has non-uniform molecular chain arrangement, and during stretching, the molecular chains in the interface layer slip and orient, storing elastic properties; After unloading, the molecular chain quickly recovers under the action of entropy elasticity. For example:
     In polyester/polyether ester composite fibers, the flexible links (such as ether bonds - O -) of the polyether ester segments form a molecular network of "rigidity and flexibility" with the rigid benzene ring structure of the polyester. When stretched, the flexible segments stretch, while the rigid segments limit fracture. After unloading, the flexible segments curl and rebound.
2、 The synergistic effect of material combination
     Composite spun fibers balance elasticity, strength, and durability through the synergistic combination of elastic and supporting components
1. The core role of elastic components
     High elasticity polymers, such as spandex (PU), polyether ester (PEE), thermoplastic elastomer (TPE), etc., have molecular chains with high elongation at break (spandex elongation at break can reach 600% -800%) and low glass transition temperature (such as below -50 ℃), ensuring that the fibers are easily stretched and deformed at room temperature and store energy.
     Case: Using spandex as the core layer of composite fibers, even if the outer layer is made of rigid polyester, the overall elongation at break can still reach over 300%, far exceeding that of single polyester fibers (about 200%).
2. Strengthening effect of supporting components
     Rigid or semi-rigid polymers, such as polyester (PET), polyamide (PA), polypropylene (PP), etc., provide mechanical support to prevent excessive deformation of elastic components from causing damage. For example:
     In polyester/spandex composite fibers, the polyester skin layer restricts the "over stretching" of the spandex core layer, avoiding excessive molecular chain slip and causing elastic fatigue, resulting in a fiber recovery rate of over 85% after 500 cycles of stretching (pure spandex fibers have a recovery rate of about 75%).
     Functional additives: Some composite fibers introduce nano fillers (such as graphene, silica) or crosslinking agents to enhance interfacial bonding and further improve elastic recovery efficiency.
3、 Optimization of elasticity through processing technology
     The elastic performance of composite spun fibers is closely related to spinning process parameters and post-treatment techniques
1. Structural control during spinning stage
     Spinning speed and cooling conditions: High speed spinning (such as 3000-5000 m/min) can promote the rapid orientation of rigid components, forming a tight skin layer, while slow cooling keeps the elastic components in an amorphous state, improving overall flexibility.
     Composite ratio optimization: Adjusting the extrusion ratio of two components (such as the proportion of skin thickness in the skin core structure of 10% -30%) can balance the elasticity and strength of the fibers. For example, if the cortex is too thick, it will reduce elasticity, while if it is too thin, it will affect support.
2. Elastic activation of post-processing technology
     Heat setting treatment: Through high temperature (such as 180-220 ℃) treatment, the molecular chains of rigid components (such as polyester) are further oriented and crystallized, forming "physical cross-linking points", while the elastic components (such as polyether esters) remain in an amorphous or low crystalline state, thereby fixing the "memory shape" of the fibers and improving rebound efficiency.
     Stretching relaxation process: Pre stretching relaxation treatment is performed after fiber forming to fully stretch and store energy in the molecular chains of elastic components, while forming "elastic recovery anchor points" through the orientation structure of rigid components. For example, the initial elastic recovery rate of nylon/spandex composite fibers pre stretched by 300% can be increased from 78% to 89%.

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