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How to improve the interfacial bonding strength of composite spun fibers
source：www.kingcharmgroup.com | Release time：2026-07-22The overall approach is divided into five directions: raw material compatibility modification → melt rheological matching → optimization of spinning components and channels → spinning process regulation → post-treatment modification. The following are all industrial feasible solutions that are suitable for the chemical fiber filter media and non-woven fabric industry.
1、 Raw material system design (the most fundamental means)
1. Choose polymers with similar chemical structures to enhance thermodynamic compatibility
Priority combination for the same category: PET/low melting point PET, PP/PE; The compatibility is naturally superior to polar/non-polar systems such as PET/PA and PPS/PTFE.
Two phases with significant polarity differences (polyester/polyamide, PPS/PTFE) require the addition of a compatibilizer.
PET/PA6 system: adding ester amide graft compatibilizer;
PP/polyester system: maleic anhydride grafted PP (MAH-g-PP);
Compatibility agent function: Form a transition layer at the interface between the two phases, reduce interfacial tension, and prevent the formation of interfacial voids.
2. Control the end groups and moisture content of the two components to reduce interface defects
Polyester is strictly dried: moisture causes spinning hydrolysis, producing small molecules that migrate to the interface between the two phases to form an "isolation layer", greatly weakening the adhesion;
Avoid excessive oligomers, lubricants, and external migratory anti-static agents; Additives are prone to accumulate at the interface between the two phases, acting as release agents and directly leading to easy peeling.
3. Moderately regulate the crystallization behavior of the melt
The significant difference in crystallization rates between the two phases leads to the generation of huge internal stresses at the interface during the cooling process, inducing microcracks.
Case: When combining PET/low melting point PET, try to minimize the difference in crystallization speed between the two.
2、 Rheological property matching (most easily overlooked in industry)
The quality of interface bonding largely depends on the viscosity ratio of the two-phase melt inside the nozzle hole.
Experience interval: It is better to control the shear viscosity ratio of the two components between 0.5 and 2.0;
The consequences of significant differences in viscosity:
Components with low viscosity wrap around high viscosity components, generating vortices, tiny bubbles, and wrinkles at the interface, forming a large number of micro gaps; Subsequent stretching and heat treatment result in direct layering;
Adjustment methods:
Adjust the spinning temperature in each zone and change the viscosity of the melt;
Adjust the molecular weight (viscosity) appropriately;
Do not rely on significantly increasing extrusion speed to forcefully produce viscosity mismatch systems.
3、 Optimization of spinning components and channel structure
Ensure that the two components have sufficient and uniform contact, and smooth laminar flow before entering the nozzle micropores
Avoid severe disturbances and eddies after diversion; Turbulence can cause irregularities in the interface, trapping air and forming interface voids.
Surface smoothness of the flow channel: reduce local overheating and degradation caused by melt shear; Degradation product aggregation interface.
Reasonably allocate pressure balance between two components to prevent one phase from invading the other phase region and causing interface distortion.
Typical negative case: Poor design of island fiber components, twisted island phases in a strip shape, poor interface bonding, and extensive premature peeling during alkali treatment.
4、 Process parameter control on spinning line (directly applicable for mass production)
1. Box/spinneret temperature
Appropriately increasing the spinning temperature enhances the mobility of the melt molecular chain, promotes mutual diffusion of molecules at the interface between the two phases (thickening of the interfacial interpenetrating layer), and increases the bonding force;
Upper limit: If the temperature is too high, it will cause thermal degradation and instead generate a degraded interface of small molecules.
2. Cooling and blowing conditions
Avoid sudden cold! Rapid cooling freezes molecules before they can diffuse into each other, and the interface is only "physically bonded";
Optimization: Moderately increase wind temperature, decrease wind speed, slowly cool down, and prolong the diffusion time of interface molecules;
However, if the cooling is too slow, it is easy to merge and float, and it is necessary to find the balance point of the process window.
3. Spinning and stretching (pre orientation, post stretching)
Insufficient stretching: Insufficient contact pressure at the interface between the two phases;
Excessive stretching: The interface generates huge shear stress, causing microcracks to expand at the original interface, which in turn weakens the bonding force;
Strategy: Adopt gradient gentle stretching to synchronize the deformation of the two phases and reduce interfacial shear.
4. Volume ratio of two components
Under the same material system, the ratio will change the interface stress state.
For example, eccentric core fibers cause internal stress due to the difference in contraction between the two phases; Concentric structures have lower internal stress and are less prone to interface debonding.
5、 Interface chemical modification scheme
Option 1: Add graft compatibilizer (mainstream industrial solution)
Mixing a compatibilizer into one of the phases, the spinning process migrates to the interface between the two phases, forming a chemical bond connection.
Option 2: Surface functional group modification
Grafting modification of one of the polymers (introducing hydroxyl, anhydride, amino) to form hydrogen bonds and covalent bonds between the two phases.
Example: PET grafted with maleic anhydride reacts with the amino group at the PA end, forming a chemical bond at the interface.
Option 3: A small amount of the third component as the interface transition layer (laboratory/R&D)
Three layer composite structure: A phase | compatible transition layer | B phase, high equipment investment, less commonly used in ordinary two-component spinning.
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