In scenarios such as reinforced layers in geotechnical engineering, automotive seat belt substrates, and high-end filter materials, polyester spunbond nonwoven fabrics not only require high strength that cannot be pulled, but also low elongation that cannot be loosened – this mechanical performance requirement of “high strength and low elongation” has become the core criterion for distinguishing ordinary spunbond fabrics from high-end products. To achieve this performance breakthrough, it is not simply a matter of upgrading raw materials, but rather a collaborative innovation of the entire process of spinning, networking, and reinforcement. It is also a key track for Chinese enterprises to break through the technological barriers of Europe and America and seize the high-end market.
Performance core: Definition and application requirements of “high strength and low elongation”
High strength and low elongation “usually refers to the longitudinal tensile strength of polyester spunbond non-woven fabric being ≥ 35N/5cm, the elongation at break being ≤ 25% (the elongation of conventional spunbond fabric is mostly 30% -40%), and the” creep rate “(continuous deformation degree) under long-term stress needs to be controlled within 5%. The core value of this performance combination lies in:
Geotechnical field: Reinforced spunbond fabric needs to withstand soil pressure without tensile deformation to avoid roadbed settlement;
In the automotive field, the seat belt substrate needs to withstand the impact force instantly without breaking, while ensuring the restraint effect with low elongation;
Filtering field: High pressure filter bags need to maintain stable shape under fluid impact to prevent filter material wrinkling and failure.
A test conducted by a certain geotechnical material enterprise showed that when ordinary spunbond fabric is used for roadbed reinforcement, the creep rate reaches 12% after one year, leading to pavement cracking; However, the creep rate of high-strength and low elongation products is only 3%, and the service life is extended to more than 5 years.
Raw material modification: laying the foundation for mechanical properties from the source
Raw materials are the first hurdle of “high strength and low elongation”. By regulating the molecular structure and optimizing the formula of polyester chips, the mechanical potential of fibers can be fundamentally enhanced.
1. Molecular chain structure optimization: long chain+high crystallinity
Using high molecular weight polyester chips (intrinsic viscosity ≥ 0.72dL/g, conventional chips are 0.64dL/g), longer molecular chains can form a tighter entangled network and are less prone to breakage when stretched. At the same time, through solid-phase thickening technology: the slices are vacuum treated at 120-140 ℃ for 4-6 hours to further polymerize the molecular chains, increasing the crystallinity from the conventional 35% to over 45% – the tight arrangement of the crystalline zone directly enhances the fiber’s tensile strength.
Experimental data from a certain enterprise: After using high molecular weight thickening slices, the longitudinal strength of spunbond fabric increased by 20%, and the elongation at break decreased by 8%.
2. Co polymerization modification: the “molecular skeleton” of rigid functional groups
Adding isophthalic acid (IPA) or dimethyl terephthalate (DMT) into polyester chips for copolymerization, introducing rigid aromatic ring groups to support the molecular chain skeleton like “steel bars”, limiting segment movement, and reducing elongation. For example, after adding 5% -8% IPA copolymer, the elastic modulus (rigidity index) of the fiber increases by 15%, and the elongation at break can be controlled within 22%.
3. Nanofiller composite: balance between reinforcement and toughening
Mixing nano calcium carbonate or carbon nanotubes (with an addition of 0.5% -2%) with polyester melt through a twin-screw extruder, the nanoparticles are uniformly dispersed inside the fibers, which can prevent crack propagation (improve strength) through the “pinning effect” and avoid embrittlement caused by excessive rigidity. A study shows that adding 1% carbon nanotubes to spunbond fabric can increase tensile strength by 25%, while reducing elongation by only 3%, solving the industry pain point of “high strength must be brittle”.
Spinning process control: “precise control technique” for fiber forming
In the spunbond process, the stretching and cooling of the melt directly determine the morphology and mechanical properties of the fibers, which is the core link to achieve “high strength and low elongation”.
1. High magnification stretching: making molecular chains stand in line
The airflow stretching ratio of traditional spunbond is usually 3-5 times, while for high-strength and low elongation products, it needs to be increased to 6-8 times. By optimizing the pressure gradient of the stretching air duct (inlet pressure of 0.3 MPa, outlet pressure of 0.05 MPa), high-speed airflow is used to strongly stretch the fine flow of the melt, forcing the molecular chains to be oriented along the fiber axis – the orientation degree is increased from the conventional 40% to over 60%, just like combing messy cotton threads into tight ropes, greatly improving strength. At the same time, due to the difficulty of molecular chains sliding, the elongation rate naturally decreases.
Misconception to avoid: The higher the stretching ratio, the better. Exceeding 8 times can easily lead to fiber breakage, forming “fuzz” and reducing the strength of the fabric surface. A certain enterprise uses “gradient drawing” (first 3 times pre drawing, then 5 times main drawing) to ensure orientation and reduce wire breakage rate to below 0.5%.
2. Ring blowing cooling: a uniformly formed “temperature code”
Adopting a ring blowing cooling system instead of traditional side blowing: the ring nozzle sprays cooling air (wind speed 0.8-1.2m/s, temperature 20-25 ℃) from 360 ° towards the fibers to evenly cool them radially, avoiding the asymmetric structure of “one side cold hard, one side soft tough” caused by side blowing. Uniform cooling can make fiber crystallization more regular, increase tensile strength by 10%, and reduce the fluctuation range of fracture elongation from ± 5% to ± 2%, ensuring consistency in fabric performance.
3. Optimization of spinneret: fine denier and hole design
Using a high-density spinning plate (with an increase in the number of holes from 600 to 1200), the fiber fineness spun decreased from 2.5dtex to 1.2dtex (fine denier). Fine fibers have a larger specific surface area, resulting in tighter entanglement between fibers after forming a web. Stress dispersion is more uniform during stretching, and the strength is increased by 15%. At the same time, irregular hole spray plates (such as trilobites and crosses) are used, with non-circular fiber cross-sections to increase friction between fibers, further suppress tensile deformation, and reduce elongation by another 3% -5%.
Mesh formation and reinforcement process: “Strength aggregation” of fabric structure
The laying method and reinforcement process after fiber formation determine the overall stress structure of non-woven fabric, which is the key to converting the strength of single fibers into the strength of the fabric surface.
1. Cross laying network: breaking the “one-way dependence”
The traditional parallel laid spunbond fabric has a “strong longitudinal strength and weak transverse strength” (longitudinal to transverse strength ratio of 3:1), while cross laid fabric (stacking fiber webs at 30-45 ° competition layers) can reduce the longitudinal to transverse strength ratio to 1.2:1. At the same time, through the mutual constraint of fiber intersections, the transverse shrinkage during stretching is reduced, and the elongation at break is reduced by 8% -10%. After a certain automotive spunbond fabric enterprise adopted cross laid mesh, the lateral strength of the product increased from 20N/5cm to 32N/5cm, meeting the bi-directional stress requirements of the seat belt substrate.
2. Hot rolling reinforcement: precise control of “bonding strength”
The core of hot-rolled reinforcement is to balance the “bond strength” and “fiber integrity”:
Temperature control: Adopting a hot rolling temperature of 165-175 ℃ (usually 150-160 ℃) to moderately melt the surface of the fibers, forming strong bonding points and avoiding “insufficient bonding force” caused by low temperature;
Pressure control: The line pressure is increased to 30-40N/mm (usually 20-25N/mm), but through “point bonding” rollers (bonding point area accounts for 20% -25%), the proportion of fibers crushed is reduced, ensuring the strength of the fibers themselves;
Speed matching: The difference between the hot rolling roll speed and the web forming speed should be controlled within 5% to avoid stretching and deformation of the fabric surface.
After optimization, the tensile strength of hot-rolled reinforced spunbond fabric increased by 18%, and the elongation at break was controlled within 23%.
3. Acupuncture+Hot Rolling Composite Reinforcement: “Dual Insurance” for Extreme Scenarios
For extreme stress scenarios such as geotechnical reinforcement and mining filtration, a composite process of “needle punched pre reinforcement+hot rolling final reinforcement” is adopted: needle punched fibers are first entangled with each other through mechanical hooks (longitudinal and transverse strength ratio of 1.5:1), and then hot rolled to form adhesive points, so that the fabric surface has both the high strength of needle punched fabric and the low elongation of hot-rolled fabric. After a certain mining filter cloth enterprise adopted this process, the tensile strength of the product reached 45N/5cm, the elongation at break was only 18%, and the service life was twice that of a single reinforced product.
Post organizing technique: “secondary upgrade” of performance
By processing the finished fabric through post-processing techniques, the “high strength low elongation” performance can be further optimized, while also endowing it with additional functions.
1. Heat setting: eliminate internal stress, stabilize dimensions
Heat setting treatment of spunbond fabric at 120-140 ℃ (maintained under tension for 30-60 seconds) can eliminate internal stresses generated during spinning and web formation, make molecular chain arrangement more stable, and reduce “shrinkage deformation” during subsequent use. After heat setting, the dry heat shrinkage rate of the product decreased from 3% to below 1%, the creep rate decreased by 40%, and the long-term stress stability was significantly improved.
2. Cross linking treatment: constructing a “three-dimensional network”
Epoxy crosslinking agents (such as ethylene glycol diglycidyl ether) are used to impregnate and bake spunbond fabrics (baking temperature 150 ℃, time 2 minutes). The crosslinking agent forms chemical bridge bonds between fiber molecular chains, constructing a three-dimensional network structure to restrict molecular chain sliding. After processing, the tensile strength of spunbond fabric increased by 10%, and the elongation at break decreased by another 2% -3%. At the same time, its washing resistance and aging resistance were greatly enhanced.
3. Coating Composite: Strong Combination of Performance Overlays
Coating the surface of spunbond fabric with polyurethane (PU) elastomer or polyamide (PA) resin to form a composite structure of “spunbond fabric substrate+coating”: the substrate provides high strength, and the coating limits the substrate elongation through its own rigidity. For example, after coating with a 10 μ m thick PA coating, the elongation at break of spunbond fabric decreases from 25% to 20%, while the waterproof and wear resistance are improved, making it suitable for outdoor tent substrates.
Technical bottlenecks and breakthrough directions: from “meeting standards” to “leading the way”
The current “high strength low elongation” process still faces two major bottlenecks: one is how to avoid embrittlement (elongation ≤ 20%) when the strength is increased to 40N/5cm or more; The second is how to reduce the production cost of high-end processes (such as equipment investment for nanocomposites and cross laying nets that is 30% higher than conventional processes). The breakthrough paths being explored by the industry include:
Application of bio based polyester: blending polylactic acid (PLA) with polyester, utilizing the high crystallinity of PLA to enhance strength, while reducing brittleness through modification;
Intelligent process control: Introducing AI vision system to monitor fiber fineness and fabric uniformity in real time, automatically adjust stretching and hot rolling parameters, and reduce scrap rate;
Equipment localization substitution: Chinese companies have developed domestically produced cross laying machines and twin-screw blending extruders, reducing costs by 40% compared to imported equipment and promoting the popularization of high-end processes.
Industrial value: the key lever for high-end transformation
The breakthrough in the “high-strength low elongation” process not only meets the urgent needs of high-end fields such as geotechnical engineering, automotive, and filtration, but also frees Chinese polyester spunbond nonwoven fabrics from the label of “low-end production capacity”. In 2024, the average export price of high-strength and low stretch spunbond fabric from China will reach 2.8 US dollars per square meter, which is 2.3 times that of ordinary spunbond fabric. The export volume will account for 35% of the global high-end market, breaking the monopoly of Germany’s Kodebao and the United States’ DuPont. A certain enterprise has become a core supplier of Tesla seat belt substrates with its independently developed “nanocomposite+cross laid mesh” process, resulting in a 50% increase in annual sales.
The optimization path of “high strength and low elongation” from precise control of raw material molecules to collaborative innovation of the entire process is essentially a microcosm of the transformation of polyester spunbond nonwoven fabric from “quantity expansion” to “quality improvement”. When Chinese enterprises can produce millions of tons of ordinary spunbond fabric and break through high-end performance processes, they can truly grasp the “value discourse power” of the global non-woven fabric industry.
Dongguan Liansheng Non woven Technology Co., Ltd. was established in May 2020. It is a large-scale non-woven fabric production enterprise integrating research and development, production, and sales. It can produce various colors of PP spunbond non-woven fabrics with a width of less than 3.2 meters from 9 grams to 300 grams.
Post time: Sep-10-2025