The spatial arrangement of fibers in wet non-woven fabric is the core factor determining product performance, and its orientation state (MD/CD strength ratio) and distribution uniformity directly affect key indicators such as mechanical strength, breathability, and filtration efficiency of the material. With the continuous improvement of material performance requirements in high-end application fields, precise control of fiber orientation and distribution has become an important breakthrough for upgrading wet non-woven fabric technology. This article systematically reviews the technological progress in this field in recent years, from mechanism analysis to technological innovation, comprehensively presenting the development trajectory and future direction of fiber control technology.
The core influencing mechanism of fiber orientation and distribution
The wet forming process is essentially a complex mechanical process in which fibers undergo dispersion migration sedimentation consolidation in an aqueous medium, and the final spatial shape of the fibers is determined by the synergistic effect of multiple force fields. Compared with dry networking (MD: CD=9-15:1), wet process can achieve lower anisotropy (MD: CD=3-6: 1) through water flow regulation, but this regulation ability faces severe challenges in low weight products.
The fluid dynamics effect is the primary determinant of fiber orientation. During the transportation process from the headbox to the forming net, the fibers are subjected to a combination of shear flow and tensile flow: the longitudinal velocity gradient will cause the fibers to be oriented in the machine direction (MD), while the turbulence intensity affects the degree of random distribution of the fibers. Research has shown that when the slurry flow rate changes by 0.1m/s, it not only causes a 4% deviation in the weight of the finished product, but also increases the MD direction strength by 12%. This sensitivity is particularly significant in low weight products below 20g/m ². Changzhou Kangjie found during the development of reverse osmosis membrane substrates that the longitudinal quantitative fluctuation of traditional long web paper machines increased from ± 5% to ± 12% when the weight was below 30g/m ², directly reflecting the important influence of flow field stability on fiber distribution.
The inherent characteristics of fibers have a regulatory effect on orientation behavior. The practice of Henan Science and Technology High School has shown that when the fiber diameter decreases from 10 μ m to 1 μ m, the surface energy increases sharply, leading to a 300% increase in agglomeration probability. This microscale interaction will counteract the control effect of the macroscopic flow field. The structural complexity of composite fibers further increases the difficulty of control. The orange petal type two-component fibers produced by Dalian Hualun have a fiber opening rate fluctuation of ± 20% at low concentrations, resulting in a deviation of air permeability exceeding 15% and forming visible “cloud spots” defects.
The secondary regulation of fixed network technology cannot be ignored. The high-pressure water flow during the water jet reinforcement process not only achieves fiber entanglement, but also changes the initial orientation state. The gradient pressure strategy of “low-pressure pre piercing+gradual pressurization” (first pass 80-100 bar, subsequent 120-150 bar) can improve the longitudinal and transverse strength ratio of the 20g/m ² product from 3:1 to 1.5:1, demonstrating the ability of the subsequent process to correct fiber arrangement.
Multidimensional Control Technology Matrix and Innovation Breakthrough
In recent years, fiber orientation and distribution control technology has shown a collaborative development trend of “equipment precision material functionalization regulation intelligence”, forming a multi technology path parallel solution.
1. Flow field engineering and equipment innovation
As the “first gateway” for fiber orientation control, the design innovation of the headbox continues to promote the improvement of control accuracy. After six years of research and development, Changzhou Kangjie has developed a “stepped slurry distributor” that controls the flow field non-uniformity within 3% through multi-stage rectification units, achieving precise control of 10-15 μ m pore size and breaking the monopoly of foreign countries in the high-end membrane substrate field. This design effectively balances the relationship between longitudinal flow velocity and lateral diffusion by optimizing the number of slurry channels and the arrangement of rectifying elements, providing a more uniform deposition environment for fibers.
The upgrade of molding equipment is equally crucial. The Laifen 5 production line introduced by Xinjiang Kaiwo Technology adopts Industry 4.0 technology. Through high-precision forming net drive system and online tension control, it can stably produce ultra-low weight products of 8g/m ² with a quantitative fluctuation of ≤ 2%. The system achieves a control accuracy of ± 0.1m/min for the speed of the forming mesh, significantly reducing fiber distribution deviation caused by mesh vibration.
2. Field assisted orientation control technology
Electric field regulation technology provides a new dimension for fiber orientation control. The electrically assisted coaxial wet spinning technology developed by Chen Xiaoming’s team at Xi’an Jiaotong University achieves radial orientation of boron nitride nanosheets (BNNSs) and in-situ polarization of polyvinylidene fluoride (PVDF) by applying a radial electric field. This technical approach can be extended to the wet networking process, utilizing the surface charge characteristics of fibers and guiding fiber orientation through customized electrode layout, especially suitable for charged fiber systems such as nanocellulose.
The research conducted by the Institute of Physics, Chinese Academy of Sciences has revealed a universal mechanism of electric field driven self-assembly: positively charged biomolecules migrate towards the cathode under the action of electric field force, and form a oriented nanofiber network induced by pH gradient. Applying this principle to wet networking can achieve ordered arrangement of fibers in local areas by regulating the electric field strength (usually 1-5kV/m) and action time, providing the possibility for the preparation of functional partition materials. Comparative experiments show that electric field assisted technology can increase fiber orientation by more than 40% without affecting fiber dispersion uniformity.
3. Intelligent monitoring and closed-loop control
The application of AI visual inspection technology has achieved real-time monitoring of fiber distribution. The fiber diameter reporting system developed by Hangzhou Tanwei Intelligent is equipped with a hyperspectral imaging module, which can complete the 0.1 μ m level accuracy detection of 240 fibers within 3 minutes and generate a diameter distribution thermal map. The system is linked with production equipment to form a closed-loop control: when fiber aggregation or orientation abnormalities are detected, the pressure of the slurry box or the speed parameters of the forming net are automatically adjusted, resulting in an increase of more than 15 percentage points in the first-class product rate. After applying this technology, a certain enterprise reduced the yarn breakage rate by 45%, fully demonstrating the benefits of intelligent control.
Breakthroughs have been made in online orientation monitoring technology. The polarization observation system based on Olympus CX33 microscope can evaluate the fiber orientation angle distribution in real time by analyzing the direction of fiber birefringence fringes. Integrating the optical system into the production line, coupled with professional analysis plugins such as FibrilTool, can quantitatively characterize the fiber ratio in the MD/CD direction, providing data support for process optimization. In actual production, this online monitoring can maintain the accuracy of orientation control within ± 3%.
Performance regulation and industrial value realization
The precise control of fiber orientation and distribution has brought performance leaps and application expansion to wet non-woven fabrics, demonstrating unique advantages in multiple high-end fields.
In the field of medical protection, by optimizing the radial distribution of fibers, the lining of 10-15g/m ² ultra-low weight surgical gowns can maintain bacterial barrier performance while reducing wearing weight by 30% and improving breathability by 25%. This performance improvement stems from the gradient distribution design of fibers in the thickness direction: the surface layer uses high orientation fibers to enhance barrier properties, and the inner layer uses randomly distributed fibers to improve moisture absorption, achieving precise functional matching.
High end filter materials achieve a balance between efficiency and resistance through fiber orientation regulation. Henan KeGao uses 0.08dtex ultra-fine polyester sea island fiber to produce 8g/m ² products. By controlling the directional arrangement of fibers along the airflow direction, the filtration efficiency reaches N95 level while reducing the air permeability resistance by 30%. This design utilizes the linear channel characteristics of directional fibers to reduce airflow losses, making it particularly suitable for applications such as air purifiers and ventilator filters.
The electronic wiping field has strict requirements for the uniformity of fiber distribution. The 8g/m ² ultra-fine fiber wiping cloth ensures a dense sampling accuracy of 10000 points per square centimeter through AI visual detection, ensuring effective removal of 0.1 μ m level pollutants. After applying this technology, a certain electronic material enterprise reduced the product defect rate from 8% to 1.5%, significantly improving the production quality of precision electronic components.
Cost benefit analysis shows that although orientation control technology increases equipment investment (about 15-20%), comprehensive cost reduction can be achieved through material savings and performance improvements. Changzhou Kangjie’s reverse osmosis membrane substrate reduces customer procurement costs by 40% after achieving import substitution through precise control of fiber distribution, while reducing unit energy consumption by 15% through large-scale production. This virtuous cycle of “precision scale” is precisely where the industrial value of directional control technology lies.
Future Trends and Challenges
The fiber orientation control technology of wet non-woven fabric is developing towards multi field collaboration, biomimetic design, and green regulation. Multi physics coupling control will become a research hotspot, and by integrating various external fields such as electric, magnetic, and sound fields, it is expected to achieve more complex fiber spatial arrangements. The biomimetic design that simulates the hierarchical structure of spider silk can achieve higher strength at a weight of less than 10g/m ². This structure combines directionally arranged nanofiber bundles with randomly distributed connecting fibers, balancing strength and toughness.
Green regulation technology will receive more attention. Biobased solvent systems can improve the dispersibility of ultrafine fibers and reduce the use of chemical dispersants; Based on the self-assembly characteristics of cellulose nanocrystals, it is expected to develop spontaneous orientation technology without external field assistance. These technologies comply with the requirements of the “dual carbon” policy and represent the direction of sustainable development.
The main challenges currently faced include the balance between orientation control and uniformity in low weight products, differentiated regulation of multi-component fiber systems, and high cost of online detection technology. To address these issues, it is necessary to develop more accurate flow field simulation software (such as combining CFD-DEM coupling algorithm), more economical multi parameter detection systems, and more adaptable adaptive control algorithms in the future.
The advancement of fiber orientation and distribution control technology has promoted the evolution of wet non-woven fabrics from “random stacking” to “precise construction”. From Changzhou Kangjie’s adherence to over 400 experiments in 6 years to the innovation of electric field control technology at Xi’an Jiaotong University, industry practitioners are constantly expanding the boundaries of material design. With the improvement of intelligence and the integration of interdisciplinary technologies, wet non-woven fabrics will achieve a qualitative leap from “macroscopic uniformity” to “microscopic order”, providing stronger material support for high-end manufacturing.
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