How to optimize the spunlace process and performance control of PET/pulp composite spunlace nonwovens?

Effect of water pressure parameters in spunlace process on the strength of PET/pulp composite nonwoven fabrics

PET/pulp composite spunlace nonwoven fabrics are widely used in medical, sanitation, filtration and other fields due to their unique properties. As a key processing method, spunlace technology plays a decisive role in the performance of nonwoven fabrics, among which water pressure parameters are the core factors affecting the strength of nonwoven fabrics. In-depth exploration of the influence of water pressure parameters on the strength of PET/pulp composite nonwoven fabrics is of great significance for optimizing the spunlace process and improving product quality and performance.

1. Overview of PET/Pulp Composite Spunlace Nonwoven Fabric

(I) Characteristics of raw materials

PET fiber has the advantages of high strength, high modulus, chemical corrosion resistance and good thermal stability, providing basic strength support for non-woven fabrics. Pulp fiber gives non-woven fabrics good moisture absorption, softness and comfort, and can improve the entanglement effect between fibers. The combination of the two can make non-woven fabrics have multiple excellent properties.

(II) Principle of spunlace process

The spunlace process uses high-pressure water jets to impact the fiber web, causing the fibers to entangle and reinforce each other. In the production of PET/pulp composite non-woven fabrics, the water jet penetrates the fiber web composed of PET and pulp fibers. Under the direct impact of the water jet and the rebounding water flow, the fibers are displaced, interlaced, entangled and embraced, forming countless flexible entanglement points, thereby giving the non-woven fabric a certain strength.

2. The influence mechanism of water pressure parameters on the strength of non-woven fabrics

(I) Relationship between fiber entanglement degree and strength

When the water pressure is low, the water jet energy is limited and can only cause some fibers to move and initially entangle. The fibers are not tightly entangled, and the number of entanglement points formed is small and the strength is low, so the overall strength of the non-woven fabric is also low. As the water pressure increases, the water jet energy increases, more fibers are driven to participate in the entanglement, the degree of entanglement deepens, the number of entanglement points increases, and the strength is enhanced, and the strength of the non-woven fabric is significantly improved. However, when the water pressure is too high, it may cause excessive damage or even breakage of the fibers, which in turn weakens the bonding force between the fibers and reduces the strength of the non-woven fabric.

(II) Effect of fiber damage on strength

Excessive water pressure will cause excessive impact force on the fiber, resulting in wear on the fiber surface, damage to the internal structure, or even breakage. Although PET fiber has high strength, it will also be damaged under excessive water pressure. Its molecular chain may break or change orientation, affecting the fiber's own strength and load-bearing capacity. Pulp fiber is relatively fragile and more easily damaged under high water pressure. After the fiber is damaged, its effective load-bearing area in the non-woven fabric is reduced, and the force transmission mechanism between fibers is destroyed, thereby reducing the overall strength of the non-woven fabric.

3. Optimization strategy of water pressure parameters

(I) Adjust water pressure according to non-woven fabric quantity and production speed

Different quantitative PET/pulp composite non-woven fabrics require different water pressures. Non-woven fabrics with larger quantitative weights have thicker fiber layers, and require higher water pressure to allow the water jet to penetrate the fiber web and achieve effective entanglement; non-woven fabrics with smaller quantitative weights can appropriately reduce the water pressure. The production speed is also closely related to the water pressure. The faster the production speed, the shorter the fiber web stays in the spunlace area, and higher water pressure is required to complete the fiber entanglement in a short time to ensure the strength of the non-woven fabric. For example, for a 45g/m² synthetic leather base fabric, when the production speed is 8m/min, the water pressure can be set to a distribution from low to high and then down, such as 9MPa for the first pass (front side), 9.5MPa for the second pass (back side), 12MPa for the third pass (front side), 11.5MPa for the fourth pass (back side), and 11MPa for the fifth pass (back side). This can reduce energy consumption and production costs while ensuring product quality.

(II) Use multi-stage water spurting and reasonable water pressure distribution

The use of multi-stage spunlace can gradually entangle the fibers, avoiding excessive damage to the fibers caused by excessive water pressure in one spunlace. In the multi-stage spunlace process, the reasonable distribution of water pressure is crucial. Generally, the first few spunlaces use a lower water pressure to initially compact the fiber web and start the fiber entanglement; the middle few passes gradually increase the water pressure to strengthen the fiber entanglement; the last few passes appropriately reduce the water pressure to make the non-woven surface smoother and more delicate, while reducing fiber damage. For example, in a certain production process, the first and second stages are rotary drum spunlace with low water pressures of 60 Bar and 80 Bar respectively, which are used to initially reinforce the fiber web; the third stage is flat net spunlace, and the water pressure is increased to 120 Bar to further strengthen the fiber entanglement. In this way, the strength of the non-woven fabric can be effectively improved.

Water pressure parameters have a complex and important influence on the strength of PET/pulp composite nonwoven fabrics. Appropriate water pressure can promote effective fiber entanglement and improve the strength of nonwoven fabrics; too high or too low water pressure will have an adverse effect on the strength. In actual production, it is necessary to comprehensively consider factors such as nonwoven fabric quantity and production speed. By reasonably adjusting water pressure parameters, adopting multi-stage spunlace and optimizing water pressure distribution strategies, the strength of nonwoven fabrics can be precisely controlled, thereby producing high-quality PET/pulp composite spunlace nonwoven fabrics that meet different application requirements.

How to optimize the air permeability and filtration efficiency of PET/pulp composite spunlace nonwovens

PET/pulp composite spunlace nonwovens are widely used in many fields, such as air filtration, liquid filtration, medical and health care, etc. In these application scenarios, its air permeability and filtration efficiency are key performance indicators. Good air permeability ensures comfort and smoothness during use, while high filtration efficiency ensures effective interception of specific substances. However, there is often a certain contradiction between these two performances. When optimizing, it is necessary to comprehensively consider multiple factors and seek a balance between the two.

1. Factors affecting air permeability and filtration efficiency

(I) Fiber characteristics

The thickness, length and shape of PET fibers have a significant effect on the air permeability and filtration efficiency of non-woven fabrics. Finer PET fibers can form a denser fiber network, which can improve filtration efficiency, but will reduce air permeability to a certain extent; thicker fibers, on the contrary, can improve air permeability, but the filtration efficiency may decrease. In terms of fiber length, longer fibers are conducive to forming a more stable fiber structure, which has less effect on air permeability, and at the same time helps to improve filtration efficiency to a certain extent. The irregularity of fiber shape will also affect the distribution of gaps between fibers, thereby affecting air permeability and filtration efficiency. The addition of pulp fibers increases the diversity of fiber types, and its softness and hygroscopicity will change the microstructure of the fiber network, affect the passage path of air and fluid, and have a complex effect on air permeability and filtration efficiency.

(II) Fiber Arrangement and Entanglement

During the hydroentanglement process, the arrangement and degree of entanglement of fibers have a significant impact on the performance of nonwoven fabrics. The pore distribution formed by disordered fibers is relatively random, and the air permeability is relatively good, but the filtration efficiency may be limited to a certain extent, because large particles can pass through irregular pores more easily. Fibers with more orderly arrangements, especially those tightly arranged in certain directions, can improve filtration efficiency, especially the interception ability of substances in a specific particle size range, but will reduce air permeability. The degree of fiber entanglement is also crucial. A tightly entangled fiber network will reduce the size and number of pores and reduce air permeability, but can improve filtration efficiency; insufficient entanglement may lead to a decrease in filtration efficiency, while the improvement in air permeability is limited, and may even affect the overall performance due to structural instability.

(III) Non-woven fabric structural parameters

The quantitative (mass per unit area), thickness and porosity of non-woven fabrics are structural parameters that directly affect air permeability and filtration efficiency. An increase in quantitative usually makes the non-woven fabric thicker, increases the number of fiber layers, reduces the number of pores and reduces the pore size, which is beneficial to improving filtration efficiency, but seriously reduces air permeability. On the contrary, reducing the quantitative can increase air permeability, but the filtration efficiency may be difficult to meet the requirements. Thickness is closely related to quantitative. Thicker non-woven fabrics have increased resistance to air and fluids and reduced air permeability, but may have better filtering effects on particulate matter. Porosity is an important parameter that reflects the proportion of pore space inside non-woven fabrics. High porosity means good air permeability, but the filtration efficiency may be reduced; low porosity means high filtration efficiency and poor air permeability.

2. Methods for optimizing air permeability and filtration efficiency

(I) Fiber selection and ratio optimization

According to the specific application requirements, the specifications and performance parameters of PET fiber and pulp fiber are accurately selected. For example, in the field of air purification, which has extremely high requirements for filtration efficiency and relatively low requirements for air permeability, finer PET fiber can be selected and its proportion in the fiber ratio can be appropriately increased, and an appropriate amount of pulp fiber can be added to improve the feel and flexibility. For some applications that have high requirements for air permeability and are not particularly strict in filtration accuracy, such as ordinary ventilation filters, coarser PET fibers can be selected to increase the gaps between fibers, and the pulp fiber content can be reasonably controlled to ensure a certain filtration capacity. Through experiments and simulation calculations, the optimal ratio of PET fiber to pulp fiber in different application scenarios is determined to maximize air permeability while meeting filtration efficiency.

(II) Adjustment of spunlace process parameters

l Water pressure and number of spunlace heads : Water pressure is a key parameter of the spunlace process and has an important influence on fiber entanglement and non-woven fabric structure. Appropriately reducing the water pressure can reduce excessive fiber entanglement, maintain more and larger pores, and thus improve air permeability. However, too low water pressure will lead to insufficient fiber entanglement, affecting the strength and filtration efficiency of the non-woven fabric. Therefore, it is necessary to find a suitable low water pressure range on the basis of ensuring filtration efficiency and strength. Increasing the number of spunlace heads can make the fiber entanglement more uniform, optimize the pore structure to a certain extent, and help improve filtration efficiency. At the same time, by reasonably controlling the water pressure distribution of each spunlace head, air permeability can also be taken into account. For example, using multi-stage spunlace, the first few stages of spunlace heads use lower water pressure to initially entangle the fibers and retain a certain amount of pores, and the latter stages of spunlace heads appropriately increase the water pressure to further strengthen the fiber entanglement and improve the filtration efficiency without seriously affecting the air permeability.

l Spunlace method : Different spunlace methods have different effects on fiber arrangement and nonwoven fabric structure. The combination of drum spunlace and flat mesh spunlace has unique advantages. During the drum spunlace stage, the fiber web is adsorbed on the drum and moves on a curved surface. The side receiving the spunlace is relaxed, and the reverse side is compressed, which is conducive to water jet penetration and fiber entanglement. It can maintain good air permeability while ensuring a certain filtration efficiency; flat mesh spunlace can further arrange and reinforce the fibers and adjust the pore structure. By reasonably arranging the order and parameters of drum spunlace and flat mesh spunlace, the air permeability and filtration efficiency can be optimized.

(III) Post-processing process

l Heat treatment : Appropriate heat treatment of the PET/pulp composite non-woven fabric after spunlace can cause a certain degree of thermal shrinkage and crystallization of the PET fibers, changing the bonding mode and pore structure between the fibers. Under appropriate temperature and time conditions, heat treatment can make the fiber network more compact and orderly, improve the filtration efficiency, and at the same time, by controlling the degree of thermal shrinkage, avoid excessive shrinkage that leads to a significant decrease in air permeability. For example, heat treatment of non-woven fabrics at 180-200℃ for 5-10 minutes can optimize its air permeability and filtration efficiency to a certain extent.

l Chemical treatment : Chemical treatment methods, such as surface modification of non-woven fabrics or addition of functional additives, can improve their surface properties and pore characteristics. By introducing specific functional groups on the surface of non-woven fabrics through chemical grafting or coating treatment, the adsorption and filtration capabilities of certain substances can be improved without significantly affecting the air permeability. Adding an appropriate amount of lubricant or softener can improve the sliding properties between fibers, adjust the pore size and distribution, and have a positive effect on air permeability and filtration efficiency. However, during the chemical treatment process, it is necessary to pay attention to the selection of appropriate chemical reagents and treatment processes to avoid pollution to the environment and negative impact on the performance of non-woven fabrics.

Optimizing the air permeability and filtration efficiency of PET/pulp composite spunlace nonwovens is a complex and systematic project, which requires comprehensive consideration of multiple factors such as fiber characteristics, fiber arrangement and entanglement, and nonwoven fabric structural parameters. By rationally selecting fiber raw materials and ratios, finely adjusting spunlace process parameters, and properly using post-treatment processes, the balance between air permeability and filtration efficiency can be achieved to a certain extent. In actual production, these optimization methods should be flexibly applied according to different application requirements, combined with experimental results and production experience, to produce PET/pulp composite spunlace nonwoven products with excellent performance that meet market demand.