Hydro-entanglement Bonding Process for Production of Nonwoven Fabric (Part-2)
Eng Mohamed Elsharkawy
Dept. of Textile Engineering
Dept. of Textile Engineering
Principle of producing non-woven fabric:
Nonwovens are typically manufactured by putting small fibers together in the form of a sheet or web (similar to paper on a paper machine), and then binding them either mechanically (as in the case of felt, by interlocking them with serrated needles such that the inter-fiber friction results in a stronger fabric), with an adhesive, or thermally (by applying binder (in the form of powder, paste, or polymer melt) and melting the binder onto the web by increasing temperature) .
2.3. Hydro-entanglement process
Hydro-entanglement is a mechanical bonding process designed to produce nonwoven fabrics with texture and appearance that resemble woven and knitted fabrics.
In a typical hydro-entanglement process, a row or multiple rows of highly pressurized, fine, closely spaced water jets impinge on a fiber web which is supported by forming wires. Due to the impact of water jets, fibers from the surface are inserted into the fibrous web, and fibers are displaced and rotated around other fibers that surround them, resulting in fibers twisting and entangling around the neighboring fibers. The fabric produced is held together by the fiber-to-fiber friction [3, 4].
Fibers are carded in the carding machine and entangled in the hydro-entangling unit. After hydro-entanglement, the water in the fabrics is removed through the drying process. There is a finishing process if desired, and the fabrics are then wound on rolls for future processing.
2.4. Methodology of hydro-entanglement
Spun-lacing is a process of entangling a web of loose fibers on a porous belt or moving perforated or patterned screen to form a sheet structure by subjecting the fibers to multiple rows of fine high-pressure jets of water. Various steps are of importance in the hydro-entangling process [5, 6].
|Figure (2.3): Principle of hydro-entanglement|
- Precursor web formation
- Web entanglement
- Water circulation
- Web drying
This pressure is sufficient for most nonwoven fibers, although higher pressures are used in specialized applications. It has been argued that 10 rows of injectors (five from each side of the fabric) should achieve complete fabric bonding .
Injector hole diameters range from 100-120 µm and the holes are arranged in rows with 3-5 mm spacing, with one row containing 30-80 holes per 25 mm .
The impinging of the water jets on the web causes the entanglement of fibers. The jets exhaust most of the kinetic energy primarily in rearranging fibers within the web and, secondly, in rebounding against the substrates, dissipating energy to the fibers.
A vacuum within the roll removes used water from the product, preventing flooding of the product and reduction in the effectiveness of the jets to move the fibers and cause entanglement.
Usually, hydro-entanglement is applied on both sides in a step-wise manner. As described in the literature , the first entanglement roll acts on the first side a number of times in order to impart to the web the desired amount of bonding and strength.
The web then passes over a second entanglement roll in a reverse direction in order to treat and, thereby, consolidate the other side of the fabric. The hydro-entangled product is then passed through a dewatering device where excess water is removed and the fabric is dried.
|Figure (2.4): Description of process|
For that reason it is necessary to develop a new filtration system able to effectively supply clean water with this high throughput; otherwise, water jet holes become clogged. This system consists of three stages: chemical mixing and flocculation, dissolved air flotation and sand filtration . Spun-laced fabrics have led to a lot of speculation regarding their manufacture because most of the manufacturing process details are considered as proprietary .
2.5. Materials used in hydro-entanglement
As previously mentioned, hydro-entanglement could be carried out using dry-laid (carded or air-laid) or wet-laid webs as a precursor. Most commonly, precursors are mixtures of cellulose and man-made fibers (PET, nylon, acrylics, Kevlar, etc.
In addition, we can use very fine fibers produced from split table composite fibers to produce hydro-entangled substrates for synthetic suede leather products.
In general, cellulosic fibers are preferred for their high strength, pliability, plastic deformation resistance and water insolubility. Cellulosic fibers are hydrophilic, chemically stable and relatively colorless. Another advantage is that cellulose has an inherent bonding ability caused by a high content of hydroxyl groups, which attract water molecules. As the water evaporates from the fabric, the hydroxyl groups on fiber surface link together by hydrogen bonds .
Influence of cotton micronaire on fabric properties has been studied. Generally, low micronaire cotton is not recommended for hydro-entangled nonwovens because of higher number of neps and small bundles of entangled fibers, resulting in unsightly appearing fabric.
In spite of this, fabrics made with lower micronaire fiber show higher strength, probably caused by a higher number of fine fibers and greater surface area .
In addition, greige cotton has been used in spun-lacing technology. It has been shown that the absorbency rate increases with increasing hydro-entangling energy. This is the result of oil and wax removal from the fiber surface. These nonwovens can be subsequently bleached, which should raise the strength of the fabric .