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Nonwoven Material Sourcing - Nonwoven Polypropylene & More - Sourcebook
The web forming process used in the first step of nonwoven manufacturing can be categorized by three main web forming techniques – drylaid, spunmelt, and wetlaid.
Drylaid nonwovens are manufactured through processes that involve combining or intermingling fibers of various lengths and compositions through various methods (ex: mechanical) to create webs. There are two types of common processes used to produce drylaid webs: airlaying and carding. Airlaid is a web forming technique that utilizes air to transport and intermingle the fibers (typically very short fibers) onto a moving surface to create a web. Unlike carded webs, airlaid webs are always randomly laid. Although airlaid webs typically possess a lower density than carded webs, they contain greater softness and flexibility. Carding is another drylaid web forming technique that includes bales of fibers being blended and formed into a web by a carding machine. A carding machine contains a drum, or multiple drums, with a rough surface that is textured with short wires or teeth to cause the loose fibers to intermingle and eventually form a web.
Spunmelt nonwovens webs are webs that are created through processes that involve extruding thermoplastic polymers. There are two types of spunmelt processes: spunlaid (spunbond), and meltblown. During the spunlaid (spunbond) process, filaments are extruded and exposed to a stream of air, intermingling the fibers and forming a web which is then deposited onto a moving surface typically a belt or drum. The meltblown process is similar to the spunlaid (spunbond) process but the airstream utilized in the meltblown process is of greater velocity than the spunlaid (spunbond) process. Therefore, the filaments are scattered to a greater degree than the filaments during the spunlaid (spunbond) process. Other common configurations of spunlaid nonwovens include different combinations of spunbond and meltblown webs. Spunbond/meltblown/spundbond nonwovens, known as a SMS nonwovens, are made by combining these three layers into a single web.
Nonwovens can also be produced through the wetlaid technique, a manufacturing method that utilizes a fluid to transport fibers onto a surface. The surface is porous, allowing the fibers to be isolated from the fluid and a web can be created that will later be bonded using thermal, chemical, or mechanical processes. Typically, wetlaid nonwovens are composed of wood pulp or other natural fibers in combination with synthetic fibers or fiberglass. This manufacturing technique is born out of the Technical Paper industry which uses a similar method.
After nonwoven webs are created, they are then bonded through thermal, chemical, and mechanical means to form a final nonwoven material. This is a critical step in the nonwoven manufacturing process which has as much, and sometimes more, impact on the functionality of the material as the web forming process does.
Thermal bonding is a technique that employs a heat or ultrasonic process applied to a web which activates a heat-sensitive material. An example of thermal bonding is calendering, a process in which the material is fed through the nip of two calender rollers, heated to exceed the melting point temperature of the binder fibers so that bonding sites are formed.
Chemical bonding techniques for nonwovens involve chemical binders (ex: adhesive resins and solvents). There are a variety of methods to apply the chemical agents to the web depending on whether the binder is applied consistently (impregnating, coating, spraying) or inconsistently (print bonding).
There are several methods commonly used to mechanically bond nonwovens, including needlepunching and hydroentaglement. Needlepunching is a mechanical binding process during which an assortment of barbed needles is moved vertically through a web of fibers. The barbs on the needles catches on the fibers, orients, and interlocks the fibers, creating a fabric of entangled fibers. Hydroentanglement creates a nonwoven fabric,(known as a spunlace fabric, by utilizing high-pressure, fine water jets that barrage a web of fibers that are eventually tangled, forming a fabric.
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