White Nonwovens are a type of textile material that is often used in applications where it will be exposed to water or liquid. Examples include diapers, sanitary napkins and adult incontinence products. In addition, these materials can be found in apparel interlinings, automotive and home furnishings and bedding construction markets.
A variety of different fibers are used in the production of White Nonwovens, including cellulosic, synthetic and fiberglass fibers. These materials can also be blended with other materials to form composites or fabrics that contain a combination of distinct properties.
Cellulosic Fibers
The primary function of cellulosic fibers in wet-laid nonwoven production is to provide the lubrication that may be missing from longer synthetic fibers in an aqueous medium. In addition, the hydrophobic character of cellulose can make it possible for the aqueous solution to surround the lignin and other oxygen-rich surfaces of the fibers on all sides. This can lead to the formation of hydrogen bonds between the aqueous medium and the surface of the fibers, thus helping them stick together.
However, cellulosic fibers can have other important roles in the production of wet-laid nonwoven mats as well. For example, the addition of wood pulp fibers during dispersion and forming can decrease the tendency for the entanglement of fibers due to crowding among the fibers in suspension.
It has also been reported that the addition of refined cellulosic pulp fibers to a matrix of long synthetic fibers can significantly reduce the entanglement problem as it can act as a kind of hydrophilic lubricant, helping to make it easier for the long synthetic fibers to be dispersed and formed into a mat.
Despite the beneficial role that these fibers can play, there are still some concerns about their compatibility with the aqueous medium. For example, the presence of lignin in some of the wood fibers can bind together with the aqueous solution and clog the pores or channels of the fibers. This can cause clumping or other defects.
In many cases, this defect can be eliminated by the application of a chemical dispersant that can break up the lignin and other contaminates in the aqueous solution. It can also be accomplished by introducing a special soluble additive to the aqueous solution that allows the lignin and other substances to separate more easily from the synthetic fibers in the matrix.
The second factor that can impact the dispersion of fibers in an aqueous environment is hydrodynamic shear. In a wet-laid nonwoven mat, the hydrodynamic shear that occurs during the forming process is especially important. The flow of water in the approach system and the headbox operations are very important in determining the degree to which the fibers in the mat will be dispersed or entangled as they move through the forming process.
In general, the length of fibers in wet-laid nonwoven systems is much shorter than in conventional papermaking processe. During the manufacturing process of wet-laid nonwovens, however, even a small number of over-length fibers can result in what are called "dumbbell" or "double-knub" defects. These defects consist of pairs of clumps of "regular" fibers that are joined at their ends by an over-length fiber.
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