Wetlaid

Wetlaid is a papermaking and nonwoven manufacturing process in which cellulose fibers and other furnish are dispersed in water to form a slurry. The slurry is deposited onto a moving forming surface and the water is drained away, leaving a continuous sheet that is subsequently pressed and dried. Unlike airlaid webs, which are formed from dry fibers transported by air, wetlaid relies on water to carry and align fibers during formation.

In practice, fibers are refined to adjust drainage and bonding characteristics. The headbox releases a uniform stream of slurry onto a forming wire or belt; drainage and suction remove most of the water, and the wet sheet is transferred through a press section and into a dryer to remove remaining moisture and set the sheet. The process can produce traditional papers as well as specialty materials, with control over basis weight, porosity, and surface properties.

Materials used in wetlaid include wood pulps (kraft, thermomechanical pulp), recycled fibers, and a range of mineral fillers and binders. The method supports diverse products such as writing, printing, tissue, and packaging papers, as well as filtration papers and battery or insulation papers. Wetlaid nonwoven webs are also made for filtration media and medical or industrial textiles; these webs may be further strengthened by hydroentangling, chemical bonding, or thermal bonding.

Advantages of wetlaid include the ability to use long fibers and fillers to tailor strength and porosity, and the formation of uniform sheets. Limitations involve high water usage, energy requirements for drying, and equipment and process complexity. The method is widely used in traditional papermaking and in specialty nonwovens and filtration media.