Wet-laid nonwovens

Wet-laid nonwovens Wetox process Wet-strength additives... 

AH these early inflation processes (41) were difficult to control, and after World War 11 they were neglected until the 1960s. Companies in Japan, the United States, and Europe then started to develop inflated—collapsed rayons (Eig. 5b) for speciaUty papers (42) and wet-laid nonwovens. 

In 1992, as much as two-thkds of all spunlace fabrics were used in medical products other appHcations included wipes, industrial apparel, intedinings, absorbent components, filtration, and coating. Medical product appHcations also accounted for about one-thkd of all wet-laid nonwovens other appHcations included tea bags, meat casings, filter media, battery separators, and wipes. Most bonded-pulp fabrics were used as wipes or absorbent components. 

Nonwovens are widely utilized as separators for several types of batteries. Lightweight, wet laid nonwovens made from cellulose, poly (vinyl alcohol), and other fibers have achieved considerable success as separators for popular primary alkaline cells of various sizes. The key nonwoven attributes include consistently uniform basis weight, thickness, porosity and resistance to degradation by electrolytes. Nonwovens are also successfully employed as separators in NiCd s. 

Paper-based processes Synthetic staple fibers as well as wood pulp libers are suspended in water and then formed into a paper-like nonwoven web on a perforated surface. The web is then bonded by interlocking the fibers by mechanical or chemical bonding techniques. Fabrics made by this type of process are known as wet-laid nonwovens. Such products can be made at very high speeds and are very uniform, but the process is capital-intensive. 

The ISO 9092 definition is as follows A manufactured sheet, web or batt of directionally or randomly orientated fibres, bonded by friction, and/or cohesion and/or adhesion, excluding paper and products which are woven, knitted, tufted, stitch-bonded incorporating binding yams or filaments, or felted by wet-milling, whether or not additionally needled. The fibres may be of natural or manufactured origin. They may be staple or continuous filaments or be formed in situ. Various notes are included in this definition including clarification on the difference between a wet-laid nonwoven and a wet-laid paper—in essence, the difference depends on the presence of a substantial proportion of libers. 

JP Patent 2003,268,691, Wet-laid nonwoven fabrics comprising biodegradable fibers consisting of biodegradable polymers derived from sonrces other than wood and petroleum , Nakahara, Makoto, 2003. 

A number of wet-laid nonwovens are made with glass fibres or ceramic fibres. Examples include Crane s Craneglas and Cranemat . These are used as heat- and flame-resistant surfacing veils, achieving demanding standards, such as UL 94. Such composites can have thermal stability up to 1200°C. 

Hydroentanglement of wet-laid sheets enables the production of wet-laid nonwovens without binders. The process creates strong and bulky products. FuUy biodegradable nonwovens can be also produced without chemical additives or thermal bonding. 

Wood pulp fibres are frequently less than 1 pm in fibre size and dominate wet-laid nonwoven filter media they are able to provide higher filtrafion efficiency and are environmentally fiiendly. Synthetic fibres (eg, polyolefin, polyester, and polycarbonate (PC) fibres) could work as electret fibres to provide additional electrostatic filtration mechanism, and also could be made binder-fitee, thermobond nonwoven fabrics if they are made Ifom thermoplastic polymers. 

Melt blown, spunbond, air-through thermobond, and wet-laid nonwoven fabrics made from PP and polyethylene fibres are also widely used as a support layer in membrane filtrations and in filtration media where chemical resistance is cmcial they also have the potential to be recycled to make it environmentally fiiendly, but such possibility needs to be explored. They, as well as co-polyester fibres, are frequently used as binders in thermobond nonwovens for filtration applications. 

Fibrillated cellulosic fibres, such as LyoceU fibres, contain fibres having much smaller diameters and are thus promising resources of cellulosic micro- and nanoscale fibres for air, water, and hydraulic filtrations. They can be blended with nonfibril-lated synthetic staple fibres in a wet-laid nonwoven fabric to form high-efficiency and high-capacity glass fibre-free filtration media. ... 

Wet-laid nonwoven fabrics are produced from wet-laid webs, which are formed via filtering an aqueous suspension of fibres onto a screen conveyor belt or perforated drum, and they are then bonded by one or more techniques to provide fabric integrity. Wet-laid nonwoven technology is originated from papermaking process, but the resultant wet-laid nonwovens are different from paper. A wet-laid material is defined as nonwoven rather than paper if (1) more than 50% by mass of its fibrous content is... 

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