Nonwoven fabric

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Nonwoven fabric is a fabric-like material made from long fibers, bonded together by chemical, mechanical, heat or solvent treatment. The term is used in the textile manufacturing industry to denote fabrics, such as felt, which are neither woven nor knitted. Nonwoven materials typically lack strength unless densified or reinforced by a backing. In recent years, nonwovens have become an alternative to polyurethane foam.

Applications

Nonwoven fabrics are broadly defined as sheet or web structures bonded together by entangling fiber or filaments (and by perforating films) mechanically, thermally or chemically. They are flat or tufted porous sheets that are made directly from separate fibres, molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibres to yarn. Typically, a certain percentage of recycled fabrics and oil-based materials are used in nonwoven fabrics. The percentage of recycled fabrics vary based upon the strength of material needed for the specific use. In addition, some nonwoven fabrics can be recycled after use, given the proper treatment and facilities. For this reason, some consider nonwovens a more ecological fabric for certain applications, especially in fields and industries where disposable or single use products are important, such as hospitals, schools, nursing homes and luxury accommodations.

Nonwoven fabrics are engineered fabrics that may be a limited life, single-use fabric or a very durable fabric. Nonwoven fabrics provide specific functions such as absorbency, liquid repellence, resilience, stretch, softness, strength, flame retardancy, washability, cushioning, thermal insulation, acoustic insulation, filtration, use as a bacterial barrier and sterility. These properties are often combined to create fabrics suited for specific jobs, while achieving a good balance between product use-life and cost. They can mimic the appearance, texture and strength of a woven fabric and can be as bulky as the thickest paddings. In combination with other materials they provide a spectrum of products with diverse properties, and are used alone or as components of apparel, home furnishings, health care, engineering, industrial and consumer goods.

Non-woven materials are used in numerous applications, including:


Medical

  • isolation gowns
  • surgical gowns
  • surgical drapes and covers
  • surgical masks
  • surgical scrub suits
  • caps
  • medical packaging: porosity allows gas sterilization

Filters

  • gasoline, oil and air - including HEPA filtration
  • water, coffee, tea bags
  • pharmaceutical industry
  • mineral processing
  • liquid cartridge and bag filters
  • vacuum bags
  • allergen membranes or laminates with non woven layers

Geotextiles

  • soil stabilizers and roadway underlayment
  • foundation stabilizers
  • erosion control
  • canals construction
  • drainage systems
  • geomembrane protection
  • frost protection
  • agriculture mulch
  • pond and canal water barriers
  • sand infiltration barrier for drainage tile
  • landfill liners[1]

Other

  • diaperstock, feminine hygiene, and other absorbent materials
  • carpet backing, primary and secondary
  • composites
    • marine sail laminates
    • tablecover laminates
    • chopped strand mat
  • backing/stabilizer for machine embroidery
  • packaging where porosity is needed
  • insulation (fiberglass batting)
  • acoustic insulation for appliances, automotive components, and wall-paneling
  • pillows, cushions, mattress cores, and upholstery padding
  • batting in quilts or comforters
  • consumer and medical face masks
  • mailing envelopes
  • tarps, tenting and transportation (lumber, steel) wrapping
  • disposable clothing (foot coverings, coveralls)
  • weather resistant house wrap
  • cleanroom wipes

Manufacturing processes

Nonwovens are typically manufactured by putting small fibres 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-fibre 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).

Staple nonwovens

Staple nonwovens are made in 4 steps. Fibres are first spun, cut to a few centimetres length, and put into bales. The staple fibres are then blended, "opened" in a multistep process, dispersed on a conveyor belt, and spread in a uniform web by a wetlaid, airlaid, or carding/crosslapping process. Wetlaid operations typically use 1/4" to 3/4" long fibres, but sometimes longer if the fibre is stiff or thick. Airlaid processing generally uses 0.5 to 4.0" fibres. Carding operations typically use ~1.5" long fibres. Rayon used to be a common fibre in nonwovens, now greatly replaced by PET and PP. Fibreglass is wetlaid into mats for use in roofing and shingles. Synthetic fibre blends are wetlaid along with cellulose for single-use fabrics. Staple nonwovens are bonded either thermally or by using resin. Bonding can be throughout the web by resin saturation or overall thermal bonding or in a distinct pattern via resin printing or thermal spot bonding. Conforming with staple fibres usually refers to a combination with meltblown, often used in high-end textile insulations. Melt Blown non wovens are produced by extruding melted polymer fibres through a spin net or die consisting of up to 40 holes per inch to form long thin fibres which are stretched and cooled by passing hot air over the fibres as they fall from the die.The resultant web is collected into rolls and subsequently converted to finished products. The extremely fine fibres (typically polypropylene) differ from other extrusions, particularly spun bond, in that they have low intrinsic strength but much smaller size offering key properties. Often melt blown is added to spun bond to form SM or SMS webs, which are strong and offer the intrinsic benefits of fine fibres such as fine filtration, low pressure drop as used in face masks or filters and physical benefits such as acoustic insulation as used in dishwashers. One of the largest users of SM and SMS materials is the disposable diaper and feminine care industry[2]

Spunlaid nonwovens

Spunlaid nonwovens are made in one continuous process. Fibres are spun and then directly dispersed into a web by deflectors or can be directed with air streams. This technique leads to faster belt speeds, and cheaper costs. Several variants of this concept are available, such as the REICOFIL machinery.[3] PP spunbonds run faster and at lower temperatures than PET spunbonds, mostly due to the difference in melting points

Spunbond has been combined with meltblown nonwovens, conforming them into a layered product called SMS (spun-melt-spun). Meltblown nonwovens have extremely fine fibre diameters but are not strong fabrics. SMS fabrics, made completely from PP are water-repellent and fine enough to serve as disposable fabrics. Meltblown is often used as filter media, being able to capture very fine particles. Spunlaid is bonded by either resin or thermally. Regarding the bonding of Spunlaid, Rieter [4] has launched a new generation of nonwovens called Spunjet. In fact, Spunjet is the bonding of the Spunlaid filaments thanks to the hydroentanglement.

Air-laid paper

Main article: air-laid paper

Air-laid paper is a textile-like material categorized as a nonwoven fabric made from wood pulp.[5] Unlike the normal papermaking process, air-laid paper does not use water as the carrying medium for the fibre. Fibres are carried and formed to the structure of paper by air.

Other

Nonwovens can also start with films and fibrillate, serrate or vacuum-form them with patterned holes. Fiberglass nonwovens are of two basic types. Wet laid mat or "glass tissue" use wet-chopped, heavy denier fibers in the 6 to 20 micrometre diameter range. Flame attenuated mats or "batts" use discontinuous fine denier fibres in the 0.1 to 6 range. The latter is similar, though run at much higher temperatures, to meltblown thermoplastic nonwovens. Wet laid mat is almost always wet resin bonded with a curtain coater, while batts are usually spray bonded with wet or dry resin. An unusual process produces polyethylene fibrils in a Freon-like fluid, forming them into a paper-like product and then calendering them to create Tyvek.

Bonding

Both staple and spunlaid nonwovens would have no mechanical resistance in and of themselves, without the bonding step. Several methods can be used:

  • thermal bonding
    • Use of a heat sealer
    • using a large oven for curing
    • calendering through heated rollers (called spunbond when combined with spunlaid webs), calenders can be smooth faced for an overall bond or patterned for a softer, more tear resistant bond
  • hydro-entanglement: mechanical intertwining of fibers by water jets (called spunlace)[6]
  • ultrasonic pattern bonding: used in high-loft or fabric insulation/quilts/bedding
  • needlepunching/needlefelting: mechanical intertwining of fibres by needles
  • chemical bonding (wetlaid process): use of binders (such as latex emulsion or solution polymers) to chemically join the fibers. A more expensive route uses binder fibres or powders that soften and melt to hold other non-melting fibres together
    • one type of cotton staple nonwoven is treated with sodium hydroxide to shrink bond the mat, the caustic causes the cellulose-based fibres to curl and shrink around one another as the bonding technique
    • one unusual polyamide(Cerex) is self-bonded with gas-phase acid
  • meltblown: fibre is bonded as air attenuated fibers intertangle with themselves during simultaneous fiber and web formation.

Disposability

The industry has attempted to define "flushability". They encourage voluntary testing of flushability by producers. They also encourage clear marking of non-flushable products as "No Flush" (rather than fine print on the bottom of products) including creating a "No Flush" logo.[7]

The wastewater industry is encouraging a standard definition (rather than one which varies with each producer) of flushability, including dispersibility, and third-party assessment or verification, such as by NSF International. They believe that products should be both safe for both septic and sewer systems (flushable and dispersible, respectively).[8] Orange County Sanitation District has created a campaign, "What 2 Flush", which recommends flushing only the "three P’s—pee, poop and [toilet] paper".[9]

See also

References

  1. ↑ http://www.gseworld.com/applications/landfill-liners.html
  2. ↑ The Diaper Industry Source The use of Non wovens in the hygiene industry (Richer Investment)
  3. ↑ manufactured by Reifenhäuser REICOFIL GmbH & Co. KG (Germany)
  4. ↑ Rieter Nonwovens Systems
  5. ↑ Paulapuro, Hannu (2000). "4". Paper and Board grades. Papermaking Science and Technology 18. Finland: Fapet Oy. pp. 95–98. ISBN 952-5216-18-7. 
  6. ↑ Xiang, P.; Kuznetsov, A. V.; Seyam, A. M. (2008). "A Porous Medium Model of the Hydro entanglement Process". Journal of Porous Media 11 (1): 35–49. doi:10.1615/JPorMedia.v11.i1.30. 
  7. ↑ "Flushability", INDA.org.
  8. ↑ "Strangled by disposables", PWmag.com.
  9. ↑ "What 2 Flush: Know what should go down the drain that is sewer safe", OCSD.com.

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