Nonwoven formation

The web formation in nonwoven production is a critical part of end-use product performance. Three basic methods used to form a web are dry laid wet laid and polymer laid (spunlaid and melt blown). Webs, other than spunlaid, have little strength in their unbonded form. The web must therefore be consolidated in some way. There are three basic types of bonding chemical thermal and mechanical. The nonwoven formation methods are summarized in Fig. 10.6. 

Lewandowski Z, Ziabicki A, Jarecki L. The nonwovens formation in the melt-blown process. Fibres Text East Eur 2007 15(50) 64-5. 

The following figure shows the market share of the nonwovens formation methods. 

Market share of nonwoven formation methods (per mass EDANA, 2010)... 

Nonwoven technologies that employ machinery and processing principles traditionally used to manufacture textile, paper, or extmded materials, when viewed collectively, form what may be termed the primary or basic nonwoven fabric manufacturing systems. These systems are or can be continuous processes. Common to each of these systems are four sequential phases fiber selection and preparation, web formation, bonding, and finishing. 

From a practical standpoint, the fiber or polymer must interact or process freely with the dynamics of web formation, and the resulting fiber network must be in register with the interlocking arrangement or media, in order for the fabric stmcture to transmit the maximum potential inherent in the properties of individual fibers. Ultimately, if a nonwoven fabric is to be totally effective and its properties fuUy utilized, it must be appropriately configured to meet its end use apptication or appropriately placed in the end use item in such a way that the performance of the product reflects the position and characteristics of individual fibers. 

Nonwoven bonding processes iatedock webs or layers of fibers, filaments, or yams by mechanical, chemical, or thermal means. The extent of bonding is a significant factor ia determining fabric strength, dexibiUty, porosity, density, loft, and thickness. Bonding is normally a sequential operation performed ia tandem with web formation, but it is also carried out as a separate and distinct operation. 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

One of the important aspects of the development of P-plastomers was the expectation that these materials were amenable to plastics processing such as fiber and film formation and yet would yield soft elastic fabrication. This combination was hitherto unknown [24]. The formation of nonwoven fabrics including spun-bond and melt-blown nonwoven fabrics as well as their laminated forms has been documented. Similarly, cast film operation to form elastic monolithic films or composite structures which are not only amenable to these processes, but also to a variety of postfabrication processes have been described. 

Web formation/spinning, for spunbonded nonwoven fabrics, 27 469-474 Web knitting, 27 507 Web layering... 

The islands-in-the-sea approach uses bico technology to extrude filaments that contain a multiplicity of small fibrils encased in a soluble matrix. After fiber processing and fabric formation, the matrix is dissolved away to leave behind the microfibers. Fibers with sub-micron diameters can be produced. The process is expensive, but luxurious fabrics and nonwoven materials such as Ultrasuede are made in this way. 

Nonwoven materials such as cellulosic fibers have never been successfully used in lithium batteries. This lack of interest is related to the hygroscopic nature of cellulosic papers and films, their tendency to degrade in contact with lithium metal, and their susceptibility to pinhole formation at thickness of less than 100 fjim. For future applications, such as electric vehicles and load leveling systems at electric power plants, cellulosic separators may find a place because of their stability at higher temperatures when compared to polyolefins. They may be laminated with polyolefin separators to provide high-temperature melt integrity. 

Polystyrene Dispersions. On account of their glass transition temperature T of ca. lOO C, polystyrene dispersions do not form films at room temperature. These rigid polymers can only be applied with means of heat drying (e.g., to stiffen fabrics and nonwovens). Film formation is not required in agents used to protect floor coverings and paper coatings (plastic pigments) in this case polystyrene is therefore applied in the form of a dispersion at room temperature. 

Nonwovens The textile and paper industries are based on the two oldest (wet and dry) processes. Manufacturers of nonwovens for plastics draw on both. With the wet, there are basically two types namely the Fourdrinier and cylinder machine types that have been modified. In addition, two basic types exist for the process formation of the web and application of the bonding agent or system where mechanical carding of fibers is used. The particular equipment and method of operation to be used, with their many modifications, is influenced by desired requirements such as mechanical properties, softness, surface condition, tenacity, etc. There are certain t) es of so-called nonwoven fabric that are directly formed from short or chopped fiber as well as continuous filaments. They are produced by loosely compressing together fibers, yarns, rovings, etc. with or without a scrim cloth carrier assembled by mechanical, chemical, thermal, or solvent methods. Products of this type include melted and spun-bonded fabrics. 

FIGURE 6.4 Images of electrospun fibers from reprocessed fibroin of B. mori to illustrate nanoscale diameter fibers with high surface area in nonwoven mat formats, compared to the micron scale diameter native fibers generated by this silkworm. Image on left (10 jtm scale bar), on right (2 xm scale bar). 

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