Thermally bonded nonwoven polymers

Coated and laminated textiles usually consist of a textile substrate, which will typically be a woven, knitted or nonwoven fabric, combined with a thin, flexible fdm composed of a natural or synthetic polymeric substance. A coated fabric is one in which the textile substrate has a polymer film applied directly to one or both surfaces as a viscous liquid in a solvent or water, the thickness of which is controlled by application via a blade or similar aperture. A transfer coated fabric is an intermediate product in which a thermoplastic film is first prepared on a release paper prior to thermally bonding to the textile substrate. A laminated fabric usually consists of one or more textile substrates that are combined with a pre-prepared polymer film or membrane by adhesives or heat and pressure (Hall, 2000). 

Wang, X.Y., Gong, R.H., 2006a. Thermally bonded nonwoven filters composed of bicomponent PP/PET fibre I. Statistical approach for minimizing the pore size. J. Appl. Polym. Sci. 101 (4), 2689-2699. 

Wang, X.Y., Gong, R.H., Dong, Z., Porat, I., 2006. Frictional properties of thermally bonded 3D nonwoven fabrics prepared from polypropylene/polyester bi-component staple fiber. Polym. Eng. Sci. 46 (7), 853-863. 

Meltblowing is a fast process of producing microfibres and nanofibres. Granular thermoplastic polymers are melted and extruded through a die, attenuated by heated, high-velocity air streams (typically at the same temperature as the molten polymer), and spun into the fibres. The fibres are then deposited on to a collector in a random manner and form a nonwoven web. The latent heat of the fibres is sufficient to enable thermal bonding. A schematic representation of the meltblowing process is shown in Fig. 4.3. 

As the new century began, we saw new beginnings in spunbond processes and products. New techniques are being developed to improve uniformity and barrier properties of spunbond fabrics to allow spunbond to compete successfully with carded thermal bonded nonwovens. Fabrics from new polymers and polymer combinations are poised to enter the market. Tactile as well as tensile properties are being improved to the point where even apparel applications may be considered as a future market (Anon., 2011). Several of these trends are described in the following paragraphs. 

A nonwoven fabric is a textile structure made from fibers, without a yam being first made knitted and woven fabrics, require yams. A nonwoven fabric normally comprises a network of fibers or continuous filament yams strengthened by mechanical, chemical, or thermally interlocking processes. Examples are bonding with hinders such as latex polymers, needling, hydroentanglement, and stitchbonding. 

Nonwoven fabrics are flat, porous sheets or web structures that are made directly from separate fibers or from molten plastics or from plastic films by entangling fibers or filaments mechanically, thermally or chemically. Nonwovens can be produced from both natural and synthetic fibers or directly from polymers by a variety of techniques that involve web formation and bonding. Different polymers/fibers are more suited for one process than the other. All of the different techniques available for web formation and bonding are discussed in sufficient detail. 

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. 

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