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Super Absorbent Nonwovens for Protective Apparels

By : technicaltextile.net
 
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The inner moisture barrier layer is a woven fabric, which protects the wearer from dampness and provides a soft, draping surface for good thermal transfer between the wearer and the clothing. The inner fabric is inherently resistant to water and wind. The outer layer is a fabric which allows free passage of water vapour and limited passage of water. Suitable thread count and thickness of the inner and outer layer fabrics provide the required properties. No coatings or surface finish treatments are used for desired results. Garment assembly needs to be dipped in water for 1-2 minutes prior to use, in order to reserve the cooling liquid in the absorbent core of super absorbent polymer. Then the excess water needs to be rinsed and the cooling vests are ready for use.


The great advantage of this type of cooling garment is that it is light, flexible and therefore portable. But this type of garment is not suitable for humid conditions as because the effectiveness of evaporative cooling is inversely proportional to ambient relative humidity. Another limitation of this technology is cooling takes place on the outer surface of the garment, not inner surface which is nearer to skin. If evaporation rate is low, it may act as a thermal insulator and increase the thermal discomfort.


Super absorbent fibres (SAFs)

Super absorbent polymers (SAP) are hydrophilic networks that can absorb and retain a large amount of water in an aqueous solution. Most commonly available SAP in the market is partially neutralised lightly cross-linked polyacrylic acid, due to its best performance verses cost ratio. Water molecules are held in the hydrogel by means of hydrogen bond formation. Cross-linking between the polymer chains form a three dimensional structure and prevent infinite swelling, i.e. dissolving. Most of the SAPs are now made from acrylic acid (AA), its salt and acrylamide (AM) via solution or inverse-suspension polymerisation techniques.


Super absorbent fibres (SAF) are produced by Technical Absorbents Ltd. are basically sodium salt cross linked polyacrylates. Raw materials used for manufacturing of SAF are acrylic acid (AA), methyl acrylate (MA) and special Acrylate/Methacrylate monomer (SMMA) in which the acrylic acid is partially neutralised to the sodium salt of acrylic acid (AA Na). SAFs are normally not considered to be the main structural component due to two reasons: (1) its strength in dry state is not as good as other fibres of same denier and (2) the fibre changes its structure to a gel form after absorption. SAFs can be blended with other fibres and nonwovens from the can be processed by any dry-laid technology followed by bonding by needle punching, or thermal bonding, or chemical bonding. SAFs should be processed at 45% RH to 75% Rh for best performance.


Experimental study


For designing the three layer evaporative cooling fabric assembly, the inner layer (which is nearer to skin) is made from some commercially available water repellent breathable fabric. Evaporative resistance of the inner layer fabric was measured as per ASTM F186812 standard on Sweating Guarded Hot Plate. The fabric has an evaporative resistance value of 12.329 Pa.m2/W. The outer layer fabric is woven from 150/96 denier multifilament yarns with varying warp thread density and weft thread density to achieve different air permeability values. Prior to weaving the 150/96 denier multifilament yarn was twisted at 316 twist per meter to avoid the problem of filamentation during weaving. Air permeability of the outer layer fabrics was measured as per ASTM D737 04(2012) standard on Textest FX 3300 instrument.

 

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