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Updated WHO specifications for netting materials and mosquito nets - page 14 / 34

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Technical consultation on specifications and quality control of netting materials and mosquito nets

4. OTHER PHYSICAL CHARACTERISTICS OF NETTING MATERIAL FOR MOSQUITO NETS

4.1 Yarn composition

The choice of yarn is usually related to economic or comfort considera- tions, and should not be part of the WHO specifications. However, if nets are to be treated in the field, before purchasing nets made of a new type of polymer or fibre type, evidence should be obtained on the uptake of insecticide formulation diluted in water during dipping, and the retention of active ingredient thereafter.

4.2 Fabrication method

Evidence for the suitability of untreated or conventionally treated nets is currently only available for polyester warp-knitted1 nets, which constitute most of the current market for institutional buyers. Warp-knitting makes the fabric "non-running", after minor damage, and this fabrication procedure has therefore been used extensively for both polyester and polyethylene nets.

Research requirements for non-warp-knitted fabrics:

  • a.

    Develop a simple standard test for resistance to shifting of the yarn (i.e., holes cannot be pulled out of shape and size).

  • b.

    Develop a simple standard test for elasticity (i.e., after stretching, the material quickly regains original size).

1 The warp, or chain-loom, machine, generally flatbed, builds vertical chains, or wales, each having a separate yarn. The wales are tied together by zigzagging the yarns from needle to needle in the basic tricot or milanese stitches, or variants of these. A warp-knit fabric is run-resistant but less elastic than weft- knitted fabric. Raschel knitting is one type of warp knitting. In weft knitting, which includes hand knitting, the fabric is constructed in horizontal courses with one continuous yarn. From http://www.bartleby.com/65/kn/knitting.html (accessed 8 December 2005).

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