Technical consultation on specifications and quality control of netting materials and mosquito nets
during all steps of preparation and handling of samples, avoiding tension on the sample in any direction. The meeting noted that this laboratory test is not necessarily comparable to any of the many different procedures used under field conditions. However it does provide a standardized comparison between products and the limits proposed are based on data from products which have proven satisfactory in the field.
The meeting noted that acceptable dimensional stability criteria for netting may not be appropriate for nets, if there is a large (but otherwise within specification) difference between warp and weft shrinkage/stretching, because unacceptable puckering or wrinkling of the seams could occur.
a. Information should be collected on the occurrence of unacceptable puckering or wrinkling of seams observed in practice, together with the corresponding test measurements of dimensional stability, to support a future review of the limits for this characteristic and of the possible need to include dimensional stability of the net itself in the specification.
3.5 Durability and storage stability
The durability of nets and netting materials is a very important charac- teristic for the user but there is a lack of simple tests which measure, or predict, resistance to the “wear and tear” arising from normal use. The most important criterion of durability is the retention of bursting strength for an acceptable time in normal storage and use. In principle, the bursting strength of all fabrics can be expected to decline over time, due to polymer degradation, and the rate of decline can be expected to be increased by handling, washing, drying, exposure to heat and light, etc. The meeting agreed that a test of “wear and tear” resistance is required and that it should measure how well bursting strength is maintained.
In the absence of an appropriate test of “wear and tear” resistance, the meeting considered the need for a test of storage stability. A well-established test of storage stability (CIPAC method MT 46.3∗) is currently referenced in WHO specifications for LLINs and includes a requirement for maintenance of bursting strength after accelerated storage. The method has not been applied to untreated nets/netting but it simulates storage equivalent to approximately 2 years storage at room temperature. The usual test involves a
∗ Accelerated storage procedure. Pages 128–130. CIPAC Handbook, volume J. Analysis of technical and formulated pesticides. Collaborative International Pesticides Analytical Council, Harpenden, UK. 2000.