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Sampling issues for cotton fiber quality measurements. Part 2 : Impact on cotton testing instruments results

Gourlot J.P., Gérardeaux E., Frydrych R., Gawrysiak G., Francalanci P., Gozé E., Dréan J.Y., Liu R.. 2005. In : Proceedings of the Beltwide Cotton Conference 2005, New Orleans, USA, 4-7/01/05. Memphis : NCCA, p. 2328-2341. Beltwide Cotton Conferences, 2005-01-04/2005-01-07, New Orleans (Etats-Unis).

The cut cotton sample used for the commercial evaluation of cotton bales is taken at a single point from one or two sides of the bale. It should be verified that this sample is sufficient to perform quality measurement hat is adequately precise to avoid litigation. On one hand, the variability of the H2SD stickiness measurement within a bale has been addressed by Gozé (2002) and Frydrych (2004) who showed that stickiness was variable within a bale. On the other hand, the studies about the within-bale variability of the other fibre characteristics measurements, while available for US cotton, are very few in a small farmers context. In another growing country where cotton is grown by small property holders, we achieved a study on technology of farmer's cotton fibre. Our study compared cotton technology of cotton farmer's samples, in four villages located in contrasted ecological conditions. Results show a broad range of quality between localities and between farmers. As in many producing countries, seed-cotton fed in the ginning plant comes from successive modules that may originate from different localities and farmers without taking into account the quality consequences; a strong variability of fibre characteristics inside a bale could result. When preparing a bale, different layers of cotton are superimposed by a tramper before pressing. Our hypothesis is that within-bale variability is concentrated between the layers (vertically) whereas within-layer variability (horizontal) is lower. If such is the case, specially designed samples taken from the entire side of the bale, i.e. in the form of a superficial strip involving all the layers, should be more representative than a simple cut cotton sample that involves only few of the layers. We tested this hypothesis by means of a sampling study involving 24 bales from 4 different origins. A three-dimensional matrix of 8x2x2 was used to study the variability in all 3 directions of the bales. Also, a comparison between the conventional cut cotton sample and the superficial vertical strips determined which method, in practice, gave the best results. The H2SD results clearly showed in the first part of this study (Frydrych, 2004) that the new sampling method is interesting to reduce the H2SD measurements variability. This paper reports the results about other fibre technological measurements on the same samples.

Mots-clés : coton; fibre végétale; fibre textile; qualité; mesure

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