Stickiness, Seed-coat Fragments: measurements and consequences. Gourlot Jean-Paul, Frydrych Richard, Bachelier Bruno Cirad, Montpellier, France 1 - Introduction Cotton fibers contain various impurities such as pieces of leaves, stems, grass or seed-coat. They may also be contaminated by insect honeydew. Although it is easy to remove the leaves, stem and grass, seed-coat fragments and sticky particles are difficult to extract. These two contaminants remain in the cotton up to and during the spinning process where they cause production and quality losses. They have now become major contaminants in cotton. Since the spinners are penalized, they become more demanding with regard to cotton cleanliness. Today, these new requirements concern both producers and ginners. 2 - Sticky cottons: various solutions to counter this contamination from the field to the mill The stickiness of cottons in the spinning process is primarily due to honeydew produced by aphids and white flies whose honeyed excretions fall onto the fibers as soon as the bolls open (Figure 1). The negative consequences appear during spinning as production losses caused by sticky deposits on the machines, leading to web, sliver and yarn breaks. Yarn quality is also affected by sticky neps (Figure 2). Moreover, these stinging-sucking insects cause production losses by attacking the cotton plants early in the growing season. Productivity losses are also noted during ginning. During the last decades, to evaluate stickiness in cotton fibers, measurement tools were developed. They can be used to counter stickiness within two approaches. 2.1 - Existing methods to measure stickiness The knowledge of the stickiness level of a cotton allows a management of the corresponding bales, at once at the gin level, at the marketing level and in the spinning mill. Different measuring techniques have been developed such as: - Simple chemical method: these methods are measuring the actual global sugar content which is not always very well correlated with stickiness. - Complex chemical tests: HPLC, Chromatography methods are able to distinguish individual sugars in order to quantify them in the fibers. These methods are efficient but remain long and costly. - Mechanical and thermo-mechanical tests such as the mini-card test, the Stickiness Cotton Thermodetector (SCT, Cirad), the High Speed Stickiness Detector (H2SD, Cirad), the Fiber Contamination Tester (FCT, Lintronics), the Fiber Quality Tester (FQT, Lintronics), the Quickspin method (ITV-Denkendorf) and the Stickiness Tester (USDA Stoneville). Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 1
To reduce stickiness in spinning mills, it is recommended to identify the sticky bales. Quantifying the stickiness means that: - the sticky part of the production in the producing zones can be identified and the nonsticky part sold without discount; - stickiness results can be used to adapt field techniques to improve their efficiency; - spinners can manage their supplies and processing conditions. 2.2 - First approach : Counter stickiness in the cotton fields Agronomists, breeders and entomologists have proposed various technical solutions and advises to growers to reduce this contamination in the field such as: - Choice of favorable sowing dates and of appropriate spacing between cottons rows ; - Use of new varieties with determined growth cycle and low leaf area ; - reasoned use of supplementary chemical treatments (from an infestation threshold) to reduce insect resistance; - manual or mechanical topping of the cotton plants at the end of their life cycle, or application of defoliants, and early cotton harvest. The use of these various technical solutions, alone or combined, may bring improvements to partially counter stickiness at the field level. However, the stickiness problem remains. This is the reason for which other techniques have been studied on the downstream side in a parallel manner. 2.3 - Second approach : Counter stickiness in the transformation stages As sticky fiber still access to the spinning mill, researchers and manufacturers designed technical solutions to limit the impact of stickiness on the productivity of the spinning mills and the quality of the yarns. The most often used solutions are: - The mixes of bales coming from various origins so that stickiest cottons are diluted among the overall mass of fibers, taking into account that this dilution will decrease the overall stickiness of the lay-down. The CFC/ICAC 11 project (Gourlot and Frydrych, 2001) highlighted this method as an efficient solution to reduce the impact of stickiness at the spinning mill. - As stickiness is mainly due to the combination of individual sugars, and as these sugars can melt more or less according to fiber water content, reducing the relative humidity of the surrounding air in the spinning rooms is also an efficient solution. - Textile machine manufacturers created new equipments that are less sensitive to stickiness than former generation. - Other solutions, that are not listed here, can also be applied as the washing of the fibers, the introduction of fungus or bacteria in the bales to induce a sugar degradation. Other technical ways still are under industrial evaluation or only are available at the prototype level (research). They mainly intend to reduce the impact of stickiness by application of heat (Rieter, 1991), or micro-waves (Polli, 1990), or a combination of vapor and pressure (Cirad, 1991). However, these possible solutions are not yet used in the industry. Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 2
2.4 - Latest information and developments Recent research reports show different progress in the understanding or the management of stickiness. - Within the CFC/ICAC 11 project, charts were designed to deduce the classification threshold to separate sticky from non-sticky cottons by taking into account the within-bale distribution of sticky points, the litigation risk taken at the classification and the acceptable maximum limit demanded by the purchaser of bales (Figure 3). - It has been demonstrated that stickiness manifestation may vary according to the type of insect infestation in the field : white fly honeydew and aphid honeydew do not induce the same type of problems during transformation (Hequet, 2002). - Some research teams are working on the stickiness behavior of individual sugars that are part of the insect honeydew. - CEN standards describing the operating methods for SCT will be edited soon (PrEN 14272, part 1), when H2SD and FCT (part 2 and 3 respectively) standards are at the final approval step (CEN TC 248, WG19). - In all cases, any measuring device should be checked against reference materials to insure an accurate reading along the time. In this goal, Cirad is studying the required conditions for producing Stickiness Reference Cottons. 3 - Seed-coat fragments, an impurity that can lead to quality and productivity troubles Seed-coat fragments (SCF) are created during ginning when the fibers are separated from the seeds (Figure 4). Some weak parts of the seed-coat, e.g. the chalaza, are separated or broken. SCF often carry fibers or linters, and this makes them difficult to remove during the spinning process. These fragments end up in the yarn and in the fabric, where they constitute a major source of defects. This contamination has economic repercussions: - during ginning, where more intense cleaning operations are required, with the risk of reducing fiber technological characteristics; - during spinning, by reducing yarn yield and quality; - during fabric processing, by increasing costs. 3.1 - Existing methods to measure SCF content in fibers or in the yarn Major measuring methods may be categorized into various categories such as: - Visual methods (Std ASTM D2496-80). The Nep-Tester method is an application of visual counting. - Mechanical methods where trash is removed and categorized so that the SCF part is measured. MDTA-3 from Zellweger-Uster is an application of this method. - Some opti-electronical methods are used in the following instruments: AFIS, Zellweger- Uster (ASTM 1995), FQT from Lintronics, Lenzing Instruments Image analysis, On line Nep Control on Trützschler cards, Trascham / CATI by Cirad (SCF counting and sizing on both fibers and yarn boards), Analyra by Cirad (can be used to measure the length of attached fibers). Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 3
- Evenness testers: UT3, UT4 from Zellweger-Uster, Yarn Tester from Superba. These methods do not always count the same types of impurity and caution has to be taken when comparing their results. 3.2 - The effects of SCF on yarn quality The SCF originated in the field (variety, environmental and growing conditions), are revealed during ginning and remain in the fibers through the downstream processing steps. Cirad designed measuring tools (such as the Trashcam/CATI) to evaluate the negative effects of these fragments on yarn characteristics (namely evenness and strength). An experiment where samples with or without SCF (SCF removed using tweezers) were spun to measure their yarn strength (Krifa, 2001 and 2002, Figure 5) demonstrated that the higher the quality of the fibers, the more negative the effects of SCF. 3.3 - Breeding is a way to reduce the number of SCF in the lint As no efficient SCF cleaning system exits, Cirad used these tools in a breeding program to try to counter the SCF problem at its origin. It was shown that the SCF content can be reduced through breeding because this character has a significant level of heritability and a high level of variability. This allows, for the future, the creation of varieties that produce fibers with a low SCF content and showing good agronomical and technological behaviors (Bachelier, 1998, Figure 6). 4 - Conclusion The results obtained for stickiness and seed coat fragments can today be used in the overall management of these two contaminants: from the field to the processing. If stickiness persists, it is possible to propose solutions at the field level and reduce its negative effects during spinning. Seed coat fragments could be better controlled using breeding. 5 - Major bibliography American Standard for Testing and Material, various standards. Bachelier B., 1998, Contribution à l'étude de la variabilité et du déterminisme génétique de la teneur en fragments de coque de la fibre de coton. Premières applications pratiques en sélection chez Gossypium hirsutum L. s.l., 271 p. Thèse (Dr : Biologie et agronomie). Gourlot J.-P., Frydrych R., Scientific Editors, 2001. Improvement of the Marketability of Cotton Produced in Zones Affected by Stickiness. CFC Technical Paper No 17. Montpellier, France, Cirad, CFC - Technical Papers. (www.icac.org/icac/projects/commonfund/stickiness/english.html). Hequet E. F. and Abidi N., 2002, High-Speed Stickiness Detector Measurement: Effect of Temperature Settings and Relative Humidity, The Journal of Cotton Science 6:68-76 (2002) Krifa M., Gourlot J.-P., and Drean J.-Y., 2001. Effect of Seed Coat Fragments on yarn strength: Dependence on fiber quality. Textile Research Journal, 71 (11): 981-986. Krifa M., Frydrych R., and Goze E., 2002. Seed Coat Fragments: The consequences of carding and the impact of attached fibers. Textile Research Journal, 72 (3): 259-265. Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 4
Figure 1 : Boll contaminated by insect honeydew (credit J.L Chanselme). Figure 2 : Honeydew on a cotton yarn (credit R. Frydrych - T. Erwin). Figure 3 : Example of chart to decide the classification threshold by taking in account a litigation risk and a valuation limit (CFC/ICAC 11 project). Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 5
Figure 4 : The chalaza torn off the seed (credit B. Bachelier). Figure 5 : Difference of yarn strength after removing SCF from the fibers for 6 cottons in relation with fiber strength (Krifa, 2001). Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 6
SCF on 20 tex yarn board 22 20 18 16 14 12 10 8 Selection for low SCF content Square root transformed data 8 10 12 14 16 18 20 SCF on card w Selection for high SCF content Figure 6 : Breeding efficiency towards SCF (Bachelier 1998). Gourlot J P Frydrych R Bachelier B Stickiness Seed coat Fragments : measurements and consequences Page 7