The thorn in the side of the cotton producers and particularly of the spinners, is the notorious honeydew. This term defines the dreadful stickiness of cotton fibres due to the contamination by two terrible insects: the cotton aphid and the white fly, which last is widely spread in case of long dry spells. The researchers have intensified their efforts to control the reproduction of these insects in the last years, during which this infestation increasingly expanded. This spreading of the phenomenon is demonstrated by the result of a survey carried out by ITMF (International Textile Manufacturers' Federation) with 201 spinning mills in 22 countries all over the world about raw cotton contamination: a good 27% of the answers reported as serious the problem of cotton stickiness originated by honeydew, and Sudan was leading the high-risk countries.
Trials are under way to identify the honeydew-affected cotton batches through:
- the analysis of the sugary substances in the honeydew, which cause the cotton stickiness;
- the development of tests on the spot in order to detect the presence of sticky cotton types.
Specific treatments to neutralise cotton stickiness due to honeydew were also studied. Already in 1988 J. Gutnecht explained the results of stickiness tests carried out by ″Minicard″ method to show the influence of the relative humidity in the spinning room on the potential stickiness of a wide range of sticky cotton types and on various blends of sticky and non-sticky materials. At the same time he presented a new thermal method, simpler and less expensive than the Mini-card test, which results correlate pretty well with the Minicard System.
To remove stickiness from cotton fibres, various systems have been used:
- spraying of chemical substances on the fibres, which however causes some problems in subsequent processing
- passage of cotton bales or of a web of opened fibres through high frequency ovens.
In the past years a project was presented by R. Demuth to eliminate the cotton stickiness caused by honeydew. The project consisted in two phases: washing of the fibre with water and detergent with subsequent mild drying followed by thorough drying of cotton in a microwave tunnel, so that the adhesive substances become brittle and are reduced to powder. These systems however are not sufficiently cost-effective, so that there is a trend to dispose of the sticky cotton by mixing it in small percentages with the regular cotton.
