Cotton fiber quality determines the type of yarn and fabric that can be produced. Parameters such as fiber length, strength, and micronaire can be
measured precisely and accurately with high volume instruments (HVI). These instruments, as well as the operating procedures associated with them, are well described and standardized. HVI data are used all over the world by the textile industry in buying
cotton and in managing the mixes in the textile mills. Important, though not yet completely standardized, are measurement, characterization, and quality control standards for lint contaminants. In this chapter, we focus on one specific type of contaminant, cotton lint stickiness.
Effect of Stickiness on Productivity and Yarn Quality
Cotton stickiness caused by excess sugars on the lint, from the plant itself or from insects, is a very serious problem for the textile industry—cotton growers, ginners, and spinners (Hequet et al. 2000, Watson 2000). During the transformation process from fiber to yarn of sticky cottons—opening, carding, drawing, roving, and spinning—the machinery is contaminated to different degrees depending on the processes involved and the location within the machines. This affects processing efficiency as well as the quality of the products.
Stickiness is caused primarily by sugar deposits produced either by the cotton plant itself (physiological sugars) or feeding insects (entomological sugars) (Hendrix et al. 1995). Insects have been documented
as the most common source of contamination in some studies (Sisman and Schenek 1984). The analysis of honeydew from cotton aphids (Aphis gossypii Glover) and sweetpotato whiteflies (Bemisia tabaci (Gennadius) strain B (= Bemisia argentifolii Bellows and Perring)) has shown that aphid honeydew contains around
38.3 percent melezitose plus 1.1 percent trehalulose, while whitefly honeydew contains 43.8 percent trehalulose plus 16.8 percent melezitose under the conditions described by Hendrix et al. (1992). Relative percentages may differ depending on environmental
or feeding conditions. Sucrose is virtually the only sugar in the phloem sap of cotton plants (Hendrix et al. 1992). The insects produce trehalulose and melezitose by isomerization and polymerization of sucrose. Neither of these sugars is produced by the cotton plant (Hendrix 1999); therefore, their presence on cotton lint demonstrates honeydew contamination. Furthermore, Miller et al. (1994) demonstrated that stickiness is related to the type of sugars present on the lint. The authors showed that trehalulose and sucrose, both disaccharides, were the stickiest sugars when added to clean cotton while melezitose (trisaccharide), glucose, and fructose (both monosaccharides) were relatively nonsticky.
Investigations have been conducted to elucidate the factors affecting the behavior of cotton contaminated with stickiness. In textile mills, the method mainly used to reduce the effects of stickiness is blending sticky cotton with nonsticky cotton (Perkins 1984, Hequet et al. 2000).
Gutknecht et al. (1986) reported that stickiness caused by honeydew depends on the relative humidity in which the contaminated cotton is processed. Relative humidity is a function of both water content and temperature of the air. Frydrych et al. (1993) reported that stickiness measured with the thermodetector is dependent on relative humidity. Price (1988) noticed that sticky cotton (with 1.2 percent reducing sugar content) when stored in high relative humidity (70
°F, 80 percent relative humidity) gave more problems during processing than the same sticky cotton stored at low relative humidity (75 °F, 55 percent relative
humidity). However, at low relative humidity the fibers are more rigid, which will increase the friction forces creating static electricity (Morton and Heade 1993). Therefore, milling machinery will require more energy to draw the lint.
Stickiness has also been reported to cause a buildup of residues on the textile machinery, which may result in irregularities or excessive yarn breakage (Hector and Hodkinson 1989). When processing low to moderately contaminated cotton blends, residues will slowly build up. This translates into a decrease in productivity and quality forcing the spinner to increase the cleaning schedule.
Perkins (1983) reported that the cause of the severe stickiness of some 1977 California San Joaquin Valley cottons was probably whitefly honeydew. The
stickiness was most severe in the picking, carding, and roving processes, with frequent interruptions in
production at carding and roving because of ends down and roll lapping. Storage of the cotton for more than 8 months did not relieve the stickiness. Processing the cotton through a tandem card eliminated the sticking problem at carding, but did not relieve the problem at roving enough to prevent production failures.
Fonteneau-Tamine et al. (2001a), studying 26 bales of Sudanese sticky cotton, reported that textile machinery performances decreased when sticky cottons were processed. At more than 50 sticky spots detected with the high speed stickiness detector (H2SD) and relative humidity between 45 and 50 percent during opening and carding, carding is not possible. In addition, stickiness reduces significantly the productivity well below the 50-H2SD-spot limit. As shown in table 1, the roving frame appeared to be the most sensitive
of all the machineries involved in the fiber-to-yarn transformation.
Fonteneau-Tamine et al. (2001b) reported on the same lot of Sudanese cottons that cotton stickiness not only affects productivity but also the quality of the end products. Although a clear decrease in productivity was noted for both the carding and draw-frame operations, it did not translate into a measurable decrease in sliver quality. It is only from the roving frame onward that there is a stickiness-induced decrease in regularity. The coeffient of variation (as a percentage: CV%) of the roving mass is slightly higher, thus increasing the irregularity of the yarn on the ring spinning frame. When considering actual spinning, the quality of ring-spun yarn is more susceptible to stickiness than that of rotor-spun yarn. As shown in the table 2, the regularity. imperfections, and tensile properties clearly highlight this difference between the two processes. The CV% of mass, number of thin places, number of thick places, and number of neps in the ring-spun yarn increases significantly with the number of H2SD sticky points. The tensile properties of the ring-spun yarn decrease
as stickiness increases. By contrast, most of the quality characteristics of the rotor spun yarn are unaffected by cotton stickiness.
Hequet et al. (2000) obtained very similar results. They examined the threshold level of stickiness for acceptable performances of both ring and rotor
spinning, in terms of productivity and quality of the yarn produced. In the short term, between 0 and 11 sticky spots (average H2SD count of sticky spot in the
cotton mixes) the stickiness contamination does not appear to influence the productivity for either ring- or rotor-spun yarns, but it clearly does above this 11-spot threshold. Nevertheless, a slight but significant negative effect on the ring-spun yarn quality has been detected even at the very low levels of stickiness tested. No negative effect has been noticed on the quality of the rotor-spun yarn. In the long term, however, it appears that some insect sugars are slowly contaminating the equipment. This accumulation of sugars may reduce both productivity and yarn quality in the long term.
Stickiness may cause a buildup of residues on the textile machinery, which may result in irregularities or excessive yarn breakage. When the cotton is very sticky it cannot be processed through the card;
however, with low to moderate stickiness levels, yarn can generally be produced. Hequet and Abidi (2002) studied the origin of the residues collected on the textile equipment after processing of sticky cotton blends with low to moderate levels of contamination. They worked with mixes having a very moderate level of stickiness in order to see, over time, a slow residue buildup on the textile equipment. This way of doing
the spinning test is more representative of the industrial practice. Indeed, a spinner will not run a very, or even moderately, sticky blend. He will rather mix the sticky cotton in such a way that no short-term effect will be noticed. Nevertheless, in the long term, residues build up and translate into a slow decrease in productivity and quality, forcing the spinner to increase the cleaning schedule.
Twelve commercial bales contaminated with insect honeydew were selected based on their insect sugar (trehalulose and melezitose) content and their stickiness as measured with the high speed stickiness detector. In addition, five nonsticky bales from one module were purchased for mixing with the contaminated cotton so that alternative stickiness levels in the mixes could be obtained.
Preliminary tests were run on ring spinning before testing the mixes. Thirty pounds of lint from each bale was carded and drawn. If noticeable problems occurred at the draw frame, the process was stopped. If not, the drawing slivers were transformed into roving. If noticeable problems occurred at the roving frame, the process was stopped. If not, the roving was transformed into yarn at the ring-spinning frame. If noticeable problems occurred at the ring-spinning frame, the process was stopped. If not, 100 pounds of
lint was processed for the large-scale test. If noticeable problems occurred at any step of the process, the cotton was mixed with 50 percent nonsticky cotton and the process was repeated. Using this procedure led to the execution of 17 large-scale tests.
High performance liquid chromatography (HPLC) tests were then performed on card slivers, flat wastes, draw frame residues, and the sticky deposits collected at the end of each test on the rotor-spinning and ring-spinning frames. These tests quantify the amount of each sugar, expressed as a percentage of total sugars present. In addition, H2SD measurements were made on card slivers.
After each spinning test was completed, the opening line and the card were purged by processing a noncontaminated cotton, then all the equipment was washed with wet fabrics and thoroughly dried.
From the 12 contaminated and the 5 nonsticky bales, 17 mixes were evaluated in both ring and open-end spinning. As expected, H2SD readings on the mixes
indicated slight to moderate stickiness (from 2.0 to 15.7 sticky spots). During the processing of the 17 mixes, sticky deposits were noticed on the textile equipment as shown in figures 1 to 3.
Figure 4 shows average HPLC results obtained on the 17 mixes for the fiber, the flat waste, and the residues collected on the draw frame and the drawing zone of the ring spinning frame. In this chart the HPLC results are normalized, the base being the HPLC results on the fiber. It shows that trehalulose content is always higher in the residues collected than on the original fiber while the other sugars are not. The same behavior was
observed in rotor spinning (figure 5). Among the sugars identified in contaminated cotton, only trehalulose exhibits higher concentration in the residues.
Figures 6-10 show the nonlinear relationship between trehalulose on the fibers and trehalulose on the residues for some selected locations on the textile equipment. These figures show that during the processing of the mixes having trehalulose content above 5 percent of the total sugars, trehalulose content has a clear tendency
to increase in the residues collected. Consequently, the authors decided to investigate the sugars' properties in order to understand why trehalulose content increases in the residues while the other sugars do not. The
thermal properties of the five sugars identified on the contaminated fiber and on the residues collected on
the textile equipment were investigated. Differential scanning calorimetry was chosen to study the thermal properties of the following dehydrated sugars: fructose, glucose, trehalulose, sucrose, and melezitose. The differential scanning calorimetry profiles were recorded between 25 °C and 250 °C. Among the selected sugars, trehalulose has the lowest melting point (48 °C), as shown in table 3. It begins to melt immediately when the temperature starts rising. The other sugars remain stable when the temperature rises until it reaches 116 °C (melting point of fructose). Therefore, any increase in the temperature of the textile processing equipment will first affect trehalulose, causing it to either stick on the mechanical parts or become the precursor of nep formation. Figure 11 shows one example of a sticky nep collected from the yarn produced in this study.
Sugars belong to the carbohydrate class. They are hydrophilic because of several hydroxyl groups (—OH), which interact with water molecules, allowing many hydrogen bonds to be established. Therefore, several authors (Gutknecht et al. 1986, Price 1988, Frydrych et al. 1993) investigated the relationship between stickiness and relative humidity. It was generally reported that contaminated cottons are less sticky at low relative humidity than at high relative humidity. Therefore, the hygroscopic properties of the five sugars identified on the contaminated fiber were investigated. The quantity of water adsorbed
on each sugar was evaluated at 65±2 percent relative humidity and 21±1 °C. Figure 12 shows the percentage weight gain during the first 12 hours of hydration.
No sugar exhibited any significant variation within this time period except trehalulose, which picks up about 12 percent moisture; this corresponds to two molecules of water per molecule of trehalulose. Then, the weight gain of the sugar samples continued to be recorded until the plateaus were reached. Trehalulose continued to pick up moisture, while fructose began to pick up moisture after 12 hours of exposure to the
laboratory conditions (figure 13). The hydration kinetic was very fast for trehalulose, with the equilibrium being reached after 80 hours, but slow for fructose, with the plateau being reached only after 500 hours. The total amount of weight gain corresponds to three molecules of water per molecule of trehalulose and three molecules of water per molecule of fructose.
If we assume that trehalulose accumulates more on the spinning equipment than other sugars because of its hygroscopicity, then fructose should accumulate in a similar way, but this is not the case. Indeed, the
HPLC tests performed on the residues collected on the
Figure 5. High performance liquid chromatography results on the 17 mixes for fiber, flat waste, and residues collected on the draw frame and the rotor spinning frame. The HPLC averages are normalized, the base being the results on the fiber. A: card flat; B: draw frame, drafting zone; I: rotor spinning frame, face plate; J: rotor spinning frame, feed table; K: rotor spinning frame, rotor groove; L: rotor spinning frame, rotor housing; M: rotor spinning frame, rotor ledge; N: dust test (Hequet and Abidi 2002).
Figure 6. Relationship between the trehalulose content on the fiber of the 17 mixes and the trehalulose content on the residues collected from the front rubber rolls of the ring spinning frame. The trehalulose content is expressed as a percentage of the total sugars (y = 14.62Ln(x) — 2.47; R2 = 0.702). The straight line is the equality line (Hequet and Abidi 2002).
textile equipment do not show any increase in fructose content, even if fructose content was high on some mixes. On the 17 mixes tested, the fructose content, expressed as a percentage of the fiber weight, ranges from 0.012 to 0.101 percent, which corresponds to 10.6 to 33.6 percent when expressed in percentage
of the total sugars identified. Thus, the fact that trehalulose is highly hygroscopic does not alone explain why this sugar has the tendency to accumulate more on the textile equipment than other sugars. The combination of high hygroscopicity and low melting point of trehalulose renders it stickier than the other sugars, allowing its higher concentration on the textile equipment.
The combination of high hygroscopicity and low melting point could explain the higher concentration of trehalulose in the residues collected on the textile equipment than on the original fiber. This research demonstrated that, among the sugars involved in cotton stickiness, trehalulose was probably the cause of the worst problems in processing. Thus, the effect of trehalulose throughout the spinning process was investigated for both conventional and compact ring spinning.
Hequet and Abidi (in press) processed 12 mixes, obtained by mixing sticky cotton with nonsticky cottons, through a short-staple spinning line. In addition to the trehalulose content (determined by HPLC), H2SD readings were obtained. The twelve mixes ranged from 0.013 percent to 0.204 percent of the fiber weight in trehalulose content and from 2.5 to 26.4 H2SD sticky spots. Among the mixes, some had high H2SD readings and low trehalulose content while others had high H2SD readings and high trehalulose content.
For this set of cottons, there was no correlation between H2SD readings and trehalulose content. Previous work done on 150 bales showed the same lack of correlation, especially in the low-to-moderate H2SD stickiness range. There was a marked evolution of the H2SD readings along the processing line and a strong interaction with the type of contaminant (aphid honeydew vs. sweetpotato whitefly honeydew), while there was only a slight evolution of the trehalulose content. It seems that some sticky spots, depending on the sugar composition, are broken into smaller particles in the opening line.
The mixes with high H2SD readings and low trehalulose content (aphid honeydew contamination) had no more ends down than mixes with low H2SD readings. Mixes with high H2SD readings and high trehalulose content (whitefly honeydew contamination) had excessive ends down or could not be processed. Cotton stickiness had a significant detrimental effect on both yarn evenness and yarn hairiness, even for the moderate levels of stickiness tested, but had no effect on yarn tenacity and CSP (count strength product).
In conclusion, stickiness affects productivity of the ring and rotor spinning processes and yarn quality. The origin of the honeydew contamination seems to affect the processability of sticky cottons. For a
given level of stickiness, as measured by the H2SD, cottons contaminated with whitefly honeydew are more problematic to run in the spinning mill than cottons contaminated with aphid honeydew.
Effect of Storage on Stickiness
Storage of cotton has been reported to either reduce or remove the incidence of stickiness. In other instances authors reported little to no effect of cotton storage
on stickiness. Perkins (1986) reported that whitefly honeydew contaminated cotton samples were still sticky after 2 years of storage, while other sticky cotton samples with high physiological sugar contents were much less sticky after only 4 months of storage. Frydrych et al. (1993) reported that some spinners store sticky cottons with the hope that the natural decomposition of the sugars present on the lint will reduce stickiness. The authors concluded that, on the range of cottons contaminated with insect honeydew tested and after storage for more than 2 years under various relative humidity and temperature conditions, there was no significant change in cotton stickiness measured using the thermodetector.
It seems that stickiness from high level of physiological sugars may disappear after several months of storage because of biotic activities on the lint, while stickiness from insect honeydew will not. This could be due to the inability of most of the microorganisms to metabolize some insect sugars.
Effect of Mill Conditions
In past publications, it has been suggested that
machinery speeds, settings, roll pressures, and
humidity levels are likely to influence processing problems, namely roll lapping, caused by sticky cotton. In fact, many have provided data that show dry (low-humidity) conditions in processing areas of a textile mill will allow for the adequate processing of sticky contaminated cottons (Reynolds et. al. 1983,
Perkins 1983, Gutknecht 1988, Price 1988). However, Backe (1996a) has suggested that (in addition to low humidity) bale bloom time, crush roll pressure, waste extraction, and cleaning cycles, either by themselves or in combination, can aid in alleviating the processing problems associated with sticky cotton.
Gutknecht (1988) has shown that the potential for stickiness increases for sticky contaminated cotton as the relative humidity of the surrounding atmosphere increases. Chellamani and Kanthimathinathan (1997) have reported that processing cottons known to be contaminated with stickiness at a relative humidity of 50 percent or lower will reduce the processing
problems associated with these cottons. Backe (1996a) states that a relative humidity of less than 42 percent in the blowroom, carding, and drawing processes was helpful in processing sticky cotton. In addition, he indicates that success was met by allowing the bales to bloom in a fairly dry atmosphere for 48 hours prior to processing. Bringing the humidity surrounding
the sticky contaminated cotton during processing to low levels dehydrates the sugars present on the sticky contaminated cottons. Hughes et. al. (1994)
demonstrated that dehydrating the cotton to low levels of moisture drives off water until the sugar of the sticky contamination changes to a crystalline structure, which is not sticky. These researchers suggest that this effect seems to occur somewhere between 4.5 and 5.0 percent moisture content.
In processing sticky cotton, it was suggested by Backe (1996a) that relieving the crush roll pressure at the card will help in reducing the roll lapping on the crush rolls. However, Perkins (1993) warned that
removing the crush roll pressure or increasing the gap between the crush rolls will allow large trash particles to remain in the stock, which could adversely affect yarn quality. Further, removing crush roll pressure
to alleviate carding difficulties with sticky cotton will only act to transfer the problem downstream to drawing, roving, combing, and spinning. At these
processes, roll lapping is a result of the sticky point on the cotton fiber attaching to the rollers in the drafting zone and subsequently collecting fiber passing through the zone. Known methods of minimizing this effect
are increasing the cleaning cycle of drafting rolls or treating the rolls with iodine to coat the rolls. Coating the rolls with iodine keeps the sticky point from adhering to the rollers and creating a roll lap (R. Insley, 2001, personal communication).
Use of Additives
Since the 1980's, there have been many reports on the use of additives to process sticky cotton. Some
success was demonstrated with nonionic combinations of hydrocarbon plus surfactant (Perkins 1983, 1984). However, Perkins (1971) warns that cationic additives will not be completely removed downstream in textile processing and will result in reduced scouring and dyeing efficiency. Chun and Brushwood (1998) have shown that treating cotton with water plus ammonia or urea at a 30 percent moisture content during storage for 15 days drastically reduced sugar content and stickiness without adverse affect on fiber properties. A practical application of these findings has not been developed.
Backe (1996b) reported on the use of a new additive, Gintex, for processing sticky cottons. This product
is a nonoil- and nonsilicon-based product that is said to reduce fiber-to-machine friction so that fiber and foreign matter move freely without static electricity. In 1995, Backe (1996b) reported that several mills used this additive to process sticky cottons from the 1995 West Texas crop, Uzbekistan crop, and the crop from Francophone Africa with good success. Some of the positives of processing with this additive were said to be less dust, improved cleaning efficiency, increased yam tensile properties, and improved mass evenness in addition to alleviating sticky cotton processing difficulties. Typically the additive is applied at the bale feeding (top feeder or hopper) stage of processing at the textile mill. Treating cottons with additives may be
feasible if the user is willing to incur the additional cost for not only the additive but also the hardware to apply it.
E.F. Hequet, N. Abidi, M.D. Watson, and D.D. McAllister
