PROCESSING STICKY COTTTON - 4
The correlations between fiber and flat strips are significant for all sugars except sucrose, showing that the individual sugar contents in the flat strips increase when the sugar content on the fibers increases. Trehalulose is the only sugar having a higher percentage in the flat strips than in the fibers, as shown in Fig 5a. . For the residues collected, only glucose and trehalulose have significant correlations with fiber. Nevertheless, Figs. 5a and b show that the percentages of glucose in the residues are equal or lower than the percentages of glucose on the fiber, while there is a marked increase in trehalulose content on the residues when compared with fiber.
Figures 6a to show the nonlinear relationship between trehalulose on the fibers and trehalulose on the residues for some selected locations on the textile equipment. This figure shows that during the processing of mixes having trehalulose content above 5% of the total sugars, trehalulose content has a clear tendency to increase in the residues collected. Consequently, we decided to investigate the sugars’properties to understand why trehalulose content increases in the residues collected while the others sugars do not. The temperature of the textile equipment increases during processing. Therefore, the temperatures on carding, drawing, roving, ring spinning, and rotor spinning frames were recorded after machine warming in a controlled environment (Table 5).
The temperature readings were all above 25degree C. The highest temperature range was recorded on the drawing frame( from 38degree C to 53degreeC) and the rotor spinning frame( from 31degree C to 38degree C). The lowest temperature was recorded on the ring spinning frame (from 25degreeC to 28degreeC). The effects of these temperatures should vary according to the thermal properties of the sugars. Therefore, we decided to investigate the thermal properties of the five sugars identified on the contaminated fiber and on the residues collected on the textile equipment.
Differential scanning calorimetry was chosen to study the thermal properties of the following sugars: fructose, glucose, trehalulose, sucrose, and melezitose. The differential scanning calorimetry profiles were recorded between 25degree C and 250degree C with a heat rate of 5degree C min-1.
Figures 7 a through c show the differential scanning calorimetry profiles.Each sugar has two characteristic peaks corresponding to melting points and decomposition (or carbonization) points (Table 6).
Among the selected sugars, trehalulose has the lowest melting point (48degrees C). It begins to melt immediately when the temperature starts rising. The other sugars remain stable when the temperature rises to 116 degree 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 to the mechanical parts or become the precursor of nep formation.
Figure 8 shows one example of a sticky nep. Resulsts showed an excellent relationship between ring-spun yarn neps and stickiness measurements on the raw material using the manual thermodetector. In this study, the authors showed that, on average, each sticky spot counted on the thermodetector translated into 2.8 additional neps on ring spun yarn (20 x 10-6 kg m-1 or 20-tex).
The build-up of residues on the textile equipment may have long-term effects, first sticking to surfaces, then catching dust, silica etc., increasing the friction forces within the machinery and leading to excessive wear and temperature increase.Sugars are carbohydrates that are hydrophilic because of several hydroxyl groups (OH-) that interact with water molecules, allowing many hydrogen bonds to be established. Therefore, several authors 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 were investigated.
The stickiness tests (thermodetector or high-speed stickiness detector) were always performed in a standard textilelaboratory atmosphere,Thus, the quantity of water adsorbed on each sugar was evaluated at 65% ± 2% relative humidity and 21degrees C± 1degreesC.
Fig. 9. (a) Hydration kinetic of selected sugars at 65% ± 2% relative humidity and 21(C ± 1(C from 0 to 12.6 h. (b) Hydration kinetic of selected sugars at 65% ± 2% relative humidity and 21(C ± 1(C from 0 to 650 h.
Figure 9a shows the percentage weight gain during the first 12 h of hydration. No sugar showed any significant variation within this time period except trehalulose, which picked up about 12% of moisture - corresponding to two molecules of water per molecule of trehalulose. The weight gain of the sugar samples was recorded until plateaus were reached. Trehalulose continued to pick up moisture, while fructose began to pick up moisture after 12 h of exposure to the laboratory conditions (Fig. 9b). The hydration kinetic was very fast for trehalulose - equilibrium was reached after 80 h, but slow for fructose - the plateau was reached after 500 h. 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 was not the case. The high performance liquid chromatography tests performed on the residues collected on the textile equipment did not show any increase in fructose content, even if fructose content was high in some mixes. In the 17mixes tested, the fructose content, expressed as a percentage of the fiber weight, ranged from 0.012% to 0.101%, which corresponds to 10.6% to 33.6% when expressed in the percentage of the total sugars identified. Thus, the fact that trehalulose is highly hygroscopic does not explain why this sugar has the tendency to accumulate more on the textile equipment than other sugars. The combination of trehalulose renders it stickier than the other sugars, allowing its higher concentration on the textile equipment.
Stickiness caused by honeydew contamination has been reported to cause residue build-up on textile machinery, which may cause subsequent irregularities or yarn breakage. We evaluated 17 mixes having a moderate level of stickiness. In both ring and rotor spinning, trehalulose content had the tendency to increase in the residues collected on the equipment while the other sugars did not. The study of the thermal properties of the identified sugars present on contaminated lint shows that among the selected sugars, trehalulose has the lowest melting point 48 degree C . It begins to melt as soon as the temperature starts rising. Therefore, any increase in the temperature of the textile processing equipment will first affect trehalulose. In addition, trehalulose is highly hygroscopic. 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.
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