Coloured fabric after dyeing and finishing
When cotton fabric is scoured in hot alkaline liquor, if the foam cannot be suppressed continuously the liquor level rises with it, the fabric is held back from tumbling, alkali spots and uneven soaping appear one after another, and the quality of the pretreatment and of the dyeing that comes after suffer together.
Chemi Tech supplies defoamers for the hot scouring, desizing and soaping systems of cotton fabric, drawn from the defoamer KM-901 series; the dosage is set by the temperature of the alkaline liquor, the auxiliary formulation and the fabric weight. KM-901 is of the modified polysiloxane type, does not break its emulsion and does not separate out in hot alkaline liquor, and suppresses foam for a long time, so that a single dose covers the whole scouring cycle; KM-902 of the same series is a composite polysiloxane, more economical for lines that only need to hold down mechanical foam in the ambient-temperature low-alkali stage. Chemi Tech compares defoaming performance against the temperature of the alkaline liquor and the suppression time, and selects the fitted model for the customer.
Advantages of Chemi Tech Defoamers
Chemi Tech defoamer KM-901 series does not break its emulsion and does not separate out in hot alkaline liquor, and the liquor stays uniform after standing for a whole day; at the same time the suppression lasts, a single dose covers the whole scouring cycle and the foam does not rise again; in addition, it is compatible in the same bath with scouring agents and wetting agents, the dosage is low and does not raise COD; moreover, it does not affect the handle of the fabric, and the scoured fabric stays as soft as before.
Industry Pain Points and Solutions
Foam in the hot scouring of cotton fabric is mostly not a matter of insufficient stirring, but of a foaming tendency strengthened by the high temperature; the consequence is a raised liquor level and a fabric held back from tumbling.
The first problem to surface is emulsion breaking at the high-temperature stage. As the temperature rises an ordinary defoamer tends to break its emulsion and separate out, the liquor turns cloudy, and the suppression decays with it. Chemi Tech's answer is to add the KM-901, which neither breaks its emulsion nor separates out, at the feed stage before the temperature is raised, so that the agent keeps suppressing through the high-temperature stage.
Next comes insufficient suppression time. Some defoamers only break the foam briefly, the foam rises again in the later part of the scouring, and the liquor level goes up once more. KM-901 from Chemi Tech is of the modified polysiloxane type with lasting suppression, and a single dose covers the whole scouring cycle.
The last issue lies in same-bath compatibility with the auxiliaries. When scouring agents and wetting agents are used in the same bath, an incompatible defoamer damages the finishing effect and the foam control together. Chemi Tech checks same-bath performance against the temperature of the alkaline liquor and the auxiliary formulation, and sets the point of addition of the low-dosage, low-COD KM-901 before the heat-up, so that the tumbling of the fabric returns to normal.
Typical Operating Conditions and Verification
Customer: a dyeing and printing enterprise in Shandong, for the hot scouring and desizing stages of cotton fabric pretreatment.
At this plant the foam pushed out over the lip of the vat once the scouring liquor was heated, the fabric was held back from tumbling, and alkali spots and uneven soaping appeared repeatedly. The solution Chemi Tech defoamer gave for the situation was: taking the temperature of the alkaline liquor and the auxiliary formulation into account, choose the KM-901 series, move the dosing point to the feed stage before heat-up, and grade the dosage by fabric weight. After the solution was switched in, the scouring liquor level returned to steady, the tumbling of the fabric came back to normal, and alkali spots and uneven soaping fell noticeably.
Frequently Asked Questions
If the defoamer is added to hot alkaline liquor, will it affect the handle of the fabric and the dyeing that comes after?
There is such a risk, since a small number of categories break their emulsion and then cling to the fabric, making the handle stiff and affecting the dyeing. For hot alkaline liquor, Chemi Tech has completed same-bath and handle checks with KM-901, and at normal dosage it does not break its emulsion and does not cling. The dosage is set by the temperature of the alkaline liquor and the fabric weight, and Chemi Tech gives a recommended range after the same-bath comparison.