Question

Scouring and cold mercerisation of cotton are carried out by treatment with aqueous sodium hydroxide. The process parameters that differ in the two processes are:

• A. Temperature and alkali concentration only
• B. Temperature and treatment time only
• C. Treatment time and alkali concentration only
• D. Temperature, treatment time and alkali concentration

Hint:

Scouring uses higher temperature, longer treatment time, and higher alkali concentration compared to cold mercerization. The goal of cold mercerization is to improve the cotton's strength and luster, while scouring is aimed at removing impurities from the cotton fibers.

Answer 1

The Correct Option is D

Both scouring and cold mercerisation are processes used to treat cotton with an aqueous solution of sodium hydroxide (NaOH), but the key difference lies in the process parameters used in each treatment. Let's take a closer look at these processes to better understand their differences.
Scouring Process: Scouring is the first step in the preparation of cotton fibers before further treatments such as dyeing. It involves removing impurities such as waxes, pectins, and other natural oils that are present in the cotton fiber. This process is typically carried out with a higher concentration of sodium hydroxide and at higher temperatures. - Temperature: The temperature is higher in scouring, usually around 80-100°C.
- Alkali concentration: The alkali concentration in scouring is typically higher than that used in mercerization, usually between 5-10% NaOH.
- Treatment time: The treatment time in scouring is usually longer to ensure that the cotton fibers are thoroughly cleaned.
Cold Mercerisation Process: Cold mercerisation, on the other hand, is a process where cotton is treated with a diluted aqueous solution of sodium hydroxide at lower temperatures compared to scouring. The goal of mercerisation is to improve the cotton fibers' strength, lustre, and dye affinity, by increasing the crystallinity of the cellulose. - Temperature: The temperature in mercerization is much lower than in scouring, typically carried out at room temperature or slightly elevated.
- Alkali concentration: The alkali concentration used in mercerization is much lower compared to scouring, generally around 18-20% NaOH.
- Treatment time: The treatment time for mercerization is shorter, typically ranging from 30 minutes to 1 hour.
Comparing the Two Processes: The differences between scouring and cold mercerisation can be summarized as follows:
- Scouring involves higher temperatures (80-100°C), longer treatment times, and higher alkali concentrations (5-10% NaOH).
- Cold mercerisation involves lower temperatures (room temperature), shorter treatment times, and lower alkali concentrations (18-20% NaOH).
Thus, the correct answer is (D) Temperature, treatment time and alkali concentration because all three parameters differ between the two processes.
Conclusion: In conclusion, scouring and cold mercerization are both used to treat cotton, but they differ in terms of the temperature, treatment time, and alkali concentration. Scouring is a more aggressive process with higher temperatures, longer treatment times, and higher alkali concentrations, while cold mercerization is a gentler process with lower values of these parameters.