To understand Desizing in textile processing, we must first understand how textile fibres are sized before the finishing step. There is a lot of doing, undoing and redoing in textile manufacturing that is coordinated to achieve the proper sleek finish of the fabrics.

The newly spun yarns are very brittle, with loose fibres and much static electricity that cannot withstand tension stress or tangling during fabric processing, hence why they are treated with cellulose, polyvinyl alcohol, and gelatine to impart a sturdy character before knitting or weaving.

Suppose the residue of these sizing agents remains in the yarn until the end of fabric processing. In that case, they hinder optimal dyeing and printing, reducing fabric softness and absorbency and, in turn, making the fabrics look yellow.

Proper desizing techniques ensure that such synthetic polymers are entirely removed from the Fabric and properly washed off any chemical traces that can interfere with the finishing process, imparting softness, vibrant colours, and improved aesthetics.

By adopting the proper desizing methods, whether enzymatic, oxidative or hydrolytic, manufacturers can achieve superior fabric softness, colour vibrancy and process efficiency – all the parameters needed for a flawless finish. Enhancing yarn strength is the primary focus of desizing, and we get to the results during weaving.

Common Desizing Methods

In light of modern advancements, let us focus on the multiple methods innovated in desizing. Considering factors like sizing material, desired output, fibre quality, and environmental concerns, chemical industry experts favour various practices.

Enzymatic Desizing

Enzymes like amylase and protease remove starch and gelatine-based sizing agents from textile fibres by soaking them in enzyme solution for a specific time and temperature. Fabrics, mainly cotton and linen, get a boost in fibre strength after such an enzymatic desizing process. They are prepared for rigorous weaving and knitting and to endure tensile strength.

Textile manufacturers often prefer this method because of its eco-friendly, energy-efficient nature and highly specific action. They are low on water consumption and are gentle on fabrics. “The oxidative desizing process carried out at a boil (98°C) temperature using alkali and oxidative persulphates is still common in small process houses. To avoid the risk of tendering cellulose fibre because of acid generation and to save energy, many processors are using enzymes.

Oxidative Desizing

Oxidising agents like hydrogen peroxide or sodium bromide remove sizing agents like cellulose and synthetic polymers. Although this method is widely used for faster action, the added brightness it imparts to fabrics and enhanced printability and dye ability, the strong and corrosive nature of peroxides is often the cause of some concerns.

Several safeguard policies must be kept in mind while using these oxidative agents:
i). Fine, synthetic textile fibres might face some damage.
ii). They require careful control to avoid over-oxidation.
iii). They generate effluents that need proper treatments and disposal.

Acid Desizing

This method is specifically suited for all synthetic textile fibres like polyester, nylon, or acrylic, which are resistant to other desizing methods. A dilute hydrochloric or sulphuric acid solution is typically used to effectively break down the sizing chemicals through hydrolysis.

This method guarantees fast and smooth desizing, removing chemicals from the delicate fibres without denaturing them. The only concern is following a few precautions like temperature control, pH monitoring, checking fibre compatibility and proper waste disposal to ensure hassle-free textile processing.

Hot Water Desizing

A method that comes with limitations applied only for simple starch-based and water-soluble sizes. Mainly used on delicate fibres like wool, this is the mildest desizing method, using hot water at ~90°C for dissolving sizes, followed by simple cold water rinsing.

This one is the easiest, most organic and cheapest desizing methods, energy-efficient and taking minimal cost. However, careful temperature control must be done so the delicate fibres do not lose their colour or shine. This is a time-consuming process and not fit for every Fabric or sizing chemical, making it less popular.

Solvent Desizing

Some synthetic sizes are difficult to remove in the absence of their specific solvents. Acrylic or vinyl sizing agents often require specific solvents during the washing or desizing. Hence, this method treats those sizes with the following solvents-

1. Perchloroethylene (PERC)
2. Trichloroethylene (TCE)
3. Methylene chloride
4. Ethanol
5. Acetone

However, due to the production of immense VOCs, solvent desizing is soon losing importance as companies now opt for cleaner, greener practices for effective size removal from textiles.

Combined Desizing & Scouring

Some mills integrate desizing and scouring into a single process using unique formulations that simultaneously remove size materials and natural impurities. This improves efficiency and reduces water consumption.

Nowadays, companies are implementing Zero Liquid Discharge policies, often favouring desizing and scouring to eliminate excess water usage. With a low affluent generation, this method is adopted for its time-saving properties and increased production efficiency.

Quality Control and Process Optimisation

Both procedures are integral for textile manufacturing; while the former ensures effectiveness of desizing, the latter is used to increase the efficiency and sustainability of the production process. A comparative analysis between the two will provide a clear concept and help in distinguishing them:

Advancements in Desizing Technology

Textile desizing has undergone major transformation in recent years. Technologies like ultrasonic desizing and plasma treatments have surfaced, following the global market that inclines towards safer practices and hygienic options that make textile processing harmless and innovative. Applying ultrasonic waves and molecular science in desizing reduces fabric penetration time and chemical usage

Ozone desizing in an aqueous medium ensures effective sizing agent breakdown and facilitates biodegradability. The supercritical CO₂ method uses carbon dioxide under high pressure and superior diffusion properties, a premium water and chemical-free process with solvent recovery prospects.

Also, microwaves are now applied to sized textile fabrics to facilitate smoother absorbency and dyeing processes.

FAQs:

• What is the most effective method for desizing cotton fabrics?

1. Enzymatic desizing is the most efficient and sustainable approach for starch-based sizes, which are commonly used in cotton textiles.

• How does desizing impact the dyeing process?

1. Desizing is an essential pre-treatment step in the dyeing process as it directly affects dye uptake, colour uniformity, and fabric quality. 

• Are enzymatic desizing methods safe for all fabric types?

1.  Enzymes are commonly used in the desizing of natural fibres like cotton. However, for synthetic fibres or blends with special finishes, compatibility tests are recommended.

• What are the main environmental concerns associated with desizing?

1. Textile desizing generates wastewater containing residual sizing agents, chemicals, and by products that can contribute to high Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) levels. 

• How can manufacturers reduce water and chemical waste in desizing? 

1.  Adopting eco-friendly techniques, implementing water recycling and reuse systems, optimising process parameters (temperature & pH), using low-liquor ratio techniques can prove to be useful. 

Sources:

• https://www.merriam-webster.com/dictionary/desize 
• https://www.shreechem.in/treatment-process-desizing
• https://www.ijfte.latticescipub.com/wp-content/uploads/papers/v3i2/B2408113223.pdf
• https://www.sciencedirect.com/science/article/abs/pii/B9780323856515000128