THEORY EXAMINATION (SEM–IV) 2016-17 TECHNOLOGY OF BLEACHING AND MERCERIZATION

Course: B.Tech (Textile Engineering)
Subject Code: EC402
Subject Title: Technology of Bleaching and Mercerization
Exam Type: Theory
Duration: 3 Hours
Maximum Marks: 100

SECTION – A (10 × 2 = 20 Marks)

Short, concept-based questions covering fundamental definitions and process principles

SECTION – B (5 × 10 = 50 Marks)

Detailed descriptive and process-based questions

(a) Desizing Process of Cotton

Purpose: Remove size materials (starch, gums, resins) applied to warp yarns.

Methods:

Enzymatic: Uses amylase to hydrolyze starch (eco-friendly).

Acid Desizing: Uses dilute HCl or H₂SO₄ to dissolve starch (less preferred).

Oxidative Desizing: Uses sodium bromite or hypochlorite for synthetic sizes.

Test for Completion: Iodine test – absence of blue color indicates full desizing.

(b) Scouring of Cotton Fabric

Objective: Remove waxes, fats, pectins, and dirt to increase absorbency.

Carried Out Using:

NaOH, soda ash, wetting agent, sequestering agent.

Temperature: 100–130°C for 2–3 hours in kier or j-box.

Check: Drop test (water drop spreads quickly = well scoured).

(c) Bleaching of Cotton Using Hydrogen Peroxide

Chemical Used: H₂O₂ + NaOH + stabilizer (sodium silicate).

Mechanism:

• H2O2→H2O+[O]H_2O_2 → H_2O + [O]H2​O2​→H2​O+[O]

The nascent oxygen oxidizes coloring matter.

Advantages: Eco-friendly, no chlorine damage, good whiteness.

(d) Scouring in Kier (with Diagram)

Kier: Closed, pressurized vessel (vertical or horizontal).

Steps:

Load fabric in rope form.

Circulate hot alkali solution.

Maintain 120–130°C for 6–8 hours.

Wash and neutralize.

Outcome: Uniform scouring with minimal fiber damage.

(e) Bleaching in J-Box (with Diagram)

Used For: Continuous bleaching of cotton.

Process:

Impregnate fabric with H₂O₂ bleaching liquor.

Pass through J-box for dwell time (1–2 hours).

Rinse and neutralize.

Advantages: Continuous, energy efficient, uniform bleaching.

(f) Physical & Chemical Changes in Cotton During Mercerization

Reason: Swelling of cellulose fibers in strong NaOH (18–25%) solution under tension.

(g) Impurities in Silk & Bio-Polishing

Impurities: Sericin (gum), wax, mineral salts.

Degumming: Treating silk with soap solution or enzyme to remove sericin.

Bio-Polishing: Enzymatic treatment using cellulase/protease to improve softness and smoothness.

SECTION – C (2 × 15 = 30 Marks)

Analytical and conceptual long-answer questions

Q3. Cotton Degradation Tests

Copper Number Test: Measures reducing substances formed after scouring.

Methylene Blue Absorption: Determines available reactive groups.

Cuprammonium Fluidity: Measures fiber degradation by viscosity comparison.

Q4. Wool Processing and Decatizing

Impurities in Wool: Grease, suint (perspiration salts), burrs, dust.

Processing:

Scouring (detergent + alkali)

Carbonizing (acid treatment for vegetable matter)

Neutralizing & Drying

Decatizing Process:

Post-dyeing heat–steam treatment.

Improves dimensional stability, hand feel, and appearance.

Q5. Singeing Technologies

Summary