Mercerization Aravin Prince PeriyasamyDKTE’S Textile Engineering Institute
MercerisationDefinition: Treatment of cellulosic materials with higher concentrated alkali for short period at lower temperature.
Objectives To improve lustre of cotton materials To improve strength and mechanical properties To improve dyeability and moisture absorbancy To improve dimensional stability of materials Improving elasticity
Action Of Alkali Cotton have resistance to alkali solutions. Mild alkalis like sodium carbonate have no action on cotton. Strong alkalis with higher concentration induce structural and physical changes in cotton fiber.
Penetration of alkali For small concentration of alkali i.e., less than 5% no penetration. As the concentration of alkali increases, penetration will increase, then automatically fiber swells.
What Happens To Cotton During Mercerization ? Swelling of the fiber takes place Cellulosic chains gets rearranged and become parallel De-convolution Cross sectional bean shape to ~ circular shape
When Mercerization Can Be Carried Out? At Grey stage After Desizing After Scouring After Scouring and bleaching
Physical Changes Improvement in strength Improvement in luster (under tension) Change in cross section from bean shape to almost circular Change in longitudinal view convoluted to cylindrical
Chemical Changes Formation of cellulose- II. Improvement in moisture regain (more hydroxyl group). Improvement in dye uptake.
Conditions Application of caustic soda solution around at a Room temperature. A dwell period of 55 sec on an average. Tension at both directions Finally, washing-off of alkali from the treated fabrics/ yarn.
What Are The Parameters Concentration of NaOH Time of Treatment Tension applied Temperature Impurities of NaOH
Mercerization machinesTension Mercerization ( treatment under tension/ Control)Slack mercerization ( Treatment without tension/ Control) Yarn mercerization Fabric mercerizationFabric mercerization machinesWoven fabric Pad chain type Pad chainless type Padless chainless typeKnitted fabric
Hot mercerizationDrawbacks with cold mercerization•Penetration of grey cotton becomes more difficult(high viscosity)•Swelling only in surface (heavy fabrics)•Poor mercerization at the core and lack of uniformity
Recipe Na OH = 26 – 30 % Wetting agent =1% Temp = 60 Degree C Time = 20 to 60 sec
Advantages of hot mercerization•Rapid alkali penetration•Improved core mercerization•More uniform treatment•Dwell time can be reduced from 50 sec. to 20-30 sec.
Dis- Advantages of Hot Mercerisation Less luster (Lower swelling) Higher energy consumption Costlier
Liquid Ammonia Mercerization Treatment of cotton fiber with liquid Ammonia (NH3) produces similar effect that of Mercerization. The liquid ammonia treatment is widely accepted for yarns used in Sewing Threads, and special fabrics like Denims, Corduroys, Pillow material, linen, Jute and blends of cellulose with PET and/ or Nylon.
Advantages of Ammonia Mercerization Less pollution Higher productivity Jute and linen can be mercerized Evenness and uniformity of swelling is comparatively better.
Dis Advantages of Ammonia Mercerization Very costly equipments Ammonia recovery problem, leakages will do great harm to the personnel working.
Comparison of mercerization processesProperty Conv. Merc. Hot Merc. NH3/Dry-steamSwelling speed Low Fast V. FastEvenness uneven Good GoodLuster Good Good Very goodDye uptake Good Not quite high GoodDimensional Good Good Goodstability