You must have heard of non-iron shirts. Wash it, hang it, wear it! Yes, these shirts retain their shape even after multiple wash cycles. You can hang them up right out of the dryer and don’t have to think about them. They’re also even less prone to wrinkling in the course of the day and remain as smooth as it was first thing in the morning. It is a boon especially if you go out straight from work.
There has been an outpouring of interest in non-iron shirts in recent years as people’s lives have generally got busier and technology has improved. First introduced in the early 1990s and slowly adopted by shirt makers, the popularity of these shirts is growing day-by-day.
Why is cotton used for your shirts?
Cotton is suitable for apparel purpose because of its durability, good absorbency and ability to take up a wide range of dyestuffs. However, during actual wear, cotton garments are prone to crease under slight crushing, and the crease is retained for a long time. Let’s have a look on what actually happens that leads to wrinkling of cotton and how this technology works.
Why cotton creases?
Cotton is a crystalline fibre. Its polymer system is 70 per cent crystalline and 30 per cent amorphous. Hydrogen bonds are the most dominant forces of attraction present in the polymer system of cotton. The crystalline polymer system of cotton makes it relatively inelastic. Bending and crushing of cotton textile materials places considerable strain on its polymer system. This causes cotton textiles to wrinkle and crease readily.
Under stress, the hydrogen bonds between adjacent cellulose chains can break allowing the chains to slip past each other. New H-bonds can form as the hydroxyl groups re-associate with different partners. Having done so, there are no forces to pull the neighbouring chains back to their former position. The stressed shape of the fibre is just as stable now as was the original shape.
How to make cotton crease resistant?
Weak Hydrogen bonds get disturbed during the course of washing and on drying they try to rearrange and reform giving rise to creases. To prevent distortion of Hydrogen bonds, cross-linking has to be introduced in between the H-H bonds, making the chains flexible.
What are resins? How do they work?
Resins are cross-linking agents, which react with the OH groups of cellulosic materials in acidic medium at a pH of 3-4 to form covalent bonds. They are commonly used to make cellulosic fabric (cotton and cotton blends) wrinkle resistant.
Resins work by the reaction of nitrogen atoms of each resin molecule with the hydroxyl group of the cotton fabric. The reaction forms a linkage between the resin and the cotton fibres giving the cotton unshrink pattern in which shape is being made & cured.
Resins are cured in acidic pH with particular heat & temperatures (145-160 C) as per Resin tech bulletin advice. Unfortunately, the process leads to a loss in fabric strength and shade change depending on fabric weight, construction & composition.
Crease resistance: The ability of a fabric to resist the formation of crease or wrinkle when slightly squeezed is termed as crease resistance. Crease recovery: The ability of a fabric to recover to a definite degree is called crease recovery of the fabric.
Resin finishing is the process of imparting the special property of “crease recovery” to cotton.
Resins mainly fall into two groups:
1. Deposition type of resins
2. Cross linking type of resins
Deposition type of resins:
These resins are deposited on the fabric as surface coating. No reaction will take place between the fibre and resin.
• Phenol-formaldehyde resins
• Urea formaldehyde resin
• Alkyd resins
• Ketone resins
• Vinyl resins
Cross linking type of resins:
These types of resins chemically react with the fibre and crosslink the fibre molecules. The type of finish obtained is durable and much better than deposition type.
• DMU (Di methylol Urea)
• DMEU (Di methylol Ethylene Urea)
• DMDHEU (Di methylol Di hydroxy Ethylene Urea)
Different degrees of crease-resistant finishes
• Anti –crease: The purpose of this finish is to prevent deformation of the fabric by undesirable and unintentionally introduced folds
• Wash-n-wear: When wash ‘n’ wear finish is applied on cotton, it does not wrinkle too much and becomes easy to maintain. If dried and handled properly, wash ‘n’ wear fabrics can be worn without ironing or with a little ironing
• Durable press: In the dry state, the cellulose chains are held together by hydrogen bonds which break on coming in contact with moisture. Formaldehyde resin cross links are quite stable to laundering and allow the fabric to be put through machine washing without wrinkling or losing desirable pleats and/or creases which were set in prior to cross linking
Advantages of resin finishing:
• It improves the crease resistance and crease recovery property
• It reduces the shrinkage during laundering
• It gives a smooth and quick drying property
• It improves resilience, handle and draping quality
• It improves the weight and dimensional stability
• It gives resistance to degradation by light and laundering
• It improves the fastness to light and washing of many dyestuffs
Disadvantages of resin finishing:
• Environmental effect – release of free formaldehyde
• It decreases the Tensile strength and Tear strength
• It decreases the Abrasion resistance
• It gives an unpleasant odour
• It gives harsh and stiff feel