27 Durable Press Finishes

S. Karpagam Chinnammal

    1.    Introduction

Fabrics pass through various finishing processes to make it suitable for its intended enduse. Finishing may change the appearance, hand, serviceability and durability of fabrics. Consumer’s desire specific performance characteristics in fabrics. Various finishing processes are therefore applied in order to provide required characteristics which are not inherent in the fiber or fabric.

2.      Learning Objectives

• To know about durable press finish
• To get an insight into the types of finishing
• To be acquainted with the characteristics of durable pressed fabrics
• To be aware of the various care practices for durable pressed fabrics

   3.      Shape Retention finishes

Unlike silk , wool and manmade thermoplastic fibers cellulosic fibres have poor resilience that is they lack the ability to retain their shape-they wrinkle and crush easily. (The cellulosic fibers lack strong natural cross links. Molecular chains are held together by weak hydrogen bonds, which break with the stress of bending. New bonds hold the fiber in this bent position and form a wrinkle) .To make them competitive with other fibres a variety of shape retentive finishes are imparted. Some of the finishes are wrinkle resistant finish, wash and wear finish and durable press or permanent press finishes.

These are all based on resins that will combine chemically with the fiber through a process known as crosslinking where by adjacent molecular chains of cellulose in the fiber are linked or tied together to provide greater molecular rigidity and to prevent intermolecular slippage. Resin cross links give fibers a memory and good wrinkle recovery. Originally urea formaldehyde was used, then melamine formaldehyde and formaldehydes were used but they produced a bad odour and were allergic to some consumers. Use of formaldehyde resin is restricted because it is a carcinogen. Polycarboxylic acid or modified glyoxal based reactants are used but both are expensive. Now widely used agent is di-methylodihydroxyethylene urea (generally referred to as DMDHEU). Another is dihydroxydimethylethylene urea (DMDMEU)

4.   Durable press or permanent press Finish

Durable press is a type of shape –retention resin finish that can be found on numerous fabrics and garments. It is a treatment applied to the fabric in the finishing process which retains creases and folds during laundering. Durable press describes items that retain their shape and their pressed appearance even after repeated uses, washings and tumble dryings.

Wash & wear and durable press or permanent press finishes are given using resin precondensates. Wash & wear finish (wash-dry –wear and no need for ironing) imparts crease recovery only and is suitable where pressed in creases are not required . This kind of finish is not suitable where pressed in creases are required or where formation of sharp creases are hindered during ironing. Inserted creases on this fabric disappear quickly during wear. For sharp retention of pressed in creases and freedom from ironing the fabrics, the garments require durable press finish.

Development of durable press finishing technique also referred to as permanent press (PP) is an outgrowth of the manufacturers difficulty in making wrinkle resistant goods into garments. The finish gave a built in memory to fabrics which interfered with shaping garments to conform to body contours, pressing creases into trousers and putting pleats in skirts. Wrinkle resistant and wash and wear are pre cured , that is cured before the goods are cut and sewn into garments, the permanent press finishes are post cured

The durable press finish is used on cotton, rayon, linen, wool or a blend of these fibers with polyester. This finish is based on resins or reactants that will combine chemically with the fiber by forming cross links between adjacent cellulose polymer chains, whereby adjacent molecular chains of cellulose in the fiber are linked or tied to provide greater molecular rigidity. There are several methods of applying the finish to the fabric. The effectiveness depends upon both the agent used and the method of application.

Fig 1.Durable pressed fabrics

4.1. Chemicals for durable press finish

4.1.1. Cross linking agent

Resin finishing is carried out with products known as cross linking agents. The most widely used agent is dimethyloldihydroxyethylene urea (generally referred to as DMDHEU). Alternatives to DMDHEU are polycarboxlic acids or citric acid. However, polycarboxlic acid is expensive to use and citric acid causes yellowing. Another approach has been to use polymers of maleic acid to form ester crosslinks, and yet another to fix a quaternary group through an epoxidation reaction to the cellulose chain to form cross links. Commercially it is the modified DMDHEU (glycolated or methylated ) that is most used today, this product is pre buffered to prevent premature curing and also pre blended with a catalyst.

4.1.2.   Catalysts

Another essential component of the resin finishing recipe is the catalyst. It allows the reaction to be carried out within the 130-180°C temperature range and within the usual curing times. Three classes of catalyst are distinguished in the dry cross linking process  a) ammonium salts eg ammonium chloride, sulfate and nitrate b) metal salts eg magnesium chloride , zinc nitrate, zinc chloride, aluminium sulfate and aluminium hydroxychloride c) catalyst mixtures eg magnesium chloride with added organic and inorganic acid donors

The reaction of DMDHEU with cellulose requires an acid catalyst for acceptable yields under conditions suitable for textile processing. The most common catalysts are magnesium chloride and zinc nitrate that generate acid conditions during the curing process, thus providing neutral liquors and good finish bath stability. Citric acid or aluminium chloride can also be blended to increase catalysis when curing times are short. Sulphuric and hydrochloric acids and their ammonium salts serve as excellent catalyst but also lead to undesirable fibre degradation

4.1.3.   Additives

The purpose is to offset partly or completely the adverse effects of the cross linking agent. Thus softening and smoothing agents are applied not only to improve the handle, but also to compensate as much as possible for losses in tear strength and abrasion resistance. A high density polyethylene restores some of the lost tear strength and abrasion resistance by providing lubrication. Other additives serve to impart a particular character to the fabric. Examples are stiffening and filling agents, water repellents, hydrophilic agents etc

4.1.4.   Surfactants

Every resin finishing contains surfactants as emulsifiers, wetting agents and stabilizers. These surface active substances are necessary to ensure that the fabric is wet rapidly and thoroughly during padding and to stabilize the recipe components and liquors eq long chain fatty alcohol or alkyl phenol groups

4.2.  Recipe For durable press finish

• DMDHEU (or any crosslinking agent)- 200gpl
• Magnesium chloride – 10- 20gpl
• Poly ethylene emulsion-25 gpl
• Softners combination-40gpl
• Non ionic wetting agent-3 gpl
• Citric acid-.3 gpl

4.3.  Process sequence

The process sequence of durable press finish is as follows

• Impregnation of the fabric in the prepared resin solution by padding    (Padding)
• Drying the padded fabric in stenter with minimum tension at 70-80 °C( Drying)
•  Garment construction and insertion of creases or pleats by hot pressing ( garment construction and Pressing )
• Curing at 120-150 ° C for 2-5 min in stenter where crosslinking and polymerisaton takes place (Curing)
• It is then washed with 1-2 gpl of wetting agent and 2-4 gpl of soda ash at 50-60 ° C for 10 min (washing)
• Rinsed in water containing softening agent
• Drying

Another method is to Make garments-treat with resin-Hydro extract- press and form creases , pleats with hot iron- dry –cure-wash-hot rinse-cold rinse-dry High concentration of resin and curing at high temperature for a longer time are required for this kind of finish. Urea Formaldehyde and melamine formaldehyde resins are not suitable for durable press finish because these precondensates cure rapidly and it is difficult to keep them in an uncured state for a long time. DMUE or ethyl carbomates may also be used for durable press finish. The resin suitable should be fast to washing and should not affect the light fastness of certain dyes.

The main disadvantages of this finish is loss in strength and reduction in abrasion resistance, because of the combination of high resin content, and prolonged curing at high temperature. Ionic and non ionic softners are therefore added to the resin finishing bath to minimize the loss in strength and abrasion resistance. Emulsion of polyethylene , polyvinyl chloride , silicones etc., are also added.

4.4.  Parameters affecting the process

Time of heat setting Temperature of heat setting Over feeding Tension of the fabric

4.5.  Types of finishing

There are several processes for durable press products, they differ as to when the chemical is applied and the stage at which cutting, sewing and pressing take place. In the precured and post cured processes, the finish is applied to the fabric. In the immersion, metered- addition, and vapor phase processes,the finish is applied to the garment or product.

4.5.1. The precured process

1.The fabric is treated with the resin cross linking solution and dried

2.Cure flat in open width form in a curing oven to form cross links between molecular chains

3. Cut and sew item. Press

4. This fabric can be used to produce garments that resist wrinkling during wearing and have a smooth appearance after washing and drying. However it is not possible to introduce sharp durable creases as the crosslinked fabric will resist any attempt to press in creases.

5. Used for shirting, draperies and other items that do not require set-in creases or pleats

6.Common with cotton/polyester blends

4.5.2. The postcured process

1.Saturate the fabric with a resin cross linking solution and dry at low temperature

2.Cut and sew the item and press shape, creases  with hot head press

3.Cure the pressed item in a curing oven at 300 to 400° F

4.Curing gives shape to the cellulosic fibres. The thermoplastic fibers are set by the hothead pressing

5.Used for skirts, slacks and other products with set in creases or pleats that are durable for the life of the garment

6.Common with cotton/polyester blends

4.5.3.The immersion process (garment dip method )

1. Dye and finish the product for a specific fashion look garments are constructed from non resonated fabric

2. Immerse the garment or product in the finishing agent and extract excess finish. Dry the product

3. Hand and performance are modified with fabric softners and other compounds so that the finished product will appeal to consumers

4. Press desired features (creases, pleats etc) into garment with special hothead press.

5. Cure product in curing oven at 300° F for 5 to 15 minutes

6. Used for fashion apparel of 100 percent cotton

7. Also known as the garment or product dip process

4.5.4.Metered addition process (Spray application)

1.Dye and finish the product for a specific fashion look.

2.Spray garment or product with the finishing agent in a rotating chamber. Tumbling continues until product is uniformly processed.

3.Hand and performance can be modified with fabric softners and other compounds so that the finished product will appeal to consumers

4.Press desired features (creases, pleats etc) into garment with special hothead press.

5.Cure product in curing oven at 300° F for 5 to 15 minutes

6. Used for fashion apparel  and furnishings ( bed linens and towels) of 100 percent cotton

4.5.5.Vapour phase process

1. Dye and finish the product for a specific fashion look/ cut and sew

2. Press desired features (creases, pleats etc) into garment with special hothead press.

3. Hand and performance can be modified with fabric softners and other compounds so that the finished product will appeal to consumers

4.Apply finish in a vapour form to the product in a closed chamber and cure while it is in the chamber

5. Used for cotton and other natural fibers, uses less finishing chemicals so the effect on hand , abrasion resistance and staining is less.

4.6. Facts about durable press finish

o   Blends of cotton/polyester use less resin than 100 percent cotton

o   The high strength and abrasion resistance of polyester make these fabrics much more durable.

o   Cotton pretreated with liquid ammonia or mercerized under tension minimizes the strength loss due to the finishing.

o   Polymer sizing added to the yarns before curing increases abrasion resistance

o   Although most curing is done using forced air convection ovens, microwave ovens produce a more uniform cure for lighter weight fabrics such as shirtings

4.7. Durable press for wool

Wool has natural memory, it is elastic, has good resiliency and tends to return to its original shape after tension or compression is exerted. It has good resiliency when it is dry, but its durable press characteristics are poor when it is wet. Durable press woolis achieved with combination resin treatments to impart durable press characteristics and control wools excessive shrinkage.

1. Flat fabric is treated with 1 to 2 percent of the durable press resin and steamed for 3-5 minutes

2. The item is made up, sprayed with more durable press resin and pressed to achieve a permanent crease effect

3.Shrink resistance resin is mixed with a dry cleaning solvent and the item is dry cleaned. The resin is cured in the item for 3 to 7 days before it is laundered

Long lasting creases or pleats are added to wool by a process in which the crease area of the garment is sprayed with a chemical reducing agent, such as monoethanolamine sulfite, which temporarily inhibits wools resilience. When the garment is pressed , the heat resets the wools memory with this crease so that the fabric always tends to return to the new creased condition. Moisture increases this reaction and when wet the crease tends to become sharper.

Another method is to pretreat wool. The goods are padded in a solution of urea and diethanolamine carbonate, dried and then pressed in an electrically heated press. After this treatment creases or pleats may be put into the fabric with the conventional steam press and then dried in the press for one minute.

4.8. Durable press for silk

Since silk wrinkles easily when wet, polycarboxylic acid is used to produce durable press or wrinkle resistant silk. The finish is durable to laundering but produces a 20 percent loss in strength, increase in stiffness and decrease in whiteness.

4.9. Polyset process (wet fixation process)

The blended fabrics are better crease resistant than 100% cellulosic fabrics. Still ironing is necessary after washing to wear in case of blends. So durable press finish is also given for blends but following a different process sequence.

Process sequence

Resin solution and additives (without catalyst)- Batch at 70 °C for 2 hours-wash-dry-pad with catalyst-dry-stitch garment-hot press to shape and form creases and pleats-cure at 160°C for 10 to 15 min- wash –hot rinse-cold rinse-dry

4.10. Characteristics of durable press finished product

4.10.1. Positives

• Improved dimensional stability and shape retention
• Less tendency to creasing
• Easier to iron
• Softer and smoother feel
• Better appearance and more durable
• Less change in shade
• Improved wet fastness of dyeing and prints
•  Less tendency to pilling, especially of fiber blends

4.10.2. Negatives

• This finishes contain cross linking agents that  reduce tensile and tearing strength of the finished fabric    by 30 to 50 percent
• Abrasion resistance is also reduced (due to the brittleness of the fiber caused by cross linkage of the molecular chain). In dyed goods this will appear as a light colored streak.-wet condensation, liquid ammonia treatment, addition of silicones other auxillaries such as polyvinyl acetate, polyurethane, polyethylene etc
• Also, the fiber becomes less absorptive and garments of such finished material are less comfortable in humid weather
• Hard handle
• Less dilatable and elastic
• Reduction of light fastness and colour changes of dyed fabrics
• Yellowing, especially in white fabrics
• Objectionable odours, sometime fishy smell
• Chlorine retention, causing market yellowing and strength loss
• Release of larger amount of formaldehyde
• Affinity for soils
• Dye migration because of high curing temperatures
• Construction problems with seam pucker

4.11. New approaches to reduce the problems/ modifications of DP finish

• Since cross linking occurs only in cellulose fibers, the loss of strength can be reduced by blending cotton or rayon with polyester fiber. A blend of at least 50% polyester with 50 % cotton or rayon is required for significant strength retention. A blend of 65 % polyester with 35% cotton will result in only about 10 percent strength reduction due to the finish. The polyester fiber also improves the abrasion resistance, hand and appearance , as well as color and styling potential.
• Molecular structure of cotton fiber is altered by swelling with sodium hydroxide without tension and allowing the cotton to shrink, then stretching the yarn while it remains in the caustic soda. This is found to increase the strength of the PP cotton so that it is equal to untreated cotton for twenty launderings
• Pretreatmnet of cotton and cotton polyester fabrics with liquid ammonia has been found to improve luster, tensile strength, wrinkle resisitance, flex life and hand of goods that are subsequently cross linked.
• A steam cure followed by a dry cure of cross linked cotton has also been shown to be effective and importantly to provide about 300 percent greater abrasion reisitance than the convetional method
• A different approach is the use of polymer sizing on yarns for cotton fabrics. Subsequently the goods are given the conventional dry cure resin treatments. A s a result, greater tensile strength and edge abrasion resistance of the permanent press fabrics are achieved.
• The handle of the fabrics can be improved by combining softners
• Elastic properties can be improved by combining with silicones such as elastomeric
• By proper selection of products such as dyestuffs, cross linkers, catalysts shade change or reduction in light fastness can be overcome
• Yellowing of fabrics may be avoided by proper selection of catalysts , fluorescent brightners and application condition
• Objectionable Odour can be avoided by proper selection of catalyst (no ammonia product), cross linkers and if necessary by washing
• Chlorine retention can be avoided by proper selection of cross linking agent
• formaldehyde free or low formaldehyde resin should be selected

4.12. Care of finished material

General care guidelines for durable press items include the following

• Wash items frequently because resins have a strong affinity for oil and grease so that soil penetrates deeply and builds up
•  Pretreat stains, collars, and cuffs. Use a spot removal agent on grease spots
• Keep wash loads small to minimize wrinkling
• Avoid setting in wrinkles with heat. Keep washing and drying temperatures cool
• Remove items promptly when dry
• One way to lessen abrasion is to launder the garment inside out, since this will reduce the wear on the crease
• Do not wring the garments or spin dry them in a washing machine dryer. Rinse them well and hang them on wooden or plastic hangers

5. Conclusion

Specific characteristics not present in fibres are imparted through functional finishes thereby adding value to the fabric. One such important finish is durable press finish. In this module we have learnt what is a durable finish, its techniques, the characteristics and care for durable pressed finish.

Reference

1. Kanwars, Varinder Pal Singh, Elementary Idea of Textile Dyeing, Printing and Finishing, Kalyani publishers, kolkatta,2009 p155-163
2. Bernard .P. Corbman, Textiles-Fiber to Fabric, Mc Graw hill book company, New York 1983 p.182-186
3. Subrata Das , Important aspects of wrinkle free finish, Asian dyer, June-July 2013 p.39-42
4. Tushar Bharat Gaikwad and A.I. Wasib, Study on wrinkle free finish on 100 % cotton fabric, Colourage, March 2016 p 42-43