Shape Retention Finishes
Apparel products retain their shape and their pressed appearance even after many wearing, washings and dry cleaning sessions“ Durable Press, Wrinkle Free, Wrinkle Resistant and Permanent Press”.
Wrinkles are due to crushes on fabric during use and care. Wrinkle recovery depends on ‘Cross Links’ in inner molecular structure of fibre. ‘Cross Links” which hold adjacent molecular chain together and pull them back in to position after the fibre is bent, Thus preventing the formation of a wrinkle. Fibers with strong intermolecular bonds have good molecular memory and they resist wrinkling. Fibres with weak bonds wrinkle easily
Resin => Dimethylol Dihydroxy Ethylene Urea (DMDHEU) – Modified glyoxal based Poly-Carboxylic Acid derived (Recent development)
1. Precured Process
Saturate the fabric with resin and dry. Cure in curing oven to form cross-linking between molecular chains. Cut and sew the products and press
Disadvantages Advantages
- No permanent creases Smooth fabric
- Puckered seams Dimensionally stable
- Strength loss Lowest cost
- Abrasion sensitive
Used for shirting, draperies and other items that do not require pleats (Curtains, Bed sheets). Common with Cotton / Polyester blends. May also used for shaped garments (pants with a center crease)
- Items are pressed with high temperature pressing equipment (Hot Head Pressers). Heat sets the Polyester component. Semi durable finish => 15 – 20 washing
- Post Cured Process
Saturate the fabric with resin and dry. Cut and sew the product and press shape with Hot Head Press. Cure the pressed item in a curing oven at 300 – 400o F
Advantages Disadvantages
- Dimensionally stable Higher Cost
- Crease retention May set prematurely
- Minimum Seam Puckering Over finished areas
Commonly used for P/C and P/V blends
Reason for using Polyester => to compensate loss of strength / Abrasion resistance due to resin for cellulose
Durable finish 40 – 50 laundering
For 100% Cotton, to reduce the resin induced loss at abrasion resistance and tensile strength, specially constructed fabric and modified techniques are required; Fabric Construction requires long staple cotton, tightly twisted yarns and compactly constructed (more yarns per inch); Semi-durable: 15 – 20 laundering
Modified techniques:
Sewn product => apply resin, semi-dried and pressed at warm temperature while still damp => cure
- Immersion Process
Dye and finish the product for specific fashion look; Immerse the garment / product in the resin solution and extract excess solution and dry the product; Hand and performance are modified with fabric softeners and other compounds; Finished product will appeal to consumers; Press desired features (creases, pleats etc) in to garment with special Hot Head Press; Cure product in curing oven at 300o F for 5 – 15 minutes
Advantages Disadvantages
No premature setting higher costs
Controlled hand and aesthetics Process control is difficult
Greater flexibility Fabric preparation critical
Semi-durable finish 20-25 laundering; Used for fashion apparels of 100% cotton.
- Metered-Addition Process
Dye and finish the product for specific fashion look; Spray garment with the resin solution in a rotating chamber; Hand and performance can be adjusted with fabric softeners and other compounds; Press desired features (pleats/creases) in to garment with special Hot Head Press; Cure the product in curing oven at 300o F for 5-15 minutes
Advantages Disadvantages
No premature setting higher cost
Control hand/aesthetics Process control difficult
Greater flexibility Fabric preparation critical
Used for fashion apparels and furnishings, bed linen, curtains, draperies of 100% cotton
- Vapor Phase Process
Dye and finish the product for a specific fashion look; Press desired features (creases/pleats) in to garment with special Hot Head Press; Hand and performance can be modified with fabric softeners and other compounds => finished products would be more appealing; Apply finish in a vapor form to the product in a closed chamber and cure while it is in the chamber.
Advantages Disadvantages
- No premature setting Higher cost
- Control hand/aesthetics Process control is difficult
- Greater flexibility Fabric preparation is critical
- Use less chemicals
Used for cotton, rayon, and their blends; since the chemical consumption is less, the effect of hand, abrasion and staining are less
Special Problems Of Durable Press Garments
Frosting: Localized color change at creases, cuffs, collars and elbows; Repairs / Alterations is difficult; When seams are opened are impossible to remove
General Care Guidelines
Resins have a strong affinity for oil/grease stains; Use spot removal agents on grease spots; Pre-treat stains at collars and cuffs; Keep wash loads small to minimize wrinkling; To avoid wrinkles to set, keep washing/drying temperature at cool; Remove items promptly when dry
Liquid Ammonia Durable Press
Used for 100% cellulosics. this process does not involve the use of resins
This process involves:
Carefully controlled treatment of fabric in Ammonium Hydroxide bath
- Temperature: 120 – 150o C; Time: 2 – 5 seconds
Precise fabric tension, time, Ammonia concentration and temperature are critical to the process and followed by compressive shrinkage treatment
- Combination of these two processes stabilizes the fibers in the fabric results improved wrinkle resistance and shrinkage control in laundering; Durable finish => 40 – 50 launderings
- Mainly used for 100% cotton denims, bottom weights, winter-weight shirts and blouse; Higher processing costs; Very rigid quality control required
Shrinkage Control Finishes
A reduction in the length or width of a fiber, yarn or fabric is known as shrinkage. Growth occurs when a fabric increases in dimension. It is essential to know shrinkage to determine the construction and design of a garment
Causes of shrinkage
- Intermolecular structure of fibers
- Yarn twist
- Fabric construction (Yarns / inch)
- Weave / knit structure
Woven fabrics generally shrink more in the warp than in the weft direction because the warp yarns are under excessive tension during weaving. When the fabric is later subjected into wet treatment or heat treatment in the case of synthetic fibers, the stress and strain within the fibers are relieved, and the fabric relaxes. Fibers that are moisture absorbent absorb water and swell. Accordingly, the yarn diameter increases and the yarns in each direction must move closer together to accommodate the yarns in the opposite direction and results in an increase the crimp of weft yarns.
Knit fabrics tend to stretch more during production than woven fabrics, and therefore knit fabrics are likely to shrink more than woven fabrics.
In the commercial dry cleaning process, the procedures and solvents used do not permit fabrics to relax, as washing does, so that garments that are dry-cleaned may not shrink as readily. Shrinkage in dry cleaning generally results from the high moisture content in the solvent or from steaming the fabric during pressing.
Relaxation Shrinkage
Occurs due to the fibers and yarns are under considerable tension during weaving knitting and wet processing, the fabric undergoes stress and strain due to tension. Later when fabric becomes wet or steamed in a tension less condition, the stresses and strains are relaxed.
Relaxation shrinkage occurs when the fabric is laundered at initial stages.
Progressive Shrinkage
Occurs each time a piece of fabric is laundered. This continuous shrinkage is due to the surface scale of the wool fiber, which also causes felting. In the case of viscose rayon this continuous shrinkage is mainly due to high absorbency and swelling nature.
Residual shrinkage
Even after fabrics have been properly pre-shrunk in finishing, there is a small amount of shrinkage potential still remaining. This shrinkage is called residual shrinkage
Shrinkage Control Methods
Compressive Shrinkage (Sanforization)
A sample of fabric is measured, the measurements are recorded, and the fabric is laundered such a way as to produce maximum shrinkage. The shrunken fabric is measured, and percentages of warp and weft shrinkage are calculated. This indicates the processor the amount of compression to be given to the fabric.
In Compressive Shrinkage process, the fabric is dampened and is placed on a machine equipped with a continuous thick woolen or felt blanket. The blanket travels around a smaller roller carrying the fabric with it as it stretches around the curve of the roller. As the carrier moves from the curve to a straight area, it compresses into a smaller, flat area. When the carrier compresses, the fabric it carries is also compressed and is then heated to set in this compressed configuration.
Shrinkage Control for Knits
During knitting and finishing, knit fabrics are subject to tension and stretching, especially in the lengthwise direction. The construction of most knits allows for greater stretch. They often shrink far more than comparable woven goods. Shrinkage may be particularly pronounced in the lengthwise direction, often accompanied by growth in the crosswise direction.
Techniques used to control shrinkage in knitted fabrics include subjecting fabrics to treatment with resin-containing solutions, wetting then drying fabrics to relax tensions applied during processing and compressive shrinkage processes similar to those described for woven fabrics.
Compressive shrinkage processes for knits use different methods to return fabrics to their relaxed position. Among these is a process that feeds fabric through a machine in which a series of rollers operating at different speeds causes the fabric become compressed. In another process, knitted fabrics are stretched in a crosswise direction.
Sanfor-Knit, another shrinkage control process of the Sanforized Company, addresses the problem of knit shrinkage in both length and width. In this process, test garments have had compressive shrinkage control treatment are made up in the desired size, washed, tumble dried and checked by a testing instrument called the Knit picker. The test instrument determines whether the garments have held both the length dimension techniques. Sanfor-Knit garments are available in men’s T-shirts, athletic shirts, and the elasticity in girth that will provide comfortable wear. If the garment does not meet the established standard, the knitter is advised as to changes that should be made in construction, yarn characteristics or production polo shirts, briefs and sports knits.
There is another technique for controlling shrinkage in knits is known as Micrex shrinkage control. Fabrics are moved between two conveyors, each 6 inches apart. The cloth is kept in constant motion, both vertical and horizontally by hot air from a high-energy nozzle system. This action allows the relaxation of the tensions that were imposed in previous operations, thereby allowing the fabric to relax to its original dimensions.
Heat setting stabilizes synthetic knits. If heat setting has not been done, the fabrics will shrink. Low priced double knits for example may shrink as a result of inadequate heat setting.
Shrinkage Control for Rayon Fabrics
Viscose rayon fabrics may shrink progressively, although high wet modulus rayon fabric’s exhibits less shrinkage. Shrinkage control for rayon is most effective when a resin finish to stabilize the fabric follows compressive shrinkage control treatments.
Careful control is needed when chemical resins are applied, as excessive concentrations can lower the quality and durability of the fabric. However, if applied correctly, chemical resins penetrate the fibres to prevent further shrinkage.
Shrinkage Control for Wool
Wool and animal hair fibers are among those few fibres that show progressive shrinkage. This continuous shrinkage is due to the scale structure of the wool fiber, which also causes felting.
In addition to felting shrinkage, wool fabrics display the same type of residual shrinkage from relaxation that other fibres show. Unlike cotton fabrics, however, wool may continue to shrink if the relaxation of the fibres is not complete after one or two washings. Shrinkage treatments for wool are of two types: those that minimize the problems of relaxation shrinkage and those that eliminate felting shrinkage.
London Shrunk
In this process controls relaxation shrinkage; Used for high quality worsted fabrics; Wet worsted cloth and cotton blanket is placed on a long platform, a layer of fabric is spread on it.
Alternate layers of blanket / fabric are built up; Weight is placed on top for 12 hours; the fabric is hung to dry naturally.
Then the fabric is layered with special perforated boards; Pre heated metal plates are inserted at intervals; This set up of fabric and plates are kept under 3000 lbs pressure for 10 –12 hrs. The tension applied during processing are thereby removed
Decating or decatizing.
In this process, wool fabric is wound on a perforated cylinder, with a blanket of another fabric between those layers. Jets of stream are released through the holes in the cylinders, causing the fabric to be dampened and relaxed. Cold air is then blown through to set the fabric. Not only does this process set the wool fabric, but it also increases its luster.
Potting or boiling.
For napped, sueded, and fine wools, the fabric may be wound on a roller, wrapped in cotton and immersed in high-temperature, but not boiling water.
IWS Super wash
Attempts to produce washable wool fabrics that will not show felting shrinkage have led to the development of processes that alter the scale structure of the fiber. Super-wash is the Wool Bureau’s trademark for fabrics that meet their standards for dimensional stability and colorfastness.
Application of resin covered the scale surface on the fibre; Semi-durable finish will withstand for 25 – 30 launderings; Provides excellent wash ability without affecting the strength or fabric hand
Degradative Processes.
Because the scale structure of wool is responsible for felting shrinkage, techniques have been developed to alter the scale structure in some way. Used alone, these processes may not meet ‘machine washable’ standards, but they are adequate for products designated as ‘hand washable’.
The most common degradative processes use chlorine gas or liquid chlorine compounds to apparently partially dissolve the edges of the wool fibre scales, thereby decreasing their tendency to catch on each other. This chemical is, however, destructive and unless the process is carefully controlled, it can weaken or seriously damage the cortex of the fiber. The texture of the fabric tends to become rough and harsh.
Fibers that have been subjected to chlorination are often blended with other wool or manufactured fibres. When blended with other wool fibres, chlorinated fibres may lead to uneven dyeing because they tend to accept dyes more readily than do un-treated fibres.
Alternative processes utilize other oxidative or reductive agents or, increasingly enzymes.
Polymer-based Processes.
A second method for the creation of washable wools is the application of a thin polymeric layer to the surface of the fabric. The polymer coats the scales, inhibiting the inter-locking action. Different processes utilize various resins. Hercosett is a branded process for polymer treatment of wool for shrinkage control. It is usually done on wool sliver and proceeded by chlorination.
Fibres can also be ‘spot welded’ with synthetic resins to prevent their migration within the fabric structure. This process is most effective for garments, especially sweaters.
Problems encountered in the use of resins or polymers include a tendency for the fabrics to become stiff or harsh to touch when enough resin or polymer is used to make the fabrics completely shrink proof. Also, some resin or polymer is lost after a number of launderings.
Shrinkage Control Through Heat Setting
Fabrics made from thermoplastic fibers may be stabilized through heat setting. Synthetics can be permanently set into shape by subjecting them to heat near their glass transition temperature. The heat allows the molecules to relax so the fiber will not exhibit further shrinkage. This process is used to establish permanent dimensions for these fabrics. Synthetic knits, for example, are relatively free from shrinkage problems during laundering if they are properly heat-set. They may, however, undergo thermal shrinkage when subjected to high heat.
Soil Release / Stain Proof / Stain Repellent Finishes
Improve in resistance to soil / releasing soil and retaining whiteness of fabric
Reduces the degree of soiling of the fabrics by:
- Repelling the soil
- Preventing formation of bond between soil and fabric
- Following chemicals are commonly used and applied by pad system
Silicone Durable
Pyridinium Durable
Fluoro carbon Durable
Fluoro Carbon / Pyridinium Durable – Water / Oil borne
Wax and metallic salt Semi durable
- Mainly applied for P/C, P/V blends and resin treated fabrics; These finishes helps to improve wet ability – during laundering for easy removal of soils by action of detergents / agitation
Water repellent / Water Proof Finishes
Water repellency depends on surface tension and fabric penetrability; Water repellent fabric resist wetting but air / moisture can penetrate; It is achieved by combination of fabric structure and finish
Commonly used chemicals are:
Paraffin Wax => Spray
Paraffin Wax with Al or Cr Salt => Spray
Pyridinum Salt => Pad -> Dry -> Bake
Reactive Silicon Resins => Pad -> Dry -> Bake
Fluoro Carbon Emulsion => Pad -> Dry -> Bake
These chemicals fill the gaps between yarns in fabric; Performance of repellency depends upon: Nature of fabric and Soaps / detergents in cleaning
Water Proof Fabrics
Completely moisture proofed; Provide protection under all conditions of wet weather; Fabric is coated or laminated with a film of natural or synthetic rubber or plastic such as Vinyl or Polyurethane; Permanent Finish
Water proof breathable laminated fabric
Laminated fabric, consisting of extremely thin laminate (0.001 inch) made from Teflon (Poly Tetra Fluroethylene); Provides a water proof yet breathable fabric; Laminate sheet contains over one billion extremely fine holes per inch; Laminate can be applied on to woven / knitted fabric;
Applications: Heavy duty, foul whether clothing’s, special military protective clothing, rain wear, ski wear, golf suits, sports footwear linings, hospital drapes, mattress, tarpaulins, tents and sleeping bag covers
Anti Microbial Finishes
Prevents growth of bacteria and odor-causing germs; Prevent decay and damage from perspiration; Control the spread of disease and reduce the risk of infection following injury; Used in intimate apparels / body-fit garments / jogging and exercise clothing / sportswear, shoe linings, hospital linen and carpets
Chemicals used are:
- Quarter nary Ammonium Compounds
- Zirconium Peroxides and N-halamines
Usually applied by padding; Semi durable finish => 20 – 25 launderings
A variety of terms are used to describe the antimicrobial finishes applied to fabric. These include sterilization, disinfectant, antiseptic, and fungistat, mildew-resistant and rot proof finishes.
Insect & Moth Control Finishes
Mainly applied for Wool and Wool Blends; Chemical finish, Permethrin is applied at the scouring or dyeing stage;( Semi Durable Finish => 15 – 20 launderings)
The prime requirement of a mothproofing agent is that it to be toxic to moths and beetles that attack wool, but it must not be toxic to human beings at concentration levels used for mothproofing.
Fabric Flammability
Fabrics can be placed in different categories with regard to flammability
Flammable: Completely consumed when exposed to fire
Flame Resistant: Chemically treated to resist the spread of the flame
Flame Proof: Fabrics made of fibers that are inherently non-flammable
Example: Glass, Kevlar, Nomex
Factors, which Affect the Degree of Fabric Flammability
Fiber content; More air spaces within the fabric to burn more easily; Light weight fabric; Low twist in yarn; Thin yarn; Low yarn/stitches per inch; Pile or napped surface
Durable Flame Retardant
Durable flame retardant is chemical finishes, which react with or physically held on the surface of the fabric or within the fiber. These finishes must withstand laundering and other cleaning procedures throughout the expected life of the fabric. Durable flame retardant are generally organic compounds, which contains phosphorus, nitrogen and / or halogen (chlorine or bromine) or combination of these in the chemical structure.
- Durable flame retardant finishes are applied to fabric by a pad-dry-cure process.
- The finish formulation usually contains the flame retardant chemical, a softener, a resin binder or cross-linking agent and catalyst.
Fabric And Garment Washes
Chemical washes / Acid wash;
In this process a chemical is added to the wash solution to alter fabric surface; Chemicals include alkalis, oxidizing agents, and others that are specific to the fibre being treated; these chemicals partially destroy the fibre and create and modify the surface configuration of fabric.
Acid wash; no acid is used for this process; White wash, snow wash are referred for denim washes.
In this case oxidative bleaching agent such as sodium hypochlorite or potassium permanganate is added during the washing.
This technique is used to produce fashion denims, comfort polyester, and washed silks.
Enzyme washes / Bio Polishing
Cellulose enzyme that dissolves part of cellulose molecule; Permanent effect on surface of the fabric; The hand becomes softer; Removes surface fuzz and reduce pilling; Improves moisture absorption and dye ability; Decreases fabric weight and strength 5 – 10%; Used mainly for cotton, rayon, tencel fabrics and denims- for bottom weights and top weights; If enzyme finishing is applied after fabric has been dyed with Vat / Sulfur or Pigment dyes => Stone Wash Effect
Stone wash / abrasive washes
With abrasive washes, pumice stones or some other abrasive material is saturated with a chemical like potassium permanganate and tumbled with the fabric or garment for 30-60 minutes.
The abrasive material is removed and the chemical is neutralized in a bath; with fabrics like cotton, the abrasion is controlled by the length of time the fabric is treated and the style and type of stone used.
With fabrics like silk that are lighter weight, the excessive abrasion may result from tumbling.
Fabrics finished in this manner are referred to by a variety of fashion terms including stone washed denim, sanded silk; golf washed cotton and mud washed silk.
Micro Encapsulated Finishes
Micro capsules are between 5 – 50 microns and may contain fragrance, insect repellents, disinfectants, cleaning agents or activated charcoal Micro capsule are sprayed on to fabric and held in place with Poly Vinyl Alcohol or Acrylic binder
Fragrance: Hand Kerchiefs, Scarves, Curtains, Fur, Women’s hosiery, sweaters, and T-shirts; Normal rubbing during wear rupture the capsules and release the fragrance
Moth Protecting agents have micro capsulated for application to wool products; Micro capsules containing bactericidal agents are applied to socks underwear, women’s intimate apparel, and active wear
Activated charcoal is used as a deodorant finish to absorb body odor for gym wear active sports wear, intimate apparels and hunter clothing.