Textile finishing

In short

Finishing is the last stage of chemical processing - everything done to a bleached, dyed or printed fabric to give it the handle, appearance, dimensional stability and performance the buyer wants. It is split into mechanical (dry) finishing such as calendering, raising, compacting and sanforizing, and chemical (wet) finishing such as softeners, crease-resist resins, water-repellent, flame-retardant and antimicrobial treatments, almost always applied by pad-dry-cure. It decides the value addition on a fabric: the same grey cloth can sell as a stiff lining or as a soft peach-finish shirting purely through finishing. Examined in Textile Chemical Processing papers, in GATE-TF (chemical processing and testing sections), and asked in interviews at Arvind, Raymond, Welspun, Trident, Vardhman, Alok, KPR, Tirupur and Erode knit processors, and at chemical suppliers (Archroma, Huntsman, Rudolf, Resil, Fineotex, Sarex, Indokem).

Explained

What finishing is and how it is classified

• Definition: any mechanical or chemical treatment after colouration that improves aesthetics (handle, lustre, drape, fullness), serviceability (shrinkage, crease recovery, pilling) or adds a function (repellency, flame retardance, antimicrobial).
• By durability: *temporary* (starch stiffening, simple calendering - lost in one wash), *semi-durable* (some softeners, 5-15 washes), *permanent/durable* (resin cross-linking, heat setting of synthetics, mechanical compressive shrinkage).
• By route: *dry/mechanical* (no chemistry, uses heat, moisture, pressure, tension) and *wet/chemical* (a finishing liquor applied and fixed).
• By purpose: aesthetic (softening, stiffening, lustre, surface effects) and functional/performance (crease-resist, water-repellent, FR, antimicrobial, UV, soil-release, anti-static).
• Sequence rule: mechanical and chemical finishes are often combined - for example pad softener on a stenter, then compact a knit, then calender; heat setting of polyester/elastane comes before dyeing, other finishes after.

Mechanical finishes

• Calendering: fabric passes through a nip of heated steel and soft (cotton/paper/nylon) bowls; closes the structure, flattens yarns, gives lustre and smoothness.
  • *Types:* chasing (several plies, linen-like soft lustre), friction/glazing (steel bowl runs faster than cloth - high glaze, chintz), Schreiner (steel bowl engraved with ~250-500 fine lines per inch at ~20° - deep silk-like lustre), embossing (engraved pattern, permanent on thermoplastics), moiré, palmer/felt calender (soft, full handle on resin-finished cloth).
• Raising / napping: rotating card-wire or teasel rollers pull fibre ends out of the yarn to form a nap - blankets, flannel, fleece; needs low-twist weft and a lubricant; reduces strength, raises GSM-feel and warmth.
• Sueding / emerising: abrasive emery rollers produce a short dense pile - peach finish, suede.
• Shearing / cropping: rotary blade against a ledger blade cuts the nap to uniform height; brushing removes loose fibre.
• Compacting (knits): short-fibre/overfeed compactor on a rubber belt or felt shrinks the loop structure lengthwise and widthwise to control residual shrinkage; the knit equivalent of sanforizing.
• Sanforizing (compressive shrinkage, wovens): damp fabric is pressed onto a stretched thick rubber belt; as the belt relaxes it compresses the fabric in the warp, forcing in the shrinkage that would otherwise happen on washing. Residual shrinkage brought from 4-8% to within ±1% (marketed as "sanforized").
• Decatising (wool and blends): steam blown through the fabric wound on a perforated roller - sets handle, removes lustre, relaxes strains; *semi-decatising* (open steaming), *full/KD decatising* (pressure vessel, permanent).
• Heat setting (synthetics): polyester/nylon held at 180-210 °C on a stenter for 20-40 s so crystalline regions re-form in the new dimensions - removes crease marks, stabilises width, essential before dyeing elastane-containing fabric.
• Milling/fulling (wool): controlled felting in alkaline or acidic liquor for fullness and cover; crabbing pre-sets the cloth; pressing for a flat, lustrous surface.
• Airo / tumble (air-jet relaxing) finishing: fabric tumbled in high-velocity hot air for a soft, bulky, lived-in handle without chemicals.

Chemical finishes - softeners, stiffeners and other handle modifiers

• Softeners lubricate fibre-fibre contact, lowering the force needed to bend and shear the fabric.
  • *Cationic* (quaternary ammonium, imidazolines): excellent softness, substantive (can be exhausted from a bath), but yellows on heat, dulls shade, reduces absorbency, and is incompatible with anionic dyes/auxiliaries.
  • *Anionic* (sulphated oils, sulphosuccinates): poor softness but hydrophilic and heat-stable - used for whites and medical textiles.
  • *Nonionic* (ethoxylated fatty amides/esters): compatible with everything, used in blends.
  • *Silicone* - polydimethylsiloxane emulsions give slip and smoothness; amino-functional silicones give the best surface-soft, elastic handle; hydrophilic (polyether-modified) silicones keep absorbency for towels and innerwear; micro/nano-emulsions penetrate better. Silicones also improve sewability and tear strength.
  • *Reactive/esterified* softeners (e.g. N-methylol stearamide) bond to cellulose - wash-durable.
• Stiffeners/fillers: starch and modified starches, CMC, PVA, polyacrylates - stiffness, body and weight; mainly temporary. Used on sarees, linings, collar/cuff fusibles, book cloth.
• Optical brightening agents: stilbene-based fluorescent whiteners added in the finishing pad or final rinse to shift yellowness; choose the OBA class for the fibre (anionic for cotton, disperse for polyester).
• Anti-pilling / biopolishing: cellulase enzymes (acid or neutral, 50-60 °C, 30-60 min) hydrolyse protruding microfibrils - clean surface, less pilling, softer, with a controlled 3-6% weight loss; must be deactivated at ~80 °C or pH 10 or hydrolysis continues.
• Anti-static: quaternary ammonium or polyethylene-glycol based conductive films - synthetics, carpets, workwear.

Crease-resist (durable press) finishing

• Why cotton creases: hydrogen bonds between cellulose chains break and re-form in the deformed position when wet; cross-linking the chains covalently lets the fabric recover.
• Agents, in order of development: urea-formaldehyde → melamine-formaldehyde (poor chlorine resistance, formaldehyde release) → DMDHEU (dimethylol dihydroxyethylene urea - the industry workhorse) → modified/low-formaldehyde DMDHEU (etherified with methanol/glycol) → non-formaldehyde polycarboxylic acids, chiefly BTCA (1,2,3,4-butane tetracarboxylic acid) and citric acid, with sodium hypophosphite catalyst (costlier; citric acid yellows).
• Catalysts: MgCl₂ (mild, needs higher cure), ZnCl₂/Zn(NO₃)₂, mixed MgCl₂ + citric/tartaric acid - they generate the acid that drives the acetal/ester cross-link.
• Process (pre-cure): pad liquor (resin + catalyst + softener + wetting agent + optionally polyethylene emulsion) → dry at 100-120 °C → cure 150-170 °C for 1-3 min on stenter or curing chamber → wash/neutralise to remove free formaldehyde and acid.
• Post-cure (deferred cure): pad and dry only; the garment is made up, pressed to shape and *then* cured - gives permanent creases and flat seams (trouser creases, formal shirts). Needs stable resin and careful storage.
• Moist cross-linking (wet fix): cured at controlled moisture and low temperature; retains more strength and gives wet-crease recovery, but handle is poorer.
• Garment finishing: garment dipped/sprayed, tumble-dried and cured in a garment oven - the normal route for "wrinkle-free"/"non-iron" shirts and for the easy-care finish on denim.
• Penalties: 30-50% loss of tear and tensile strength, 20-40% loss of abrasion resistance, slight yellowing, chlorine-retention yellowing, fishy formaldehyde odour, shade change on reactive dyes. Mitigated by adding polyethylene/silicone softener, using mDMDHEU, lower add-on, or blending with polyester.
• Side benefits: lower shrinkage, better smoothness after wash, and a drier handle.

Functional and performance finishes

• Water repellent (breathable): lowers surface energy so water beads but air passes - silicones, fluorocarbons (C8 chemistry with PFOA/PFOS is restricted under the Stockholm Convention, which India has ratified; the market has moved to C6 and non-fluorinated paraffin/dendrimer/silicone systems), and older wax-metal (aluminium stearate) finishes. *Waterproof* is different - a continuous coating or laminate (PU, PVC, PTFE membrane) that blocks air too.
• Oil/soil repellent and soil release: fluorochemicals for repellency; hydrophilic acrylic/fluoro-acrylic copolymers for soil release (they let water-borne detergent lift the stain) - hotel linen, uniforms.
• Flame retardant: act by forming char, releasing non-combustible gas or scavenging radicals.
  • Cotton: THPC-ammonia (Proban) polymer-forming process; Pyrovatex-type N-methylol phosphonopropionamide cross-linked with a resin; both durable. Non-durable: borax-boric acid, diammonium phosphate.
  • Polyester: phosphorus-based thermosol/pad-cure; antimony oxide-halogen synergistic systems for coatings.
  • Wool: zirconium/titanium complexes (Zirpro).
  • Evaluated by vertical flame test (char length, afterflame, afterglow), 45° flammability and LOI (limiting oxygen index); cotton ~18%, treated cotton >26%, aramid ~29%.
• Antimicrobial: quaternary silanes (bonded, non-leaching), silver (ionic/nano), PHMB, chitosan, triclosan (now largely avoided); for socks, innerwear, hospital and home textiles. Durability is quoted as "AATCC 100 reduction after N washes".
• UV protection: UV absorbers (benzotriazole/benzophenone) plus tight construction; rated as UPF.
• Insect/moth-proofing for wool (permethrin-type), rot and mildew proofing for tents and tarpaulin, anti-slip (silica) for filament fabrics, shape-memory/elastomeric finishes for stretch recovery.
• Moisture management / wicking: hydrophilic polyester finishes and dual-face knits - sportswear.
• Coating and lamination: knife-over-roll, foam and transfer coating; PU/acrylic coatings for blackout, airbag, tarpaulin and technical textiles.

Application machinery, add-on control and curing

• Padding mangle (pad-dry-cure): the universal applicator - trough + 2 or 3 rubber-covered bowls; nip pressure sets the wet pick-up (cotton 60-80%, polyester 30-45%, knits 70-100%).
• Low wet pick-up methods (save drying energy and stop migration): kiss-roll/engraved roll, foam finishing (blow ratio 10-20:1, 15-30% pick-up), spray, slop-pad plus vacuum extraction, and Lick roller.
• Stenter (stenter-cum-dryer): pin or clip chains hold the selvedges; sections give overfeed (length relaxation), width setting, drying and curing with hot air; exhaust humidity and air velocity control the drying rate.
• Curing chambers: hot-flue or float dryer for continuous cure; garment ovens (batch) for post-cure.
• Migration control: two-stage drying (pre-dry with IR or gentle air before high velocity) prevents resin and softener migrating to the surface, which causes patchy handle and shade.
• Finish add-on is never measured directly on line - it is controlled by measuring wet pick-up and knowing bath concentration, with periodic lab checks (ash, nitrogen, phosphorus analysis).

Testing, standards, environment and safety (Indian practice)

• Crease recovery angle (CRA): Monsanto/Shirley tester, warp + weft, dry and wet; untreated cotton 90-110°, durable-press 250-290° (sum).
• Dimensional change on washing (AATCC 135 / ISO 6330 wash cycles; BIS has an equivalent standard for dimensional change in domestic laundering - quote the current IS edition), durable-press smoothness appearance (AATCC 124, replica grade 1-5, DP ≥3.5 is commercially acceptable).
• Stiffness/handle: cantilever bending length (ASTM D1388, Shirley stiffness tester), heart-loop, Kawabata KES and FAST for objective handle.
• Repellency: spray rating (AATCC 22), hydrostatic head (AATCC 127), Bundesmann rain test; absorbency: drop test, vertical wicking.
• Strength: Elmendorf tear (ASTM D1424) and grab/strip tensile - always run before and after resin finishing.
• Free formaldehyde: sealed-jar (AATCC 112) or water-extraction (ISO 14184-1). Buyer limits come mainly from Oeko-Tex Standard 100 (16 ppm for baby articles, 75 ppm for direct skin contact, 300 ppm for outerwear - check the current year's edition, as limits are revised); India's own statutory textile chemical control is strongest on banned azo dyes releasing specified aromatic amines, prohibited under a notification issued under the Environment (Protection) Act, 1986, and BIS Quality Control Orders now cover specified technical and protective textiles.
• Effluent and air: finishing contributes formaldehyde, VOCs from resins and softeners, and high-COD oily waste; dyehouse effluent is regulated by CPCB/SPCB consents under the Water (Prevention and Control of Pollution) Act, 1974, and the Tirupur knit cluster operates on Zero Liquid Discharge via CETPs with RO and multiple-effect evaporators. Stenter exhausts need oil-mist/VOC scrubbing.
• Worker safety: finishing chemicals (formaldehyde donors, THPC, acids, solvent coatings) fall under the Occupational Safety, Health and Working Conditions Code, 2020, in force from 21 November 2025, which replaced the Factories Act, 1948 - hazardous-process duties, exposure monitoring, PPE and safety committees now sit there. GST on textile finishing job-work and chemicals follows the current slabs (5%/18%/40% since 22 September 2025); confirm the rate for the specific HSN/SAC before quoting.

Key points

• Finishing - all mechanical/chemical treatment after colouration to build handle, stability, appearance and function.
• Mechanical finishing - uses heat, moisture, pressure and tension only; no chemistry (calendering, raising, compacting, sanforizing, decatising).
• Sanforizing - compressive shrinkage on a rubber belt; brings residual shrinkage within ±1%.
• Heat setting - 180-210 °C for synthetics; must precede dyeing for elastane blends.
• Pad-dry-cure - the standard chemical finishing route: apply → dry (100-120 °C) → cure (150-170 °C).
• Wet pick-up % - liquor retained per 100 parts dry fabric; cotton 60-80%, polyester 30-45%.
• Add-on % = wet pick-up (%) × bath concentration (%) / 100; this is what actually performs.
• DMDHEU - main cellulose cross-linker for crease recovery; mDMDHEU and BTCA/citric acid cut formaldehyde.
• Durable press trade-off - CRA up, tear and abrasion strength down 30-50%.
• Post-cure (deferred cure) - resin padded on fabric, cured after garment pressing; gives permanent creases.
• Softener classes - cationic (softest, yellows, non-absorbent), anionic (whites, hydrophilic), nonionic (compatible), silicone (best handle, amino-functional).
• Biopolishing - cellulase enzyme removes surface microfibrils; anti-pill and soft, 3-6% weight loss, must be deactivated.
• Water repellent ≠ waterproof - repellent lowers surface energy and stays breathable; waterproof is a coating/laminate.
• FR finishes - THPC-ammonia and phosphonopropionamide for cotton; measured by char length and LOI (cotton 18%, FR cotton >26%).
• Low wet pick-up (foam, kiss-roll, vacuum) - cuts drying energy, the biggest cost in finishing.
• Migration - uneven drying moves finish to the surface; two-stage drying prevents patchy handle.
• Flexural rigidity G = W c³ - links measured bending length to perceived stiffness.
• Compliance - banned azo amines (Environment Protection Act notification), Oeko-Tex formaldehyde limits, ZLD in Tirupur, OSH Code 2020 for chemical safety.

Formulas and examples

Example 1 - recipe from add-on (resin finishing). A shirting lot of 100 kg has wet pick-up 65% on a 2-bowl padder. Target DMDHEU add-on 6% owf, with catalyst at 25% of resin weight.

• Concentration = 6 × 100 / 65 = 9.23% → 92.3 g/L DMDHEU, catalyst 92.3 × 0.25 ≈ 23 g/L.
• Check: liquor retained = 65 kg ≈ 65 L; 65 × 92.3 g = 6,000 g = 6 kg = 6% of 100 kg. ✓
• Cost at ₹120/kg resin and ₹70/kg catalyst: 6 × 120 + 1.5 × 70 = ₹720 + ₹105 = ₹825 per 100 kg = ₹8.25/kg fabric.

Example 2 - sanforizing for residual shrinkage. Grey-washed poplin marked 50.0 cm shrinks to 48.1 cm after one wash.

• Shrinkage = (50.0 − 48.1)/50.0 × 100 = 3.8% (warp).
• To leave ≤1% residual, the belt must take out about 3.8 − 1.0 = 2.8%. Feeding 1,000 m, delivered length = 1,000 × (1 − 0.028) = 972 m; overfeed = (1,000 − 972)/972 × 100 = 2.88%.
• After the pass, 50.0 cm marked wash-shrinks to 49.5 cm → residual 1.0% - inside the "sanforized" claim.

Example 3 - stiffness change from a softener. Fabric 150 g/m², cantilever overhang at 41.5° = 3.8 cm before softener and 2.8 cm after.

• W = 150 g/m² = 15 mg/cm². Before: c = 0.5 × 3.8 = 1.9 cm → G = 15 × 1.9³ = 15 × 6.859 = 102.9 mg·cm.
• After: c = 0.5 × 2.8 = 1.4 cm → G = 15 × 2.744 = 41.2 mg·cm.
• Reduction = (102.9 − 41.2)/102.9 × 100 = 60% - a large, clearly perceptible softening.

Example 4 - drying energy and the case for low wet pick-up. A stenter runs 1,000 kg/h of cotton at 60% wet pick-up and must dry it to 6% moisture. Thermic-fluid heater efficiency 85%, furnace oil CV 40 MJ/kg at ₹60/kg.

• Water to evaporate = 600 − 60 = 540 kg/h. Heat = 540 × 2,676 kJ/kg ≈ 1.445 GJ/h; fuel heat = 1.445/0.85 = 1.700 GJ/h.
• Oil = 1,700,000/40,000 = 42.5 kg/h → ₹2,550/h = ₹2.55 per kg fabric.
• Switch to foam finishing at 25% pick-up: water = 250 − 60 = 190 kg/h → heat 0.508 GJ/h → 0.598 GJ fuel → 14.9 kg oil → ₹897/h. Saving ≈ ₹1,653/h, about 65% of drying cost.

Example 5 - the durable-press trade-off. Before resin: CRA (W+F) 102°, tear strength 1,400 g, tensile 480 N. After 6% DMDHEU, cure 160 °C × 2 min: CRA 268°, tear 880 g, tensile 345 N.

• CRA gain = (268 − 102)/102 × 100 = 163% improvement; tear loss = (1,400 − 880)/1,400 = 37%; tensile loss = 28%.
• Adding 2% polyethylene-silicone softener recovers tear to 1,050 g (loss down to 25%) with CRA 255° - the usual commercial compromise.

Where it is used

• Shirting and suiting mills (Arvind, Raymond, Mafatlal, Siyaram's): sanforizing, easy-care DMDHEU finishing, Schreiner and felt calendering, garment post-cure for non-iron shirts.
• Knitwear clusters (Tirupur, Ludhiana, Kolkata): silicone softening, biopolishing, compacting and tubular/open-width compactors on T-shirts and innerwear, all inside ZLD effluent systems.
• Home textiles (Welspun, Trident, Indo Count, Karur): hydrophilic silicone and soil-release on towels and bed linen, antimicrobial on institutional linen, durable press on sheeting.
• Technical and protective textiles: FR workwear for refineries and steel plants, defence tentage with rot/water-proofing, airbag and tarpaulin coating - increasingly under BIS Quality Control Orders.
• Job roles: finishing shift in-charge, process/quality engineer (recipe, add-on and shade continuity), application/technical service chemist with Archroma, Rudolf, Resil, Fineotex or Sarex, lab in-charge for CRA, shrinkage, spray rating and formaldehyde, and buying-house QA at Tirupur and Gurugram.
• Sportswear and denim: moisture-management and anti-odour finishes, denim softening and easy-care resin, enzyme/mechanical finishes replacing stone and chlorine processes.

Interview questions

• Q: What is the difference between wet pick-up and add-on? A: Wet pick-up is the weight of liquor retained per 100 parts dry fabric; add-on is the dry chemical deposited, equal to wet pick-up times bath concentration divided by 100.
• Q: Why does cotton crease and how does resin finishing stop it? A: Hydrogen bonds between cellulose chains re-form in the deformed position when wet; a cross-linker like DMDHEU forms covalent bridges so the chains spring back, raising crease recovery angle.
• Q: Why is resin finishing always followed by a strength check? A: Cross-linking makes cellulose brittle and acid catalysis can cause tendering - tear strength typically drops 30-50%, so tear and tensile must be verified against the buyer specification.
• Q: What is the difference between pre-cure and post-cure durable press? A: Pre-cure cures the resin on the fabric at the mill; post-cure pads and dries only, and curing happens after the garment is made and pressed, so creases and seams are set permanently.
• Q: Sanforizing versus compacting - what is the difference? A: Both are compressive shrinkage; sanforizing uses a stretched rubber belt on woven fabric, compacting uses a rubber belt or felt on knits where loop distortion is the main source of shrinkage.
• Q: Why must polyester-elastane fabric be heat set before dyeing? A: Heat setting at 180-195 °C stabilises the elastane and removes creases; doing it after dyeing would cause shade change, width variation and set-in crease marks.
• Q: Which softener would you choose for a white terry towel, and why? A: A hydrophilic amino/polyether-modified silicone or an anionic softener - cationic softeners yellow on heat and reduce absorbency, which is fatal for a towel.
• Q: Water repellent or waterproof - how do you decide? A: Repellent finishes lower surface energy and keep the fabric breathable (rainwear, uniforms); waterproofing needs a continuous coating or membrane and blocks air, used for tarpaulin and rainwear where comfort is secondary.
• Q: How is a flame-retardant finish evaluated? A: By vertical or 45° flammability tests measuring char length, afterflame and afterglow time, and by limiting oxygen index - untreated cotton is about 18% LOI, FR-treated cotton above 26%.
• Q: What causes patchy handle after softener padding? A: Finish migration during rapid one-stage drying, uneven nip pressure across the padder, or an unstable emulsion breaking in the trough; fix with two-stage drying, nip profiling and the correct emulsion/pH.
• Q: How do you cut finishing energy cost? A: Lower the wet pick-up - vacuum extraction, kiss-roll or foam application can halve the water carried, and drying is the single largest energy item in the finishing house.
• Q: Why must cellulase enzyme be deactivated after biopolishing? A: The enzyme keeps hydrolysing cellulose; without heating above about 80 °C or shifting to pH 10, weight and strength loss continues and the fabric is over-polished.

Common mistakes

• Confusing bath concentration with add-on - quoting "6% resin in the bath" when the specification is 6% on weight of fabric.
• Forgetting to divide by wet pick-up when calculating g/L, which under- or over-doses the recipe by a factor of 1.5-3.
• Claiming a finish is permanent when it is only semi-durable; durability must be stated as performance after N wash cycles.
• Writing that water-repellent and waterproof are the same thing, or that a repellent finish closes the fabric pores.
• Ignoring the strength penalty of crease-resist finishing in exam answers, and ignoring free formaldehyde and chlorine-retention yellowing.
• Using cationic softener on whites or on fabric that must stay absorbent, and mixing cationic with anionic auxiliaries (coagulation in the pad trough).
• Reporting shrinkage on the wrong base - it is computed on the original marked length, and warp and weft must be reported separately.

Related topics

Pretreatment: desizing, scouring and bleaching · Dyeing · Textile printing · Fabric testing and quality control · Technical textiles and coating · Effluent treatment and sustainable processing