Unit 2: Mechanical and functional finishes
Textile Finishes notes · PTU syllabus (BSTD 301-20)
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Unit summary
Mechanical and chemical finishes change surface and function, and denim relies on special washes. This unit covers mechanical finishing operations, resin finishing, finishing of wool and silk, functional finishes, denim washes, spotting and washing.
After this unit you can
- Describe mechanical finishing operations
- Explain resin (crease-resistant) finishing
- Describe finishes for wool and silk and functional finishes
- Describe denim washes and stain removal
PTU syllabus topics
- Detailed mechanical finishing operations
- resin finishing
- finishing of wool and silk
- functional finishes
- denim washes
- spotting and washing
Stone wash
Tumbled with pumice stones
Faded, worn look
Enzyme wash
Cellulase enzymes
Softer, eco-friendlier fading
Acid wash
Stones soaked in bleach
High-contrast marbled look
Bleach wash
Bleaching agents
Overall lighter shade
Topic 1
Mechanical finishing operations
Calendering
Heated rollers under pressure; variants — friction, glazing (chintz), schreiner, embossing, moiré
Smoothness, lustre, patterns
Raising (napping)
Wire-covered rollers pull fibres from the surface
Soft, warm nap — flannel, blankets
Shearing
Cuts surface fibres to even height
Velvet-like even pile
Sanforising (compressive shrinkage)
Fabric compressed on a rubber blanket
Residual shrinkage below 1%
Sueding (emerising)
Abrasive rollers
Peach-skin, suede-like feel
Decatising
Steam and pressure on wool
Lustre and stability
Beetling
Linen hammered
Lustre and firmness
Topic 2
Resin finishing
- Crease-resistant (wrinkle-free) finish: cellulose fibres crease because hydrogen bonds break and re-form; cross-linking resins (DMDHEU — dimethylol dihydroxy ethylene urea) form stable bonds between cellulose chains.
- 1Pad with resin, catalyst (magnesium chloride), softener and wetting agent
- 2Dry
- 3Cure at 150–170 °C
- 4Wash off (optional)
- Benefits: crease recovery, shape retention, reduced shrinkage. Drawbacks: loss of tensile and tear strength, formaldehyde release (low-formaldehyde or formaldehyde-free resins now used), harsher handle — balanced with softeners.
Topic 3
Finishing of wool and silk
Key finishes
Crabbing (setting worsted cloth), fulling or milling (controlled felting for density), decatising, shrink-resist (chlorine–Hercosett or plasma), moth-proofing
Degumming, weighting with metal salts (adds body), scroop finish (rustle with acids), softening
Purpose
Stability, density, washability
Lustre, drape and handle
Topic 4
Functional finishes
Water repellent
Fluorocarbons (being phased out — PFAS concerns), silicones, waxes
Rainwear, outdoor wear
Flame retardant
Phosphorus and nitrogen compounds (Proban, Pyrovatex)
Children's nightwear, upholstery, uniforms
Antimicrobial
Silver, quaternary ammonium, chitosan
Socks, sportswear, medical textiles
UV protection
UV absorbers
Summer and outdoor wear (UPF rating)
Soil release and stain repellent
Hydrophilic polymers, fluorochemicals
Workwear, table linen
Anti-static
Hygroscopic agents
Synthetics
Softening
Cationic and silicone softeners
Most apparel
Topic 5
Denim washes
Rinse wash
Simple wash with detergent
Removes starch; dark, soft
Stone wash
Pumice stones tumbled with jeans
Faded, worn look; damages machines
Enzyme (bio-stone) wash
Cellulase enzymes
Faded look with less damage
Acid wash (snow wash)
Pumice soaked in bleach (permanganate or hypochlorite)
High-contrast mottled look
Bleach wash
Hypochlorite or peroxide
Lighter shades
Sand blasting
Abrasive sprayed
Banned in many places — silicosis risk to workers
Laser finishing and ozone
Laser and ozone fading
Eco-friendly, precise
- Dry processes: whiskers, hand-sanding, potassium permanganate spray, tacking, destruction (rips).
Topic 6
Spotting and washing
- Spotting: removing localised stains before or after finishing using the right solvent or chemical at a spotting table (spotting gun): oil stains — solvent; rust — oxalic acid; dye stains — reducing agents. Test on a hidden area first.
- Washing: removing unfixed chemicals and dyes after finishing — garments washed in washing machines with controlled temperature, detergent and rinsing; then hydro-extraction and tumble drying.
Key terms
- Calendering
- Pressing fabric between heated rollers
- Sanforising
- Controlled compressive shrinkage
- DMDHEU
- Resin cross-linking cellulose for crease resistance
- Fulling
- Controlled felting of wool
- Enzyme wash
- Fading denim with cellulase
Quick revision
- Calendering types, raising, shearing, sanforising, sueding, decatising, beetling.
- Resin finishing chemistry, process, pros and cons.
- Wool: crabbing, fulling, shrink-resist; silk: weighting, scroop.
- Water repellent, flame retardant, antimicrobial, UV, soil release finishes.
- Denim washes; laser and ozone; spotting and washing.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.What is sanforising?
- Q2.Name the resin commonly used for crease resistance.
- Q3.Give one drawback of resin finishing.
- Q4.What is fulling?
- Q5.Distinguish stone wash and enzyme wash.
- Q6.How is a rust stain removed?
Long-answer questions
- Q1.Describe mechanical finishing operations.
- Q2.Explain resin finishing of cotton.
- Q3.Describe functional finishes with examples.
- Q4.Describe denim washing techniques.
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