Yarn characteristics affected by fibre characteristics:
Yarn Strength: influenced by fibre strength, length, fineness, and number per cross-section, as well as twist level.
Yarn Fineness: affected by fibre fineness, fibre length, and twist level.
Yarn Lustre: impacted by fibre surface characteristics and twist level.
Surface Integrity (Hairiness and Abrasion Resistance): depends on length, fineness, and twist level.
B. Spacing and Interlacing of the Yarns
Sett: Term used to denote the spacing of ends and picks in woven cloth, expressed as threads per centimeter.
Affects strength, tear, abrasion, crease, drape, and weight.
Types of Sett:
Square Sett: Ends and picks per cm are approximately equal.
Unbalanced Sett: Noticeable difference in ends and picks per cm.
Open Sett Structure: Voids between warp and weft yarns that influence comfort, flammability, thermal insulation, and air permeability.
Fabric structure, number of warps and wefts per cm, amount of twist, size of yarns, and yarn structure type significantly influence physical and performance characteristics.
Interlacing sequence of warp and weft yarns results in various weave structures from plain weaves to complex computer-generated interlacings affecting the properties of the final fabric.
Warp and weft visibility can lead to either:
Warp-faced Textile: Warp covers the weft due to closer spacing.
Weft-faced Textile: Weft covers the warp with wider spacing.
C. Modifications Produced by Finishing
Finishing techniques such as mercerization, crease-resistant resin finish, calendering, coating, and anti-static finish impact physical properties and performance characteristics:
Mercerization and calendering improve lustre.
Resin finishes affect tear resistance and handle.
Calendering and coating influence air permeability and thickness.
Brushing and raising enhance insulation properties and softness.
Important Aspects of Fabric Production
Fibres and Filaments
Fibres are the foundation of all fabrics, both natural (like cotton, flax, and wool) and synthetic.
Fibres can be twisted together to form yarns; filaments such as silk may be used directly.
Types of Yarns:
Continuous-Filament Yarns (c.f.): Consist of endless filaments, do not depend on twist for strength.
Usually smooth, lustrous, and uniform.
Can be produced as flat or textured, bi-component, and tape/split yarns.
Sub-groups include:
Flat Continuous Filament Yarns:
Standard 'flat' yarns that can be dull/matt or bright/lustrous.
Monofilament yarns: single extruded synthetic filaments with a solid geometrical form.
Multifilament yarns: composed of several filaments twisted together.
Spun Yarns: Spun from comparatively short, variable-length fibres that rely on inter-fibre cohesion for strength.
Tend to be hairy, less lustrous, and irregular compared to continuous-filament yarns.
Yarn Density
Yarn structure comprises fibres and air pockets; bulk density determined by packing fraction.
High packing fraction leads to stiff, likely weak yarns; low packing fraction may lack bulk and structure.
Yarn density significantly influences fabric performance characteristics:
Comfort: high packing fraction leads to compact yarns that result in stiffness and greater contact with skin.
Thermal insulation: air pockets help with insulation.
Also influences dimensional stability, strength, extensibility, flexibility, air permeability, and absorption characteristics.
Yarn Strength and Fineness
Yarn Strength Factors:
Influenced by fibre strength, length, fineness, number per cross-section, and twist level.
Longer and more numerous fibres contribute to greater strength.
Yarn Fineness Measurement:
Count, diameter, and linear density measures both relate to yarn fineness and influence fabric structure and cover.
Twist in Yarns
Twist is essential for holding fibres together; can affect yarn properties, including strength and appearance.
Defined by:
Twist Direction: S-direction or Z-direction.
Twist Level: Measured in turns/unit length.
Twist Factor: Considers yarn radius and twist level.
Twist direction affects fabric appearance, particularly in twill patterns (e.g., Z twist for right-handed twill).
Relationship between twist level and yarn strength must consider the point of optimal twist before decreasing strength.
Surface Integrity and Yarn Characteristics
Abraaion Resistance
Determined by the wear of yarn surface against another surface; measured through cycles until breakage occurs.
Hairiness
Extent of fibre ends protruding from yarn; measured by:
Hair Count Method: Counting protruding fibres.
Hair Length Method: Measuring light scattered by protruding fibres.
Thread Count and Crimp
Thread Count: Number of warp and weft threads per square inch; higher counts improve fabric quality.
Crimp Definition: Refers to the yarn bending during interlacing; expressed as:
extCrimp=L<em>fL<em>y−L</em>f (where L</em>y = yarn length in fabric, Lf = original length).
Crimp percentage can be calculated similarly.
Finishing and Post-Processing Techniques
Enhances fabric usability and value through treatments including:
Bleaching, decatising, printing, dyeing, calendering, and other specialty applications such as anti-bacterial finishes and non-flammable treatments.
Effects of Specific Finishing Techniques
Crease Resistance: Chemical treatments reduce wrinkling based on fibre type and structure.
Calendering: Involves pressing fabric between heated rollers to improve feel, density, and finish.
Moiré Effect: Produces wavy watermark patterns by moisture and pressure treatment.
Complex Yarns
Complex, Fancy, or Novelty Yarns: Characteristics include uneven size and color variations arising from deliberate manufacturing irregularities.
Single Novelty Yarns: Include slubs or knots.
Ply Complex Yarns: Composed of a base yarn, effect yarn, and binder yarn.
Types of Novelty Yarns
Slub Yarns: Single or 2-ply with varying twist and bulk.
Typically used in fabrics like shantung and butcher rayon.
Thick-and-Thin Yarns: Uneven yarns made from filament fibers with variations in extrusion pressure.
Flock Yarns: Single yarns with tufts of fibres for texture, common in tweed fabrics.
Bouclé Yarns: Looped structures of 3-ply, soft, and textured.
Core-spun and Covered Yarns: Formed by wrapping one yarn around another for added strength or aesthetic value.
Elastomeric Yarns: Offer stretch with high recovery, essential for activewear fabrics.
Usage and Applications
Complex yarns primarily valued for appearance, providing textural and visual interest in fabric.
Important to take care regarding durability due to irregularities in yarn structure.
Conclusion
Continuous-Filament Yarns vs. Spun Yarns: Understanding differences is crucial for fabric production and characteristic expectations.
Overall properties of yarn and woven fabrics highlight the intricate relationship between materials, processes, and end-use applications.
Yarn characteristics including twist, density, finishing processes, and structure features determine the final fabric usability.