Cotton Fiber (Natural Cellulose / Seed Fiber)
Cotton is a single-cell seed fiber composed of ~95% cellulose. It is the dominant natural fiber — over 75% of all natural fiber consumption — and the benchmark for comfort, absorbency, and versatility in staple-fiber spinning.
Quick Facts
| Type | Natural cellulose (seed fiber) |
| Cellulose content | 94–95% |
| Length range | 15–45 mm (variety-dependent) |
| Fineness range | 1.0–4.0 dtex |
| Moisture regain | 7–8.5% (standard conditions) |
| Cross-section | Kidney-shaped, with collapsed central lumen |
| Key morphology | Natural convolutions (转曲); ribbon-like twist along length |
| Thermal behavior | Decomposes at ~150°C; does not melt-drip |
| Wet strength | 10–20% higher than dry strength |
Classification
Cotton is classified by four independent criteria. Each matters for a different reason in yarn engineering.
By Variety (品种)
| Type | Species | Length | Fineness | Significance |
|---|
| Upland (细绒棉) | G. hirsutum | 23–33 mm | 1.43–2.22 dtex | >90% of world production; general-purpose spinning, Ne 10–100 |
| Sea Island (长绒棉) | G. barbadense | 33–45 mm | <1.43 dtex | Longest, finest; premium shirting, sewing thread, fine-gauge knits |
| Asiatic / African (粗绒棉) | G. arboreum / herbaceum | 15–24 mm | 2.5–4.0 dtex | Coarse, short; rarely spun — mainly filling material |
By Maturity (成熟度)
| Maturity coefficient M | Classification | What it means for spinning |
|---|
| M = 0 | Completely immature | No secondary wall; unusable |
| M < 0.7 | Dead fiber (死纤维) | No strength; causes neps and dye defects |
| M < 1.5 | Immature | Weak, poor dye uptake, nep-prone |
| M = 1.5–2.0 | Mature (细绒棉) | Optimal spinning range; best at M = 1.7–1.8 |
| M = 1.7–2.5 | Mature (长绒棉) | Ideal at M ≈ 2.0 |
| M > 2.0 | Over-mature | Stiff, reduced convolutions, poor cohesion |
Maturity affects every fiber property except length: strength, modulus, luster, dye uptake, bending, elasticity, and convolutions. It is the single most important quality indicator after staple length.
By Color (色泽)
| Type | Cause | Spinning value |
|---|
| White (白棉) | Normal mature bolls; ranges white to cream | Primary mill raw material |
| Yellow (黄棉) | Frost-damaged bolls; pigment-stained | Low-grade; limited mill use |
| Gray (灰棉) | Excess rain / low sun / low temperature during growth | Weak; poor spinning quality; good for viscose pulp |
By Processing (初加工)
| Type | Method | Result |
|---|
| Saw-ginned (锯齿棉) | Saw-tooth gin tears fiber from seed | Shorter by 0.5–1 mm; less short fiber; faster; dominant method |
| Roller-ginned (皮辊棉) | Rollers squeeze and pull fiber | Length preserved better; more root-end fibers (黄根); slower |
Properties
| Property | Rating | Engineering implication |
|---|
| Strength | ★★★★☆ Good | Wet strength ↑10–20% — unique among common fibers; ideal for wash-frequent products |
| Moisture absorption | ★★★★★ Excellent | 7–8.5% regain; comfortable, processes well in humidity |
| Alkali resistance | ★★★★★ Excellent | Withstands concentrated NaOH — enables mercerization for improved luster, strength, dye uptake |
| Elasticity | ★★☆☆☆ Poor | Low elastic recovery → wrinkling; blend with polyester or use resin finishing to compensate |
| Acid resistance | ★☆☆☆☆ Very poor | Dilute mineral acids hydrolyze cellulose → strength loss; avoid acid environments |
| Thermal stability | ★★★☆☆ Moderate | Decomposes ~150°C, no melting; safe (no melt-drip) but flammable without finish |
| Bleach / solvent resistance | ★★★★☆ Good | Tolerates oxidizing bleaches and organic solvents; aggressive cleaning possible |
| Microbial resistance | ★★☆☆☆ Poor | Prone to mildew in damp conditions; requires antimicrobial finish for high-humidity use |
Advantages vs. Limitations
Advantages
- Soft, natural hand — comfort benchmark
- Strength increases when wet (unique)
- Excellent moisture absorption
- Alkali-resistant → mercerization possible
- Broadest count range among natural fibers
- Compatible with all spinning systems
- Easy to dye and finish
- Biodegradable and renewable
Limitations
- Poor elasticity → wrinkles easily
- Attacked by mineral acids
- Prone to mildew and microbial growth
- Flammable without treatment
- Hairiness in ring-spun yarns
- Quality varies with weather and region
- Shrinks without finishing treatment
- Long growing cycle; water-intensive crop
Yarn Engineering: Selection Guide
| Application | Recommended cotton type | Key fiber criteria |
|---|
| Fine shirting (Ne 60–100+) | Sea Island / long-staple; combed | Length ≥ 35 mm; fineness <1.5 dtex; M ≥ 1.8; high uniformity |
| General apparel (Ne 20–40) | Upland; carded or combed | Length 27–30 mm; M = 1.5–1.8; moderate fineness |
| Denim (Ne 6–20) | Upland; carded; rotor-spun | Medium length; M ≥ 1.5; trash-tolerant; cost-driven |
| Sewing thread | Sea Island / long-staple; mercerized | Length ≥ 35 mm; high strength; low hairiness; mercerized |
| Knitwear (soft-touch) | Upland / Sea Island; compact or siro-spun | Good maturity; low nep count; soft handle priority |
| Towels & terry | Upland; rotor or vortex-spun | Good absorbency; medium count; low cost acceptable |
| Technical / industrial | Upland; carded; possibly blended | Strength and consistency over aesthetics; cost-sensitive |
Specialty Cotton
| Type | What it is | Key trade-off |
|---|
| Mercerized cotton (丝光棉) | NaOH-treated under tension; cross-section becomes round, convolutions disappear | Luster ↑, strength ↑10–30%, dye uptake ↑; hand slightly firmer |
| Colored cotton (彩棉) | Naturally pigmented (brown, green, etc.); no dyeing needed | Lower yield, shorter, weaker, duller colors; heavy-metal pigment concerns |
| Transgenic cotton (转基因棉) | Bt / herbicide-tolerant GMO varieties | Higher yield, pest resistance; seed quality and long-term stability debated |
| Organic cotton | Grown without synthetic pesticides or fertilizers | Lower environmental footprint; lower yield, higher cost, quality variability |
Summary
Cotton is the reference natural fiber for staple-yarn spinning. Its combination of softness, absorbency, wet-strength gain, and alkali resistance is unmatched by any synthetic. The key to engineering with cotton is matching variety, maturity, length, fineness, and processing route to the target yarn structure and end use — not simply selecting by fiber name. See the Textile Material framework for the broader substance–form–performance logic.