PLA (Polylactic Acid / 聚乳酸纤维 / Bio-based Polyester)
PLA (polylactic acid) is a bio-based, melt-spinnable thermoplastic polyester made from fermented plant starch — typically corn, but also sugarcane, cassava, or other carbohydrate-rich crops. Chemically it is an aliphatic polyester, distinct from the aromatic PET polyester. Its defining market proposition is bio-based origin + industrial compostability: it is promoted as a renewable alternative to petroleum-based synthetics. However, the textbook is frank about its limitations: spinnability and fiber quality are notably inferior to PET, and its biodegradability — while real under industrial composting conditions (58°C, high humidity) — is far slower than natural cellulose fibers and essentially non-existent in seawater or soil at ambient temperature. Global PLA production is ~400,000 tons/year (predominantly for packaging), with textile-grade PLA fiber at less than 20,000 tons — a tiny niche within synthetic fibers.
Quick Facts
| Type | Bio-based synthetic (aliphatic polyester); melt-spinnable thermoplastic |
| Raw material | Fermented plant starch (corn, sugarcane, cassava) → lactic acid → lactide dimer → ring-opening polymerization → PLA |
| Commercialized | 1990s (Cargill); 2002 NatureWorks Ingeo™ plant (70,000 t/yr); primarily for packaging, not fiber |
| Global PLA production | ~400,000 tons/year (all uses); textile-grade PLA fiber: <20,000 t/yr — extremely small fiber market |
| Density | 1.25–1.27 g/cm³ (lighter than PET at 1.38) |
| Strength | 3.0–5.0 cN/dtex (comparable to PET); high-tenacity PLLA: up to 18.2 cN/dtex (specialty) |
| Elongation | 30–40% (higher than PET at 15–30%) |
| Melting point | 170–175°C (significantly lower than PET at 255°C) |
| Tg | 56–58°C (lower than PET at ~70°C — limits ironing and hot-wet processing) |
| Moisture regain | 0.4–0.6% (same as PET; hydrophobic) |
| Key trade names | Ingeo™ (NatureWorks), PLA, EcoPLA; medical: Vicryl® (PLGA suture) |
Properties: PLA vs. PET (the honest comparison)
| Property | PLA | PET Polyester |
|---|---|---|
| Bio-based | ★★★★★ Yes (plant-derived) | ★☆☆☆☆ Petroleum-based |
| Strength (cN/dtex) | 3.0–5.0 (standard); up to 18.2 (PLLA) | 3.5–5.5 |
| Melting point | 170–175°C · ★★☆☆☆ | 255–265°C · ★★★★☆ |
| Tg | 56–58°C · ★★☆☆☆ | ~70°C · ★★★☆☆ |
| Heat setting | Poor (low Tm, narrow window) | Excellent (industry standard) |
| Moisture regain | 0.4–0.6% · Both hydrophobic | 0.4% · Both hydrophobic |
| Flame resistance | Slightly better than PET | Melt-drip hazard |
| Chemical resistance | Poor — sensitive to acids and alkalis | Excellent |
| Spinnability & fiber quality | ★★☆☆☆ Inferior to PET | ★★★★★ Reference standard |
| Biodegradability | Industrial compost only (58°C); not in soil/seawater | None |
| Cost | Higher than PET | Lowest of all fibers |
Advantages vs. Limitations
Advantages
- Bio-based (plant-derived, not petroleum) — renewable feedstock
- Melt-spinnable on modified PET equipment
- Comparable strength to PET (3–5 cN/dtex standard)
- Slightly better flame resistance than PET
- Industrial compostable (ISO 17088 / EN 13432 certified conditions)
- Medical-grade biocompatible and bioresorbable (PLGA sutures, implants)
- High-tenacity PLLA variant possible (research-grade, up to 18 cN/dtex)
- Lower carbon footprint than PET (plant carbon sequestration during growth)
Limitations
- Lower melting point (170°C) and Tg (57°C) — cannot survive PET-level heat processing
- Inferior spinnability and fiber quality vs. PET (the textbook is explicit about this)
- Poor chemical resistance (acid + alkali sensitive)
- NOT biodegradable in soil, seawater, or landfill — industrial composting ONLY
- Degrades as crystalline fragments in physiological conditions, not dissolved molecules
- Far slower degradation than cotton, viscose, and other natural cellulosics
- Very small textile fiber market (<20,000 t/yr); supply chain immature
- Higher cost than PET with worse performance — difficult commercial proposition for commodity textiles
- Competes with food crops for land (corn-based PLA)
Niche Applications
| Application | PLA form | Key criteria |
|---|---|---|
| Medical sutures (PLGA / Vicryl®) | PLGA copolymer multifilament; bioresorbable | Controlled degradation in the body (hydrolysis → lactic acid); the most successful PLA fiber application |
| Disposable nonwovens (wipes, hygiene) | PLA staple; spunbond or carded | Bio-based marketing claim; industrial compostability; single-use acceptable |
| Eco-apparel (niche sustainable brands) | PLA staple or filament | Bio-based story; limited durability expectations; cold-wash, line-dry care instructions mandatory |
| Packaging textiles (tea bags, coffee filters) | PLA nonwoven | Food-contact safe; bio-based; industrial compostable after use |
Summary
PLA is a fiber with an attractive story — plant-based, renewable, industrially compostable — but its textile performance lags significantly behind PET in spinnability, heat resistance, chemical durability, and cost. The textbook's assessment is measured: PLA's biodegradability claim must be qualified ("industrial composting only"), and its spinnability and fiber quality are "明显差于涤纶" (clearly inferior to PET). Its real success has been in medical (PLGA sutures) and single-use packaging, not in durable textiles. For the yarn engineer, PLA is currently a niche bio-based option for cold-wash, low-durability, sustainability-marketed applications — not a general-purpose PET replacement. See the Textile Material framework.