Polylactic Acid (PLA / Ingeo) Fibre Technology
topic
PLA fibre (polylactic acid, Ingeo by NatureWorks, Blair NE USA) is produced from dextrose derived from corn starch via bacterial fermentation to lactic acid, ring-dimerisation to lactide monomer, ring-opening polymerisation to PLA polymer, melt spinning — the most commercially established bio-based synthetic fibre with 180,000 tonnes/year PLA polymer capacity at NatureWorks' Nebraska facility (BlueScope Steel biorefinery partnership, Cargill corn supply). PLA synthesis pathway: corn → wet milling → dextrose (glucose syrup) → L-lactic acid fermentation (Lactobacillus acidophilus, 40°C, pH 6.0, 50–60% conversion) → lactic acid purification → condensation oligomerisation → depolymerisation to L,L-lactide (dimer ring, 98% L-isomer purity required for crystalline PLA) → ring-opening polymerisation (Sn-octoate catalyst, 185°C, MW 80,000–200,000 g/mol, IV 0.7–1.0 dL/g) → PLA chip. Melt spinning parameters: PLA Tm 170–175°C → melt at 190–210°C → spinneret (0.2–0.3 mm holes, 230–288 filaments) → quench at 20°C → draw ratio 3.0–4.5× at 65–75°C → FDY at 1,500–3,000 m/min. PLA fibre properties: tenacity 3.8–5.0 cN/tex (FDY), elongation 20–35%, moisture regain 0.4–0.6% (similar to PET), Tg 60°C (higher than room temperature, good shape retention), LOI 26% (natural FR advantage — PLA does not melt and drip at ignition as PET does). PLA thermal limitations: low heat distortion temperature (HDT 55–60°C → garments cannot be ironed above 40°C, cannot withstand commercial laundry temperatures >45°C without dimensional change) — severe limitation for apparel compared to PET (200°C ironing). PLA carbon footprint: 0.8 kg CO₂e/kg (NatureWorks Ingeo 2023 EPD, credit for biogenic carbon sequestration) versus virgin PET 5.5 kg CO₂e/kg — 85% reduction — but contested: if biogenic carbon not credited, PLA 3.2 kg CO₂e/kg (42% reduction). Industrial composting biodegradation: PLA EN 13432 certified compostable (>90% biodegradation in 12 weeks at 58°C composting — requires industrial composting, NOT home compost or ocean biodegradable: half-life in ocean >100 years) — industrial composting infrastructure availability critical for end-of-life performance claim validity.
Role
PLA fibre demonstrates both the commercial viability and current performance limitations of bio-based synthetic fibres — achieving 85% carbon footprint reduction versus virgin PET at competitive cost ($1.20–1.50/kg versus PET $0.90–1.10/kg) but constrained by 55–60°C heat distortion temperature that limits apparel applications to cold-wash care label products, making PLA the leading proof-of-concept for bio-based synthetic fibre at scale while simultaneously defining the thermal performance gap that next-generation high-Tg bio-based polymers must overcome to fully displace petroleum-based fibres in mainstream apparel.