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What is the production principle of polylactic acid fiber
source：www.kingcharmgroup.com | Release time：2026-06-221. Starch saccharification and fermentation to produce L-lactic acid
Raw materials: Starch from crops such as corn, cassava, and straw;
Hydrolysis: Starch is hydrolyzed into glucose by adding water and amylase;
Microbial fermentation: Lactic acid bacteria ferment glucose to produce L-lactic acid monomers;
Purification and concentration: Remove impurities and pigments to obtain high-purity lactic acid aqueous solution.
2. Lactic acid polymerization (two-step method, mainstream in industry)
Step 1: Oligomerization (Prepolymerization)
Lactic acid is dehydrated by heating, and intermolecular hydroxyl and carboxyl groups are dehydrated and condensed to produce oligomeric lactic acid (with a molecular weight of several thousand).
Step 2: Depolymerize to generate lactide
Low molecular weight lactic acid undergoes high-temperature and vacuum cracking to remove cyclic dimer - L-lactide;
Lactide undergoes distillation purification to eliminate impurities, which is the key to producing high-quality PLA.
Step 3: Open Loop Aggregation
High purity lactide is added to the catalyst, and at high temperatures, the cyclic molecules open and the chain segments continue to elongate, forming a high molecular weight polylactic acid resin;
Squeeze and slice to obtain milky white PLA slices (spinning material).
Reaction essence: Lactic acid small molecule → cyclic lactide intermediate → long-chain polyester polymer.
2、 Downstream: Melt spinning to manufacture polylactic acid fibers
PLA is a thermoplastic polyester that uses melt spinning and is similar to polyester spinning equipment, without the need for solvents.
dry
PLA is highly hygroscopic and will hydrolyze and break chains at high temperatures. Slices should be vacuum dried until the moisture content is low.
melt extrusion
Dry slices are fed into a screw extruder and heated to 160-180 ℃ to melt into a uniform melt;
The melt is filtered to remove impurities and ensure that spinning does not block the pores.
Spray forming
The high-pressure melt is transported to the spinning box and extruded into a liquid fine stream from the micro holes of the spinneret;
Cold air at room temperature rapidly cools, and the liquid filament solidifies into solid primary filaments.
Drawing and shaping (determining fiber strength)
The strength of the initial silk is low, and through multiple sets of hot roller stretching, the molecular chains are aligned neatly along the fiber axis, greatly improving the strength and modulus;
Low temperature heat setting eliminates internal stress and reduces shrinkage during later water washing.
Post sorting by category
Long filaments: oiled and coiled into silk cakes;
Short fibers: bundled, cut, and packaged, can be directly used for cotton spinning blends;
Non woven fabric: melt spun into a mesh, hot-rolled/hydroentangled PLA non-woven fabric.
3、 Core Chemical Reaction Logic
Lactic acid structure contains both - COOH (carboxyl) and - OH (hydroxyl), belonging to hydroxy acids:
Condensation dehydration: n HO-CH (CH3) - COOH ⇌ Low molecular weight lactic acid+H ₂ O
Cyclization depolymerization: oligolactic acid → lactide (cyclic dimer)
Ring opening polymerization: Lactide is ring opened to form long-chain polylactic acid
Spinning only involves physical changes: polymer melting, stretching orientation, and no chemical reactions
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