A polylactic acid supplier explains what the production methods of polylactic acid are.

Polylactic acid suppliers explain that polylactic acid is produced using lactic acid as the raw material. Traditional lactic acid fermentation typically relies on starch-based feedstocks. Currently, countries such as the United States, France, and Japan have developed and are utilizing agricultural by-products as feedstocks to produce lactic acid, which is then used to manufacture polylactic acid.

1. Direct polycondensation

Polylactic acid suppliers explain that condensation polymerization is the direct condensation of lactic acid monomers, also known as one-step polymerization. In the presence of a dehydrating agent, the hydroxyl and carboxyl groups in lactic acid molecules are heated and dehydrated, leading to the direct polycondensation of oligomers. By adding a catalyst and continuing the heating process, polylactic acid with a lower molecular weight is further polymerized into polylactic acid with a higher molecular weight.

2. Two-step method

Polylactic acid suppliers explain that lactic acid first forms cyclic dimeric lactide, which is then subjected to ring-opening polymerization to yield polylactic acid. This technology is relatively mature. The main process involves fermenting raw materials to produce lactic acid, followed by purification, dehydration, oligomerization, and thermal decomposition, ultimately leading to the synthesis of polylactic acid.

3. Preparation of high-molecular-weight polylactic acid via reactive extrusion

By combining a batch stirred reactor with a twin-screw extruder and carrying out continuous melt polymerization of lactic acid, PLA with a molecular weight as high as 150,000 can be obtained. Low‑molecular‑weight lactic acid oligomers are further polycondensed in the twin‑screw extruder to produce high‑molecular‑weight polylactic acid. At a reaction temperature of 150°C, with a catalyst loading of 0.5% and a screw speed of 75 r/min, reactive extrusion–based polycondensation in the twin‑screw extruder can rapidly and efficiently increase the molar mass of PLA, reduce the dispersity of the extruded product, and enhance its uniformity. Comparison of DSC curves reveals that PLA prepared via reactive extrusion–induced polycondensation exhibits reduced crystallinity, which helps mitigate the brittleness of PLA materials during service.

Extrusion-grade resin is the primary market application for PLA, mainly used for packaging fresh vegetables and fruits in large supermarkets. Such packaging has become an integral part of European supply chains. Additionally, it is employed in electronic product packaging to promote safety, energy efficiency, and environmental protection. In these applications, PLA’s advantages—high transparency, high gloss, and high rigidity—are fully leveraged, shaping the direction of its use. Moreover, extrusion-grade PLA is increasingly being recognized for horticultural applications, with uses extending to slope greening, wind‑blown sand control, and other fields.

However, PLA extrusion processing is not straightforward. It can only be carried out on certain advanced PET extrusion lines, and the resulting sheet thickness typically ranges from 0.2 to 1.0 mm. The process is highly sensitive to both moisture content and processing temperature. During extrusion, moisture levels are usually required to be below 50 ppm, which places new demands on the equipment’s drying and temperature‑control systems. Moreover, without appropriate crystallization equipment, recycling scrap material poses a significant challenge—this is one of the reasons why large quantities of PLA scrap are readily available in the market.