Advanced Thermoforming, 2nd Edition

Chapter 34Thermoformed Packaging Made of PLA

Polylactides (PLA) represent a relatively new group of thermoplastics for packaging applications obtained from renewable resources. In extensive tests the functional and thermoforming properties of PLA are compared with those of other polymers.¹

PLA’s properties make it suitable for various thermoforming applications, particularly cups for cold bevarages and trays for fruit and vegetables. To produce high‐molecular PLA, a process is used that is sustainable, solvent‐free, and environmentally friendly. PLA is obtained entirely from maize. PLA can equally be produced from other renewable resources, such as wheat, sugar beet, or agricultural by‐products containing natural plant sugars.

First, dextrose is fermented to form lactic acid, which is subsequently converted into cylic dimers (lactides) by condensation and esterification. The dimers are converted to polylactide by catalytic ring‐opening polymerization. Lactic acic occurs in two isomeric forms: L‐lactic acid and D‐lactic acid. The ratio of the isomer units in the polymer chain can be varied during the polymerization process.

34.1 PHYSICAL PROPERTIES

At room temperature, PLA is a crystal‐clear polymer with glass transition temperature between 55°C and 65°C. The physical properties of PLA are improved by orientation of the material, for example, biaxially oriented sheets. PLA with a D‐lactic acid content of less than 8% can be semicrystalline if it has been nucleated, annealed, ...