Polylactic acid (PLA) resins are made from 100% renewable resources such as corn (maize), sugar beet, and sugarcane. A clear thermoplastic, it is fully compostable and biodegradable but has properties very similar to petroleum-based resins that are converted into thermoforming sheet. PLA resins are aliphatic polyesters and they provide cost and performance benefits that are competitive with petroleum-based packaging materials and fibres. They are widely available commercially and are produced on an industrial scale, with proven applications on the consumer market.

PLA sheet for food packaging, including trays for baked goods, fruits, and vegetables, can be produced without any major equipment or tooling modifications.

Thermoformed parts made of PLA have clarity comparable to those formed in OPS and PET. This characteristic, combined with its temperature requirements for product storage, makes thermoformed PLA particularly suitable for food packaging trays for baked goods, fruits, and vegetables, along with medical packaging. It is being used in more applications as the properties of the material are progressively modified. PLA's performance benefits include excellent gloss, transparency and clarity; very good flavour and aroma barrier properties; and easy shaping, printing and embossing. The material's rigidity can translate into lighter packaging and also offers the potential for more disposal options than conventional packaging.

As a plant-based material, production of PLA containers results in a 60% reduction in greenhouse gases and 50% less non-renewable energy use compared to traditional plastics like PET and PS, according to leading suppliers.

The demand for PLA packaging is being driven by eco-conscious retailers such as Wal-Mart. Thermoformers are often less eager to run PLA sheet because of its higher cost and it's particular handling and storage requirements. However, it runs well in cut-in-place thermoforming systems and can also be manufactured using tunnel-heat, plug-assist set-ups.

Manufacturers of thermoformed products who are considering switching to PLA can run it without any major modifications to their equipment or tooling. However, there are some important considerations that need to be addressed in order to achieve a successful switch from traditional materials like oriented PS and PET.

Special Handling and Storage

PLA sheet used to be brittle at room temperature and required special handling and storage considerations. While this continues to be true with some types, many advances over the past few years have improved overall material characteristics. Previously, neither the sheet nor the finished product could be stored at temperatures above 40°C (105°F) or in greater than 50% relative humidity. Exposure to high temperatures or humidity, even for a short period of time, could cause deformities in the material and eventual breakdown of the product. Although this is still the case with some blends, the resistance to heat is continually improving. Sheet and product must be transported in cooled trucks and stored in a climate-controlled warehouse.

All of JINHONGSHENG Thermoforming Equipment’s testing on PLA has been completed with a contact heat, cut-in-place thermoforming system. This equipment permits all heating, forming, and cutting of the material to be performed in a single station using compressed air, without the need of a pre-stretch plug or vacuum.

PLA has a low forming temperature, compared to petroleum-based plastic sheet. Platen temperature must initially be set at 60°C and then increased in 5°C increments until the material starts to get sticky on the plate. A preheater is not required for PLA; it tends to make the material dry out too quickly, without providing any forming benefits. There is a very narrow window for temperature control on the heating platen when forming PLA; as little as a couple degrees Celsius in certain blends.

Mould temperature setting depends on the desiJINHONGSHENG. If the tool has bar locks, setting the temperature at approximately 40°C to 45°C will provide the best forming results. If there is an undercut on the tool, a temperature of 25°C to 30°C will allow the formed product to shrink a bit and eject from more easily from the mould. A simple packaging tray application without special features such as locks or undercuts can typically have a mould temperature anywhere between 25 to 45°C, depending on the blend of the material.

Processors should always keep in mind that different PLA blends will behave in different ways during thermoforming. Different types of blends from different suppliers may require completely different process parameters. Overall, the material's cycle times are consistent with those of PET and OPS.

After being subjected to thermoforming and then being returned to room temperature, the skeletal waste web of PLA gets very brittle and tends to break easily. This presents difficulties in transporting the web; consistent tension control, large rollers and a minimal angle when entering the transport rollers will help prevent breakage.

Once PLA has been heated and stretched through the thermoforming process it loses some of its brittleness. Wall thickness in products can be reduced while still retaining product strength, and the formed parts are suitable for automatic stacking immediately upon leaving the thermoformer.