Technical Disscussion

The Energy-saving Packaging Solution—Drying, Crystallizing PLA

13.02.2019 By: Oude

Virgin PLA resin, is crystallized and dried to 400-ppm moisture level prior to leaving the production plant. PLA picks up ambient moisture very rapidly, it can absorb around 2000 ppm moisture at open room condition and most of the problems experienced on PLA arise from inadequate drying. PLA is required to be properly dried before processing. Because it is a condensation polymer, presence of even a very small amount of moisture during melt processing causes degradation of polymer chains and loss of molecular weight and mechanical properties. PLA needs different degrees of drying depending on the grade and how it will be used. Under 200 PPM is better because viscosity will be more stable and ensure product quality.

Like PET, virgin PLA is delivered pre-crystallized. If not crystallized, PLA will become sticky and clump when its temperature reaches 60℃. This is PLA's glass-transition temperature (Tg); the point at which the amorphous material begins to soften. (Amorphous PET will agglomerate at 80℃) Regrind material recovered from in-house production such as extruder edge trim or thermoformed skeleton scrap must be crystalized before it can be reprocessed. If crystallized PLA enters the drying process and is exposed to heating above 140 F, it will agglomerate and cause catastrophic blockages throughout the vessel. Therefore, a crystallizer is used to allow PLA to transition through the Tg while being subject to agitation.

Then PLA needs Dryer and crystallizer.

1. Conventional drying system --- a dehumidifying (desiccant) dryer

Amorphous grades used for heat seal layers in film are dried at 60℃ for 4 hours. Crystallized grades used to extrude sheet and film are dried at 80 ℃ for 4 hours. Processes with long residence times or higher temperatures like fiber spinning need more drying, to less than 50 PPM of moisture.

In addition, Infrared crystal dryer--- IR Dryer have been shown to effectively crystallize Ingeo biopolymer during drying. using Infrared drying (IR). Due to the high rate of energy transfer with IR heating in combination with the specific wave length used, the energy costs can be greatly reduced, along with the size. First test has shown that virgin Ingeo biopolymer can be dried and amorphous flake crystallized and dried within only about 15 minutes.

Infrared crystal dryer --- ODE Design

1. With the processing of Drying and crystallizing at a time

2. Drying time is 15-20mins (Drying time also can be adjustable as customers' requirement on drying material)

3. Drying temperature can be adjustable (Range from 0-500℃)

4. Final moisture: 30-50ppm

5. Energy cost save about 45-50% comparing with Desiccant dryer & crystallizer

6. Space saving: up to 300%

7. All the system is controlled Siemens PLC, easier for operation

8. Faster to start up

9. Quick change-over and shutdown time

Typical PLA (polylactic acid) applications are:

Fiber extrusion: tea bags, clothing.

Injection moulding: jewel cases.

Compounds: with wood, PMMA.

Thermoforming: clamshells, cookie trays, cups, coffee pods.

Blow moulding: water bottles (non carbonated), fresh juices, cosmetic bottles.

More details, please enquire:

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