Degradable plastics- Processing methods and precautions of polylactic acid (PLA)

Polylactic acid (PLA) uses corn, cassava, and other crops as raw materials. It is fermented and extracted by microorganisms to obtain lactic acid and then refined, dehydrated, oligomerized, pyrolyzed, and polymerized. PLA has excellent biodegradability and can be completely degraded by microorganisms in the soil to generate CO2 and water without polluting the environment. PLA has good mechanical properties, a transparent gloss, and low shrinkage and is widely used in producing packaging materials, disposable tableware, home appliance shells, fibers, and 3D consumables. With the strengthening of the plastic restriction order, the market size of degradable plastics has expanded rapidly. PLA occupies a critical position as a well-developed degradable plastic.

Performance comparison between PLA and other polymer materials

The mechanical properties of PLA are similar to polypropylene, and it can replace PP and PET in some fields. It can be processed by the processing method of available plastics, such as injection molding, extrusion, blister, blow molding, spinning, and other molding processing technologies. But the biggest flaw of PLA is its poor heat resistance. Even at around 60°C, ordinary polylactic acid tableware will become soft. However, some modified polylactic acid has overcome this shortcoming, and the long-term use temperature of some modified polylactic acid can reach 120 degrees Celsius. PLA also has the disadvantages of easy hydrolysis and poor impact properties, which must be paid attention to during processing.

PLA processing methods and precautions

  1. PLA extrusion molding

A screw extrusion molding machine can produce PLA sheets, film, fiber, pipe and foam sheets, etc. The main steps are melting→extrusion→cooling→winding and other steps.

  1. PLA injection molding

Injection molding is the most extensive processing method for PLA, and most PLA injection molding machines use reciprocating screw injection machines. Since injection molding is a very mature processing method, injection molding of PLA is relatively simple.

  1. PLA thermoforming

Thermoforming is a processing method that uses sheets as raw materials to produce products. The main principle is to heat and soften flat plastic rigid sheets and then absorb or press them on the surface of the mold, including die forming, vacuum forming, and pressure forming.

PLA thermoforming is suitable for the production of transparent plastic products such as cold drink cups, fruit trays, salad plates, etc. The products have good transparency and gloss and can also be used to produce heat-resistant products such as plastic cup lids and lunch boxes...

 

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