September 8th, 2011 | Published in Information
In this article we will explore the use of sustainable plastics in 3d printing. What does it mean to be sustainable, what are the various types of plastics which are used in 3d printing, and what are the pros and cons of these plastics? We will explore the history of these materials and their attributes as part of our continuing series to educate and inform the rep rap community.
There are two main consumer filament plastics, PLA and ABS. Poly(lactic acid) or polylactide (PLA) is a thermoplastic aliphatic polyester. It is sustainable in that it is derived from renewable resources, such as corn starch (in the United States), tapioca products (roots, chips or starch mostly in Asia) or sugarcanes (in the rest of world). Most consumers of 3d printers purchase their supplies through an online store, and 3d printer companies may have a unique cartridge system for filament deployment. It can biodegrade under certain conditions, such as the presence of oxygen, and is difficult to recycle. Therefore it would never be used in off-planet infrastructure, however is still a viable and exciting source of renewable materials.
PLLA has a crystallinity of around 37%, a glass transition temperature between 60-65 °C, a melting temperature between 173-178 °C and a tensile modulus between 2.7-16 GPa. However, heat resistant PLA can withstand temperatures of 110C (230F).
PLA is more expensive than many petroleum-derived commodity plastics, but its price has been falling as production increases. The demand for corn is growing, both due to the use of corn for bioethanol and for corn-dependent commodities, including PLA.
Stereocomplex blends of PDLA and PLLA have a wide range of applications, such as woven shirts (ironability), microwavable trays, hot-fill applications and even engineering plastics (in this case, the stereocomplex is blended with a rubber-like polymer such as ABS).
Because it is biodegradable, it can also be employed in the preparation of bioplastic, useful for producing loose-fill packaging, compost bags, food packaging, and disposable tableware. In the form of fibers and non-woven textiles, PLA also has many potential uses, for example as upholstery, disposable garments, awnings, feminine hygiene products, and diapers.
ABS, or Acrylonitrile butadiene styrene, is the second most used option in the 3d printing and rapid prototyping community. Its melting point is approximately 105 °C (221 °F). Production of 1 kg of ABS requires the equivalent of about 2 kg of petroleum for raw materials and energy. It can also be recycled.
The advantage of ABS is that this material combines the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber.
The most important mechanical properties of ABS are impact resistance and toughness. A variety of modifications can be made to improve impact resistance, toughness, and heat resistance. The impact resistance can be amplified by increasing the proportions of polybutadiene in relation to styrene and also acrylonitrile, although this causes changes in other properties. Impact resistance does not fall off rapidly at lower temperatures. Stability under load is excellent with limited loads. Thus, changing the proportions of its components ABS can be prepared in different grades. Two major categories could be ABS for extrusion and ABS for injection moulding, then high and medium impact resistance. Generally ABS would have useful characteristics within a temperature range from 10 to 80 °C (50 to 176 °F).
ABS’s light weight and ability to be injection molded and extruded make it useful in manufacturing products such as drain-waste-vent (DWV) pipe systems, musical instruments (recorders and plastic clarinets), golf club heads (due to its good shock absorbance), automotive trim components, automotive bumper bars, enclosures for electrical and electronic assemblies, protective headgear, whitewater canoes, buffer edging for furniture and joinery panels, luggage and protective carrying cases, small kitchen appliances, and toys, including Lego bricks.
I hope that gives a better understanding of the two main 3d printer filament plastics, PLA and ABS.