Today, PLA is a very popular filament material for Makers. The number of PLA printed products are already huge. Amorphous PLA combines a low melting point, relatively low shrinkage, and is insoluble in water, which makes it ideal for 3D printing at home. But what do you do with your waste or disposed PLA printed products? What is the best, most sustainable way to dispose PLA printed products?
There are several ways PLA products can be disposed. The PLA can be:
- Landfilled, so as to end-up in waste “mountains” in many countries (not all!)
- Combusted
- Composted
- Recycled
Landfilling
In 2012, the citizens of the USA generated 251 million tons of municipal solid waste. 135 million tons of this amount was discarded to landfills, so roughly half of it. I think it is unbelievable that we still discard such huge amounts of waste this way! At 30%, containers and packaging is a top contributor to total municipal waste, which is not a big surprise, I think. PLA is applied in plastic packaging and disposables a lot. This bio-degradable material deserves a better end-of-life destination than a waste mountain.
Combustion
The waste volume for combustion in incinerators for energy recovery is fairly stable and amounted to about 29 million tons in 2012, so about 12% of the total municipal waste. This energy can then be converted into heat and/or electricity. Combustion of PLA printed products yields energy, but waste can be burned only once. So, it is interesting to learn more about other end-of-life alternatives for PLA.
Composted
There is confusion about the compost-ability and the bio-degradability of PLA. As PLA is made from renewable sources, such as starch (e.g. corn, potatoes, etc.), soy protein, cellulose, and lactic acid, it is compostable, but this process is only considered “composted” when 3 criteria are met:
- The material breaks down into carbon dioxide, water, and biomass.
- The PLA fully disintegrates
- No toxic residues are left and the compost supports plant growth
Biodegradable plastic is plastic that will degrade through the action of naturally occurring microorganisms, such as bacteria, fungi etc. over a period of time. Note that there is no requirement for leaving “no toxic residue“, as well as no requirement for the time it needs to take to biodegrade.
In an industrial composting facility, the complete composting process takes about 1 to 6 months, depending on (relatively high) temperature conditions and material type. The rate of composting PLA in industrial facilities is much higher in comparison to the composting rate of PLA at home. As an example, composting disposed PLA containers and cups take 1 – 3 month’s in an industrial facility, and it takes up to 6 month’s at home.
Despite that PLA producers, retailers, and consumers are positive about the compost-ability of PLA, Jenifer Shen argues that most PLA ends up at landfills and not in composting facilities! Why? Transfer stations that sort municipal solid waste have difficulties sorting mixed PLA and PET plastic streams, as they are both transparent. In case PLA contaminates waste streams of other plastics, buyers offer lower prices or are not interested in purchasing the recycled material at all. In addition, the compost of composters in the USA must be compliant with Organic Materials Review Institute (OMRI) regulations. In accordance to Shen, PLA is not 100% compostable. In case the compost still contains PLA residues, their compost does not meet the OMRI regulation requirements. Therefore, many composters regard PLA as a “contaminant”, too. Despite this, the general trend for composting organic municipal waste is growing and amounted up to 21 million tons, so roughly 5% of the total generated waste in the USA.
Recycling
In accordance to Shen, the best PLA end-of-life option is recycling, just like other plastics. In a European study it appears that the environmental impact of recycling PLA is over 50 times better than composting and 16 times better than combusting PLA! So, Makers should recycle their own PLA! Two opportunities come to mind. The first opportunity is to utilize instant plastic recycling machines, such as the Filabot, for home or small business purposes. These machines collect the printed waste and extrude filament which can be re-used in the printer. Based on my experience in the recycled plastics business, beware of mixing different waste and/or contaminated plastics in such home recycling machines! Basically an inhomogeneous or contaminated plastic mixture might result in poor printing results. Wash and dry only one plastic type before extruding it and clean your machine regularly. The second opportunity is to simply apply ready-to-use PLA filaments based on purified recycled PLA, which are commercially available now. Both ways help reduce one’s environmental footprint and increase sustainability. In conclusion, printing recycled PLA makes sense!
There is big issue related to PLA recycling – specific weight of PLA which is similar to other non natural sourced polyesters like PET. It can make serious problems with rycycling of PET – due to different properties. PLA easily loose molecular weight and this contamitanion can spolil good quality PET flakes what can influent properties of product made of PET flakes (usualy fabrics)
From my point of view, industrial composting of PLA is the best way.
Josef Dolecek
Fillamentum.com
Also use of PLA for filament can be problem – if you loose molecular weight, than recycled filament (having in mind sensitive printing processs) can show volatilities (irregularities) of mechanical parametrers and also color changes.
Attached you can see impact of lost molecular weight in case of recycled PLA compared to virgin polymer.
Dear Josef,
At first, thank you for this very illustratively picture! Of course, when plastics are thermally recycled, degradation occurs. In other words, the polymer chains shorten (the molecular weight distribution changes like you say), the cohesion forces between the polymer (backbone and side) chains reduce, resulting in reduced tensile and elogation after break & impact properties. In addition, temperature sensitive materials, such as PLA, can also turn darker/yellowish. There is technology available to avoid these issues. Finally, in my view you can not conclude that the reduced properties of thermaly recycled PLA are good or bad. That also depends on the printing conditions and requirements of printed products!
Hello Jan,
sorry for delay in discussion.
I wanted you know that my behavior is from my naturality really green – I always try to “calculate” all consequenies of any material choice. I worked in packaging business (and still packaging is big part of our production), so I am familiarized with polymers used in this business…what is really sad. Thats why I reacted your article abour recycling of such particular goods as is filament.
I don´t say “it is impossible” …. I just have in mind huge amount of oil based polymers (especially polyolefins) used for consumables bags – which are not effectivelly recycled – or which cannot be turned back into quality recycled polymer, because oxo additives are used just to dissappear the bag optically, but not chemicaly.
And these agents of oxo degadation affects also scraps of quality polymers, if they are collected togheter.
I just consider question of recyclation of PLA as goal for future, when we solve much bigger issue with standard polymers – polyolephins. Or we should force our government to ban PE bags for retailers because the situation with plastic waste in oceans is dramatical.
There PLA is ready to be good solution..I expect further fall of PLA prices when new technology of synthesis from glycerol is in operation – and PLA become more interesting to be used in packaging, where can replace polyolefins in most cases.
For sure you can transfer scraped filament into new one …but I consider this as not so effective way – because it is not mass production so the effect is not strong.
Hi Josef,
The density of PLA ranges from 1.21 – 1.43 g/cm3; the density of PET bottle grade is about 1.38 g/cm3. In case, there is density difference between PLA and PET, both materials can be simply separated by applying appropriated mineral – water baths after collection by a recycling company. However, when the density of specific PLA grades approaches the density of PET bottle grade, then separation becomes more difficult. In that case contamination of PLA and PET might occur resulting in detoriation in final properties. Those streams are not right for both further plastic processing and composting, but there are enough PLA and PET grades that can be recycled efficiently indeed.
Thank you for writing this article! It is very informative.
I’m slightly confused… You say, “In accordance to Shen, PLA is not 100% compostable. In case the compost still contains PLA residues, their compost does not meet the OMRI regulation requirements.” I wonder if this is just referring to certain compost facilities that don’t achieve high enough temperatures to completely consume all of the polylactic acid? I also think we need to place great consideration on the dye used to color the PLA. If the dye is not compostable, then the compost stream will get contaminated by this dye when the PLA is consumed, which I imagine to be a much bigger concern than unconsumed polylactic acid.
I generate a lot of waste prints when I’m using my 3D printer and I really want to make sure that they are completely compostable. I’m using Ingeo PLA ( http://www.fargo3dprinting.com/products/clearly-natural-ingeo-pla/ ) which I believe is fully compostable in a commercial facility equipped to handle manufactured compostables. Do you think this filament is compostable?
Thanks for writing this Joel – it is extremely informative. We wrote an article on how to be more sustainable when 3d printing and we referenced this article quite a bit. https://blog.pinshape.com/guide-green-3d-printing/