RepRap Life Cycle Assessment
Based on a debate started in the forums, this page attempts to provide information relevant to a Life Cycle Assement of the RepRap. Due to limitations of manpower and materials, the assesment is based on extrapolating information from other sources. E.g. the American Chemistry Council, The Australian Governments "Review of the Environmental Impact of Wood Compared with Alternative Producs Used in the Production of Furniture" and similar reports.
Only a few hours of searching on the Internet will make it patently obvious that the various LCAs published by various organizations, does show vested interests by most publishing agencies. Some have blatant oversights, e.g. that dumping a substance in a landfill constitutes End of Life, completely ignoring mechanical, biological and chemical decomposition. Furthermore the actual numbers presented in the published LCAs vary hugely, more than what I believe can reasonably be explained by regional differences.
I have tried to take a conservative approach, e.g. trusting the numbers published by organizations like the American Chemistry Council, even though they do appear to have an interest in demonstrating that plastics have a very low impact, the numbers presented by ACC are lower than the comparable numbers by the European counterpart, but the conservative approach dictates that I choose the ACC numbers. I have filtered out some information, which I suspect of being falsified, e.g. a plastic pallet company, which has numbers in excess of 5 times better than the ACC's numbers.
To make matters even worse, PLA and Wood initially performs a storage of CO2 which is then released at the End of Life, whereas expenditure of fossil fuels immediately releases CO2 into the atmosphere. Accounting for this temporary storage of CO2 in an attempt to make CO2 levels of fossil fuels and materials like PLA and Wood appears to somewhat of an "art form", where different reports use different formulas and even where they use the same formulas, certain constants are tweaked, depending on expected lifetime, and other reasonings which appears rather opaque to me. In short, I get the impression that when comparing Wood and similar CO2 storing materials with fossil fuel, you can get almost any result you desire.
There are lies, damn lies and then there is statistics. So any numbers taken from this page is certain to be incorrect; they are based on the intention of being objective, but I have no doubt that anybody can produce any results they may wish.
Most of these numbers originate from the ACC's LCA, in the report called: "CRADLE-TO-GATE LIFE CYCLE INVENTORY OF NINE PLASTIC RESINS AND TWO POLYURETHANE PRECURSORS" (pdf), note this report only takes the plastics to the gate of producer of the plastic granulate, and does not describe the full cradle to grave of the plastics.
The numbers for PLA is taken from: "Applications of life cycle assessment to NatureWorksTM polylactide (PLA) production", and take a similar approach, i.e. it takes PLA only to the gate, since PLA is produced from plant starches, it stores CO2. However the report only takes the PLA to the gate of the factory and does not consider the End of Life situation, thus the CO2 values for PLA are horribly skewed. On top of that are problems related to Cargill Inc. not releasing actual numbers only graphs, making exact readings difficult.
To further compound matters, PLA releases nitrates and phosphates into the waterways during composting, and according to: "Degradation of Biologically Degradable packaging items in Home or Backyard Composting Systems, Schriftenreihe des Lehrstuhls Abfallwirtschaft und des Lehrstuhls Siedlungswasserwirtschaft Nr. 11" there is almost no sign of degradation in backyard composting.
To even further make matters difficult, the LCAs for the subtypes of ABS, HDPE, PET and PLA vary, depending on additives and different processing methods.
|**Content of Delivered Fuel||32.7||13.1||29.7||?|
|** Fuel-related CO2||2,684||1,163||2,147||?|
|** Process CO2||465||315||390||?|
When the PLA is broken down it should be expected that approx 2.8Kg CO2 per 1Kg of PLA is returned to the atmosphere.
The definitions of the various types of energy can be found here. The actual fuel - and even consumed the GJ - varies, depending on what materials are used to produce electrical power, mode of transportation, etc. The energy expenditure is per metric tonnes plastic
|Energy Content of Delivered Fuel||The energy that is received by the final operator who consumes energy|
|Transport Energy||The energy associated with fuels consumed directly by the transport operations as well as any energy associated with the production of non-fuel bearing materials, such as steel, that are taken into the transport process|
|Feedstock Energy||The energy of the fule bearing materials that aare taken into the system but used as materials rather than fuels|
The various Green House Gases (Carbon dioxide, Methane, Nitrous oxide, and the rest defined as GHG are converted into their equivalent CO2 values, based on their different impact), all values given are kg of CO2 per metric tonne of plastic
In conclusion, if any kind of conclusion is possible with this mess of data, it must be said that, without specific knowledge about the subtype of plastic being used, the means of waste disposal in the local neighborhood, the structure of the power grids in both the country of the granulate producer as well as the region where the plastic is consumed, one component appears to be as good as any other. On top of that should be added hard to quantify things like land use for production of starch, material reuse, etc.