March 13, 2013
PLA, Raw Materials
Digital Design is a fairly new category within design, and with it came the birth of 3D printing. Now, one may ask themselves, “What exactly is a 3D printer and what can it do?” In essence, it is a new technology where one may take a digital file and use that file to create an actual, physical replication. The results may only be limited by one’s own imagination. However, in order to even utilize technology of this form, one needs to possess the hardware that corresponds with the applied science. A couple machines that qualify for such a role include the MakerBot and RepRap. While both produce similar results, I am going to focus on the MakerBot for the sake of this paper.
MakerBot is a company based in New York with several kinds of 3D printers. However, in order to make the 3D models that they were built for they first require some sort of filament. The two filaments in use primarily for the MakerBot are ABS, also known as Acrylonitrile butadiene styrene, and PLA, or Polylactic Acid. Both of these items are fall under the category of thermoplastics. Basically, in laymen’s terms, it is a polymer that becomes moldable upon heating to a certain temperature. After it has cooled, the material returns to solid. Unfortunately, like many products in this day and age, it is not found in any sort of common state where it may be harvested in a readily state. In fact, both of these materials need to be synthesized in a particular way. Of the two proposed materials, PLA stands out due to how it is manufactured, as well as its proclaimed “greenness”. The overall materials that go into the production of polylactic acid and where they originate from are important areas of interest.
First and foremost, it is easiest to start off with the raw materials that are far less complicated to acquire and utilize in order to make PLA. Generally, PLA is derived from 100% renewable resources, such as corn and sugar beets. According to information on NatureWorks, “In North America, corn has been used first because it is the most economically feasible source of plant starches” (NatureWorks LLC: Raw Materials 1). PLA in itself does not require corn, but rather just some sort of sugar source. The chosen crop - whether it is in fact corn, sugar beets or some other crop - is then put through a series of steps in order to achieve the final product.
Production of Dextrose
Initially, the corn is sent to a wet mill, which essentially separates the corn into several byproducts. The crucial byproduct needed, however, is the cornstarch. From there, the cornstarch is, “separated and converted into dextrose” (Rogge 2070). In order to retrieve the dextrose, the cornstarch must be “in the presence of acid at a high temperature” (Rogge 2070). Unfortunately, I could not find the specifics as to what acid. Then, after the intended substance is achieved, it is then neutralized with soda ash. The dextrose then eventually crystallizes from the solution once all the impurities are removed. Immediately afterwards, a couple of materials are then, “employed for the refining of the hydrolyzate” (Rogge 2070). These two ingredients are bone char and activated vegetable carbon.
Bone char, in simple terms, is a “black, granular solid” achieved by calcining bones – involves the heat treating, or process for driving off volatiles, that essentially cause a change in either “crystalline or molecular structure due to rearrangement or phase change” (Staffin 5). The United States’ source of bone char usually stems from Scotland, Egypt and Brazil, who consequentially receive it from Afghanistan, Argentina, India, and Pakistan. The bones originate from the cattle of the land.
Activated Vegetable Carbon is the second material used in the continued refinement of the crystallized dextrose. This raw material is just a fancier way for denoting a form of charcoal. Activated charcoal is a type of carbon that is processed to possess small pores that effectively increase the overall surface are available for adsorption. Activated Charcoal can be produced from any type of plant material, and thus is readily available in nature, and only requires a slight process to bring to fruition.
The preparation of activated carbon generally requires two separate steps. The first step requires the actual carbonization of carbon containing material at relatively high temperatures without exposure to oxygen of any sort. However, these temperatures never exceed 800 degrees Celsius. The second step requires the activation of the transformed product.
First, the initial step involves the elimination of “non-carbon elements such as oxygen and hydrogen as volatile gases by pyrolytic decomposition of the starting material” (Mondragon 1). The pores that form as a result of the first step are not yet fully developed, and as a result, retain a low surface area. Therefore, the adsorption capacity needed has failed to be reached thus far, naturally leading into the second step of the process to create the raw material of activated vegetable carbon.
Next, the second step increases the preliminary pore surfaces created during the initial step. The pores are essentially enhanced overall, with and increase in the volume and diameter of the pores. This enhancement of the material is carried out by “an oxidation reaction at high temperatures” (Mondragon 1). The oxidizing agents that are utilized in the process vary from steam to carbon dioxide to air, or even a mixture of these items. This oxidation creates the prime surface area with pores of numerous sizes and shapes upon the conversion of the raw carbonized material. Once the dextrose is obtained through the numerous steps of refining and processing, it is then the conversion of the aforementioned material into lactic acid that proceeds the next few steps.
Production of Lactic Acid
There are two ways in which one can create lactic acid. One way is through chemical synthesis, while the other entails carbohydrate fermentation. Despite the fact that both are ways of retrieving lactic acid, it is ultimately through the process of carbohydrate fermentation that most lactic acid, used in the production of Polylactic Acid (PLA), is created. Therefore, it is unimportant in this manner to cover the raw materials used in the chemical synthesis procedure since it is not used.
Cargill Dow created a whole new process for creating lactid polymers and products. In this procedure, “sodium lactate is produced by fermentation and the broth is concentrated and extracted with a tertiary amine solvent mixture under CO2 pressure to produce and precipitate a sodium bicarbonate salt and an amine lactic acid extract” (Henter 1127). This fermentation takes place with the manufactured yeast, CB1. However, there is little information in regards to the specifics of this yeast. Luckily, the byproduct can be broken down and then recycled back into the process. The amine is then back extracted with the implementation of hot water – usually at around 140 degrees Celsius – and 100 psig. Psig stands for the measure of pressure it is put under.
However, seeing as Cargill Dow’s process is fairly new, it is noteworthy to mention the previous manufacturing process employed. In the traditional practice, lactic acid is normally created through the process of carbohydrate fermentation. In simple terms, the dextrose that was made from the corn is then allowed to ferment through use of certain bacteria, and even fungal strains at times. The factors that go into picking the carbohydrate fermenter are, “...price, availability, and its purity” (Datta 1123). Then, “calcium hydroxide/carbonate is added to the fermenters” in order to keep the pH balance at a reasonable number – usually at around 5-6. The resulting liquid solution is then filtered and purified further. Sulfuric acid is then added to convert the salt into lactic acid, as well as an insoluble material that is filtered out.
The organisms usually implemented are “Lactobacillus delbrueckii, L. amylophilus, L. bulgaricusand L. leichmanii” (Datta 1123). These organisms still need some nutrients in order to provide their services in the production of lactic acid. Unfortunately, seeing as these organisms are naturally occurring on Earth, it is impossible to find any sort of direct source from which these bacteria spawn. However, seeing as they do need nutrients, it can be assumed that they occur in larger numbers when there is an abundance on which these organisms may thrive.
The nutrients and materials needed to sustain these fermenters are provided usually by corn steep liquor – a byproduct of wet milling. During the initial stages of the milling process, the corn is soaked in water. It is this liquid that comes out at the end of it all that makes up the CSL, or corn steep liquor. To get and even more in depth look of the composition of corn steep liquor, please take a look at Table 1. The reason CSL is such a prime candidate as a nutritive source, is that it, “is very low in fat and fiber” (Keller 4).
The calcium carbonate added to the fermenters is not exactly a hard substance to come by. There are in fact several geological sources, as well as some biological sources of which this compound can be retrieved from. The geological sources consists primarily of rocks, specifically calcite, aragonite, vaterite, travertine, marble, chalk, and limestone.
Next, is the sulfuric acid used for the conversion of the salt into lactic acid. Generally, there exist a single, well-documented process for creating sulfuric acid. This method is know as the contact process, in which sulfur is burned to form sulfur dioxide, and then oxidized to sulfur trioxide in the presence of vanadium (V) oxide catalyst. This sulfur trioxide is added to “free water to produce sulfuric acid” (Petheric 5). The end result is the sought after sulfuric acid used for retrieving the lactic acid to proceed with polylactic acid production.
Production of Polylactic Acid
Lactic acid is the main component for synthesizing PLA. To turn lactic acid into polylactic acid, it has to go through a series of steps in order to get the end result. According to a work produced by David Henton and his esteemed colleagues, “Cargill Dow LLC has developed a patented, low cost continuous process for the production of acid-based polymers” (Henton 1841). In doing so, a commercially feasible polymer made from renewable resources.
The process initiates with the “continuous condensation of aqueous lactic acid to produce low-molecular PLA pre-polymer” (Henton 1841). Basically, the lactic acid is allowed to condensate so that the removal of water can occur – thus producing a low-molecular weight PLA pre-polymer. This pre-polymer is then turned into a “molten lactide mixture” with the addition of a tin catalyst. This tin catalyst is usually the material know as Tin (II) 2-ethylhexanoate, or more commonly referred to as tin (II) octoate. This catalyst produces the end result, high-molecular weight polymer. Without this catalyst, the process would be near impossible.
Unfortunately, there is limited material on the catalyst, tin (II) 2-ethylhexanoate. This makes it somewhat difficult to trace back as far as the acquisition and production of this material. The only information pertaining to this is not exactly the most scholarly – that source being Wikipedia. However, out of sure interest as to the origins of this, I took a look at the information available on the site. In essence, the catalyst is a compound of tin (II) oxide and 2-ethylhexanoic acid.
Then, based on basic chemistry, it can be deduced that tin (II) oxide is produced through the oxidation of Sn(II). Tin, in itself is a naturally occurring element on Earth and is therefore readily available. Oxygen, for obvious reasons, is also easily obtained.
On the other hand, 2-ethylhexanoic is a bit more complex as far as manufacturing goes. According to the Kirk-Othmer Encyclopedia of Chemical Technology, it is “Produced by the aldol route from butyraldehyde in three steps: aldol condensation; hydrogenation of the carbon-carbon double bond; and oxidation of the branched-chain saturated aldehyde to 2-ethylhexanoic acid” (p. V5: 177). As much as I would like to cover the rest of the production of this acid to its core elements, it is realistically impossible to cover in full length due to the brevity of this paper and many subjects that need to be encompassed. There are still other factors to account for as far as other categories go within the entire topic of polylactic acid.
Transportation and Distribution, Use/Re-use/Maintenance, Recycling
Transportation and Distribution is a integral component when thinking in terms of PLA, because in order to be utilized for the purpose it was created then it needs to get taken to the appropriate facilities. However, there is limited information as to the transportation and distribution, and when Dylan made a request as to specifics, but MakerBot would not oblige. Therefore, fossil fuels are really the only raw materials that can be assumed in the use of this category because the methods most likely rely on the crude material – much like most transportation nowadays. This is not the only category with limited specifics.
Use, Re-use, and Maintenance also lack an abundance of documentation. There are no raw materials that I could find pertaining to this subject matter. However, seeing that once PLA is used in a print there is no material required for needed for any kind of upkeep or maintenance. The same applies to re-use portion of this. It truly is a shame that there is such a limited supply of material to find.
Recycling is the only subject that has some material as to what happens with PLA. Unfortunately, despite polylactic acid’s biodegradability and recyclability, it is not the case in real life. In fact, currently the statistics for PLA are as follows, “Current – 23.5% incineration/76.5% landfill” (Madival 6). This is primarily due to the lack of commercially available centers for recycling polylactic acid.
Ultimately, the materials that go into the production of PLA are expansive. However, there are many areas where there just simply is not enough matter on the subject matter, such as transportation. The use of PLA in the upcoming development could be revolutionary. That is assuming that it does become commercially recyclable and implemented universally. Regardless of how green like PLA may be, there will still be some sort of fossil fuel consumption at some point in life cycle of the product.
Jamshidian, M., Tehrany, E. A., Imran, M., Jacquot, M. and Desobry, S. (2010), Poly-Lactic Acid: Production, Applications, Nanocomposites, and Release Studies. Comprehensive Reviews in Food Science and Food Safety, 9: 552–571. doi: 10.1111/j.1541-4337.2010.00126.x
Drumright, R. E., Gruber, P. R. and Henton, D. E. (2000), Polylactic Acid Technology. Adv. Mater., 12: 1841–1846. doi: 10.1002/1521-4095(200012)12:23<1841::AID-ADMA1841>3.0.CO;2-E.
Kirk-Othmer Encyclopedia of Chemical Technology. 4th ed. Volumes 1: New York, NY. John Wiley and Sons, 1991-Present., p. V5: 177]
Garlotta, Donald. A Literature Review of Poly(Lactic Acid). 2. 9. Plenum Publishing Corporation, 2002. 63-83. Web.<http://naldc.nal.usda.gov/download/4048/PDF>.
Davenport, W.G., M.J. King, B. Rogers, and A. Weissenberger. Sulphuric Acid Manufacture. 2006. Web. <http://www.saimm.co.za/Conferences/Pyro2006/001_Davenport.pdf>.
Mondragon, Fanor; Fernandez, John; Jaramillo, Alfredo; Quintero, Gustavo. “PROCESS FOR MAKING ACTIVATED CHARCOAL” Patent 5,614,459. Mar. 25, 1997. Web <https://docs.google.com/a/google.com/viewer?url=www.google.com/patents/US5614459.pdf>
Rogge, Robert H. PILOT PLANTS: Dextrose from Cornstarch. Industrial & Engineering Chemistry 1949 41 (9), 2070-2077. Web. <http://pubs.acs.org/doi/abs/10.1021/ie50477a058>
Madival, Santosh, Rafael Auras, Sher Paul Singh, and Ramani Narayan . "Assessment of the environmental profile of PLA, PET and PS clamshell containers using LCA methodology."Journal of Cleaner Production. 17.13 (2009): 1183–1194. Web. 12 Mar. 2013. <https://vpn.lib.ucdavis.edu/,DanaInfo=ucelinks.cdlib.org,Port=8888 sfx_local?sid=EI:Compende&xgenre=article&issn=0959-6526&date=2009&volume=17&issue=13&spage=1183&epage=1194&title=Journal of Cleaner Production&atitle=Assessment of the environmental profile of PLA, PET and PS clamshell containers using LCA methodology&aulast=Madival&aufirst=Santosh&isbn>.
Henton, David E., Patrick Gruber , Jim Lunt, and Jed Randall. "Polylactic Acid Technology." Natural Fibers, Biopolymers, and Biocomposites. (2005): 527-577. Web. 12 Mar. 2013. http://www.jimluntllc.com/pdfs/polylactic_acid_technology.pdf.
Petherick, Jonathon. "THE MANUFACTURE OF SULFURIC ACID AND SUPERPHOSPHATE ." . Farmers Fertiliser Ltd. Web. 12 Mar 2013. <http://nzic.org.nz/ChemProcesses/production/1B.pdf>.
Datta, R. and Henry, M. (2006), Lactic acid: recent advances in products, processes and technologies — a review. J. Chem. Technol. Biotechnology., 81: 1119–1129. Web. <http://onlinelibrary.wiley.com/doi/10.1002/jctb.1486/full>
Investigating the Embodied Energy of MakerBot PLA Filament
The 3-D printer has the potential to revolutionize product design and manufacturing. A 3-D printer builds objects layer by layer, without the need for industrial machinery or molds. Currently, 3-D printers are primarily used for prototyping product designs, but MakerBot Industries, which creates low-cost printers for hobbyists, is creating a market for a much larger scale of implementation. The printing material commonly considered to be most environmentally friendly is polylactic acid (PLA). The investigation presented below attempts to illuminate the life cycle and thus the embodied energy of items produced by MakerBot printers using PLA.
Who Makes PLA?
The embodied energy of MakerBot PLA filament obviously depends on the manufacturing process used. It appears that MakerBot Industries does not disclose the source of its PLA. When asked by email, the company declined to provide information on its manufacturing process or facilities, distribution chain, or supplier. A 2009 life cycle assessment of PLA clamshell containers claims: "In the USA, PLA is manufactured by NatureWorks™ PLA, Blair, Nebraska" (Madival et al. 1186).
I sought to confirm that NatureWorks is the primary supplier of PLA in the United States. In an article written by Cargill Dow, the parent company of NatureWorks, Cargill explains that "the commercial viability [of PLA] has historically been limited by high production costs (greater than $2/lb)" (Henton et al. 528). Cargill has developed a number of processes to decrease the production cost of PLA, presumably making the material more commercially viable. Based on these process improvements, the company built a facility in Blair, Nebraska with a PLA production capacity of 300 million pounds per year. To provide the PLA factory with lactic acid, the principal raw material used in PLA production, the company opened a "lactic acid plant, with a capacity of 400,000,000 lb, [which] exceeds that of all producers combined" (Henton et al. 531). Based on Cargill's dominance in lactic acid production and its heavy investment in PLA technologies as well as lactic acid, it is likely that its subsidiary, NatureWorks, is in fact the primary supplier of PLA in the United States. As such, I assume MakerBot manufactures its PLA filament using NatureWorks PLA pellets. Thus, the embodied energy of NatureWorks pellets determines, in part, the embodied energy of MakerBot PLA filament. To understand the embodied energy of these pellets, I researched the production process that NatureWorks uses.
The basic process by which PLA is produced is a series of chemical transformations beginning with a sugar source. In the case of NatureWorks PLA, this sugar source and primary raw material is corn. Vink et al. describe the transformation as a five-step process: production of corn, processing of corn into dextrose, fermentation of dextrose into lactic acid, and two final chemical processes: “conversion of lactic acid into lactide [and] polymerization of lactide into polylactide polymer pellets” (59).
I found no information on the production of corn for the NatureWorks facility. I assume that the Blair, Nebraska location was chosen in part because Nebraska and nearby Iowa are well known for their corn production. NatureWorks provides detailed information on the benefits of its environmental practices; based on the lack of information about its corn sources, it seems reasonable to conclude that the company either uses conventional farming methods or outsources its corn production altogether.
Once corn and other raw materials arrive at the NatureWorks facility, the remainder of the PLA production process occurs on-site. The corn is processed into dextrose at “a corn wet mill (CWM), where the starch is separated … and hydrolyzed to dextrose using enzymes” (Vink et al. 60). I found no information on the specific processes in use. Cargill is a major producer of “corn and sugar-based products serving the Food, Feed, and Fermentation segments” with facilities in at least eight states (“Cargill Corn Milling North America”). Thus, I assume the processes NatureWorks uses to produce dextrose are similar to those of Cargill’s other subsidiaries. I found no information readily available on this subject, and because it is tangential to the process of PLA production for the MakerBot, further investigation is outside the scope of my research.
The earliest stage of PLA production that I was able to explain is the fermentation of dextrose into lactic acid. The established method of fermenting lactic acid depends on various bacteria that produce lactic acid as a metabolic byproduct (Datta and Henry 1123). At various stages of this process, calcium hydroxide or calcium carbonate, sulfuric acid, and numerous nutrients must be added (Datta and Henry 1123). Cargill Dow employs proprietary yeast that it asserts “significantly reduces the need for lime and sulfuric acid, as well as the production of gypsum” (“Cargill wins”). Cargill’s yeast produces sodium lactate, which is “extracted with a tertiary amine solvent mixture under CO2 pressure.” A high-pressure, high-temperature water stream extracts and separates the lactic acid and solvent, and the solvent is recycled. The process also generates sodium bicarbonate, which is broken down by heat and recycled (Datta and Henry 1127). Numerous details remain unclear. The exact process by which Cargill’s yeast produces lactic acid is not specified, nor are any other additives, waste products, or energy requirements. The lactic acid produced must be purified for use in polymers, but I found no information on the purification process that Cargill uses (Datta and Henry 1127).
The conversion of lactic acid into lactide is a multi-step process. The exact process, and therefore the energy requirement of each step, is proprietary. A water-lactic acid mixture is condensed into “low molecular weight PLA prepolymer.” The resultant material is “converted into a mixture of lactide stereoisomers using a catalyst…” (Henton et al. 529). An older edition of Henton et al. specifies that this lactide stereoisomer conversion uses “tin catalysis” (Drumright, Gruber, and Henton 1841). I found neither indications that the process has changed nor any justification for the removal of this detail; I therefore cannot determine whether tin is still used as a catalyst at this stage or what other materials might be introduced or produced. As the final step of lactide production, “the molten lactide mixture is then purified by vacuum distillation” (Henton et al. 530). I was unable to find specific information on the processes by which these transformations take place. Therefore, I cannot speculate regarding the energy embodied in this process or the embodied energy of any additional materials that may contribute to, or result from, lactide production. However, the description of the lactide mixture as “molten” implies a considerable component of heat in the process.
The final process in the production of NatureWorks PLA is the polymerization of lactide. Henton et al. describe this as “an organo tin-catalyzed, ring-opening lactide polymerization in the melt” (530). Specifically, this reaction employs tin octoate, and it requires two to five hours at 180-210 degrees Celsius (Henton et al. 537). A much earlier paper unassociated with Cargill indicates “the formation of a side product, hydroxytin(II) lactate (HTL)” (Schwach et al. 3431). I found no indications that HTL is recyclable, which indicates it may be a waste product and may necessitate the loss of a portion of the tin octoate catalyst, both of which increase the embodied energy of PLA. However, I was unable to confirm that the NatureWorks polymerization process has an HTL byproduct. The ring-opening polymerization appears to be very similar to the production of lactide; according to Drumright, Gruber, and Henton, both products apply a tin catalyst to molten lactide (1841-2). This suggests that there are likely additional components to these reactions that NatureWorks .
NatureWorks produces PLA pellets that are then distributed to manufacturers (Vink et al. 59). I found no information regarding the processing of PLA pellets into MakerBot PLA filament. It appears that no information on either the process or the manufacturer is publicly available.
Once pellets leave the NatureWorks factory, they must be transported to a MakerBot facility for filament production. I asked MakerBot Industries about its manufacturing and distribution infrastructure by email; the company declined to answer. Therefore, I can provide very little information on the production or transportation of PLA filament for MakerBot Industries. As a generalization, however, I did find a remarkable variation in the energy of transportation depending on how the cargo is conveyed. The authors of a life cycle assessment of PLA clamshell containers similarly could not find specific information about transportation. However, they provide approximate energy requirements for the transportation of materials. Since NatureWorks is the primary supplier of PLA in the United States, the PLA resin used in these clamshell containers originates in the same factory as MakerBot PLA filament. This study found that “by transporting by train, the global warming impact and non-renewable energy are reduced by around 96% compared to a 16-ton truck” (Madival et al. 1190). While I cannot determine MakerBot's method of conveyance for PLA filament, the mode of transportation clearly affects the product's embodied energy.
Unlike many plastic products, the end use of MakerBot filament further increases its embodied energy. Most PLA products have two stages of production. Once NatureWorks pellets are formed into end products, no further processing or transformation is required. MakerBot filament is unique: its end use requires substantial energy, because it must be melted and re-formed into specified shapes. MakerBot allows its users to customize the extrusion temperature, but the company suggests heating the PLA to between 220 and 230 degrees Celsius ("Printing with PLA"). Additionally, this step takes much longer than industrial processes. The MakerBot Replicator 2, for instance, is able to print layers at thin as 100 microns (“MakerBot Replicator 2”). The complex process of printing with MakerBot printers is outside the scope of my research, but the energy that the process imbues in printed materials is in excess of the requirements of typical PLA products, which the end user typically does not melt and extrude.
Re-Use, Recycling, and Waste Management
When end users are finished with PLA printed objects, they face a unique challenge: printed objects bear no markings to indicate their material or recyclability. I found no indications of any existing system or process to enable the re-use of PLA after printing. Thus, I assume printed materials are discarded in a similar fashion to PLA clamshell containers. According to Madival et al., “commercially available recycling centers for the composting and recycling of PLA are not available” (1187). Thus, the disposal of PLA products as of 2009 was 23.5% incineration and 76.5% landfill, with no indication of significant composting or recycling (Madival et al. 1187). I found no information on the energy requirements of any of these processes.
Since I was unable to find any information about the manufacturing of MakerBot PLA filament from NatureWorks pellets, or, indeed, any aspect of the filament production beyond the NatureWorks factory gate, I cannot report on the energy sources or uses of these processes. NatureWorks, however, provides an eco-profile with detailed information on its energy uses.
NatureWorks states that it has "on-site renewable generation, such as installed photo-voltaic systems and on-site windmills" (Vink et al. 64). However, Vink et al. also state, "NatureWorks production is not located on a site with an economically competitive wind resource. Therefore, on-site production of wind energy is not an option" (65). The data in the company's eco-profile confirm the latter assertion. Solar contributes 0.00 megajoules of energy per kilogram of PLA, and although Wind contributes 6.68 megajoules, this wind power is categorized as "energy content of delivered fuel" (Vink et al. 67). Clearly, these data indicate that on-site renewable energy sources do not contribute to the production of PLA.
In order to offset its non-renewable energy use, NatureWorks purchases Renewable Energy Certificates (RECs) (Vink et al. 64). According to NatureWorks, "For each megawatt-hour of power from renewable resources in the US, there is one less MWh of power generated from conventional sources such as coal or natural gas" (Vink et al. 64). However, the company acknowledges that RECs are sold separately from power, and that when RECs are sold to different consumers than the associated power, the energy "is no longer emissions-free" (Vink et al. 65). The company's states that "NatureWorks must purchase its electricity from the local utility, OPPD, which did not have sufficient green power available for NatureWorks in 2006. Therefore, today RECs are the only renewable energy source accessible for NatureWorks" (Vink et al. 65).
Because OPPD cannot provide NatureWorks with sufficient renewable energy, NatureWorks uses almost exclusively non-renewable energy sources despite its purchase of RECs. Each kilogram of PLA uses 0.2 MJ of hydroelectric energy, 0.00 MJ of geothermal, solar, and tidal energy, and 6.68 MJ of wind energy, for a total of 6.70 MJ of energy from renewable sources out of a total 58.41 MJ of energy used (Vink et al. 67). Thus, 88.5% of the energy used in the production of NatureWorks PLA pellets comes from non-renewable resources. On average, each kilogram of PLA requires 534.2 grams of fossil fuels, in the forms of crude oil and gas, 19.4 grams of coal, and one milligram each of peat and wood (Vink et al. 67).
I cannot provide an estimate of the embodied energy of MakerBot PLA filament for the same reason I was unable to determine the transportation energy or overall sources of energy: beyond the NatureWorks factory gate, I found no information on the process of filament production. The pellets the company uses have an embodied energy at the NatureWorks factory gate of 58.41 MJ, as specified previously. Transportation to MakerBot Industries, filament manufacturing, distribution, and end use surely require substantial energy, although I cannot calculate these energies at this time. In short, the embodied energy of one kilogram of PLA filament is almost certainly well above 58 MJ.
Overall, I found very limited information about the production of MakerBot PLA filament. The vast majority of available information concerns the company's likely supplier, NatureWorks. The reputation of PLA as a green material belies the complex, industrial processes involved in producing it. In addition, since most of the information about these processes comes from voluntary and partial disclosures on the part of the manufacturer, it is impossible to determine the accuracy or completeness of the analysis presented here. Although the material is widely reputed as green, this analysis make it clear that a great deal of energy is required to produce polylactic acid.
“Cargill Corn Milling North America.” Cargill. Cargill, n.d. Web. 28 Feb. 2013.
“Cargill Wins 2010 Industrial Biotechnology Award.” Cargill. Cargill, 2010. Web. 24 Feb. 2013.
Datta, Rathin and Michael Henry. “Lactic acid: recent advances in production processes and technologies – a review.” Journal of Chemical Technology and Biotechnology 81: 1119-1129 (2006). 28 Feb. 2013.
Drumright, R. E., P. R. Gruber, and D. E. Henton. “Polylactic Acid Technology.” Advanced Materials 12.23: 1841-1846 (2000). 22 Feb. 2013.
Henton, David E., Patrick Gruber, Jim Lunt, and Jed Randall. “Polylactic Acid Technology.” Natural Fibers, Biopolymers, and Biocomposites. Ed. Amar K. Mohanty, Manjusri Misra, and Lawrence T. Drzal. Boca Raton: Taylor & Francis, 2005. 527-577. Print.
Madival, Santosh, Rafael Auras, Sher Paul Singh, and Ramani Narayan. “Assessment of the environmental profile of PLA, PET and PS clamshell containers using LCA methodology.” Journal of Cleaner Production 17 (2009): 1183-1194. 24 Feb. 2013.
“MakerBot Replicator 2™ Desktop 3D Printer.” MakerBot. MakerBot Industries, n.d. Web. 2 Mar. 2013.
“Printing with PLA. ” MakerBot. MakerBot Industries, n.d. Web. 16 Feb. 2013.
Schwach, G., J. Coudane, R. Engel, and M. Vert. “More about the Polymerization of Lactides in the Presence of Stannous Octoate.” Journal of Polymer Science 25.16: 3431-3440 (1997). 22 Feb. 2013.
Vink, Erwin T.H., David A. Glassner, Jeffrey J. Kolstad, Robert J. Wooley, and Ryan P. O’Connor. “The eco-profiles for current and near-future NatureWorks® polylactide (PLA) production.” Industrial Biotechnology 3.1: 58-81 (2007). 22 Feb. 2013.
March 13, 2013
The Waste and Emissions Associated with Polylactic Acid
3-D printing involves the creation, or “printing,” of a solid object from a digital file via the additive process, which individually compiles layers one top of one another; virtually any shape can be created through this printing process (Pearce, et. al., 2010). To print the digital designs created with the printing software, plastic filament must be fed into the printer; the printer then melts the filament and additively prints the design.
Most largely, 3-D printers utilize acrylonitrile butadiene styrene (ABS) and, more recently, polylactic acid (PLA) filaments to print the designs. Interestingly, these plastics is used not solely to print 3-D trinkets, but can also be found in everyday items such as plastic grocery bags to styrofoam meat packaging. Additionally, and more specifically, PLA is being marketed as a green technology due to its origination in renewable corn feedstocks (as opposed to crude oils, as other plastics such as polystyrene (PS) and Polyethylene terephthalate (PET) are).
Although PLA is being marketed as a green plastic, the public should recognize that the life cycle of PLA still emits noxious gases and contributes largely to the waste attributed by plastic production. Until society acknowledges the environmental consequences of such production, then plastics such as PLA will remain a necessary evil – corn will continue to monopolize the agricultural industry and greenhouse gas emissions will continue to rise.
The preliminary search for PLA
In early January, after being assigned to research an area of Digital Design, it was first concluded that 3-D printers would be the most interesting subject to research. Next, it was a matter of determining which particular 3-D printer to research since each printer operated differently and required different materials for printing.
In October, a few months before the research paper was announced, WIRED, the leading magazine on the culture surrounding science & technology, had published its annual Design Issue. On the cover, Bre Pettis proudly presented his new creation: MakerBot Replicator 2x; the headline read: “This machine will change the world” (WIRED). The choice for which 3-D printer to research instantly became clear.
In an attempt to learn more about the MakerBot, specifically its construction and production process, the MakerBot forums and website were searched. While the website provided contact information for MakerBot headquarters, it did not provide details regarding the specifications of the MakerBot itself. Following the contact lead, the MakerBot headquarters were contacted via telephone. The speaker on the other line, however, refused to divulge any information regarding the MakerBot's production or manufacturing.
To bypass this problem, it was decided to explore not the machine itself, but the product which the machine utilized – the filament.
The MakerBot Replicator 2x is advertized to melt either ABS, and, more recently, PLA filaments – both of which are common commercial plastics. It was decided that, rather than research both filaments, to focus on PLA due to it being a relatively recent development in the world of plastics.
In an assessment of the environmental profile of PLA and other commercial plastics, researchers from Michigan State University cited NatureWorks LLC in Blair, Nebraska as “the sole PLA resin supplier in the United States” (Madival, et. al).
From there, the real research for the environmental viability of PLA began.
The source of PLA
Cargill Dow asserts that its methods for producing PLA abide by the Principles of Green Chemistry (Mohanty, Manjusri, and Lawrence), a phrase coined by the current Environmental Protection Agency (EPA) Assistant Administrator Paul Anastas; the principles provide for chemists a series of twelve guidelines to prevent pollution and fulfill the definition of sustainability (Twelve Principles of Green Chemistry).
To assess Cargill Dow's claim, researchers from Michigan State University surveyed the life cycle analysis of polylactic acid (Madival, et. al). A life cycle analysis quantifies the sustainability of a product by assessing its production process “from raw materials…to disposal” (Mohanty, Manjusri, and Lawrence).
In their assessment, the Michigan State University researchers originated PLA production to corn growing and harvesting, followed by starch production from the harvest. In contrast, the researchers reported that other plastics such as ABS and PET originate from crude oils – namely petroleum, a fossil fuel and one of the largest contributors to global warming. Thus, the researchers postulate that, in comparison to other plastics, PLA is an “environmentally viable option to its functional alternatives.” Moreover, a report the U.S. Department of Energy claimed that starch “represent[ed] only a small fraction of our nation's abundant biomass resources.”
Yet, in 2004, Cargill Dow reported a production capacity of more than 300 million pounds of PLA per year; such production requires 40,000 bushels of corn a day (Datta and Henry). Additionally, in an article analyzing the ecological effects of corn and soy farming, Mother Jones food and agricultural writer Tom Philpott stated that corn and soy, the most-major sources of starch for plastics, “now blanket nearly half of [U.S.] farmland” (Philpott).
According to one study by researchers from the University of Tennessee and Bard College, converting 10 million hectares of cropland to farmland would annually reduce agricultural greenhouse gas emissions by 36% (Hellwinckel and Philips). Yet, Philpott asserts that the opposite is taking place, that the amount of cropland is increasing exponentially while the amount of farmland is decreasing.
Regardless, NatureWorks' production of PLA alone contributes a great deal of carbon dioxide emissions. While it was difficult to pinpoint specific wastes attributed to the production of PLA – which is assumed because the only publications evaluating the production of PLA have been published by NatureWorks itself –, NatureWorks provided plenty of information regarding its carbon dioxide emissions.
Up in the air
In 2006, NatureWorks reported a total carbon dioxide emission of approximately -156,000 milligrams per kilogram of PLA produced. The negative emission was largely attributed to the biomass intake of the carbon dioxide; this intake accounted for more than the emissions associated with fuel production, fuel use, transportation, and the actual production of PLA combined.
Two years later, in 2008, NatureWorks claimed that its then-improved method of PLA production would successfully “[eliminate]…the emissions of greenhouse gases” (Vinks, et. al). Within the updated publication, however, NatureWorks reported a total carbon dioxide emission of approximately 826,000 milligrams per kilogram of PLA produced – a 630% increase in carbon dioxide emissions from 2006.
A closer examination of NatureWorks' data from both 2006 and 2008 revealed a positive correlation between the amount of primary PLA production fuels and the resultant carbon dioxide emissions. The three primary fuels used to produce PLA are gas/condensate, crude oil, and coal – all of which are non-renewable fossil fuels.
The data from 2006 records approximately 550,000 milligrams of primary fuels used per kilogram of PLA produced. Gas/condensate accounted for roughly 75% of the primary fuels at 418,166 milligrams per kilogram of PLA produced, with crude oils representing 21% at 115,986 milligrams and coal representing 4% at 18,721 milligrams. Natural gas, while still one of the greater contributors to global warming, burns cleaner than crude oils and coal.
The data from 2008, in contrast, reveals that approximately 1,016,000 milligrams of primary fuels were used to produce one kilogram of PLA, almost doubling the use of primary fuels within two years. This time around, gas/condensate accounted for only 37% of the primary fuels at 378,876 milligrams per kilogram of PLA produced, with crude oils representing 6% at 60,300 milligrams and coal representing 57% at a whopping 577,430 milligrams. While the updated method essentially halved the usage of crude oils from 2006, it also increased the usage of natural gas and, most alarmingly, increased the usage of coal by nearly 3000%.
From an economic standpoint, coal is a viable alternative to crude oils and gas/condensate due to its abundance in the region. According to the National Mining Association, Nebraska ranks 29th in the nation for coal use, generating 69% of its electric power from coal (Coal in America).
From an environmental standpoint, however, coal is arguably the most detrimental of the three main primary fuels.
In a testimony before the Iowa Utilities Board, James Hansen, Professor of Earth and Environmental Sciences at Columbia University, presented evidence illustrating the impact of coal-fired power plants on the Earth's climate. He did so “on behalf of the planet, of life on Earth, including all species,” acknowledging his humanly duty to protect the planet and to make known the dangers which threatened to end it.
“Coal is the largest contributor to the human-made increase of [carbon dioxide] in the air,” Hansen postulated. Supporting his claim, Hansen explained that coal reserves contain much more carbon than do oil and natural gas reserves, thus releasing greater amounts of carbon dioxide into the atmosphere and increasing air pollution.
What's more, in 2011, NatureWorks announced plans to launch a second manufacturing plant in Thailand in conjunction with its parent company PPT Global Chemical. While not directly related to the waste currently emitted by the production of PLA, it is worth exploring the possible effects of such expansion of PLA production.
Meet the Parents
NatureWorks is owned by the Cargill Corporation, America's #1 private company, and PPT Global Chemical.
Based in Thailand, PPT Global Chemical is a state-owned petrochemical and refining company with extensive gas lines throughout the country and a petroleum production capacity of 280,000 barrels per day (Forbes). Additionally, PPT Public Company Limited, PPT Global Chemical's parent company and a Fortune Global 500 company, claims ownership of coal mine operators in Singapore and petrol stations in the Philippines. The full integration of these and twelve other subsidiaries through the parent company allows for the simple transfer and use of raw materials between locations. With a vertically integrated hand in each step of fuel production, from private mining to public distribution, PPT Public Company Limited can only benefit from additional investments – especially one that will positively contrast its current investments in crude oils.
According to the country's Minister of Energy Pichai Naripthaphan, Thailand seeks to “[become] a regional hub for green technologies and solutions” (NatureWorks, 2011). Because PPT Global Chemical is state-owned, meaning that it is owned and operated by the Thai government, investing in NatureWorks would allow the company, and Thailand, to boast “renewable and environmentally friendly materials in its portfolio” (Nuttachat).
Should this joint project be successful, the second polylactide manufacturing plant will be completed by 2015. And should NatureWorks maintain its current production process, well, at least there will be plenty of coal.
NatureWorks assumes that the PLA it produces will be recycled by consumers (Vinks, et al. 2010). Yet, widespread recycling facilities for PLA do not exist; and while NatureWorks does advise the composting of its PLA, the company does not advocate for the widespread creation of such facilities. Rather, NatureWorks simply states that composting PLA will solely produce carbon dioxide, water, and humus, a soil nutrient (Garlotta, 2001).
The researchers from Michigan State University, however, acknowledge what NatureWorks fails to mention: the resultant emissions from the degradation of PLA. The literature reports a total emission of 3.84 kg of carbon dioxide per kilogram of PLA produced; 1.82 kilograms of carbon dioxide originates from the growth of the corn feedstock. Furthermore, the research approximates that the plastics' degradation is 25% incineration and 75% landfill. In this cradle-to-grave scenario, the raw material, corn, is no longer sustainable and environmentally viable.
Having the “only large-scale commercial production facilities for polylactide worldwide,” is it not, then, the responsibility of the company to ensure that the products are successfully renewed – especially if the company continually claims as its objective “[the elimination of] nonrenewable energy use” (Vinks, et. al, 2007; Vinks, et. Al, 2010)?
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