13 March 2014
Biodegradable Cutlery: Embodied Energy
Embodied energy is a major component that should be assessed when looking at the life cycle of a product. It accounts for all the energy required to make something from cradle-to-grave. Due to waste being a major issue in the world, there has been a stronger emphasis on making products that are recyclable or compostable. Traditional plastic utensils are a major contributor to landfills and many companies try to remedy this by creating more eco-friendly and/or compostable utensils. They can be made from different materials, ranging from bioplastics to bamboo. Some of these utensils are biodegradable, but what does that mean in terms of energy use? It matters less if a product is biodegradable if it still consumes a large amount of energy from cradle-to-grave. Embodied energy for Polylactic acid to make utensils is less than that of other plastics, such as Polyethylene terephthalate, but still requires a good deal of energy from the many stages of its life cycle.
Everyone has used plastic cutlery. About 40 billion plastic utensils are used in the United States alone (Packer, 2009). It is such a common item that is sold cheaply and is a convenient product for the times when cleaning utensils is undesirable or impossible. Plastic utensils can be used once and thrown away or can be cleaned and used multiple times. The latter is a more sustainable practice, but it is not something that is done frequently. This is because they are meant to be thrown away and, because they can be replaced cheaply, few people consider reusing them until they lose their function. There are many biodegradable options that market off of being better for the environment. “Better” has to include the embodied energy of the entire lifespan of these utensils. Embodied energy must take into account everything from the harvesting of raw materials to make the utensils all the way to their end of life options.
Non-biodegradable plastic utensils are usually made from polymer 1 or Polyethylene terephthalate (PET). PET is refined from petroleum and natural gas, and is popular because it is strong and lightweight. Because the materials needed for production come from overseas, there is a lot of energy consumption related to transportation. There are a good amount of sustainable materials used as substitutes for traditional plastics in the production of utensils. Polylactic acid (PLA) is currently considered one of the most widely used biodegradable plastic alternatives to traditional petroleum based plastics because PLA resin produces a lower environmental footprint than its petroleum based counterparts. PLA is used to make utensils, amongst other products, because of its biodegradable properties and is produced from the starch of renewable materials (usually corn). However, like PET, PLA still uses fossil resources for process energy. Unlike PET, though, PLA is significantly easier to break down at the end of its life, which aids in its sustainability aspect (NatureWorks, 2014; Shen, 2011).
Due to the positive connotations with sustainability and biodegradability, especially now, companies producing sustainable products are very willing to share information on the lifecycle of their products. This includes, of course, energy use. They want to prove that they are what they say they are and that they have nothing to hide. NatureWorks LLC focuses on manufacturing products using plants and is the largest PLA manufacturer in the United States. They make Ingeo plastic which uses dextrose from feedstocks (mainly corn) rather than oil. “Since 1998, NatureWorks has been developing new lactic acid production technology, with the objectives of developing a process with higher yields, better economics, lower carbon footprint, lower energy use, lower water use, and less waste” (NatureWorks, 2014).
To calculate the embodied energy of PLA one must include the broad categories of agriculture, manufacturing, transportation, and the end of life options. The agriculture and manufacturing for PLA includes corn production, harvesting, and drying; transportation to the corn-wet mill; conversion of starch into dextrose; conversion of dextrose into lactic acid; conversion of lactic acid into lactide; and then finally polymerization of lactide into Ingeo polymer pellets which can be made into utensils (Vink et al., 2010). The utensils are then transported and distributed to the consumers, and after they are used they are either transported to be incinerated, put in a landfill, composted, or recycled (Madival et al., 2009).
The life cycle starts with corn production. All free energy consumed by the corn plant comes from solar energy captured by photosynthesis. This means all carbon, hydrogen, and oxygen found in the starch molecule originated from water and carbon dioxide. Corn production also includes production of corn seed, fertilizers, limestone, electricity, and fuels used on the farm, such as natural gas, diesel, propane, and gasoline. It includes the atmospheric carbon dioxide utilization through photosynthesis and the irrigation water applied to the cornfield. Finally it includes the production of the herbicides and insecticides used to protect the corn. The gross energy use during this segment of production is approximately 28.86 MJ/kg Ingeo. 24.97 MJ of this is renewable feedstock energy (Vink et al., 2003).
After harvest, the corn grain is transported to a corn-wet mill (CWM), where the starch is separated from the other components of the corn kernel. These include water, proteins, fibers, fats, and ash. This involves slow cooking the corn in water for thirty or forty hours at approximately 50°C to cause it to soften and release its starch. The corn is then ground, allowing for the starch to be separated out (Lee, 2009). The starch gets hydrolyzed to dextrose using enzymes. The gross energy use during this segment of production is approximately 5.08 MJ/kg Ingeo. 5 MJ is nonrenewable energy used as processed energy and the other 0.08 MJ is renewable energy used as processed energy (Vink et al., 2010).
The dextrose solution is transported by pipeline to the lactic acid fermentation process. The other products of the CWM are corn gluten feed, corn gluten meal, heavy steep water, and corn germ. The energy use includes “inputs for dextrose production such as the production and delivery of natural gas, electricity, and steam, as well as the production of potable and cooling water, compressed air, chemicals, and enzymes” (Vink et al., 2010). Lactic acid is produced by fermentation of dextrose received from the CWM. The process combines dextrose and other media, adds a microbial inoculum, and produces crude lactic acid. The gross energy use during this segment of production is approximately 20.96 MJ/kg Ingeo. 20.30 MJ of this is nonrenewable energy used as processed energy; 0.39 MJ of this is renewable energy used as processed energy; and 0.27 MJ is nonrenewable feedstock energy (Vink et al., 2010).
Ingeo is prepared through the polymerization of lactide to make polylactide polymer in a continuous process. In the first step, water is removed in a continuous condensation reaction of lactic acid to produce low molecular weight prepolymer. Next, the prepolymer is catalytically converted into the cyclic dimer, lactide, and vaporized. The lactide mixture is then purified by distillation. Finally, high molecular weight Ingeo is produced using a ring-opening lactide polymerization. After the polymerization is complete, any remaining lactide monomer is removed and recycled within the process. The gross energy use during this segment of production is approximately 12.94 MJ/kg Ingeo. 12.69 MJ of this is nonrenewable energy used as processed energy; 0.18 MJ of this is renewable energy used as processed energy; and 0.07 MJ is nonrenewable feedstock energy (Vink et al., 2010).
These different stages in the production process fall under cradle-to-factory gate. This is not the entire process that needs to be considered for embodied energy, but it is a large portion. For cradle-to-gate, Ingeo since 2005 used approximately 50 MJ nonrenewable energy/kg. Ingeo’s currently implemented technology uses approximately 42 MJ nonrenewable energy/kg Ingeo. This is compared to the 80 MJ nonrenewable energy/kg polymer used for PET from cradle-to-gate (Vink et al., 2010).
Once the Ingeo plastic resin is made, it needs to be transported to companies that use it to make utensils. For the most part, trucks are used for transportation to take the raw materials to refineries/producers, from producers to retailers/consumers, and from consumers to disposal sites (Shen, 2011). 0.5211 MJ of energy from the 42 MJ described above comes from transportation in the cradle-to-gate process. The amount of total energy (cradle-to-grave) used during transportation depends, of course, on how far the trucks have to travel. In general, for a heavy duty diesel truck driving on a highway, 0.35 L/km of fuel are consumed and the high heating value of diesel is 38 653 kJ/L. If the full capacity weight of the product and the fuel in the vehicle is assumed to be approximately 22 tons, 0.6634 kJ/kg km can be calculated as the rate of energy consumption of a truck (Lee, 2009).
There is not a lot of specific data specifically on PLA biodegradable cutlery in terms of the transportation process, but there is some data on PLA containers. The distance between NatureWorks LLC and Pinnacle Plastic Container in Oxnard, California (a PLA container supplier) was found to be 2592 km by truck and 3136 km by train. Transportation of resin from resin supplier to container manufacturer by a 16-ton truck uses 477 MJ of energy. In this case, the containers are being used for strawberries. Transportation of containers from strawberry filler to distributors/market by a 16-ton truck uses 697 MJ of energy (Madival et al., 2009). The transportation of strawberry filled PLA containers from exporter to market by a 16-ton capacity truck used 993 MJ of energy when it was going from California to Washington. For comparison purposes, this data was 3760 MJ when going to New Hampshire. The data for this when in a 28-ton capacity truck is 610 MJ and 2310 MJ, respectively (Madival et al., 2009). This shows that it is more efficient to travel in higher capacity trucks. Of course this data would be a little different if it were specifically about the transportation of PLA cutlery, but the general trend would be the same.
The point of these PLA utensils is that they are biodegradable. However, there is a lack of commercially available recycling and composting centers for PLA (Madival et al., 2009). Ingeo plastic does not biodegrade in landfills (NatureWorks, 2014), so it’s not an effective situation if it gets thrown away. In a very detailed life cycle assessment of PLA clamshell containers, the cumulative primary (nonrenewable) energy demand for the base scenario life cycle of 1,000 PLA containers is 579,030 kJ. This number is 743,188 kJ when the PLA is composted, 666,959 kJ when the PLA goes through anaerobic digestion, and 547,517 kJ when it goes through chemical recycling. This includes everything (production, transportation, disposal, etc.). For PET, the base scenario is 1,222,106 mL, a much higher number than for PLA (Detzel & Krüger, 2006). Ingeo PLA can also be incinerated and uses approximately 8,368 Btu/lb (NatureWorks, 2014).
The embodied energy to fulfill the process of making cutlery from Polylactic acid must also include the energy it takes to make the fuel used in the process. PLA’s fossil resource depletion is about 30 MJ/kg (Essel, 2012). The gross primary fuels used to produce 1kg of Ingeo include crude oil, gas/condensate, coal, metallurgical coal, lignite, peat, and wood. Crude oil has an input of 60,300 mg for 1 kg Ingeo, gas/condensate has 378,876 mg, and coal has 577,430 mg (Vink et al., 2010). The lifecycle of each of these energy sources could be looked at in great depth, making it hard to summarize briefly. Energy is consumed when, for instance, the coal is being mined, when it is being transported, and when it is being generated into power. To produce 1kg of Ingeo (cradle-to-gate), 11.8048 MJ are used for the fuel production and delivery energy of coal. For oil, it is 0.1362 MJ, for gas it is 1.7609 MJ, for hydro it is 0.4694 MJ, and for nuclear it is 2.7637 MJ (VInk et al., 2010).
As NatureWorks intended, overall energy use for the life cycle of Polylactic acid—which includes a lot of processes and steps—is lower than that of some other materials, such as Polyethylene terephthalate. However, the production of PLA, to make items such as utensils, still requires energy from fossil fuels. If more energy used in the process came from renewable sources, it would have a smaller embodied energy. It is crazy to look at an item as simple as a plastic fork and understand how much energy and steps go into making it. It is great when a utensil is biodegradable, but if it ends up in a landfill, then it’s not as effective. If people were more aware of the energy consumption throughout the entirety of a utensils life, they would probably be more likely to reuse utensils or avoid using them all together.
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DES 40A Winter 2014
13 March, 2014
Biodegradable Utensils: Waste and Emissions
The story of today's fork is no longer the same as it was even from just a few years ago. Though the function of the common fork utensil has remained the same, its materials have changed from silver to stainless steel and now there are biodegradable options. In today's world, it is not out of the norm to hear talk of global warming, alternative energies, and the popular movement to “Go Green”, because our old ways of energy use do not meet today's demand of energy consumption. While change may not be happening fast enough, there are still many attempts—on a small scale—to cut back and to better adapt to consumer demands. You’re probably wondering what this has to do with the simple fork. Well, the fork is a basic yet straightforward example of how the world is changing our most common household items to meet consumer demand for “greener” products. Yet, this image of “green” is quite skewed, as we can see from the life-cycle—known as cradle-to-gate or cradle-to-grave—of our new “green” invention, the biodegradable fork. In this paper I will be showing the emissions of the production of the resources, and the end of life including: landfill, incineration, feedstock recycling, recycling and composting of NatureWorks’ Ingeo polylactide (PLA) biodegradable fork.
Although it has been difficult to find the waste and emissions of the life cycle of specifically the NatureWorks PLA biodegradable utensil, there are several sources detailing other NatureWorks products or PLA products more generally. First of all, NatureWorks LLC, limited liability company, manufactures Ingeo bipolymers—which are bioplastics, or plastics made from renewable plant resources—which could eventually be made into a variety of consumer goods. These goods include apparel, bottles, serviceware, food packaging, cards, durable goods, folded cartons, home textiles, and nonwoven goods. The NatureWorks goal is to replace petroleum-based plastics, which are and have been the dominant production base. Ingeo is the NatureWorks owned trademark for the PLA bipolymers, defined by NatureWorks as “ingenious materials from plants not oil,” while PLA is “a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch (in the United States), tapioca roots, chips or starch (mostly in Asia), or sugarcane (in the rest of the world) [the actual name] "polylactic acid" does not comply with ISUPAC standard nomenclature, and is potentially ambiguous or confusing, because PLA is not a polyacid (polyelectrolyte), but rather a polyester”.
NatureWorks’ Ingeo PLA biodegradable utensils use revolutionary methods, moving away from petroleum based products to biomass based. PLA is a beneficial material that has received praise from many places worldwide including Hawaii, as seen in this article, “The Greenhouse Gas Emissions and Fossil Energy Requirement of Bioplastics from Cradle to Gate of a Biomass Refinery”.The two common assessments analyzing the impacts of a product on the environment are the Life Cycle assessment and Cradle-to-factory-gate analysis. While cradle-to-gate focuses mostly on the impacts from raw materials acquirement to the finished product leaving the factory, life cycle assessments consider the aforementioned in addition to the impacts through end-of-life-options the product has. Overall, PLA
Though I do not know the specific greenhouse gas emissions of producing and consuming NatureWorks’ PLA biodegradable utensils, the statistics of our “green” fork are very similar to the stats of Polylactic acid shown in the comparison between Polylactic acid and Polystyrene trays, as shown in the article “Life Cycle and Energy Consumption and Greenhouse Gas Emissions of Polylactic Acid (PLA) and Polystyrene (PS) Trays”.
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