Functional unit and system boundaries
The functional unit chosen for this study is 1 m2 of packaging film. This is (mostly) laminated, printed film that is delivered on reels to the food factory, where the laminate is cut, sealed and filled. Cutting of the sheets and sealing and filling of the bags are excluded from the analysis because this step can be assumed to be identical across all packs of the same size and function, and to produce the same level of waste. The results of the environmental assessment are reported both for the system ‘cradle-to-factory gate’ (CF) and for the system ‘cradle-to-grave’ (CG): The system CF includes all activities in the process chain starting from the extraction & processing of non-renewable resources (e.g. oil and gas) or agricultural & silvicultural production (e.g. maize from seeds, including fertiliser and machinery use) up to and including film production, lamination and printing; it also covers all transportation activities and treatment of any process waste up and until the laminated film is delivered on reels to the food producer. The system CG includes the system CF plus waste management of the post-consumer packaging wasteFootnote 2 where all key options are studied, i.e. incineration (with and without energy recovery), landfilling, composting, and digestion. We calculate GWP for the system cradle-to-factory gate for all bio-based products by adding all emissions of fossil greenhouse gas emissions and subtracting the biogenic carbon that is physically embedded in the product. As a consequence, both fossil and biogenic emissions of greenhouse gases from the waste treatment stages are considered.
System expansion
In this study, we applied system expansion (also referred to as ‘avoided burdens’) to account for the co-generation of electricity and heat. To determine the credit, electricity that is co-produced, e.g. during the incineration of waste, is assumed to replace electricity produced according to the average power generation in Europe (see Section 3.3) and heat is assumed to replace average production in a gas-fired boiler.
Environmental impact assessment
In this study, we used the CML 2 baseline 2000 method (Guinée et al. 2001) for calculating the mid-point results, adding water use and land use as impact categories. For CF, the so-called LCA mid-point results are presented for the following impact categories: Non-renewable energy use, Total energy use (total of non-renewable and renewable energy use), Global warming potential, Depletion of abiotic resources, Photo-oxidant formation, Acidification, Eutrophication, Water use, and Land use;Footnote 3 for CG, only results for the categories Non-renewable energy use and Global warming potential are shown because of the large uncertainties related to estimating individual process emissions other than CO2, CH4 and water during the waste treatment phase, especially of novel materials such as polylactic acid (PLA).
So far, water use as an impact category has not been very common in LCA studies but is receiving more and more attention (Mila i Canals et al. 2009; Pfister et al. 2009). Within the category of water use, we consider process water, cooling water and irrigation water. Process water includes all the water used during the production of raw materials, films and laminates but excludes the water used for electricity production from hydropower. The subcategory cooling water includes water used for cooling in any of the process steps. Irrigation water means water fed to the agricultural system during crop growth; it excludes rainfall because there is no generally accepted methodology that would allow a consistent comparison of rainfall quantities across agricultural as well as silvicultural crops and across geographical regions of production.Footnote 4 Energy consumption for irrigation is excluded because it only contributes to a small extent to the total energy consumption of agricultural crops (Mila i Canals 2003).
Land for agriculture and forestry will be increasingly important in the future because of increasing land requirements not only for the production of food and feed but also of bio-energy, bio-fuels, and bio-materials. A growing number of environmental assessments of bio-materials include land use in their analyses (see Dornburg et al. 2003; Hermann et al. 2007; Kim and Dale 2005b) and methodological work is under way (see e.g. Jolliet et al. 2003; Kloverpris et al. 2008; Mila i Canals et al. 2007) but has not yet established one single accepted methodology in terms of how different types of land use should be compared. In this study, we focus on land use for agriculture and for (sustainable) forestry. The different types of land use (e.g. agriculture and forestry) are aggregated 1:1. The rotation period of forestry is taken into account. Land use for industrial plants, transportation infrastructure and waste management is comparable for different types of material and thus not taken into account.
Methodological problem: how to incorporate ‘green electricity’?
As can be observed among private consumers, companies are also increasingly purchasing ‘green electricity’ in order to reduce their environmental footprint; one such company is NatureWorks, the most important producer of PLA. Purchasing green electricity is an option for any producer - and this raises the question if such environmental credits should be considered when conducting an LCA. In order to describe the different views, we distinguish between the company perspective and the technology perspective. An LCA carried out from a company perspective includes not only the processes operated by the company itself but also the purchasing decisions the company makes regarding materials and energy inputs. As a consequence, a study using the company perspective gives credits for the avoided environmental burden related to green electricity. We argue that the company perspective should be applied for decisions concerning business relations. A comparison from a technology perspective of materials production and processing strives to eliminate the effect of whether the company uses power generated by using wind energy, natural gas or coal, focussing instead on the core technology. (Here, core technology refers to the production of materials and their subsequent processing to produce packaging film, but excludes the generation of green power as an optimisation strategy.) The technology perspective is the adequate choice when making decisions concerning material choice or R&D strategies. In this paper, we focus on the technology perspective because we are mainly interested in material choice; but we include a case of company perspective to show the difference between the two.
In the following, we describe the effect of a company’s decision to purchase ‘green electricity’, using the example of wind energy. The accounting practice adopted by the International Energy Agency (IEA 2003) for their energy balance tables is that the primary energy form should be the first energy form downstream in the production process for which multiple energy uses are practical. The application of this principle leads to the following primary energy forms: 1) Heat for nuclear electricity, for geothermal heat or electricity and for solar heat production 2) Electricity for hydro, wind, wave/ocean and photovoltaic electricity production. This convention has been agreed upon internationally for energy balances. As there is no such agreement for LCAs in general, we follow the IEA convention. As a consequence, the primary energy consumption related to the production of 1 kWh of electricity is lower if it is generated from hydropower, wind, wave/ocean and/or photovoltaics compared to its generation from fossil resources (oil, gas, coal) or nuclear, geothermal or solar heat.
PLA is the only material in this LCA for which renewable energy credits were bought (starting in 2006). As shown in Table 1, moving towards wind energy in 2006 meant replacing 23 MJ/kg PLA of primary fossil energy by 6 MJ/kg PLA primary renewable energy. The total primary energy use decreased from 77.3 MJ/kg PLA to 60.3 MJ/kg PLA without any change in technology or secondary energy use and therefore solely as a consequence of the accounting practice for wind energy. The wind credits also have a large influence on impact categories other than energy use, most notably global warming potential, abiotic depletion and acidification.
Table 1 Renewable energy use (REU) and non-renewable energy use (NREU) for the production of 1 kg of polylactic acid (PLA) with and without wind energy credits, derived from Vink et al. (2007)