Materials Energy use
Materials Energy use (MJ/ton resin) MJ/ton resin 0 20,000 40,000 60,000 80,000 100,000 PE-HD PE-LD PP PS PET PLLA Fig. 4: Comparison of the non-renewable primary energy demand 100,000 88,500 90,000 83,000 500 79,000 78,500 80,000 76,000 1,000 76,000 1,000 2,000 500 70,000 42,000 28,000 42,000 23,000 60,000 42,000 0 50,000 0 38,500 40,000 23,000 0 0 0 30,000 52,000 46,000 20,000 40,000 35,000 39,500 10,000 25,000 0 0 PLLA PET PS PP PE (LDPE) PE (HDOE) Process renewable Process non-renewable Feedstock renewable Feedstock non-renewable Fig. 5: Comparison of total energy demand PLLA and thus further increase environmental sustainability. It is found that the CO 2 emission for PLLA is much lower than for fossil based polymers (as indicated in fig 3), and this is the key reason for producing bio-based polymers and plastics. Energy use Another way of looking at the ecoprofile of bioplastics is to compare the gross nonrenewable primary energy demand of the process. Fig. 4 shows the non-renewable primary energy demand for a number of polymers. The primary energy demand for the PLLA is lower than that for fossil based polymers, again showing the attractiveness of the biopolymer. In fig. 5 both the amount of renewable and non-renewable primary energy demand is considered. For the sake of clarity the energy demand is split into feedstock related renewable and non-renewable energy and process related renewable and non-renewable energy. Although obviously the sum of renewable and non-renewable energy may be in the same order of magnitude for biobased and fossil based polymers the renewable energy demand for the biobased polymer should be considered for free, as it was supplied by the sun and fixated in the sugar cane plant as sugar. Summary and outlook The results of the study indicate that PLLA results in significantly lower emissions of greenhouse gases, less use of material resources and non-renewable energy, compared to the petrochemically derived plastics. With the present calculations the CO 2 emission in L-lactide production is 348 kg/ton and for PLLA 500 kg/ton. Purac aims for CO 2 neutrality through process development, with potential to use the biopolymer as a carbon sink. The favorable CO 2 footprint is the result of the PLA being based on renewable resources combined with the co-generation of electricity in the sugar refining. In addition to these findings, for PLA being based on an agricultural system the LCA also considers other ecological factors such as non-renewable abiotic resource use, farm land use, acidification, photochemical ozone creation, human toxicity and nutrient enrichment (full details to be published later). Since the disposal routes after use for different materials also play an important role when evaluating a material‘s environmental impact, a section in the LCA is devoted to the discussion of different end-oflife scenarios for PLA. A cradle to grave analysis has been performed based on incineration of different types of polymers taking into account the intrinsic carbon content as proposed by Prof. Narayan. This approach allows for a better comparison of different polymers and confirms the favorable carbon footprint of PLLA. The current calculation is based on plant designs, and for the future certification of Purac’s plants is foreseen, as well as efforts to further minimize environmental impacts. The production of biobased polymers is intricately linked to agriculture, through benefits such as electricity from bagasse, and through emissions by growing crops. A Life Cycle Analysis is an indispensable tool to quantify all these effects and guide industry towards the development of green chemicals. www.purac.com 26 bioplastics MAGAZINE [02/10] Vol. 5
