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bioplasticsMAGAZINE_0905

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bioplasticsMAGAZINE_0905

Basics [tonnes of

Basics [tonnes of bioplymer /(ha*annum)] 35 30 25 20 15 10 5 0 Cellulose regenerates 2 Cellulose acetates 1 Theoretical minimum and maximum biopolymer yield per unit of land area Thermoplastic starch (TPS) 3 Starch blends 4 Polylactic acid (PLA) 5 Polylactic acid blends 6 Polyhydroxyalkcanoates (PHA) 7 Fig 4: Minimum and maximum possible biopolymer yields per hectare per annum Bioenthanol 8 Biopolyesters 9 Biopolyethylene (BIO-PE) 10 explained - to be modified or blended with other polymers. The second component of the blend usually represents the continuous phase in the resultant 2-phase blend (for details please see the respective section in the book). The assumption is made that in starch blends there is 30 to 85 % by weight of material coming directly from the starch. For this figure the values of thermoplastic starch from the above assumption 3 have been used. For the remaining 15 to 70 % of the starch blends it is assumed that a petrochemical-based material is used. 5: PLA: PLA-based percentage 90 - 97 percent by weight With the PLA polymers produced from lactic acid the assumption is made that only functional additives (nucleating agents, colour batches, stabilisers etc) in amounts from maximum 3 to 10 % by weight, are added to the PLA. It is assumed that maize starch is used as the raw material for PLA. Around 0.7 tonnes of PLA are obtained from 1 tonne of maize starch. 6: PLA blends: PLA-based material percentage 30 - 65 percent by weight For these suitably ductile PLA blends, used overwhelmingly for film applications, it can be assumed a percentage of PLA-based material of between a maximum of 65 % and a minimum of 30 % by weight. For the PLA components the PLA values from the previous assumption 5 were used. The second component of the blend is mainly a bio-polyster. For the bio-polyester (30 to 65 % by weight) the assumptions described under point 9 were made. Also, for PLA blends, the addition of 5 % by weight of a petrochemical-based additive is assumed, for example processing aids or components to improve the interaction of the two basic materials. 7: Polyhydroxyalcanoate: PLA-based material percentage 30 - 65 percent by weight With the Polyhydroxyalcanoates (PHA), produced by fermentation, there is a very small amount of additive used and thus an average bio-based material content of 90 to 98 % by weight can be assumed. To produce one tonne of PHA about 4 to 5 tonnes of sugar are required. 8: Bioethanol To produce bioethanol as an intermediate, particularly for bio-polyethylene and various bio-polyesters, it is assumed that 100% of the bio-alcohol is sugar-based. In addition it can be assumed that in the most favourable case about 1.7 (and in the least favourable case 2.7) tonnes of sugar are required per tonne of bioethanol. 36 bioplastics MAGAZINE [05/09] Vol. 4

9: Bio-polyester: Bioalcohol content 30 - 40 percent by weight, remainder based on petrochemical raw materials With bio-polyesters a bioalcohol-based input of 30 - 40% was assumed to calculate the conversion efficiency, i.e. viewed from the opposite perspective 60 - 70% of the so-called bio-polyester is not based on renewable raw materials. For the bioalcohol content the raw material requirement for bioethanol, as specified in point 8, is assumed. 10: Bio-polyethylene (bio-PE): Bioalcohol-based content 95 - 98 percent by weight As with conventional PE, bio-polyethylene also requires between 2 and 5% by weight of other additives, which means that a bioalcohol-based material content of 95 to 98% by weight can be assumed. Furthermore it is assumed that 2.3 - 2.5 tonnes of ethanol are required per tonne of polyethylene. For the bioethanol content the same assumptions are made as in point 8. Finally, to define the annual output of various biopolymers per unit of land area working from the bio-based material content of each of the biopolymers (cf. Fig 2), the required input amount of renewable raw material for each biopolymer (cf. Fig 3) and the related annual yield per unit of land area for each of the renewable raw materials (cf. Fig 1) the theoretical achievable annual amount of each of the biopolymers per unit of land area can be calculated and is shown in Fig. 4. Because of the wide range of yields from renewable resources, and the possibility of using different renewable raw materials to produce the same biopolymer (e.g. starch instead of sugar), plus the, at times, very different bio-based material content, there is ultimately a very wide range of the theoretical biopolymer yields per unit of arable land. Because, in biopolymer manufacture, there is pressure on economic grounds for maximum material usage and the maximum possible yield per hectare, a comparison of the values detailed above is more representative of the effective trends in biopolymer yield per hectare. Accordingly to these considerations a bio-PE for example, despite the high sugar yield available per hectare, exhibits the lowest land use efficiency because of the high demand for sugar at the bioethanol stage and the high ethanol demand for polymerisation of the polyethylene. The relatively low land-use efficiency of the PHAs can, as with cellulose regenerates, also be traced back to the high bio-based material input and the lack of a petrochemical component not related to land use or to another bio-based material. By contrast the high percentage of non bio-based material components in particular with bio-polyesters, starch blends, PLA blends and cellulose acetate, leads to what seems to be a high land-use efficiency that is, however, traced back to the addition of significant amounts of non landdependent substances of petrochemical origin. However, what is important at the end of the analysis is the fact that, in comparison with bio-fuels, to achieve a perceptible share of the plastics market biopolymers would require a significantly smaller land area in absolute terms (see article on Land Use for Bioplastics in issue bM 04/2009), as well as exhibiting a higher land use efficiency. With a cautious estimate of the average yield per unit of land area of at least 2.5 tonnes per hectare the current global biopolymer output (about 0.4 million tonnes per annum) would need only 0.01 % of the world‘s agricultural land. Basics www.fakultaet2.fh-hannover.de bioplastics MAGAZINE [05/09] Vol. 4 37

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