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bioplasticsMAGAZINE_0905

Basics Raw materials and

Basics Raw materials and required for In the last issue of bioplastics MAGAZINE we looked at the basic principles of ‘Land use for Bioplastics’. Following this general introduction we now put forward some more concrete facts concerning the specific biopolymers. The following article is an edited extract from the new book entitled ‘Technical Biopoymers’, written by Hans-Josef Endres and Andrea Siebert-Raths. The book has already been published in German and will be available in English at the beginning of next year (see also page 15). To evaluate the land area required for biopolymer production the annual yield from different renewable raw materials is illustrated below. In Fig. 1 the raw materials have been grouped into sugars, starches, plant oils and cellulose or fibrous materials to facilitate comparison. It can be seen that the sugars offer the highest yield. Starches too deliver relatively high yields, whilst the yield from renewable plant sources of oils or cellulose is, in comparison, significantly less. Among the oils it is only palm oil and perhaps jatropha oil that offer yields approaching that of the starches. In order to determine the annual amount of biopolymer that can be produced per unit of land area (the biopolymer yield per area) it is also necessary to take into account the data in Fig. 2, i.e. the various biobased percentage of each biopolymer. With the blends in particular there is a wide range of bio-based content because petrochemical components and additives are often also used in the blend. Furthermore, consideration must be given to the efficiency of converting the biobased materials listed, i.e. the initial amount of the raw material required to produce the particular bio-based component. Based on the respective percentage of bio-based material and the amount of renewable raw material required for this, Fig. 3 shows the representative relationship of the amount of bio-based input material to the total amount of material output. When ethanol is used as an intermediate step almost 0.5 tonnes of ethanol per tonne of sugar is output. But it must be noted that almost no biopolymers are 100% bio-based. At times the bio-based element of the material is below 25% by weight, i.e. in such a case 75 % of the weight of the material is in no way to be considered when calculating the necessary amount of land because it is not based on renewable raw materials. Basically the lower the percentage of bio-based material the higher the relationship of the absolute quantity of bio-polymer to the area under cultivation. This also shows the direct comparison of the data in figures 2 and 3, each of which represents a basically inverted proportionality. A statement of the biopolymer output per unit of arable land without taking into consideration the percentage of bio-based material in that polymer is therefore not sufficient. When calculating the outputs of biopolymer materials and the input of renewable raw material required, as shown in Fig. 3, the following assumptions were made: 1: Cellulose acetate (CA): Percentage of cellulose based material 40 – 50 percent by weight Since even with partially biodegradable cellulose acetate at least about 2/3 of the hydroxyl groups in the glucose element unit are replaced by acetal groups (for details please see the respective section in the book), i.e. the degree of substitution is as a rule greater than 2.0, and in addition non-bio-based softeners of up to a maximum of 30 % by weight are used, for cellulose acetate an initial input amount of between 40 and 50 % 34 bioplastics MAGAZINE [05/09] Vol. 4

Basics arable land biopolymers by weight is required. This means that under certain circumstances up to 60 % of the material is not cellulose at all but is based on acetic acid (largely produced under pressure by catalytic conversion of petrochemical methanol with carbon monoxide), and other petrochemical softeners. With an assumed minimum degree of substitution of 2 the acetate content alone represents 30 and the plasticizer 20 % by weight. 2: Cellulose regenerate: Percentage of cellulose based material 90 - 99 percent by weight Cellulose regenerates are used in the biopolymer sector mainly as coated film (e.g. with a barrier coating or sealing layer). From the point of view of the weight of the dominant material a cellulose percentage of near enough 100 % can be assumed. For the coating, a percentage by weight of at the most 10 % is assumed. Normally the coating will account for a much smaller percenatge. 3: Thermoplastic starch (TPS): Starch based percentage of the material 70 - 80 percent by weight To optimise the performance of thermoplastic starch in processing and use, native starches must be modified and/or in particular be added with a softener such as glycerine or sorbitol (for details please see the respective section in the book). To calculate the average starch content, a total conversion of 100 % of the unmodified starch to a biopolymer was assumed. For starch acetate on the other hand, similar to cellulose acetate with a high degree of substitution, a starch requirement of only 600 kg per tonne is required. For the remaining additives or softeners raw materials of petrochemical origin were assumed. We can therefore assume on average that thermoplastic starch materials require an input of 70 to 80 % by weight of starch itself. 4: Starch blends: Starch-based percentage 25 - 70 percent by weight To optimise the properties in the processing and use of thermoplastic processable starch polymers it is necessary for native starch - as already Raw material yield [t/(hectare*annum)] The percentage of material in biopolymers that is biobased, i.e. obtained from renewable resources (% by weight) Output: tonnes of biopolymer or bioethanol / Input: tonnes of regenerating raw materials 25 20 15 10 5 0 100% 80% 60% 40% 20% 0% 6 5 4 3 2 1 0 Sugars Starches Plant oils Cellulose (fibres) Sugar (cane) Sugar (beet) Maize starch Potato starch Wheat starch Rice starch Palm oil Jatropha oil Cocoa oil Castor oil Rapeseed oil Sunflower oil Soy oil Wood fibres Wheat straw Hemp Flax Cotton Fig 1: Absolute yield of various renewable raw materials per hectare per annum Cellulose regenerates 2 Cellulose acetates 1 Thermoplastic starches (TPS) 3 Starch blends 4 Polylactides (PLA) 5 Polylactide blends 6 Polyhydroxyalkcanoates (PHA) 7 Fig 2: Percentage of renewable raw materials by weight in various biopolymers Cellulose regenerates 2 Cellulose acetates 1 Thermoplastic starches (TPS) 3 Starch blends 4 Polylacticdes (PLA) 5 Polylactide blends 6 Polyhydroxyalkcanoates (PHA) 7 Bioenthanol 8 Bioenthanol 8 Fig 3: Total Biopolymer output in relation to the input of renewable raw materials Biopolyesters 9 Biopolyesters 9 Biopolyethylene (BIO-PE) 10 Biopolyethylene (BIO-PE) 10 bioplastics MAGAZINE [05/09] Vol. 4 35

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