Biobased thermoplastic resins from starch and lignocellulose
Presentation held at Sino-German Symposium on Biomaterials from Lignocelluloses, March 6-11, 2016, Beijing, China
Lignocellulose is the most abundantly available raw material on earth and used since time immemorial as energy source as well as construction material (wood). For various reasons (CO2 neutrality, decrease of oil in places etc.) substantial use of renewable resources is becoming ever more important. Lignocellulose offers good possibilities for creation of value in the field of material development caused by the low price. In this contribution a series of lignocelluloses like beech, spruce, poplar, wheat straw, and bagasse a fibrous residue of the sugarcane industry were treated by chemical modification to achieve thermoplastic resins. The esterifications of these different lignocelluloses were carried out with or without the use of commercial ILs. The highly substituted lignocellulose acetates and propionates were processed in an extruder and an injection molding machine to achieve test specimen for the investigation of the mechanical properties. In dependence on the content of acetyl or/and propionyl groups, the content of plasticizer and in dependence on the lignocellulose a strength in the range of 15-30 MPa, stiffness in the range of 0.5-2.3 GPa and elongation at break in the range of 1-29 % were achieved. Concerning recovery of the used solvents it was possible to recycle the IL and reuse it as dissolution media for synthesis of lignocellulose acetates, but the mechanical properties of these products have decreased. In comparison to lignocelluloses also starch is a low cost biomaterial which becomes more and more important in the field of bioplastics. Starch itself can be processed by thermal treatment using a plasticizer to give e.g. several kinds of packaging material. However the high water uptake of such materials together with relative low values for tensile strength or modulus is a disadvantage. These problems can be avoided by chemical modification of starch. Starch esters are the most promising material to reach properties which are comparable to PP and PE. This presentation will show a comparison of different possibilities to synthesize thermoplastic starch esters and will show the effect of the synthesis pathway on the mechanical properties of starch esters. Further on a novel and simple as well a fast synthesis pathway of starch mixed esters will be described. This synthesis stands for a toolbox to create different starch mixed esters with a variety of mechanical properties. A plasticized starch acetate propionate laurate can already reach the mechanical properties like PP.