Non-Food Denaturation +
Non-Food Denaturation + heat + pressure + chemical additives Folded Quaternary and Tertiary Structure Hydrogen Bonds Hydrophobic Interactions Ionic Interactions Covalent cross-linking Unfolded Secondary and Primary Structure Hydrogen Bonds Peptide Bonds blocking the extruder or injection moulder. It was found that processing requires sufficient protein denaturing leading to the exposure of different amino acid functional groups, followed by rearrangement of chains by means of plasticisation and shear flow and finally allowing new interactions to be established during the solidification stage and appropriate additives. Successful processing therefore requires appropriate modification by eliminating or introducing intermolecular bonds at the correct time during processing. Bloodmeal is a powdery product and processing is therefore required to consolidate the particles to prevent adhesive failure. It was found that denaturation of bloodmeal using water, heat and pressure was not enough to break covalent bonds, resulting in a heterogeneous material. Thermoplastic processing required a combination of aggressive denaturants, reducing reagents and plasticizers to form a homogenous and extrudable material. By relying on Fourier Transform Infrared analysis (FTIR) the structure of a processable bloodmeal based bioplastic could be assessed. Results confirmed a shift from α-helix to a predominantly β-sheet and random coil structure. It is interesting to note the similarity between the mixed random coil/ α-helix structure of these proteins compared to that of synthetic semi-crystalline polymers. In synthetic polymers chains in the crystalline regions are typically kept in position by hydrogen or van der Waals forces in an extended zigzag conformation. Chains then fold into and out of this crystalline lamella forming amorphous regions. It is therefore an important observation that the β-sheet/ random coil structure of extrudable proteins closely resembles that of synthetic semi-crystalline thermoplastic polymers. Initial trials showed mechanical properties of extrudable bloodmeal bioplastics to vary depending on the moisture and plasticiser content. The tensile strength of linear low density polyethylene (14 MPa) was easily surpassed, however, the material was considerably stiffer. Potential applications are in the agricultural and horticultural markets, more specifically products such as seedling trays, tree guards and possibly extruded netting. Technology in the area is still in its infancy and considerable research is still required to improve properties such as long term stability and embrittlement. This patented technology is currently owned by Novatein Ltd., a spin-off company by WaikatoLink Ltd., the commercial arm of the University of Waikato. www.eng.waikato.ac.nz/research/comps/ bioplastics MAGAZINE [05/08] Vol. 3 31
Non-Food Bioplastic Products from Biomass Waste Streams Article contributed by Dr Alan Fernyhough, Bioproduct Development Group, Scion, Rotorua, New Zealand Introduction The exploitation of non-food biomass resources and industrial waste streams in bioplastic products has been a major theme of research and development at New Zealand Crown Research Institute ‘Scion’ for nearly 10 years (see bM 04/07). Among this research two major strategies for manufacturing bioplastic products have been pursued: utilisation of forestry resources and utilisation of industrial biomass waste streams. Such resources or residues can, depending on their nature and on the modification technology employed, be transformed into bioplastics, or into functional additives for bioplastics, especially polylactic acid (PLA), polyhydroxyalkanoates (PHAs) and other biopolymers. Thus these bioplastics products are made from non-food resources. Exampe 1: Microbial Waste Water Treatment For PHA Bioplastics Huge volumes of wood waste, bark, paper and pulp processing waste – solid and liquid (waste water) are generated each year in commercial forestry and forest processing operations. About 10 years ago Scion recognised these underutilised and readily available residues were sources of chemicals and polymers for use as bioplastics and/or as bioplastics functional 32 bioplastics MAGAZINE [05/08] Vol. 3
