|dc.description.abstract||Current environmental and economic concerns surrounding the use of petroleum-based plastics, has led to increased study of renewable natural polymers, such as proteins. Bloodmeal (BM) is a by-product of the meat industry and large volumes is sold as a low-cost fertilizer or animal feed. It contains 90 wt% proteins giving it the potential as a renewable precursor for bioplastic production. The objective of this study was to investigate the use of BM for the production of bioplastics, focusing on the use of chemical additives to facilitate thermoplastic extrusion.
Literature revealed that bioplastics formation from proteins requires denaturation and unfolding using thermal and chemical means, allowing new interactions to form between chains. Thermoplastic extrusion also requires sufficient chain mobilization, enabling flow through the barrel. The proteins physiochemical characteristics, plasticizer content and chemical additives will govern its processing behavior, structural and material properties.
Bloodmeal powder was extruded and injection moulded using water, sodium sulfite, sodium dodecyl sulfate (SDS) and urea as additives. The efficiency of these chemical additives was characterized by:
Processability. Temperatures between 100 and 125 C produced a successful material, above this excessive covalent cross-linking occurred which reduced chain mobilization. Sodium sulfite was essential, breaking covalent bonding which allowed chain extension. The plasticizer content also strongly influenced the processability, while water and urea were essential for improved processing.
Consolidation, water absorption and solubility. It was found that SDS's influence on hydrophobic interactions in combination with sodium sulfites cleavage of covalent cross-links resulted in good consolidation, water absorption and solubility. Increasing sodium sulfite increased water absorption, indicative of cross-link reduction. However, high sodium sulfite at low water concentration resulted in a degraded material. The degraded polymer showed an increase in ordered structures, due to the formation of helical conformations of the short peptide chains.
Protein conformation. It was found that BM was already highly denatured, with considerable amounts of β-structures. Successful processing with required increased chain mobilization through the reduction of inter- and intra-molecular interactions which led to less ordered structures.
Mechanical Properties. Water was shown to be critical for processing, enhancing the action of sodium sulfite, SDS and urea. During conditioning, water would evaporate, allowing new intermolecular forces between chains, often resulting in a brittle material. SDS was essential for consolidation, but excessive amounts could restrict formation of new intermolecular forces during conditioning. The highly plasticized proteins resulted in ductile materials after conditioning. Lowering the water, sodium sulfite or urea concentration would result in a brittle material after conditioning.
Successful processability, consolidation, water absorption, solubility, and mechanical properties were achieved using 3 pphbm sodium sulfite, 60 pphbm water, 3 pphbm SDS and 20 pphbm urea. This optimal material resulted in increased unordered structures shown by Fourier transform infra-red spectroscopy. The resulting bioplastic was ductile after conditioning and had a tensile strength of 9.6 MPa and a Young's modulus of 536 MPa, comparable to low-density polyethylene.||en_NZ