|dc.description.abstract||Renewable and compostable bioplastics can be produced from biopolymers such as proteins. Animal blood is a by-product from meat processing and is rich in protein. It is dried into low value bloodmeal and is used as animal feed or fertiliser. Previous work has shown that bloodmeal can be converted into a thermoplastic using water, urea, sodium dodecyl sulphate (SDS), sodium sulphite and triethylene glycol (TEG). This material is currently being commercialised as Novatein Thermoplastic Protein (NTP) and studies are working on improving its properties through production of composites and blends. In addition further studies are working on understanding its molecular structure before and after thermoplastic processing by utilising various analytical techniques.
A specific area identified for improvement is its colour and smell. NTP is black in colour and has an offensive odour which means its current potential applications are limited to agriculture and waste disposal. Approximately 30 to 40% of plastics are used in short life span applications such as packaging and using bioplastics in these applications would be advantageous because of their compostability. To increase NTP’s possible range of applications to common applications such as packaging and increase its acceptance from consumers, its colour and odour must be removed without compromising its mechanical properties.
Oxidative treatment methods for removing colour and odour from red blood cell concentrate (RBCC), modified red blood cell concentrate (mRBCC) and bloodmeal were investigated using hydrogen peroxide, peracetic acid (PAA), sodium hypochlorite, sodium chlorite, sodium chlorate and chlorine dioxide. Treatment effect on protein molecular weight, crystallinity, thermal stability, solubility, product colour and smell were investigated. Treating RBCC and mRBCC required multiple processing steps, had high water contents (67% and 93% respectively), foamed during treatment with peroxides and the protein was prone to hydrolysis. Bloodmeal contained 95% solids and was less sensitive to hydrolysis.
The best decolouring and deodorising results were obtained by treating bloodmeal with 5% PAA. Using this novel treatment method, decolouring was completed within five minutes and produced a powder which was 67% white based on the RGB colour scale. Protein molecular weight was unaffected by PAA concentration, with a number average molecular weight ranging between 190-223 kDa for 1-5% PAA treated bloodmeal. However, its crystallinity decreased from 35% to 31-27% when treated with 1-5% PAA. Treating bloodmeal with 1-5% PAA also reduced the protein’s thermal stability, glass transition temperature (225°C down to 50°C) and increased its solubility from 11% to 85% in 1% SDS solution at 100°C.
3-5% PAA treated bloodmeal powder was extruded using different combinations of water, TEG, glycerol, SDS, sodium sulphite, urea, borax, salt and sodium silicate at concentrations up to 60 parts per hundred parts bloodmeal (pphBM). Partially consolidated extrudates and fully consolidated injection moulded samples were obtained using a combination of water, TEG and SDS. 4% PAA treated bloodmeal produced the best extruded and injection moulded samples and was chosen for investigating the effects of water, TEG and SDS concentration on consolidation and specific mechanical energy input (SME) as well as product colour and mechanical properties.
Analysis of variance (ANOVA) showed SDS was the most important factor influencing ability to be extruded because it detangled protein chains and allowed them to form new stabilising interactions required for consolidation. The best extruded sample, which was 98% consolidated and 49% white, contained 40 pphBM water, 10 pphBM TEG and 6 pphBM SDS.
TEG had the greatest effect on the product’s mechanical properties and colour after injection moulding because of its plasticisation effect. ANOVA showed TEG contributed 30.5% to changes in Young’s modulus, 66.9% to strain, 39.7% to toughness, 0.1% to UTS and 38.1% to colour. However, SDS also contributed 8.1% to changes in Young’s modulus, 13.7% to strain, 15.2% to toughness, 12.5% to UTS, 0.5% to colour. Initial water content contributed 19.7% to Young’s modulus, 1.0% to strain, 0.6% to toughness, 30.0% to UTS and 29.9% to colour. The best injection moulded sample was produced using 50 pphBM water, 20 pphBM TEG and 3 pphBM SDS. This produced a material which was 39% white, which had an almost transparent yellow/orange colour with a tensile strength of 4.62 MPa, Young’s modulus 85.48 MPa, toughness 1.75 MPa and 82.62% strain.
The mechanical properties of the product manufactured in this study were comparable to those of NTP, but the product was mostly decoloured, allowing it to be easily pigmented and without an offensive odour.||