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Processing Extrudable Sheets using Decoloured Bloodmeal

This study investigated the feasibility of blending decoloured bloodmeal thermoplastic (DBT), a thermoplastic protein material, with poly (lactic acid) (PLA), a semi-crystalline polymer, and subsequently processing the blend into a sheet using extrusion. Free radical grafting was used to graft itaconic anhydride onto PLA to create reactive side groups. Blends of DBT and PLA compatibilized with itaconic anhydride were produced using different processing conditions, different formulations of DBT and different blend compositions. Decoloured bloodmeal thermoplastic powder (DBTP) was easier to process into injection mouldable samples than were decoloured bloodmeal thermoplastic granules (DBTG). The compatibility between the produced material blends was investigated using mechanical testing, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and wide-angle X-ray scattering (WAXS). Blending DBT with PLA increased the tensile strength and modulus of DBT while strain at break decreased. The glass transition temperature of the blends increased compared to neat DBT. SEM revealed a more homogenous microstructure, which provided evidence of enhanced interfacial adhesion between both phases in the blends with PLA grafted with itaconic anhydride (PLA-g-IA). An insignificant decrease in the crystallinity of the blends compared to neat material was observed in the WAXS result, indicating that blending with PLA has no structural effect on DBT. Ratios (DBP:PLA) of 30:70 (DP37), 50:50 (DP55), 70:30 (DP73) and 90:10 (DP91), with and without compatibilizer (PLA-g-IA), were examined to determine the optimal blend ratio for DBT/PLA blends. DBP content below 30 wt.% was considered to defeat the main aim of maximizing the use of decoloured bloodmeal. Below 50 wt.% and above 70 wt. % DBT content, either DBT or PLA overwhelmed the compatibilizing effect of itaconic anhydride resulting in poor mechanical properties of the blends. Four DBT formulations with varying water, SDS and TEG content were blended with PLA or PLA-g-IA to determine the best DBT formulation for DBT/PLA blend system. From the mechanical properties and digested surface morphology obtained, a compatibilized DBT formulation containing 40 parts per hundred DBM (pphDBM), 3 pphDBM SDS and 20 pphDBM TEG (F2)/PLA showed a considerable increase in tensile strength, elongation at break and impact strength compared to other formulations trialled. Also, an improvement in interfacial interaction, evidenced by a finer phase structure with relatively uniform void, was observed for this blend. However, a balance can be achieved between this blend and a compatibilized blend containing 40 PPHDBM, 6 PPHDBM SDS and 30 PPHDBM, if elongation at break is compromised depending on the desired material properties and functionality of the desired end product. The data obtained from SEM and WAXS of the blends indicated an improvement in the blend’s compatibility with the addition of itaconic anhydride. However, no significant effect was observed in the blend’s mechanical properties with the addition of compatibilizer. This led to the investigation of possible ways to improve the blend’s mechanical properties. Compatibility between DBT and PLA, the effect of different compatibilizer type, and plasticizer type used were investigated using mechanical testing, SEM and DMA. DBT/PLA blends were produced using three different compatibilizers: itaconic anhydride grafted PLA (PLA-g-IA), poly (2-ethyl-2-oxazoline) (PEOX) and poly (phenyl isocyanate)-co-formaldehyde (pMDI). Compatibilizing DBT/PLA blend with PEOX or PLA-g-IA was relatively straightforward, while using dual compatibilizer (PEOX and pMDI) required the addition of compatibilizer at different stages of blending to achieve a compatible blend. PLA-g-IA produced high tensile and impact strength as well as an evenly dispersed DBT domain and finer morphology compared to PEOX/pMDI and PEOX only. Two compatibilization approaches were used for DBT/PLA blends; one in which a compatibilizer (PLA-g-IA) was added as a third blend component and another in which a reactive group (itaconic anhydride) capable of interacting with the DBT and PLA phase was grafted onto PLA to improve the interfacial interaction between both phases. The data obtained suggested that adding the compatibilizer as a third blend component may be a successful approach. Two plasticizer types, tri ethylene glycol (TEG) and glycerol, were trialled to determine the best for the DBT/PLA blend system. The washed surface morphology of blends plasticized with TEG revealed finer morphology with more evenly distributed pores and small DBT domain sizes than blends plasticized with glycerol. The feasibility of sheet extruding DBT/PLA blends was assessed, and the properties of the sheets produced were measured. The effects of different processing methods and different processing steps on the produced sheets were investigated in terms of mechanical, structural and water absorption properties. With a fundamental understanding of the blending method for DBT/PLA blends, different sheet processing methods (M1, M2, M3, M4 and M5) and processing steps (2- and 3-step processing) were used to successfully process D463.4.1 (DBT/PLA blend containing 50 parts DBT, 40 parts PLA and 10 parts compatibilizer) into a sheet using extrusion. The viscosity of the blends produced using different methods was measured, to better understand the sheet processing of DBT/PLA blends. M4 produced the most promising sheet, with better consolidation and a relatively smooth surface, as revealed by SEM topography of DBT/PLA blends sheet. The tensile properties and water absorption of the produced sheets suggested that the collective effects of reduced heat processing (method M4) and 2-step processing improved the sheet properties. This study demonstrated the feasibility of blending DBT with PLA, improving the properties of DBT/PLA blends and processing the produced blends into sheets for use in agricultural (such as weed mat) and packaging applications.
Type of thesis
Izuchukwu, S. C. P. (2019). Processing Extrudable Sheets using Decoloured Bloodmeal (Thesis, Doctor of Philosophy (PhD)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/12991
The University of Waikato
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