Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid)
Walallavita, A. S. (2018). Biopolymer foams from Novatein thermoplastic protein and poly(lactic acid) (Thesis, Master of Philosophy (MPhil)). The University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/12049
Permanent Research Commons link: https://hdl.handle.net/10289/12049
Novatein is the only commercial thermoplastic protein made from bloodmeal, a highly denatured protein and a readily available by-product of the meat processing industry. One of the major limitations of Novatein is its hydrophilic nature and loss of plasticizer during processing which leads to poor mechanical properties. To address these issues, Novatein has been blended with another biodegradable polymer with good mechanical properties, polylactic acid (PLA). Blending two components can lead to poor mechanical properties of the blend due to weak interfacial adhesion and thermodynamic incompatibility. These problems can be overcome with the use of a compatibilizer which helps to stabilize the interface by coalescence suppression of the dispersed domains. In this work, itaconic anhydride grafted PLA (PLA-g-IA) was chosen as a compatibilizer for Novatein-PLA blends because IA is extremely stable when reacted with proteins and less harmful compared to maleic anhydride. Reactive extrusion was used to blend different proportions of Novatein and PLA and the compatibilizing effects of itaconic anhydride was examined. Results showed that fewer agglomerated Novatein particles and less phase separation was visible in the presence of compatibilizer. At 50-50 Novatein/PLA, the absence of compatibilizer produced a dispersed morphology which caused the material to disintegrate in chloroform. Upon the addition of itaconic anhydride, the 50-50 blend stayed intact which was thought to be a result of co-continuous morphology. Incorporating 50 wt.% of PLA-g-IA improved the tensile strength of Novatein by 42% and impact strength by 36%. The effect of compatibilizer was evident in wide-angle x-ray scattering. Three phases were detected in the absence of compatibilizer: crystalline Novatein, amorphous Novatein, and amorphous PLA phases. With compatibilizer, the blend was moving toward two phases: crystalline Novatein, and an amorphous blend of Novatein and PLA. Itaconic anhydride grafted PLA improved miscibility between Novatein and PLA, which lead to the fabrication of Novatein-PLA foams. Foaming Novatein is a new area of study which has never been investigated before. The foamability of a material depends on the ability of the material to withstand the stretching forces during bubble growth and hold the newly formed cellular structure. The low melt strength of Novatein, however, make it difficult to induce a cellular structure in the proteinous bioplastic. Therefore, the foaming ability of Novatein can be improved by blending with PLA, which can successfully be foamed using a batch process with carbon dioxide as the blowing agent. Various compositions of Novatein/PLA were batch foamed with and without compatibilizer. Results showed that pure Novatein cannot form a cellular structure at a foaming temperature of 80°C, however, in a blend with 50 wt.% PLA, micro cells formed with a higher cell density (8.44x1021 cells cm-3) and smaller cell sizes (3.36 µm) compared to pure PLA and blends with higher amounts of PLA. A further reduction in cell size and increase in cell density was observed upon the addition of compatibilizer due to the higher crystallinity of grafted PLA. The co-continuous morphology obtained upon the addition of compatibilizer led to the development of foams with more uniform cell sizes, which was stable for cell nucleation even at high temperatures.
The University of Waikato
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