3D printing materials for large-scale insulation and support matrices : thesis by publications presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering, Massey University, Albany, New Zealand

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Additive manufacturing (AM) techniques have promising applications in daily life due to their superiority over conventional manufacturing techniques in terms of complexity and ease of use. However, current applications of polymer-based 3D printing (3DP) are limited to small scale only due to the high cost of materials, print times, and physical sizes of the available machines. In addition, the applications of 3DP are yet to be explored for insulation of different large-scale mechanical structures. For example, milk vats are large structures with complex assemblies (like pipes, joints, couplings, valves, ladders, vessel doors) that requires insulation to store the milk at a low temperature of 6 °C as per the NZCP1 regulations in New Zealand. Generally, milk vats lack any kind of proper insulation around them and require additional cooling systems to keep the milk at a prescribed temperature. Any variations in the temperature can lead to deterioration in the quality of milk. Therefore, there exists a research gap that can not only help to solve an industrial issue but also can be a first step towards real large-scale 3DP applications that can potentially lead to many others in future. For example, pipe insulation, food storage tanks, chemical storage tanks, water treatment. This research explores new and inexpensive materials for large-scale 3DP. For this purpose, the current state of the 3DP materials is analyzed and based upon this analysis two distinct approaches are devised: 1) in-process approach to improve the mechanical properties of the existing materials like polylactic acid (PLA), and 2) modification of inexpensive materials (like materials used in injection, rotational, and blow moulding) to make them printable. In the first approach, by controlling the process parameters, mechanical properties are studied. While in the second approach, blends of high density polyethylene (HDPE) and polypropylene (PP) with different thermoplastics (acrylonitrile butadiene styrene, ABS and polylactic acid, PLA) are investigated to achieve printability. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) are used to analyze the proposed materials. The overall objective of this research is to devise low-cost materials comparable to the conventional processes that are capable of providing good mechanical properties (tensile, compressive and flexural) along with high resistance to thermal, moisture, and soil degradation. The results present significant enhancement, up to 30%, in tensile strength of PLA through in-process heat treatment. However, the softness induced during printing above 70 °C directs to the second approach of developing the novel blends of HDPE and PP. In this regard, the research develops three novel blend materials: 1) PLA/HDPE, 2) ABS/HDPE, and 3) ABS/PP. These materials are compatibilized by a common compatibilizer, polyethylene graft maleic anhydride (PE-g-MAH). PLA/HDPE/PE-g-MAH provides highest tensile strength among all existing FDM blends (73.0 MPa) with superior resistance to thermal, moisture and soil degradation. ABS/HDPE and ABS/PP provide one of the highest mechanical properties (tensile, compressive, and flexural) in ABS based FDM blends with superior thermal resistance to six days aging. ii The chemical characterization of aforementioned novel FDM blends shows partial miscibility with sufficient signs of chemical grafting. The significant intermolecular interactions are noted in FTIR that shows the grafting through compatibilizer (PE-g-MAH). The DSC analysis shows visible enhancement in different thermal parameters like glass transition, melt crystallization and degradation along with signs of partial miscibility. Furthermore, TGA analysis confirms the partial miscibility along with the enhanced onset of degradation temperature. The increase in onset temperatures of each of the three blends proves the thermal stability to high temperatures. Hence, each of the developed blends is capable of resisting any material deterioration during routine cleaning operation at 70 °C of milk vats. This research has resulted in 5 journal publication (four published and one submitted), two conference proceedings and a number of posters presented at local conferences. This research is the part of food industry and enabling technologies (FIET) research program funded by the ministry of business, innovation and employment (MBIE), New Zealand in collaboration with Massey University, Auckland.
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Dairying, Equipment and supplies, Vats, Cold storage, Insulation, Three-dimensional printing, Materials, Plastics, Polymers, Industrial applications