Cellulose nanocrystals: plant design for up-scaled production and applications in green construction materials.
Two main problems were addressed in this project. Firstly, upscaling technologies from the laboratory scale to industrial scale is difficult in the absence of pilot scale facilities. This research entailed the development of upscaling protocols for large scale production of cellulose nanocrystals (CNC) from sawdust waste biomass to meet increasing end-user demands at the Biorefinery Industry Development Facility (BIDF). Secondly, despite CNC having excellent properties for potential applications in high performance products and materials, CNC applications are still in their infancy, thus needing the demonstration of high impact applications. To propose potential solutions to these problems, the purpose of this research was to firstly design up-scaled CNC production plants with production capacities ranging from 1 kg/day to 1000 kg/day. These upscaling protocols will ease the difficulty of upscaling the CNC production from the laboratory scale to industrial scale without pilot scale facilities. The second research purpose was to demonstrate the application of CNC in novel green construction materials. The widespread use of ordinary Portland cement (OPC) in the construction industry, and the current landfilling of fly ash are environmentally-degrading. Hence, the CNC-enhanced novel green construction materials used fly ash as a precursor to potentially replace OPC in the construction industry. Furthermore, a database of the mechanical, electrical, thermal, and microstructural properties of the novel green construction material was produced to guide further research and optimizations. Additionally, a universal iterative empirical framework was produced to develop novel green construction materials, whose properties can be customized per the requirements of the target application. Based on the two main research purposes, the dissertation was divided into two parts: Part A dealt with the up-scaled CNC production process design, and Part B dealt with the application of CNC in the development of novel green construction materials. Regarding the research design and methodology, the Project Life Cycle Management framework commonly applied in Industry, in conjunction with literary design standards and guidelines, were used in the process design. Software simulations were also used for certain aspects of the process design. The CNC production process design included a de-mineralization (process) water plant and an acid recovery plant. The equipment sizing and degree of automation were different for each production scale. For the development of the novel green construction material, meta-analyses coupled with statistical experimental design were used to optimize the experimental trials. The mechanical and electrical test results were used to generate three-dimensional response plots of the CNC effects, thus forming the property database. CNC was found to improve the strength, density, and corrosion resistance (dictated by the electrical resistivity) of the fly ash-based geopolymer construction materials produced at small quantities (optimally 1.7% by volume) when cured for 48 hours with sample rotation. The geopolymer exhibited endothermic properties based on the heat flow analysis, implying its suitability in thermal resistance applications. Furthermore, higher CNC concentrations were found to induce thermal stability during thermal variations in the curing and elevated temperature exposure. Overall, the application of CNC in green construction materials and the empirical framework for the custom development of green construction materials showed substantial potential, thus holding the ability to improve the commercial viability of novel green construction materials to improve their competition against OPC. The study concluded that the up-scaling protocols developed for CNC production from sawdust waste biomass can be applied in the absence of pilot scale facilities. Furthermore, this study demonstrated that CNC can be applied to develop high performance green construction materials. Only small quantities of CNC (less than 0.5% concentration) were required to improve the thermal and mechanical properties of the novel green construction materials. These small CNC concentrations yielded compressive strengths of up to 8000 kPa and generally reduced the mass loss of samples when exposed to elevated temperatures up to 7%. The broader implication of this project is that the implementation of the desired up-scaled CNC production plant can create employment and boost the economy while providing a steady supply of CNC to meet the growing end-user requirements. Furthermore, the two environmental issues of unsustainable industrial waste disposal and unsustainable OPC building materials can be solved by applying suitable industrial waste materials to produce novel green construction materials as alternatives to OPC using the empirical framework provided in this work.
Doctoral Degree. University of KwaZulu- Natal, Durban.