Theses and Dissertations

Bioplastic Development, Characterisation, and Optimization of Fused Filament Fabrication Parameters

2026-05-05T11:48:41Z

Bioplastic Development, Characterisation, and Optimization of Fused Filament Fabrication Parameters Andanje, Maurine Naliaka Additive manufacturing, commonly known as 3D printing, is a rapidly expanding technology that has the potential to support a circular and sustainable economy. This technology supports a wide variety of raw materials and offers design flexibility, expanding its use in prototype and custom part production. One of the most common additive manufacturing technologies is Fused Filament Fabrication (FFF), which utilizes thermoplastic polymers as the raw material. Thermoplastic polymers commonly used in FFF include polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), polyamide (PA), polycarbonate (PC), and Nylon 12. Despite its popularity, high-density polyethylene has not been thoroughly studied in fused filament fabrication due to problems with warping and significant thermal shrinkage of printed parts after solidifying. It has been suggested that adding organic fillers will lessen these difficulties. The use of organic fillers in polymers results in biocomposites that have improved thermal properties and potential for biodegradation. However, printability, low-layer agglomeration, and reduced mechanical properties are some of the challenges that have to be overcome during FFF. Determining the best combination of printing parameters can significantly improve the printability of these biocomposites. In this study, rice husk waste was used as an organic filler in recycled high-density polyethylene to develop a biofilament for FFF. High-density polyethylene was chosen as the polymer since, though it is highly recyclable, it has not qualified as a potential raw material in FFF. This is due to challenges such as high thermal shrinkage that causes it to warp during printing. Organic fillers in polymers have been recommended as a means of reducing warpage of HDPE and enhancing printing directionality. Through the design of an experiment, various filler-to-polymer combinations were tested with the addition of a compatibilizer to enhance the filler’s miscibility in the polymer matrix. Using the ball mill, the rice husks were ground into powder with particles smaller than 75 μm. The biofilament's highest composition included 35 wt.% rice husk filler, 35 wt.% recycled high-density polyethylene, and 30 wt.% compatibilizer, indicating an improvement in rice husk filler content compared to earlier research. Digimat 2024.1 was used as the platform for material modeling and printing simulation to identify printing issues, such as warpage and residual stresses. Through a coupled simulation, a finite element model was analyzed to predict part performance. The model was validated experimentally using the standard tensile test specimen. The Taguchi Grey Relational Analysis (TGRA) was used to optimize the printing process due to its efficiency and robustness for multi-response experiments. Printability was successful up to the biofilament whose composition comprised 30 wt.% rice husk filler, 40 wt.% recycled high-density polyethylene, and 30 wt.% compatibilizer. This biofilament's mechanical properties included a tensile strength of 8.53 MPa with a standard deviation of 1.32 MPa, a tensile modulus of 128.56 MPa with a standard deviation of 13 MPa, and a maximum tensile strain of 6.6% with a standard deviation of 0.03%. Experimental validation of warpage yielded a maximum error margin of 5.43%, while validation of residual stresses resulted in a maximum error margin of 5.56%. The incorporation of rice husk filler, a natural reinforcement, into recycled high-density polyethylene improved the crystallinity of the biofilaments, which helped reduce shrinkage and warpage in printed parts. Biodegradability was also enhanced up to 10 % in a period of 24 weeks. The outcome of this study will provide valuable information for the manufacture of functional parts, such as biomedical devices, including microfluidic substrates, from biocomposite materials using FFF. Doctor of Philosophy in Mechanical Engineering

Evaluation of Ball Mill Performance and Energy Consumption through the Discrete Element Method

2026-05-05T11:19:41Z

Evaluation of Ball Mill Performance and Energy Consumption through the Discrete Element Method Kyalo, Mathew Ndeto Ball mills are a frequently used technology for comminution in the chemical and mineral processing industries, yet their characteristically low energy efficiency presents a persistent operational challenge; even marginal improvements can yield substantial economic and environmental benefits. This research investigates the relationship between mill geometry, operational parameters, and grinding efficiency by employing an integrated computational and experimental framework. The study compares the performance of two distinct mill designs - polygonal and cylindrical geometries—under varied configurations (with and without lifters). The Discrete Element Method (DEM) was used to simulate particle dynamics, charge motion, and wear, while a Population Balance Model (PBM) was applied to determine ore-specific breakage parameters and predict product size distributions. Simulations were validated against experimental data obtained from a custom-designed milling setup capable of precise speed control and in-line torque monitoring. Key findings from the DEM analysis demonstrate that geometry fundamentally alters charge behavior. At 75% of critical speed, a polygonal mill without lifters increased effective interparticle interactions by 10% and minimized particle centrifuging compared to a lifter-less cylindrical mill. The introduction of lifters further optimized performance: in the polygonal design, lifter addition enhanced collision frequency, resulting in a significant 26% reduction in power draw and a reduced Archard wear rate of 1.18×〖10〗^(-3) m. The cylindrical mill equipped with lifters achieved high collision intensity similar to the polygonal design but exhibited superior operational stability and about 30% lower wear rate. The developed DEM model demonstrated strong predictive capability, achieving a high Pearson correlation coefficient (>0.9) between simulated and experimental results. Predictions showed excellent quantitative agreement with experimental data, with root mean square errors (RMSE) of 2.3 W for power draw and 2.1° for shoulder angle. The grinding kinetics of two ore types, a gold ore and a malachite copper ore (averaging 4.7% Cu), were characterized using the PBM. The specific breakage rate (S_i) for the malachite ore increased with particle size, reaching a maximum of 2.892 min⁻¹ at 2 mm, a phenomenon attributed to the reduced agglomeration tendency and lower surface energy of larger particles. Breakage distribution functions and the optimum feed size for efficient milling were established. Furthermore, investigations into binary ore blends revealed that overall grindability is non-linear and disproportionately influenced by the harder ore component, potentially leading to a broader product size distribution when ores of differing hardness are combined. The DEM-calibrated parameters and PBM-derived kinetic models generated in this study provide a robust, scalable foundation for the design and optimization of industrial grinding circuits, directly linking particle-scale mechanics to full-circuit performance. Keywords: Ball mill, Discrete Element Method, Population Balance Model, Milling kinetics. Doctor of Philosophy in Mechanical Engineering

The Influence of Safety Training on Technicians’ Safety Culture in the Pharmaceutical Manufacturing Industries in Kenya

2026-05-05T07:36:58Z

The Influence of Safety Training on Technicians’ Safety Culture in the Pharmaceutical Manufacturing Industries in Kenya Miring’u, Josephine Muthoni Technicians in pharmaceutical manufacturing industries work in sensitive occupational settings. They are routinely exposed to chemical hazards due to the nature of their work. In order for them to perform, safety is paramount. This research assessed the influence of safety training on safety culture of technicians in pharmaceutical manufacturing industries in Nairobi County. To achieve the objective, descriptive survey research design was employed. In selecting the study sample purposive sampling was utilized. Thirty-three (33) Pharmaceutical Manufacturing Industries were selected based on the inclusion criteria from the study area, Nairobi Metropolitan. Pharmaceutical Manufacturing Industries formed the sampling unit from where respondents were drawn. The population of the study was 4,000 employees drawn from the sampled Pharmaceutical Manufacturing Industries. The sample of the study was three hundred and seventy nine (379) respondents, who comprised of Technicians. Data was collected through self-administered structured questionnaires and observation. The collected data was subjected to quantitative and qualitative analysis by employing SPSS. The results show that the safety maturity level recorded in 85% of the pharmaceutical manufacturing industries is at continually improving safety maturity level and only 15% of the sampled industries were at the involving safety maturity level. This was based on an analysis of the safety culture key dimensions. The findings have also shown that majority of the respondents at 75.4% had their first encounter with OSH training at work environment commonly referred to as On the Job Training (OJT) and only 23.3% were trained during their academic/professional education. The findings have shown that a majority of the respondents; 89.0 % and 80.8% of the respondents had been trained on the requirements of OSH Act 2007 and Evacuation procedures respectively. Notably, the training area with the least awareness was Exposure Limits of hazardous chemicals and substances at 29.1% across all PMI’s. The p values for OSH Training and Safe work documentation are p<0.001 and 0.421 respectively, indicating that OSH training is a statistically significant predictor of Safety Culture. Based on the results the study accepts the null hypothesis; there is a statistically significant difference in influence of safety training on safety culture of technicians among pharmaceutical manufacturing industries. The study therefore concludes that OSH training has a significant positive influence on safety culture in pharmaceutical manufacturing industries in Nairobi, Kenya. The study indicates that there is need to incorporate OSH competency in the professional training of potential employees in the pharmaceutical manufacturing industries in Kenya. Master of Science in Occupational Safety and Health

Budgeting Practices and Financial Performance of Manufacturing Firms in Kenya

2026-05-04T13:37:45Z

Budgeting Practices and Financial Performance of Manufacturing Firms in Kenya Otieno, Moses Odongo The objective of this study was to establish the effect of budgeting practices and financial performance of manufacturing firms in Kenya. The following specific objectives were addressed by this study: to establish the effect of budget planning on financial performance of manufacturing firms in Kenya, to examine the effect of budget monitoring & control on financial performance of manufacturing firms in Kenya, to determine the effect of budget evaluation on financial performance of manufacturing firms in Kenya, to evaluate the effect of budget communication on financial performance of manufacturing firms in Kenya, and to assess the firm size as a moderating factor on the financial performance of manufacturing firms in Kenya. This study was anchored on four theories, namely; Incremental Budgeting Theory, Goal Setting Theory, Agency Theory, Resource-Based Theory, and Theory of the Growth of the Firm. Most researches have concentrated mainly on single budgetary control on the financial performance of manufacturing firms. It is on this premise that there existed a knowledge gap on the collective budgeting practices by manufacturing industry, hence the need for this study. This study utilized a mixed research design. The study used primary data and secondary data collection sheet. The study target population were 741 manufacturing firms operating in Kenya. The unit of observation were finance managers, accountants, and supervisors from the supervisory level management. Questionnaires were administered as the main tool of data collection. Secondary data was administered from the financial reports in the books of sampled manufacturing. To check the validity and reliability of the questionnaires, a pilot study was carried out. Descriptive statistical methods were applied to describe application of budgeting practices in the sampled manufacturing firms. Inferential statistical techniques such as correlation analysis and regression analysis were applied to test the hypotheses of association and differences. The collected data was processed using the statistical package for social science (SPSS). The study findings revealed that budget planning, budget monitoring & control, budget evaluation, and budget communication, have significant positive effect on the financial performance of manufacturing firms in Kenya. Furthermore, the firm size significantly moderates the relationship between budgeting practices and financial performance of manufacturing firms, with R-Squared value increasing after including the interaction terms. The budgeting practices ‘null hypotheses were all rejected implying a significant effect on financial performance. This study recommends that by setting spending limits and monitoring actual expenditure against budget, firms can prevent overspending and ensure resources are used efficiently. The study suggests the need for further research on other external economic factors besides the budgeting practices that affect the financial performance of manufacturing firms and other companies. PhD in Finance