https://www.um.edu.mt/library/oar/handle/123456789/929 Wed, 08 Apr 2026 05:33:54 GMT 2026-04-08T05:33:54Z https://www.um.edu.mt/library/oar/handle/123456789/145343 Title: Crystallization behavior of recycled semi-crystalline polymers in 3D printing : progress, challenges, and opportunities Authors: Zakaria, Zunaida; Rochman, Arif; Refalo, Paul Abstract: In recent years, plastic recycling has emerged as a critical concern in environmental protection and waste management. Among the various techniques for repurposing plastic waste into valuable products, extrusion of filaments for 3D printing has proven to be a highly effective method. A thorough understanding of the crystallization behavior of recycled plastics used in 3D printing is essential, as it significantly influences their final performance. This review provides an in-depth analysis of the crystallization behavior and crystallinity of recycled semi-crystalline polymers, with particular emphasis on recycled commodity plastics such as recycled polyethylene terephthalate (rPET), recycled polypropylene (rPP), and recycled high-density polyethylene (rHDPE). Recent research published between 2015 and 2025 was systematically synthesized and provides information on sources of plastic waste, additives employed, and recycling processes involved, with the findings summarized in a table that highlights their effects on polymer crystallinity. Furthermore, the key factors impacting the crystallinity of 3D-printed recycled plastics were examined, including the influence of additives, multiple processing cycles, printing parameters, and thermal treatments. Research gaps and the challenges faced during the printing process were also identified and discussed. By consolidating recent findings, this review provides a comprehensive understanding of the crystallization behavior of recycled plastics in 3D printing, thereby providing guidance for future research and developing strategies to optimize the performance of these materials. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145343 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145168 Title: Assistive device selection for operators with disabilities in industry 5.0 manufacturing : a Kansei engineering approach Authors: Bonello, Amberlynn; Francalanza, Emmanuel; Refalo, Paul; Gauci, Maria Victoria Abstract: Human-centricity, a cornerstone of Industry 5.0, calls for accessible manufacturing environments. Inclusive workstations comprise assistive devices which facilitate information reception, task execution and inspection for operators with various disabilities. Nonetheless, state-of-the-art literature fails to acknowledge the negative impacts of such assistive devices on operators with disability. Additionally, whilst one assistive device can be used to enhance physical accessibility, it could cause adverse effects on one’s cognitive or sensory abilities. This study therefore addresses these gaps by adopting Kansei Engineering to capture the emotions and perceptions of 48 persons with disabilities towards assistive devices in manufacturing workstations. Both positive and negative emotions and perceptions are elicited, addressing another gap. A unique physical, cognitive and sensory accessibility index for eight assistive devices was created, with each index then employed in a Pareto optimisation approach which maximises accessibility whilst reducing the number of devices. The most optimal combination (achieving an 88% total accessibility score) comprised a microphone, a keyboard and mouse, a touch screen, projected instructions and a monitor. This study has contributed an innovative approach towards guiding which and how assistive devices can be chosen carefully to address diverse abilities, ensuring a more inclusive manufacturing shopfloor in the age of Industry 5.0. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145168 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145166 Title: A value-sensitive design approach for embedded systems in Industry 5.0 Authors: Galea, Thomas John; Francalanza, Emmanuel; Refalo, Paul; Micallef, Andre Abstract: The emerging paradigm of Industry 5.0 seeks to advance the Industry 4.0 strategy into a broader context in addressing wider human, environmental and economic implications. Embedded systems play a critical role in supporting the next generation of industrial innovation and enabling Industry 5.0 technologies. Despite this, current literature offers limited guidance on how value-driven methodologies can be applied in the context of embedded hardware and systems engineering. This paper contributes the application of the value-sensitive design (VSD) methodology to embedded systems design for Industry 5.0. This involved conceptualising and proposing design values, norms and requirements for human-centricity, environmental sustainability and resilience. Through a combination of literature, Delphi methods with Industry 5.0 experts and consultation with embedded systems engineers, this research presents the value-driven approach for supporting Industry 5.0 principles in embedded systems design. This resulted in a set of fourteen values for the design of embedded systems in I5.0 and fifty one embedded system design requirements which were subsequently evaluated by embedded systems engineers to identify implementation challenges and stakeholder perspective. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145166 2026-01-01T00:00:00Z https://www.um.edu.mt/library/oar/handle/123456789/145039 Title: Process parameter optimization for 3D printing of post-industrial recycled PP through in-situ thermal analysis Authors: Zakaria, Zunaida; Rochman, Arif; Refalo, Paul Abstract: Fused filament fabrication (FFF) is commonly used to manufacture polymer components and has emerged as a sustainable manufacturing method when recycled materials are utilized. However, achieving consistent mechanical performance of recycled polymers remains challenging as semicrystalline polymers are highly sensitive to thermal history from prior manufacturing. This study investigates the effect of printing parameters on cooling behavior, crystallinity, and tensile performance of post-industrial recycled polypropylene (rPP). Additionally, an in-situ infrared thermal imaging approach was introduced to directly monitor temperature changes during the FFF process. A systematic experimental design was implemented by varying the wall thickness of the printed samples and the nozzle temperature, and their effects were correlated with real-time cooling rates, crystallinity measured by differential scanning calorimetry and Raman spectroscopy, and tensile properties. The results demonstrate that the cooling rate acts as a unifying parameter linking process conditions to crystallization behavior and mechanical response. The printed sample fabricated at a nozzle temperature of 190 ℃ and a wall thickness of 2.4 mm achieved an optimal balance between ordered and disordered crystalline regions, a good surface finish, uniform pigment dispersion, and a tensile strength of 20.95 MPa, which is comparable to previously reported values for rPP. This study presents a new experimentally validated method to predict and optimize printing parameters through real-time process-structure–property relationships for recycled semicrystalline polymers during material extrusion, thereby supporting sustainable manufacturing processes. Thu, 01 Jan 2026 00:00:00 GMT https://www.um.edu.mt/library/oar/handle/123456789/145039 2026-01-01T00:00:00Z