Abstract
Some of the most promising sustainability solutions fail – not because they don’t work, but because people cannot agree on what “working” means. My capstone project examines the feasibility of mass-producing polylactic acid (PLA), a biodegradable polymer, from sugarcane bagasse, a waste byproduct of the sugar industry. It explored how waste can be repurposed within a circular economy while evaluating technical, economic, and environmental feasibility. My STS paper investigates how circular technologies succeed or fail not purely on technical merit, but also through social interpretation. It examines why some initiatives – like aluminum recycling – stabilize, while others, such as plastics recycling or paper straw adoption, remain contested. Both projects focus on circularity: the capstone evaluates feasibility, while the STS paper examines how social expectations shape adoption.
The capstone addresses the need for sustainable materials by converting sugarcane bagasse into PLA, transforming a waste product into a valuable biopolymer. Bagasse is produced in large quantities and does not compete with food resources, making it an attractive feedstock. The project contributes to reducing waste and reliance on petroleum-based plastics by designing a plant producing 270,000 metric tons of PLA per year. Feasibility was evaluated through process design, including material and energy balances, flow diagrams, equipment sizing, and economic, energy, and safety assessments.
Results show that large-scale PLA production from bagasse is technically achievable, with improvements enabling output beyond the initial design capacity. However, the process was economically and practically unfeasible. The plant requires a fixed capital investment of $2.415 billion, and financial analysis showed it does not achieve discounted payback within 20 years, making profitability sensitive to assumptions like the discount rate. Nonetheless, the process could become viable through improved downstream purification, bioengineered bacterial strains with greater pH tolerance, or better pilot-scale data to refine separation costs.
The STS paper asks: how do technological design and cultural beliefs about waste, purity, and sustainability interact to shape and stabilize contemporary visions of circularity? Many sustainability initiatives are evaluated on technical metrics, yet adoption depends heavily on social acceptance and shared definitions of success. The paper applies two STS frameworks: the Social Construction of Technology (SCOT) and Jasanoff’s concept of co-production, with qualitative discourse analysis of corporate reports, policy documents, and media narratives to examine how actors define problems, evaluate performance, and negotiate trade-offs.
The analysis compares aluminum recycling and plastics recycling. Aluminum recycling represents a stabilized system, where perspectives largely agree on purpose and metrics, such as recycled content and carbon reduction. In contrast, plastics recycling remains contested. Actors disagree on the problem recycling solves, what counts as success, and whether trade-offs – including material degradation, cost, and environmental risk – are acceptable. Plastics recycling has not reached interpretive closure and remains unstable despite institutional support. The paper concludes that circular technologies do not succeed on technical feasibility alone. They stabilize only when social groups converge on shared definitions of value, performance, and responsibility. This insight reinforces the capstone findings: even technically viable solutions may fail if they do not align with economic constraints and social expectations, highlighting that circularity is fundamentally a sociotechnical challenge rather than purely an engineering problem.
