This thesis addresses the urgent need for more effective environmental sustainability assessments that can be integrated into the early stages of product design. Designers play a critical role in the environmental impact of their products, yet they often struggle to integrate environmental assessments into the early stages of design. Traditional linear production models cause environmental challenges such as resource depletion and pollution, while the Circular Economy offers a more sustainable alternative by aiming to reduce waste and close resource loops. However, simply applying CE principles does not guarantee sustainability, as unintended effects such as "CE rebound" can occur. This highlights the need for advanced tools that can accurately assess the environmental impact of circular designs early in the design process.

The primary objective of this study was to establish the requirements for an early-stage quantitative assessment tool that integrates Life Cycle Assessment (LCA) into circular design processes. The research aimed to determine how LCA can be effectively incorporated into early decision-making stages, identify suitable methods for evaluating circular design strategies, assess the usability of existing LCA tools, and address the challenges designers encounter when implementing environmental sustainability assessments.
The research was conducted in three phases. The first phase involved a detailed examination of designers' decision-making workflows. In the second phase, existing sustainability assessment methods and LCA tools were evaluated. The third phase focused on developing a program of requirements for a new assessment tool. Methodologies included comprehensive literature reviews, analysis of grey literature, interviews with experts in environmentally sustainable design, and usability testing of existing tools.

Key findings revealed a mismatch between the complexity of current LCA tools and the practical needs of designers in the early stages of design. Most tools are either too complex or too simple, making them unsuitable for the iterative and creative nature of early design processes. Designers often rely on intuitive approaches that are not adequately supported by traditional, data-intensive LCA tools. To address this gap, the study proposed a dual-interface tool: one interface for designers to facilitate easy integration into creative workflows, and another for sustainability experts to manage detailed modeling and scenario analysis. The tool emphasizes ex-ante LCA for predictive analysis, allowing for early-stage assessment and scenario modeling using estimated data. Additionally, integrating qualitative assessments alongside quantitative data will provide a more comprehensive evaluation of circular design strategies. This holistic approach aims to align LCA tools with designers' practical needs, enhancing the integration of environmental sustainability into early-stage product design.

The research concludes with recommendations for developing user-friendly LCA tools, improving the assessment of circular design strategies, and fostering collaboration between academia, industry, and tool developers. These advancements aim to improve the integration of environmental sustainability into early-stage product design.