Cellulose & Lignin in Additive Manufacturing: Potential and challenges in the fabrication of structural nodes for free-form building envelope structures

The building stock and the construction industry combined are responsible for a large share of greenhouse gases emissions. At the same time, every year tons of wood, paper and agricultural residues are wasted instead of recycled and upcycled into the production chain. In the fabrication field, the relevance of additive manufacturing processes is constantly growing, allowing for maximum customisation and optimisation of material and energy usage.Lignocellulosic polymers are the most abundant in nature, although meanwhile cellulose is seen as a valuable raw material, lignin is treated as a by-product to be burned and generate energy. Based on the increasing use of both as fibre reinforcements and fillers in feedstocks for additive manufacturing, there is a potential to be explored.The combination of the development of a novel material for an innovative fabrication process such as liquid deposition modelling, is the scope of work presented in this research.Cellulose and lignin were studied, analysed and manipulated before mixing them with a vast selection of binding agents and additives. The outcome was evaluated according to a pre-established criteria set and documented, and a comparison drawn to define the best and most promising material mixes for additional investigation. From a universe of twelve mixes and numerous iterations for each recipe, four alternatives were picked for further characterisation and determination of their mechanical properties.In parallel, the printability of the material considered as the most promising mix was explored through the extrusion of a sequence of simple geometries and shapes designed to understand and define the most adequate printing parameters. Limitations and challenges were observed and general directions and guidelines were documented.With a complete dataset and overview of this novel bio-based and wood-based material for additive manufacturing, a simple structural node was designed. The fabrication of a prototype was used to further enhance the material properties and to clarify its potential and limitations for applications in the construction industry.From the initial material exploration to the final prototyping phase, an extensive documentation was prepared to validate the potential and limitations of this novel material and indicate the directions for further research works.Architecture, Urbanism and Building Sciences | Building Technolog