Additive manufacturing of hygromorphic structures using regenerated cellulose/PLA biocomposites

Abstract

Three-dimensional printing technologies are at the forefront of the current industrial revolution, enabling the production of complex shapes using a wide range of materials without relying on large production facilities. Increasing it further, 4D printing is a new concept in which printed objects respond to environmental stimuli and change shape or other characteristics with time in a controlled and predicted manner. However, the development of bio-based material alternatives that can be integrated into a circular economy is limited if compared with other non-renewable polymers traditionally used for these applications. Bioderived and/or biodegradable thermoplastics reinforced with bioderived fibres have compelling attributes in this context; they can be recycled, can be used in smart materials (4D printing), and, if necessary, can biodegrade at the end of their life cycle, leaving no harmful waste in the environment. In this work, we demonstrate the potential of PLA-based biocomposites with high content of regenerated cellulose fibres (lyocell) for 3D printed structures produced by fused deposition modelling (FDM) that change shape in response to moisture (hygromorphic). The main mechanism involved in this behaviour is related to the anisotropic swelling of the cellulose fibres that are preferentially aligned in the composite during printing. Using a bi-layered architecture of passive and active layers, we developed different prototypes with 2D to 3D transformation capability triggered by moisture with a high degree of shape change.