Abstract
The use of wood particles in wood-plastic composites (WPC) is well known and similar use could occur in materials for fused deposition modeling (FDM) 3D printing. Wood particles could be one of the possible solutions in the search for natural-based materials to minimize the use of synthetic-origin materials in additive manufacturing. Wood particles for 3D printing filaments can be made from wood waste and could serve as a cheap filler or as a value-added reinforcing component, depending on their properties and incorporation. The disadvantages of wood (dimensional changes due to water adsorption and desorption) could be used as functions when dimensional change is desirable, such as in shape-changing 4D printing materials. In this research, FDM printing materials made of polylactic acid (PLA), with different amounts of wood particles, were used to design moisture-induced shape-changing bilayer actuators, which could serve as a principle for active façade or ventilation valves. The initial research shows that the wood content in the WPC causes dimensional changes and thus shape changes of the designed actuators under changing climates. The shape change depends on the ratio of the materials in the two-layered actuator and the wood content in the wood-PLA composite used, and thus on sorption. The rate of the shape change behaves in the same way: the higher the wood content, the greater the change observed. The dynamics of the hygromorphism of bimaterial composites is greater with a small amount of added hygromechanically active material.
Highlights
The use of natural fibers and particles in wood-plastic composites has been increasing in recent decades, including in materials for 3D printing [1]
Natural fibers are anisotropic and moisture sensitive, which is one of their main disadvantages when used for structural applications [3], but could be used as a positive attribute when shape change is desired, as in 4D printing or when used as shapememory materials/stimuli-responsive materials. 4D printing has evolved from 3D printing and aims to achieve a predictable and predefined time-dependent change in functionality that the 3D-printed structure undergoes when it encounters an external stimulus [5]
Bimaterial actuators made from polylactic acid (PLA) and wood-PLA composites show the potential to be used as hygro-induced shape-changing products
Summary
The use of natural fibers and particles in wood-plastic composites has been increasing in recent decades, including in materials for 3D printing [1]. Natural fibers are anisotropic and moisture sensitive, which is one of their main disadvantages when used for structural applications [3], but could be used as a positive attribute when shape change is desired, as in 4D printing or when used as shapememory materials/stimuli-responsive materials. 4D printing has evolved from 3D printing and aims to achieve a predictable and predefined time-dependent change in functionality (shape, property, self-assembly, or self-repair) that the 3D-printed structure undergoes when it encounters an external stimulus (e.g., temperature, ultraviolet light, humidity, electric and magnetic fields) [5]. Actuation in response to a stimulus by pre-programmed hierarchical structures can provide a bio-inspired model useful for the functional gradation of natural fibers to develop hygroscopically induced morphing (i.e., hygromorphing). In 3D-printed structures, these properties can be influenced by proper design of the model, selection of the material, and printing properties (e.g., wall thickness, infill density, infill pattern, printing line orientation, etc.)
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