Mechanical Properties of Ultraviolet-Assisted Paste Extrusion and Postextrusion Ultraviolet-Curing of Three-Dimensional Printed Biocomposites

Abstract

Three-dimensional (3D) printing of biomaterials has the potential to become an ecologically advantageous alternative compared with conventional manufacturing based on oil-derived polymer materials. In this study, a novel 3D printing technology is applied that combines ultraviolet (UV) curing with paste extrusion. This hybrid manufacturing technique enables the fabrication of complex geometries from high filler-ratio pastes. The developed biocomposite aims for suitable mechanical properties in terms of tensile and compressive strength. It is composed of acrylic acid, cellulose acetate, a-cellulose, and fumed silica with a cellulose ratio of more than 25 vol-%. The material is extruded with an in-house-developed 3D printer equipped with a 12 W UV light curing source, which enables concurrent curing and extrusion. Two different UV-curing strategies were tested: postcuring without concurrent curing and postcuring with concurrent curing. The total UV-curing duration was kept constant with all samples. Tensile testing in accordance with ASTM standard D638-14 Type 4, compression testing according to ASTM D695-15, and overhang tests were conducted. As a result, samples without notable shrinkage, suitable tensile strength (up to 17.72 MPa), competitive compression testing parameters (up to 19.73 MPa), and an enhanced overhang angle (increase of more than 25°) were produced, leading to new applications and more freedom in design due to higher possible unsupported overhangs when using UV-curing during the print. Overall, constant UV light radiation during the print leads to improved mechanical properties due to the possibility of bypassing the UV-penetration depth constraint. It should be considered when extruding photopolymer-based composites, especially for large and complex components with a low degree of translucency.

Folding photopolymerized origami sheets by post-curing

“…Then it undergoes the post-curing step for ten minutes to finish and enhance the mechanical properties of parts fabricated by SLA/DLP printing. The post-curing step is often necessary and is especially important for functional resin [ 17 , 37 ].…”

“…Several studies have been performed to understand the mechanical effects of post curing [ 17 , 31 ], from characterizing curing strategies [ 25 ], investigating the use of epoxy additives [ 18 ], to the influence of photo-initiators [ 33 ]. Wu et al [ 37 ] studied the influence of post-curing on shape integrity and dimension accuracy and characterized the evolution of samples’ mechanical behavior during post-curing.…”

Ystruder: Open source multifunction extruder with sensing and monitoring capabilities

“…For example, Pusch et al [23] used the frame of an open source PrintrBot combined with a OSHW design to produce a large volume extruder suitable for printing of hydrogel structures. Similar configurations have been used for multi-material printing [24,25], bioproduct printing [26][27][28] and bioprinting [29][30][31][32]. OSHW based research equipment facilitates efficient and agile application-centric research of these manufacturing processes.…”

“…The modular structure also promotes extensibility. Advanced functionality such as in situ UV curing [28], heating [36] or mixing can be easily added to the Ystruder. The control electronics of the Ystruder have been designed in a way that they can be interfaced with a wide range of equipment types such as robotic arms, delta robots and box frames.…”

Quantifying the Shape Memory Performance of a Three-Dimensional-Printed Biobased Polyester/Cellulose Composite Material

“…35,36 The 3D printing with thermoset materials typically involves photocuring the formulation during and/or after the printing process. [36][37][38][39] The requirements for photocuring place restrictions on formulation design and create difficulties in achieving 100% biobased content in a 3D printable formulation. The shape memory behavior of the CNC composite adapted for 3D printing techniques with a completely biobased thermoset matrix has not yet been explored.…”