Digital Light Processing of Highly Filled Polymer Composites with Interface-Mediated Mechanical Properties

Abstract

Digital light processing (DLP) is a popular method of additive manufacturing of thermosetting polymer composites with high resolution. While DLP of composite systems has been demonstrated, only a few studies comment on the role of interfacial interactions on resulting mechanical properties. In this work, high volume fraction (50 vol %) glass microsphere-reinforced composites were fabricated via DLP. The effects of surface chemistry and interfacial interactions on the mechanical and thermal properties of additively manufactured composites were investigated. Interfacial interactions between the urethane acrylate-based resin system and glass microspheres were found to dictate the overall performance of the composites. Greater resin−glass wettability led to simultaneous and anomalous increases in stiffness, toughness, and strength. Interestingly, composites where glass was functionalized to covalently bond with the resin phase only showed moderate improvements in mechanical properties as compared to systems with high resin−glass wettability. Finally, complex structures with fine details were printed to demonstrate printability.

Additively manufactured thermosetting elastomer composites: small changes in resin formulation lead to large changes in mechanical and viscoelastic properties

“…22 In other previous work, we demonstrated that changes to glass microsphere surface chemistry led to interface-mediated mechanical properties. 23 In this work, we extend the principles from both of those reports and show that increasing resin wettability to the glass reinforcement surfaces through resin modification leads to stronger and stiffer composite materials. It is not always practical or feasible to functionalize a reinforcement's surface, so this work demonstrates that improvements in composite stiffness and strength can be made through improving resin wettability.…”

“…In other previous work, we found that when only non-covalent bonding is available for the composite, decreasing resin contact angles on silane-functionalized surfaces led to stiffer and stronger composites. 23,35 In comparing all of these studies, we observe that surface functionalization leads to more pronounced changes in wettability and mechanical (adhesive and tensile) properties. One likely reason for this difference is that silane coupling agents are able to achieve complete coating of a surface, while migration of resin additives to the glass surface is less effective.…”

“…For example, use of an amine silane coupling agent on glass fibers with a similar silanization process to what was used in Wang et al resulted in an amine surface concentration of 0.32 amines nm À2 . 23,35,36 To achieve the same surface concentration of HEMA, only 0.11 wt% of the resin would need to be HEMA if all of the HEMA migrated to the glass surface. A homogeneous distribution of HEMA throughout the polymer network would provide approximately 0.066 HEMA nm À2 .…”

“…Printability of complex parts with fine details was demonstrated using one of the highly filled formulations. We also compare two approaches for tailoring interfacial interactions (modifying the resin formulation and modifying the reinforcement's surface chemistry 23 ) and discuss the relative advantages of each for achieving high performance additively manufactured composites.…”

4D Printing of Single-Network Shape Memory Polyurethanes with Two-Way Actuation Properties

“…3D printing, also known as additive manufacturing (AM), has received widespread attention from academia and industry for its potential advantages, such as fabricating customized geometry without the need for molds or machining, reducing production costs and extending applicability to a wide range of materials. − Common 3D-printing techniques include fused deposition modeling (FDM), , selective laser sintering or melting (SLS/SLM), stereolithography (SLA)/digital light projection (DLP), , and so forth. In 2013, Tibbits et al from MIT first combined AM with smart materials that can change their shape in response to an applied stimulus such as temperature, electricity, light, radiation, and chemical stimuli (such as a pH change). , The use of smart materials in 3D printing adds the fourth dimension of time to create 3D-printed structures with programmable and adaptable shapes, properties, or functionalities and defined this new technology termed “4D printing”.…”