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3D printing of strong lightweight cellular structures using polysaccharide-based composite foams Hugo Pierre Voisin, Korneliya Gordeyeva, Gilberto Siqueira, Michael K. Hausmann, André R. Studart, and Lennart Bergström ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04549 • Publication Date (Web): 01 Nov 2018 Downloaded from http://pubs.acs.org on November 2, 2018
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ACS Sustainable Chemistry & Engineering
3D printing of strong lightweight cellular structures using polysaccharide-based composite foams Hugo P. Voisin1, Korneliya Gordeyeva1, Gilberto Siqueira2, Michael K. Hausmann2,3, André R. Studart3, Lennart Bergström*1 1
Department of Materials and Environmental Chemistry Stockholm University
Svante Arrhenius väg 16C, 10691 Stockholm, Sweden 2
Empa –Swiss Federal Laboratories for Materials Science and Technology
Überlandstrasse 129, CH-8600 Dübendorf, Switzerland 3
Complex Materials, Department of Materials ETH Zürich, 8093 Zürich, Switzerland
Corresponding Author Lennart Bergström email:
[email protected] KEYWORDS: hybrid cellular material, low-weight, air-drying, 3D printing, nanocellulose
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ABSTRACT:
Polysaccharides are attractive sustainable resources for the fabrication of advanced materials, but the assembly of these building blocks into complex-shaped structures combining the high strength and low weight required in many applications remains challenging. We have investigated and optimized the rheological and mechanical properties of polysaccharide-based composite foams based on mixtures of methylcellulose (MC), cellulose nanofibrils (CNF), montmorillonite (MMT), glyoxal and tannic acid. Such foams were found to be stabilized by the co-adsorption of MC, CNF and MMT at the air-water interface, while the complexation of the polysaccharides with tannic acid improved the foam stability. Tannic acid could also be used to tune and optimize the microstructure and the viscoelastic properties of the wet foam for direct ink writing of robust cellular architectures. Glyoxal had no noticeable effect on the properties of the wet foams but significantly enhanced the water resilience and stiffness of the lightweight material obtained after drying at ambient pressure and elevated temperatures with minimum shrinkage. The foams possessed a high porosity and displayed a specific Young’s modulus and yield strength that outperformed other bio-based foams and commercially available expanded polystyrene. The strong and water-resilient 3D printed foams can be surface modified using for example aminosilanes, which opens up applications for air purification and thermal insulation.
Introduction: There is a strong demand to develop versatile processing routes to produce lightweight materials based on renewable sources for a wide range of applications, including e.g. packaging,1 thermal insulation,2 and energy storage.3 Many applications also require that the materials possess a high surface area and low weight, which has generated a significant research effort in utilizing renewable nanomaterials, e.g. nanocellulose, to produce lightweight foams and aerogels.4,5,6 While there has been a significant progress in the field, the produced nanocellulose-based foams and aerogels are often relatively small, and the solvent (usually water) is often ACS Paragon Plus Environment
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ACS Sustainable Chemistry & Engineering
removed by freeze drying or supercritical drying to avoid shrinkage or collapse of the structure,4,6 which limits the scalability. Previous studies have shown that particle-stabilized foams7 and emulsions can withstand the stresses involved during drying without significant shrinkage and collapse.8–10 Cellulose nanocrystals (CNC) have been shown to enable long-term stabilization of oil-in-water emulsions11–13 without further modification, but CNC or cellulose nanofibrils (CNF) alone are not able to stabilize aqueous-based foams. However, addition of surface active molecules such as octylamine,14 nonionic polyoxamer,15 or methylcellulose (MC)16 to aqueous dispersions of CNC or CNF can generate stable foams. 3D printing has recently attracted much attention due to the opportunities it provides in the design and manufacturing of objects with tailored morphologies and structures. Direct ink writing (DIW) is an additive manufacturing technique in which a gel-like material defined as ―ink‖ is extruded through a nozzle to build complex structures and scaffolds.17 The ink is usually a concentrated dispersion, the rheological properties of which must be tailored for specific printing conditions.18,19 Whereas 3D printing has primarily been used to generate materials with dense filaments, DIW of emulsions20,21 or foams has recently also been described. Particle-stabilized foams produced from dispersions of partially hydrophobized ceramic particles (alumina with butyric22 or propionic23 acid) were 3D printed in cellular architectures with high compressive strength. However, the high specific gravity of the ceramic particles used and the high solid content needed for the ink to withstand drying24 resulted in 3D printed porous materials with relatively high densities (above 100 kg.m-3). 3D printing of foams into lightweight structures of lower densities should be possible if polysaccharide-based inks are developed. This requires the investigation of printable foam formulations with optimized rheological and mechanical properties. Here, we develop and investigate stable polysaccharide-based composite foams suitable for 3D printing of lightweight cellular structures using dispersions of MC, CNF, montmorillonite (MMT), glyoxal and tannic acid (TA). The rheological properties of the wet foams, the resistance to shrinkage during evaporative drying, and the mechanical properties of the dry foams were tuned by controlling the composition and the drying conditions. Highly porous, low-weight and strong foams could be produced by rapid air-drying at elevated ACS Paragon Plus Environment
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temperature with minimum shrinkage (
