Design of edible materials for 3D printing applications
Publication Date
July 31, 2019
Creator
Abstract
Binder jetting and high viscosity ink jetting are both AM techniques in which deposition of an ‘ink’ is crucial to 3D structuring. Key formulation challenges in binder jetting include the requirements of low viscosity, controlled surface tension and density at printing shear for the ink component. These constraints are less applicable in high viscosity jetting processes where more viscous feedstocks may be used, as long as particulate matter does not clog the nozzle and flow is controllable at all printing temperatures. Binder jetting also requires the formulation of a powder component which the ink interacts with to create a 3D object. Edible macrostructures formed through binder jetting have predominantly used sugar-based powders, due to the ease of binding and structure creation they provide. Edible materials have not previously been applied to high viscosity jetting to create 3D structures.
The research presented in this thesis aimed to design edible feedstocks whose interaction in the desired AM process controlled the microstructure of the printed material. Plant-derived polysaccharides (cellulose, hemicelluloses, xanthan gum and agar) were selected as suitable raw materials due to their natural abundance, synergistic interaction with one another and potential health benefit as dietary fibres.
Cellulose and hemicellulose in admixture were ball milled to create a powder with reduced crystallinity. Selective binding of the powder was achieved to create micron-scale structure via an induced recrystallization approach. This was facilitated by jetting an ink formulation (with xanthan gum) onto certain portions of the powder then applying heat to recrystallize these areas, leaving the surrounding powder unbound. Mechanical modification of xanthan gum was found to be beneficial to its performance in the ink formulation and a 9:1 ratio of cellulose to konjac glucomannan was the most successful powder for structure creation. Structures produced in this way could be used as ‘skeletons’ for replacement of self-assembled structures in food products such as gluten networks in breadsticks or biscuits.
Fluid gels were created by shearing an agar solution through its sol-gel transition, creating a suspension of gelled particles. This material was stable and flowable at ambient temperature, conferring an advantage for high viscosity ink jetting of thermoreversible gels. Fluid gels prepared from two agars were characterised by their different particle morphologies (long, protruding tails or smooth), effective particle phase volume and response to temperature (rheology and microDSC). A high viscosity ink jet printer with a heated nozzle was able to print stacked layers of these fluid gels at different temperatures. Hardness of the printed layers was dependent on the nozzle temperature, due to the varied portion of agar gel particles melted during printing which were then able to re-form a partial quiescent gel network upon post-print cooling. Future developments on this ambient gel feedstock could involve the use of multiple polysaccharides, for further structure control, or enable encapsulation of live cells or bioactives for food and biomedical applications.
Item Type
ethesis
Thesis Type
PhD
Supervisors
Associated Schools / Departments
School of Biosciences (UK)
eprints ID
55579
UoN Repository URI
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Name
HOLLAND, S.F. 2018. Design of Edible Materials for 3D Printing Applications. PhD Thesis. UoN..pdf
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25.74 MB
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