Design and characterisation of edible biopolymer mixtures for use in additive manufacturing

Warner, Eleanor Lucy (2019). Design and characterisation of edible biopolymer mixtures for use in additive manufacturing. University of Birmingham. Ph.D.

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Abstract

Recent interest in personalisation of food through additive manufacturing has identified a need for more information on the formulation and printability of potential ingredients. Fused deposition modelling is a type of additive manufacturing technique which uses a thermal extrusion process in order to create objects in a layer by layer method. Key challenges posed for the creation of formulations using this additive manufacturing technique include the need for the material to be thermoreversible, shear thinning during extrusion, but then have the ability to retain its shape after extrusion. The majority of research of edible manufacturing using this technique have thus far only been investigated at single temperatures and predominately on materials that only maintain their shape due to a yield stress, reducing the amount of available materials. Therefore, the aim of this work was to develop novel edible material feedstocks for the creation of objects through the use of an additive manufacturing process.
Initially, the printability of a mixture of two food hydrocolloids, gelatin and kappa-carrageenan, were investigated. Design rules were established in order to determine if the materials fit the requirements of the process. The gelling temperatures of the systems were established, then, the rheological characteristics including: flow profiles, evolution of elastically dominated structures and frequency dependent behaviour were examined. The mixtures were subsequently printed at two temperatures, just above and much greater than, the gelling temperatures. It was observed that the rheological behaviours accompanying the coil-helix transitions of the systems were key to printing in a well-defined way. Printing resolution could be described by the changes in elastic modulus, where rapid formation of an elastic network gave rise to highly defined shapes with the ability to self-support under multiple layers.
The printability of the mixtures of gelatin and kappa-carrageenan were then further probed by changing the properties of the printer, including the nozzle diameter, printing temperature and printing speed. Alteration of these properties affected the viscosity of the material during extrusion, which affected the behaviour of the material and altered the printability. The viscosity of the formulations at various speeds and temperatures was established, and these were related to the printability. Further design rules were established in order to deepen the understanding of the properties necessary for a material to possess in order to be printable. It was also shown that with the materials that met the design rule criteria, a range of mechanical properties could be produced using these two biopolymers, just by altering the properties of the printer.
Finally, it was demonstrated that the design rules established held for formulations of gelatin and other secondary biopolymers (gellan and agar). Relevant testing, including establishing the gelling temperature, and investigation of the rheological characteristics including the frequency sweeps was undertaken in order to determine the material properties of the new formulations. The formulations that met the design rules produced defined printed objects, whereas the formulations which did not meet the design rules did not. Complex structures, including a ring and a star were able to be printed using several of the formulations.
Overall, this thesis demonstrates the range of formulations which can be printed, as well as exhibiting some of the exciting structures that can be produced using an additive manufacturing technique.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):