Hot-Extrusion Printing of Starch Compositions With Two-Stage Heating
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Solution Overview
Problem
Conventional additive manufacturing by hot-extrusion faces limitations in mass flow rate and printing speed due to the need for long residence time in the nozzle for gelatinization of non-gelatinized starch granules, leading to issues with viscosity and mechanical resistance of printed objects.
Innovation Solution
A method involving a printable composition with non-gelatinized starch granules dispersed in an aqueous matrix, subjected to a two-stage heating process: a storage temperature below gelatinization and a printing temperature above gelatinization, allowing for faster gelatinization and improved mechanical resistance of printed objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If non-gelatinized starch granules are used in printable composition, then the composition can maintain low viscosity for easy extrusion, but long residence time in nozzle is required for gelatinization which reduces printing speed
Solution Approach 1:
The starch granules are pre-treated through partial gelatinization or modification before being incorporated into the printable composition. This preliminary action reduces the gelatinization temperature and accelerates the gelatinization kinetics during printing, allowing faster extrusion and deposition without requiring long residence times in the nozzle, thus resolving the contradiction between ease of extrusion and printing speed
Solution Approach 2:
The gelatinization temperature and kinetics of the starch granules are modified through pre-treatment methods such as heat-moisture treatment, enzymatic modification, or chemical treatment. These parameter changes enable the starch to gelatinize rapidly at lower temperatures during the printing process, improving both extrusion ability and printing speed by reducing the time required for adequate gelatinization
2Strength
If longer residence time in nozzle is used for complete gelatinization, then mechanical resistance of printed object is improved, but printing speed decreases
Solution Approach 1:
The starch granules are modified to achieve rapid gelatinization at lower temperatures with shorter times. This parameter change in gelatinization kinetics allows adequate mechanical resistance to be achieved during fast printing processes, resolving the contradiction between strength and printing speed by enabling complete gelatinization in reduced residence time
Solution Approach 2:
The printable composition uses a composite system combining pre-treated starch granules with appropriate binders and plasticizers that facilitate rapid gelatinization and strong network formation. This composite approach ensures adequate mechanical resistance is achieved quickly during printing, balancing strength requirements with high printing speed
3Stability of the object's composition
If high viscosity composition is used to ensure self-supporting structure, then vertical assembly is enabled, but circulation through narrow printing die becomes difficult
Solution Approach 1:
The printable composition exhibits dynamic rheological properties where viscosity is shear-thinning: high viscosity at rest to maintain self-supporting structure, and low viscosity under shear stress during extrusion to enable easy circulation through narrow printing dies. This dynamic behavior resolves the contradiction between self-supporting ability and circulation ability
Solution Approach 2:
The viscosity of the printable composition is optimized through selection of starch type, granule size distribution, and addition of rheology modifiers that create shear-thinning behavior. This parameter optimization allows the composition to be pumpable and extrudable through narrow dies while maintaining adequate viscosity for self-supporting structure after deposition
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances printing speed and mechanical resistance of printed objects by reducing nozzle residence time and improving the ability to extrude the composition, resulting in higher quality and smoother surfaces.
Implementation Method 1
non-gelatinized starch granules which undergo heating and gelatinization only at the printing step
Implementation Method 2
After deposit as a layer, the printable composition undergoes solidification thanks to natural cooling
Data Source
AI summary
Disclosed is a method of additive manufacturing by hot-extrusion, which method of additive manufacturing includes the following successive steps: a providing step, wherein a printable composition is provided, the printable composition including an aqueous printing matrix, in which non-gelatinized starch granules are dispersed, wherein the non-gelatinized starch granules are in a non-gelled state and have a gelatinization temperature below 70° C.; and a printing step, wherein the printable composition is subjected to a heat treatment and is deposited layer by layer. During the printing step, the printable composition is subjected to a succession of two different heating temperatures: a storage heating temperature, lower than the gelatinization temperature, in order to heat the printable composition without gelatinizing the non-gelatinized starch granules, and a printing heating temperature, higher than the gelatinization temperature, in order to gelatinize the non-gelatinized starch granules in the layers.