Insight 1 |
Increased surface area leads to strong, but irreversible polymer-textile bonds.
Insight 2 |
Interface design is an influential parameter for separation, as it defines the arrangement of the surface area.
tellurian
“How can technology contribute to circular textiles?”
Master’s graduation project
Supervisors: Dr. ir. Doubrovski, E.L. & Prof. dr. Balkenende, A.R.
Duration: 120 days
Circularity – 3D printing – Textiles – Research
A step towards circularity for 3D printing combined with textiles
3D printing is currently blooming in a lot of different industries, including fashion in the form of 3D printing onto textiles. In parallel, fashion circularity is an increasing movement that has emerged due to the negative impact that fashion creates on the life on this planet and the planet itself. Therefore, a shift to responsible consumption and production methods (sustainable development goal 12) is necessary.
To join this circularity movement, 3D printing onto textiles for fashion is required to fulfil certain requirements, including recycling. However, recycling is hindered by the lack of methods to separate the 3D printed structures from the textile at the End of Life (EoL). This graduation project researches the possibilities to achieve material separation at the EoL, so that the materials can be independently recycled and turned into new products.
The envisioned material journey
To enable material circularity, a framework for the materials’ lifecycle needed to be established. The materials circulate in the system through loop 1 as much as possible by separation and recycling. When this is not possible anymore, the materials enter loop 2 and return to their original form as described by the butterfly diagram developed by Ellen McArthur foundation for renewable materials.
Theoretical background for separation
Through desk research, the parameters that influence polymer-textile adhesion are identified. On this overview they are located based on their origin to the categories: printing process, polymer and textile. The intersections include dependent parameters that are related to more than one category. Connections amongst the parameters are indicated with arrows. For example, textile surface free energy together with polymer surface free energy influence wetting, that in turn affects the contact area.
How does textile roughness and temperature influence the polymer – textile separation? An experimental testing.
While there is plenty of information available about adhesion in the context of 3DP onto textiles, material separation is hardly researched. As a starting point an evaluation test with two variables is executed. One of the variables is textile roughness, aka yarn density or pore size of a woven textile and the other variable is the temperature of the area during separation. Therefore, the experiment uses dollies 3D printed onto two kinds of textiles – cotton, plain weave, undyed – with different pore size to create 5 samples for each. These are later separated by a tensile tester at room temperature (23oC) and at 40oC.
Textile A: small sized pores
Textile B: large sized pores
The “sandwitch” method for 3D printing onto textiles.
Dolly 3D printed onto textile
The other side of the textile
A snapshot of the printing
Tensile test setup with thermocouple
Insights from experimentation
Insight 1 |
Increased textile roughness leads to irreversible polymer-textile bonds.
After the test at 21oC – textile A reaches one-sided adhesive failure (1) and textile B reaches cohesive failure on the textile substrate (2). After the test at 40 oC– textile A reaches two-sided adhesive failure (3) and textile B reaches again failure on the textile substrate (4).
Insight 2 |
Increased local temperatures during separation enables polymer-textile bond reversibility.
Microscopic images after the test at 40 oC– textile A (5) and textile B (6), upper layers with free standing fibres (7) and bottom layers (8).
Design Possibilities
3D printing a polymer can be used to create functional, decorative or protective elements on a textile. The aspect that matters the most for the applications discussed in the context of this project is circularity. The following graphic depicts an exploration of the solution space where circular textiles and 3DP onto textiles intersect. This space is here named: “design spectrum”. The design spectrum constitutes from applications that either already use 3DP onto textiles, or applications that could benefit from applying this method.
The selected product application
The criteria are based on different aspects of circularity and EoL. With descending order of importance, the criteria are: Disassembly, longevity, functionality innovation, user attachment. Apart from the criteria, there are some boundary conditions that the application should comply to, namely: size and complexity.
The product categories are evaluated using the application of the Harris Profile method, which indicates that footwear is the most promising product application. The focus of the research is narrowed down to aspects that concern the circularity and relate to adhesion and delamination and therefore limited to the mid-sole and its connection to the fabric.
Harris profile evaluation method for the 6 categories.
Typical shoe composition – Nike
Sketches of the concept
How does the design of the surface area influence the polymer – textile separation? An experimental testing on the product application.
Τhe materials used in this experimentation are PLA and textile A. as the textile. The 3D structure printed onto the textile is a woman’s EU38 size footwear mid-sole. The prototypes consist of four types of layers: top, textile, middle and bottom. The interface is defined by the middle layers, because they come in contact with the textile. Thus, the design of these layers is key to enabling separation at the EoL. 4 different designs are tested:
Design 1
a 100% infill model – baseline
Design 2
a mesh – withstands deformation in both directions.
Design 3
perpendicular to the separation direction
Design 4
3 with a backbone – more support.
Surface Area Size:
DESIGN 1 > DESIGN 4 > DESIGN 3 > DESIGN 2
(14.291,47 mm^2) > (3.522 mm^2) > (3.292 mm^2) > (3.160 mm^2)
This experimentation on the surface area is elaborated into two scenarios, since there must be a balance between separation at the EoL and performance during usage. Hence, it is divided into two tests, one that focuses on the effects of scaling up the surface area on separation – test EoL – and one that focuses on the effects of bending during usage on deformation.
Test scenario for End of Life
Test scenario for deformation during usage
Insights from experimentation
Insight 3 |
The condition to achieve reversible polymer-textile bonds is to use 3D structures and textiles that are more resistant to separation forces than their bond.
Insight 4 |
Shear forces are present in polymer-textile separation for footwear.
The separation test setup of the scenario at the EoL led to separation for all the designs. For design 1 (1), the separation was one-sided. Designs 2 (2), 3 (3) and 4 (4) resulted into two-sided material separation. During the tests, the 3D printed structure of designs 1 and 3 failed.
The separation setup of the scenario at deformation during usage led to failure and breakage throughout the 3D structure, especially for design 3 where it happened multiple times.
Future Research
1 | To come a step closer to the envisioned material journey, recycled materials need to be tested in the same separation conditions to investigate their response and if it coincides with
the virgin materials.
2 | For the sake of improving the application of polymer – textile interfaces on footwear, the tested designs of the mid-sole middle layers should be replaced by lattice structures and
flexible polymers instead of stiff PLA.
3 | Form fitting of the product needs to be designed. Specifically for footwear, the upper shoe textile can be shaped to fit the user by 3DP a few layers onto the textile according to the desired shape-change (image).
4 | The fabrication of responsive textiles such as wool or heat responsive fibres can create a foldable shoe that would activate itself by coming in contact with the 3D printed polymer structure.
Poster
To access the full report through the TU Delft repository click here:
