Bringing Eggshell Waste into the Circular Economy

Reducing Plastics Production with Eggshell Waste

Plastic production has been increasing every year since the 1950s.

Keeping that in mind, we need to define the concept of circular economy.

According to Ellen MacArthur, from the MacArthur Foundation:

‘’A circular economy is based on the principles of designing out waste and pollution, keeping products and materials in use, and regenerating natural systems.’’

This diagram from Québec circulaire helps illustrate the concept.

Our work fits well with this approach as we aim to reduce resource consumption, in this case virgin plastic, replacing it in part with waste eggshell powder (i.e. calcium carbonate). At the same time, this contributes to divert waste from landfills by repurposing or giving a new life as the eggshells used are sourced from breaking plants. Breaking plants are industrial facilities where the shell eggs are converted to liquid or further-processed egg products. They typically dispose of their eggshell waste in landfills at a cost to the industry.

How is eggshell waste problematic?

First, several billions of eggs are produced yearly per country.

In most developed countries, 30% of produced eggs go to egg breaking plants.

• Most of the eggshell waste around the world ends up in landfills.
• For example, in the US and Europe, egg breaking plants pay approximately USD $100,000 per year to dispose of eggshells in landfills.
• This poses an environmental problem as their decomposition produces compounds like ammonia, hydrogen sulphide, and amine releasing high levels of contaminants and odours.
• Eggshells can also carry pathogens such as E.coli or salmonella.

A review [1] on the production and availability of eggshell waste and its potential as a filler in other fabrication processes—injection molding, hot pressing, compression molding, film casting—was done previously by Prof. Cree and one of his students. All the previous statements are also backed by this review.

Objectives of this Research

Our main goal is to develop a new sustainable and high-performing material for 3D printing that fits within a circular economy, as additive manufacturing is predicted to play an important role in the shift toward a more circular economy, due to its lean (i.e. less waste during manufacturing) and agile nature.

More specifically, in this work, we evaluated the flexural performance and the ductility of PLA/eggshell composite test specimens. In other words, we try using waste to not only reduce waste streams but also to improve PLA ductility.

Preparing and Testing Composite Specimens

First, we will show the material preparation process starting with the filler preparation.

Following is a simplified flowchart of the filler preparation.

• The eggshells are rinsed with hot water to remove any remaining egg white and organic membrane.
• Then, they are crushed into coarse particles of a few millimeters.
• Water is then added to form a slurry and the coarse particles are milled into smaller particles.
• Finally, the powdered particles are dried at about 105 °C for 24 h before being sifted through a 32-micron sieve.

The final product takes the form of a fine white powder as shown in image C.

Here is another flowchart representing the composite material and sample production process.

• The waste product is the powdered eggshell.
• It is mixed with PLA pellets to be processed by melt blending to obtain composite pellets.
• Composite pellets with different weight percentages of filler are produced.
• These composite pellets are then used to extrude 3D printing filaments.

Here is an image of the equipment that we used to extrude the composite 3D printing filament.

The unit is a Filabot setup composed of:

• an extruder to the right
• a cooling station in the middle
• a spooling station to the left

A digital measuring device is put in place to ensure the diameter of the filament produced is constant and within specs.

With this filament we can now print composite samples that will be used for the flexure testing.

Here is a brief summary of the printing parameters used to produce the composite samples, as well as a brief summary of the parameters regarding the 3-point bending flexure test.

• The samples were printed using a Ultimaker 3 3D printer
• The extruder temperature was set to 200 °C and the printing speed was set at 60 mm/s.
• The geometry of the samples is as specified by ASTM D 790-17
• Flexure testing was done using an Instron 1137 machine with a load cell of 10 kN
• The distance between the supports was 57 mm and the grip displacement rate was 1.5 mm/min

Comparing Composite Material Properties with Pure PLA

Here are the results of the flexural strength and flexural modulus or flexural stiffness.

In both graphs, the darker grey columns represent eggshell reinforced samples while lighter grey columns represent limestone reinforced samples.

Also, the red horizontal line represents the performance of pure PLA.

Why Compare Eggshell to Limestone?

Eggshell is ~95% calcium carbonate, limestone is also calcium carbonate, and it is one of the most popular plastic fillers throughout the plastic industry [1]. Therefore, it makes sense to use it as a comparative.

• In the first graph, where flexural strength is compared, the PLA/eggshell composite samples that performed the best were the ones with 5% filler, exceeding pure PLA samples by ~12%.
• In the second graph, where flexural modulus is compared, the PLA/eggshell composite samples that performed the best were the ones with 20% filler, exceeding pure PLA samples by ~38%.

As more filler is added, the flexural modulus increases but the flexural strength decreases significantly.

Below are SEM (Scanning Electron Microscopy) images of samples with different weight percentages of eggshell and limestone filler as well as pure PLA.

First, looking at pure PLA, there is very little texture and directional crack branching.

Pure PLA

With 5% eggshell, there is a very slight difference in texture, but nothing significant. There is in fact good bonding of the filler particles with the matrix.

5% eggshell

With 5% limestone, there is already a marginal increase of textures. Also, dimple-like features with a filler particle at their base can be observed.

5% limestone

Finally, in both 20% filler images, there is a significant change in texture with many dimple-like features.

Left : 20% eggshell ; Right : 20% limestone

The dimples suggest a more ductile failure mode than in pure PLA samples, which exhibited typical brittle failure characteristics given by its flat, smooth features.

Conclusions

• Eggshell powder incorporated into 3D printed PLA can improve flexural properties, such as flexural strength and flexural modulus.
• In comparison to pure PLA, there was an increase of ~12% in flexural strength and ~19% in flexural modulus in testing the samples with 5% eggshell filler content.
• From experimental results, 5% eggshell filler content was found to be the optimal weight percentage of eggshell powder.
• As seen previously, when more filler is added, flexural modulus increases but flexural strength decreases significantly.
• Finally, the SEM observations have shown that eggshell powder in 3D printed PLA has a direct impact on the fractured face texture, suggesting a more ductile failure mode than in pure PLA samples.

Additional Information

For more details on the results presented in this short version, please refer to the original article:

10. -P. Leclair, N. Borges, D. Cree, and L. A. Hof, “Towards Circular Manufacturing: Repurposing Eggshell Waste As Filler For Poly Lactic Acid Feedstock For 3D Printing,” Progress in Canadian Mechanical Engineering. Volume 4, Jun. 2021, https://doi.org/10.32393/csme.2021.120

Further investigation on the mechanical properties of this new composite material is ongoing and the results will be published soon.