Plastic How Grass Makes Plastic More Sustainable

Related Vendors

Hochschule Darmstadt

FAULHABER Drive Systems

dataTec AG

SIMTOS (Seoul International Machine Tool Show)

How can plastics be produced more sustainably? One possible solution lies in the meadow: In the “Gras-to-Plast” project, Prof. Dr. Martin Moneke from Darmstadt (Germany) University of Applied Sciences (h_da) and his team have further developed grass-fiber-reinforced plastics. 

Contrary to popular belief, plastic is an expensive raw material. “When you buy plastic in large quantities,” explains Prof. Dr. Martin Moneke from the Polymer Engineering program at h_da, “it can be more expensive than aluminum or steel, depending on the production method.” And that’s how the idea with grass came about: Grass-fiber-based plastics have been on the market for about ten years. The higher the fiber content, the fewer petroleum-based raw materials are needed for production, and the more affordable and sustainable the product is.
The “Grass-to-Plast” project, on which plastics expert Moneke and his team worked for a year and a half, focused on further improving such bioplastics. Everyone is familiar with the raw material from clothing stores or drugstores: a plastic that the Hessian company Cortec uses to produce clothes hangers. According to the company, it ships more than 60 million of them worldwide every year. Moneke’s team set out to solve various problems related to the plastic used in clothes hangers: The material needed to be more durable so that it could be used to manufacture more sophisticated items. At the same time, the goal was to improve sustainability: achieving the highest possible grass fiber content, saving energy during production, and ensuring the grass came from responsible sources.

Gallery

Gallery with 5 images

Grasses from Fallow Meadows Were Used

The grass used up to now came from monocultures—in other words, it was grown specifically for plastic production. The h_da team wanted to change that, so they experimented with grasses from fallow meadows. There are more and more of these because the dairy industry in Germany is shrinking. However, the species-rich flowering meadows should still be preserved, including as a source of income for farmers. But when nature meets science, things can sometimes get a bit chaotic: A natural meadow is home to around 20 different grasses, herbs, and flowers. Depending on the season and weather, their composition and properties change. Despite this “chaos factor,” Moneke’s team has succeeded in developing a robust formula for a material that exhibits stable, reproducible properties.
The new formula consists of 30 percent grass fibers and 60 percent polypropylene; the remaining 10 percent are additives that improve the material’s properties and make it easier to process. This material can now be used to manufacture additional products made of bioplastic, such as small stackable boxes and large transport crates. These products have to withstand a lot when they’re stacked on top of each other or moved with a forklift. “That means you can hit them hard—and still, nothing should break,” says Prof. Dr. Martin Moneke, summarizing the principle.

Impact Resistance Increased by About 20 Percent

Things sometimes got pretty rough in the lab: The objects, manufactured using injection molding, were subjected to a number of stress tests. “We dropped the stacking boxes from a height of five meters and conducted puncture tests.” In the end, the material passed all the tests, and its “impact strength” was increased by about 20 percent. The new plastic blend is therefore particularly durable and less prone to cracking. Processing is also easier and more efficient: “In the previous version, many fibers were exposed on the surface and could therefore absorb water,” explains Moneke. “This led to buildup, increased maintenance and cleaning efforts—and a lot of scrap.”
The new formulation integrates the grass better into the plastic, can be processed at lower temperatures and pressures, and flows more stably through the injection molding process. Clothes hangers, stacking boxes, and other items can now go into production using the new material blend once the project is complete. “We’ve reached a Technology Readiness Level of 8 or 9 in the project,” the researcher says happily. On the nine-point scale, this means the product is ready for use.