Materials innovations sparked from agricultural waste
Seth Price | January 18, 2025Much of what is grown or raised in agriculture is wasted. Think about all of the corn stalks, sunflower stalks, waste from annuals, Christmas trees, coconut shells, bean pods, peanut hulls and other such materials that are removed to get the edible or useful product. Some of this material is ground up and used as composting or soil-enhancing material, but a large percentage of it ends up in the landfill.
Any time a waste stream can be converted into useful material, there is potential to make a profit as well as reduce the amount of waste that ends up in landfills. Because of this, research in reusing agricultural waste has become a growing field.
Bio-based plastics
It is no secret that most plastics are derived from petroleum. In order to fully move away from petroleum, yet continue to enjoy the benefits of plastics, new plastics must be developed. Multiple agencies are working on the development of plastics made from agricultural waste streams.
Discarded fruit is one possible source for bio-based plastics. The U.S. Food and Agriculture Office (FAO) estimates that 20-30% of fruit and vegetables are wasted, and much of this waste could be converted into plastic. These waste streams could be converted into polylactic acid (PLA) and polyhydroxyalkanoates (PHA) through a fermentation process. Both of these materials can be injection molded, cast, pressed and processed into consumer goods.
One of the primary uses for these polymers is packing materials. Packing materials are ephemeral in their nature, so high strength is not a big requirement. Furthermore, packing materials are discarded soon after shipping; therefore, the ability for these materials to quickly break down is much higher on the priority list.
Packing peanuts made from starch (likely corn). Source: Christian Gahle, nova-Institut GmbH/CC BY-SA 3.0
Bioplastics have the added advantage of biodegradability. While the original plant material was also biodegradable, it rarely is placed in an environment where it can biodegrade. At the end of the plastic’s service life, it can be discarded in a flower bed, compost heap or other such place. Provided it does not blow away, it will break down in the soil. However, the real advantage is that if these materials get discarded carelessly, they stand a better chance of degrading in the oceans and on the ground than traditional, petroleum-based plastics.
Textiles
Agricultural waste is often fibrous and filled with sugars that can lead to decay of the material, making it difficult to process. However, one novel approach is to speed up the decay by allowing the sugars to be consumed with mycelium fungus. The mycelium fungi remove the sugars and leave behind thin fibers that can be woven into numerous items. The fungus is stabilized after it has consumed the plant material, making it much longer lasting than its natural occurrence would allow.
Fiberboards for insulation, mats, brooms, and even artificial leather can be made using mycelium. Tufts has found that the textile materials that can be created from mycelium are similar to styrofoam in terms of insulation and acoustic dampening. They also found that these textiles can be used to absorb water and can be used in passive cooling.
Outside of mycelium fibers, agricultural waste products are being fermented and then spun into plastic fibers. These fibers can be stabilized with other chemicals to form rugs, blankets, and articles of clothing. The key is to extract the PHA and PLA. Typically, some additives, such as plasticizers, epoxies, stabilizers, dyes and other components are added. While some of these additives are derived from petroleum, the bulk of the material can be made from recycled agricultural waste.
Building materials
Some agricultural waste materials are suitable for creating building materials. Coconut husks, bamboo stalks, rice hulls, hemp and mycelium fungus have been used to build fiberboards and other building materials.
Coconut husks are difficult to dispose of, due to their dense nature. This dense nature can instead be made into an advantage. Coir wood uses coconut hulls and a resin to make particle board and plywood-like sheets that can be used as a building material.
Another example of agricultural waste as a building material is the use of corn stalks as a fiber reinforcement in composites and concrete. Researchers at Colorado State University have been developing a cement block that is reinforced with corn stalks. Preliminary research shows that these blocks are stronger and more resistant to cracking than traditional concrete blocks.
Challenges
While these projects all sound promising, they are not without their challenges. First, waste material does degrade over time. This degradation can take the form of mold, mildew, fungus, bacteria and other methods of spoilage that are both detrimental to their final usage and potentially hazardous.
Currently, much of the waste material is either stripped out and discarded on the spot by combine harvesters in the field or removed at the food processing facility. In either event, the collection and transportation of the waste material is a major challenge. It is not economical to pick up the corn stalk shreds that litter the field, and some of these are used to add nutrients back into the soil anyhow. If the stalks and chaff were removed entirely, the long-term effects on the soil would need to be studied carefully.
A combine harvester collects the corn stalks, rips off the ears of corn, and threshes them to remove the kernels. The kernels go in the bin, and the rest is typically discarded into the field (hence the dust trail behind the combine). Source: Wikideas1/Public domain
Final thoughts
As Earth’s population continues to increase, so too will its demand for food. This growing demand for food will only create more agricultural waste. While plastic waste often takes the spotlight for conservation efforts, agricultural waste and its disposal cannot be ignored. With new innovation, perhaps some of this waste can be directed to new uses, both feeding the growing population and reducing the waste that ends up in a landfill.
Just to be clear, corn stalks are not "collected" by a combine harvester. In the corn header, the stalks are pulled downward at high speed by counter-rotating "rollers" through a pair of gapped "stripper plates" where the ear of corn pops off and proceeds into the combine. Stalks rarely enter the inside of the combine, though small bits and pieces may do so if they fracture during the stripping off of the ears. The residue out the back end of a combine includes cob pieces, dust, a few corn leaves, husks, silks, pieces of tassel, and occasional stalk chunks. If one were to try and collect any quantity of stalks, it would be necessary to do some secondary processing of the standing and broken-down stalks, move them into windrows, then bale them. Cattle feeding operations do this routinely for bedding/fodder.