Researchers from the University of Hohenheim use waste in the form of chicory roots to extract basic chemical building blocks for producing nylon and plastics. Hydroxymethylfurfural (HMF) is one of 12 platform chemicals used to produce plastics. The raw material obtained from the chicory root improves the plastics’ environmental performance, notably because it is an oil substitute and does not compete in any way with food production.
Frederick the Great, King of Prussia from 1740 to 1786, banned the importation of coffee into Prussia, thereby encouraging the cultivation of chicory or witloof (Cichorium intybus var. sativum) throughout most of the 18th century. When roasted, chicory root has a similar flavour to coffee. Radicchio and sugarloaf, which are modern salad varieties, derive from another type of chicory. In the late 19th century, Belgian farmers noted that chicory, when left in darkness in the soil, developed a white bulb with tightly packed, overlapping leaves with yellow tips that were really tasty. Nowadays, more than 14,000 hectares of chicory are grown in Europe. The largest producers are France, Belgium and the Netherlands.
A group of researchers headed up by Prof. Dr. Andrea Kruse at the University of Hohenheim, have found out that apart from salad leaves or coffee, chicory can also be used as the chemical basis for making plastic bottles and stockings. In autumn, the milky sap of the plant contains an average of 15 to 20 percent inulin, a fructose-based polysaccharide in which the plant stores the energy that it needs to grow and bloom the following summer. This sap can be used to produce hydroxymethylfurfural (HMF), a yellow-brown powder that is one of 12 platform chemicals used for producing plastics. Dominik Wüst, chief engineer at the Institute of Agricultural Engineering at the University of Hohenheim explains: “At first we tried to produce HMF from wood cellulose. However, we only achieved poor yields. Then we tried molasses, which is a by-product of refining sugar beet or sugarcane. This worked quite well, but we nevertheless decided to look for a waste material and eventually discovered that chicory worked for our purposes.” In order to extract the coveted chemical, the root stump was chopped, mixed with diluted acid and heated to a temperature of 200 °C in a pressure container. Chicory roots turned out to be the perfect raw material as they accumulate as waste in agricultural production and so do not compete with food production.
In autumn, chicory farmers harvest the roots and leave them to grow in dark greenhouses. Up until several years ago, the roots were covered in soil and grown to a typical size of 12 to 15 cm. Nowadays, the plants are stacked in wooden crates and kept in dark forcing chambers. During this time, the roots are watered with a nutrient solution and chicory as we know it can be harvested after about three weeks. After harvesting the chicory salad, the roots are disposed of in composting plants and to a minor extent used in biogas plants or as animal feed. In Europe, around 800,000 tons of waste in the form of chicory roots is generated during the production of chicory salad per year.
The sugar-containing roots are far too valuable to use as compost. Chicory-derived HMF currently sells at 2,000 euros a kilo on the wholesale market. The HMF yield from one hectare of chicory root could therefore bring in almost six million euros. “Unfortunately, this is only a theoretical value to illustrate the plant's huge potential” says Wüst laughing. He goes on to explain: “Prices will fall once we are able to produce large quantities of HMF. To make it interesting for the plastics industry, we need a per kilo price of no more than two to three euros.” The researchers’ industrial partner, a company called AVA Biochem from Basel, is developing a large-scale HMF-production plant and, from 2019 onwards, has plans to produce between 30,000 and 120,000 tons of HMF from biomass per year. The Swiss company runs the world’s first industrial HMF production plant in the municipality of Muttenz in the canton of Basel. The plant produces HMF from molasses that accumulate during sugar production. A pilot plant for producing HMF from chicory roots is currently in development. In Basel, the oxidation of HMF results in furandicarboxylic acid (FDCA), which in turn enables the production of materials from biobased PEF (polyethylene furanoate).
PET (polyethylene terephthalate) is produced from crude oil and consists of up to 85 percent terephthalate. The goal is to replace the “T” in PET with “F”, i.e. plant-based furandicarboxylic acid and use this material to produce bottles, stockings, sportswear, films and even vascular grafts. The goal is to use biobased PEF in all areas where PET is presently used. Andrea Kruse points out: “ Chicory root is not only extremely well-suited for the production of HMF because it is a waste product, it also produces a much higher-value chemical than its crude oil equivalent.” This makes it possible to produce thinner PEF bottles, which in turn would save on transport costs and further improve the material’s environmental performance.
The greatest difficulty in producing industrial bioplastics from chicory lies in the fact that chicory is a seasonal business. Large quantities of root mass accumulate as waste when chicory leaves are harvested in winter. If they are left on the field, the sensitive sugars are rapidly degraded enzymatically and are no longer available for conversion into HMF. So ways to store the roots without going bad have to be found. The researchers are therefore testing whether it is possible to vacuum dry the root chaff. They are confident that the process can be implemented on a larger scale in about two years’ time. “It doesn't take much to switch from conventional PET bottle production to PEF production. And the PEF bottles would be 85 biobased, which is the great thing about it,” says Wüst highlighting the researchers’ vision.
But people who think that bioplastic bottles can easily be thrown on the compost heap are mistaken. Not all plastics produced from renewable raw materials are automatically biodegradable. According to the German Environment Agency1, even bioplastic bags that are explicitly labelled “biodegradable” can only be processed in industrial composting plants. Bioplastics produced from HMF need to be collected in the same way as other recyclable crude oil-based materials, and must not be thrown on the compost heap. The main benefit of bioplastics is the fact they replace oil with renewable raw materials.
Plastics, polymers, polysaccharides
Polymers or plastics are materials that consist of macromolecules, i.e. very large molecules with repeated subunits. Oil-based polymers are the major components of synthetic plastics such as polyethylene (PE) or polypropylene (PP). Living organisms produce biopolymers such as enzymes, nucleic acids, lipids and polysaccharides such as starch, cellulose or the inulin of the chicory root. Up until the 1930s, plastics like celluloid and cellophane were almost exclusively produced from renewable raw materials. At the end of WWII fossil resources such as oil and gas were increasingly used to produce plastics. In view of sustainability and closed material cycles, plastics production has recently started to increasingly involve plant-derived polymers.