Silk-Inspired Process Creates Strong Biodegradable Plant-Based Plastic

Researchers from Wageningen University & Research, the University of Amsterdam and institutions in China have developed a strong, biodegradable plastic from maize protein. They call the transparent material ‘plantymer’. It absorbs considerably less water than many existing protein-based plastics. The team published its findings in Nature Communications.

Learning From Natural Protein Structures

The researchers produced plantymer using zein, a protein found in maize. Manufacturers have explored this protein as a raw material for fibres and bioplastics for several decades. First, the team dissolved it in a mixture of ethanol and water. The solution then reached a transition point and formed a thick, protein-rich substance.

The researchers pressed this substance through a small opening to produce textile fibres. Alternatively, they rolled it onto a flat surface and dried it to create a film. The film has a thickness similar to that of a heavy-duty refuse bag.

The process takes inspiration from the way spiders produce silk. During extrusion or rolling, mechanical forces alter the protein chains. Spring-like alpha helices change into flatter beta sheets. These sheets interlock and form physical crosslinks without additional chemicals.

This structural change gives the material a higher tensile strength than commonly used polyethylene. However, it remains less strong than metal. Similar protein structures occur in spider silk, mussel adhesive and squid sucker teeth. Achieving this effect with a plant protein surprised the researchers.

Improved Resistance To Water

Water sensitivity remains a major challenge for biobased plastics. After one hour under water, the plantymer film had absorbed around 25% of its own weight. In comparison, soy-based plastic can absorb approximately 175%. Conventional PET still performs much better, with water absorption of no more than around 0.1%.

Most of the plantymer reportedly biodegraded within four weeks and left no microplastics. This combination of strength and biodegradability could suit agricultural films and other short-lived products. The researchers also see potential for disposable cutlery, plates, drinking straws, packaging films and textile fibres.

Raw Material And Scaling Challenges

The technology remains at an early research stage. So far, the Chinese team has produced approximately one square metre of film. The process appears suitable for scaling up. However, maize protein could present a challenge because it may compete with food and animal feed.

The researchers are therefore exploring alternative protein sources. Possible options include poultry feathers and residual streams from beer production. The material also requires further applied research. Researchers must assess its manufacture, safety, performance and end-of-life behaviour before commercial use becomes possible.

Source: Wageningen University & Research (WUR)
Photo: Qin Li