Growing concern about plastic waste has increased the search for environmentally friendly alternatives to conventional plastics. Among the most promising options is polyhydroxybutyrate (PHB), a biodegradable plastic that can naturally break down in the environment and is produced by microorganisms. While PHB offers important environmental benefits, its wider use has been limited by a major drawback: it is naturally brittle and lacks the flexibility needed for many packaging and medical products. New research shows a way to overcome this challenge by combining PHB with cotton fibres and carefully designed chemical modifications, creating a stronger and more durable biodegradable material.

The research was led by Associate Professer Jin Zhang’s team at University of New South Wales, including  Dr. Yilin He, Dr. Vinod Kumar Kannaujiya,PhD student Linguangze Zhuo,, in collaboration with Professor Chun Wang and Professor Cyrille Boyer. ,Together with Ecopha Biotech Pty. Ltd., the team developed a new composite material, a material made by combining different ingredients, that strengthens PHB with cotton fibres coated in polyvinyl alcohol, commonly known as PVA, a water-friendly coating material. A. Prof. Zhang’s team improved the material by modifying the PHB so it could bond more effectively with the fibres. Their findings were published in the peer-reviewed journal Advanced Sustainable Systems.

Building on previous efforts to improve biodegradable plastics, Professor Zhang focused on solving a long-standing problem: helping natural fibres and PHB stick together more effectively. A. Prof. Zhang noted, “This study enhances PHB’s strength and ductility by reinforcing it with polyvinyl alcohol (PVA)-coated cotton fibres and further improving interfacial bonding through maleic anhydride (MA) grafting.” Ductility refers to a material’s ability to bend or stretch without breaking. Cotton fibres naturally attract water, while PHB tends to repel it, making it difficult for the two materials to work well together. By coating the fibres and modifying the PHB, the team created a much stronger connection between the different parts of the material.

Several improvements were observed. Adding untreated cotton fibres already increased both strength and flexibility compared with pure PHB. However, the greatest gains were achieved when coated fibres were used. At the highest fibre content tested, the material became nearly four times stronger than the original plastic while also stretching much farther before breaking. This result is especially important because materials often become less flexible when they are made stronger. In this case, both qualities improved at the same time. The modified material could also absorb much more energy before breaking, making it far tougher and more resistant to damage.

Further benefits appeared when the PHB underwent an additional modification step. This treatment helped the plastic form stronger links with both the coating and the cotton fibres. As a result, the material showed a dramatic increase in toughness, meaning its ability to resist cracking and breaking, and much better resistance to layers separating under stress. A. Prof. Zhang highlighted this achievement, stating that “MA grafting further enhances toughness (ninefold increase) and interlaminar fracture toughness (twofold rise), while reducing helium permeation to 60%.” Helium permeation refers to how easily gas can pass through a material. These improvements suggest that the material not only becomes stronger but also develops better protective properties, which are highly desirable for packaging applications.

Microscopic examinations, detailed imaging at a scale too small to see with the naked eye, helped explain why the material performed so well. In composites without the additional modification, fibres often pulled away from the surrounding plastic when the material broke, showing that the connection between the two was relatively weak. By comparison, the modified composites displayed much stronger attachment between the fibres and the plastic, with fewer signs of separation. Additional testing confirmed that the changes successfully improved the material while maintaining its overall stability. The modified plastic also became more compatible with the coated fibres, allowing them to work together more effectively.

Beyond strength and durability, the team also examined how well the material could block gases. This property is especially important for food and medical packaging. Pure PHB allowed the highest level of gas movement. When cotton fibres and coatings were added, gas movement decreased significantly. The combination of coated cotton fibres and modified PHB delivered the best results, reducing gas movement by roughly forty percent compared with the original plastic. Such improvements could help products stay fresh longer while still benefiting from environmentally friendly packaging.

Together, A. Prof. Zhang’s findings show that combining natural cotton fibres with carefully designed modifications can transform PHB from a brittle biodegradable plastic into a material with greatly improved strength, durability, flexibility, and protective performance. These advances address several of the limitations that have slowed the wider adoption of PHB and related biodegradable plastics. By improving performance while maintaining sustainability, A. Prof. Zhang and her team’s new approach could support future use in packaging, healthcare products, and many other applications that are seeking alternatives to plastics made from fossil fuels.

Journal Reference

He Y., Kannaujiya V.K., Zhuo L., Ling W., Wang C.H., Boyer C., Zhang J. “Enhancing the Mechanical Properties of Inherently Brittle, Biobased and Biodegradable Polyhydroxybutyrate (PHB) Polymer by Cotton Fibre Reinforcement and Interfacial Grafting.” Advanced Sustainable Systems, 2025; 9: e00294. DOI: https://doi.org/10.1002/adsu.202500294