A bioinspired composite material made from all-natural raw ingredients could offer a possible alternative to petroleum-based structural plastics.
A bioinspired composite material made from all-natural raw ingredients could offer a possible alternative to petroleum-based structural plastics, according to researchers from the University of Science and Technology of China in Hefei
Plastics have found their way into every aspect of modern life but pose a significant environmental threat both in terms of their manufacture and end-of-life disposal. More sustainable alternatives made from bio-resources tend to have limited mechanical properties or require complex manufacturing processes.
“Petroleum-based plastics pose a great threat to the environment and human health,” points out Shu-Hong Yu, who led the work. “Developing sustainable structural materials as substitutes is one of the options for solving the pollution of petroleum-based plastics but remains challenging.”
Yu and his colleagues have devised a composite material based on cellulose nanofibers (CNFs) and mica platelets that they claim possesses better mechanical and thermal properties than conventional plastics. Inspired by nacre, the bricks-and-mortar-like material that makes up shells and other natural structures, the researchers devised a simple directional deforming assembly process that produces a material with promising strength, toughness, stiffness, and thermal stability.
To make the material, CNFs and TiO2-coated mica platelets, pretreated with (3-aminopropyl)triethoxysilane (APTES), are simply mixed together to form a hydrogel. The cross-linked hydrogel is then deformed – or squeezed – to align the platelets in the fibrous matrix, forming a nacre-like bricks-and-mortar structure.
The pretreatment with APTES is a crucial step because it improves the interfacial interaction between CNFs and TiO2-mica, which are otherwise poor, explains Yu. As a result, hydroxyl groups form on the nanosized TiO2 grains, which react with silane groups to form a silanized surface. In turn, the silanized surface helps the attachment of TiO2-mica to CNFs. Simultaneously, carboxyl groups in the CNFs are crosslinked by calcium ions in the mica to create a strong ionic bond network. The resulting composite has a strength of 281 MPa and a modulus of 20 GPa, higher than the constituent materials or typical natural nacres.
It is the bricks-and-mortar like structure of the composite that accounts for the mechanical properties. Under deformation, cracks have to propagate along tortuous paths around the TiO2-mica ‘bricks’, serving to relieve local stresses. Nanograins of TiO2 on the surface, meanwhile, slide past each other when strained to dissipate energy.
“Our biomimetic design of highly ordered brick-and-mortar like structure provides key ideas to fabricate sustainable structural materials for plastic replacement,” says Yu. “The bioinspired structural material possesses better mechanical and thermal properties than petroleum-based plastics, making it a high-performance and eco-friendly alternative to structural plastics.”
Different color materials can be produced using naturally occurring micas. The combination of strength, toughness, and thermal stability, together with the simple fabrication process, make the composite potentially suitable for a range of applications, believe the researchers, including personal electronic devices.
“Faced with the increasingly serious problem of plastic pollution, high-performance sustainable materials show great potential as an ideal alternative to plastics,” says Yu.
Petroleum-based plastics are a very well-established and mature industry, with significant price advantages, but there is a new desire and drive emerging for sustainable alternatives. The processing of bioinspired structural plastics is very different from conventional practices and will require new approaches.
“For a new process and new material to truly land, a complete industrial chain must be structured,” admits Yu. “If complex manufacturing processes can be simplified, bioinspired structural materials could play a key role in the future.”
Yu and his team are confident that their directional deforming assembly method could be scalable to enable mass production. The bioinspired material, moreover, could potentially be processed into a wide variety of sizes and shapes, such as mobile phone cases.
Originally Published By materialstoday