30 January 2019

Scientists have been exploring how to design materials that respond to changes in the environment and that can also be 3D printed – a concept known as 4D printing.

A 4D printed tree that stands up when triggered by water or heat has been created.

The tree is made from plastic with added cellulose. Cellulose is one of the materials that contributes to plant shapes and strength in standing upright and is the most abundant biomaterial on earth. In different forms it has different properties; the tangled fibres of cotton wool absorb water and the knitted fibres in a tee-shirt stretch, for example.

Added cellulose can change the properties of other materials, particularly if the long cellulose nanocrystals are all oriented in the same direction. Aligned cellulose can reinforce and increase strength, resulting in materials that are stronger than steel in some cases.

3D printing has the potential to control the orientation of cellulose nanocrystals in plastic polymers. This opens up the possibility of producing materials that have enhanced/tailored physical properties and respond to their environment.

The best way to view the arrangement of sub-microscopic cellulose added to plastics is to bombard the samples with X-rays and look their diffraction patterns. The only place to do this in the Southern Hemisphere is the Australian Synchrotron in Melbourne.

A joint project between Scion and the National Science Challenge: Science for Technological Innovation has enabled Dr Stefan Hill and Dr Marie Joo Le Guen (Scion), Dr Jerome Leveneur (GNS Science) and Dr John MacDonald-Wharry (University of Waikato) to take advantage of rapid sample throughput and extremely high resolution X-rays at the Australian Synchrotron.

The preliminary results from experiments on 3D printed samples made from different cellulose/plastic composites show that 3D printing parameters and the way materials are treated after printing strongly influence the alignment and self-assembly of the cellulose nanocrystals.

This new knowledge opens up the possibility of designing novel responsive materials and products such as valves that open and close as water temperature changes, solar cells that unfold in response to light, new wound management products, or flotation for devices for products or people entering water.