Shells inspire composite material

The scientists from Manchester and Leeds Universities successfully reinforced calcium carbonate, or chalk, with polystyrene particles that are used to make drinks cups.

They have developed an effective method of combining calcite crystals with the polystyrene particles and have found that this makes the material more ductile compared to its original brittle form. The polystyrene also acts as a toughening agent, assisting the prevention of the growth of cracks.

Their technique could be used to make ceramics with high resistance to cracking - which could in turn be used in crack-resistant building materials and bone replacements.

Scientists also observed that when the reinforced material cracked, the polymer lengthened within the cracks - a well-known mechanism for absorbing energy and enhancing toughness.

Researchers say their method allows the properties of the new material to be tweaked by selecting particles of different shapes, sizes and composition.

Dr Stephen Eichhorn from the School of Materials at Manchester University said: ’The mechanical properties of shells can rival those of man-made ceramics, which are engineered at high temperatures and pressures. Their construction helps to distribute stress over the structure and control the spread of cracks.

’Calcium carbonate is the main ingredient of chalk, which is very brittle and breaks easily when force is applied. But shells are strong and resistant to fracturing because the calcium carbonate is combined with proteins that bind the crystals together, like bricks in a wall, to make the material stronger and sometimes tougher.’

The researchers replicated nature’s addition of proteins using polystyrene to create their strong, shell-like structure with similar properties to those seen in nature.

Further research and testing is still needed, but the research potentially offers a straightforward method of engineering new and tough chalk-based composite materials with a range of applications.

The research was funded by grants from the Engineering and Physical Sciences Research Council (EPSRC) and was conducted in collaboration with Prof Fiona Meldrum in the School of Chemistry at Leeds University.