- Researchers develop a new processing technique to create see-through polythene films that are stronger and lighter than aluminum.
- These films can be used in windscreens, visors, glazing, and electronic displays.
When it comes to creating see-through polymeric materials, poly(methyl methacrylate), polystyrene and polycarbonate are usually the materials of choice. They provide up to 92% transmittance in the visible light regime.
However, mechanical characteristics of such polymers such as tensile strength and elastic modulus are not up to the mark. High-density polyethylene materials used to create transparent products also have limited mechanical properties, which restrict their applications to packaging only.
Now, researchers at the University of London and the University of Warwick, England, have developed a new processing technique to create see-through polythene films that are stronger and lighter than aluminum. They can be used in windscreens, visors, glazing, and electronic displays in such a manner that adds flexibility and strength while decreasing weight.
The microstructure of polymers can carry heavy loads, especially polythene materials, but they typically have an opaque appearance due to voids and defects generated in the drawing process.
Scientists have already made these polymer 90% transparent and stronger, by adding highly specific additives in hot-drawn high-density polyethylene materials.
What researchers have done in this study is more than impressive: they have created a post-manufacturing method for high-density polyethylene that requires no additives and endows both resilience and strength while preserving transparency.
How Did They Do This?
The research team drew out sheets of high-density polyethylene at temperatures below the polyethylene’s melting point. They found that the best balance between transparency and strength can be obtained by adjusting the temperatures between 90°C and 110°C.
Reference: ScienceDirect | DOI:10.1016/j.polymer.2019.03.036 | University of Warwick
Greater polymer chain mobility at such temperatures results in fewer defects in the drawn sheets. This leads to higher clarity due to less light scattering by defects.
These sheets are 10 times stronger and flexible than polycarbonate and poly(methyl
methacrylate). In tests, new transparent films showed a maximum tensile strength of 800 MPa and maximum Young’s Modulus (resilience) of 27 GPa.
To put this into perspective, aerospace grade aluminum alloy has a maximum tensile strength of 500 MPa and aluminum has a Young’s Modulus of 69 GPa. Moreover, aluminum is almost 3 times denser than polythene.
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All these figures clearly state that new high strength transparent polymer sheets can outperform metals like aluminum and steel. They can be used in laminated composites, strengthening or replacing conventional polymeric/inorganic glass for applications in automotive glazing, electronic displays, and more.
