You’ve probably come across thermoplastics in packaging, where their superb mouldability allows the material to be shaped to fit around any product, but the design possibilities of thermoplastics allow them to venture into a variety of other applications. Kim Sjӧdahl explores the properties of thermoplastics and the industries they’re advancing.
Thermoplastics are polymers that become highly flexible when heated, and hard when cooled. Their structure consists of monomer chains with weak bonds between them that can break upon heating. Thermoplastics can be heated and cooled a number of times without losing much of their chemical or mechanical properties. When heated, they can be moulded into virtually any shape.
For example, a thermoplastic composite could be pultruded into a flat structure, and then bent afterwards to create a curved shape. Thermoplastics can also be shaped through injection moulding. In this manufacturing process, plastic pellets are loaded into a barrel where they are melted and injected at pressure into a mould cavity, which fills and solidifies to create the final product.
Injection moulding can be used for more than just a standalone part, as it opens the possibility of over-moulding. During this process, additional components are moulded around an existing part to add to the overall structure. It’s essentially adding one layer over another.
Thermoplastics can be over-moulded onto a different material, such as a metal, to create a top layer with advantageous aesthetic and performance characteristics. This could involve, for example, creating a softer handle for a more comfortable grip on a tool, such as a hammer. It’s also possible to over-mould a thermoplastic on top of another thermoplastic part, which melts them together to create a strong bond that removes the need for gluing.
Moulding the market
Thermoplastics are advancing the composite market, with a report by MarketsandMarkets predicting the thermoplastic composites market size to increase at a compound annual growth rate (CAGR) of 7.5% to reach US$31.8bn by 2025.
The report outlines the ability of thermoplastics to be moulded and remoulded as a key reason for their popularity growth, along with their recyclability. Thermoplastics can be easily recycled at the end of their use cycle as their polymer chain does not degrade significantly when melted down, so the material can be reshaped into a new product without diminishing its performance.
Thermoplastics have the potential to create advanced products for a variety of applications, and because of this, Exel Composites is developing its thermoplastic offering. For example, as part of Exel’s olive picking system, thermoplastic thread connectors are over-moulded onto the picking rods so that they can easily be fitted to the handle.
Exel is also using the material in electric fences for animal enclosures, where thermoplastic parts, such as the sharp peg that helps the fence enter the ground and the holders for the electric wire, are over-moulded onto a thermoplastic rod to create a durable bond.
While thermoplastics prove a valuable material for containing and protecting products of all shapes and sizes, their benefits span far beyond the packaging industry. The ability of thermoplastics to be melted and remoulded into practically any 3D shape unlocks a plethora of design possibilities, making them influential in a wide range of industries.
Kim Sjӧdahl is the Senior Vice-President – R&D and Technology at Exel Composites.