Alex Collins from Ecodek says that wood polymer composites present a new world of sustainable, durable construction materials.
Wood Polymer Composites (WPCs) were first developed in the US in the early 1990s as an alternative to timber used in applications where durability, rot and infestation resistance were required.
Currently, the most widespread use of WPCs in North America is in outdoor deck floors, but they are also used for railings, fences, landscaping timbers, cladding and outdoor furniture for parks and recre- ational areas.
For such applications, a wood-polymer composite material is also considered to be more environmentally friendly, as it requires less maintenance than the alternatives of solid wood treated with preservatives or rot-resistant solid wood species.
WPCs are manufactured from a mixture of finely ground wood particles (‘wood flour’) and heated thermoplastic resin – both virgin and recycled polymers can be used. In the case of Ecodek, the raw materials for the thermoplastic resin element of the WPC mix are millions of recycled plastic milk bottles. The relative proportion of the mix is also important and is usually around 35 per cent resin to 65 per cent wood flour, to minimise moisture absorption.
In the UK, wood flour is a waste product of the timber processing industry and is generally sourced from FSC or PEFC accredited suppliers.
Some WPCs therefore have an almost 100 per cent recycled composition and products are capable of being fully recycled at the end of their working lives. Few other materials are able to claim such strong envi- ronmental and sustainability credentials.
The most common method of production is to extrude WPC into the required shape or profile, although injection moulding techniques are also widely used. Because
of the organic content of the wood flour in the mix, WPCs tend to be processed at relatively low temperatures compared to traditional thermoplastic extrusion and injection moulding methods.
Solid and hollow sections can be extruded with ribbed, curved and grooved surface profiles readily achieved, allowing a considerable degree of flexibility in
both function and aesthetic. WPC materials can also be moulded, with or without simulated wood grain detail to further improve their appeal.
Where do WPCs fit?
WPCs have many advantages over comparable timber alternatives. A good quality WPC will not erode and is resistant to rot and attack by wood-boring insects etc. It is extremely stable, does not crack or split, has excellent workability and can be shaped and cut using conventional woodworking tools. WPC can also be readily curved with the application of heat to form strong, arching contours.
In the UK, markets where WPC products have proved to be most popular are in decking boards for the commercial and domestic landscape sector and in particular, for balcony decking in luxury apartment developments.
Here, the durability, clean, sharp profiles as well as the minimal maintenance require- ments have persuaded many of the leading housing development companies to install WPC decks. As WPC is permanently pigmented and requires no preservative coating, there is no risk of leachate dripping from beneath the deck and falling on properties below.
Carbon negative production
Another important factor in the success and popularity of WPC in the UK is the sustain- ability of its composition and manufacture. In a recent life-cycle assessment programme undertaken by the BioComposites Centre at Bangor University, production of Ecodek WPC decking products was considered on a cradle to factory gate basis, including all significant materials, transport, energy use and packaging inputs.
Results showed the products had a net effect of ‘removing’ carbon dioxide from the atmosphere rather than adding to it. Production actually being carbon negative was a huge achievement in modern manufacturing and believed to be a first for a UK manufacturer, clearly illustrating the environmental credentials of WPC. The study showed that Ecodek’s 2016 production absorbed the same amount of carbon as 300,000 trees.
To achieve carbon negativity – effectively removing carbon dioxide from the atmosphere rather than adding to it – requires a much more aggressive approach than carbon neutrality, which merely nullifies the effect that an entity has on the environment.
Clearly, WPC products have an important role to play in the UK construction and landscape markets. The potential for product and market extension is huge, and manufacturers will continue working closely with industry bodies to identify new and innovative ways of capitalising on the unique characteristics of this exciting material.
Alex Collins is technical director for Ecodek