Picking up the durable baton29 June 2018
Dr. Simon Curling FIMMM, project officer at the BioComposites Centre in Bangor, outlines how biological durability needs to be a critical element of product development.
With the shock news that Mark Irle had decided to hang up his keyboard and retire from writing the Technically Speaking column the question was “Who can replace Mark?” Well, no one person can! Instead the team from the BioComposites Centre in Bangor, North Wales, UK are going to pick up the baton and take turns writing the column. We thank Mark for his sterling work and hope we can adequately fill his lab coat!
The BioComposites Centre (BC) is an industry focused academic unit within Bangor University that has been working on wood based panels, timber and other composites for over 25 years, and has expertise in panels ranging from manufacture (the centre possesses a pilot scale MDF/particleboard plant), to durability, recycling and life cycle assessment. As BC work so closely with industry, we aim, with this column, to discuss topics that currently are or will become major issues for our readers.
In this issue I will touch on the subject of biological durability and how this needs to be a critical element of product development. It is obvious that as natural materials, wood based panels are at risk of decay, depending on where they are used and how wet they could get. Indeed, this hazard forms the basis of Use Class categories as described in the European standards EN 335 (2013) and EN 350 (2016). This type of standard requires the testing of wood and wood based materials against fungi using either lab or outdoor tests following protocols detailed in the appropriate regional standards (European (EN), or US (ASTM) for example).
When developing panels, the wood furnish, adhesive system and processing all play major roles in the ultimate durability of the product. In terms of the wood component, heartwood durability (sapwood is not durable) has been determined for many wood species, with values for some of the more commonly used species given in EN 350:2016. These values are not set in stone, however, as the values given in the standard have been adjusted in the 2016 version from previous version to account for new sources (e.g plantation grown) of wood.
Recent developments in panel manufacture have looked at enhancing panel durability by adding preservative treatments to either the wood or the glue components or by modifying the wood component by chemical or thermal methods. Panels using modified wood would seem to be on the increase, especially given the start of building of the world’s first Tricoya acetylated wood chip plant at Hull in the UK.
With new sources of wood (e.g the aforementioned plantations), new wood modification technologies and new adhesive systems and technologies, standards and testing protocols are changing to accommodate the new technologies. EN 350 in Europe and AWPA guidelines in the US (e.g AWPA Guidance document N: data requirements for listing thermally modified wood with enhanced durability in the AWPA standards) detail the information that needs to be provided. There are also new standards for testing additives such as ASTM Standard D7857 (2016) that details how to determine the effects of preservative or fire retardant chemicals on the properties of wood based panels.
As old technology and chemicals are phased out or removed, biological, weathering and long-term exposure testing are still a vital part of product development.