PineXLAM - Courage to CLT (cross laminated timber) from pine! Successfully completed FFG industrial project
The IQEC team (indoor quality and emission control) of the area Tulln was recently able to record a great success: Within the framework of the FFG Collective Research program line the 3-year industrial project PineXLAM has been successfully completed. PineXLAM, short for CLT (cross laminated timber) made of pine wood, dealed with the characterization and optimization of the production processes for pine wood based cross laminated timber with regard to the reduction of VOC emissions, to enable its use for interior purposes. The consortium comprised he five largest Austrian cross laminated timber manufacturers (Stora Enso, KLH, Mayr-Melnhof, Binderholz and Hasslacher Group) as well as the professional association of wood industry.
CLT is currently produced out of spruce wood. However, the availability of spruce is limited due to increased competition and a decline in the available raw material potential. The demand for solid wood such as CLT is increasing at the same time. In order to meet this increasing demand, new raw material sources are needed for the production of CLT. Pine, which has both excellent properties and a high unused raw material potential, would be an ideal choice. However, pine is a wood species containing a high amount of extractives, leading to increased emissions of volatile organic compounds (VOC). For this reason, pine wood has so far only been used to a very limited extent in solid wood construction. In order to make pine wood usable for the CLT production in the future, the CLT production process was adapted accordingly in the project:
After a comprehensive material and process characterization, an optimized production process for pine and hybrid CLT (pine core with a top spruce layer oriented to the interior) was developed and evaluated in a final large-scale test set-up.
For this purpose, the technical center in Tulln with its excellent infrastructure in terms of woodworking and processing was extended by 4 congruent, air-conditioned, 30 m3 model rooms, which enabled the measurement of emissions in realistic interior scenarios. The longitudinal walls of the model rooms were constructed from differently manufactured, conventional or optimized CLT materials, and the VOC-emissions in the interior were measured over 6 months and toxicologically evaluated.
The results of the process optimization in the emission test chambers are impressive: Already after increasing the drying temperature of the raw material pine wood for the production of cross laminated timber from 70 °C to 85 °C and extending the drying time from 1.8 to 5.4 days, a reduction of the VOC emissions (expressed as TVOC value = Total volatile organic compounds) from the CLT elements of up to 68 % could be achieved. In addition, a 60 % reduction in VOC emissions was achieved in only 1.8 days by applying high temperature drying at 110 °C for the raw material used for the CLT manufacturing.
The use of spruce in the interior-oriented layer in so called hybrid CLT elements and the surface bonding both have a strong influence on the VOC-emissions. A closed glue-layer on the pine board surface already reduced the VOC-emissions by 41 to 68 %. With a combination of gluing and the spruce layer oriented to the interior of the room, a reduction of VOC-emissions by over 90 % was achieved. In addition, a significant influence of the drying temperature on the VOC-emissions was observed.
The emission reduction of hybrid-CLT by increasing the drying temperatures for raw material could finally be demonstrated in long-term tests in model rooms: Throughout the entire measurement period of over 200 days, the VOC-emissions in model rooms with optimized CLT elements (drying temperature 85 °C) were 20 % lower than in those made of conventionally produced material (drying temperature 70 °C). Furthermore, hybrid CLT emitted significantly less VOC compared to CLT made exclusively from pine wood.
The project results will supply the basis for using pine wood for CLT production in the future and will deliver findings and knowledge available for companies and representatives of the solid wood industry, as well as for designers, architects and customers.