Global greenhouse gas emission performance and -optimization of magnesium oxychloride binder formulations used in novel plywood products

The construction sector is currently a main contributor to global greenhouse gas (GHG) emissions and will likely contribute even more with increasing demand. The lever for reducing overall global GHG emissions is therefore big, when using more sustainable construction materials. Potentially, the built environment could even serve as an intermediate carbon sink, helping to actively reduce the atmospheric carbon content [1]. Engineered wood products (EWP) are gaining more and more interest as a sustainable building product, but usually contain substantial amounts of petroleum based binders. For example, plywood can contain up to around 25% by weight of urea formaldehyde, that can contribute to well more than 50% of the total GHG emission of the final product [2]. A potential alternative binder for EWPs is magnesium oxychloride cement [3]. While offering additional benefits such as inherent fire-retardation or being formaldehyde-free, it also offers the potential to have significantly lower GHG emissions compared to typical petroleum based binders. Conventionally produced reactive magnesium oxide, however, still has a significant GHG emission and is often not locally produced. While there would be sources for low or even negative CO2 emission magnesia, these might be again geographically limited, as well as energy intense to produce [4]. A potential alternative would be to use half calcined dolomite (HCD) as a source for reactive magnesium oxide for the binder formulation that can be used to manufacture EWPs like plywood. This work not only compares the GHG emissions of traditional binders used in EWPs like urea formaldehyde with MOC based binders, it especially also focuses on the impact of exchanging magnesite-based magnesia with half calcined dolomite. The results of analytical tests such as XRD and SEM will be presented to demonstrate the influence of replacing magnesite-based magnesium oxide with HCD on binder reactions with a focus on the important formation of phase 5. Consequences, like increasing binder viscosities that impact for instance the workability and related practical limitations, are taken into account and respected in formulation considerations. The influence of regional vs global sourcing of raw materials is also investigated. It is shown that the GHG emission is highly reduced by replacing magnesia with half calcined dolomite. The limits for the maximum proportion of half calcined dolomite in the binder formulation is critically considered to obtain a binder with sufficient workability and performance. The influence of potentially necessary dispersants on the binder formulation’s GHG emission is presented as well. SEM and XRD results also show, that phase 5 crystals are substantially present in the hardened binder containing half calcined dolomite. Finally, the full potential of low to negative CO2 magnesia source-based formulations is demonstrated. This work highlights the potential of MOC in practical applications and the realistic contribution to lowering the GHG footprint of engineered wood products. Otherwise seldomly reported and actually quantified GHG reduction potential is in depth discussed.