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Biorefinery products in structural materials

Composite panel boards, used for the construction and furniture industries, commonly employ organic filler, such as wood fibre or particles with a synthetic binder. The binders are often based on formaldehyde, recently classified as a possible carcinogen and thus likely to be phased out. An effective alternative are aqueous inorganic metal silicates, that polymerise due to evaporation and/or a chemical reaction which causes lowering of the pH of the alkaline binder solution.

Scientists at the York Green Chemistry Centre of Excellence have invented a new method of deriving biogenic silicates from organic, renewable resources, such as wheat straw and Miscanthus, that are rich in silicas and additionally contain alkali-metals, often in ratios which are preferred for binder applications.

After combustion of the biomass (e.g. for energy generation), the remaining ash is rich in silica and alkali metal oxides and is treated with aqueous alkali metal solution at elevated temperatures to form a silicate solution. The ash is normally allowed to cool before the dissolution, but in this process the alkali metal oxides in the ash react with atmospheric CO2 and are converted to less alkaline and less soluble carbonates.

The uniqueness of the York process is that the ashes are treated with water directly after combustion and before any substantial reaction with CO2 occurs thus maintaining the natural high alkalinity in the ashes. The alkali metal oxides are then converted to hydroxides on addition of water without the need for auxiliary base.

Furthermore the same bio-resources can provide a hardener for the binder system that consumes the base, thus lowering the solution pH and initiating the polymerisation of silica. Importantly the hardening process needs to be controllable to suit normal processing restrictions. Typically esters or other chemical functionalities are used that consume the base through hydrolysis, and setting is controlled by the rate of hydrolysis.

Plant components such as oils which are present in situ in the residues can be used to perform this hardener function and this eliminates the need for auxiliary synthetic formulations. If insufficient chemical functionalities are present in the aggregate these can typically be introduced through simple aggregate pre-treatment processes.

Benefits

• Production of materials without the use of toxic chemicals such as formaldehyde
• Uses renewable sources within minimal environmental impact

Applications

This invention enables the production of fully bio-based structural panel boards for the construction and furniture industry, where all components are derived from biomass, demonstrating the biorefinery concept. Biomass can be used as aggregate, to produce the silicate binder, and a hardener, which avoids the necessity of sourcing FSC wood for sustainable development.

Investment readiness status

IP status