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Improvement of wood product properties by increased hydrophobicity obtained by the use of silicon compounds

The newly implemented Biocidal Products' Directive and future restriction of toxic preservatives will reduce the overall use of biocides. The proposed project aims to develop silicon-based hydrophobisation treatments to improve wood properties
in many ways, such as improved dimensional stability, durability against bio-organisms, applicability of various components to fit-to-purpose end uses. These treated and hydrophobic components will be safe to handle, environmentally acceptable and will not produce hazardous waste. The expected results are a better understanding of preventative mechanisms and the promotion of the use of hydrophobisited European-grown softwood, instead of tropical hardwoods, for value added markets.

The main objective of the project is to develop non-fungicidal (environment-friendly) silicon-based hydrophobisation agents to protect wood-based materials against bio-deterioration and weather conditions.
The main objective will be achieved through the following preliminary objectives:
1) to identify the potential silicon-based systems by evaluating the function of the hydrophobisation agents
2) to establish working protocols for lab scale treatments
3) to establish fundamental and practical knowledge on the effect of the potential agents on the durability of wood
4) to determine models for moisture transport within modified wood and coated modified wood
5) to assess physical/chemical properties of treated wood by EN standard tests
6) to up-scale the methods to pilot scale
7) to provide working models for potential uses of the treated timber
8) to evaluate the environmental impact of the hydrophobisation systems and to assess the comparison with the biocidal preservatives.

Progress to Date
Most of the work in the first reporting year was focused on Work Package 1: Identification of suitable compounds and type of bonding. Under the leadership of the industrial partner, the PCC decided to screen Si-compounds from the following three categories:
Category 1: Testing of silanes. Experience on chemical reactivity of silanes and hydrophobing technology those of potential interest for wood modification were selected (Alkyl, epoxy, vinyl etc.).
Category 2: Testing of intermediates, which could be potentially polymerised in the wood. A self-catalytic amino function oligomer ,OH terminated fluids of different molecular weight, Si reactive cyclics and polymers and a unreactive PDMS reference were chosen. Those materials were evaluated at suited concentration in solvents.
Category 3: Water-based silicon technology. From the vast range of industrial emulsions a standard OH terminated PDMS emulsion, a silane/SiH reactive emulsion and a silicone/organic blend emulsion (already sold for wood treatment) were chosen for the first evaluation.
With reactive chemicals (category 1 compounds) chemical grafting has been confirmed for carboxylation, etherification and alcoholysis reactions. Reactions have been confirmed by FTIR and NMR spectroscopy (13C and 29Si). With non-reactive chemicals, the distribution of compound in wood was assessed by P5. Light microscopy turned out to be suitable for inorganic compounds and fluorescence microscopy for organic silicons.
Properties of treated wood were studied thoroughly. Results of category 1 silicones indicate that in spite of proven reaction in cell wall only slight dimensional stability occurred. On the other hand, leachability of grafted chemicals is small. Non-reactive silicones from category 2 and 3 did not prove any improvement in ASE. However, they gave a good hydrophobicity in water soaking. Contact angle measurements by P1 also indicate that apparently there are is a linear relationship between the water absorption and contact angle measurement values.
With category 1 chemicals, efforts were focused on optimising solvent type and catalyst quantities. Accordingly, isopropanol (already used in the building industry for concrete protection) was selected as a carrying solvent for wood hydrophobisation. A catatalyst/reactant molar ratio of 0.05 was also selected after several experiments. With regard to cost optimisation, expensive compounds were excluded from the selection after discussion with the consortium. In addition pilot plant treatment experiments were carried out with other category chemicals. Process variants were working pressure as well as curing procedure in terms of temperature increase.
In Work Package 2, a standard basidiomycetes test according to European standards was set up. This standard testing will allow evaluation the treatments on their potential to be assessed as wood preservatives. However, there are no results ready to report yet.


Scientist responsible for the project

Senior Research Scientist ANTTI NURMI
Puumiehenkuja 2 A Box 1806
02044 VTT Espoo
Finland - FI

Phone: +35 894565522
Fax: +35 894567027


Project ID QLRT-2001-01439
Area 5.3.2
Start date 01 January 2003
Duration (months) 48
Total cost 2 479 782 €
Total EC contribution   1 804 892 €
Status Ongoing
Web address of the project

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