Acronym

SilWoodCoat

Contract number

N4-0117

Department:

Department of wood science and technology

Chair:

Chair of Adhesives, Wood Composites, Surface Treatment and Construction

Type of project

ARIS projects

Type of project

ERC projects

Role

Lead

Duration

01.01.2020 - 30.06.2021

ARRS FTE value

1.6 FTE

Total

1.6 FTE

Total

€121,530.12

Project manager at BF

Petrič Marko

Project Abstract:

Silicate coatings are products using alkali metal or alkyl silicates as binders. They have long been used for mineral substrates (stones or concrete) and for corrosion protection of iron and steel. They have been proven to provide high durability, UV resistance, high water vapour permeability, scrub and fire resistance, resistance to fungi, and can be easily renovated. They are highly competitive to conventional organic coatings for mineral substrates (about 10-15% of architectural paint market in EU is based on silicate emulsion paints). Alkali-metal silicates are produced from natural mineral compounds, and are of a reduced environmental impact. The other major components of silicates coatings such as fillers (calcium carbonate, talc) or pigments (TiO2, Fe oxides) are also of natural origin and environmentally friendly. The main critical points of silicate coatings as wood finishes are adhesion and durability of the layer on wood. Wood is more dimensionally unstable than traditional mineral substrates and so, a durable silicate coating for wood must meet a compromise between adhesion, liquid water and water vapour permeability and its flexibility. This is essential to accommodate surface strains developed, when wood swells and shrinks, to avoid cracking and debonding. The poor film ability of silicate layers and porosity that allow water permeability could be a drawback for wooden substrates. This research project is focused on the development of silicate coating formulations exhibiting good adhesion and able to perform durably on wood. These coatings systems offer various modifications routes including the silica-to-alkali ratio (module) of the silicate binders, addition of flexibility and adhesion promoters such as organosilanes, organic resins, and porosity reducers (nanoclays). Mineralization of wood surface can also be useful in the improvement of the adhesion and stability of the coatings.

 

The research activities are divided into four work packages:

WP1: Adhesion and durability of K silicate coatings on wood

WP2: Adhesion and durability of silicates hybrid coatings on wood

WP3: Influences of pre-treatment of wood by mineralization

WP4: Potential of Na silicate as binders for silicate wood coatings

 

PUBLISHED ARTICLES

 

CHEUMANI-YONA, Arnaud Maxime, ŽIGON, Jure, DAHLE, Sebastian, PETRIČ, Marko. Study of the adhesion of silicate-based coating formulations on a wood substrate. Coatings. 2021, vol. 11, iss. 1, str. 1-15, ilustr. ISSN 2079-6412. https://www.mdpi.com/2079-6412/11/1/61. [COBISS.SI-ID 46144771], [JCR, SNIP]

Abstract

Silicate coatings are environmentally friendly inorganic-based products that have long been used for mineral substrates and protection of steel against corrosion. The development and acceptance of these coatings in the wood sector require some adjustments in formulations or special preparation of the surface to be coated to obtain durable finishes. In this work, the adhesion of various silicate-based formulations to a beech wood substrate (Fagus sylvatica L.), was assessed with the main objective to study relevant parameters and potential improvements. Adhesion strength was determined by pull-off and cross-cut tests. Other coating properties such as scratch, impact, and water resistance were also determined. Surface roughness and interface were analyzed using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM), and coating curing was studied by attenuated total reflection-infrared spectroscopy (ATR FTIR). The results showed that adhesion was highly dependent on formulation, penetration of the coatings into wood, and mechanical anchoring. Increasing the content of solid particles in the coating formulations or adding a polyol (glycerol, xylose), which probably acted as a coalescent, considerably decreased the adhesion strength, probably by blocking penetration into the wood by forming aggregates. Adhesion was improved by pre-mineralization of the surface, and substitution of a part of the potassium silicate binder with potassium methyl siliconate reduced the formation of cracks caused by dimensional instability of the wood.

Keywords: coating; silicate; water glass; wood; potassium methyl siliconate; adhesion

 

CHEUMANI-YONA, Arnaud Maxime, ŽIGON, Jure, PAVLIČ, Matjaž, PETRIČ, Marko. Potentials of silicate-based formulations for wood protection and improvement of mechanical properties : a review. Wood Science and Technology. 2021, vol. 55, iss. <v tisku>, str. 1-32, ilustr. ISSN 0043-7719. https://link.springer.com/article/10.1007/s00226-021-01290-w, DOI:10.1007/s00226-021-01290-w. [COBISS.SI-ID 62099971], [JCR, SNIP]

Abstract

Silica or silica-precursor systems are attractive for wood protection against biotic and abiotic damages, and improvement of fire resistance. Alkali metal silicate solutions, also known as water glasses, colloidal silica (nanosilica dispersions) and other inorganic-organic hybrids resulting from the sol-gel chemistry of alkoxysilane compounds are products available for this purpose. These chemicals are increasingly considered to formulate wood modification products or to develop surface coatings. This review article is focused on in-depth treatments of wood through dipping, soaking or vacuum-pressure impregnation methods. The techniques used to convert monomers and low molecular weight silicate species in water glasses into less soluble and leaching-resistant silica particles, such as heat treatment, acid treatment and reactions with multivalent metal cation salts are discussed. The similarities and differences between the various raw-impregnation materials and the properties of the final products are highlighted. Water glasses after appropriate curing, colloidal silica and tetraalkoxysilane-based formulations all lead to deposition of silica particles (SiO2) at the surface of the cell walls, in lumens and pores. Low molecular weight organosilanes and other organo-modified formulations that are able to penetrate the wood cell walls and react with wood components are good dimensional stabilizers. The treated wood exhibits in general increased mechanical properties (strength, hardness) and improved resistance to biodegradation and fire retardancy. The efficiency of the treatments can significantly be enhanced to a level fulfilling the requirements for industrial applications by the addition of biocides, ultraviolet absorbers or antioxidants, fireproofing compounds (boron or phosphorus-based compounds, multivalent metal salts) and hydrophobic alkylalkoxysilanes. Silica acts as a barrier/support to many of these additives preventing them from leaching.

Keywords: Colloidal silica, fire resistance, impregnation, water glass, wood