SinodosChemistry

 

Furniture and other wood products require refurnishing and protection against aggressive environments. Refurnishing and protection means attempt to minimize effects of various factors on wood quality. Most important of these factors include moisture, solids, oil stains, scratches of mechanical origin, degradation due to UV radiation and heat degradation effects. These factors tend to degrade wood quality in a number of ways:

- Water most often is absorbed into the wood composite and leads to local swelling which is irreversible. Such swelling can cause loss of mechanical strength, loss of breathing effect, opening of cracks, hydrolysis of ester bonds and other undesired effects. Water also initiates color loss due to adsorption and absorption of inorganic agents [such as metal oxides] that are not covalently bond on the surface. Other effects include formation of fungus or appearance of bacteria populations.

- UV radiation [and other sources of radiation] provokes reversion of cross linking and de-polymerization of the composite structure and/or the coating itself. UV radiation offers the required energy to initiate a series of undesired reaction that lead to destruction of the nano and microstructure and thus eventually of the appearance and mechanical properties of the wood surface and body.

- Oil coming in contact with wood or coated wood surfaces can lead to stains and loss of color in the case of organic based dyes. Oil also degrades the composite surface via interaction with acidic functional groups and leads to permanent flaws on the surface.

- Solids affect wood surfaces in two ways: abrasion and stains. Stain formation is a function of absorption kinetics and permanent bond [covalent] formation between the solid and the surface functional groups. Abrasion is commonly observed when nanosized particles of solids come in contact with the surface.

- Heat as other forms of energy [radiation] initiate degradation and de-polymerization. Composite structure loses mechanical strength due to cross linking disruption and pores are locally widened. The change of structure and the opening of spaces worsen the effects caused by other factors such a water or oil presence.

To protect wood’s surfaces from the above factors, various protection coatings approaches have been utilized. In general the properties that need to be added or enhanced in order to increase the life time and chemical and mechanical properties of a wooden [or similar] surface are:

Hydrophobicity. Hydrophobicity protects wood against moisture by minimizing contact area of water droplets with the surface. Hydrophobic surfaces have contact angles larger than 90 degrees and super hydrophobic surfaces have contact angles of more than 120 degrees. Hydrophobicity occurs via two routes: surface roughness and surface chemistry. Both of these factors lead to minimization of surface energy.

Oleophobicity. Oleophobicity creates surfaces with contact angles similar to those of hydrophobic surfaces, but for oil droplets. Again, the surface energy is a function of functional groups and surface roughness. When a surface is both oleo and hydro phobic, it is called amphi phobic and it cannot be affected by either of the two factors

Slide angles. Slide angles govern the kinetics of stain formation and color loss; they are a measure of whether a drop or viscous material drop slides away from a surface or stays on the surface, thus providing sufficient time for covalent bond formation and staining.

UV reflection/ adsorption. Different approaches enhance this attribute; either reflective coatings are used or radiation absorbing structures are utilized to minimize the effects of falling UV radiation on the surface of wood.

Other mechanical properties are enhanced via either extensive cross linking on the surface or the use of nanoparticles and other agents that provide anti scratch [mainly] character on the surface.

Thermal resistance. This attribute is enhanced by adding polymers with higher thermal resistance than wood or used composite and my adding insulating polymeric films on the surface.