Aracet, wood glue or PVA adhesive: characteristics, properties, frost resistance

The most commonly used adhesives for wood joining are polyvinyl acetate-based adhesives, which many call aracet (I'll tell you where the name comes from). They get on so well with wood that they are often called adhesives for wood, without specifying the type. There are different types of such adhesives, ranging from used for DIYto industrial products used for joining massive panels or of stuck objects standing outside. The problem with these adhesives is that, being water-based, they freeze at temperatures below 0ºC. About the characteristics and uses of these adhesives, their behaviour in cold weather and the changes that occur when the temperature drops very low, and about a frost-resistant adhesivethat can be used without risk and after thawing I will talk to you further.

What is a polyvinyl adhesive (PVA)

PVA adhesives are aqueous dispersions of polyvinyl acetate. Dispersion means that the polyvinyl acetate molecules are not dissolved in water but float in it. When the water leaves the system (for various reasons) the molecules react with each other - polymerise - and form the adhesive.

Polyvinyl acetate molecules also result from a polymerisation process, when several smaller acetate molecules bond together. Yes, it's chemistry, and it's usually scary. But I promise it doesn't take long and all this explaining is for a purpose. I said at one point why polyurethane varnishes are more resistant than other varnishes. Something similar happens here. Polymerisation involves several small elements bonding together to form a larger molecule. Polyvinyl acetate molecules are linear and can be of different lengths. When the water disappears, the molecules come together and react with each other to form a very strong three-dimensional network, and so the pieces of wood stick together. The strength of the glue film depends on the ability of the molecules to bind to each other in as many different ways as possible. This is where manufacturers come in to make adhesives more resistant to tensile stress, compression, moisture, UV radiation or weathering.

Adhesives of this type were invented in 1912 by the German chemist Fritz Klatte. In Romania, the adhesive was produced at the Cominatul Chimic Râșnov under the name Aracet, an abbreviation of the Romanian (R) acetate-based adhesive (ACET). Although it is a brand name, the name has become synonymous with wood glue and is used to name PVA adhesives.

Characteristics of PVA adhesives

They are among the most widely used for gluing wood and wood-based boards such as plywood, chipboard or MDF. Ease of use, the fact that they are water-based and many other qualities lead many in both industry and DIY to use them. The convincing features are:

• have no odour or colour that could influence the final appearance of the work
• are water-based and non-toxic
• do not yellow over time
• are flexible and retain flexibility over time
• are pH neutral
• does not give off dangerous gases during the process, even when soldering is hot
• in most cases become transparent after gluing.

PVA adhesives do not only bond wood but also paper or textiles. For best adhesion and bonding, materials must be porous. Or at least one of them. Porosity helps because the adhesive gets into the material and anchors itself very well to it. Porosity also allows water to escape which leads to bonding.

Influence of temperature. How to identify an adhesive that has gone through a freeze-thaw cycle

Adhesives are influenced by both high and low temperatures. At high temperatures the water in the dispersion starts to leave the system and allows molecules to come together and react. Therefore, storage at high temperatures is not recommended, nor do they have a very long shelf life. Over time, the water-polyacetate balance can break down and then the adhesive polymerises in the packaging and can no longer be used.

At low temperatures adhesives, being aqueous dispersions, freeze. This can affect them in two ways. On the one hand, freezing can upset the equilibrium and cause the polyacetate molecules to react. On the other hand, the ice crystals formed can interfere with the bonds of the polyvinyl acetate molecules, breaking them apart and thus losing their adhesive properties.

Many PVA adhesives lose their properties after a freeze-thaw cycle. Sometimes, when viewed in the original packaging, it looks like nothing has happened and it can be used. But if used the glue line will have no strength and will crack when the object is used. As you know, a glued object should never fail on the glue line. If it is subjected to forces then the failure must be in the wood.

A good glue should be free flowing, not sticky or crumbly, like homemade cheese (sweet cheese). If the viscosity has increased, the adhesive should be shaken. If it does not become fluid and free of lumps, it is not good for use. Another way to check is to put a small amount on a surface and let it harden. If the appearance is chalky, the adhesive is no good. Also, if instead of becoming transparent it becomes whiter and chalky, then the adhesive is compromised and cannot be used.

Frost-resistant adhesive

However, there are also adhesive that withstands even several freeze-thaw cycles and can be used afterwards. This is the case with adhesive TISZABOND D3-D 3011, fromSzolvegyfrom Târgu Mureș. It is an adhesive developed for a customer in Miercurea Ciuc, the pole of cold weather in our country. The risk of the adhesive freezing in the warehouse during the winter was very high, so the manufacturer was asked to help develop a product that would work even after freezing. Szolvegy succeeded in this, with the customer using the adhesive for two winters already.

TISZABOND 3011 is a D3 adhesive which can be used for both carpentry and construction work. It can be used for gluing objects used indoors in high humidity conditions, but also outdoors in sheltered or moderate climate areas. When needed,can be processed into D4 adhesive by adding a cross-linking agent (D3D4).

Recommendations that could help you

If you work with wood and use polyvinyl acetate-based adhesives, here are some recommendations and tips:

• Unhardened adhesive is easy to clean with warm water (possibly with detergent) unlike hardened adhesive which is quite difficult to remove. If glue has fallen on the wood or excess has come out wipe it off while it is still fluid.
• The adhesive cures faster in areas where there are draughts. Ventilation helps to remove water faster and trigger the polymerisation reaction.
• If you glue different materials together, at least one of them must be porous (wooden steps on a concrete staircase, for example).
• Moderate pressure speeds up curing. Clamping in clamps or presses forces the glue deeper into the wood which results in a faster and stronger bond.
• High temperature, dry wood and low humidity decrease the reaction time, while low temperature, high humidity of the wood and the working environment lead to a longer curing time.
• Diluted glue solution (1:1 with water) can be used to seal the fiber ends to solid wood. This is the way to reduce absorption and prevent staining when tapping.
• It can be used in combination with wood dust to make putties used to repair small defects in wood (holes, scratches).

Polyvinyl acetate-based adhesives are simple to use and affordable. They can be used in industry, construction or household and DIY projects. And don't forget! If you need a frost-resistant one, they exist and are already tested.