Adhesives used for Plywood manufacturing process - lceted

Plywood is made by glueing / bonding multi-layer wood veneers (thin pieces/layers of wood) to each other. These thin pieces are obtained by rotary cutting or cutting wood logs. Rotary-cutting is the most common and involves rotating wood veneers using a large lathe-like machine, while a cutter peels the layers from the logs. while a cutter peels the log at the set thickness (each layer is usually less than 2.5 mm in thickness).

 

Then, using a glue-spreading machine (the machine helps to achieve a uniform glue distribution) the adhesives are spread on these veneers.

 

After this, the layers are placed one on top of the other and pressed together using a hot pressing machine. The high temperature and pressure created by the machine ensure that the adhesive fully cures, thus bonding the layers firmly to each other.

 

The number of layers in each plywood sheet varies depending on the need (3-ply, 5-ply, 13-ply, etc.).

What type of glue is used in making plywood?

Two main types of glues are used to make plywood, 'urea formaldehyde' and 'phenol-formaldehyde.

 

1. Urea-formaldehyde resins:

These are a type of adhesive (glue) called aminoplastic synthetic resins. These pastes are cheaper than phenolic formaldehyde, produced by the chemical reaction between urea and formaldehyde.

 

Commercial MR grade plywood (moisture resistant type) is often made using this type of adhesive.

Also Read: Types Of Wood Used For Making Plywood | Lceted

 

2. Phenol formaldehyde resins.

Phenol formaldehyde resins are synthetic or artificial polymers produced by a chemical reaction between 'phenol' and 'formaldehyde (methanal)'.

 

The ratio of formaldehyde and phenol is usually 1.5:1. These types of phenolic synthetic resins are known as 'resoles'.

 

Sometimes extensions are added to the adhesive mixture to reduce the total cost and the amount of adhesive that can penetrate through the individual veneer layers.

 

Also read: How Strong Is Plywood to make furniture? | Plywood Strength Comparison with Other Wood Products

 

Formaldehyde health risks

In recent years, many concerns have been raised about the potential health risks posed by formaldehyde emissions, and the general consensus is that high emissions may pose some health risks to humans.

 

As for plywood, the synthetic resins used contain formaldehyde, so it cannot be considered as environmentally friendly as natural solid wood. However, another important point, in this case, is that the emission decreases significantly over time. The proper finishing, such as painting or using laminates, can help make the product more secure for people to use.

Also Read: BWR Plywood Vs. Marine Plywood | Differences Between BWR And Marine Plywoods - Lceted

 

Also, nowadays more eco-friendly types of adhesives (formaldehyde-free) are being researched all over the world to counter this concern.

 

Moreover, nowadays eco-friendly types of glues (non-formaldehyde) are being researched around the world to address this concern.

 

Phenolic resins exhibit stronger bonding compared to urea-based resins, so they are used in the manufacture of exterior grade plywood (BWR-boiling water-resistant) and marine-grade plywood.

Also Read Woodworking Materials Guide for Beginners! | Woodworking Handbook

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