WOODEN GLUE TYPES

For Plywood manufacturing technology, glue plays a decisive role in quality and production cost. The development of wood glue is also the development of plywood production technology.

1.  Definition

Wood glue is an adhesive to bond the glued materials (filler board), under the appropriate temperature and pressure conditions of the production process, the glue films will harden, shape the glued objects into product blanks plate form.

The curing process is the process by which the glue changes from a solution state to a solid state. This process is promoted by some or all of the following factors: Evaporation, osmosis of the solvent makes the concentration of the solution constantly increase (PVAc milk glue); Glue were heated and colded (thermoplastic glue: EVA; EEA); The chemical reaction produces water particles and evaporates to harden the glue (thermosetting glue: PF; UF; MUF).

2.  Adhesive quality

The leading factors affecting to the quality of glue and glue films of plywood products include:

Adhesive object factor(wood):

Type of wood, wood texture, surface quality, wood temperature, wood moisture and wood pH (compatible or not with the acidity or alkalinity of the glue used) ;

Glue factor:

Type of glue, amount of glue used, quality of glue, …;

Gluing temperature:

Reasonable high temperature softens the wood grain, ensures the best physical and mechanical properties of the wood and accelerates the curing process;

Pressing pressure:

Appropriate pressure for each type of glue, each type of wood will help the glue and glue have close contact, the glue will flow evenly on the surface of the material, penetrate into the voids,… continuous glue film;

Pressing time:

The time required to maintain the temperature and pressure to obtain the best adhesive strength. Pressing time depends on temperature, humidity, product thickness,…;

Environment and usage:

Factors of humidity, temperature of the environment as well as the way of use contribute to the longevity of the product.
Among the factors listed above, adhesive of glue is a factor that can be actively controlled in terms of quality, quantification and standardization to produce plywood products of the desired quality.

3.  Glue classification

Artificial glue products are very rich, with diverse and complex chemical compositions, the same glue products but there are many ways to distinguish and name them differently.
Here are some common classifications: By origin of materials; according to the curing mechanism; according to durability; according to the properties of joints and characteristics of use, classified according to DIN EN 12004 standards; …
In this post, we mainly talk about plywood products used as construction materials and supplies, so we only learn about how to classify glue according to the curing mechanism, specifically:

3.1. Thermoplastic glue:

It is a type of glue that retains the fiber form after increasing the heat. When the glue receiving heat softens or melts, it can return to its original state after cooling, this phenomenon is repeated many times. No chemical reaction occurs during bonding, heating or cooling. The most commonly used thermoplastic adhesive is Polyvinyl acetace (PVAc); Polyamide (PA),…;

3.2. Thermosetting glue:

A type of glue that can’t return to its original state after solidify (no reversible reaction).
This colloidal molecule, after solidify, forms a spatial network structure. This glue has UF glue; PF; Epoxy, MF,…;
Glue type Field of application Curing mechanism/time Main advantages/disadvantages
Thermoplastic glue
Protein and starch Furniture and decorative wood
  •  Evaporate water;
  • About 2-4 hours.
  • Fill the voids;
  • Not resistant to moisture
Tannins and thermoplastic lignin Furniture 
  • Heat solidify
  • Need to mix with other glues.
Casein Furniture wood 
  • Evaporate water;
  • About 2-4 hours
  • Cheap cost;
  •  Not resistant to moisture
Polyvinyl Acetace Furniture wood
  • Evaporate water;
  • From 40 min.
  • Easy to use
Glue from rubber plastic Gluing wood to metal, plastic, glass
  • Solvent evaporation
  •  Adhesive immediately upon contact;
  • Low durability
Hot Melt Glue Edge gluing, plastic coating in high-speed line
  • Solidify when cooled.
  • Adhesion strength decreases at high temperature.
Polyvinyl Acetace Catalyst Interior and exterior furniture
  • Evaporate water;
  • From 40 min..
  • Easy to use
Thermosetting glue
Phenol and Resorcinol formaldehyde Production of artificial boards (glued, chips, fibers, …)
  • Solidify 2 minutes at high temperature and 6 hours at room temperature.
  • Waterproof;
  • Price matching.
Urea and  Melamin formaldehyde Production of artificial boards (glued, chips, fibers, …).
  • Solidify 2 minutes at high temperature and from 30 minutes to 12 hours at normal temperature..
  • Waterproof;
  • Price matching.
Epoxy (2 components) Laminating products that require high durability (wood, metal, ceramic, plastic)
  • 5 minutes at ambient temperature
  • Hight durability
  • Moisture resistant, heat resistant
  • Hight price

Currently, in the plywood industry, the most commonly used glues are thermoset adhesives because of their advantages of reasonable price, supply to meet the industrial scale, suitable for production methods.

Among these glues that are prominent and used a lot in the production of Film Faced Plywood water-resistant plywood are Phenol Formaldehyde (PF), Melamine Formaldehyde (MF), we will learn more about these glues in the private post.

  Reference sources: WOODEN GLUE – Assoc. Prof. Dr. Pham Van Chuong, Dr. Nguyen Trong Kien, Vietnam Forestry University.