Getting confused with the glue your supplier is manufacturing the plywood with?
Why plywood are different in formaldehyde emission?
Where some plywood are waterproof?
This article give you full insight into the content of plywood in every aspects.
- Phenolic UF Resin (Exterior)
- Urea-formaldehyde Resin(Interior)
The resin polymers are the key elements that make the glue sticky. More than 80% of plywood glues are made with Urea-formaldehyde resin.
Phenolic UF resin is great for making exterior plywood and marine plywood. Its usage is limited because of its dark colour and high prices.
2. Curing Agent (Hardener)
Curing agent can help reduce the PH of adhesive and fasten the curing of glue in production. In order the reduce the PH, curing agent must be acid.
A too strong acid is not good for glue curing too. It can make the curing time too short and harm the production process.
Best curing agent keeps glue PH at 4-5 and curing time 35-45 seconds. A weak acid can do this job well. Ammonium Chloride is a perfect curing agent for plywood thanks to below reasons:
- Cheap price
- Water Soluble
The percentage of Ammonium Chloride in the glue shoud stay 0.1% – 1.2% according to press types, wood species, glue characteristic, climate, etc. Shall not exceed 1.5% at any circumstances.
Fillers in the adhesive can reduce glue consumption, increase Initial viscosity and bonding strength. It can prevent the glue to immerse too deep into the veneers. It also helps to reduce formaldehyde emission.
There are a few criteria to be a filler in plywood glue. Chemical PH value should be netural or close to 7. It can absorb water and cure after water evaporate.
Typical filler for plywood glue are:
- Wood powder
- Soy powder
- Nutshell powder
- Hydroxymethyl cellulose (HMC)
Modifier is used to modify the adhesive and increase its performance.
4.1 Formaldehyde scavenger
Formaldehyde Scavenger is added directly to plywood glue to reduce formaldehyde emissions from plywood, and formaldehyde odor in factories.
Toughners reduce the brittleness of the glue line, increase the toughness, and improve the aging phenomenon of the adhesive layer. PVA and Polyvinyl Acetate are common toughners used in plywood glue.
4.3 Water repellent
Urea-formaldehyde can be polymered with Phenol, resorcinol, melamine, thiourea, tannin to get Phenol-Resorcinol-formaldehyde adhesive. This glue is a true WBP glue for production of structural and exterior plywood.
5. Other Additives
- Foaming agent
- Surface active agent