Plywood Glue adhesive : Polyurethane adhesives

Plywood Glue adhesive : Polyurethane adhesives

Polyurethane adhesives
Polyurethane (PUR) adhesives are isocyanate-based systems. While these
adhesives are not traditionally used in the manufacture of veneer products they
have been adapted for some applications, particularly in Europe, and are gaining
popularity.
Advantages of PUR adhesives are:
◆ most are thermosetting polymers and do not soften when heated (at least in
normal service conditions);
◆ they can be effective for bonding a variety of materials including wood,
metals, rubbers, cured epoxy, leather, tile and glass, many plastics, concrete
and brick;
◆ they do not emit formaldehyde;
◆ they work effectively within a higher range of veneer moisture content;
◆ they are used mainly as cold-setting adhesives which makes them suitable for
production facilities where heated presses are not available or for products
where heat transfer is challenging due to product dimension (such as glulam,
multilaminar wood and finger-jointed products);
◆ they are suitable for products used in weather exposed applications as they
have good UV resistance and are durable;
◆ a wide range of systems are available offering varying curing times providing
flexibility in production applications;
◆ they produce clear or white glue lines.
Disadvantages of PUR adhesives are:
◆ they can have a limited shelf life, especially once opened and exposed to the
atmosphere;
◆ they require the use of solvents (e.g. acetone, thinners) for cleaning
application equipment and cleaning must take place while the adhesive is still
uncured;

◆ curing times can vary considerably due to their sensitivity to humidity and
veneer moisture content;
◆ performance may be compromised in extreme temperatures;
◆ they can be unsuitable for high density (>750 kg/m3
) hardwoods in external
structural applications

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