Waterborne Adhesives and Sealants and Major Classes

Waterborne Adhesives
Waterborne Adhesives

Waterborne Adhesives are very popular and are conceived as an environmentally friendly and economically viable alternative to solvent-based adhesives. One of the major advantages of water-based adhesives is the absence of volatile organic compounds (VOCs). Furthermore, water can be used to clean the excess adhesive off of mated parts and to clean the equipment. These adhesives are usually considered very environmentally friendly.

For this class of adhesives, a wide variety of polymers are used (usually thermoplastics and/or elastomers), which are either dispersed or dissolved in the continuous aqueous phase.

Water-based adhesives can be divided into major classes:

Water-Based Solution Adhesives

These Waterborne Adhesives harden and build strength when the water evaporates or when it is absorbed by the substrates. After the application of the adhesive, the substrates must be bonded while the adhesive is still wet. Waiting for some time to evaporate some of the water prior to bonding (set time) will usually increase the initial strength of the adhesive bond and it also allows for quicker assembly. These adhesives are formulated with natural and synthetic polymers that readily dissolve in water. They harden by evaporation of water or by absorption of water into the porous substrate.

Water-Based Polymer Dispersions/Emulsions

Water-based dispersion adhesives are formulated with a larger number of polymers including vinyl acetate polymers (PVA) and copolymers (PVAC), ethylene-vinyl acetate (EVA), polyacrylates, natural rubber latex, and synthetic elastomers such as styrene-butadiene rubber (SBR) and polyurethane (PUR). Like latex paint, these adhesives are heterogeneous mixtures consisting of a dispersed liquid or solid polymer phase in an aqueous phase. They can be applied by brush, roller, spray, or in beads. The wet adhesive can be easily removed with water. However, the dried adhesive is usually no longer water dispersible and requires either solvents and/or mechanical cleaning.

Similar to solvent-based adhesives, emulsion/dispersion adhesives can be classified as either wet or dry bonding:

Wet Bonding Adhesives

These adhesives harden and build strength when the water evaporates. After the application of the adhesive, the substrates must be bonded while the adhesive is still wet. Waiting for some time to evaporate some of the water prior to bonding (set time) will usually increase the initial strength of the adhesive bond and it also allows for quicker assembly. However, waiting too long, i.e. evaporating too much water, will result in poor bond performance because the adhesive will no longer be wet. Full bond strength is obtained after the remaining water is fully evaporated or absorbed by the substrate. Since the water has to be able to evaporate after bonding, at least one substrate has to be porous; otherwise, hardening will be rather slow

Contact Adhesives

As with solvent-based contact adhesives, both substrates are coated with adhesive, and the water is allowed to evaporate before the parts are bonded. Some contact adhesives require up to 24 hours to fully dry. The parts are then mated using only light pressure to ensure intimate contact between the two adhesive films. The adhesive has to have sufficient tack to provide some bond strength. In many cases, there is no need for clamping. Contact adhesives have much higher initial strength and generally also have higher final strength. They also have better heat and creep resistance than wet bonded Waterborne Adhesives.

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