Even though industrial adhesives and sealants share many characteristics, they aren’t structurally and chemically identical, and can’t always be used interchangeably.
Generally, a sealant is a viscous material which becomes solid when applied and it creates a barrier. The barrier provided by the sealant prevents the penetration of many different elements, like fire, noise, air and liquid, depending on the sealant’s nature. Sealants are usually used to close the gaps that adhesives can’t.
An adhesive on the other hand, is used to bond items together and it can be either in a liquid or a powder state. It oftentimes requires a specific temperature to “cure” the bond, and it is most commonly used to bond thin materials. The stronger sealants sometimes qualify as adhesives, but the weaker types usually fill the space, such as sealant putty.
Moreover, industrial sealant and adhesives differ in terms of how additives affect their physical and chemical composition. Additives are categorized based on the type of function they perform instead of their composition, and even though industrial sealant and adhesives have similar chemical characteristics, they oftentimes require separate additives.
When using a sealant, you’ll usually need a stabiliser as well. The right stabiliser will depend on the components of the mixture and its sole role is to prolong the life-span of the sealant and to help improve its properties. Plasticisers are also commonly used in latex sealants, where the main base ingredient is vinyl acrylic. Polyurethane sealants on the other hand, use plasticisers to soften the mixture, and in that case benzoates are usually added.
On the other hand, when you use an adhesive, you’ll usually need to add a catalyst to enable the cross-linking and polymerisation. When using epoxy adhesives, the catalyst will usually include anhydriders and amines. Reactive acrylic adhesives use peroxides and UV adhesives usually include photo-initiators.
Adhesives that add colour (colourants) are also sometimes added to adhesives, and they usually include pigments and dyes like titanium oxide coated particles of mica. Similarly to when combined with sealants, plasticisers increase the workability and flexibility of adhesives. For instance, benzoate plasticisters are added to latex adhesives as they work great in conjunction with their base ingredients (polyvinyl acetate and ethylene-vinyl acetate). Most hot melt adhesives however, don’t require any plasticisers. Lastly, fillers are used to enhance the material’s properties, they’re typically used with both sealants and adhesives and include talc, silica, mica, alumina, and calcium carbonate.