How many different types of adhesives are there?
Adhesives have been around for an incredibly long time, with evidence of their use dating back over 200,000 years. Our ancient ancestors recognized the adhesive properties of birch pitch, which they obtained through dry distillation. This primitive glue was used by Neanderthals and early humans to bond wood and stone together when making tools, at least 45,000 years ago
- Wet adhesives
- Contact adhesives
- Reactive adhesives
- Hot-melt adhesives
- Pressure-sensitive adhesives
- Superglue
The use of adhesives continued to evolve over the millennia. Around 6,000 years ago, the ancient Mesopotamians used asphalt as an adhesive for constructing temples. A thousand years later, the Sumerians utilized animal blood, proteins, and boiled animal skins to create adhesives.
The Egyptians, too, employed animal glues for veneering work around 3,500 years ago. In ancient Greece, the profession of glue-maker emerged, with the word “kolla” for glue still used in the Greek language today.
The importance of adhesives in Europe increased significantly with the advent of letterpress printing around the year 1500, as glues made the production of books possible. The first dedicated glue factory opened in the Netherlands in 1690.
Modern adhesives as we know them today have their origins in the late 19th and early 20th centuries. In 1888, a master painter named Ferdinand Sel from Hanover developed the first ready-to-use wallpaper paste. Several patents for synthetic adhesives followed in the early 1900s, culminating in the development of a clear, synthetic resin adhesive in 1932, which is still sold in yellow tubes.
Other milestones in adhesive technology include the patenting of transparent adhesive tape in 1940 (developed in 1935), the discovery of superglue in 1942, the production of adhesives for metal and plastics in 1960, the launch of the first glue stick in 1969, and the introduction of sticky notes in 1980.
While the first adhesive patents of the early 20th century marked the beginning of a century-long transformation, the real adhesive revolution gained momentum when our parents and grandparents were young. This is a relatively recent development compared to the over 200,000-year history of adhesive use. As of 2008, there were over 30,000 different adhesives from over 1,500 companies, and the development of new adhesives continues unabated.
Wet adhesives
One example of wet adhesives is “3M Super 77 Multipurpose Adhesive“. This adhesive is a solvent-based aerosol adhesive that provides a strong bond for lightweight materials such as fabric, foam, and plastic. It is commonly used in industries such as automotive, construction, and crafts.
solvent-free wet adhesives
In solvent-free wet adhesives, water acts as the carrier substance. For adhesives containing solvents, various solvents can be employed, which influence the rate at which the adhesive develops its bonding strength. This process occurs gradually as the solvent or water evaporates, meaning that the bonding time is also affected by the materials being joined.
Not all water-based adhesives include the words “water-based” on the label, yet federal law requires that solvent-based adhesives be clearly labeled with that information. Instructions for the proper use of those products also must be included on the label.
Solvent-based adhesives
Solvent-based adhesives are particularly useful when a rapid bond is required.
For example, they can prevent wrinkling or corrugation caused by moisture absorption in paper or cardboard, or when bonding non-porous materials such as metals, hard plastics, or ceramics.
In these applications, resins or rubbers dissolved in alcohol or acetone are often used. The adhesive strength is achieved through the evaporation of the solvent.
With impermeable materials, the liquid can only escape laterally, potentially taking some time during which the bonded parts should remain undisturbed if possible. For such materials, it is advisable to use a narrow, elongated adhesive surface to ensure uniform solvent evaporation through the lateral gap.
Porous materials like cardboard, wood, or leather allow the solvent to escape easily through the material itself. Solvent-free wet adhesives are particularly suitable for these applications.
Here’s all about surfaces:
Porous Surfaces
Porous surfaces are those that absorb liquids quickly and evenly. Examples include unfinished soft woods, uncoated paper, fabric, unfinished plaster, air-dry clay, and dried plant matter.
Semi-porous Surfaces
Semi-porous surfaces absorb liquids slowly and unevenly.They include sealed soft wood, hard wood, coated paper, treated fabric, craft foam, and sealed plaster.
Non-porous Surfaces
Non-porous surfaces are often slick and shiny and do not absorb liquids.Types of nonporous surfaces include painted or varnished wood, glossy paper, painted or varnished plaster, hard plastic foam, polymer clay, acetate, acrylic, glass, and metal.
With permeable materials like wood, the solvent can easily evaporate through the material, allowing for uniform curing of the bonded area. In contrast, for impermeable materials, the solvent must escape through the sides of the adhesive joint. Additionally, it is advisable to apply the wet adhesive to only one of the two parts being joined together.
When Using Solvent-based Adhesives, Remember…
Adhering to proper usage guidelines is crucial when handling these products, as many possess flammable properties. Carefully review and comply with all label instructions.
Upon completion of use, securely fasten caps and lids, storing the products out of children’s reach. To maintain the integrity of warnings and instructions, refrain from transferring the products from their original containers to alternative ones.
Under no circumstances should solvent-based products be handled by children; their use should be restricted to products explicitly labeled as “safe” or “suitable” for children.
Expectant mothers are advised to steer clear of solvent-based products, while nursing mothers and individuals with severe allergies should exercise extreme caution when selecting products for use.
Federal regulations mandate that companies producing glues and adhesives furnish a Material Safety Data Sheet (MSDS) upon request. If you harbor any uncertainties regarding the appropriate use of a product or wish to ascertain if it may pose a health risk, reach out to the company to procure the product’s MSDS.
Contact adhesives
Contact bonding differs from wet bonding in that the adhesive is applied in a thin, even layer to both surfaces that need to be bonded.
Before joining the two parts, the adhesive surfaces are allowed to remain exposed, allowing the solvent to evaporate. The duration of this process is influenced by the thickness of the applied adhesive and the type of solvent used. Only when the adhesive no longer feels tacky to the touch should the parts be carefully positioned on top of each other and aligned as desired.
Following this, the parts must be firmly pressed together for a brief period. In contact bonding, the strength of the pressure applied is more critical than the duration of the pressing. If the contact bonding process is executed properly, the parts cannot be realigned afterward. The bonded areas quickly achieve a high level of strength and remain flexible even after drying.
This flexibility makes contact adhesives particularly well-suited for materials that require ongoing pliability, such as shoe soles. Another common application for contact adhesives is in large-surface processing, including veneering.
Reactive adhesives
One example is the Loctite Epoxy Plastic Bonder. It is is a two-component epoxy adhesive that comes in a double-barrel syringe, making it easy to dispense and mix the two parts (resin and hardener) together.
Reaction adhesives are usually so-called two-component adhesives. This means that the adhesive is delivered in two tubes, the binder and the hardener. The individual components can be liquid, powder or paste. The binder and hardener are mixed in the required quantity and ratio immediately before use.
As soon as both components come into contact with each other, the curing process begins. This leaves only little time to process the adhesive. The curing time depends on the type of adhesive. Processing times of around one to several hours are common. The ambient temperature also affects the processing time available. A working temperature of around 20° C is ideal.
One-component adhesives come ready to use. They contain a non-active hardener that does not react under normal conditions in the packaging. The curing process only begins when they come into contact with the second reaction component. Depending on the nature of the adhesive, this can be atmospheric oxygen, UV light or humidity. One-component adhesives must be applied to one side of the bonded area.
Hot-melt adhesives
One example is the Cir-Cut Archery Super Grip Hot Melt Glue Stick.
The best-known example of this is the hot glue gun. Depending on the system, the melting point is between around 110° C and over 220° C.
Pressure-sensitive adhesives
They are used where an adhesive bond can be removed at any time. This means that they only play a minor role in model making, for example, as they hardly achieve the stability needed to keep a model aircraft in operation for a long time. “Hold together”. Adhesives include adhesive banks, post-it- notes and self-adhesive labels.
Superglue
Superglues are preferably used for repair purposes, as they have the myth of providing particularly strong and long-lasting bonds. In fact, cyanoacrylate adhesives are neither moisture-resistant nor temperature- stable.
This means that bonds made with them can easily come loose again. This property is also used in medicine, albeit with “instant adhesives” designed for this purpose. In addition, superglues only worked really well if only small areas are bonded with them. Superglue bonds can also be removed with nail polish remover containing acetone.
I’m Ronald Stevens, a Mechanical Engineer obsessed with adhesives, glue, and all things sticky! My passion began in childhood when I’d always be the one playing with glue during arts and crafts. And I’d spend hours researching and experimenting. Happy reading, and remember: stick with the best, and you’ll never be stuck in a mess!
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