Which is stronger: Glue or tape?

The oldest sticky stuff in the world is more than 8,000 years old, and it was found in a cave near the Dead Sea. In ancient times, people used this sticky substance, which they made from mixing animal bones and plant stuff. They used it to keep their baskets waterproof and build tools. For thousands of years, people relied on natural materials from plants and animals to stick things together. Nowadays, we have many types of tape and glue for building and fixing stuff. But what makes glue and tape sticky, and is one stronger than the other?

Glue and tape stickiness can come from either man-made molecules or natural proteins and carbs, like dextrin from vegetables, casein from milk, and terpenes from tree resin. For glue and tape to work, they need two kinds of bonds: one to stick to the surface and another to hold themselves together. Most glues have adhesive polymers mixed in a liquid that keeps them from sticking inside the bottle. The strong smell of some glues comes from this liquid, which evaporates when it touches air. Some glues use water as a liquid, but others use chemicals that can be harmful to breathe. Glues with more than one part that chemically react instead of just drying can create stronger bonds. Both adhesive and cohesive bonds in glue are strong, but once it dries, you can't easily put things back together if they break.

On the other hand, when you apply tape to something, it forms weaker bonds that you can undo. The stickiness of tape comes from something called Van der Waals forces, which can happen between any two things but only when they're super close together, too close for the naked eye to see. Tape usually has a backing with a rubbery part and a sticky part called a tackifier. When you press tape onto a surface, the sticky part flows into tiny gaps and stays there, forming these Van der Waals forces. This is called viscoelasticity. It's easy to peel tape off a surface and use it again because of these weak bonds.

In terms of pure strength, glue bonds are stronger than tape, but there's no single adhesive that works best for everything. Super glues might make the strongest bonds, but two-component epoxy glues are much better with heat and heavy-duty tasks. So, it depends on what you need to stick together. If you want to hang an anvil in the air, super glue is the way to go. But if you're doing it over an active volcano, epoxy is the better choice. Also, glues need surfaces that touch each other to work, while tape can be handy for odd jobs like connecting bowling balls.

Engineers consider all these factors when choosing the right adhesive for specific tasks. Picking the right glue for an engine's extreme conditions can be a life-or-death decision. And even though duct tape can't compete with epoxy glues in terms of strength, it has the advantage of sticking instantly in emergencies. While glue may be essential for launching rockets into space, duct tape is the go-to for repairs in zero gravity when you're out there among the stars.