Which is stronger: Glue or tape? - Elizabeth Cox

The oldest glue in the world is over 8,000 years old 00:11 and comes from a cave near the Dead Sea. 00:14 Ancient people used this glue, 00:16 made from a mixture of animal bone and plant materials, 00:20 to waterproof baskets and construct utensils. 00:23 And for thousands of years after, 00:25 plants and animals were the glue that held human civilization together. 00:29 Today, we have enough types of tape and glue to build and repair almost anything. 00:34 But what gives glue and tape their stickiness? 00:38 And is one stronger than the other? 00:41 Adhesives can be made from synthetic molecules 00:44 or natural proteins and carbohydrates 00:47 like the vegetable starch dextrin, 00:49 the milk protein casein, 00:51 and the terpenes in tree resin. 00:53 In order to work, glue and tape need both adhesive bonds and cohesive bonds. 00:59 Adhesive bonds occur between an adhesive's molecules 01:03 and the molecules of whatever it's sticking to. 01:06 Cohesive bonds happen between a glue or tape's own molecules, 01:11 holding it together. 01:13 Most glues consist of adhesive polymers dissolved in a solvent 01:17 that prevents them from sticking to the inside of the bottle. 01:20 The strong smell of many glues comes from the solvent, 01:23 which evaporates when exposed to air. 01:26 Some glues use water as a solvent, 01:28 but others use chemicals that can be harmful to inhale. 01:32 Glues with two or more components that chemically react instead of just drying 01:37 can create stronger bonds. 01:39 Both the adhesive and cohesive bonds of glue are strong, 01:43 but the drying process makes them irreversible. 01:46 This is why, if a glued surface is broken after it dries, 01:50 it can't be reattached without new glue. 01:53 By contrast, when tape is applied to a surface, 01:57 it forms weaker, reversible bonds, 02:00 so you can peel a piece of tape off a surface and use it again. 02:04 These weak bonds, called Van der Waals forces, 02:08 can occur between any two materials, 02:10 but only if they're extremely close together, 02:13 closer than the naked eye can see. 02:15 Tape usually consists of a backing coated with a combination of a rubber 02:20 or rubber-like "stretchy" component, 02:23 and a compound called a tackifier. 02:25 That's the "sticky" component. 02:29 A tape's stickiness is determined 02:31 by the proportion of elastic component and tackifier, 02:34 the thickness of adhesive spread onto the backing, 02:37 and the type of backing material. 02:39 No chemical reaction occurs when tape is pressed onto a surface. 02:43 Instead, the soft adhesive flows into the cracks and grooves of the surface. 02:49 This ability to slide into cracks and then stay in place is called viscoelasticity. 02:56 Once the viscoelastic adhesive fills these microscopic crevices, 03:01 it is close enough to form Van der Waals forces. 03:05 So what's the world's strongest adhesive? 03:08 Well, there's no one answer. 03:11 In terms of absolute strength of adhesive bonds, 03:14 glue is stronger than tape, 03:16 but no single adhesive works well in all circumstances. 03:20 Of the glues, cyanoacrylates, or super glues, 03:25 may form the strongest bonds, 03:27 but two-component epoxy glues have much higher resistance to heat and shearing, 03:32 and are compatible with a wider range of surfaces. 03:36 So, if you wanted to dangle an anvil in the air, 03:40 super glue might be your best bet. 03:42 But if you're doing so over an active volcano, 03:46 you'd want an epoxy instead. 03:48 And in order to work at all, 03:49 glues need enough real estate where surfaces touch. 03:52 If for some reason you wanted to make a chain of bowling balls, 03:56 duct tape would be better. 03:58 Engineers weigh similar, if less absurd, factors all the time. 04:03 Choosing the right glue to withstand the heat inside an engine 04:06 is a matter of life and death. 04:08 And though the strength of duct tape's adhesive bonds 04:11 can't compete with those of epoxy glues, 04:14 tape does have the advantage of instantaneous stickiness in an emergency. 04:18 Glue may be necessary to get a rocket to space, 04:22 but when it comes to extraterrestrial repairs, 04:25 stick to duct tape: liquid glues don't work in zero gravity.