From: veritasium
Super glue, also known as Eastman 910 Adhesive, is a powerful adhesive where a single drop can support a person [00:00:04] or even lift over three tons [00:00:32]. It consists of identical monomer molecules, specifically ethyl cyanoacrylate [00:03:02]. Super glue typically sets in 10 to 30 seconds [00:05:23], much faster than other adhesives available in the 1950s that relied on drying out [00:05:27]. Its rapid setting is triggered by water, specifically the slightly negative oxygen atoms in water molecules and negative hydroxide ions, which initiate the polymerization reaction [00:06:25]. Moisture is abundant in the air and on most surfaces, allowing super glue to set rapidly on nearly every surface [00:06:40].
Applications
Super glue’s strength and rapid setting make it useful in various fields:
- General Adhesion Super glue bonds to a wide array of materials, including plastic, rubber, metal, glass, wood, and paper [00:02:16], [00:02:51]. Its first industrial sale was in 1956 to Mason and Hanger, who used it for assembling atomic bombs [00:13:48]. Additives like fumed silica can be used as thickening agents to create a gel consistency [00:14:05], while acid is often added to inhibit polymerization inside the tube [00:14:14].
- Accelerated Setting The setting time can be accelerated by adding more negative ions, which are polymerization initiators [00:14:20]. Accelerators are commercially available, but baking soda (sodium bicarbonate) is also commonly used by DIYers [00:14:32]. Baking soda reacts with air moisture to produce hydroxide ions, causing the glue to set faster and form a hard composite [00:14:38]. This layered super glue and baking soda combination can strengthen joints and fill gaps, and can even be drilled or sanded after setting [00:14:50]. If super glue is poured into water with dissolved baking soda, it sets even faster, creating a continuous length of polymer [00:15:15].
- Underwater Adhesion To glue objects underwater, the polymerization reaction needs to be slowed down [00:15:31]. Gel cyanoacrylate, with its thickeners, achieves this, allowing sufficient time for application and detachment [00:15:38].
- Forensics Super glue fumes are used in a forensic technique to lift fingerprints from non-porous surfaces [00:06:58]. Hand moisture and oils left behind are ideal for super glue to bind with, which also makes skin an ideal surface for the glue to stick to [00:07:04].
- Medical Uses The inventor, Harry Coover, first observed super glue’s potential in medicine when he used it to seal his son’s accidental finger cut [00:16:01]. He envisioned a medical glue that could replace sutures [00:16:18]. During the Vietnam War, the U.S. military developed a medical super glue spray that saved lives by stopping severe bleeding, such as from bullet wounds to the liver [00:18:44]. Despite its battlefield success, regulatory approval was delayed for years, and it was not until 1998 that a medical glue, 2-octyl cyanoacrylate (Dermabond), was approved [00:19:22]. The medical super glue industry has since grown to $900 million annually [00:19:38].
- Recycling and Sustainability Scientists are exploring the use of cyanoacrylate as a recyclable plastic [00:19:56]. Unlike other plastics that degrade when recycled mechanically or thermally, super glue polymers can break back down into pure monomers when heated to 210 degrees Celsius [00:20:10]. These monomers can then be distilled and reactivated into fresh polymer, achieving a high yield of around 93% [00:20:40], [00:23:30]. This process offers a sustainable solution for plastic waste [00:20:56]. Chemically inert materials like polypropylene, polyethylene, and Teflon, which do not activate super glue, are perfect for handling its monomers during this process [00:21:32]. To reduce brittleness in this recyclable plastic, a very weak base like DMSO (dimethyl sulfoxide) is used as an initiator, leading to the formation of longer, stronger polymer chains [00:22:17]. Additionally, a solvent like acetone provides mobility for these polymers to form even longer, more stable chains [00:22:50].
Weaknesses
Despite its strengths, super glue has several limitations:
- Brittleness Super glue polymers are rigid and densely packed, making them strong in compression [00:09:24]. However, it is brittle and can easily fall apart under sudden impact [00:09:53]. The rapid reaction produces short polymer chains with built-in stress, creating potential failure points [00:10:03]. Unlike squishy plastics like polyethylene or polypropylene that can absorb impact by deforming, super glue’s rigid bonds break under force [00:10:22].
- Weakness in Shear and Peel Super glue is weak when force is applied perpendicular to the polymer chains, meaning it has low shear strength [00:10:52]. During a shear test, stress is released, breaking the bond [00:11:00]. Shear force is not spread evenly, being highest at the edges, and super glue’s brittleness prevents it from redistributing this stress, leading to bond failure [00:11:27]. It is even weaker when peeled, as the force concentrates on a few polymers, causing the chains to break one by one, like a zipper unzipping [00:11:38].
- Lack of Adhesion to Chemically Inert Materials Super glue does not bond to chemically inert materials such as polyethylene, polypropylene, and Teflon [00:12:28]. These materials lack reactive sites and are hydrophobic and non-porous [00:13:07]. Even with added initiators like water, the glue will not adhere, forming a film that can be peeled off [00:13:02]. This property is, however, beneficial as it allows super glue to be stored and contained without setting [00:13:36].
- Medical Limitations of Original Formulation
The original super glue formulation had several drawbacks for medical use:
- Heat Release: As bonds form during setting, heat is released. On surfaces with high surface area and absorbed water, like cotton, this can cause a significant temperature increase (e.g., up to 120°C on a cotton ball), irritating wounds [00:16:25].
- Toxicity: Over time, super glue breaks down in the body into toxic chemicals like formaldehyde [00:17:15].
- Rigidity: The hard and brittle nature of the glue made it unsuitable for flexible living tissue, which requires a soft and flexible adhesive for healing [00:17:25].
These medical problems were addressed by increasing the number of carbons in the alkyl chain of the molecule, which slowed the reaction rate, reduced heat release, extended breakdown time (allowing healing before toxin release), and resulted in longer, more flexible polymers that could absorb stress better [00:17:42].
- Accidental Misuse Due to similar packaging, there are hundreds of cases of people accidentally putting super glue into their eyes instead of eyedrops [00:18:14]. In such cases, attempting to separate eyelids or using acetone is not the solution; immediate medical attention is necessary [00:20:00].