Super glue is the common name for cyanoacrylate adhesive, a fast-acting bonding agent used widely in household, commercial, and industrial settings. Exposure to trace amounts of moisture, typically from ambient humidity, triggers a chemical reaction called anionic polymerization. This process rapidly transforms the liquid monomer into a solid plastic polymer, which provides the adhesive’s strength. The flammability of super glue depends entirely on its state: liquid or fully cured.
Flammability of Liquid Cyanoacrylate
The uncured, liquid state of super glue is primarily composed of cyanoacrylate esters, such as ethyl or methyl cyanoacrylate monomers, along with stabilizing agents. In this liquid form, the adhesive is classified as a combustible liquid, meaning it requires a significant amount of heat to ignite, unlike highly flammable liquids like gasoline. Pure cyanoacrylate typically has a flash point—the minimum temperature at which its vapors ignite—that is above \(80^\circ C\) or \(176^\circ F\). This relatively high flash point indicates that the liquid is stable at room temperature and not easily ignited by a stray spark or common heat source.
However, some commercial formulations may contain additional ingredients, such as primers or solvents, which can dramatically lower the flash point and increase flammability. For instance, certain primers use highly volatile aliphatic hydrocarbons that can form explosive vapor-air mixtures. Users should check product-specific safety data sheets, especially when working with large volumes or in poorly ventilated spaces.
Fire Risk of Cured Super Glue
Once fully polymerized, the liquid transforms into solid polycyanoacrylate, a type of rigid acrylic plastic. This cured polymer is significantly less flammable than the liquid state and presents a low fire hazard. Like most solid plastics, cured super glue is combustible, but it requires exposure to an intense and sustained heat source to ignite. The material will often melt or char before sustaining a flame, and it typically burns slowly or may self-extinguish when the heat source is removed.
A unique fire hazard is presented not by the cured product, but by the curing process itself when the liquid contacts certain materials. The polymerization reaction is exothermic, meaning it releases heat. When the adhesive soaks into highly porous, fibrous materials with large surface areas, such as cotton, wool, or leather, the reaction rate accelerates rapidly. This rapid curing can generate enough localized heat to cause the material to smoke, scorch, or even spontaneously combust. This chemical reaction hazard is why disposable nitrile gloves, not cotton, are recommended for handling the adhesive.
High-Heat Hazards: Thermal Decomposition and Fumes
While cured super glue is difficult to ignite, exposing it to extreme temperatures, even without an open flame, presents another significant safety concern: thermal decomposition. When the solid polymer is heated to high temperatures, often starting around \(160^\circ C\) or \(320^\circ F\), the chemical structure begins to break down. This process, known as pyrolysis, releases various gaseous products from the plastic.
The fumes produced during the thermal breakdown of polycyanoacrylate are highly irritating. These gases can include small nitrogen compounds, such as poisonous nitrogen oxides. Other decomposition fragments, including esters and aldehydes, are also released into the air. If the cured adhesive were to catch fire, the combustion would produce thick, noxious smoke containing these toxic components. If cured super glue might be heated, such as during repair work or accidental exposure to a heat source, ensure the area is well-ventilated to minimize the inhalation risk.