Hot melt adhesive is a thermoplastic material—or a polymer—that generally becomes pliable at warm temperatures. Conversely, in the process of cooling down, hot melt solidifies to eventually form the kind of lasting bond for which it’s become known. Temperature and the ways in which it changes have a major impact on the way hot melt adhesives perform.
There are nearly countless varieties of hot melt adhesives. Therefore, there are just as many ways in which temperature can affect them. Generally, the most noticeable effects temperature has on hot melt impact its viscosity, strength, elasticity, and toughness or stiffness.
If the effects of extreme temperature changes on hot melt aren’t understood and managed, the results can be dangerous. That’s why, in this article, we’ll strive to make you aware of some of the major ways in which heat and cold can impact your hot melt and the bonds upon which you rely.
How Temperature Affects the Strength of Hot Melt
While different types of hot melt adhesive have different levels of temperature resistance, a good rule of thumb is that, as temps go up, the strength of a hot melt adhesive goes down as it loses its ability to hold two substrates together solidly. On the flip side, low temperatures do not usually have such an extremely adverse effect on the strength of adhesives. Typically, they will cause some simple stiffness rather than compromise their strength.
Stiffness, Heat, and Hot Melt
In most cases, it’s the cooling and drying process that causes adhesives to become stiff and create a solid bond. Extreme heat applied to a solid bond can still decrease the solidity, stiffness, or “toughness” of the hot melt and lead to the substrates sliding apart as the adhesive’s hold gives out. The safety issues here are obvious, as loose bonds in buildings and heavy equipment can easily injure people and wreak havoc.
Conversely, some adhesive can become overly stiff and tough at high temperatures—which is why another big lesson here to is read up on and understand exactly what kind of adhesives you’re working with. For adhesives that are meant to remain flexible, such as those used in settings that need to include some “give,” this increase in stiffness can diminish the effectiveness of the adhesive.
Temperature Changes Hot Melt’s Elasticity
The tendency for adhesives to strain or break increases as their temperatures rise because the chemical makeup changes, certain components break down, and the adhesive crystallizes and becomes unstable. This decreased elasticity may result in the cracking or total shattering of the adhesive, which, obviously, renders the bond useless. That isn’t to say that elasticity is always what you want. An adhesive that’s too stretchy can be harder to extrude, swirl, spray, or coat than one with less elasticity.
Temperature and Viscosity
Viscosity is the measure of a liquid’s ability to resist flow. If hot melt adhesive is overheated and becomes too viscous, it can mean a serious burn risk, a major mess, and the overall slowdown of the assembly process as you stop and wait for runny adhesives to solidify. On the other hand, a cold adhesive that isn't viscous enough to flow through an application tool is similarly detrimental to the assembly process.
While it’s difficult to provide a single blanket statement that correctly conveys the effects of temperature on hot melt, we hope that it’s easy to see that these effects can, indeed, be extreme and detrimental if not planned for and managed properly. If you aren’t sure how the temps at your job site or the environment in which the bond is meant to perform will affect the adhesive you’re using, don’t hesitate to get in touch with the adhesive experts at Hotmelt today.