Chemical adhesives have been around for quite some time. With the advancements in chemistry today, the newest chemical adhesive on the market is able to bond fifty degrees below zero without any thinners or other additives. This synthetic rubber-like glue works by forming tiny plastic filaments that bond to either metal or ceramic surfaces. This glue has also been used in space on satellites and probes because it can be cured in cold temperatures.
What are the latest developments in the chemistry of adhesives?
The following are the types of bonds that can be made with an adhesive. These all rely on one or more molecules (usually from two different substances) coming together and forming a new bond. Combining two substances, such as when the glue is mixed, is not considered to be a bond.
Fire-Bonded Glue (aka Fire-Toughened Adhesive) is a type of adhesive in which two surfaces that have been oxidized by burning are bonded together. This method helps to reduce corrosion, but it is not as strong as some of the other bonding methods. One example of fire bonded glue is the application of epoxy or cyanoacrylate adhesive to wood. When the wood starts to burn, the adhesive will chemically bond with whatever has been burned. The result is a stronger bond between what has been burned and what is left (the adhesive).
Other examples are PVC pipes and metal pipes that are cross-connected using waterproof glue/adhesive. Fire-Bonded epoxy pipe and adhesive contain two epoxies, each containing different compounds that bind when they come into contact. These materials can be used on plastics, concrete, and most metals. Their bond is stronger than the two materials being held together.
The following are some examples of the different bonds made using adhesives:
Fused Bond – This type of bond occurs when the molecules in one substance combine with the molecules in another, but there is no chemical reaction (or “going off”). A good example is a superglue and wood. The superglue holds pieces of wood together, but it does not act as a chemical adhesive – this is called a mechanical bond. Some other examples of fused bonding include burning two pieces of wood to make them burn better together and welding metals together by melting their surfaces.
Mechanical Bond – A mechanical bond occurs when two materials are held together, but no chemical reaction occurs. This is a temporary bond, and the substances involved can be separated relatively easily. When the glue is applied to paper, it creates a mechanical bond because paper fibers are twisted/entangled together, and wood fibers are also intertwined.
Mechanical bonds can be both strong and weak, depending on the material that is being bonded together. The most important factor in mechanical bonding is the point at which the molecules of one substance meet up with those of another substance. If they loosely interlace each other, then there will be a weak bond (as with paper). If they are tightly interlaced, then there will be a stronger bond (as with wood).
A great example of a strong mechanical bond is in a bicycle seat. The metal frame of the bicycle is bonded to the plastic seat. A strong intermolecular bond forms between these two materials, which allows the seat to stay rigid without deformation over many years. Another example is when bolts are screwed into nuts. This type of bond creates a very tight mechanical fit between the bolt and nut, securely keeping them together.
Electrical Bond – Electrical bonding is the strongest bond of all and can be used in many different ways. The two most common methods of electrical bonding are soldering and brazing.
Solder – Soldering is a type of mechanical bond in which melted lead or solder is applied to two surfaces that need to be connected. Typically, the solder includes traces of metals such as tin, zinc, or lead. These metals do not react with other materials when heated (or molten). The molten solder will then flow through the interconnecting space and adhere to the other surfaces.
Brazing is similar to soldering, except that an alloy called brass (of copper-zinc composition) also melts during this process. This type of bond is used to join steel and copper.
Metal Joining – A metal joining bond is one in which the surface of one substance is fused to the surface of another substance. This occurs when the surfaces are heated up to a temperature that is almost enough to melt both substances. The result should be a permanent bond between the two materials being joined together. This can be done with a torch, which can heat up both pieces of metal at the same time (as long as they are in contact with each other). Using an adhesive as an alternative to this process can cause certain problems to occur:
Plastic Joining – Two plastics can be bonded together using adhesives called plastic welding compounds. They are used in order to join two plastic parts together. A small amount of heat is needed for this bond to form. It works by having a polymer (a plastic chain-like molecule) from one surface come into contact with a polymer from the other surface, thus interlacing and creating a strong bond between them. The plastic parts can be put on either side of the welding compound, but the plastic part that needs to be joined is placed on the topmost of the time.
It is not always necessary for an adhesive to chemically bond two materials together in some instances. Some other types of adhesive bonds are the oleo dynamic bond and mechanical bond. There is also a cross-linked type of bonding called dispersion bonding.
The oleo dynamic bond occurs when two solutes (saturated liquids) are mixed together, a process that generates heat as the result of a chemical reaction. After the mixing, the two solutes will separate (as the heat dissipates). The dissolved salts in one liquid will go into the solution in the other liquid and form a strong chemical bond due to intermolecular hydrogen bonds.
The salt content of both liquids can be controlled by adjusting concentrations or temperatures. The bonding between both substances is not just between one substance and another but also between several molecules within each liquid. This type of bonding is what causes emulsions to work as they are designed.
Dispersion bonding is when a fine solid powder is mixed with a liquid and then is used to join two materials together. This adhesive bond forms a gel-like substance that holds the two surfaces together, although the adhesion process can be weak. Dispersion bonding is most commonly used in the rubber and plastics industries, but it can also be found in food products.
The rate of adhesion (how fast an adhesive bond forms) is important to consider when using an adhesive to join two objects together. If a quick bond must be formed, heat can be applied to increase the rate at which the glue or cement cures and bonds. One way to increase the rate of adhesion between two materials is by increasing the temperature. This can be done using a tool called an infrared heater. The benefit of using a machine like this is that it takes only a few minutes for the bond to cure (as opposed to an hour or more), which improves manufacturing efficiency and reduces costs.
Another method of increasing the adhesive bond rate is by ensuring that both surfaces that need to be joined are dry and free from oil, grease, or other contaminants. Both surfaces must also have flat, smooth surfaces in order for adhesion to occur properly. Chopping off any rough edges or blobs with a sharp tool (such as a razor blade) will achieve this necessary flat surface.
The strength of an adhesive bond is also important to consider. Strength is broken down into two different categories: mechanical and physical. Mechanical strength is the ability of an adhesive bond to resist deformation or strain, whereas physical strength is the resistance to breaking when tested for the tensile load.