By: Matthew Wong, Date: 2/13/2018

• Adhesive bonding is a joining technique that attaches two surfaces together using a middle layer of substance.  The substance is a bonding agent and is commonly glue or epoxy.  The adhesive material can be treated multiple ways such as through the application of heat or pressure.  Current methods have improved such as using superglue which is a plastic-based agent that self-cures with heat.  Adhesive bonding is known for creating common products such as plywood (thin layers of wood glued together) and fiberglass (a sheet of glass fibers joined by polymers such as epoxy).

• There is no distinct inventor of adhesive bonding.  Instead it has been an evolving method that dates back 200,000 years ago when Neanderthals first applied tar to bind their stone tools to wooden handles.  Around 500 AD, the Greeks and Romans advanced the technology greatly with their development of animal glues which are adhesives created by boiling the tissue of animals.  Since 1900, adhesive bonding has grown rapidly due to the production of new plastics and resins.  For example, Scotch tape has flourished and is an example of a pressure-sensitive adhesive (PSA).

• Adhesive bonding is designed to join dissimilar materials such as plastic to metal.  It also distributes the stresses of loads over a large area instead of concentrating the stresses - this minimizes the possibility of cracking or distortion in the two materials being joined.  Adhesive bonding resists flex and vibration stresses, and due to the seal and bond it creates, it can protect the joint from corrosion.  This method can easily join irregularly shaped surfaces while adding negligible weight to the assembly.
• Advantages include the property of low bonding temperatures and the absence of electric voltage and current.  One drawback is that when using adhesives on small structures, it will take up more space which might negatively affect nearby designs.  Also, the penetration of moisture in the materials will limit the strength of the bonding.
• The rivals to adhesive bonding for plastics and metals are more traditional methods such as mechanical fasteners and welding.  However, these two methods have their limitations.  Mechanical fasteners create stress concentration points from applied forces at the small area of the fastener instead of the overall surface area, which could lead to cracking or distortion.  Also, the part will require holes for the fasteners so the design might be altered in order to account for that.  Welding is limited to joining similar materials such as metal to metal or thermoplastic to thermoplastic.  It cannot be used to join plastics or rubber to materials like metal or glass, and it also has a higher chance of creating cracking or distortion just like fasteners.

• Adhesive bonding can be broken down into four steps and can commonly be accomplished by one person.  
  1. The first step is to properly prepare surfaces for the adhesive.  They must be cleaned and dried to prevent any waste from weakening the bond.  They should also be roughened because small peaks and valleys will provide a better mechanical grip than just a flat surface.
  2. The second step is applying the adhesive to the base surface - the better an adhesive wets the surface, the better the bond.
  3. The third step is joining the two surfaces and closing the bond line within the specified open time and work life of the adhesive.
  4. The final step is to apply a form of curing such as pressure or heat for a specified period of time before the parts can be moved and handled.

• For small-scale operations, a 2 ounce bottle of Gorilla Super Glue is about $5 and a 0.47 ounce bottle of instant epoxy is about $4.
• For large-scale operations, a 1 pound bottle of Gorilla Super Glue retails at about $120 and 1 gallon of an epoxy resin kit retails at about $60.
• For materials, there is a wide array to choose from such as plastics, metals like steels, rubber, and wood so the price varies considerably for the substrates.